Band-Gap Modulation for Enhancing NO Photocatalytic Oxidation over Hollow ZnCdS: A Combined Experimental and Theoretical Investigation

The photocatalytic treatment of NO at ppm-level concentrations for the environment and human health protection has attracted ever-increasing interest in academia and industry. Here, hollow ZnCdS nanocage catalysts with different Cd dopings were prepared and used to remove NO under visible light, and a high removal rate of 85% was achieved. Density functional theory (DFT) theoretical calculations and experiments showed that Cd ions could effectively modulate the band gap of ZnS into the visible-light-absorbing range (2.69 eV). Zn 0.5 Cd 0.5 S with a cavity structure has an excellent photoelectric response and low electron–hole recombination probability. A relaxation signal of up to 2.33 μs was detected in the transient absorption spectrum, indicating the long lifetime of the photoexcited carriers. Furthermore, the photocatalytic oxidation process of NO was dynamically monitored by in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). It is found that NO adsorbed on the surface of Zn 0.5 Cd 0.5 S rapidly transformed into dimers (N 2 O 2 ) under dark and facilitated NO conversion to nitrate via intermediates such as nitrite after illumination (N 2 O 2 → NO → NO 3 – ). The high activity and stability of Zn 0.5 Cd 0.5 S present a high potential for scale-up application of the catalyst for NO oxidation under visible light.