TiO₂–SnO₂ Nanocomposites: Effect of Acid–Base and Structural-Adsorption Properties on Photocatalytic Performance

The article considers the influence of acid–base and structural-adsorption properties on the photocatalytic activity of TiO₂ and TiO₂–SnO₂ nanocomposites obtained by hydrolytic (HL) and hydrothermal (HT) synthesis methods. Acid–base properties were evaluated by Hammett indicator method. Structural-adsorption properties were studied using Brunauer–Emmett–Teller surface analysis (BET). Photocatalytic activity of the nanocomposites was determined using photodegradation of methylene blue (MB) and Congo red (CR) organic dyes. Synthesized materials were also characterized by X-ray fluorescence (XRF), powder X-ray diffraction (PXRD), high-resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). All the synthesized photocatalysts are mesoporous materials with developed surface area. The results demonstrated that HT series samples with both acidic and basic sites of Brønsted type are universal sorbents and photocatalysts that effectively remove both cationic and anionic dyes. HL series composites with Brønsted basic sites are only selective towards cationic dyes. The improved photocatalytic performance of the HT series sample containing 1% of SnO₂ may attribute to the increased surface area and high content of Brønsted sites of different types.