Smart Materials for Waste Water

Applications

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Smart Materials for Waste

Water Applications

Edited by

Ajay Kumar Mishra

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Library of Congr ess Cataloging-in-Publication Data:

ISBN 978-1-119-04118-4

Printed in the United States of America

10 9 8 7 6 5 4 3 2 1

v

Contents

Preface xv

Part 1 Carbon Nanomaterials 1

1 Easy and Large-Scale Synthesis of Carbon Nanotube-Based Adsorbents for the Removal of Arsenic and Organic Pollutants from Aqueous Solutions 3

Fei Yu and Jie Ma1.1 Introduction 41.2 Removal of Arsenic from Aqueous Solution 5

1.2.1 Activated Magnetic Carbon Nanotube 51.2.1.1 Synthesis Method 51.2.1.2 Characterization of Adsorbents 51.2.1.3 Adsorption Properties 9

1.2.2 Sulfh ydryl-Functionalized Magnetic Carbon Nanotube 121.2.2.1 Synthesis Method 121.2.2.2 Characterization of Adsorbents 131.2.2.3 Adsorption Properties 19

1.3 Removal of Organic Pollutants from Aqueous Solution 221.3.1 Magnetic Carbon Nanotubes for Dye Removal 22

1.3.1.1 Synthesis Method 221.3.1.2 Characterization of Adsorbents 221.3.1.3 Adsorption Properties 26

1.3.2 Magnetic CNTs/C@Fe/Chitosan for Tetracycline Removal 311.3.2.1 Synthesis Method 311.3.2.2 Characterization of Adsorbents 311.3.2.3 Adsorption Properties 34

1.4 Summary and Outlook 39Acknowledgment 40References 40

vi Contents

2 Potentialities of Graphene-Based Nanomaterials for Wastewater Treatment 47

Ana L. Cukierman, Emiliano Platero, María E. Fernandez,

and Pablo R. Bonelli2.1 Introduction 482.2 Graphene Synthesis Routes 492.3 Adsorption of Water Pollutants onto

Graphene-Based Materials 522.3.1 Adsorption of Heavy Metals 542.3.2 Adsorption of Organic Contaminants 63

2.3.2.1 Dyes 642.3.2.2 Other Organic and Emerging

Contaminants 672.4 Comparison of the Adsorption Performance of

Graphene-Based Nanomaterials 722.5 Regeneration and Reutilization of the Graphene-Based

Adsorbents 732.6 Conclusion 77Acknowledgements 78Nomenclature 78References 79

3 Photocatalytic Activity of Nanocarbon-TiO2 Composites

with Gold Nanoparticles for the Degradation of Water Pollutants 87

L.M. Pastrana-Martínez, S.A.C. Carabineiro,

J.L. Figueiredo, J.L. Faria, A.M.T. Silva, and J.G. Buijnsters3.1 Introduction 883.2 Experimental 90

3.2.1 Carbon Materials Preparation 903.2.2 Synthesis of Carbon–TiO

2 Hybrid Catalysts 90

3.2.3 Synthesis of Au-Loaded TiO2 Catalysts 91

3.2.4 Catalysts Characterization 913.2.5 Photocatalytic Degradation of DP Using

Hybrid Catalysts 923.3 Results and Discussion 93

3.3.1 Materials Characterization 933.3.2 Diphenhydramine Photocatalytic Degradation 98

3.4 Conclusions 101Acknowledgements 102References 102

Contents vii

4 Carbon Nanomaterials for Chromium (VI) Removal from Aqueous Solution 109

Pavel Kopel, Vedran Milosavljevic, Dorota Wawrzak,

Amitava Moulick, Marketa Vaculovicova, Rene Kizek,

and Vojtech Adam4.1 Introduction 1104.2 Carbon Nanomaterials for Heavy Metal Removal 1114.3 Latest Progress in Nanocarbon Materials for

Cr(VI) Treatment 1134.3.1 Graphene and Graphene Oxide–Based Materials 1134.3.2 Magnetic-Based Graphene Materials 1164.3.3 MWNT and SWNT 1184.3.4 Magnetic Carbon Adsorbents 120

4.4 Summary 121Acknowledgement 121References 121

5 Nano-Carbons from Pollutant Soot: A Cleaner Approach toward Clean Environment 127

Kumud Malika Tripathi, Nidhi Rani Gupta, and

Sumit Kumar Sonkar5.1 Introduction 1275.2 Separation of Nano-carbon from Pollutant BC 1315.3 Functionalization of Nano-Carbons Isolated

from Pollutant BC 1355.4 Nano-Carbons from Pollutant Soot for

Wastewater Treatment 1415.4.1 Removal of Organic Pollutant 1415.4.2 Water Purifi cation, Sensing, and Removal of

