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

We proposed a two-step synthesis process to fabricate floating TiO2 and Ag-decorated TiO2 (Ag/TiO2) 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 TiO2 and Ag/TiO2 was evaluated to remove methyl orange (MO) as a dye pollutant in two suspended and floating photocatalytic systems. Ag decoration on TiO2 improved the optical and textural properties by narrowing the bandgap energy to 2.9 eV and increasing the surface area from 10 m2/g to 30 m2/g. Ag/TiO2 exhibited higher photocatalytic activity compared to TiO2 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/TiO2@PUF maintained 89 % of its initial photoactivity, while suspended Ag/TiO2 lost 50 % after the five cycles. Moreover, we investigated the effect of operating conditions on the photocatalytic performance of floating Ag/TiO2@PUF. Optimal conditions for the complete removal of MO below detection limits were obtained as follows: Ag/TiO2@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.