Biomimetic cobalt single atomic sites in carbon nitride nanosheets for photocatalytic reductive dechlorination of diclofenac.

Photocatalytic reductive dechlorination (PRD) represents a promising approach for the removal of chlorinated organic contaminants, however persisting a challenge in the development of catalytic sites capable of simultaneously enhancing the accumulation of photogenerated electrons and facilitating the selective adsorption of chlorine (Cl). In this study, single atomic Co sites with a Co-N4 enzyme-like structure, mimicking the active center of Dechloromonas, were successfully integrated into urea-cyanuric acid-derived g-C3N4 (5Co-UCCN), achieving production at a large-scale level. The 5Co-UCCN demonstrated a 30-fold enhancement in degradation kinetics relative to unmodified UCCN for the PRD of diclofenac (DCF), accompanied by improved environmental adaptability, which facilitated the effective degradation of DCF in natural water and real wastewater samples under visible-light irradiation. By means of time-resolved technology, in-situ techniques, and chromatography-mass spectrometry, the excellent degradation activity is attributed to the unique biomimetic Co-N4 sites. These sites (i) introduce a novel intermediate band that broadens the visible-light absorption and improves the transfer of photoelectrons from the UCCN framework to the Co single atom, (ii) display distinctive selectivity in adsorbing Cl of DCF via Co-Cl interactions, which collectively promote the accumulation of photoelectrons at the Co single atom, thereby facilitating the targeted cleavage of the C-Cl bond to enhance PRD of DCF.