RESUMEN
To fully exploit pore engineering in the design of more efficient zeolite adsorbents for volatile organic compound (VOC) treatment, the roles of meso- and micropores need to be clarified to provide the theoretical basis and feasible measures. In this work, the three VOC sorption properties of conventional and hierarchical porous beta zeolites were comparatively investigated to study the roles of meso- and micropores. There is a division of functions between micro- and mesopores, with micropores being the main VOC adsorption sites and mesopores greatly enhancing VOC diffusion and adsorbent reusability. On the one hand, micropores should be preserved as much as possible because obtaining mesopores by sacrificing micropores (i.e., alkali treatment) results in 28-60% decreases in adsorption capacities. On the other hand, mesopore introduction is highly desirable, which results in an enhancement of VOC intraparticle diffusion rates by 1.3-2.3 times (at the VOC concentration of 600 ppm) and chlorobenzene adsorption capacity on the 20th cycle increasing from 78% of the initial value to 89 and 93%. The findings may provide valuable information about zeolite-based adsorbents for adsorption removal or recovery of VOCs.
RESUMEN
Highly crystalline nano-MFI-type zeolites containing different elements were synthesized, and the sorption effects of the elements on volatile organic compounds (VOCs) were investigated. The results showed that the optimal toluene and acetone breakthrough time of the synthesized zeolites was 2.1 and 1.9 times as long as that of the commercial zeolite, respectively. For a weakly polar toluene molecule, MFI zeolites (aluminum-free) showed better adsorption properties than aluminum-containing zeolites. For the highly polar acetone molecule, zeolites with a Si/Al ratio of 87 showed the highest adsorption capacity, which was 7% higher than that of the all-silica zeolite and 1.4 times that of the commercial zeolite. Furthermore, MFI zeolites with Ti replacing part of Al proved to have better performance for highly polar molecules. In the adsorption process of VOCs, in addition to internal diffusion, diffusion on the external surface of the zeolite also played a remarkable role, and the adsorption data of all samples fitted better with the pseudo-first-order model. This study may provide a reliable structure-performance relationship for the synthesis of nanosized zeolite-based adsorbents and their use in the industrial recovery/treatment of VOCs.
RESUMEN
The sorption behaviors of hexane, toluene and mesitylene as probe volatile organic compounds (VOCs) over hierarchical and conventional zeolite ZSM-5 were investigated by a series of experiments, such as dynamic adsorption, temperature-programmed desorption and cycle adsorption tests. The results showed that hierarchical ZSM-5 exhibited better adsorption capacity for toluene and mesitylene, better diffusion of VOCs and superior cycle adsorption efficiency. As we believe, these findings will offer valuable information for the development of zeolite based adsorbents for VOC elimination or recycling.
RESUMEN
Nano-structuring of polymeric carbon nitride (PCN) is an important strategy to improve its photocatalytic performance, while facile and green methods are scarce yet. Herein, we proposed a novel steam-assisted method to prepare holey PCN nanosheets in one step. Only a green gas template, i.e. steam, decomposed from the recyclable steam source Mg(OH)2 is needed for PCN nano-structuring. Moreover, in situ element doping of nano-structured PCN can be synchronously realized via this method. The holey PCN nanosheets and doped counterparts have boosted visible-light photocatalytic H2 evolution activities 12-35 times that of bulk PCN, benefitting from enlarged specific surface area, suppressed photogenerated electron-hole recombination and prolonged charge carrier lifetime. Steam-assisting may be a useful strategy for the facile and green synthesis of other nanosized PCN materials.