Graphene metal organic framework composites and their potential applications 1

Chapter 1: Introduction 1.1 History and properties of graphene Human beings have been using carbon and its allotropes for a long time. In 1960s, nanodiamond was first synthesized in Russia using a detonation method.1 Carbon research was given a new impetus with the discovery of fullerene,2 C60, in 1985. The Japanese scientist, Sumio Iijima, discovered carbon nanotubes in 1991 with the help of the transmission electron microscope.3 In 2004, two physicists at the University of Manchester first isolated individual graphene planes using adhesive tape4 (Figure 1.1(a)). Graphene is an allotrope of carbon with one-atom-thick planar sheets of sp2-bonded carbon atoms that are densely packed in a honeycomb crystal lattice. The term graphene was coined as a combination of graphite and the suffix -ene by Hanns-Peter Boehm,5 who described single-layer carbon foils in 1962. Graphene is most easily visualized as an atomic-scale thick wire made of carbon atoms and their bonds. The crystalline or "flake" form of graphite have many graphene sheets stacked together. The carbon-carbon bond length in graphene is about 0.142 nanometers. Graphene sheets stack to form graphite with an interplanar spacing of 0.335 nm, which means that a stack of three million sheets would be only one millimeter thick. Graphene is the basic structural element of some carbon allotropes including graphite, charcoal, carbon nanotubes and fullerenes (Figure 1.1(b)). It can also be regarded as an indefinitely large aromatic molecule, the limiting case of the family of flat polycyclic aromatic hydrocarbons. Graphene is distinguished by its еxcеptіonаl physіcаl propеrtіеs, such аs exceptional mobility, excellent thеrmаl stаbіlіty аnd mеchаnіcаl strеngth.8 Othеr forms of grаphеnе-rеlаtеd mаtеrіаls can be derived from graphite, іncludіng grаphеnе oxіdе, rеducеd grаphеnе oxіdе, аnd еxfolіаtеd multilayer graphene. Thе multifunctional propеrtіеs, togеthеr wіth thе еаsе of procеssіbіlіty, render grаphеnе-bаsеd mаtеrіаls highly useful for іncorporаtіon іnto а vаrіеty of functіonаl mаtеrіаls. Grаphеnе аnd іts composites hаvе bееn used for various аpplіcаtіons, such аs еlеctronіc аnd photonіc dеvіcеs, еnеrgy storage and conversion devices10 аnd catalysts.11 Figure 1.1 (a) Timeline of carbon nanostructure discovery. (b) Schematic representation of graphene, which is the fundamental starting material for a variety of fullerene materials; bucky balls, carbon nanotubes, and graphite.12 Image reproduced from reference 12. 1.2 Synthetic method to produce Graphene Graphite is made up of adjacent graphene layers that are bound by weak van der Waals forces13. Graphene can be obtained by mechanical exfoliation of graphite using adhesive tapes. This method was discovered by A.K. Geim and K.S. Novoselov, who have been awarded the Nobel Prize in Physics for their work on graphene 14 (Figure 1.2(a)). However, an economically viable method for large scale production is needed to be used in industry and mechanical exfoliation is clearly unsuitable. Therefore, other methods for the synthesis of graphene have been developed. These methods can be grouped into two major categories: bottom-up synthesis and solution-processed synthesis. Figure 1.2 (a) Mechanical exfoliation of graphite by using adhesive tapes (b) CVD method of growing Graphene sheet.15 Image reproduced from reference 15. The bottom-up synthesis of graphene typically uses chemical vapor deposition (CVD) 16 method (Figure 1.2(b)). In this method few-layer graphene sheets are deposited on copper foil or metal catalyst-coated surfaces such as silicon. Such type of graphene typically show good electrical properties as can be judged from the presence of quantum hall states, and are used mainly in bench top experiments by physicists to probe the behavior of Dirac electrons, however they are not amenable to solution-processing. Unlike the bottom up synthesis, the solution route typically produces graphene oxide (GO) using the exfoliation and oxidation of graphite, followed by chemical reduction to convert it to reduced graphene oxide (r-GO).17 GO can be produced by the oxidative treatment of graphite via one of these three methods: Brodie, Hummers, and Staudenmaier. Brodie’s method18 involves the addition of potassium chlorate (KClO3) to a slurry of graphite in fuming nitric acid. Staudenmaier 19 improved Brodie’s method by adding the chlorate in multiple aliquots over the course of reaction