Development of Nanoporous Inorganic Carbonates for...

ACTAUNIVERSITATIS

UPSALIENSISUPPSALA

2019

Digital Comprehensive Summaries of Uppsala Dissertationsfrom the Faculty of Science and Technology 1801

Development of NanoporousInorganic Carbonates forPharmaceutical and EnvironmentalApplications

MARIA VALL

ISSN 1651-6214ISBN 978-91-513-0638-4urn:nbn:se:uu:diva-381336

Dissertation presented at Uppsala University to be publicly examined in Polhemssalen,Ångströmslaboratoriet, Lägerhyddsvägen 1, Uppsala, Monday, 3 June 2019 at 09:30 forthe degree of Doctor of Philosophy. The examination will be conducted in English. Facultyexaminer: Professor Jessica Rosenholm (Åbo Akademi).

AbstractVall, M. 2019. Development of Nanoporous Inorganic Carbonates for Pharmaceutical andEnvironmental Applications. Digital Comprehensive Summaries of Uppsala Dissertationsfrom the Faculty of Science and Technology 1801. 65 pp. Uppsala: Acta UniversitatisUpsaliensis. ISBN 978-91-513-0638-4.

Mesoporous magnesium carbonate (MMC) is a highly porous, anhydrous material whichcan be synthesized without the use of templates. This thesis shows how post- and insynthesis modification of MMC can create porous inorganic carbonates suitable for differentpharmaceutical and environmental applications.

Controlled release of IBU was achieved by loading IBU onto amine modified MMC (aMMC).The amine coverage was varied and there was a clear correlation between the release rate of IBUand the amine coverage, the higher the amine coverage the slower the release rate. aMMC wasalso used to load salicylic acid (SA). SA was then released within 15 minutes in a phosphatebuffer (pH 6.8). The cytotoxicity of aMMC was evaluated and it was found non-toxic for humandermal fibroblast cells with particle concentration up to 1000 µg/mL for 48 h of exposure. aMMC also showed a high adsorption capacity for three different types of anionic azo dyes; acid red 183, amaranth and reactive black 5. The addition of amine groups to the surface ofMMC significantly increased the uptake of the three dyes tested. Composite materials weresynthesized by combining the synthesis of MMC and the synthesis of highly porous amorphouscalcium carbonate. The calcium magnesium carbonate composite materials were evaluated fortheir CO2 sorption capacity (at 650 °C) and their CO2 cyclic stability. Addition of Al(NO3)3 to thebest performing composite further improved its cyclic stability and the composite maintaineda high CO2 uptake over 23 sorption/desorption cycles. Composite materials were also madeby adding Al2O3 and SiO2 nanoparticles to the synthesis liquid of MMC. This resulted inmaterials with Al2O3 and SiO2 incorporated into the porous MMC structure. The MMC materialswith Al2O3 and SiO2 nanoparticles was then impregnated with Ni(NO3)2, calcined and usedfor catalytic conversion of syngas to natural gas. The material containing Al2O3 nanoparticlesperformed the best and had a CO conversion of close to 100% at 350°C as well as a high CH4

yield and selectivity.In this thesis porous inorganic carbonates have been developed and evaluated for their

performance in different pharmaceutical and environmental applications.

Keywords: Mesoporous magnesium carbonate, drug delivery, water purification, CO2 capture,catalysis

Maria Vall, Department of Engineering Sciences, Nanotechnology and Functional Materials,Box 534, Uppsala University, SE-75121 Uppsala, Sweden.

© Maria Vall 2019

ISSN 1651-6214ISBN 978-91-513-0638-4urn:nbn:se:uu:diva-381336 (http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-381336)

Till min familj

List of Papers

This thesis is based on the following papers, which are referred to in the text by their Roman numerals.

I Vall, M., Zhang, P., GaO, A., Frykstrand, S., Cheung, O.,

Strømme, M. (2017) Effects of amine modification of mesopo-rous magnesium carbonate on controlled drug release. Interna-tional Journal of Pharmaceutics, 524:141–147

II Vall, M., Ferraz, N., Cheung, O., Strømme, M., Zardán Gómez de la Torre, T. (2019) Exploring the use of amine modified mesoporous magnesium carbonate for the delivery of salicylic acid in topical formulations: in vitro cytotoxicity and drug re-lease studies. Submitted

III Vall, M., Hultberg J., Strømme, M., Cheung, O. (2019) Inor-ganic carbonate composites as potential high temperature CO2 sorbents with enhanced cycle stability. Submitted

IV Vall, M., Strømme, M., Cheung, O. (2019) Amine-modified mesoporous magnesium carbonate as an effective adsorbent for azo dyes. ACS Omega, 4:2973-2979

V Hao, W., Vall, M., Shi, Y., Wang, Q., Strømme, M., Yan, X.,

Cheung, O., Li, R. (2019) Novel Ni/MgO catalysts from meso-porous magnesium carbonate for highly efficient CO methana-tion: Effects of Al and Si stabilization. In manuscript

Reprints were made with permission from the respective publishers.

Author’s contribution to included papers

Paper I I participated in planning the study, developed and performed the modifica-tion and performed most of the characterization of the materials. I took part in writing the paper. Paper II I participated in planning the study. I performed the synthesis, modification and characterization of the materials. I took part in writing the paper. Paper III I participated in planning the study. I performed the synthesis and character-ization of the materials and I did most of the experimental work. I took part in writing the paper. Paper IV I participated in planning the study. I performed the synthesis of the materi-als, modification, characterization and the experimental work. I took part in writing the paper. Paper V I performed the synthesis and some of the characterization, took part in writ-ing the manuscript.

Also published

Journal Articles

Pochard, I., Vall, M., Eriksson J., Farineau, C., Cheung, O., Frykstrand, S., Welch, K., Strømme, M. Amine-functionalized mesoporous magnesium carbonate: Dielectric spectroscopy studies of interactions with water and stability. Materials Chemistry and Physics, 2018, 216, 332-338

Conference contributions Vall, M., Zhang, P., Cheung, O., Strømme, M. (2017) Amine modified mes-oporous magnesium carbonate for rate controlled drug delivery. Poster presentation at 5th International Conference on Multifunctional, Hybrid and Nanomaterials, Lisbon, Portugal. Vall, M., Strømme, M., Cheung, O. (2018) Nanoscale surface modification of mesoporous magnesium carbonate and the effect on ibuprofen release rate in vitro. Oral presentation at XIV International Conference on Nanostruc-tured Materials, Hong Kong. Vall, M., Strømme, M., Cheung, O. (2019) Adsorption of carbon dioxide on inorganic carbonate sorbents. Poster presentation at 6th International Con-ference on Multifunctional, Hybrid and Nanomaterials, Sitges, Spain. Vall, M., Strømme, M., Cheung, O. (2019) Modification of mesoporous magnesium carbonate and its applications in drug delivery and waste water treatment. Oral presentation at 6th International Conference on Multifunc-tional, Hybrid and Nanomaterials, Sitges, Spain.

Abbreviations

ACMC ACMO AM aMMC API APTES AR183 BET CaL CCS CEL CIN CMC CMO DFT DSC EDX FTIR GRI hDF HPACC IBU ITZ IUPAC MMC

Aluminium calcium magnesium carbonate composite Aluminium calcium magnesium oxide composite Amaranth Amine modified mesoporous magnesium carbonate Active pharmaceutical ingredient (3-Aminopropyl)triethoxysilane Acid red 183 Brunauer-Emmett-Teller Calcium looping Carbon capture and storage Celecoxib Cinnarizine Calcium magnesium carbonate composite Calcium magnesium oxide composite Density functional theory Differential scanning calorimetry Energy dispersive X-ray spectroscopy Fourier transform infrared spectroscopy Griseofulvin Human dermal fibroblasts Highly porous amorphous calcium carbonate Ibuprofen Itraconazole International union of pure and applied chemistry Mesoporous magnesium carbonate

MOF PTES RB5 SA SEM SNG TEOS

Metal organic framework n-Propyltriethoxysilane Reactive black 5 Salicylic acid Scanning electron microscopy Synthetic natural gas Tetraethyl orthosilicate

TGA XRD XPS UV/Vis

Thermogravimetric analysis X-ray diffraction X-ray photoelectron spectroscopy Ultraviolet-visible

Contents

1. Introduction ............................................................................................... 11

2. Aim of thesis ............................................................................................. 13

3. Background ............................................................................................... 14 3.1. Porous Materials ................................................................................ 14

3.1.1. Different porous materials ......................................................... 15 3.1.2. Methods for synthesizing porous materials ............................... 16 3.1.3. Functionalization of porous materials ........................................ 17 3.1.4. Applications ............................................................................... 18

3.2. Inorganic carbonates ......................................................................... 22 3.2.1. Mesoporous magnesium carbonate (MMC) .............................. 22 3.2.2. Highly porous amorphous calcium carbonate (HPACC) ........... 25

4. Synthesis, characterization and functionalization of nanoporous inorganic carbonates ..................................................................................... 26

4.1. Characterization methods .................................................................. 26 4.1.1. N2 adsorption ............................................................................. 26 4.1.2. X-ray diffraction (XRD) ............................................................ 26 4.1.3. Scanning electron microscopy (SEM) ....................................... 26 4.1.4. Thermogravimetric analysis (TGA) ........................................... 27 4.1.5. Fourier transform infrared spectroscopy (FTIR) ....................... 27 4.1.6. Raman spectroscopy .................................................................. 27 4.1.7. Ultraviolet-visible (UV/Vis) spectroscopy ................................ 27 4.1.8. X-ray photoelectron spectroscopy (XPS) .................................. 27 4.1.9. Differential scanning calorimetry (DSC) ................................... 28

4.2. Synthesis and properties of inorganic porous carbonates .................. 28 4.2.1. Nanoporous inorganic carbonates (MMC and HPACC) ........... 28 4.2.2. Nanoporous inorganic carbonate composites ............................ 29 4.2.3. MMC with additives .................................................................. 31 4.2.4. Grafting of APTES .................................................................... 31 4.2.5. Impregnation of Ni .................................................................... 34

5. Applications of functional porous inorganic carbonates ........................... 36 5.1. Drug loading and delivery ................................................................. 37

5.1.1. Controlled release of IBU – Paper I ........................................... 37 5.1.2. Loading and release of SA – Paper II ........................................ 39