Heavy Metal Ions 1435.5 Conclusion 145Acknowledgments 146References 146

6 First-Principles Computational Design of Graphene for Gas Detection 155

Yoshitaka Fujimoto6.1 Introduction 1556.2 Computational Methodology 157

viii Contents

6.3 Nitrogen Doping and Nitrogen Vacancy Complexes in Graphene 158

6.3.1 Atomic Structures 158 6.3.2 Energetics 161 6.3.3 Electronic Structures 163

6.4 Molecular Gas Adsorptions 166 6.4.1 Energetics and Structure 166

6.4.1.1 Hydrogen Adsorption 166 6.4.1.2 Water and Ammonia Molecular

Adsorptions 169 6.4.2 Electronic Properties 171

6.5 Summary 174Acknowledgments 174References 175

Part 2 Synthetic Nanomaterials 179

7 Advanced Material for Pharmaceutical Removal from Wastewater 181

Parisa Amouzgar, May Yuan Wong, Bahman Amini Horri,

and Babak Salamatinia 7.1 Introduction 182 7.2 Advanced Materials in the Removal of

Pharmaceuticals from Wastewater 185 7.3 Activated Carbon (AC) 185 7.4 Modifi ed Carbon Nanotubes (CNTs) 186 7.5 Modifi ed Polysaccharide Matrices 188 7.6 Metal Organic Framework (MOF) 190 7.7 Reactive Composites 191 7.8 TiO

2-Coated Adsorbents 192

7.9 Adsorption by Zeolite and Polymer Composites 1927.10 Adsorption by Clay 1937.11 Conventional Technologies for the Removal of

PPCPs in WWTP 2007.12 Membrane Filtration 2017.13 Ozonation and Advanced Oxidation Process (AOP) 2017.14 Electro-oxidation 2027.15 Adsorption by Coagulation and Sedimentation 2027.16 Conclusion 203References 203

Contents ix

8 Flocculation Performances of Polymers and Nanomaterials for the Treatment of Industrial Wastewaters 213

E. Fosso-Kankeu, F. Waanders, A.F. Mulaba-Bafubiandi,

and A.K. Mishra8.1 General Introduction 2148.2 Conventional Treatment of Water with

Inorganic Coagulants 2148.2.1 Inorganic Coagulants 2148.2.2 Electrofl occulation 216

8.3 Development of Polymer-Based Coagulants and Mechanisms of Turbidity Removal 2198.3.1 Inorganic and Organic Polymers 219

8.3.1.1 Inorganic Polymers 2198.3.1.2 Organic Polymers 221

8.3.2 Copolymerisation 2228.4 Synthesis of Nanomaterials-Based Flocculants and

Utilisation in the Removal of Pollutants 2238.4.1 Flocculants Derived from Carbonaceous

Nonomaterials 2248.4.2 Flocculants Derived from Magnetic

Nanomaterials 2268.5 Conclusion 227References 228

9 Polymeric Nanospheres for Organic Waste Removal 237

Ambika and Pradeep Pratap Singh9.1 Introduction 2379.2 Method of Preparation of Nanospheres 239

9.2.1 Polymerization (Emulsifi cation Polymerization) 2399.2.2 Solvent Evaporation 2399.2.3 Solvent Displacement Technique

(Nanoprecipitation) 2419.2.4 Phase Inversion Temperature Method 241

9.3 Applications of Diff erent Type of Nanospheres in Water Purifi cation 2419.3.1 Magnetic Polymer Nanospheres 2419.3.2 Silica Nanospheres 2449.3.3 Carbon Nanospheres 2459.3.4 Dendritic Polymer Nanospheres 246

x Contents

9.3.5 Iron Oxide-graphene Oxide Nanocomposite 2469.3.6 Polyaniline (PANI) Nanospheres 2469.3.7 Quantum Dot-based nanospheres 2469.3.8 Miscellaneous 247

9.4 Future Aspects 2489.5 Conclusions 248Acknowledgment 249References 249

10 A Perspective of the Application of Magnetic Nanocomposites and Nanogels as Heavy Metal Sorbents for Water Purifi cation 257

Hilda Elizabeth Reynel-Avila, Didilia Ileana

Mendoza-Castillo, and Adrián Bonilla-Petriciolet10.1 Introduction 25810.2 Description of Magnetic Nanoparticles and Nanogels 25910.3 Routes for the Synthesis of Magnetic Nanoparticles

and Nanogels 260 10.3.1 Magnetic Nanoparticles 260 10.3.2 Nanogels 262 10.3.3 Nanocomposites 264

10.4 Heavy Metal Removal from Aqueous Solutions Using Magnetic Nanomaterials and Nanogels 266

10.4.1 Magnetic Nanomaterials for Heavy Metal Removal 267

10.4.2 Nanogels 27510.5 Desorption, Regeneration, and Final Disposal 27810.6 Conclusions and Future Perspective 279Acknowledgments 280References 280

11 Role of Core–Shell Nanocomposites in Heavy Metal Removal 289

Sheenam Th atai, Parul Khurana, and Dinesh Kumar11.1 Introduction 289

11.1.1 Types of Materials 29111.2 Core and Shell Material: Synthesis and Properties 29211.3 Nanocomposites Material: Synthesis and Properties 29511.4 Nanocomposite Materials for Water Decontamination