instead of a single addition as Brodie had done. This resulted in a similar degree of oxidation compared to Brodie’s multiple oxidation approach. Thereafter, Hummer and Offeman20 developed an alternate oxidation method by reacting graphite with a mixture of KMnO4 and concentrated sulfuric acid (H2SO4), and achieved similar oxidation levels as well. The formed GO has a basal plane decorated with epoxide and hydroxyl groups, while its edges are decorated with carboxyl and carbonyl group (Figure 1.3). Figure 1.3 Scheme showing the chemical route to the synthesis of aqueous graphene dispersions. (1) Oxidation of graphite to graphite oxide, GO, with greater interlayer distance. (2) Exfoliation of graphite oxide in water by sonication to obtain GO colloids. (3) Controlled conversion of GO colloids to conducting graphene colloids by hydrazine reduction. 21 Image reproduced from reference 21. Solution processed graphene can be scaled up industrially, thus it has the potential for cost-effective applications. In this thesis, solution-processed graphene is the main ingredient used for the preparation of composites with Metal Organic Framework (MOF). 1.3 Reactions of Graphene Graphene can be functionalized covalently or non-covalently to form chemically modified graphene. GO platelets have chemically reactive oxygen functionalities, such as carboxylic acid at the periphery and epoxy and hydroxyl groups on the basal planes. The carboxylic acid of GO sheets can react with thionyl chloride (SOCl2),22 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC),23 or N,N’-dicyclohexylcarbodiimide (DCC)24. Their nucleophilic species like amines or hydroxyls can be added to carboxylic groups to form amide or ester bonds with GO. Ring-opening reactions activate the epoxy group of GO which involves nucleophilic attack at the α-carbon. For example, octadecylamine can be attached to GO to make dispersible colloidal suspension of graphene in organic solvents.25 Non-covalent functionalization of GO can occur by hydrogen bonding and electrostatic interaction on its oxygen functionalities, or π-π stacking, van der Waals interactions and cation- π interaction on the aromatic rings on GO.26 Reduced GO (rGO) platelets have partially recovered π-conjugation.27 rGO can undergo covalent interaction by its residual functional groups after reduction, for instance through diazonium reaction. In order to prepare fuctionalized graphene in this thesis, rGO is linked to functional ligands by diazonuim reaction.28 In Diels-Alder reaction, graphene can act as diene and dienophile via covalent interaction.29 Indeed, graphene-based derivative can be modified readily by covalent route to tune the chemical structure for specific applications. (Figure 1.4). Figure 1.4 Selection of currently available non-covalent and covalent functionalized graphenes.30 Image reproduced from reference 30. 1.4 Graphene-based composites Graphene has attracted enormous research interest in recent years, due to its interesting properties. Graphene derivatives such as graphene oxide (GO) and reduced graphene oxide (rGO) offer various possibilities to synthesize graphene-based functional materials for different applications such as the Li-ion batteries,31 supercapacitors,32 fuel cells,33 photovoltaic devices,34 photocatalysis,35 as well as Raman enhancement 36 (Figure 1.5). Figure 1.5 Schematic naming some grapheme-based composites and their potential applications 37 Image reproduced from reference 37. 1.4.1 Graphene- polymer composites Carbon-based materials, such as amorphous carbon and carbon nanotubes (CNTs), are conventional fillers for enhancing the electronic, mechanical and thermal properties of polymer matrices.38 CNT has been rendered as one of the most useful filler materials, although it is relatively costly. Graphene-based fillers are often promoted as favorable replacement or supplement to CNTs. To use lower amount of graphene filler, the dispersity and its bonding with the polymer matrix are important in order to have desirable properties of the composites. Therefore, graphene-filled polymer composites are usually prepared by solution mixing, melt blending, and in situ polymerization. 