Effect of the Synthesis and Post-Treatment of Twin-Crystal ZSM-5 Zeolites on Their VOCs Adsorption Performance

Abstract

The synthesis and post-treatment of twin-crystal ZSM-5 zeolites with varying high silica/alumina ratios (SARs) were studied and characterized by XRD, SEM, N₂-TPD, and TG-DTG. The effects of SARs and post-treatments on the adsorption–desorption behavior of volatile organic compounds (VOCs) over ZSM-5 were investigated. Ethyl acetate, toluene, and p-xylene were used as VOC probe molecules. The results showed that both acid treatment and acid–base composite treatment significantly influenced the morphology and pore structure of ZSM-5 zeolites. The saturated adsorption capacity of ZSM-5 zeolites was affected by the SARs, the kinetic diameters and polarity of VOC molecules, and the polarity and pore structure of the zeolites, in which the kinetic diameters of VOC molecules and pore structure were the key determinants. The post-treatment significantly increased the specific surface area and pore volume of ZSM-5, resulting in excellent adsorption performance for the different adsorbates investigated. In the present study, the as-prepared Na-HZSM-5-750 showed a higher saturated adsorption capacity for toluene (120.61 mg/g) and ethyl acetate (160.71 mg/g), whereas H-ZSM-5-1380 exhibited a higher adsorption capacity for p-xylene (149.72 mg/g).