Application 297

Contents xi

11.5 Stability of Metal Nanoparticles and Nanocomposites Material 299

Acknowledgements 302References 303

Part 3 Biopolymeric Nanomaterials 311

12 Adsorption of Metallic Ions Cd2+, Pb2+, and Cr3+ from Water Samples Using Brazil Nut Shell as a Low-Cost Biosorbent 313

Juliana Casarin, Aff onso Celso Gonçalves Jr, Gustavo

Ferreira Coelho, Marcela Zanetti Corazza, Fernanda

Midori de Oliveira, César Ricardo Teixeira Tarley, Adilson

Pinheiro, Matheus Meier, and Douglas Cardoso Dragunski12.1 Introduction 31412.2 Materials and Methods 314

12.2.1 Material 314 12.2.2 Obtaining Biosorbent and its

Characterization 315 12.2.3 Studies on Adsorption as a Function of pH

and Biosorbent Mass 315 12.2.4 Adsorption Kinetics 316 12.2.5 Obtaining Equilibrium Isotherm 316 12.2.6 Desorption 317 12.2.7 Adsorption as a Function of Temperature 317 12.2.8 Comparative Studies Between Biosorbent

and Activated Coal 31712.3 Results and Discussion 318

12.3.1 Characterization of the Biosorbent 318 12.3.2 Dependence of pH and Adsorbent Mass 319 12.3.3 Adsorption Kinetics 322 12.3.4 Infl uence of Initial Concentrations of

Cd2+, Pb2+, and Cr3+ 324 12.3.5 Equilibrium Isotherms 324 12.3.6 Desorption 328 12.3.7 Th ermodynamic Parameters of Adsorption 329

12.4 Conclusion 330Acknowledgments 330References 331

xii Contents

13 Cellulose: A Smart Material for Water Purifi cation 335

Bharti Arora, Eun Ha Choi, Masaharu Shiratani, and

Pankaj Attri13.1 Introduction 33613.2 Cellulose: Smart Material for Water Treatment 337

13.2.1 Cellulose-Based Materials as Contaminant Adsorbents 337

13.2.1.1 Heavy Metal Ion Removal from Wastewater 337

13.2.1.2 Removal of Organic Compounds and Dyes 339

13.2.2 Cellulose-Based Membranes for Water Filtration 330 13.2.2.1 CA Membranes 340 13.2.2.2 Chemically Modifi ed Cellulose

Membranes 341 13.2.2.3 Ultrafi ne Polysaccharide Nanofi bers-

Based TFNC Membranes 342 13.2.2.4 Cellulose Triacetate and Propionated

Lignin 34213.3 Conclusion 343References 343

14 Treatment of Reactive Dyes from Water and Wastewater through Chitosan and its Derivatives 347

Mohammadtaghi Vakili, Mohd Rafatullah, Zahra

Gholami and Hossein Farraji14.1 Introduction 34814.2 Dyes 34914.3 Reactive Dyes 35014.4 Dye Treatment Methods 35114.5 Adsorption 35214.6 Adsorbents for Dye Removal 35214.7 Chitosan 354

14.7.1 Unmodifi ed Chitosan 355 14.7.2 Physically Modifi ed Chitosan 360 14.7.3 Chemically Modifi ed Chitosan 361

14.7.3.1 Cross-Linking 361 14.7.3.2 Functionalization 364

14.8 Conclusions and Future Perspectives 368Acknowledgement 369References 369

Contents xiii

15 Natural Algal-Based Processes as Smart Approach for Wastewater Treatment 379D. Annie Jasmine, K.B. Malarmathi, S.C.G. Kiruba Daniel, and S. Malathi15.1 Introduction 38015.2 Algal Species Used in Wastewater Treatment 38215.3 Factors Aff ecting the Growth of Algae 385

15.3.1 Factors Increasing the Growth of Algae 386 15.3.2 Harvesting Algal Biomass 386 15.3.3 Flocculation 386 15.3.4 Aggregation by Alum or Metal Salts 387 15.3.5 Aggregation by Cationic Polymers 387 15.3.6 Biofl occulation/Auto-Flocculation 387 15.3.7 Centrifugation/Gravity Sedimentation 387 15.3.8 Filtration 387 15.3.9 Immobilization Techniques 388

15.4 Microalgae and Wastewater Treatment 388 15.4.1 Algal Approach to Treat Municipal

Wastewater 388 15.4.2 Algal Approach to Treat

Agricultural Wastewater 39015.5 Case Study of Algal Approach in the

Treatment of Municipal Wastewater 390 15.5.1 Case Study 1: Collaborative Work of Rice

University and Houston Public Works for Algal-Based Municipal-Based Wastewater Treatment 390

