Tailored Synthesis of Hierarchical All-Silica MEL Zeolites for Efficient Removal of Versatile VOCs

The efficient removal of volatile organic compounds (VOCs) with different molecular sizes remains a great challenge in the field of zeolite-based adsorption technology. The conventional composite zeolite systems (e.g., MFI/FAU) suffer from nonuniform crystalline distribution. Herein, a novel synthesis strategy for all-silica MEL zeolites was developed featuring 10-membered ring (10-MR) micropores, extra-large micropores (0.8∼2.0 nm), and small mesopores (2.0∼5.0 nm). The hierarchical pore structure conferred exceptional adsorption capabilities for VOCs across diverse molecular dimensions. The volume and accessibility of extra-large micropores and small mesopores could be tuned by controlling the tetrabutylammonium hydroxide (TBAOH) content in the synthesis gel and crystallization temperature, while prolonged crystallization enhanced framework hydrophobicity due to the decrease of silanol group density. Notably, the optimal sample exhibited a superior m-xylene adsorption capacity of 85.2 mg/g. Meanwhile, high adsorption capacities of acetone, ethyl acetate, and toluene were also obtained, which can be attributed to its high 10-MR micropore volume of 0.178 cm³/g. Importantly, its m-xylene adsorption capacity remained unchanged across multiple regeneration cycles, demonstrating perfect recyclability and structural stability. Low desorption peak temperatures (<115 °C) for all adsorbates were acquired that facilitated regeneration under mild conditions. By integrating hierarchical pore engineering and surface chemistry control within a single zeolite framework, this work overcomes the limitations of traditional composite systems, offering a versatile and efficient system for industrial VOC abatement.