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

Abstract

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.