15.5.2 Case Study 2 39115.6 Biofuel from Algae Treated Wastewater 391

15.6.1 Algal Bioethanol Production Process 392 15.6.1.1 Process 1: Fermentation of Easily

Available Starch and Sugar in Microalgae to Ethanol 392

15.6.1.2 Process 2: Direct Production of Ethanol from Microalgal Species 393

15.6.1.3 Process 3: Saccharifi cation and Fermentation of Microalgae for Ethanol Production 394

15.7 Conclusions 394Acknowledgment 395References 395

Index 399

Preface

Smart materials have been a thrust area to the researchers in the develop-ment of new materials that lead to create new tools and techniques, which will help in the development of advance technology. At the nano size, smart materials oft en take on unique and sometimes unexpected properties. Th is means that at the nanoscale, materials can be “tuned” to build faster, lighter, stronger and more effi cient devices and systems. “Smart materials” have been extensively used in a variety of applications due to the change in the characteristics of the materials with small variation on stimuli. Th ey are also known as responsive materials. Smart materials change their proper-ties abruptly in response to small changes in the environmental conditions such as pH, temperature, electric and magnetic fi elds. Due to the versatil-ity of such characteristics, these materials are highly applicable in the area of materials science, engineering, sensors and environmental applications. Besides, such materials are applied to develop newer composites, ceramics, chiral materials, liquid crystals, conducting polymers, hydrogels, nano-composites and biomaterials. Th ese smart materials are highly suitable for environmental remediation.

Water used for drinking and household needs must have good taste and no odour and be harmless to human health as well as the livestock. Clean water is always a need, which oft en calls for a cheap and effi cient water purifi cation system. Th ere are several technologies and have been utilized for the water treatment process. Smart materials have been used to develop more cost-eff ective and high-performance water treatment systems as well as instant and continuous ways to monitor water quality. Smart materials in water research have been extensively utilized for the treatment, remedia-tion and pollution prevention. Smart materials can maintain the long-term water quality, availability and viability of water resource. Th us, water via smart materials can be reused, recycled and desalinized, and it can detect the biological and chemical contamination as well as whether the source is from municipal, industrial or man-made waste.

xv

xvi Preface

Th e present book describes the smart materials for waste water applica-tion and it will be highly benefi cial to the researchers working in the area of materials science, engineering, environmental science, water research and waste water applications. Chapters included in the book have been diff er-entiated in three sections: fi rst section includes the various “carbon nano-materials” with a focus on use of carbon at nanoscale applied for waste water research. Second section involves “synthetic nanomaterials” for pol-lutants removal. Th e third section includes “biopolymeric nanomaterials” where the authors have used the natural polymers matrices in a composite and nanocomposite material for waste treatment. Th e potential researchers working in the area will benefi t from the fundamental concepts, advanced approaches and application of various smart materials towards waste water treatment described in the book. Th e book also provides a platform for all researchers to carry out advanced research as well as to delve into the background in the area. Th e book also covers recent advancement in the area and prospects about the future research and development of smart materials for the waste water applications.

Ajay Kumar MishraEditor

December 5, 2015

Part 1

CARBON NANOMATERIALS

3

Ajay Kumar Mishra (ed.) Smart Materials for Waste Water Applications, (3–46) © 2016 Scrivener

Publishing LLC

1

Easy and Large-Scale Synthesis of Carbon Nanotube-Based Adsorbents

for the Removal of Arsenic and Organic Pollutants from Aqueous Solutions

Fei Yu1 and Jie Ma2*

1College of Chemistry and Environmental Engineering, Shanghai Institute of

Technology, Shanghai, P. R. of China2State Key Laboratory of Pollution Control and Resource Reuse, College of

Environmental Science and Engineering, Tongji University, Shanghai, P. R. of China

AbstractTh e as-prepared carbon nanotubes (APCNTs) synthesized by chemical vapor

deposition method usually contained carbon nanotubes (CNTs) and quantities

of iron nanoparticles (INP)–encapsulated carbon shells. Th e traditional research

mainly focuses on how to remove the INPs using various chemical and physical

purifi cation methods. In this chapter, we have synthesized many kinds of CNTs-

based adsorbents based on the aforementioned iron/carbon APCNT composites

without purifi cation, which can be used for the removal of arsenic and organic

pollutants from aqueous solutions with excellent adsorption properties. Th is syn-

thesis method is applicable to as-prepared single-walled CNTs and multi-walled

CNTs containing metal catalytic particles (e.g., Fe, Co, Ni), and the resulting mate-

rial may fi nd direct applications in environment, energy storage, catalysis, and

many other areas. Results of this work are of great signifi cance for large-scale prac-

tical applications of APCNTs without purifi cation.

