Development of a novel hierarchical porous and hydrophobic silica from montmorillonite for benzene adsorption

A hierarchical porous and hydrophobic adsorbent is the key to removing the volatile organic compounds through adsorption technology, especially under humidity conditions. In this work, we synthesized a hierarchical porous and hydrophobic montmorillonite-derived adsorbent by a facile strategy, i.e., a combination of ball milling, acid activation, and thermal treatment. Our results showed that ball milling could efficiently grind the montmorillonite sheets into small fragments, which caused the rapid dissolution of octahedral cations from the edges of these fragments during the subsequent acid activation process. The resulting porous silica showed more porosity (including micropores and mesopores) and a larger specific surface area (664 m2 g-1), compared with the product (345 m2 g-1) obtained by only acid washing without ball milling. The next thermal treatment readily removed the surface hydroxyl of porous silica, leading to the formation of the target product (HP-SiO2) with enhanced hydrophobicity and well-preserved pore structures. As an adsorbent for benzene molecules, HP-SiO2 exhibited a high dynamic benzene adsorption capacity (257.1 mg g-1) due to the large specific surface area and abundant micropores. Furthermore, HP-SiO2 maintained outstanding benzene adsorption performance under different humidity conditions (with a high adsorption capacity of 185.0 mg g-1 even under 40% relative humidity). Our work provided a low-cost and facile strategy for the synthesis of hierarchical porous and hydrophobic silica materials, and this adsorbent would serve as a promising adsorbent for the elimination of practical volatile organic compounds.