5.2. High temperature sorption of carbon dioxide – Paper III .................. 41 5.3. Adsorption of azo dyes – Paper IV ................................................... 45 5.4. Catalysis, methanation of syngas – Paper V ..................................... 50

6. Conclusions ............................................................................................... 52

7. Future work ............................................................................................... 53

Svensk sammanfattning ................................................................................ 54

Acknowledgement ........................................................................................ 56

Appendix I. Characterization methods .......................................................... 58 N2 adsorption ............................................................................................ 58 X-ray diffraction ....................................................................................... 59 Scanning electron microscopy .................................................................. 59 Vibrational spectroscopy (IR and Raman) ............................................... 60 Ultraviolet-visible spectroscopy ............................................................... 60 X-ray photoelectron spectroscopy ............................................................ 61 Inductive coupled plasma optical emission spectroscopy (ICP-OES) ..... 61 Differential scanning calorimetry ............................................................. 61

References ..................................................................................................... 62

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1. Introduction

Porous materials are not a new phenomenon, they are naturally occurring and have been around for as long as we can account for. In more recent times the possibilities of porous materials have been recognized and many synthetic forms have since been developed. Further, different functionalities of porous materials have been investigated and optimized for various appli-cations. The porosity and high surface area of porous materials mean that there are large surfaces with many active sites available for interaction. It is also possible to incorporate different active substances into the porous struc-ture which offers great opportunities. With the progression of nanotechnolo-gy and new characterization and synthetic methods, the development of new porous materials has greatly increased. This together with insight into the nanostructure of the materials and the ability to alter the materials at a na-noscale has contributed vastly to the field of functional porous materials. There is an increasing need for smart materials and new solutions for many pharmaceutical and environmental applications, some of the current prob-lems in these fields are introduced in the following sections.

With the development of more active pharmaceutical ingredients (APIs) the request for good delivery systems and drug carriers are increasing. The ability to control the release rate and the bioavailability of the APIs means that it is possible to expand the number of active ingredients available for oral delivery and raise patient compliance as well as enable for better treat-ment regimes.

Emission of carbon dioxide (CO2) and its contribution to global warming is rising up to be one of the biggest environmental challenges of our time. We therefore need solutions to reduce the CO2 outlet from human activities. One of these solutions is to adsorb CO2 from point sources that can be found for instance in different types of industries.

The textile industry is one of the highest water consuming industries in the world1. The lack of good water purification systems means that a lot of contaminated water is released every day. One of the most used coloring agents for textiles are azo dyes2. They have great coloring properties but they also have some serious drawbacks, some of the dyes and their metabolites are cancerogenic3 and their discoloration of natural water sources is both esthetically displeasing as well as it disturbs the light transmission which affects the aquatic ecosystem4.

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Catalysis is important in many industrial applications; a catalyst lowers the activation energy and speeds up the reaction without participation in the reaction itself. Nickel has been proven a great catalyst for the conversion of syngas (CO and H2) into synthetic natural gas (SNG)5 which is a potential solution to the shortage of natural gas. Nickel does however need some sort of support to avoid sintering and carbon deposition6.

Porous materials might offer solutions to these problems; with their high porosity they can stabilize poorly soluble drugs in an amorphous state and through that enable a faster dissolution and possibly a higher bioavailability. By attaching functional groups to the surface the release rate can be further controlled. A porous structure is also a key element for adsorption. The high surface area alone offers many sites of interaction and by modifying the sur-face stronger interactions can be enabled and the adsorption capacity can be more specified and/or increased. This can be utilized in the adsorption of gases and substances in an aqueous environment. As stated before, porous materials offer many sites of interactions and the ability to incorporate active elements into the structures offer great opportunities in the field of catalysis.

In this thesis mesoporous magnesium carbonate (MMC) has been used as a base material to create functional porous materials designed to target specific pharmaceutical and environmental applications. MMC can be synthesized without the use of structural directing agents and can be produced at a large scale.

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2. Aim of thesis

The aim of this thesis has been to develop nanoporous inorganic carbonate materials for pharmaceutical and environmental applications. The focus is on MMC and how post- and insynthesis modification can tune the properties of the material and affect its performance and functionality. The applications that are included in this thesis are controlled release of the drug ibuprofen, stabilization and release of salicylic acid, sorption of CO2, adsorption of reactive azo dyes and as a support for Ni in the catalytic conversion of CO to CH4.

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3. Background

3.1. Porous Materials The definition of porous materials is that the material contains empty spaces (void or cavities) i.e. pores within their structure7. Pores can have different geometry; be regular or irregular, open, closed or interconnected. Porous materials can be either naturally occurring or made synthetically, they can be organic or inorganic or even a mixture of both. The definition of porous ma-terials is wide and hence includes a lot of different materials.

The size of the pores in the material is essential to its functionality. Po-rous materials are therefore often divided into groups based on their pore size. The international union of pure and applied chemistry (IUPAC) define porous materials according to their pore width as micro-, meso- or macro porous8. Microporous materials have a pore width of less than 2 nm, meso-porous materials contain pores with pore width between 2-50 nm and macroporous materials contains pores with a pore width larger than 50 nm.

Figure 1. Illustration Micro-, Meso- and Macropores

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3.1.1. Different porous materials As stated earlier the definition of porous materials is wide, in this section some of the most common classes of porous materials will be introduced.

3.1.1.1. Zeolites Zeolites are aluminosilicate minerals, they are naturally occurring but can also be made synthetically. They are constructed of covalently connected tetrahedra, with a central atom (T-atom) coordinating four oxygen atoms9. The T-atom is traditionally silicon or aluminum and the tetrahedra are con-nected to build up a porous network. The zeolite framework has a net nega-tive charge, which is balanced by cations9. The building blocks can be ar-ranged in numerous ways and the ratio between Al and Si can be varied. With the numerous possibilities for variations, a large number of different zeolite networks can be constructed. Some examples of zeolites are Zeolite A10 which is a synthetically made zeolite with a high aluminum content and mordenite11, 12 which is naturally occurring with high silica content. Zeolites usually have pores in the micro porous range. Their narrow pore size and high surface area have proven to be very useful for different applications e.g. gas adsorption13 and catalysis14.

3.1.1.2. Metal organic frameworks Metal organic frameworks (MOFs) is another class of microporous materi-als, they are built up of metal ions linked together with organic linkers. They are highly porous materials with surface areas of up to 10000 m2/g 15. The synthesis of MOFs is originated from the synthesis of zeolites. A variety of different organic linkers and metal ions can be used which means that there are many different structures that can be created. Some examples of MOFs are MOF 516 which are built up of Zn4O tetrahedra linked with 1,4-benzodicarboxylate and MIL-5317 which is a chromium dicarboxylate. MOFs have also, in similarity with zeolites, been suggested as good per-forming materials in the field of gas adsorption18 and catalysis19.

3.1.1.2. Porous carbon Porous carbon, also called activated carbon, is highly porous carbon based material. There are several different ways to synthesize porous carbon but typically a carbon precursor i.e. an organic moiety is used to form a porous structure that can then be carbonized through pyrolysis20. A template can be used to form the pores in the carbon material. The carbon structure is amor-phous and usually have a very high surface area21. These properties makes porous carbon attractive to use in water purification22, gas adsorption23 and as an oral supplement to prevent poisoning24

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3.1.1.3. Mesoporous silica The synthesis of mesoporous silica was first described in 1990s25, 26. The most commonly known forms of mesoporous silica are probably MCM-4125 and SBA-1527, but numerous of other types have also been made with differ-ent pore and particle sizes. Mesoporous silica is usually synthesized via the sol-gel process using a silica precursor i.e. Tetraethyl orthosilicate (TEOS) and the porous structure is created by using a soft template (discussed in section 3.1.2.). This results in an amorphous structured silica material with a regular and narrow pore distribution. The mesoporous silica structure has proven very useful for applications in drug delivery28, 29 and catalysis30, 31.

3.1.2. Methods for synthesizing porous materials There are many different methods for synthesizing porous materials. In this section some of the most common techniques and processes are described.

3.1.2.1. Sol-gel process The sol-gel process is a three-step method used to form a solid material from smaller molecules or particles. The first step is hydrolysis forming a colloi-dal suspension or “sol” which then condensates and forms a continuous solid network “gel” which is then dried and upon drying forms a solid material32. When the sol-gel synthesis is used to create porous materials typically a template is used, for instance mesoporous silica is typically synthesized with the sol-gel method and different types of surfactants are then used to create the mesoporous structure.

3.1.2.2. Hydrothermal process The hydrothermal process is, as the name suggests, a synthetic process car-ried out in water, it can also be referred to as the solvothermal process if a solvent other than water is used33. It is the common method for synthesizing zeolites and MOFs. For zeolites the precursors are usually dissolved in water and then allowed to crystallize under hydrothermal/solvothermal conditions forming the porous network. The process is carried out in an autoclave and by adjusting the chemical and the physical parameters i.e. temperature, pres-sure, amount of precursors a number of different frameworks can be created.

3.1.2.3. Use of templates To create a porous structure the most convenient and exercised method is to use a template to create a uniform distribution of pores. Surfactants are am-phiphilic molecules that are commonly used as templates to create porous structures. Their amphiphilic nature (one hydrophilic and one hydrophobic part) allows them to self-assemble into larger structures called micelles, the micelles serves as a template and allows the material to form around it34. The

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use of surfactants to create porous structures is referred to as “soft” templat-ing, but there is also “hard” templating were instead a solid template is used to create voids (pores) in the material35. SiO2 opals have been used as a hard template to create porous carbon36. The use of templates gives good control over the porosity and often gives a narrow distribution of pore size. Tem-plates have to be removed after the synthesis, which is usually done by heat treatment, washing or a combination of both. The use of templates to create porous materials is commonly combined with different synthetic routes, both the sol-gel and the hydrothermal processes (described in the previous sec-tions) are often carried out in the presence of a template.

