Efficient Photocatalytic Degradation of CI Reactive Red 195 Using UV‐C/ZnO Heterogeneous System: Process Optimization and Degradation Kinetics

ABSTRACT This study investigates the photocatalytic degradation of CI Reactive Red 195 (RR195) using a UV‐C/ZnO slurry annular photoreactor. Key parameters—ZnO loading (0–5.0 g L − 1 ), dye concentration (150–550 mg L − 1 ), aeration (0–1.0 L min − 1 ), and temperature (283–323 K)—were examined at natural pH (∼5.6). Degradation improved with higher catalyst loading, aeration, and temperature, but decreased at higher dye concentrations due to light attenuation and competition effects. Under optimal conditions (4.0 g L − 1 ZnO, 0.5 L min − 1 aeration, 293 K), complete decolorization of 150 mg L − 1 RR195 occurred within 30 min. The process followed pseudo‐first‐order kinetics with a low activation energy (12.18 kJ mol − 1 ), indicating efficiency under mild conditions. LC–MS/MS and FTIR analyses confirmed a stepwise mechanism involving azo bond cleavage and subsequent oxidative mineralization. Overall, the UV‐C/ZnO system proves to be an effective method for treating dye‐contaminated wastewater.