pH-Regulated Sequential Ti–Al Incorporation for Enhanced Water Vapor Adsorption and Mechanical Robustness of Silica-Based Desiccants

Silica-based desiccants are widely used in rotary dehumidification systems but are limited by insufficient water adsorption and mechanical durability. Herein, Al–SiO2, Ti–SiO2, and sequentially co-doped TiAl–SiO2 adsorbents were prepared on glass fiber honeycomb substrates to investigate the effects of metal incorporation and pH regulation on pore structure, adsorption performance, and mechanical strength. Al incorporation under mildly acidic conditions (pH 2.5–2.7) promoted the formation of a homogeneous mesoporous network, whereas Ti incorporation under strongly acidic conditions (pH ≈ 1.0) caused rapid precursor hydrolysis, resulting in the aggregation of Ti-containing species, pore blockage, and deteriorated adsorption performance despite improved mechanical strength. A pH-mediated sequential incorporation strategy was therefore developed by introducing Ti while maintaining the reaction pH at approximately 2.0, effectively suppressing uncontrolled hydrolysis and promoting uniform Ti dispersion within the aluminosilicate framework. The resulting TiAl–SiO2 exhibited a specific surface area of 460 m2 g−1, a pore volume of 0.37 cm3 g−1, a low fractal dimension of 2.60, and an equilibrium water uptake of 23.08%, while maintaining a compressive strength of 1.25 MPa. These findings demonstrate that regulating precursor hydrolysis through pH control provides an effective strategy for tailoring heterometal incorporation, simultaneously optimizing pore structure and mechanical robustness, and highlighting the potential of the prepared materials as candidate desiccants for rotary dehumidification applications.