Comparing the photocatalytic activity of suspended and floating Ag-decorated TiO2 for dye removal

We proposed a two-step synthesis process to fabricate floating TiO 2 and Ag-decorated TiO 2 (Ag/TiO 2 ) photocatalysts. In the first step, an ultrasound-assisted sol-gel method followed by spray drying was adopted to synthesize powder photocatalysts. Next, the powder samples were immobilized onto a floating polyurethane foam (PUF) support with an ultrasound-assisted impregnation method. The photocatalytic activity of TiO 2 and Ag/TiO 2 was evaluated to remove methyl orange (MO) as a dye pollutant in two suspended and floating photocatalytic systems. Ag decoration on TiO 2 improved the optical and textural properties by narrowing the bandgap energy to 2.9 eV and increasing the surface area from 10 m 2 /g to 30 m 2 /g. Ag/TiO 2 exhibited higher photocatalytic activity compared to TiO 2 for MO removal, which was 98% for suspended and 95% for floating catalysts under simulated sunlight irradiation. In addition, floating photocatalysts exhibited higher photocatalytic activity over five cycles of reuse. Floating Ag/TiO 2 @PUF maintained 89% of its initial photoactivity, while suspended Ag/TiO 2 lost 50% after the five cycles. Moreover, we investigated the effect of operating conditions on the photocatalytic performance of floating Ag/TiO 2 @PUF. Optimal conditions for the complete removal of MO below detection limits were obtained as follows: Ag/TiO 2 @PUF loading = 0.4:200 g/mL, initial MO concentration = 5 mg/L, time = 90 min, and pH = 4 under simulated sunlight irradiation. This study highlights the potential of floating photocatalyst systems as a sustainable, reusable, and scalable approach for wastewater treatment, addressing challenges in catalyst recovery and efficiency under real-world conditions.