TiO2-Based Photocatalysts for Removal of Low-Concentration NOx Contamination

The removal of low-concentration NOx contamination in the urban atmosphere has been regarded as an urgent issue to be solved in the context of urbanization. In the past few decades, TiO2 photocatalysis has been intensively investigated as an economical, efficient, and environmentally friendly means for the abatement of low-concentration NOx. Up to now, however, there have been few reviews focusing on TiO2-based photocatalysts for photocatalytic NO removal. In this review article, we will summarize the latest advances in the photocatalytic removal of NOx contamination with TiO2-based photocatalysts, which have been endowed with the reputation of being star catalysts for atmospheric environment remediation. We will begin with a survey of the mechanistic investigations of photocatalytic NOx removal, focusing on the in situ Fourier Transform Infrared Spectroscopy (in situ FTIR) and Electron Paramagnetic Resonance (EPR) studies and the theoretical calculation of reaction pathways with Density Functional Theory. We will then introduce the test methods and the ISO standards for photocatalytic NOx removal and discuss the effect of reaction parameters (catalyst mass, irradiation conditions, temperature, and humidity). Meanwhile, we also elaborate the latest modification methods to enhance photocatalytic efficiency and summarize the progress in recent years in modified TiO2-based photocatalysts applied in NOx abatement. Lastly, we will put forward some feasible suggestions. In the end, this review may provide some inspiration in designing more effective TiO2-based photocatalysts for removing NOx contamination from the ambient atmosphere.