Uncovering Original Z Scheme Heterojunctions of COF/MOx (M = Ti,Zn, Zr,Sn, Ce,and Nb) with Ascendant Photocatalytic Selectivity for Virtually 99.9% NO-to-NO3− Oxidation

Novel Covalent organic skeleton/metal oxide (COF/MO_x; M = Ti, Zn, Zr, Sn, Ce, Nb) Z scheme heterojunction is constructed to achieve highly selective oxidation of nitric oxide (NO). Under visible-light irradiation, the optimized COF/TiO₂ (CF/TS0.05) catalyst showed an excellent NO removal rate (64.5%), resulting from the improvement of light absorption performance, the separation efficiency of photoexcited electron-hole pairs, and O₂ activation due to the uniform coating of COF. Meanwhile, the electrons are captured by the adsorbed oxygen to effectively render into superoxide radicals as the main active species, and the corresponding holes are retained at the complex interface due to the hydrophobic COF coating, which extremely reduced the ability of activated water to produce hydroxyl radicals and limited the production of intermediate nitrogen dioxide (NO₂), thereby improving the oxidation selectivity toward nitrate (NO₃⁻) at 99.9% in the Z scheme heterojunction. More importantly, other COF/MO_x catalysts also exhibited superior selectivity and activity, meaning that this scheme is credited with universality. In short, this study reveals that the generation of only one main reactive oxygen species is enhanced by reasonable control of electron-hole pair in the new Z scheme heterojunction to significantly increase photocatalytic performance and selectivity.