Figure 2. Illustration of soft and hard templating

3.1.3. Functionalization of porous materials Porous materials are functional materials on their own. The high surface area alone offers many active sites for interactions with guest molecules. The elements in the framework will also affect the functionality of the material. In zeolites and MOFs there are different types of atoms in the framework which will offer different reactivity. In zeolites the ratio between the silicon and the aluminum atoms will have a substantial impact on the properties and functionality of the material. Zeolites with a low Si/Al ratio, i.e. a high con-tent of Al, have a higher net charge of the framework. They are more hydro-philic37, less thermally stable and have an increased ion exchange capacity38 compared to the zeolite with a high Si/Al ratio. The different metals present in the frame works of MOFs will also affect their functionality. For example MOFs with unsaturated metal sites have shown an affinity towards different gases for instance CO2

39. Depending on the size of the target molecules, the

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pore size of the porous material will also have an impact on the material’s functionality. For example the pore size is very important in drug delivery applications where it can be used as a tool for controlling the release rate40. Also, for gas adsorption a variation in pore size will affect the adsorption of different gases because of the different size and shape of the gas molecules41. The high surface area also offers great possibilities for further functionaliza-tion i.e. attaching or adding molecules or elements to the surface that will have a higher affinity towards a target molecule in a certain application. Grafting of different molecules to the surface of porous materials is one common way of adding an additional functionality. Aminosilanes are, as the name suggest, aminegroups linked to alkoxysilanegroups. Aminosilanes have been widely used to introduce amine groups into porous structures. The alkoxygroups can be grafted to a surface and condensate together which can offer an additional functionality and create a more interactive surface. (3-Aminopropyl)triethoxysilane (APTES) is one of the most commonly used aminosilanes42 and have been used to introduce additional functionality to the surface of mesoporous silica43, zeolites44 porous carbon45 etc. The addi-tion of amine groups have been proven useful for a variety of applications such as prolonged drug delivery46, CO2 adsorption47 and for adsorption of dyes48. Impregnation of different molecules or elements to the structure is also a common way of adding functionality to a porous material. Typically, a functional specie can be added to a porous material if the porous material is placed in a solvent in which the desired functional species/molecules are dissolved. The solvent is thereafter removed, usually by evaporation, and the impregnated porous material is obtained. Impregnation of polyethyleneimine have been done to mesoporous silica (SBA-15) to improve its CO2 adsorp-tion capacity49. Impregnation of Calix [4] arene bis(-2,3 naphtho-crown-6) to the zeolite mordenite showed an improvement in the adsorption of cesium from low level radioactive liquid waste50.

3.1.4. Applications Porous materials have been tested for a number of different applications in various fields. In this section the applications relevant for this thesis will be discussed.

3.1.4.1. Pharmaceutical applications There is a lot of research of creating new APIs and the most practical route of administration is orally51. In drug delivery bioavailability is important. Bioavailability is defined as the amount of the API that is entering the blood system and is able to give an effect. A lot of new APIs suffer from poor dis-solution52 and consequently a low bioavailability. Therefore finding ways to enhance the dissolution will open up the possibility for more APIs to reach the market. One way to enhance the dissolution of a poorly soluble API is to

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use a porous material as a carrier53, 54. The porous structure can stabilize the API in an amorphous state and through that enable a faster dissolution52. A fast dissolution can enable a faster release of the API and through that give a faster therapeutic response. Depending on the nature of the API one might also want to control the release rate. A prolonged release can enable a longer effect of the drug and reduce the number of administrations and thereby raise patient compliance. This can be an interesting strategy especially for drugs with a short biological half-life, meaning that they break down rapidly in the body and the therapeutic response is therefore during a short period of time55. Some different strategies have been purposed to achieve a prolonged release from a porous matrix. It has for instance been achieved by varying the pore size, the larger the pores the faster the release56 and also by adding functional groups that can interact with the API and thereby prolong its re-lease have also been proven a feasible strategy57. Furthermore, local treat-ment of some conditions e.g. skin or muscular related has become more popular as it does not take the systemic route and therefore has less impact on the body. Porous materials can also be useful for this type of administra-tion route as it can control release rate as well as work as a carrier for APIs targeting the specific condition58.

3.1.4.2. Gas adsorption Adsorption is defined as an enrichment of a substance at the interface be-tween two bulk phases59. Adsorption of gases is a common application for porous materials, as has been stated earlier, their high surface area enables for this type of interactions. Gases can interact both through physisorption which is generally through Van der Waals interactions that origins from an induced dipole moment, or through chemisorption which is when covalent bonds between the gas molecules and the substrate are formed.

Figure 3. Illustration physisorption and chemisorption

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Physisorption and chemisorption are dependent on temperature. The creation of a chemical bond requires more energy e.g. higher temperature, which is in contrary to physisorption. Physisorption generally occurs at lower tempera-tures than chemisorption. Today a lot of focus is directed towards the re-moval of greenhouse gases, i.e. gases that contributes to the greenhouse ef-fect. CO2 is believed to be one of the main anthropogenic contributors to the greenhouse effect60. As a result a lot of focus has been directed towards re-ducing CO2 from its emission sources i.e. burning of fossil fuels and various industrial processes among others. Carbon capture and storage (CCS) is one strategy to reduce the emission. Different sorbents are then used to capture CO2 and thereby lowering the amount that is released. Depending on the temperature different sorbents can be utilized. At lower temperatures capture can be done using liquid amines61 or by solid porous adsorbents49, 62. Many different porous materials have been reported as good candidates for gas adsorption e.g. zeolites62, porous carbons63, MOFs64 among others. High temperature CO2 capture can be done with a method called calcium looping (CaL). CaL is based on the reversible reaction CaO+CO2 ↔ CaCO3

65. At temperatures above 600°C CaO will bind CO2 forming CaCO3, when heated to above 700°C CO2 will be released and CaO will form again. The CaL process does however have a big disadvantage which is that the sintering temperature of CaCO3, also called the tamann temperature, is between 276-533°C66. This temperature is well below the required operating temperature, and will cause the material to sinter during cycling. Sintering results in the loss of sorption capacity, different methods to hinder the sintering has there-fore been suggested. One way to prevent sintering is to incorporate CaO into a more inert framework and sterically hinder the sintering. Different types of metal oxide have been suggested as good candidates for this as they are usu-ally stable at the required operating temperatures67.

3.1.4.3. Water purification Water is used in many industrial chemical processes e.g. in textile and phar-maceutical industries, which results in a vast amount of contaminated wastewater1. Today there are not enough sufficient methods available to remove contaminants from the effluent water. A lot of the contaminants are subsequently released into natural water sources. In the textile industry, one of the most common classes of dyes that is used are called azo dyes. Azo dyes are popular coloring agents due to their good coloring properties, good variation of colors and low cost2. Unfortunately azo dyes and their metabo-lites have some serious disadvantages. By discoloring natural water sources azo dyes hinder the light transmission which causes disturbance in the aquat-ic ecosystem4. Several of the azo dyes have also been proven to be carcino-genic3. There are two types of strategies to remove hazardous substances from wastewater, the first one is separation and the other one is degradation68. One technique of separation is adsorption onto a sorbent. Po-

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rous materials with their high adsorption ability might prove efficient in removal of these and for purifying the outlet water. Several different adsor-bents have been tested for this purpose for instance modified zeolites69 and activated carbon70

3.1.4.4. Catalysis Catalysis is the process of speeding up a specific chemical reaction by low-ering its activation energy. The most known application of a catalyst is prob-ably the use of catalytic convertors that are coupled with automatic internal combustion engines to purify the exhaust gas. There are many catalysts that are used in various types of industrial processes. Different types of porous materials e.g. zeolites14 and MOFs71 have been proven useful in the field of catalysis. The methanation of syngas (CO and H2) using a Ni catalyst was first described in 1902 by Sabatier and Senderens5. The methanation reaction is currently being used in ammonia plants purifying H2 streams72, but recent-ly the conversion of carbon oxides into methane have been suggested as a potential source of energy by making SNG. Natural gas is a fossil fuel mean-ing that there are limited resources of it, natural gas holds a lot of advantages compared to other fossil fuels (e.g. coal or oil) it has a high energy density and the process of converting it to energy is much cleaner73. There is also a functioning infrastructure to utilize natural gas i.e. pipe lines. The use of nickel as the catalyst have been proven beneficial due to its high methane conversion and low costs, however using nickel does hold some disad-vantages. To reach a good level of conversion and selectivity, the operating temperature needs to be high (400 °C). At that temperature nickel would undergo sintering and would suffer from carbon deposition74. The catalytic efficiency dramatically decreases as a result. Therefore different types of substrates (e.g. Al2O3

75 and SiO276) have been use to stabilize nickel, reduce

the level of sintering and the carbon deposition. Previous studies have shown that catalyst supports could allow the reaction to run at a lower temperature with a similarly high conversion rate77.

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3.2. Inorganic carbonates Inorganic carbonates are structures containing carbonate ions [CO3]

2- togeth-er with metal counter ions. Examples of inorganic carbonates include the carbonates of group two alkaline earth metals e.g. Ca2+, Mg2+, Sr2+, Ba2+. Many inorganic carbonates are naturally occurring but can also be made synthetically. Calcium and magnesium carbonate are present in different types of naturally occurring minerals, both in pure carbonate form (i.e. mag-nesite or calcite), in hydrated forms (i.e. nesequehonite) and in mixed forms (i.e. dolomite MgCO3CaCO3

33). Strontium and barium carbonates are much rarer naturally78 but they can be made synthetically. Different ways of syn-thesizing inorganic carbonates have been suggested, for instance, through a hydrothermal process79. Magnesite have been proven hard to synthesize at low temperature, which is believed to be because of the strong hydration of the Mg2+ ions80 promoting the formation of hydrated forms. Magnesium car-bonate is commonly used as an antacid and as moisture sorbent in climbing powder. Calcium carbonate is an important component in many biominerals, for example in seashells33. Calcium carbonate is used in the production of cement and in the paper industry as coating and filler81. It is also used as an antacid. Strontium carbonate have been utilized in photacatalyst for waste water treatment82 and in chemical sensors83. Barium carbonate have been proven useful for removing sulphates and metals from wastewater84.

3.2.1. Mesoporous magnesium carbonate (MMC) In 2013 the synthesis of MMC was first described85. Details of the MMC synthesis can be found in section 4.2.1. MMC is highly porous, anhydrous and with a surface area of up to 800 m2/g. MMC has the highest Brunauer-Emmett-Teller (BET) surface area recorded for an alkaline earth metal car-bonate85. The porous structure is built up of aggregated nanoparticles and the porosity originates from the void in between them. The morphology of MMC can be viewed in the scanning electron microscope (SEM) image (Figure 4). The size of the mesopores in MMC can be varied between 3 and 20 nm by adjusting the drying conditions. The higher the energy input during the drying step the smaller the pores86. MMC is X-ray amorphous, X-ray diffraction (XRD) pattern of MMC can be viewed in Figure 5. MMC is syn-thesized without the use of templates. In contrast to many other mesoporous materials, the pore size in MMC is instead controlled by the release rate of the remaining CO2 in the synthesis liquid (Figure 6).

