Synthesis, Functionalization, Properties And Applications Of Novel Carbon-based Ordered Mesoporous Materials

Ordered mesoporous materials (OMMs) possess regular, uniform and interpenetrating mesopores. Compared with their bulk counterparts, they can interact with atoms, ions, molecules or even larger guest spices not only at the external surface, but also through the whole internal pore system, which makes them one of the research hot spots in chemistry and material science. After a two-decade development, mesoporous materials with tunable framework compositions, mesostructures, morphologies and porosities can be easily obtained. Presently, OMMs that tend to be most possible for large-scale production and practical application are silica and carbon materials. Among them, mesoporous carbon materials hold several fascinating properties including high specific surface areas, uniform and tunable mesopores, good chemical and thermal stability and electric conductivity, showing promising potential for adsorption and separation, catalysis, gas storage, energy storage and conversion as well as delivery of biomolecules. As such this thesis mainly focuses on the synthesis and application of mesoporous carbon and carbon-based materials.A larger number of ordered mesoporous carbon materials (OMCs) with different mesostructures, morphologies and porosities can be obtained through either hard or soft-templating methods, which have been fairly developed since 1999. However, there are still several challenging issues that need further investigation, including, (1) synthetic methods for large-scale production, (2) further graphitization of carbon framework, (3) fine control of either surface or framework functionality and (4) exploration of practical application. Research activities regarding the above issues are still limited especially for the OMCs fabricated through soft-templating. Through rational consideration of the research frontiers and possible requirements in practical applications of OMCs, this thesis presents a systematic study regarding the following well-connected aspects of OMCs, including graphitization, surface functionalization, framework modification, novel composites construction, synthesis of metal oxides with OMCs as hard templates, and their applications in water treatment, gas storage, etc.In Chapter 2, a new route has been developed to fabricate a series of OMCs with highly graphitized mesopore walls by using mesoporous silica materials as hard templates, methane as a new carbon precursor and chemical vapour deposition at 700～1000℃for carbon loading. The synthesis procedure is quite simple and time-saving without any carrying gas or impregnation step. Meanwhile, the rate of carbon deposition through thermal decomposition of methane is fast so that large quantities of OMCs can be obtained within a short time. Through adjusting several factors including different silica templates, various deposition temperatures and durations, the mesostructure (p6m, laid etc.), surface area (200～1200 m2/g), pore volume (0.2～2.2 cm3/g) and graphitization degree of the final OMCs can be easily manipulated. The prepared OMCs show good thermal stability, with a further improved graphitization degree upon a thermal treatment at 900～1200℃under vacuum condition. Due to their high surface area, large pore volume and graphitic nature, these OMCs can be adopted as electrodes in lithium ion batteries, showing good performance with high reversible capacity and good cyclic stability.In Chapter 3, the pore evolution, mesostructure stability and simultaneous surface functionalization with oxygen-containing groups of FDU-15 under different wet oxidation conditions (different oxidants, various temperature and periods) are systematically investigated for the first time. The OMC FDU-15 shows overwhelmingly better stability than the mesostructural analogue CMK-3. Upon oxidation, high concentration of surface oxygen-containing groups, especially carboxylic groups, can be readily generated, which make the carbon materials hydrophilic and dispersible in aqueous environment. After oxidation, the surface area and pore volume of the carbon material both decrease to a large extent, which are mainly due to the reduction of microporosity because a large proportion of micropores are blocked by the surface oxides. The surface functionalized carbon material shows highly promising performance for immobilization of heavy metal ions, basic dyes and biomolecules. On the other hand, a new and simple pathway has been explored to introduce nitrogen-containing functionalities onto the surface of soft templated OMCs with melamine as a precursor. The final content of nitrogen can be easily controlled by simply impregnating OMCs with melamine and heating the composites at different temperature (500～900℃). Under a low temperature (～500℃), the nitrogen content can be achieved to～20.6 wt%, with carbon nitride as a major contribution, while the nitrogen content significantly drops down to～2.0 wt% with the increase of temperature to 700～900℃. The nitrogen-containing functionalities are highly and uniformly dispersed in the whole carbon frameworks, rendering the carbon materials very attracting adsorbents for heavy metal ion removal and CO2 capture.In Chapter 4, novel ordered