Photochemically deposited nano-Ag/sol–gel TiO2–In2O3 mixed oxide mesoporous-assembled nanocrystals for photocatalytic dye degradation

•Photochemically deposited nano-Ag/sol–gel TiO2–In2O3 mixed oxides were synthesized.•Photocatalytic activity of Ag/TiO2–In2O3 was strongly influenced by Ag dispersion.•1.5 wt.% Ag loading on 0.95TiO2–0.05In2O3 showed the best photocatalytic activity.•Water hardness in aqueous dye solution negatively affected photocatalytic activity.•Adjusting solution pH improved photocatalytic activity in the presence of hardness.

This work focused on the improvement of the photocatalytic activity for Congo Red (CR) azo dye degradation of mesoporous-assembled 0.95TiO2–0.05In2O3 mixed oxide photocatalyst (with a TiO2-to-In2O3 molar ratio of 0.95:0.05) by loading with Ag nanoparticles. The mesoporous-assembled 0.95TiO2–0.05In2O3 mixed oxide photocatalyst was synthesized by a hydrolytic sol–gel method with the aid of a structure-directing surfactant, prior to loading with various Ag contents (0.5–2 wt.%) by a photochemical deposition method. The optimum Ag loading content was found to be 1.5 wt.%, exhibiting a great increase in photocatalytic CR dye degradation activity. The 1.5 wt.% Ag-loaded 0.95TiO2–0.05In2O3 mixed oxide photocatalyst was further applied for the CR dye degradation in the presence of water hardness. Different types (Ca2+ and Ca2+–Mg2+ mixture) and concentrations (200 and 500 mg/l) of water hardness were investigated. The results showed that the water hardness reduced the photocatalytic CR dye degradation activity, particularly for the extremely hard water with 500 mg/l of Ca2+–Mg2+ mixture. The adjustment of initial solution pH of the CR dye-containing hard water to an appropriate value was found to improve the photocatalytic CR dye degradation activity under the identical reaction conditions.

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