Maximizing photocatalytic efficiency with minimal amount of gold: Solar-driven TiO2 photocatalysis supported by MICROSCAFS® for facile catalyst recovery

Multicomponent oxide (i.e., SiO2-TiO2) microspheres with interconnected meso and macroporosity, called MICROSCAFS®, are attractive for various applications. Here, we present them as robust and efficient catalyst supports, facilitating straightforward purification of wastewater through solar-driven photocatalysis, and an easy recovery and reuse. We report on the immobilization of titanium dioxide (TiO2) and gold nanoparticles (Au NPs) into the MICROSCAFS® and their characterization using various analytical techniques. The supported catalysts were tested for solar (1 sun) photocatalytic degradation of two different pollutants: the organic dye methyl orange (MO) and the antibiotic minocycline (MC). The results showed that the presence of Au NPs, in nominal concentrations between 0.02 and 0.08 wt.%. improved the photocatalytic performance, achieving up to 20% higher degradation for MO, compared to the sample without gold. In the case of MC, we observed an initial 45.5% adsorption, followed by complete photodegradation under irradiation in less than 1 h. The supported catalysts also demonstrated good recyclability, with improved photocatalytic performance observed in the case of MC, and decreased adsorption tendency for the subsequent cycles. The transformation products (TPs) were elucidated by high-resolution mass spectrometry experiments. For MO, the results showed the generation of three TPs, with lower toxicity for aquatic species, while for MC there were only two TPs, which are completely removed within less than 2 h of irradiation. Overall, this study highlights the potential of MICROSCAFS® as an efficient photocatalyst support for the degradation of organic pollutants under solar light irradiation.