Adsorption and desorption characteristics of hydrophobic hierarchical zeolites for the removal of volatile organic compounds

Zeolites have been widely used in the adsorption and removal of volatile organic compounds (VOCs). In this study, we investigated the adsorption properties of 9 commercial zeolites and MCM-41 mesoporous silica for p-xylene. And then zeolites with hierarchical structures were prepared by alkali (0.1–0.8 mol•L−1 mixed alkali solution) modification and their adsorption and desorption properties were investigated for various VOCs. The structure of these materials was thoroughly characterized, and the relationship between the adsorption capacity and physical parameters was investigated. It was found that the pore diameter and Si/Al ratio were the most important parameters for p-xylene adsorption under humid conditions, which should be optimized simultaneously to achieve satisfactory adsorption capacity. And the best adsorption capacity could reach approximately 100 mg•g−1 in humid conditions. Meanwhile, enhancing the diffusion of the VOC molecules in microporous zeolites with micron crystals through the manufacture of hierarchical structure was also important. The adsorption capacity of the modified zeolites increased by more than 25%, and the desorption temperature decreased. It showed that the alkali modification not only improved the utilization efficiency of the adsorption sites, but also facilitated desorption, which is crucial for adsorbing materials.