Optimization of C/N co-doped TiO₂ for enhancing photocatalytic denitrification of real waste brine under visible light: A reusable catalyst with an economical hole scavenger

Un-doped TiO2 (U-TiO2) and C/N co-doped TiO2 (CNT) with various C/N ratios were successfully synthesized for photocatalytic denitrification (PD) of real waste brine. To analyze the materials' physicochemical characteristics, XRD, FESEM-EDX, elemental mapping, BET, and UV-Vis absorption spectra were utilized. Under visible light, the optimized CNT with the highest PD efficiency (>95 %) and the lowest band gap (2.6 eV) was immobilized on granular activated carbon (CNT/GAC) as a reusable catalyst. More than 98 % PD efficiency with 100 % N-2 selectivity were achieved using glycerol, a waste product of the biodiesel manufacturing process, as an economical and eco-friendly hole scavenger (HS) substitute for formic acid as a conventional HS. In addition, the CNT/GAC became stable and active, even after five cycles.