Photocatalytic activation of peroxymonosulfate by carbon quantum dots: rational regulation of surface functionality and computational insights

Carbon quantum dots (CQDs) are emerging carbonaceous photocatalysts, but the efficiency is unsatisfactory due to a narrow visible-light response and high electron-hole recombination. In this work, we fine-tuned the surface chemistry of CQDs via selectively substituting surface carbonyl group (C=O) with phenylhydrazine (PH). Such a modification optimized the conductivity and band structures of the derived products (CQDs-PH) with improved light absorption and separation of photogenerated electron-hole pairs, leading to boosted generation of reactive oxygen species (ROS) via peroxymonosulfate (PMS) activation. In addition, the primary ROS are identified as superoxide radicals (O2•−) and holes, whereas O2•− are produced from CQDs-activated PMS rather than from dissolved oxygen. Theoretical calculations illustrate that the electrons and holes on CQDs are spatially separated due to the spontaneous surface polarization induced by PH functionalization. This study provides a feasible approach to enhancing the photocatalytic activity of CQDs for sustainable water decontamination.