Molecular Design And Targeted Synthesis Of Nanoporous Materials For Energy And Environmental Applications

Reducing the anthropogenic emission of CO2has recently become a political and technological priority, particularly in light of the World Climate Conference (WCC-3) held in Copenhagen last year and the increasing awareness of the problems associated with greenhouse gas-induced climate change. One approach is Carbon Capture and Storage (CCS), in which carbon dioxide is sequestered to reduce its concentration in the atmosphere; another is the development of renewable and clean energy sources, or energy carriers, in order to reduce our dependence on fossil fuels which contribute significantly to global CO2emissions. In this dissertation, we mainly focus on three promising alternative fuels:(1) hydrogen;(2) nature gas;(3) solar energy. One of the main obstacles preventing the widespread usage of the first two energy gases, particularly in automotive transportation, is their safe and efficient storage. Adsorptive storage of hydrogen, methane and carbon dioxide by nanoporous materials, which is energetically efficient and technically feasible, is one of the important technologies. Metal-organic frameworks (MOFs) and covalent-organic materials (COMs), as two class of versatile porous materials, have been everincreasingly studied for energy gas storage and separation, magnetism, drug deliver, catalyst and photovoltaic application due to their high porosity, tunable structural characteristics as well as their multi-chemical functionality. In this dissertation, many novel MOF/COM materials were synthesized and modified for energy and environmental applications by combination of molecular simulation and experimental synthesis. The detailed contents and novelty are concluded as following:(1) A combination of theoretical method and experimental synthesis. The experimental investigation of the gas storage properties of MOFs/COMs is, however, time consuming due to its ever-changing structures. Furthermore, some of the structural details at a molecular level are not easily accessible by using experimental methods. Here, a "multiscale simulation method" was proposed to solve these problems. First, a structure-properties relationship can be established in theoretical way, and new materials can be then theoretically designed and subsequently predicted the gas adsorption capacities by the multiscale simulation method. The preparation of these simulation-synthesized materials can then be accomplished in the laboratory. Next, the experimental adsorption capacities of these materials can be used as a benchmark for the identification of effective gas adsorbents, and also to help improve the models and calculation methods. Repetition of the "theory-experiment-theory" process could potentially lead to the rapid development of effective new materials for industrially relevant applications. All of studies of this dissertation are guided with the multiscale simulation method. For example: we successfully predicted that the hydrogen capacity in UMCM-1reaches9.5wt%at77K and100bar, higher than the U.S. DOE’s requirement6wt%, by the multiscale simulation method. Additionally, we designed a series of covalent organic polymers (COPs) with ultrahigh porosities and the highest accessible surface area of these COPs reaches9000m2g-1, much higher than the experimentally reported record of7140m2g-1of NU-100. Moreover, the pore volumes of all the hypothetical COPs are over7cm3g-1and the highest one reaches17.25cm3g-1, about four times of the experimentally reported record of4.4cm3g-1. Furthermore, the void volumes of all these COPs are more than90%, suggesting the skeletal proportions are very low and allowing much more energy gas molecules adsorbed in pore.(2) Development of a facile synthesis method, i.e., a combination of the microwave-assisted solvethermal method and supercritical CO2activation. Compared with the traditional solvethermal method, the reaction time can be reduced from dozens of hours or days or weeks to a couple of minutes with the microwave-assisted solvethermal method. Moreover, pore blockage can be avoided dynamically, and there is less collapse of interparticle after removal of solvent in the supercritical activation process due to the smaller surface tension of supercritical CO2. In this dissertation, Cu3(BTC)2, MOF-5, MIL-101(Cr), ZIF-67, ZIF-4, COF-1and COF-5were successfully prepared by this new synthetic method. Particularly, the Brunauer-Emmett-Teller (BET) surface area of Cu3(BTC)2prepared by this new method is increased by～70%compared with the traditional method. At T=77K and p>15bar, the hydrogen storage performance of Cu3(BTC)2prepared by this new method is better than all the reported Cu3(BTC)2prepared by other methods. Therefore, this new method may provide a facile synthesis method to prepare novel materials with high performance for large-scale industry application.(3) Targeted synthesis of novel materials. With the guide of the multiscale simulation method, CNT@Cu3(BTC)2hybrid material and series of novel COPs were prepared by the new synthetic method mentioned in (2). These synthesized COPs with the BET surface area in range of1000-4000m2g-1as well as multifunction could be directionally achieved by tuning building block. Moreover, these COPs are insoluble in the usual solvents and resistant against acids and bases. Particularly, the porosity of these COPs keeps the similar level after boiling in water for a week. All these novel materials show the promising potential for industrial applications. For example: CNT@Cu3(BTC)2shows promising potential in nature gas separation and purification and its adsorption selectivities are at least two times larger than the unmodified Cu3(BTC)2. Interestingly, COP-3and COP-4show very fast responses and high sensitivity to the nitroaromatic explosives, and also high selectivity for tracing picric acid (PA) and2,4,6-Trinitrotoluene (TNT) at low concentration (<1ppm).(4) Development of systematic modifications for MOFs/COMs. By screening out the best modification routes with the multiscale simulation method, experimentally targeted modification were subsequently performed, including functional groups introduction, incorporation of CNT and MOFs/COMs and Li modification. With the theoretical guide about Li modification, a series of Li-doped materials were prepared, e.g. Li@CNT@Cu3(BTC)2, Li@MIL-101and Li@COP-1.300%improvement for CO2adsorption can be achieved by incorporation of carbon nanotubes and doping the resulting framework with lithium ions. Additionally, incorporating polar acidic functionalities into the porous materials was suggested as an alternatively suitable approach for enhancing CO2capture, based on the theoretical and experimental investigations. (5) A novel synthetic method for preparation of N-doped graphene was developed by considering the synthesized N-contained COPs as the templet. This novel method allows us to precisely manipulate the positions and concentrations of the doping N atoms by tuning the matrix COP template. Moreover, much more high-capacity N-doped graphene could be prepared by optimizing the building blocks of the matrix COP template with the multiscale simulation method according to the electronic means of transmission. Therefore, this method provides an important foundation for the preparation of the3D graphene material.