Preparation Of Porous Carbons And Control Of Porosity And Surface Functional Groups

Porous carbons (PCs) with well-developed pore structure and diverse surface chemical property have been widely and successfully used in the fields of adsorption, separation and catalysis. Study on preparation and application of PC has been regarded as frontier fields and the focus of the research on carbon materials for many years. As a typical porous material, PC is believed to be composed of nanospace, ultra fine parties and surface solid. Study on control of porosity and surface functional groups over PC would not only benefit the development of the theory related to PCs, also help to expand the application of PCs. In this paper, we mainly focus on the preparation of PCs from petroleum coke and polyacrylonitrile (PAN)-based preoxidized fiber, and the effects of experimental conditions on the pore size and surface functional groups of PCs are systematically investigated. The pore size and surface functional groups are systematically characterized by techniques including nitrogen adsorption, X-ray diffraction. The possibility for control of pore size and surface functional groups by heat treatment, oxidative reaction and chemical vapor deposition (CVD) are also explored. PCs made in our laboratory have show great potential in the field of catalysis either as catalyst alone or as catalyst support, and can be used as decolorant for diesel purification. The main results are summarized as follows.Powdered PCs were prepared from Daqing, Shengli and Minxi petroleum cokes by different activation methods that includes chemical activation with KOH and NaOH as active agents, physical activation with H2O as active agent and co-activation with KOH and H2O as active agents in the same activation process. Furthermore, shaped PCs were prepared from those powdered PCs.It has been found that Daqing petroleum coke is an ideal raw material for preparation of PC with high surface area. The microscopic structure and the transitional metals in raw material are crucial factors to the properties of final PC. The sequence of active agents in the preparation of PC in terms of efficiency is as follows: KOH + H2O > KOH > H2O. It is found that the weight ratio of active agent to raw material, activation temperature and time are also crucial for preparing high quality PCs. In comparison to NaOH, KOH is more suitable to prepare PC with good properties. PCs with different surface area have different surface functional groups. From the viewpoint of economy, coal pitch is a suitable binder to prepare molded PC. It is essential for shaped PC to be activated in H2O agent, which can effectively open the blocked mouth of pore in shaped porous carbon.A series of PAN-based PCs with high BET surface area of 2500-3000m2/g and well-developed microporous structure have been obtained with less KOH and shorter activation time in comparison to the traditional methods reported in literature. It has been found that the different methods of loading KOH play an important role in the preparation of PC, i.e. the impregnation pretreatment of raw material is better than direct mixing with KOH. The strength of the PC from the carbonized cloth is better than that from the preoxidized fiber, but in the latter case much less KOH is required. Benzene adsorption is tested to be aneffective technique to characterize the pore size of PC. As the activation increases, the surface area increases, the size of graphite-like crystal becomes smaller, and at the same time, the amount of carboxyl group decreases while the amount of ether group increases.PCs from petroleum coke and PAN-based preoxidized fiber were pretreated at high temperatures and the pore size and surface functional groups of PCs were characterized. After heat treatment, the pore size of PCs both from petroleum coke and PAN-based preoxidized fiber has changed and the specific surface area becomes smaller. After heat treatment, the percentage of macropore in the total pore of PC decreases, while the percentage of micropore increases. The size of graphite-like crystal also increases after heat treatment. A...