37 Graphene fillers can be dispersed in the polymer matrixes in layered structures, which are used in specific applications, such as the directional load-bearing membranes, and thin films for photovoltaic applications. For example, GO can be deposited onto poly(allylamine hydrochloride) (PAH) or poly(sodium 4-styrene sulfonate) (PSS) to form layer-by-layer (LbL) assembling via the Langmuir– Blodgett (LB)39 method (Figure 1.6(a). The resulting composited membrane shows enhanced directional elastic modulus with vol% loading of the graphene (Figure 1.6(b)).40 Figure 1.6 (a) Schematic illustration of fabrication and assembly of the free-standing GO-LbL film. (b) Plot showing the variation of elastic modulus calculated theoretically (under parallel and random orientation) and that obtained experimentally (using buckling and bulging measurements) with the volume fraction of GO.40Image reproduced from reference 40. 1.4.2 Other graphene-based composites Other than inorganic nanostructures and polymers, materials such as organic crystals, 41 metal– organic frameworks (MOF),42 biomaterials,43 and carbon nanotubes (CNTs)44 have also been mixed with graphene derivatives to target various applications. For example, N,N’-dioctyl-3,4,9,10perylenedicarboximide (PDI)–graphene core/shell nanowires used in organic solar cells have been formed through – interaction.45 MOF, a recently emerging material, is used for gas purification and storage applications, and has also been used to form composites with GO/rGO sheets.46 Moreover, biomaterials like DNA hybridized with GO or rGO are used in fluorescent sensing platforms based on the fluorescence resonance energy transfer (FRET).47 Graphene–CNT composites have also been prepared via solution blending or in situ CVD growth48 to be applied in Li ion batteries, transparent conductors,44 and supercapacitors.49 1.5 Overview of Metal-Organic Frameworks (MOFs) The design and synthesis of extended network materials has been an area of intense research over the past decade. Specifically, the porous nature of many of these materials makes them attractive for numerous applications. This section provides background information on many areas concerning the chemistry of MOFs including: (1) the design of MOFs from precursors, (2) various applications of MOF materials, (3) previous works concerning the use of MOF and carbon composites. 1.5.1 The Design of MOFs MOFs can be formed through a node and linker approach that was first reported by Yaghi, Robson,50 Fujita.51 This method uses metal ions as nodes and organic molecules as linkers. The metal ion, with a preferred coordination number and geometry, in combination with divergent linker molecules, creates an extended network in one, two, or three dimensions. The interactions of the metal ion and the linker molecule vary widely and have included ionic, covalent, and coordinate interactions,52 as well as hydrogen bonding and π-π interactions.53 Often, the strengths of these interactions directly influence the overall stability of the resulting framework. As shown in Figure 1.7, the principles of coordination complexes can be used to construct extended network assemblies. Figure 1.7 Illustration of the paradigm shift from molecular coordination chemistry involving terminal ligands to extended assemblies using diverging ligands. The single metal center used as a node can change the structure owing to the preference for a specific geometry and coordination environment of the given metal. For example, in the compound [Cu2(4,4’-bipy)4]·(D-HCam)·(4,4’-bipy)2·12H2O synthesized by Zhang, et.al., the Cu2+ metal centers adopt a tetrahedral coordination geometry and assemble into a network via 4,4’bipyridine linkages54 (Figure 1.8). Figure 1.8 The Cu2+ ion in [Cu2(4,4’-bipy)4]·(D-HCam)·(4,4’- bipy)2·12H2O adopts a tetrahedral geometry and acts as the node for the extension of a network linked via 4,4’-bipyridine.54 Image reproduced from reference 54. In comparison, the compound [Cd(4,4'-bpy)2(H2O)2](ClO4)2.1.5(4,4'-bpy)], synthesized by Liu et al., contains Cd2+ centers that adopt an octahedral geometry. 55 The axial positions of the octahedron are occupied by terminally water molecules. The equatorial positions are assumed by four 4,4’-bipyridine which act as the linker molecules. Therefore, a square network is formed as a result of the geometry around the metal center. (Figure 1.9) Figure 1.9 The Cd2+ ion in [Cd(4,4'-bpy)2(H2O)2](ClO4)2 .1.5(4,4'-bpy)] adopts an octahedral geometry by binding to two water molecules (red = oxygen atoms) and four 4,4’-bipyridine molecules.55 Image reproduced from reference 55. Yaghi introduced the second approach of the MOF design through the use of secondary building units (SBUs).56 This method makes use of many common structural motifs known in molecular cluster chemistry by incorporating them