An efficient, green, and easily recoverable macroscopic photocatalyst for upscaling solar water treatment

The continuous release of persistent organic contaminants into aquatic environments is a major concern due to their resistance to conventional treatment methods. Among advanced oxidation technologies, solar photocatalysis is one of the most sustainable approaches for pollutant removal, although its large-scale implementation remains limited. A novel bulk photocatalytic composite was prepared for sunlight-driven degradation of organic pollutants in water. Natural clay and titanium dioxide were homogeneously mixed, extruded into 0.5-cm pellets, and calcined. Physicochemical characterisation of the material provided insight into its catalytic activity. Experiments with several representative persistent pollutants (phenol, methyl orange, terbumeton, and N-hexylpyridinium bromide) in different aqueous matrices (river water, sewage, and seawater) demonstrated its broad versatility. Together with its low cost and ease of production, this may enable wider application of heterogeneous photocatalysis in water and wastewater treatment. Kinetic studies under various composition ratios and operational conditions revealed optimal performance at a photocatalyst (80% titanium dioxide and 20% clay) load of 20 g/L in a solar batch photoreactor. The half-lives of 10-mg/L pollutant solutions in distilled water were approximately 72 min, 68 min, 27 min, and 48 min for phenol, methyl orange, terbumeton, and N-hexylpyridinium bromide, respectively. Phenol degradation was slower in river water, sewage, and seawater, with half-lives of approximately 81 min, 106 min, and 129 min, respectively. The photocatalyst exhibited strong activity under sunlight and, owing to its appropriate size and mechanical stability, allowed easy and efficient recovery and reuse, which are key factors for large-scale applications in water treatment systems. This photocatalytic composite is highly promising for upscaling solar photocatalytic water treatment as a cost-effective, green, efficient, easily recoverable, and reusable material.