Highly efficient photocatalytic removal of NO and synchronous inhibition of NO2 via heterojunction formed by ZnAl-LDH and MXene-Ti3C2-derived TiO2@C

Abstract

The key challenge in oxidizing NO using photocatalysis is controlling the selectivity of products to avoid the generation of toxic byproducts like NO₂. Here, we propose regulating the generation of reactive oxygen species by constructing Type-II heterojunctions to facilitate the deep oxidation of NO to nitrates. Experimental characterization and Density Functional Theory (DFT) simulations demonstrate that the outstanding photocatalytic activity of heterojunction materials stems from their superior charge separation efficiency and stronger adsorption capacity for NO and O₂ molecules, promoting the formation of reactive oxygen species. These results indicated that the best-performing sample, ZATC15, demonstrated an impressive NO removal efficiency of 65.43%. However, the selectivity rate of NO₂ was only 4.78%, much lower compared to the NO₂ selectivity rates of pure ZnAl-LDH (48.17%) and TiO₂@C (72.46%). The intermediate and final products, the generation pathways of active free radicals (h⁺ and •O₂^-) and the mechanism behind the profound oxidation of NO were elucidated based on in-situ Fourier Transform Infrared Spectroscopy (in-situ FTIR), Electron Spin Resonance (ESR), and capture experiment. This investigation will offer valuable insights for modifying LDH in order to effectively remove ppb-level NO through photocatalysis.