as nodes for network extension. Two examples of this strategy are shown in Figure 1.10. The “paddlewheel” structure of copper(II) acetate is a common example in this regime, where the acetate anions can be replaced by a variety of dicarboxylates to provide four points for network extension to form a square net. 57 Figure 1.10 Common transition metal acetate clusters and the divergent linker benzene dicarboxylate creating SBUs. Top: the copper acetate paddlewheel becomes a square planar SBU. Bottom: The [Zn 4O]6+ cluster becomes an octahedral SBU. (Color scheme: Zn, green; Cu, light blue; C, black; N, blue, O, red.)57 Image reproduced from reference 57. The “basic” zinc acetate structure, composed of a molecular [Zn4O]6+ cluster and six acetate anions, is another example of an SBU for framework extension. The acetate anions in this oxo-centered cluster can be replaced by divergent ligands. 58 This SBU serves as an octahedral node for the formation of a primitive cubic network. Additionally, SBUs formed from metal clusters can also be combined with neutral, divergent Lewis basic ligands to provide further points of extension for network growth. Figure 1.11 shows that these Lewis bases can be replaced by divergent molecules, such as 4,4’-bipyridine, to create an octahedral node. 10 Figure 1.11 Replacement of the Lewis base, DMF, in the square planar SBU with divergent 4,4’bipyridine creates an octahedral node with two additional points of extension 58 Image reproduced from reference 58. 1.5.2 Potential Applications of MOFs MOFs have received considerable interest in recent times due to their potential applications in areas such catalysis, optics, electronics, small molecule storage, and separation science.59 There have been hundreds of reports of hydrogen storage in MOF materials. 60 The interaction of H2 and the MOF surface is typically quite weak, being dominated by dispersion forces. Various strategies for enhancing the H2-surface interaction have been explored, including systematically varying pore structure, minimizing pore size to increase van der Waals contacts with H2, and embedding coordinately unsaturated metal centers within the MOF structure to interact with H2. For example, Yaghi has reported many MOFs based on the [Zn4O]6+ SBU which are effective in storing H2. Probably the most popular MOF, MOF-5 or [Zn4O(BDC)3]∞ (BDC = benzene dicarboxylate), was shown to store 4.5 wt % H at 77K and 1.0 wt % at ambient temperature.61 MOFs have shown useful in the storage of other small molecules besides hydrogen gas. For instance, the gas adsorption of N2, CO, CO2 and CH4 has been reported.62,63 MOFs can also be used in catalysis. For example, Lin reported [Cd3Cl6L3] (L = (R)-6,6΄-dichloro-2,2΄-dihydroxy11 1,1΄-binapthyl-4,4΄-bipyridine) can be covalently modified with titanium isopropoxide. This material was used to catalyze the enantioselective addition of diethylzinc to aromatic aldehydes. MOFs also have exciting potential as light-weight molecular selective sieves, due to their extremely high surface areas, low density, interconnected cavities and very narrow pore size distributions.64 Some frameworks are also adaptive materials which respond to external stimuli (for example, light, electrical field, presence of particular chemical species), promising new advanced practical applications. However, in order to use MOF in next generation sensing, separation, catalysis and delivery devices, we may require the introduction of extrinsic functionality. Incorporation of functional species in MOFs has to date been demonstrated through post-impregnation mostly of metal nanospecies by chemical vapour deposition and one-pot synthesis (adding either the functional species or its precursors directly into the MOF growing medium). Both these approaches cause the doping species to grow inside the MOF cavities and on the MOF outer surface. The resulting lack of spatial control of the functional components within the MOF crystals compromises the molecular selectivity of the final composite. The investigation of MOFs in electrochemistry is quite recent. Important applications of electrochemistry are energy storage and conversion65 (supercapacitors, batteries, fuel cells). The poor electron-conductive properties of most MOFs would limit them from being used as electrode. Although MOFs have been successfully used as electrode materials for rechargeable batteries,66 we need some strategies to overcome their insulating nature. The redox behavior of metal cations inside MOFs could provide a pathway for electrons. Alternatively, the tuning of the linker structure may lead to better charge transfer inside the framework. An efficient strategy is to mix MOFs with conductive phases (metal nanocrystals, carbon nanostructures, fuctionalized graphene, conductive polymers)67. 