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Figure 4. SEM image of MMC. Scale bar 200 nm.

Figure 5. N2-isotherm (left), XRD pattern (right) of MMC

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Figure 6. Illustration of formation of pores in MMC.

3.2.1.1. Applications of MMC The high surface area and the ease and scalability of the synthesis of MMC make it highly desirable for utilization in various applications. MMC have been proven to have antibacterial properties87. The antibacterial properties together with a GRAS (generally recognized as safe) classification of MgCO3 from the FDA88 makes MMC interesting for use in various pharma-ceutical applications. The mesoporous structure of MMC gives the oppor-tunity for loading APIs into MMC. The pores can stabilize the APIs in an amorphous state and increase their dissolution, this has been done to try to enhance the release rate of the poorly soluble drugs ibuprofen (IBU)89, itraconazole (ITZ)90, celecoxib (CEL)91, cinnarizine (CIN)91 and griseofulvin (GRI)91. The APIs were proven to be incorporated in the pores of MMC in an amorphous state. The release rate was then tested in phosphate buffer (pH 6.8) for IBU, CEL, CIN and GRI in simulated gastric fluid for ITZ (pH 1.3). For all of the APIs tested the release rate was significantly increased com-pared to the crystalline drug. MMC have a high water adsorption capacity at relatively low humidity compared to other materials85. MMC have also been proven useful as a hard template for making porous carbon. By adding citric acid to the MMC sol, magnesium citrate can be created. By pyrolysis and following acid wash a highly porous carbon material with a surface area around 2000 m2/g can be obtained 92.

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3.2.2. Highly porous amorphous calcium carbonate (HPACC) The synthesis of HPACC is developed from the synthesis of MMC and a more detailed description of this synthesis can also be found in section 4.2.1. HPACC is constructed in a similar way as MMC i.e. built up of smaller na-noparticles and have a surface area of over 350 m2/g which is the highest reported for CaCO3.

3.2.2.1. Applications of HPACC HPACC has shown potential in drug delivery applications for enhanced re-lease of the poorly soluble drugs ITZ and CEL93. The released amount of ITZ from HPACC in simulated gastric fluid (pH 1.2) was 65 times higher after 30 minutes compared to the crystalline ITZ and the release of CEL in phosphate buffer (pH 6.8) was 23 times higher than that of crystalline CEL. HPACC was also used in the synthesis of porous carbon using the same method as for creating porous carbon from MMC i.e. by adding citric acid to the HPACC sol creating calcium citrate. Via pyrolysis and acid wash a high-ly porous carbon material is left. The porous carbon made from calcium citrate also had a surface area of around 2000 m2/g 92

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4. Synthesis, characterization and functionalization of nanoporous inorganic carbonates

4.1. Characterization methods The different techniques used for most of the material characterization in this thesis are presented in this section. A brief introduction to some of the tech-niques can be found in appendix 1.

4.1.1. N2 adsorption N2 sorption was used to measure the porosity of the different samples. The porosity of the inorganic carbonates was determined by recording nitrogen adsorption and desorption isotherms, respectively, (at 78 K) using a Mi-cromeritics ASAP 2020 surface area analyzer (Norcross, GA, USA).The samples were heated to 373 K under dynamic vacuum (1 x 10-4 Pa) prior to the analysis using a Micromeritics SmartVacPrep sample preparation unit. Equilibrium sorption data points were recorded when the change in pressure dropped below 0.01 % within a 10 s interval (with minimum 100 s delay). The surface area was calculated with the BET equation94 using the adsorp-tion points between p/p0 = 0.05 and 0.15. The Density Functional Theory (DFT) method was used to determine the average pore size (slit shape pore, N2 model)

4.1.2. X-ray diffraction (XRD) XRD was used evaluate the crystallinity of the inorganic carbonates. Powder XRD patterns were recorded using a Bruker D8 Twin Twin diffractometer (Billerica, Massachusetts, USA) with Cu–Kα radiation (λ = 1.54 Å) for 2θ = 10.0 to 90.0 ° at room temperature. The instrument was set to operate at 45 kV and 40 mA.

4.1.3. Scanning electron microscopy (SEM) The morphology of the inorganic carbonates were examined using Zeiss LEO 1550 and 1530 electron microscopes (Oberkochen, Germany; operated

27

at 2kV), and an in-lens secondary electron detector was used for imaging. Inorganic carbonates samples were mounted on aluminum stubs with double adhesive carbon tape and sputtered with Au/Pd prior to analysis to avoid charge build up in the non-conductive materials.

4.1.4. Thermogravimetric analysis (TGA) For studying decomposition of the materials TGA was used. The experi-ments were carried out using a Mettler Toledo TGA2 instrument (Schwerzenbach, Switzerland). The samples were heated from 25-900 °C at a heating rate of 10 °C/min under a constant flow of air (20 mL/min).

4.1.5. Fourier transform infrared spectroscopy (FTIR) IR spectra of the inorganic carbonates were obtained using a Varian 670-IR Fourier transform IR spectrometer (Santa Clara, USA) coupled with a Varian 670-IR IR microscope and a Linkam THM-600 (Tadworth, UK) heating stage (room temperature to 600 °C). Prior to analysis the inorganic carbonate samples were placed on a small piece of aluminum foil which was then placed on the heating stage. The aluminum foil reflects the IR beam after it goes through the sample. The beam was then detected by a mercury-cadmium-telluride (MCT) detector. Before measurement the inorganic car-bonate samples were heated to 150 °C in situ under flow of dry nitrogen. The IR spectra were recorded between 600-4000 cm-1 with a 4 cm-1 resolution. The background and sample signal was recorded as an average of 128 scans.

4.1.6. Raman spectroscopy Raman spectra were recorded using a Horiba Labram HR spectrometer equipped with an Nd:Yag laser (532 nm/50 mW).

4.1.7. Ultraviolet-visible (UV/Vis) spectroscopy UV/Vis spectroscopy was used for measuring the concentration both for evaluation of adsorption capacity and for release studies. The measurements were carried out on a Shimadazu UV1800 instrument (Kyoto, Japan), in a quartz cuvette with a path length of 10 mm.

4.1.8. X-ray photoelectron spectroscopy (XPS) XPS was used to evaluate the elemental composition and the chemical and electronic state for the different elements present in a sample. The experi-ments were conducted on a Phi Quantum 2000 scanning electron spectros-copy for chemical analysis (ESCA) microprobe instrument. The inorganic

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carbonate samples were first sputter-cleaned using argon ions for 10 min at 200 V in order to remove any possible surface-adsorbed contamination. The non-conductive samples were neutralized during data acquisition by an elec-tron beam of 20 mA with argon ions. The peak fitting was done using Cas-aXPS software. Gaussian-Lorentzian functions were used to fit the curves, and a Shirley function was used to subtract the background. The spectra were calibrated against the C1s peak at 284.5 eV for adventitious carbon.

4.1.9. Differential scanning calorimetry (DSC) DSC was mainly used for evaluating the state of the loaded APIs. Experi-ments were performed on a Q-2000 DSC instrument (TA Instruments, New Castle, United States) at a heating rate of 5 °C min-1 from -35 to 250 °C. Sample weights ranged from 4 to 6 mg, and all samples were sealed in alu-minum pans for analysis.

4.2. Synthesis and properties of inorganic porous carbonates In this section the various methods of synthesizing and functionalizing the materials that were used in this thesis are summarized. In section 5 the per-formance of these materials in different applications are discussed.

4.2.1. Nanoporous inorganic carbonates (MMC and HPACC) MMC was synthesized according to the procedures described by Cheung et.al.90. MgO (20 g) was mixed in 300 mL of MeOH and pressurized with 4 bar of CO2 in a sealed reaction vessel and left stirring for 24 h. After reacting for 24 h the unreacted oxide was separated from the synthesis liquid with centrifugation. After centrifugation a clear suspension of MgCO3 nanoparti-cles was obtained. The solvent in the suspension was then evaporated in a ventilated fume hood under constant stirring at 0 °C, until forming a white powder. The powder was then further dried at 110 °C until it was completely dry. When the solvent was evaporated, micrometer sized particles with a peak pore diameter around 5 nm (calculated by DFT) and a specific BET surface area of ~600 m2/g was obtained. The synthesis of HPACC was first described by Sun et. al.93 and it is carried out in a similar way as MMC syn-thesis. CaO (5 g) was dispersed in pre-heated MeOH (50 °C, 300 mL). The mixture was then pressurized with 4 bar of CO2 in a sealed reaction vessle93. After reacting for 4 h at 50 °C unreacted oxide was removed by centrifuga-tion. The solvent was then removed by evaporation in a ventilated oven at

29

150 °C overnight. The material had a surface area around 350 m2/g and an average pore size of 8-9 nm.

4.2.2. Nanoporous inorganic carbonate composites The synthesis of an inorganic carbonate composite material was developed from the syntheses of MMC and HPACC. MgO (0.5 g - 1.45 g) and CaO (0.67 g - 2.1 g) were mixed in 150 mL of MeOH pre-heated to 50°C. The mixture was then pressurized with 4 bar of CO2 and then left stirring at 50°C in a sealed reaction vessel. The reaction was carried out for 24 h under con-stant stirring and then remaining unreacted oxides were removed by centrif-ugation. The resulting suspension was dried at 150 °C overnight yielding a porous calcium magnesium carbonate composite (CMC). The ratio of the two metals in the composite was varied which resulted in materials with different characteristics. The surface area was slightly affected by the ratio as can be seen in Table 1. The difference in ratio also had an effect on the functionality of the material, which will be further discussed in the applica-tion section.

Table 1. Surface area and Ca:Mg ratio of CMC materials.

Sample Ratio Ca:Mg BET surface area(m2/g)

CMC-1 1:3 623 CMC-2 1:1 543 CMC-3 3:1 490

The composite material appeared to have a similar morphology as MMC and HPACC i.e. nanoparticles building up micrometer sized particles which can be seen from SEM images (Figure 7). XRD patterns (Figure 8, left) showed that the composite materials were all X-ray amorphous. The decomposition of the materials (Figure 8, right) clearly demonstrates the presence of the two different inorganic carbonates (MgCO3/CaCO3) in the composite materials. The drop in mass at ~400 °C was attributed to the decomposition of MgCO3 to MgO and the drop at ~700 °C was for the decomposition of CaCO3 to CaO.

