Design and Synthesis of a Water-Resistant Mesoporous Silica Gel for the VOC Adsorption–Desorption Treatment

Herein, to improve the water resistance of silica gel without sacrificing its adsorption capacity to volatile organic compounds (VOCs), the silica gel surface was modified by hydrophobic chemical groups, including methyl (–CH3), vinyl (–C2H3), and phenyl (–C6H5). After preliminary screening and optimization by molecular simulation, the optimal pore sizes and structures of the potential modified silica gel adsorbents were obtained. Based on the results of molecular design, a hydrophobic mesoporous silica gel has been successfully prepared by the co-condensation method with sodium silicate and phenyltriethoxysilane (PTES) as mixed precursors under acidic conditions. After systematic characterizations, it is found that the synthesized silica gel possesses a well-developed mesoporous structure (5.1 nm) and hydrophobicity. According to the adsorption tests to polar and nonpolar VOCs with humidity, it is observed that the humidity resistance of the synthetic adsorbent was significantly enhanced. For p-xylene, the adsorption capacity of Qwet/Qdry increased from 54.1 to 80.2% (Qdry and Qwet stand for the adsorption capacity under dry and wet conditions, respectively). Results also showed that the synthetic adsorbents possessed a high desorption rate (up to 89.7%) at the first recycling by vacuum desorption under wet conditions. The adsorption/desorption recycling tests proved the stability in adsorption capacity after five repeated cycles.