12 1.6 Literature review on MOFs at carbon interfaces Carbon-based materials such as activated carbon, fullerene (C60), carbon nanotubes (CNTs), graphite and graphene are of technological interests because of their mechanical strength, hydrophobicity, potential in adsorption and catalysis, and interesting electronic properties. Thus, there have been various composite systems with MOF for myriad applications, ranging from energy storage to the production of catalyst. 1.6.1 Composite of MOF and Activated carbon Many studies have been done on MOF and activated carbon composites. 68 As an example, Seung Jae Yang et al. reported69 a facile method for the preparation of novel ZnO-based nanostructured architectures using a metal organic framework (MOF) as a precursor. In this approach, ZnO nanoparticles and ZnO@C hybrid composites were produced under several heating and atmospheric (air or nitrogen) conditions. The resultant ZnO nanoparticles formed hierarchical aggregates with a three-dimensional cubic morphology, whereas ZnO@C hybrid composites consisted of faceted ZnO crystals embedded within a highly porous carbonaceous species, as determined by several characterization methods. The newly synthesized nanomaterials showed relatively high photocatalytic decomposition activity and significantly enhanced adsorption capacities for organic pollutants. 1.6.2 Composite of MOF and Fullerene (C60) Fullerene-MOF composites are very promising materials for gas storage applications. A lot of researches have been focused on the use of these materials for methane and hydrogen storage materials. For instance the incorporation of magnesium-decorated fullerenes within metal−organic frameworks (MOFs) was reported by Aaron W. Thornton. 70 The system is modeled using a novel 13 approach underpinned by surface potential energies developed from Lennard-Jones parameters. Impregnation of MOF pores with magnesium-decorated Mg-C60 fullerenes, denoted as Mg−C60@MOF, places exposed metal sites with high heats of gas adsorption into intimate contact with large surface area MOF structures. They predicted a very high hydrogen adsorption enthalpy of 11 kJ mol−1 with relatively little decrease as a function of H2 filling. This value is close to the calculated optimum value of 15.1 kJ mol−1 and is achieved concurrently with saturation hydrogen uptake in large amounts at pressures under 10 atm. 1.6.3 Composite of MOF and Carbon nanotubes (CNTs) CNTs have also been used as surfaces for MOF growth, particularly for the preparation of composite materials with enhanced gas storage capacity. Yang et al. have reported 71 the hydrogen storage properties of MOF-5/CNT composites, including in the presence of Pt. The composites were prepared by adding acid-treated multi-walled CNTs (MWCNTs) or Pt-loaded MWCNTs dispersed in DMF to the MOF-5 synthesis mixture. Acid treatment of the MWCNT surface prior to composite formation introduces carboxylate functionalities for MOF binding. Figure 1.12 HRTEM micrograph of a MOF-5/CNT composite crystal. (b) Enlarged view of the boxed area in (a), (c) typical selected area electron diffraction patterns of (a).72Image reproduced from reference 72. 14 HRTEM and selected area diffraction of the MOF-5/CNT composites clearly demonstrate efficient mixing of the two components (Figure 1.12)72 showing enhanced thermal and moisture stability and higher Langmuir surface area compared with MOF-5 alone. A recent report by Chen et al. details the increased moisture and electron beam stability of MOF-5 confined within the interior of MWCNTs,73 where stability is dependent on the number of walls. Hydrogen storage capacity of MOF-5/CNT at bar and 77 K, increased by 25% compared to the parent MOF as shown by the isotherms presented in Figure 1.13, which is further enhanced at higher pressures where a 100% increase is observed (298 K, 95 bar). This increased H capacity under a wide range of experimental conditions is largely attributed to the increased porosity at the interface and the improved structural integrity of the MOF component. Pranath et al. have reported enhanced hydrogen storage capacity at high pressure for MIL-101/SWCNT (single-walled carbon nanotube) composites.72 A layer-like structure is observed by TEM indicating growth of the MOF on the functionalized surface of SWCNTs and N2 adsorption isotherms reveal an increase in ultra micropores for the composite, as previously reported for MOF/GO and MOF/MWCNT materials. For a composite of MIL-101 with wt% SWCNTs, hydrogen uptake at 60 bar was increased by 44% at 77 K and 178% at 298 K over pure MIL-101. Figure 1.13 H2 adsorption isotherms measured at 77 K and bar using a volumetric method for MOF5/CNT composites compared to the parent MOF and MWCNTs. 