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Figure 7. SEM images of CMC materials, scale bar 200 nm.

Figure 8. XRD patterns (left) and TGA curves (right) of CMC samples.

An addition of aluminum was made to the composite with the highest calci-um content (CMC-3) by adding different amounts of Al(NO3)3 (10-55 wt.%) to the MeOH during the pre-heating step. The synthesis was then carried out in the same way and the suspension was dried at 150 °C overnight yielding a porous aluminum calcium magnesium carbonate composite (ACMC). The addition of Al affected the surface area slightly, but all ACMCs were highly porous (Table 2). The inorganic carbonate composite materials were evalu-ated for their CO2 sorption capacity in Paper III.

Table 2. Surface area and Ca:Mg ratio of ACMC materials.

Sample Al/(Al+Ca+Mg) mol.% BET surface area(m2/g)

ACMC-1 3.3 501 ACMC-2 12.5 418 ACMC-3 18.1 306 ACMC-4 19.7 288 ACMC-5 23 349

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4.2.3. MMC with additives The formation of the porous structure of MMC, as described in section 3.2.1., occurs during the solvent evaporation of the suspension which causes the aggregation of the MgCO3 nanoparticles. Nanoparticles of SiO2 and Al2O3 were incorporated into the structure of MMC. This was done by add-ing 10 wt.% of SiO2 and Al2O3 nanoparticles to the suspension obtained during the MMC synthesis as described in section 4.2.1. The mixture was then dried at 60 °C until a white powder was formed.

The white powder was then further dried at 150 °C overnight. This result-ed in MMC materials with the different oxides incorporated into the porous matrix. The materials will hereafter be referred to MMC-Si and MMC-Al, properties of the materials can be seen in Table 3. The MMC materials with additives were then impregnated with Ni and used for the catalytic conver-sion of CO (Paper V).

Table 3. Surface area of MMC materials with additives.

Sample BET surface area (m2/g)

MMC 631 MMC-Si 586 MMC-Al 773

4.2.4. Grafting of APTES APTES was grafted to the surface of MMC, the coverage was varied in order to demonstrate the effect of surface amine density. The APTES grafting was carried out under dry conditions, all the glassware was dried at 150 °C prior to the experiment and the setup was continuously flushed with dry N2. MMC (5 g) was dispersed in 300 mL of toluene in a round bottomed flask and heated to 110 °C using an oil bath. The temperature of the setup was then left to stabilize for 1h. After that 1 - 43 mmol/g of APTES was added to the mixture and the amine grafting was carried out under reflux for 24 h. The amine modified (aMMC) material was then filtered of and washed twice with EtOH (50 mL) before drying at 70 °C over night. An illustration of the setup can be viewed in Figure 9. The surface area decreased slightly after the amine grafting (Table 4) but both materials still remained highly porous.

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Table 4. Properties of amine modified materials.

Sample Amine coverage (1/nm2)

Peak pore diame-ter (nm) DFT

Pore volume (cm3/g)

BET surface area (m2/g)

MMC 0 5.0 0.82 608 aMMC-1.2 1.17 4.5 0.65 601 aMMC-1.7 1.68 4.0 0.50 509

Figure 9. Illustration of amine grafting setup and aMMC-1.7.

In the IR spectra (Figure 10) of aMMC-1.7 two bands were visible at 3275 cm-1 and 3340 cm-1 which were related to the N-H stretch from the amine groups. A series of bands were also visible just below 3000 cm-1 which were related to the C-H stretching vibration of the –CH2 groups in APTES. Those bands confirmed the presence of APTES in aMMC. The TGA curves showed a difference in decomposition for the modified materials compared to MMC. The addition of the amine groups seemed to have a stabilizing effect on the carbonate, which was indicated by the increase in decomposi-tion temperature with and increased amine coverage (Figure 11). The modi-fied samples were X-ray amorphous. From calculations based on ICP data the amine density of aMMC was 1.7 groups/nm2 for the high coverage and 1.2 groups/nm2 for the low coverage.

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Figure 10. IR spectra of aMMC-1.7 (red) and MMC (black). Left; full spectra, Right; zoom in (area shown in full spectra).

XPS was performed to evaluate the interactions between APTES and MMC. The peak at 50.5 eV was related to Mg-O bonds95 this showed that APTES was bound to the surface of MMC. The Si2p peak at 102.0 eV was related to Si-O-Si bonds. This suggested that the silane groups were linked together across the surface. This link was caused by condensation of the ethoxy groups. XPS also confirmed the presents of amine groups with the N1s peak at 399.6 eV which was related to N-C bonds (Figure 12). aMMC have been used for prolonged release of IBU (Paper I), loading and release of salicylic acid (SA) (Paper II) and adsorption of azo dyes (Paper IV).

Figure 11. XRD patterns (Left) and TGA curves (Right) of MMC and aMMC sam-ples.

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Figure 12. XPS; Mg2p spectrum, Si2p spectrum and N1s spectrum of aMMC. Black; Spectra, Magenta; Peak fitting, Blue; Background.

4.2.5. Impregnation of Ni MMC, MMC-Si and MMC-Al were impregnated with Ni(NO3)3. Impregna-tion was carried out by dissolving Ni(NO3)3 (corresponding to 10 wt.% of the final product, equation 1) in an aqueous solution, after that the different substrates were added.

10%/

1

The mixtures were then left in room temperature for 12 h and then dried at 110°C for 12 h. Thereafter the impregnated materials were calcined at 500 °C in air forming NiO/MgO, NiO/MgO-Si and NiO/MgO-Al. The impregna-tion of Ni and following calcination of the materials reduced their surface area (Table 5) but the impregnated materials were still porous. SEM images showed that the morphology of the impregnated samples was similar to the materials before the impregnation (Figure 13) and XRD showed the presence of NiO in the impregnated samples (Figure 14). The Ni impregnated materi-als were evaluated for their catalytic performance (Paper V)

Table 5. Surface area of impregnated samples.


NiO/MgO 81 NiO/MgO-Si 90 NiO/MgO-Al 76

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Figure 13. SEM images of MMC samples with additives before and after impregna-tion and calcination. Scale bar 500 nm.

Figure 14. Left; XRD patterns before impregnation and calcination, Right; XRD patterns after impregnation and calcination.

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5. Applications of functional porous inorganic carbonates

The different applications of nanoporous inorganic carbonates are discussed in this section. In Table 6 the different materials and their abbreviation are listed which can be of help when reading this section.

Table 6. Samples used for the various applications.

Abbreviation Sample

MMC aMMC-1.2 aMMC-1.7 p-MMC HPACC CMC/O-1 CMC/O-2 CMC/O-3 ACMC/O-1 ACMC/O-2 ACMC/O-3 ACMC/O-4 ACMC/O-5 NiO/MgO NiO/MgO-Si NiO/MgO-Al

Mesoporous magnesium carbonate Amine modified mesoporous magnesium carbonate, 1.2 groups/nm2 Amine modified mesoporous magnesium carbonate, 1.7 groups/nm2 Propyl modified mesoporous magnesium carbonate Highly porous magnesium carbonate Ca/Mg carbonate/oxide (Ca:Mg 1:3) Ca/Mg carbonate/oxide (Ca:Mg 1:1) Ca/Mg carbonate/oxide (Ca:Mg 3:1) Al-Ca/Mg carbonate/oxide (Al 3.3 mol %) Al-Ca/Mg carbonate/oxide (Al 12.5 mol %) Al-Ca/Mg carbonate/oxide (Al 18.1 mol %) Al-Ca/Mg carbonate/oxide (Al 19.7 mol %) Al-Ca/Mg carbonate/oxide (Al 23 mol %) Ni/Mg oxide Ni/Mg/Si oxide Ni/Mg/Al oxide

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5.1. Drug loading and delivery 5.1.1. Controlled release of IBU – Paper I As stated in section 3.1.4.1., controlled drug release is an interesting ap-proach for the release of APIs with a short biological half-life. The pro-longed release can possibly contribute to a sustained effect of the API for a longer period of time. IBU is a poorly soluble API with a short biological half-life (around 2 h)55. Therefore it would be beneficial to have an enhanced dissolution followed by a controlled release of IBU to achieve a good thera-peutic response. Both MMC, aMMC-1.2 and aMMC-1.7 was loaded with ~20 wt.% with IBU, from ethanol via a solvent evaporation method. The loaded amount was calculated from TGA and was around 20 wt.%. N2-adsorption verified that IBU was successfully loaded into the porous struc-ture of aMMC with a reduction in the pore volume (Table 7). IBU was then released from the aMMC carrier in a phosphatebuffer (pH 6.8) and the re-lease was monitored over 24 h with UV/Vis (219.4 nm). The release curves can be viewed in Figure 15 together with the IBU release curve from unmod-ified MMC. Both aMMC-1.7 and aMMC-1.2 had a similar release profile; first an initial burst release followed by a slower release step. During the first 30 minutes MMC had released almost 98 % of the loaded IBU whereas for aMMC-1.2 and aMMC-1.7 the released amount was 86 % and 68 % respec-tively. When studying the release rate from the two aMMC materials we can clearly see the effect that amine density has on the release rate; the higher the amine density the slower the release. This was believed to be an effect of an interaction between the amine group of aMMC and the carboxylic group of IBU

Table 7. Loaded amount and pore volume of MMC, aMMC-1.2 and aMMC-1.7.

Sample Loaded amount (wt.%) Pore volume before loading (cm3/g)

Pore volume after loading (cm3/g)

MMC 19.3 0.82 0.44 aMMC-1.2 19.2 0.65 0.35 aMMC-1.7 20.4 0.50 0.21

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Figure 15. Release rate of IBU from MMC (blue, ▲), aMMC-1.2 (black, ■) and aMMC-1.7 (red, ●).

