New insights into high temperature hydrothermal synthesis in the preparation of visible-light active, ordered mesoporous SiO2-TiO2 composited photocatalysts

Visible-light active, carbon doped and ordered mesoporous SiO2-TiO2 nanocomposites (C-OMS@TiO2-xs) were synthesized from the self-assembly of Si and Ti precursors with block copolymer templates (F127 and P123), hydrothermally treated at 180 degrees C, and calcination or extraction for removing the templates. XRD patterns and TEM images indicate highly ordered mesopores were formed in C-OMS@TiO2-xs, and TiO2 species with a high crystalline degree were homogeneously dispersed into the samples, which formed a stable brick-and-mortar nanostructure. N-2 adsorption-desorption isotherms indicate very large BET surface areas (224-553 m(2) g(-1)) and pore volumes (0.45-1.4 cm(3) g(-1)) in these samples. EDX spectra and elemental maps further confirm successful doping and homogeneous dispersion of TiO2 nanocrystals in C-OMS@TiO2-xs. XPS spectra confirmed the doping of carbon atoms into the lattice of TiO2 species under high temperature hydrothermal conditions, which results in C-OMS@TiO2-xs with enhanced visible light response properties, as confirmed by UV-vis diffuse reflectance spectra and photocurrent-time (I-t) curves. Catalytic tests indicate that the synthesized C-OMS@TiO2-xs show excellent activities for degradation of organic pollutants irradiated with visible light. For instance, degradation of highly concentrated rhodamine B (RhB, 100 ppm) can be completely catalyzed in the water within 50 min. This work provides a facile approach to the targeted synthesis of visible active and ordered mesoporous materials.