Intermediate layer engineering with composite sols for enhanced separation efficiency and hydrothermal stability of 1,2-bis(triethoxysilyl)methane-derived hybrid silica membranes

Organic-inorganic hybrid silica membranes, which combine the thermal stability of inorganic frameworks with the flexibility of organic groups, are promising for pervaporation applications. The intermediate layer, a crucial structural component bridging the particulate support and dense separation layers, plays a decisive role not only in governing the film-forming quality but also in determining interfacial compatibility and structural integrity. In this study, 1,2-bis(triethoxysilyl)methane (BTESM) was employed as the precursor to fabricate multilayer SiO₂ hybrid membranes via the sol-gel method, with TiO₂-SiO₂, TiO₂-ZrO₂, and SiO₂-ZrO₂ composite sols introduced as intermediate layers. The effects on membrane microstructure, pervaporation performance, and hydrothermal stability were systematically investigated. Among the three systems, the TiO₂-SiO₂ derived membrane exhibited the highest performance, achieving a permeation flux of 0.88 kg m⁻² h⁻¹ and a separation factor of 1960 under optimized conditions of six coating cycles, 0.5 wt% sol concentration, and 550 °C calcination. It also showed excellent structural integrity during both hydrothermal treatment and long-term testing. Mechanistic analysis revealed that the formation of Ti-O-Si bridging bonds effectively inhibited grain growth and retarded the amorphous-to-crystalline transition, thereby stabilizing the intermediate layer structure and enhancing membrane robustness. This study establishes a structure-performance relationship for intermediate layer design and offers practical guidance for the development of durable, high-performance hybrid membranes in industrial pervaporation processes.