Keywords: Magnetic carbon nanotubes, arsenic, organic pollutants, adsorption

*Corresponding author: jma@tongji.edu.cn

4 Smart Materials for Waste Water Applications

1.1 Introduction

Magnetic carbon nanotubes (MCNTs) are of intense research interests because of their valuable applications in many areas such as magnetic data storage, magnetic fi eld screening, and signal transmission [1]. Synthetic methods of MCNTs include chemical and physical techniques. For instance, magnetic nanoparticles (MNPs), such as cobalt, iron, or nickel and their oxide NPs, can be encapsulated by carbon nanotubes (CNTs) [2, 3]. In addition, MNPs could be deposited on the external surface of CNTs [4, 5]. However, existing synthesis methods may have the following critical disad-vantages: fi rstly, the as-prepared carbon nanotubes (APCNTs) are usually purifi ed using strong acids to remove metal particles and carbonaceous byproducts [6], and then MNPs are loaded on the wall of purifi ed CNTs. As a result, the synthesis process is expensive and time consuming with a low yield. Secondly, uncovered MNPs may agglomerate when a magnetic fi eld is applied. Th irdly, bare MNPs could be oxidized in air or erode under acidic conditions [7]. Th ese issues may ultimately hinder widespread prac-tical applications of the MCNTs composite. In recent years, CNTs could be produced in ton-scale quantities per year with high quality. However, APCNTs oft en contain a large fraction of impurities, including small catalytic metal particles and carbonaceous byproducts such as fullerenes, amorphous, or graphitic carbon particles. Th e current research direction in this area mainly focuses on the purifi cation of APCNTs through physi-cal separation [8], gas-phase oxidation [9], and liquid-phase oxidation [6], aiming at applications of purifi ed CNTs. However, these purifi cation processes are complex, time consuming, and environmentally unfriendly. Hence, the existing approach is suitable for fundamental research but not for large-scale applications of MCNTs.

To overcome the aforementioned issues, we herein report several new-typed methods to produce MCNTs using APCNTs. We show that MCNTs can be well dispersed in water with excellent magnetic properties. Th is fac-ile synthesis method has the following advantages: fi rstly, metal nanopar-ticles in the APCNTs can be utilized directly without any purifi cation treatment; secondly, the carbon shells provide an eff ective barrier against oxidation, acid dissolution, and movement of MNPs and thus ensure a long-term stability of MNPs. MCNTs were used as adsorbents for the removal of environmental pollutants in aqueous solutions, and arsenic and organic pollutants were chosen as target pollutants. MCNTs exhibit excel-lent adsorption and magnetic separation properties. Aft er adsorption, the MCNTs adsorbents could be eff ectively and immediately separated using a magnet, which reduces potential risks of CNTs as another source of

Easy and Large-Scale Synthesis 5

environmental contaminant. Th erefore, MCNTs can be used as a promis-ing magnetic adsorbent for the removal of arsenic and organic pollutants from aqueous solutions.

1.2 Removal of Arsenic from Aqueous Solution

1.2.1 Activated Magnetic Carbon Nanotube

1.2.1.1 Synthesis Method

Th e APCNTs were p repared using a chemical vapor deposition(CVD) method [10]. Ethanol was used as the carbon feedstock, ferrocene was used as the catalyst, and thiophene was used as the growth promoter. Argon fl ow was introduced in the quartz tube in order to eliminate oxygen from the reaction chamber. Th e ethanol solution dissolved with ferrocene and thiophene was supplied by an electronic squirming pump and sprayed through a nozzle with an argon fl ow. Aft er several hours of pyrolysis, the supply of ethanol was terminated, and the APCNTs were collected from a collecting unit connected to the quartz tube.

Th e Magnetic iron oxide/CNTs(MI/CNTs) composites were prepared by an alkali-activated method using APCNTs. Th e APCNTs were prepared by the catalytic chemical vapor deposition method [10]. In a typical syn-thesis, APCNTs and KOH powder were mixed in a stainless steel vessel in an inter-gas atmosphere. Th e weight ratio of KOH to APCNTs was 1:4. Th e APCNTs and KOH powder were mixed for 10 min using a mortar, which resulted in a uniformly powder mixture. Th e mixture was then heated to 1023 K for 1 h under fl owing argon in a horizontal tube furnace, washed in the deionized water, and then dried.

1.2.1.2 Characterization of Adsorbents

Figure 1.1a displays the transmission electron microscopy (TEM) images of APCNTs; the diameter of APCNTs is about 20–30 nm and the length is about 1 μm. Aft er the activation treatment, the structure of APCNTs has been clearly modifi ed, and the length of MI/CNTs is obviously short-ened. Furthermore, part of the hollow tubular structure is destroyed, large quantities of defects are produced, and many fl aky apertures are gener-ated on the surface, as shown in Figure 1.1b. Th e X-ray diff raction (XRD) patterns of MI/CNT hybrids indicated that the MI/CNTs were a mixture of two/three phases: γ-Fe

2O

3/Fe

3O

4 and CNTs. Well-resolved diff raction

peaks reveal the good crystallinity of γ-Fe2O

3/Fe

3O

4 specimens; no peaks

6 Smart Materials for Waste Water Applications

corresponding with impurities were detected. Peaks of C with relatively high intensity and symmetry are clearly observed in Figure 1.1c. Th is observation suggests the graphite structure remained, even aft er strong activation reaction; therefore, we may conclude that MI/CNT heterostruc-tures were formed using the KOH activation method.

