Highly mesoporous X zeolites synthesized by microwave-assisted sequential dealumination-desilication for methylene blue adsorption and toluene photocatalytic removal
摘要
Although Zeolite X is highly effective at adsorbing volatile organic compounds and synthetic dyes, its micropores can hinder this process, thus, the sequential dealumination-desilication with microwave assistance is used to convert it into mesoporous zeolites with enhanced properties. After modifying, the zeolites increased significantly in mesopore surface area to about 136–155 m2/g, much higher than the original zeolite one of 18 m2/g. The modified mesoporous zeolites show higher methylene blue (MB) adsorption capacities, reaching 88.94 mg/g for the M4 sample, influenced by the solid/liquid ratio and initial MB concentration. The MB adsorption isotherm and kinetics are well-described by the Langmuir model and the pseudo-second-order reaction model, respectively. Regeneration of the mesoporous zeolite X saturated with MB is most efficient using chemical regeneration with ethanol immersion and ultrasound, maintaining about 75% adsorption capacity after four cycles. For toluene treatment, combining mesoporous zeolite X with TiO₂ at a 9:1 ratio enhances toluene removal through adsorption and photocatalytic oxidation, showing a 3.3 times improvement over using TiO₂ alone, provided the zeolite has suitable mesoporous properties. The efficiency of toluene photocatalytic oxidation is influenced by the mixing ratio, flow rate, initial toluene concentration, and relative humidity. Additionally, regenerating the TiO₂/mesoporous zeolite X photocatalyst with UV treatment in a humid environment improves its performance during the first 30 min of toluene oxidation.