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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