In-situ , grafted, and nonselective synthesis of Ag–TiO₂/SBA-15: Differences in catalyst properties and photocatalytic performance

Materials with comparable nominal compositions can exhibit different functional properties when their synthesis histories produce different spatial organization and interfacial coupling. This study examines that process–structure–property relationship by comparing in-situ , grafted, and nonselective Ag–TiO₂/SBA-15 photocatalysts prepared with comparable nominal Ag/Ti precursor compositions and evaluated under identical photocatalytic conditions. XRD, FTIR, XPS, UV–Vis diffuse reflectance, and photoluminescence analyses showed that the in-situ material had relatively sharper anatase reflections, the strongest Ti–O–Si-related band, a Ti³⁺-related contribution not clearly resolved in the other materials, enhanced visible-light absorption, and the lowest steady-state photoluminescence emission. These differences were accompanied by a consistent performance ranking of in-situ > grafted > nonselective across chemically distinct substrates. The in-situ catalyst exhibited apparent rate constants of 0.0194 ± 0.0005 min⁻¹ for methylene blue and 0.0108 ± 0.0004 min⁻¹ for phenol (n = 3), ~ 1.6 times those of the grafted catalyst and 2.2–2.5 times those of the nonselective catalyst. During polyethylene treatment, the median diameter of the recovered ≥2 μm particle fraction decreased from 41.8 ± 0.7 to 26.5 ± 0.5 μm after 6 h, while 88.0 ± 2.5% of the initial particle-size-reduction performance was retained after five cycles. The convergence of structural, optical, and functional measurements supports the materials-science hypothesis that concurrent formation of active and supporting phases can generate a more functionally integrated composite than post-synthesis combination. Because thermal treatment, hydrothermal processing, and templating also differed among protocols, the advantage cannot be assigned to incorporation route alone. Moreover, absorbance loss does not establish mineralization, and particle-size redistribution does not establish polymer destruction. The findings identify synthesis history and interfacial organization as material design variables warranting direct quantitative investigation.