Artificial Solar Light-Driven APTES/TiO₂ Photocatalysts for Methylene Blue Removal from Water

A visible-light photocatalytic performance of 3-aminopropyltriethoxysilane (APTES)-modified TiO₂ nanomaterials obtained by solvothermal modification under elevated pressure, followed by calcination in an argon atmosphere at 800-1000 °C, is presented for the first time. The presence of silicon and carbon in the APTES/TiO₂ photocatalysts contributed to the effective delay of the anatase-to-rutile phase transformation and the growth of the crystallites size of both polymorphous forms of TiO₂ during heating. Thus, the calcined APTES-modified TiO₂ exhibited higher pore volume and specific surface area compared with the reference materials. The change of TiO₂ surface charge from positive to negative after the heat treatment increased the adsorption of the methylene blue compound. Consequently, due to the blocking of active sites on the TiO₂ surface, the adsorption process negatively affected the photocatalytic properties. All calcined photocatalysts obtained after modification via APTES showed a higher dye decomposition degree than the reference samples. For all 3 modifier concentrations tested, the best photoactivity was noted for nanomaterials calcined at 900 °C due to a higher specific surface area than materials calcined at 1000 °C, and a larger number of active sites available on the TiO₂ surface compared with samples annealed at 800 °C. It was found that the optimum concentration for TiO₂ modification, at which the highest dye decomposition degree was noted, was 500 mM.