Photocatalytic Removal of CO From Polluted Air by TiO 2 and ZSM‐5 Supported ZnCr 2 O 4 Nanocatalysts—Catalyst Optimization by Response Surface Methodology

ABSTRACT The photocatalytic oxidation of carbon monoxide (CO) in polluted air was investigated using ZnCr 2 O 4 nanocatalysts supported on TiO 2 and ZSM‐5, synthesized via a sol–gel auto‐combustion method. Comprehensive characterization including Fourier transform infrared (FTIR), scanning electron microscopy (SEM), x‐ray photoelectron spectroscopy (XPS), photoluminescence spectroscopy (PL), x‐ray diffraction (XRD), UV–vis diffuse reflectance spectroscopy (DRS), and Brunauer–Emmett–Teller (BET) analysis was conducted to elucidate the structural, optical, and surface properties. Due to the superior performance of ZnCr 2 O 4 /ZSM‐5, subsequent investigations on CO removal were focused on this catalyst, and response surface methodology (RSM) was applied to optimize its synthesis parameters. The optimized catalyst, with a ZnCr 2 O 4 :ZSM‐5 mass ratio of 0.27:0.73 and calcined at 700°C, achieved maximum removal efficiency at an operating temperature of 25–40°C, as confirmed by strong agreement between the experimental and predicted RSM results ( R 2 = 93.5). The findings highlight the dominant influence of support dosage on photocatalytic activity, while minimal water vapor was found to be critical for efficient hydroxyl radical formation. In contrast, high humidity reduced performance by inhibiting surface adsorption. Pareto analysis showed that the support dosage had the greatest influence on the efficiency of ZnCr 2 O 4 /ZSM‐5. The band gap of ZnCr 2 O 4 and ZnCr 2 O 4 /ZSM‐5 was determined to be 2.9 and 2.8 eV, respectively.