72 Image reproduced from reference 72. 15 1.6.4 Composite of MOF and Graphene oxide Oxidation of graphite increases its hydrophilicity making a water dispersible functional carbonaceous interface for enhanced interactions with small molecules. 74 Bandosz and co-workers reported42 the synthesis and ammonia adsorption properties of a number of MOF-GO nanocomposites including MOF-5, HKUST-1 and MIL-100(Fe), by simply dispersing GO powder in the usual MOF synthesis. MOF-5 and HKUST-1 crystallites interact strongly with the hydroxyl, epoxy and carboxylate groups expressed at the GO surface to readily form MOF/GO composites. It is proposed that the MOF-5/GO composites are comprised of a sandwich like structure of alternating MOF/GO/MOF layers, although the SEM images shown in Figure 14 indicate changes in composite as the content of GO increases; perhaps through preferential MOF interaction with the carboxylate groups at the edges of the GO sheets. 75 Figure 1.14 SEM images for MOF-5/GO composites at GO loadings of (C) wt%, (D) highermagnification of wt% sample, (E) 10 wt% and (F) 20 wt%. A clear change in morphology from the layer-like structures observed at and 10 wt% of GO is seen on increasing the carbon content. 75 Image reproduced from reference 75. 16 Composite formation is dependent on the functional groups present on the GO surface. A related study with HKUST-1 and unfunctionalised graphite reveals only the formation of physical mixtures. The relative orientation of metal coordination sites on the MOF available for GO binding is highlighted in Figure 1.14. For example, MIL-100(Fe) forms disordered MOF/GO composite materials, arising from interaction of its spherical cages with GO layers rather than the cubic MOF-5 and HKUST-1 structures, where metal coordination sites lie along regular planes. 76 (Figure 1.15). Figure 1.15 Schematic comparison of the coordination between GO layers and MOF units in different types of MOF network: MOF-5, HKUST-1 and MIL-100(Fe). For MOF-5 and HKUST-1: the atoms involved in coordination are indicated. For MIL-100(Fe): the red pyramids represent supertetrahedra units made of trimers of iron octahedra linked by molecules of BTC.76 Image reproduced from reference 76. Ammonia adsorption by the MOF/GO composites is strongly dependent on the porosity and chemical nature of the MOF, and the nature and synergy of the MOF/GO interface, shown in Figure 1.16 for HKUST-1/GO composites.42 Both MOF-5/GO and HKUST-1/GO composites display increasing ammonia absorption capacity and retention with increasing GO content which attributed to a synergetic effect between the two components. The high surface of GO and small 17 pore spaces at the interface between the GO and MOF (Figure 1.16) improve both ammonia and hydrogen physisorption.77 By contrast, the poor interface between MIL-100(Fe) and GO leads to a decrease in adsorption capacity with GO content. The specific nature of the MOF also plays a role in the adsorption process, particularly where there can be strong chemical interactions between NH3 and the MOF. Activated HKUST-1 has open metal sites arising from removal of water molecules bound to the paddlewheel SBUs; these are known to coordinate a variety of molecules, and bind readily to ammonia and H2S in the HKUST-1/GO composites. NH3 and H2S adsorption by the HKUST1/GO composites follow the same multi-step adsorption behaviour: increased adsorption occurs due to the MOF/GO interface and reactive binding to the Cu sites, which ultimately leads to an irreversible reaction between the MOF and the adsorbate. This necessarily makes it difficult to understand the exact role of the GO in complex adsorption systems. Unlike MOF-5/GO, ammonia adsorption in HKUST-1/GO composites is enhanced in humid conditions due to dissolution of the adsorbate, and moist conditions also appear to slow down reaction with the MOF despite an increased NH3 concentration, likely resulting from competitive water binding. For MIL100(Fe)/GO composites ammonia is also retained by interaction with open metal sites, and Brønsted interactions with water molecules are also involved. GO itself has a relatively low density of carboxylate groups on the surface of the sheets; rather, this functionality tends to be most prevalent on the sheet edges. This has some consequences for MOF growth as seen in the work of Petit et al., 74 where MOF-5/GO composites tend to form layered materials at low GO content but disordered wormlike structures at high GO loading due to the greater number of carboxylate interactions with increasing GO, favoring edge growth. 