To support the theory of the prolonged release being an effect of the interac-tion with the amine another modification was made. The second modifica-tion was made with N-propyltriethoxysilane (PTES) where the amine group was substituted with a metyl group. The grafting of PTES was done in a comparable way to APTES and PTES had a similar effect on the porosity of the material (Table 8). Release from the PTES modified material (pMMC) differed from the release from aMMC (Figure 16). This supports the theory that the prolonged release from aMMC is due to an interaction between the amine groups and the carboxylic groups of IBU. Table 8. Properties of pMMC and pMMC loaded with IBU.

Sample PTES Coverage (1/nm2)

Peak pore diameter (nm) DFT

Loaded amount (wt.%)

Pore volume (cm3/g)

BET sur-face area (m2/g)

pMMC 1.76 4.8 - 0.58 452 pMMC-IBU

1.76 5.0 19.0 0.29 211

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Figure 16. Release rate of IBU from MMC (blue, ▲), pMMC (green, ♦) and aMMC-1.7 (red, ●).

The relation between the number of amine groups and the IBU release rate was calculated using equation 2;

2 where n is the number of functional groups grafted to the surface and k is the release rate of IBU from the sample during the first 30 minutes. Kf gives information about the effect that the number of functional groups have on the release rate. For the two amine modified materials Kf was 1.23 x 103 mg/(L mol min) for aMMC-1.7 compared to 1.51 x 103 mg/(L mol min) for aMMC-1.2. This also attests to the effect that the amine density has on the release rate. Further the Kf value for pMMC was 1.94 x 103 mg/(L mol min) that also indicates the weaker interaction between IBU and pMMC com-pared to the aMMC samples. This clearly shows the effect of the amine groups and the amine density had on the release rate of IBU.

5.1.2. Loading and release of SA – Paper II SA has been used for a long time to treat different skin conditions. Its ability to break down the outer layer of the skin together with its anti-inflammatory, bacteriostatic and antifungal properties makes it a good substance in the treatment of various skin conditions e.g. acne. This study shows a possible way to incorporate SA into aMMC, its release in vitro and an evaluation of aMMCs cytotoxicity towards human dermal fibroblast (hDF) cells. Loading SA onto MMC is problematic due to the basic nature of MMC and the acidic nature of SA (pKa 2.97). SA was successfully loaded onto aMMC with high amine coverage. aMMC loaded with SA had the same morphology as aMMC and both samples were X-ray amorphous (Figure 16).

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Figure 17. Left; XRD patterns of aMMC, aMMC-SA and MMC, Right; DSC curves of aMMC, aMMC-SA and pure SA.

DSC further showed that the loaded SA was confined in an amorphous state in aMMC (Figure 17) due to the lack of the endothermic peak in the DSC curve related to the melting point of crystalline SA. TGA was used to calcu-late the loading degree of SA on aMMC (Figure 18) and aMMC was found to be loaded with 8 wt.% SA. The release of SA from aMMC was done in a phosphate buffer at pH 6.8, all of the loaded SA could be released within 15 minutes which is much faster than the corresponding crystalline drug (Figure 18). The cytotoxicity of aMMC was also evaluated using the almar blue assay. The cells were exposed to different concentrations of aMMC (1000, 500, 200 and 50 μg/mL) for 24 and 48 h. It was found that aMMC showed no cytotoxicity for concentrations of up to 1000 µg/L for 48h of exposure (Figure 19). This then opens up for the possibility of using aMMC-SA in topological formulation to target various skin conditions and also the ability to load and release APIs with a low pKa from aMMC.

Figure 18. Left; TGA curves for aMMC, MMC and aMMC-SA, Right; Release curves for aMMC-SA and SA.

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Figure 19. Cell viability of hDF cells exposed to MMC (left) and aMMC (right) for 24 h (black) and 48 h (grey). Cell viability larger than 70 % of the negative control indicates a non-cytotoxic effect (70 % indicated by dotted line).

5.2. High temperature sorption of carbon dioxide – Paper III CCS has, as stated earlier, been proposed as a feasible strategy to reduce the outlet of CO2 into the atmosphere. Here we have evaluated different inorgan-ic oxide composite materials as potential sorbents for CO2. In this study CaL has been used as the basis for CO2 sorption. The CMC materials are a mix-ture of CaCO3 and MgCO3 nanoparticles. Upon calcination, both carbonates will decompose into their corresponding oxides. The CaO will then function as the CO2 sorbent and MgO as a stabilizer, hindering the sintering of Ca-CO3. To further enhance the stability of the composites towards sintering Al(NO3)3 was introduced creating ACMC. By using the CMC and ACMC materials we can see an enhancement in the cyclic stability as well as a maintained high uptake for CO2. The CMCs were tested for CO2 sorp-tion/desorption using a TGA. CMCs were first calcined to form calcium magnesium oxide composites (CMO) at 850 °C under N2 flow (50 mL/min). Afterwards CO2 uptake experiment was carried out at 650 °C with a flow of CO2 (50 mL/min) for 60 min. Regeneration of the CMOs was carried out by heating the CMOs to 850 °C under N2 flow (50 mL/min) for 60 min. An illustration of the formation and cycling of the CMC materials can be viewed in Figure 20.

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Figure 20. Illustration of formation and CO2 cycling of CMC materials.

It was clear that the ratio of Ca/Mg had a significant impact of the CO2 up-take capacity and the cyclic stability (Table 9). The CO2 uptake for the first cycle of CMO-1, -2 and -3 was 0.274 g/g, 0.445 g/g, 0.586 g/g respectively. Over 23 adsorption and desorption cycles capacity loss for CMO-1, -2 and -3 was 0.7 %; 19.8 % and 35.7 % respectively. This can be compared with HPACC that had an initial uptake of 0.658 g/g and a capacity loss of 51.3 %. There is a clear correlation between the CaO content and the CO2 uptake. The importance of MgO for an enhanced cyclic stability was also clear when viewing the obtained data. The uptake for the different materials over 23 cycles can be seen in Figure 21. The higher loss in capacity for the CMOs with a higher Ca:Mg ratio is believed to be caused by the sintering of the CaCO3. This could also be seen in SEM images (Figure 22). The CMO with the highest Mg content (CMO-1) appeared to be much more porous after cycling compared to the CMO with higher Ca content (CMO-3) and to the CaO-HPACC material. The addition of Al to CMO-3, creating aluminum calcium magnesium oxide composites (ACMO), also further improved the cyclic stability (Table 10). The ACMO-4 material which contained 19.7 mol% Al had a high stability. Over 23 cycles the capacity loss was 5.2 % which can be compared to the 51.3 % capacity loss of calcium carbonate for the same number of cycles.

Table 9. Uptake and capacity loss of CMO materials and HPACC

Sample CO2 uptake 1stcycle (g/g)

CO2 uptake 23rd

cycle (g/g) Capacity loss after 23 cycles (%)

CAO-HPACC 0.658 0.320 51.3 CMO-1 0.274 0.246 0.7 CMO-2 0.445 0.356 19.8 CMO-3 0.586 0.377 35.7

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The uptake over 23 cycles can be seen in Figure 23. The higher stability and improved cyclic capacity is believed to be due to the stabilization from the addition of the MgO and Al. MgO can sterically hindering the CaCO3 from sintering, thus retaining a higher capacity as observed for ACMO-4 during cycling. The reduction in sintering is believed to have caused the improve-ment in cycling capacity of the ACMO samples. The reduction in sintering could also be seen from SEM images (Figure 24).

Figure 21. Left; CO2 uptake for each cycle, Right; kinetics of uptake during first cycle. For CMO-1 (magenta, ▼), CMO-2 (blue, ▲), CMO-3 (red, ●) and HPACC (black, ■).

Figure 22. SEM images before (top) and after (bottom) CO2 cycling of HPACC and CMC samples. Scale bar 200 nm.

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Table 10. Uptake and capacity loss of ACMO materials.

Sample CO2 uptake 1stcycle (g/g)

CO2 uptake 23rdcycle (g/g)

Capacity loss after 23 cycles (%)

ACMO-1 0.594 0.392 34 ACMO-2 0.579 0.477 17.6 ACMO-3 0.538 0.482 10.4 ACMO-4 0.537 0.509 5.2 ACMO-5 0.517 0.502 2.8

Figure 23. Left; CO2 uptake for each cycle. Right; kinetics of uptake during first cycle. ACMO-1 (black, ■), ACMO-2 (Cyan, ▲), ACMO-3 (light magenta, ▼), ACMO-4 (dark green, ♦) and ACMO-5 (dark blue, ◄).

Figure 24. SEM images before (top) and after (bottom) of ACMC samples. Scale bar 200 nm.

45

The two best performing ACMO samples over 23 cycles (ACMO-4 and ACMO-5) were also tested for 100 CO2 uptake and desorption cycles (Fig-ure 25). The cycling conditions were then adjusted, the adsorption step was reduced to 30 minutes and the desorption step to 15 minutes and the heating rate was increased to 20 °C/min. Over a 100 cycles it was clear that ACMO-4 performed the best both in terms of stability and uptake. The reduction in uptake over multiple cycles is believed to be due to sintering and also possi-bly to the formation of mayenite, which increases the stability but reduces the CO2 uptake. ACMO-4 lost 59 % of its capacity over 100 cycles, this can be compared to HPACC that lost 51 % during the first 23 cycles. This clear-ly shows the increase in stability over multiple cycles for the composite ma-terials.

Figure 25. CO2 uptake of ACMO-4 (dark green) and ACMO-5 (dark blue) over 100 cycles.

5.3. Adsorption of azo dyes – Paper IV The need for good adsorbents for the removal of azo dyes from wastewater was discussed in section 3.1.4.3. Here the adsorption capacity of aMMC of three different types of anionic azo dyes, Acid red 183 (AR183), Amaranth (AM) and Reactive black (RB5), were evaluated. The adsorption capacity of aMMC-1.7 was compared to that of MMC, non-porous MgCO3, MgO and amine modified non-porous MgCO3 (aMgCO3). The BET surface area for the different samples can be viewed in Table 11.

46

Table 11. Surface area of adsorbents.


MMC 660 aMMC 510 MgO 120 MgCO3 20 aMgCO3 20

The uptake of the different dyes using different sorbents can be viewed in Figure 26. The uptake was calculated using equation 3.