Th e Raman spectrum of MI/CNTs is shown in Figure 1.1d. For MI/CNTs, the remaining peaks at 224 and 285 cm–1 are assigned to the A1g and Eg modes of α-Fe

2O

3, the peak at 397 cm–1 is assigned to the T2g

modes of λ-Fe2O

3, and the peak at 667 cm–1 is assigned to the A1g modes

of Fe3O

4 [11]. Th e results indicate that magnetic iron oxide in MI/CNTs

may be a mixture phase composed of α-Fe2O

3, λ-Fe

2O

3, and Fe

3O

4. Th e G

peak at 1585 cm−1 is related to E2g graphite mode [12–14]. Th e D-line at ~1345 cm−1 is induced by defective structures. Th e intensity ratio of the G and D peaks (IG/ID) is an indicator for estimating the structure quality of CNTs, as shown in Figure 1.1d, which suggests the structure of the CNTs was destroyed aft er the KOH activation process.

In Figure 1.2a, the thermogravimetric analysis (TGA) of the MI/CNTs exhibits two main weight-loss regions. MI/CNTs are considerably stable and show a little weight loss close to 5% below 200 °C in the fi rst region, which can be attributed to the evaporation of adsorbed water and the

10 20 30 40 50 60

Fe

FeC

70

2θ (degrees)

0 500 1000 1500 2000 2500 3000 3500

Raman shift (cm-1)

Inte

nsi

ty (

a.u

.)

Inte

nsi

ty (

a.u

.)

1327D

200 nm100 nm

(c) (d)

(a) (b)

– -Fe2O3/Fe3O4

285

224397667

G

1603G'

2654

Figure 1.1 TEM images of (a and b) APCNTs and MI/CNTs, (c) XRD patterns, and

(d) Raman spectrum of MI/CNTs.

Easy and Large-Scale Synthesis 7

elimination of carboxylic groups and hydroxyl groups on the MI/CNTs. Th e rapid weight-loss region can be due to the oxidation of CNTs. It is clearly seen that the main thermal events temperature was at ~500 °C; however, the thermal events temperature is so high that MI/CNTs could readily meet the application needs of adsorbent in water treatment.

Th e specifi c surface area (SSA) and pore size characterization of MI/CNTs were performed by nitrogen (77.4 K) adsorption/desorption experi-ments with density functional theory (DFT) methods [15], as shown in Figure 1.2b. Th e M I/CNTs had a high SSA of ~662.1 m2/g (calculated in the linear relative pressure range from 0.1 to 0.3). Th e SSA of MI/CNTs is drastically increased by ~5 times than APCNTs; such increases corre-spond with a decrease in mean pore diameter from ~11.03 to ~2.26 nm (BJH). Aft er alkalis activation treatment, not only the tube tip was opened, but also large quantities of new micropore structures with small sizes were produced. Th is implies that the MI/CNTs possess more small pores aft er the present activation treatment and thus could lead to a higher SSA. Th e detailed features of the pore distribution analysis are presented in Table 1.1.

Figure 1.2b displays the results of the cumulative pore volume (PV) and pore size analysis from nitrogen adsorption by applying a hybrid Non-local Density Functional Th eory (NLDFT) kernel, assuming a slit-shape pore for the micropores and a cylindrical pore for the mesopores.

200 0.0 0.2 0.4 0.6 0.8 1.0

adsorptiondesorption

400 600 800

TG DTA

0

20

40

60

80

100

100

200

300

400

5006

0

–6

–12

–18

Temperature (°C) Relative pressure (P/P0)

We

igh

t (%

)

DT

A (

V)

Vo

lum

e a

dso

rbe

d (

cm3g

-1 S

TP

)

Figure 1.2 (a) Th ermal analysis and (b) adsorption/desorption isotherms of N2 and pore

distribution of MI/CNTs.

Table 1.1 Physical properties of APCNTs and MI/CNTs.

Adsorbents

Surface area (m2/g) Average

pore

size

(nm)

Pore

volume

(cm3/g)

Pore volume (cm3/g)

SSA ESA ISA Micropore Mesopore Macropore

APCNTs 113.5 127.5 0 11.03 2.004 0.048 0.305 1.651

MI/CNTs 662.1 617.8 44.3 2.26 0.726 0.275 0.451 0.037

8 Smart Materials for Waste Water Applications

Th e obtained pore size/PV distribution indicates this MI/CNTs sample is distinctive from APCNTs. Compared with APCNTs, the total PV of MI/CNTs decreased due to the disappearance of maro pores. Th e meso-PV and micro-PV of MI/CNTs improved by almost ~1.48 and ~5.73 times than that of APCNTs. Th e stronger peak of pore distribution of MI/CNTs exists at ~2 nm, which indicates the presence of plenty of micropores aft er the alkalis activation treatment.

