Baojuan Dou

Adsorption performance of VOCs in ordered mesoporous silicas with different pore structures and surface chemistry.

Ordered mesoporous silicas with different pore structures, including SBA-15, MCM-41, MCM-48 and KIT-6, were functionalized with phenyltriethoxysilane by a post-synthesis grafting approach. It was found that phenyl groups were covalently anchored onto the surface of mesoporous silicas, and the long-range ordering of the mesoporous channels was well retained after the surface functionalization. The static adsorption of benzene and the dynamic adsorption of single component (benzene) and bicomponent (benzene and cyclohexane) on the original and functionalized materials were investigated. As indicated by the adsorption study, the functionalized silicas exhibit improvement in the surface hydrophobicity and affinity for aromatic compounds as compared with the original silicas. Furthermore, the pore structure and the surface chemistry of materials can significantly influence adsorption performance. A larger pore diameter and cubic pore structure are favorable to surface functionalization and adsorption performance. In particular, the best adsorption performance observed with phenyl-grafted KIT-6 is probably related to the highest degree of surface functionalization, arising from the relatively large mesopores and bi-continuous cubic pore structure which allow great accessibility for the functional groups. In contrast, functionalized MCM-41 exhibits the lowest adsorption efficiency, probably owing to the small size of mesopores and 1D mesoporous channels.

Adsorption and desorption performance of benzene over hierarchically structured carbon-silica aerogel composites

Hierarchically structured carbon-silica aerogel (CSA) composites were synthesized from cheap water glass precursors and granulated activated carbon via a post-synthesis surface modification with trimethylchlorosilane (TMCS) and a low-cost ambient pressure drying procedure. The resultant CSA composites possess micro/mesoporous structure and hydrophobic surface. The adsorption and desorption performance of benzene on carbon-silica aerogel composite (CSA-2) under static and dynamic conditions were investigated, comparing with pure silica aerogel (CSA-0) and microporous activated carbon (AC). It was found that CSA-2 has high affinity towards aromatic molecules and fast adsorption kinetics. Excellent performance of dynamic adsorption and desorption observed on CSA-2 is related to its higher adsorption capacity than CSA-0 and less mass transfer resistance than AC, arising from the well-developed microporosity and open foam mesostructure in the CSA composites.

Porous Graphitized Carbon for Adsorptive Removal of Benzene and the Electrothermal Regeneration

Graphitized carbons with mesoporous and macroporous structures were synthesized by a facile template-catalysis procedure using resorcinol and formaldehyde as carbon precursors and particulate hydrated metal oxides as both template and catalyst precursors. The materials were used as novel adsorbents for low-concentration benzene vapor. Furthermore, on the basis of the good electrical conductivities associated with the graphitized structures, an electrothermal desorption technique, which involved passing electric currents through the adsorbents to generate Joule heat, was employed to regenerate the saturated adsorbents and produce enriched benzene vapors. In comparison to microporous activated carbon, the porous graphitized carbons could afford a much quicker and more efficient regeneration by electrothermal desorption technique due to their enhanced conductivity and larger pore sizes. In addition, the concentration of the desorbed organics could be controlled by adjusting the applied voltages, which might be interesting for practical secondary treatment. It is promising that the joint utilization of porous graphitized carbon adsorbents and electrothermal desorption technique might develop effective and energy-saving processes for VOCs removal.

Adsorption of benzene, cyclohexane and hexane on ordered mesoporous carbon.

Ordered mesoporous carbon (OMC) with high specific surface area and large pore volume was synthesized and tested for use as an adsorbent for volatile organic compound (VOC) disposal. Benzene, cyclohexane and hexane were selected as typical adsorbates due to their different molecular sizes and extensive utilization in industrial processes. In spite of their structural differences, high adsorption amounts were achieved for all three adsorbates, as the pore size of OMC is large enough for the access of these VOCs. In addition, the unusual bimodal-like pore size distribution gives the adsorbates a higher diffusion rate compared with conventional adsorbents such as activated carbon and carbon molecular sieve. Kinetic analysis suggests that the adsorption barriers mainly originated from the difficulty of VOC vapor molecules entering the pore channels of adsorbents. Therefore, its superior adsorption ability toward VOCs, together with a high diffusion rate, makes the ordered mesoporous carbon a promising potential adsorbent for VOC disposal.

Adsorption properties of benzene and water vapor on hyper-cross-linked polymers

A series of hyper-cross-linked polymers (HCPs) was synthesized via a post-cross-linking reaction using low-cross-linked polydivinylbenzene (PDVB) as precursor and 4,40-bis(chloromethyl)biphenyl (BCMBP) as cross-linking reagent. The effects of various amounts of BCMBP on the structures of the hyper-cross-linked polymers were discussed. The resultant typical HCP-1.3 possesses hierarchical micro/meso pore structures and a high stability up to 400 degrees C. The increased specific surface area and total pore volume of HCP-1.3, which reach 1231 m(2) g(-1) and 1.99 cm(3) g(-1), respectively, imply the high cross-linking ability of BCMBP. In order to study the adsorption properties of HCP-1.3, benzene and water were selected as typical adsorbates for their non-polar and polar characteristics. The static adsorption amount of benzene on HCP-1.3 is 30.0 mmol g(-1), which is two times higher than the corresponding adsorbed water amount, suggesting a potential hydrophobic property of HCP-1.3. Dynamic adsorption was performed with a fixed-bed column to simulate the real situation under dry and 30% relative humidity conditions. The results show the dynamic adsorption amount under the 30% relative humidity condition is as high as 90% of the value under dry conditions, implying HCP-1.3 would be a promising adsorbent for VOC adsorption under both dry and humid conditions.