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  • POWDER X-RAY DIFFRACTION STUDY OF ZEOLITIC IMIDAZOLATE FRAMEWORK-8

    Owen J. Gledhill

    ID22, European Synchrotron Radiation Facility ESRF,

    Grenoble, France

    ABSTRACT

    Powder X-ray diffraction was used at ID22 at the ESRF to study the zeolitic imidazolate

    framework ZIF-8. ZIF-8 was synthesised using a variety of methods, all of which were

    adapted from previously reported studies. The diffraction patterns of the samples from the

    different syntheses were analysed using Pawley and Rietveld refinement techniques.

    Samples produced in DMF, ethanol and acetone produced ZIF-8 in good agreement with

    the literature. It was decided that the samples produced in DMF were most suitable for gas

    adsorption measurements. The effects of loading CO2 onto the samples up to pressures of

    12.5 bar were studied. The gas adsorption measurements showed an expansion of the unit

    cell as CO2 pressure was increased. It was seen that CO2 occupied the pores of the

    framework but with no specific interactions between the framework and the gas molecules.

    Theoretical calculations on the gas position, average gas loading and pore structure were

    performed for comparison with the empirical findings. In general, there was good

    agreement between the two but it would be useful to perform further measurements with

    different gases as well as industrially relevant gas mixtures. There was an issue with

    solvent remaining in the pores once synthesised, even after evacuation of the samples.

    Further studies would include solvent exchanges in an effort to completely remove it and

    thus make gas adsorption measurements more accurate.

  • LAY REPORT

    Zeolitic Imidazolate Frameworks (ZIFs) such as ZIF-8 are a class of compounds which

    have recently garnered much interest due to the properties that they possess. Specifically,

    they tend to be highly crystalline, highly porous and ZIF-8 in particular is extremely

    thermally and chemically stable [10]. These properties make ZIFs particularly attractive as

    candidates for applications such as gas storage, gas separation and catalysis.

    This project aimed to investigate the synthesis of ZIF-8 using a range of synthetic

    techniques based on those reported in previous studies, followed by analysis of the samples

    to choose the most appropriate candidate for gas adsorption measurements. Also to

    examine the effect of adsorbing CO2 gas onto the ZIF-8 samples and gain an insight into

    the behaviour of the gas once inside the pores.

    The European Synchrotron Radiation Facilitys high resolution powder X-ray

    diffraction (PXRD) beamline, ID22, was used to collect diffraction patterns. Patterns were

    collected on all the as synthesised samples as well as selected samples which had CO2 gas

    loaded onto them over a range of pressures. The diffraction patterns were indexed and

    refined to gain structural information as well as being the basis for calculating the position

    of gas molecules within the pores. Several pieces of specialised software were used to

    perform these calculations such as TOPAS which was used for refinements; Materials

    Studio which was used for 3D modelling of the structures and gas position determination;

    and Mercury which was used to model the pore structures.

    It was seen that ZIF-8 was successfully synthesised using several of the methods

    tried and that they were in accordance with the literature data. However, for the samples

    produced in DMF, there was an issue with solvent remaining in the pore and a ZnO

    impurity being present. The gas adsorption experiments showed that CO2 was readily

    adsorbed into the pores of ZIF-8 which was indicated by an increasing lattice parameter as

    the gas pressure was increased. It was shown that there were no specific interactions

    between the framework and the CO2 molecules which was probably due to the fact that all

    the metal binding sites are occupied in ZIF-8. The theoretical calculations showed good

    agreement with the empirical results.

    There are some limitations with the results of the study. For example, the fact that

    there was an impurity in some of the samples and solvent remained in some of the pores,

    could reduce the accuracy of the gas adsorption results. This is because the pores would

    already be partially filled, and hence prevent the maximum amount of CO2 being adsorbed.

    Also, another issue faced was that ZIF-8 appeared to be very sensitive to radiation and only

    very short scans could be taken. This suggests that PXRD isnt a perfect technique for the

    analysis of ZIF-8 and it would perhaps benefit from being coupled with other techniques

    such as elemental analysis and spectroscopy.