Th e composition of MI/CNTs was further determined by XPS, as shown in Figure 1.3. Typical XPS survey scans of the MI/CNTs are shown in Figure 1.3a. Figure 1.3b is the principal deconvoluted component of the C1s region recorded for the MI/CNTs. We can see that the strongest peak at 284.6 eV is assigned to double-bonding carbons for CNTs and results from non-functionalized carbon. Th e peak at the binding energy of about 285.1 eV is a consequence of single-bonding carbon for CNTs [16]. Th e O1s spectra consist of three peaks that are assigned to Fe–O (529.8 eV), C=O (531.2 eV), and C–O (533.0 eV) bonds [17], which suggests the intro-duction of new functional groups and the iron oxide nanoparticle loading

735

Fe3+

Fe2p

Fe2+

Fe2+

Fe3+Fe

728

800

(a) (b)

(c) (d)

Fe2p Fe2p

600 400 200 290 288 286

C=C

>C=O

C-C C1s

284 282 280

721 714 707 540 537 534

O-C

O=C

O-Fe

O1s

O1s

C1s

531 528

Binding energy (eV) Binding energy (eV)

Binding energy (eV) Binding energy (eV)

Inte

nsi

ty (

a.u

)

Inte

nsi

ty (

a.u

)

Inte

nsi

ty (

a.u

)

Inte

nsi

ty (

a.u

)

Figure 1.3 X-ray photoelectron spectroscopy (XPS) survey scans of the MI/CNTs (a),

the C1s deconvolution of MI/CNTs (b), for Fe2p region of MI/CNTs (c), and the O1s

deconvolution of MI/CNTs (d).

Easy and Large-Scale Synthesis 9

on the surfaces of MI/CNTs. Th e Fe2p spectrum (Figure 1.3c) shows two broad peaks with satellite peaks at 711.4 and 724.5 eV, representing Fe2p3/2 and Fe2p1/2, respectively. Th e presence of these chemical bonds demon-strates that iron oxide nanoparticles formed on the surface of MI/CNTs.

Th e magnetization properties of MI/CNTs were investigated at room temperature by measuring magnetization curves (Figure 1.4). Th e satu-ration magnetization (Ms) of MI/CNTs is 27.2 e mu·g–1 for MI/CNTs ( magnetic fi eld=+10 kOe), indicating that MI/CNTs have a high magne-tism. Th e loop of MI/CNTs exhibits very low coercive fi eld (40 Oe) and remanence values (0.76 emu·g–1), indicating that MI/CNTs hybrids are very close to behaving as superaramagnets at room temperature, which can be benefi cial to the reuse without reunite for magnetization. Aft er magnetic separation, the concentration of residual CNTs in an aqueous solution was estimated using a UV–visible absorption-based approach [18, 19].

Th e MI/CNT powders can be well dispersed in water during adsorption, so the removal of arsenic by MI/CNTs was found to be rapid at the initial period (in the fi rst 1 min) and then became slower (1–10 min). Th e rate of removal reached a plateau aft er ~10 min of the experiment, as shown in Figure 1.5.

1.2.1.3 Adsorption Properties

Th e MI/CNTs’ adsorption isotherms for removing As(V) and As(III ) are shown in Figure 1.6, which indicates that APCNTs have a smaller adsorp-tion capacity of As(V)/As(III), due to poor interaction between CNTs and arsenic pollutants. Aft er the KOH activation treatment, a larger number of iron oxide nanoparticles were decorated on the surface of MI/CNTs, and the resulting adsorption capacity increased signifi cantly, which suggests that the iron oxides contributed to the increase of adsorption capacity.

–10–30

–20

–10

0

2Mr

Hc–0.1 0

–2

0.1

10

20

30

–5 0 5 10

Magnetic field (kOe)

Ma

gn

eti

zati

on

(e

mu

/g)

Figure 1.4 Hy steresis loop of MI/CNTs and the digital photograph of MI/CNTs with

magnetic separation.

10 Smart Materials for Waste Water Applications

0

1

2

3

4

5

As(V)

As(III)

600500300 4002001000Time (s)

Ab

sorp

tio

n c

ap

aci

ty (

mg

/g)

Figure 1.5 Kinetic curves of arsenic removal on MI/CNTs (As(V)/As(III)

concentration=2 mg/L, MI/CNTs=0.2 g/L).

0

3

6

9

As(V) - MI/CNTsAs(III) - MI/CNTsAs(V) - APCNTsAs(III) - APCNTs

0 2 4 6 8 10 12Ce (mg/L)

qe

(mg

/g)

Figure 1.6 Equilibrium adsorption isotherms of As(V) and As(III) on APCNTs and MI/

CNTs.

