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This paper describes the chemical engineering aspects for the preparation of highly active and stable nanocomposite photocatalysts based on N-doped TiO2. The synthesis is performed using titanium oxysulfate as a low-cost inorganic precursor and ammonia as a precipitating agent, as well as a source of nitrogen. Mixing the reagents under a control of pH leads to an amorphous titanium oxide hydrate, which can be further successfully converted to nanocrystalline anatase TiO2 through calcination in air at an increased temperature. The as-prepared N-doped TiO2 provides the complete oxidation of volatile organic compounds both under UV and visible light, and the action spectrum of N-doped TiO2 correlates to its absorption spectrum. The key role of paramagnetic nitrogen species in the absorption of visible light and in the visible-light-activity of N-doped TiO2 is shown using the EPR technique. Surface modification of N-doped TiO2 with copper species prevents its intense deactivation under highly powerful radiation and results in a nanocomposite photocatalyst with enhanced activity and stability. The photocatalysts prepared under different conditions are discussed regarding the effects of their characteristics on photocatalytic activity under UV and visible light. [ABSTRACT FROM AUTHOR]

Highlights: [•] Different forms of SiO2 react slowly with methanol at 350°C to give mainly TMOS. [•] Some N-unsubstituted benzazoles increase considerably the amount of reacted SiO2. [•] The key role of heterocycles is nucleophilic assistance to the reaction. [•] Azole ring of heterocycles is methylated by MeOH during the reaction. [•] Both SiO2-surface and TMOS catalyze the methylation of benzazole. [ABSTRACT FROM AUTHOR]