(3)

By comparing the dye uptake of the different adsorbents some conclusions could be made. From the isotherms it was clear that the addition of amine groups to the surface of MMC significantly increased the dye uptake. Fur-ther the importance of porosity was also clear when comparing the uptake on aMgCO3 to the uptake on aMMC. Both materials have amine groups which theoretically should enhance the adsorption of the anionic dyes. Indeed both aMMC and aMgCO3 showed a higher uptake than their unmodified counter-part for two of the dyes tested. For AR183 and RB5 both aMMC and aMgCO3 had a higher uptake than MMC and MgCO3 respectively. For AM aMMC had a higher uptake than MMC whereas aMgCO3and MgCO3 had a similar uptake. These results clearly showed the importance of both porosity and the presence of amine groups for enhanced adsorption of anionic dyes. Three different models, Langmuir, Freundlich and Sips, were used to fit the data from the adsorption isotherms for aMMC. The Langmuir equation96 describes the adsorption of a monolayer onto a homogenous surface (equa-tion 4).

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Figure 26. Adsorption isotherms RB5, AM and AR183; (▼) aMMC, (■) MgO, (●) MMC, (▲)MgCO3 and (♦) aMgCO3. The lines are draw for clarity and do not repre-sent the data points.

(4)

Here q is the uptake (mg/g), qe the equilibrium uptake (mg/g), k the Lang-muir isotherm constant (L/mg) and c the equilibrium concentration (mg/L).

The Freundlich97 equation describes a heterogeneous system and is ex-pressed in equation 5.

(5)

With q being the uptake (mg/g), Ce the equilibrium concentration (mg/L), k the Freundlich constant and 1/n is the Freundlich exponent. The Sips equation98, also called the Langmuir-Freundlich, is a combination of the Langmuir and the Freundlich models (equation 6).

(6)

Here q is the uptake (mg/g), qe the equilibrium uptake (mg/g), C is the equi-librium concentration (mg/L), k the model constant (L/g) and the Sips con-stant n (0 < n < 1) represents the homogeneity of the system; a fully homog-enous system will have an n value of 1 and Equation 4 will become the Langmuir equation. A heterogeneous system will be represented with n val-ue lower than 1, with increased heterogeneity as n approaches 0. The constants from the different models can be viewed in Table 12. For all of the dyes the sips model shows the best fit to the data points. The sips con-stant n was not 1 or close to 1 which is an indication that the adsorption was not homogeneous.

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Table 12. Constantsand R2 from the three different models.

Model Constant RB5 AM AR183

Langmuir R2 0.9647 0.9917 0.9864 qe (mg/g) 357.298 141.512 284.392 Freundlich R2 0.9428 0.9158 0.9895 Sips R2 0.9942 0.9971 0.9906 qe (mg/g) 407.621 146.988 552.872 n 0.477 0.743 0.747

The kinetics of the adsorption was also evaluated by measuring the uptake every 10 minutes. The data points were then fitted the pseudo-first99 (equa-tion 7) and pseudo-second100 (equation 8) order. For AM and RB5 the pseu-do-second order gave the best fit (Table 13). This was an indication that the adsorption is dependent on both the adsorbent and the adsorbed dye. It also indicates that the adsorption is driven by chemisorption. The kinetics for AR 183 had a different pattern then the other two dyes, there seems to be an onset period for the first 20 minutes. The uptake of AR183 could therefore not be fitted to the kinetic models.

1 (7)

(8)

With qt being the amount adsorbed at time t (mg/g), qe being the amount adsorbed at equilibrium (mg/g), and k being the rate constant.

The effect of salt (NaCl) and pH was also evaluated to see the effect on the dye adsorption capacity. The addition of NaCl (0-1000 mM) reduced the uptake of all the dyes on aMMC. The reduction was more prominent for AR183 and AM. At the highest NaCl concentration (1000 mM) the uptake of AR183 and AM was 20 % and 70 % of their original values (no salt), respec-tively (Figure 27). This further indicates that the uptake was driven by an electrostatic interaction between the amine groups and the anionic dyes. The addition of NaCl caused a shielding effect from the additional ions and re-duced the interaction between the dye and aMMC.

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Table 13. Constants from kinetic models.

Model Constant RB5 AM AR183

Pseudo-first R2 0.9950 0.9792 Not possible qe (mg/g) 263.39 86.809 k 0.0473 0.0729 Pseudo-second R2 0.9941 0.9930 Not possible qe (mg/g) 353.76 105.109 k 1.17 x 10-4 7.96 x 10-4

Figure 27. Effect of NaCl (Left) and pH (Right) on dye uptake. AR183 (●), AM (■) and RB5 (▲).

The initial pH was also varied between (2 and 12). For RB5 and AM the uptake was unaffected between pH 4 and 10 but reduced at pH 2 and 12. The decrease in dye uptake at pH 2 was believed to be an effect of the sorbents sensitivity to low pH and the reduction at high pH was probably caused by deprotonation of the amine groups. The amine groups of aMMC would be protonated at pH below 10 101, and these protonated amine groups could then interact with the anionic dyes. The interaction increases the amount of azo dye that can be adsorbed on aMMC when compared to unmodified MMC. The uptake of AR183 at different pH differed from the other dyes, at higher pH the uptake increased. The increase in uptake at higher pH for AR183 is not fully understood.

50

5.4. Catalysis, methanation of syngas – Paper V The conversion of syngas into SNG using a Ni catalyst has, as stated earlier, been suggested as a strategy for the production of SNG. The need for stabi-lizing Ni on a support material to prevent sintering and carbon deposition was discussed. Here the Ni containing oxide materials NiO/MgO, NiO/MgO-Si and NiO/MgO-Al, that were obtained after impregnation of Ni(NO3)2 onto MMC mixed with metal oxides and calcination, were evalu-ated based on their catalytic performance. The CO methanation was carried out in a fixed bed reactor under 0.1 MPa at three different temperatures (300, 325 and 350 °C) with a gas flow of 50 mL/min and a ratio of H2/CO=3. Ac-tivation of the catalyst was performed prior to the experiment at 550 °C in H2 for 2 h. The CO conversion, CH4 selectivity and yield were calculated with equation 9, 10 and 11 respectively.

% , ,100

, 9

% ,, ,

10

% 100

11

Xco is the conversion of CO, SCH4 is the selectivity of CH4, YCH4 is the CH4 yield and Fx,in and Fx,out are the volume flow rates of X (X= CO or CH4) at the inlet or outlet. The results for the conversion, selectivity and yield can be viewed in Figure 28. Results showed that Ni/MgO-Al performed the best out of the catalyst tested in terms of CO conversion and CH4 yield. At 350 °C Ni/MgO-Al had a CO conversion close to 100 % and a CH4 yield of around 75 %. The CH4 selectivity was however slightly lower (75 %) for the Ni/MgO-Al catalyst compared to the others. The results show the possibility of using modified MMC as a support for Ni to achieve a high performance in the methanation of syngas.

51

Figure 28. Left; CH4 selectivity, Middle; CO conversion and Right; CH4 yield of NiO/MgO catalysts.

52

6. Conclusions

A variety of different porous materials have been developed based on the synthesis of MMC. They have been thoroughly characterized and evaluated for use in different pharmaceutical and environmental applications.

Amine modified MMC, have here been proven effective for controlled re-lease of IBU, loading and release of SA and enhanced adsorption of various azo dyes. These applications show that adding an amine group to the surface of MMC can alter the properties and performance of the material.

Further alterations to the synthesis and additions to the synthetic liquid to create composite materials were also successfully carried out. By combining the synthesis of MMC with the synthesis of HPACC and adding Al(NO3)3, a composite material was made which showed a high CO2 uptake at high tem-perature (650 °C) as well as a high cyclic stability.

Composite materials were also synthesized by adding Al2O3 or SiO2 na-noparticles to the synthetic liquid of MMC. This created highly porous mate-rials with the oxide nanoparticles incorporated into MMC. These materials were then impregnated with Ni(NO3)2 and tested for their catalytic perfor-mance for the conversion of syngas to natural gas. The material containing Al2O3 performed the best and showed a high conversion, selectivity and yield.

This thesis has discussed several different applications for modified MMC. It shows that this material has great potential in different fields. This thesis also demonstrates many different ways to modify this material to target various applications.

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7. Future work

This thesis demonstrates a variety of different methods to modify MMC and the possibility to tailor its properties to be more suitable for different appli-cations. These findings open up for further investigations in these areas. More in detail, drug release can be further evaluated for other APIs and also include substances with a lower pH by using aMMC. The dye adsorption can also be tested for other types of reactive dyes and mixtures of dyes. The work of using MMC as a support for catalysis shows very promising results. The next step would be to vary the amount and try to find an optimal ratio between the different oxides. The CO2 work also shows great potential and it proves that it is possible to add an additional specie i.e. Al(NO3)3 to the syn-thesis and incorporate it into the porous structure. Further this work also shows methods to incorporate other species in- or onto MMC to alter its functionality, which can be utilized to modify the material for other applica-tions.

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Svensk sammanfattning

Porösa material är material som har håligheter i sin struktur. Det innebär att porösa material har en mycket större yta i jämförelse med icke porösa material. Porositeten och den höga ytarea hos dessa materials innebär att det finns många platser tillgängliga för interaktion med andra ämnen. Det till-sammans med möjligheten att addera olika aktiva substanser till den porösa strukturen öppnar upp för möjligheten att använda dessa material inom många olika områden. I den här avhandlingen är nanoporösa oorganiska karbonater i fokus, mer specifikt mesoporöst magnesiumkarbonat (MMC) och olika modifierade versionen av detta material. MMC är uppbyggt av aggregerade nanopartiklar och porositeten i detta material kommer ifrån hålrummen mellan dessa partiklar. Ytan på materialet har använts för att fästa amingrupper (-NH2) och därige-nom ökat möjligheten för interaktion mellan ytan och olika substanser. Det aminmodifierade materialet kallas för aMMC. aMMCs möjlighet att intera-gera med olika substanser på ett sätt som skiljer sig från MMC har visats i olika studier. Genom att ladda och frisätta den antiinflammatoriska substan-sen ibuprofen (IBU) från aMMC, ses en fördröjd frisättning av IBU jämfört med frisättningen från MMC. Den fördröjda frisättningen tros vara en effekt av en interaktion mellan amingrupperna och karboxylgrupperna i IBU. Vi-dare har aMMC också visat ett ökat upptag av olika azofärgämnen från vat-tenlösning jämfört med MMC. De azofärgämnen som har testats är alla an-joniska, negativt laddade, och det ökade upptaget av dessa tros vara på grund av en elektrostatisk interaktion mellan de negativt laddade färgämnena och de positivt laddade amingrupperna. aMMC har också laddats med salicylsyra och visat på en snabb frisättning av denna substans. Ett kompositmaterial av magnesium- och kalciumkarbonat har också synteti-serats. Komposit materialet har sedan testats för upptag av CO2 vid 650 °C och regenerering vid 850 °C. Förhållandet mellan magnesium och calcium i materialet visade sig vara av stor vikt då ett högre innehåll av magnesium bidrog till en ökad cyklisk stabilitet, alltså ett bibehållet högt upptag efter regenerering. Medan en högre mängd kalcium i materialet visade på ett högre upptag av CO2 men en sämre cyklisk stabilitet. Till kompositen med den högsta mängden kalcium gjordes en tillsats av aluminiumnitrat

55

(Al(NO3)3). Detta gav ett högt upptag av CO2 samt ökade den cykliska stabi-liteten.