Th e equilibrium adsorption of arsenic on MI/CNTs was analyzed using the Langmuir [20] and Freundlich [21] isotherm models. Figure 1.7 shows the isotherms based on the experimental data, and the parameters obtained from linear regression using adsorption models are shown in Table 1.2. Based on the determination coeffi cient (R2), Langmuir model fi ts the experimental data better than the Freundlich model. Th e applicability of the Langmuir isotherm suggests that specifi c homogenous sites within the adsorbent are involved [22]. Th e computed maximum monolayer capaci-ties have wonderful values of ~9.74 mg/g for As(V) and ~8.13 mg/g for As(III ) onto the MI/CNTs, which are also higher than those of previously reported adsorbents [23–26]. Th ese results suggest that MI/CNTs have great potential for As(V) and As(III) removal. Th e Dubinin–Radushkevich (D–R) [27] isotherm model was applied to distinguish between the physical

Easy and Large-Scale Synthesis 11

Figure 1.7 (a) Langmuir, (b) Freundlich, and (c) D–R isotherms for As(V) and As(III)

adsorption onto MI/CNTs.

1.42.5

2.0

1.5

1.0

0.5

0.0

As(V)

As(III)

As(V)

As(III)

As(V)

As(III)

(a)

(c)

(b)

1.2

1.0

0.8

0.6

0.4

0.2

–0.2

–2.5

–3.0

–3.5

–4.0

–4.5

–1x106

0 1x106

2x106

3x106

4x106

5x106

6x106

ε2

0 2 4 6Ce InCe

Ce/q

e

Inq

e

Inq

e

8 10 –1.5 –1.0 –0.5 0.0 0.5 1.0 1.5 2.0 25

Table 1.2 Langmuir, Freundlich, and Dubinin–Radushkevich isotherms param-

eters of As(V) and As(III) adsorption on MI/CNTs system.

Adsorbate Langmuir model Freundlich model Dubinin-Radushkevich model

qm

(mg/g)

KL

(l/ mg)

R2 KF n R2 B

(mol/

kJ2)

Qm

(mg/g)

E (kJ/

mol)

R2

As (V) 9.74 0.589 0.998 3.54 2.44 0.967 4E-7 10.02 1118 0.463

As (III) 8.13 0.490 0.999 2.70 2.31 0.971 4E-7 8.28 1118 0.417

and chemical adsorption of As(V) and As(III) on MI/CNTs, as shown in Figure 1.7c. Th e values of E (mean energy of adsorption) exceed 16 10 kJ·mol–1 for As(V) and As(III), suggesting the removal process may follow chemisorption between As(V)/As(III) and MI/CNTs [28]. Surface struc-ture information of MI/CNTs was analyzed by XPS aft er arsenic adsorp-tion. Th e XPS spectra of As 3d are shown in Figure 1.8. Th e quantitative analysis of As(III)-adsorbed MI/CNTs shows 50.8% of As(III) and 49.2% of As(V) on the sorbent surface; however, only As(V) exists on the As(V)-adsorbed MI/CNTs. Th is result indicates solid-state oxidation between arsenate and arsenite on the surface of MI/CNTs. It has been reported

12 Smart Materials for Waste Water Applications

that the arsenic adsorption mechanism involves electrostatic attraction [29] and surface complexation [30, 31] between the arsenic species and iron oxides in solution. Arsenate surface complexes possibly exist in three forms of binuclear, bidentate, and monodentate complexes through the ligand exchange reaction [32]. Aft er arsenic adsorption, the atomic ratio of Fe on the surface decreased from 6.58% to 5.35% for As(III) and 5.86% for As(V) with the increase of As atomic ratio, indicating that Fe atoms were overlaid by the adsorbed arsenic. Th e higher adsorption capacity of MI/CNTs can be attributed to the following reasons: fi rst, a large number of Fe

2O

3 nanoparticles formed on the surface of MI/CNTs, and iron oxide

adsorbents have demonstrated superior adsorption performance [33–35]. Second, oxygen-containing functional groups of MI/CNTs would improve hydrophilicity and dispersibility in aqueous solutions. For As(V)/As(III) with considerable solubility, a better dispersion of MI/CNTs in water will increase the available adsorption sites, which may be favorable for the aqueous-phase adsorption [36]. Th ird, the increased SSA and meso-PV/micro-PV would provide more adsorption sites for As(V)/As(III) [37]; therefore, the adsorption properties obviously increased aft er the KOH

activation treatment.

1.2.2 Sulfh ydryl-Functionalized Magnetic Carbon Nanotube

1.2.2.1 Synthesis Method

Briefl y, APCNTs were fi rstly treated by a two-step heat treatment. In the fi rst step, the APCNTs were heated in the air at 400 °C for 60 min to destroy the carbon cages and oxidize the iron nanoparticles (INPs). Air was intro-duced into the quartz tube at a slow rate to provide oxygen continuously. In the second step, the hybrids obtained from step one were heated at 850 °C for 60 min under Ar gas protection to remove the rest carbon by the redox

50(a) (b)

48 46 44Binding energy (eV)

Inte

nsi

ty (

a.u

)

42 40 50 48 46 44Binding energy (eV)

Inte

nsi

ty (

a.u

)

42 40

As(III) As(V)As(V)

Figure 1.8 As 3d XPS spectra of MI/CNTs aft er As(III) (a) and As(V) (b) adsorption.