  • COMPANY OVERVIEW

    The European Synchrotron Radiation Facility (ESRF) is Europes most powerful

    synchrotron located in Grenoble, France and is an internationally renowned research

    institute. More than 6000 users and around 600 staff perform experiments in an

    increasingly wide range of scientific areas every year at one of the ESRFs 41 highly

    specialised beamlines. From the 1500 experiments performed yearly at the ESRF, over

    2000 publications are produced which equates to over 20,000 since its inception in 1994

    [1].

    Funding

    The ESRF operates with a budget of around 80M a year which is provided by the ESRF

    member states as well as some additional contributors [2].

    ESRF Member contributions:

    27.5% France 24% Germany 13.2% Italy 10.5% United Kingdom 6% Russia 4% Spain 4% Switzerland 5.8% Benesync (Belgium, The Netherlands) 5% Nordsync (Denmark, Finland, Norway, Sweden)

    Additional contributors:

    1.5% Israel 1.3% Austria 1% Poland 1% Portugal 1.05% Centralsync (Czech Republic, Hungary, Slovakia) 0.3% South Africa

    ESRF history: [2]

    1975: Idea for a European third-generation synchrotron source

    1988: Signing of the agreement between the governments of 12 Member States

    1992: First electron beam in the storage ring. Commissioning phase.

    1994: User operation begins with 15 beamlines

    1998: Forty beamlines in operation

    2009: Start of the ESRF Upgrade Programme

    2011: Inauguration of the first Upgrade Beamline

    2015: Completion of Phase I Upgrade Programme

    The ESRF and similar facilities

    The ESRF is Europes premier synchrotron facility, which operates at 6 GeV. However,

    there are many other synchrotron facilities in Europe, such as Diamond in the UK (3 GeV)

    and ALBA in Spain (3 GeV); as well higher energy synchrotrons outside Europe like

    SPring-8 in Japan (8 GeV) and the APS in the USA (7 GeV) [3].

  • The ESRF differs from these other facilities as it employs staff from more than 40

    countries who are typically on short term contracts which promotes innovation and ensures

    that new ideas are always being brought to the ESRF [1].

    Beamlines and science at the ESRF

    Figure 1 shows the layout of the ESRF with the beamlines running tangential to the storage

    ring as well as where the different types of beamlines are positioned.

    Figure 1. Layout of ESRF beamlines after completion of Phase I upgrade [1].

    There are two types of beamline based on the way in which X-rays are produced.

    These being insertion device (ID) or bending magnet (BM) beamlines. Most BM

    beamlines are CRG (collaborating research groups) beamlines and are not operated by the

    ESRF but by external institutions from ESRF member states [1].

    The diverse range of techniques used at the beamlines is what allows such a wide

    range of science to be carried out at the ESRF. The ESRF currently performs research in

    areas from chemistry to paleontology, and physics to biochemistry as shown in figure 2.

    Figure 2. Scientific research areas studied at the ESRF [4]

  • Users

    Users at the ESRF help to drive this diversification of science carried out at the ESRF.

    Users from external institutes submit proposals for time at one of the beamlines to perform

    their experiments. Proposals are considered twice a year and are reviewed by independent

    review committees [1]. They are chosen using criteria such as scientific merit, and

    beamtime is also allocated according to the percentage stake each member state has in the

    ESRF. Beamtime is free for users of member countries if their research is made public [5].

    However, the number of industrial users is increasing at the ESRF as they have access to

    techniques that are not available at any other facilities. Figure 3 shows some of the

    industrial sectors that use the ESRF.

    Figure 3. Industrial sectors using the ESRF [4]

    My Role at the ESRF

    I am part of the experiments division which is one of six divisions at the ESRF which

    covers all aspects of the organisation. The experiments division is further divided into

    beamline groups which have similar research areas. I work on beamline ID22 which is one

    of five in the structure of materials group as shown in figure 4.

    Figure 4. Organisation of structure of materials group [6]

    Stru

    ctu

    re o

    f M

    ater

    ials

    Gro

    up

    ID01: Microdiffraction imaging

    ID03: Surface diffraction

    ID11: Materials science, time resolved diffraction

    ID15A/B: High energy diffraction/scattering

    ID22: Powder diffraction Me

  • ID22 is the ESRFs high res