Tillsats av Aluminiumoxid (Al2O3) och kiseldioxid (SiO2) gjordes också genom att blanda nanopartiklar av de båda oxiderna med syntetsvätskan av MMC. Detta skapade modifierade MMC-material med Al2O3 och SiO2 i den mesoporösa strukturen. Dessa material impregnerades sedan med nickelni-trat (Ni(NO3)3) och upphettades därefter till 550 °C vilket genererade mixade oxidmaterial. Dessa användes sedan för att katalysera reaktionen av syntes-gas (CO och H2) till naturgas (CH4). Materialet med Al2O3 uppvisade en hög katalytisk konversion och en hög selektivitet för CH4 vid 350 °C.

I denna avhandling har MMC använts som ett basmaterial för att skapa funktionella porösa material avsedda för specifika läkemedels- och miljöap-plikationer. MMC kan syntetiseras utan att använda surfaktanter och kan framställas i stor skala.

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Acknowledgement

First and foremost I want to thank my main supervisor Ocean Cheung, for your enthusiasm, support and that your office door has always been open (even when you were 1300 km away). I really appreciate all the help and guidance that you have given me through the years and I am forever grateful for it. I also want to thank my co-supervisor and professor Maria Strømme, for your inspiring enthusiasm for all the different projects, I am forever thankful for this opportunity. I would also like to thank other members of the NFM group: Jonas Lindh, for supervising me during my master degree project and for introducing me to the NFM group. Christian, Simon, Lisa, Mia and Alex; I am so happy that I have shared this experience with you! You have made all the lunches, fikas and AWs so much better! Rui, for great company on all the conferences, for proofreading this thesis and for being patient when teaching me to eat hotpot. Hao, for your support, your cooking and for being a great friend! Chao, for good company, I would also like to say that I am sorry for all the times that I have bumped in to your chair trying to get to my desk (I blame the size of our office!). Peng, Teresa, Sara, Natalia, Ken, Cecilia for all the support, help and in-put regarding my work. The students that have helped me through the years: Joakim, Ao, Philip, Lukas and Jonas. Your help have been invaluable to my work and I can’t thank you enough! And to past and present members of the NFM group, Albert, Levon, Mar-tin, Petter, Huan, Lulu, Michelle, Rikard, Shengyang, Igor, Kai, Jiaojiao, Li, Viviana, Thanos, Changqing, Gopi, Christoffer, Daniel and others. Thank you, I have really enjoyed my time here! Tack till vänner, familj och släkt för allt stöd. Det här hade inte varit möjligt utan er! Peter och Niklas, Emma och Elias, Anne-Marie och Sören, Karin och Per, Inga och Janne, Lotta och Krister med familjer.

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Sofie, tack för att jag alltid får stöta och blöta problem med dig, så glad att jag fortfarande har dig i mitt liv! Till mina Vackstatjejer, Sjukgymnaster (/Fysioterapeuter) och Ingenjö-rer; min studietid hade inte varit densamma utan er. Jimmy, för att du alltid finns där även när det är svårt. Tack för ditt tålamod, din kärlek och oförstörbara optimism. Lars, för att du alltid ställer upp för mig. För att du visade mig Uppsala och gav mig tak över huvudet när jag först flyttade hit. Mamma, för att du har stöttat mig i det jag vill göra och för att du alltid tror på mig. Pappa, för att du alltid uppmuntrade mig och såg styrkor även i mina svag-heter. Någonstans inom oss är vi alltid tillsammans.

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Appendix I. Characterization methods

N2 adsorption Nitrogen adsorption is one of the most common methods for measuring po-rosity of a material. N2 gas is firstly adsorbed and then desorbed from the surface of a material at different pressures and constant temperature (77°K), creating an isotherm. The shape of the isotherm, plot of the adsorbed amount of N2 (mmol/g) against the relative pressure (P/P0), will have a characteristic shape depending on the porous nature of the material. There are six different isotherms defined by IUPAC102 (Figure 29).

Figure 29. Different isotherms defined by IUPAC. I. Microporous materials, II. Non-porous or macroporous materials, III. Weak interaction with adsorbent-adsorbate, IV. Mesoporous materials, V. Mesoporous non-wetting material, VI. Well-ordered non-porous material

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The type IV isotherm is characteristic for mesoporous materials and it con-tains a hysteresis, i.e. a difference in uptake between the adsorption and de-sorption curve. The hysteresis is caused by the capillary condensation of N2 in the mesopores when the pressure is reduced, making the N2 desorb at a lower pressure. The surface area, pore size and pore volume can also be cal-culated from N2 adsorption. The Langmuir model96 can be used for calculat-ing the surface area. The model makes the assumptions that the measured surface is uniform, that there are no interactions between adsorbed species and only a monolayer is formed. However, the most common method to calculate the surface area is the BET method94. The BET method is based on the Langmuir model but it makes the assumption that there is multilayer adsorption, the Langmuir model can be applied to each layer and there is no interaction between the adsorbed layers. The BET method calculates the surface area from the N2 uptake at P/P0 between 0.05 and 0.3. The pore vol-ume is calculated based on the maximum uptake of N2. The pore size is usu-ally calculated with the DFT or the BJH equation.

X-ray diffraction XRD is used to evaluate the crystallinity of different samples. X-rays are irradiated at the sample at different angles, the atoms will then reflect the X-rays and a detector will record the intensity of the reflected X-rays at a spe-cific angle. Crystalline materials have long order arrangements and will have distinct diffraction patterns. The long order arrangement means that these materials will reflect X-rays with a high intensity at specific angles. Amor-phous materials, that only have short order arrangements, will not create a distinctive pattern. Amorphous materials will give a diffractogram with broad humps rather than sharp peaks, this is due to the amorphous nature and the higher degree of disorder in the material.

Scanning electron microscopy SEM is a technique that allows you to view the texture and topography of materials at a higher resolution than with an optical microscope. The sample is exposed to an electron beam and by detecting the electrons emitted from the sample an image of the surface is built up. SEM allows the user to exam-ine the morphology of the sample down to a nanometer scale. The electrons from the beam will cause charging of the material that might interfere with the imaging, therefore non-conductive materials usually need to be coated with a conductive material e.g. gold or palladium, before being scanned. The sample will also emit X-rays when exposed to an electron beam. The X-rays

60

are emitted with different energies which can be analyzed by EDX and iden-tify the elements that are present.

Thermogravimetric analysis TGA is used to show the change in mass of a sample as a function of tem-perature. By heating up the sample at a constant heating rate and measuring its weight continuously, TGA can give both qualitative and quantitative in-formation. Different types of gases can also be connected to the instrument, which means that the measurment can be carried out in different atmos-pheres. This also means that the instrument can be used to measure the ad-sorption of a gas at a specific temperature.

Vibrational spectroscopy (IR and Raman) Vibrational spectroscopy techniques are primarily qualitative techniques where bonds present and the composition of different compounds can be evaluated. They are based on molecular bond vibrations. If the frequency of the vibration is the same as the frequency of the electromagnetic light source, the light will be absorbed. IR- and Raman spectroscopy are com-plementary techniques to each other. Information that can be obtained from IR spectroscopy may not be possible to obtain from Raman spectroscopy and vice versa. For a mode to be IR active it needs to change the electric dipole moment and for a mode to be Raman active it needs to be a change in the polarizability.

Ultraviolet-visible spectroscopy UV/vis spectroscopy is based on the adsorption of electromagnetic radiation in the UV/vis region (190-750 nm). Molecules that are UV-active, i.e. ab-sorbs light in the UV/vis region, will have a high absorbance at a specific wavelength. By letting light pass through a sample and record the difference in intensity from ingoing light and the detected outgoing light the absorbance can be obtained. The absorbance can be used to determine the concentration of a sample. The relation between absorbance and concentration is described by Beer-Lambert law (equation 12)

ɛ ∗ ∗ (12)

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Where A is the measured absorbance, ɛ is the coefficient related to the wave-length, b is the path length and c is the concentration of the analyte.

X-ray photoelectron spectroscopy XPS is a surface analytical technique which gives information elemental composition of the sample as well as the chemical and electronic state of the elements. By probing the surface of the sample with an X-ray and simulta-neously measuring the kinetic energy and the number of electrons emitted from it information about the surface composition and chemistry can be ob-tained. The binding energy (Eb) is the difference between the energy of the incident radiation (hv) and the kinetic energy of the ionized electron. The Eb value is characteristic for each element and can therefore be used to identify the types of atoms present in the sample.

Inductive coupled plasma optical emission spectroscopy (ICP-OES) ICP-OES is used to detect different elements in a sample. The inductive coupled plasma excites the atoms or ions and the characteristic electromag-netic radiation emitted from the samples. An emission spectra is recorded and the elements present within the sample can be quantitatively identified using the emission spectra. Liquid samples can be analyzed directly but solid samples needs to be dissolved before being analyzed. The intensity of the emission can also be used to quantify the amount of the specific element.

Differential scanning calorimetry DSC is widely used to determine purity of different samples and to examine the different transition temperatures i.e. crystallization and for polymers the glass transition temperature. DSC measures the heat flow versus the temper-ature. It will show how much the sample needs to be heated to reach a cer-tain temperature. Usually a reference sample is measured simultaneously and the heat flow is the difference between the reference and the measured sam-ple. This gives information about the crystallinity of the sample and if the crystallization is endo- or exothermic. It can also be used to evaluate if a sample is amorphous, as it will then lack its peak corresponding to the melt-ing point of the crystalline material.

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