Photocatalytic denitrification of water using polystyrene immobilized TiO2 as floating catalyst

The current work demonstrates the feasibility of polystyrene (PS) immobilized TiO2 (PS-TiO2) as a floating catalyst for the photocatalytic reduction of nitrate in aqueous solution with formic acid as a hole scavenger. The synthesized PS-TiO2 was characterized by X-ray diffraction (XRD), scanning electron micrograph (SEM), Fourier transform infrared spectroscopy (FT-IR), and the Brunauer–Emmett–Teller (BET) surface area analysis. The experimental conditions including initial pH of the solution, formic acid concentration, and catalyst dosage were varied to demonstrate their effect on the denitrification efficiency and nitrogen selectivity. The complete denitrification of water with 40 mg L-1 nitrate (as N) was observed within 135 min of irradiation at initial pH of 2.5, catalyst dosage of 15 g L-1, and 16 mM formic acid concentration. The floating nature of the catalysts allowed for their easy recovery with ≥ 98 % catalyst recovery after 5 cycles of denitrification experiments. A potential mechanism for photocatalytic denitrification in the process is also discussed.