Spherical Mesoporous Silica Synthesis for Catalytic Applications: pH-Regulated Mesostructural Evolution Mediated by Ostwald Ripening

In this study, we introduce a rational, surfactant-free synthetic strategy for the scalable preparation of relatively uniform spherical mesoporous silica with moderate-to-high surface area particles (MSPs), engineered specifically as advanced heterogeneous catalytic supports. Leveraging Ostwald ripening as the core morphogenetic driver—rather than conventional organic structure-directing agents—our approach improves process simplicity and reduces reliance on organic templates. Precise pH modulation to 8.0 using biocompatible organic acids enables controlled silica dissolution–reprecipitation kinetics, yielding MSPs with good spherical morphology, a relatively narrow particle-size distribution, a specific surface area of up to 484 m2/g, and uniform mesopores centered at approximately 3.02 nm. A systematic pH-screening study reveals a distinct structural transition: at pH < 7.5, incomplete condensation and suppressed ripening yield polydisperse aggregates with disordered worm-like porosity; at pH > 8.5, accelerated silicate dissolution induces particle coalescence and partial mesostructural degradation. Critically, pore ordering, channel dimensionality, surface area, and particle morphology are all systematically influenced by pH, establishing it as a key synthetic parameter for hierarchical textural programming. This study compares the methoxychlor (MXC) removal efficiency of polyhedral Bi2WO6 and Bi2WO6/MSP under identical irradiation conditions to assess MSPs’ catalytic impact. The enhanced photocatalytic performance is mainly associated with the improved dispersion of Bi2WO6 and enhanced interfacial contact between Bi2WO6 and the silica support. Considering the substantial decrease in surface area and pore volume after Bi2WO6 loading, the role of MSP is discussed primarily as an interfacial support rather than as a fully open mesoporous transport network in the final composite.