18 Figure 1.16 Simple visualization of the two sites of ammonia adsorptionin HKUST-1/GO composites with (1) physisorption at the interface between graphene layers and MOF units and (2) binding to the copper centers of the paddlewheel SBUs. Ammonia molecules are represented by the dark gray circles. Note that the relative MOF and GO domain sizes are not to scale. 77 Image reproduced from reference 77. 1.7 Scope of study Solution processed functionalized graphene offers large-scale production of graphene-based material for various applications. By using functionalized graphene and MOF in the composites, it is expected that graphene sheets will contribute to the enhancement in the dispersive interactions, whereas the MOF component will contribute to the expansion of the pore space, in which the initial property of graphene and MOF can be changed. The main aim of this research is to investigate the effect of intercalation of functionalized–graphene on the structure of metal organic frameworks and its electrochemical performance. Three foremost functionalized groups, pheylCOOH and pyridine–Dye, and oxygen groups were chosen to study the influence of functionalized graphene on the structure of MOF. Reduced GO was reacted with a phenyl carboxylic diazonium salt to prepare benzoic-acid functionalised grapheme (BFG). This produces a 3-fold increase in carboxylate functionalities over GO, and subsequently this was applied as a template for directing MOF growth. The nitrogen 19 adsorption properties of the MOF/BFG nanowires and the electrical properties of composite nanowires were investigated in chapter 3. Pyridine-functionalized graphene flakes were used as building blocks in the assembly of metal organic framework. By reacting the pyridine-functionalized graphene with iron-porphyrin, a graphene-metalloporphyrin MOF was synthesized. This composite was used as catalytic material for the oxidation of cyclohexane (chapter 4) and also for oxygen reduction reactions (ORR) (Chapter 5). Oxidation of graphite increases its hydrophilicity through the introduction of differential surface functionalities and defects, such that the resulting graphite oxide (GO) constitutes a water dispersible functional interface. In chapter 6, The GO/Cu.MOF hybrid is used as a novel electrocatalyst for hydrogen evolution, oxygen evolution, and oxygen reduction reaction. The performance of the composite as a Pt-free cathode in Fuel Cell was also tested More specifically in this thesis, we sought to examine: 1) Changes in the morphology of metal organic framework after intercalation of graphene; 2) Role played by functionalized groups in MOF for forming composites and in enhancing MOF activities; 3) Effect of the surface area of graphene on the catalytic activities of MOF. 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MOF, and the nature and synergy of the MOF/GO interface, shown in Figure 1. 16 for HKUST -1/ GO composites. 42 Both MOF-5/GO and HKUST -1/ GO composites display increasing ammonia absorption capacity and retention with increasing GO content which attributed to a synergetic effect between the two components The high surface of GO and small 17 pore spaces at the interface between the GO and MOF (Figure 1. 16)... with 8 wt% SWCNTs, hydrogen uptake at 60 bar was increased by 44% at 77 K and 17 8% at 298 K over pure MIL -10 1 Figure 1. 13 H2 adsorption isotherms measured at 77 K and 1 bar using a volumetric method for MOF5/CNT composites compared to the parent MOF and MWCNTs 72 Image reproduced from reference 72 15 1. 6.4 Composite of MOF and Graphene oxide Oxidation of graphite increases its hydrophilicity making... 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Figure 1. 13 H 2 . growth. 19 Figure 1. 16 Simple visualization of the two sites of ammonia adsorptionin HKUST -1/ GO composites with (1) physisorption at the interface between graphene layers and MOF units and