Sub-nm titanium dioxide clusters: efficient photocatalysts for clean SO_x conversion under visible light irradiation

In this study, the hydrolysis of TiCl₄ was utilized to synthesize titanium dioxide clusters (TiO₂ NCs) at a sub-nanometer scale. Precise control over the synthesis process resulted in the production of stable particles with well-defined size distributions. These TiO₂ NCs were specifically developed to facilitate the conversion of SO_x into organo-sulfonic acid derivatives under visible light irradiation. Various characterization techniques such as TEM, EDX, XRD, UV–Vis-DRS, Raman, and FTIR were employed to analyze the formed photocatalysts, including TiO₂ nanoparticles (NPs) and NCs. The efficiency of catalytic SO_x removal depended significantly on the particle size and surface area of the nanocatalysts, as well as the presence of thymol or naphthol (1,2). These materials (1,2) proved to be highly effective in removing SO_x from flue gas under ambient conditions, specifically at room temperature. The conversion of thymol or naphthol involved a combination of adsorption and catalytic oxidation–reduction reactions. This photocatalytic approach for SO_x conversion offers several advantages, including high performance, elimination of the need for high temperature or pressure, and rapid catalytic removal within a short reaction time of 10 min. TiO₂ NCs demonstrate high efficiency in SO_x removal, offering a promising solution for pollution control. Unlike some other methods, TiO₂ nanoparticles can be potentially regenerated and reused, making them a more sustainable approach.