Carbonyl heterocycle modified mesoporous carbon nitride in photocatalytic peroxydisulfate activation for enhanced ciprofloxacin removal: Performance and mechanism

Polymer carbon nitride is considered to be a promising photocatalyst with broad application prospects in water treatment. However, the defects of pristine polymer carbon nitride (PCN), such as small specific surface area, fast photogenerated electron-hole recombination, and low mass transfer efficiency, limit its photocatalytic activity. In this work, by introducing 2-thiouracil into the precursor, a carbonyl heterocycle-containing mesoporous carbon nitride photocatalyst (TCN) was successfully obtained with significantly enhanced peroxydisulfate (PDS) photocatalytic activity. In this study, the modulation mechanism of carbonyl heterocycle introduction on surface electronic structure and the band structure were fully discussed by means of a combination of experiments and theoretical calculations. The carbonyl and vicinal carbon-modified heterocycles dominated the electrons, while the adjacent heptazine ring dominated the holes. The photogenerated electron-hole pair recombination efficiency and the electron transition energy barrier were greatly reduced. According to the findings of density functional theory (DFT) calculations, the introduction of carbonyl and vicinal C modulated the electronic structure of catalyst, enhanced the adsorption of PDS at the carbonyl ortho N site, which promoted the electronic interaction between TCN and PDS molecules. Experiments showed that the free radical pathway and non-radical pathway coexisted in TCN/PDS/Vis system. The reactive oxygen species were mainly derived from PDS molecules. DFT calculations provided a more comprehensive theoretical basis for the experimental results. This study provided a fresh perspective on the rational design of carbon nitride-based catalysts and the reaction mechanism of persulfate advanced oxidation systems.