mesoporous calcium oxide/carbon (CaO/C) composite materials are obtaied through one-pot co-assenbly of resol, calcium nitrate and surfactant. The porosity, CaO content as well as the particle size can be easily tuned by varying the molar ratio between the carbon and calcium precursors and the carbonization temperature. With high specific surface areas (up to～1058 m2/g), high contents of CaO (up to～20 wt%) of uniform dispersion and small particle size, the composite materials delivery highly attracting properties for CO2 adsorption and separaton over a wide range of temperatures (0～600℃). At a low temperature range (0～150℃), the composite materials can uptake CO2 with high capacities (up to～7 mmol/g) though physisorption. At a high temperature range (250～600℃癈), high CO2 uptake capacities (up to 3.2 mmol/g) can be still achieved through chemisorption based on the rection between CaO nanoparticels and CO2. The CaO nanoparticle are fully available and can be completely converted to carbonate within 3 mins at～450℃due to the high activity of the small CaO nanopartices. Besides, due to the confiment effect in the nanopore space, the sintering of CaO nanopartices during CO2 chemisorption is significantly restricted, leading to a much improved cyclic stability during CO2 chemisorptipon and sorbent regeneration.In Chapter 5, for the first time, a novel ordered mesoporous tungsten carbide/carbon (WC/C) composite with platinum-like behavior is cooperatively constructed at a nano-scale by hard-templating method with silica as the template, tungsten heteropolyacid as the precursor, and methane or methane/hydrogen mixtrue as a reduction and carburization agent. Tungsten heteropolyacid is first loaded into the mesopores of silica template, followed by thermal decompostion, reduction and carburization, which convert the precursor into WC. The large pore volume released during the conversion is simultaneously occupied by deposited carbon which can stabilize and connect the WC nanocrystals to form continuous nanowires and support the ordered mesostructure. The WC/C composites hold high specific surface (up to 169 m2/g), much larger than any other reported WC nanostructured materials. The influcing factors including different silica template, pore size of the template, precursor loading level and carburization temperature are systematically studied, allowing the successful synthesis of a series of WC/C composites with different mesostructures (p6m,Ⅰa3d, etc.), surface areas (80～170 m2/g) and free carbon amounts (15～50 wt%).In Chapter 6, ordered mesoporous magnetic iron oxide/carbon (Fe2O3/C) composites with novel nanostructures and excellent performance for arsenic removal have been rationally designed and fabricated. A surface functionalized mesoporous carbon with bimodel mesopores (2.3 and 5.9 nm) obtained from soft-templating is adopted as a template and iron nitrate as the precursor. With a simple impregnation step followed by calcination, very high contents (up to 40 wt%) of y-Fe2O3 nanoparticles can be loaded into the main mesopores (5.9 nm), with the nanoparticles highly and uniformly dispersed in the whole carbon matrix. On the other hand, the empty small mesopores (2.3 nm) maintain a high surface area (up to～1000 m2/g) and keep the whole pore system quite open, which can facilitate the diffusion and transportation of guest molecules. As a result, these composite materials show excellent performance for arsenic removal, with very high adsorption capacities (up to 30 mg/g), fast adsorption rate (peseudo-second order kinetics), ready magnetic separation and good cyclic stability. Besides, several influencing factors on arsenic removal including temperature, pH value and content of iron oxide are studied in detail, with a best adsorption temperature and pH value of about 35℃and 7, respectively. Finally, the synthesis method is versatile for loading a series of other nanoparticulate metal oxide into the pore system of the carbon matrix.In Chapter 7, an efficient route is developed for controllable synthesis of ordered mesoporous alumina (OMA) materials with variable pore architectures and high mesoporosity, as well as crystalline framework. The route is based on the nanocasting pathway with a bimodal mesoporous (2.3,5.9 nm) carbon as the hard template. The method here first realizes the possibility of creating two ordered mesopore architectures by using a single carbon hard template obtained from organic-organic self-assembly, which is also the first time that such carbon materials are adopted to replicate ordered mesoporous materials. The bimodal mesopores and the surface oxygen-containing functionalities make it possible to selectively load alumina into the small mesopores dominantly and/or with a layer of alumina coated on the inner surface of the large mesopores with different thicknesses until a full loading achieved. Thus, OMA materials with variable pore architectures (similar and reverse mesostructures relative to the carbon template) and controllable surface areas (158～450 m2/g), pore volumes (0.17～1.2 cm3/g) and pore sizes (3.6～10 nm) are achieved. Furthermore, our method is versatile enough to be used for general synthesis of other important but difficult-to-synthesize mesoporous metal oxides, such as magnesium oxide.