Improving photocatalytic oxidation of semiconductor (TiO2, SnO2, ZnO)/CNTs for NOx removal

[Display omitted] •Semiconductor/CNTs were mixed by ball milling route.•Photocatalytic ability of ZnO/CNTs was easily inactivated.•TiO2/CNTs has a strong NO photocatalytic oxidation to green products.•Holes are a primary factor for photocatalytic NO degradation. Traditional semiconductors, i.e., SnO2, ZnO, and TiO2 have a good photocatalytic activity but still many disadvantages to applying in industry. In this study, these semiconductors are combined by commercial CNTs to form heterojunctions by a ball-milling route. The physical–chemical analyses include X-ray diffraction pattern (XRD), diffused reflectance spectra (UV–Vis DRS), Fourier transform infrared spectrum (FTIR), Mott-Schottky analysis, high-resolution transmission electron microscopy (HRTEM), and selected area electron diffraction (SAED) are run to characterize the as-prepared materials. The total photocatalytic NOx efficiency of SnO2/CNTs, ZnO/CNTs, and TiO2/CNTs composites generate green products, i.e., NO3–, HNO3, etc. with 10%, 10.1%, and 41.25% after 30 min under visible light illumination, respectively. We also found that ZnO/CNTs easily inactivated the photocatalytic ability and converted NO gas to a more toxic product. Meanwhile, the highest selectivity of green products conversion belongs to SnO2/CNTs nanocomposite. Our findings will design and select an excellent photocatalytic oxidation system for NOx removal towards a flue gas treatment established.