Efficient photocatalytic water decontamination over a wide pH range by C and O co-doped carbon nitride with tunable band structure

Abstract

The metal-free, non-toxic, and highly tunable structure of carbon nitride confers unique advantages in photocatalytic advanced oxidation processes. Regulating the generation of radical and non-radical species during photocatalysis to maintain high degradation efficiency across different water matrices is of great practical significance for the application of carbon nitride. In this study, a C and O co-doped modified carbon nitride (UCN) with a high specific surface area was developed for efficient photodegradation of p-chlorophenol (p-Cl) without exogenous oxidants. Characterizations demonstrated that UCN in higher specific surface area exposed more active sites. Additionally, with rising doping levels, UCN exhibited enhanced light absorption capability and a narrower bandgap, which favored the separation of photogenerated electron-hole pairs. The primary active species were identified as holes, accompanied by the generation of superoxide radicals (·O2–) and singlet oxygen (1O2) depending on the pH value. Under acidic conditions, 1O2 was predominantly generated, whereas ·O2– dominated under alkaline conditions. As a result, the removal efficiency of p-Cl was enhanced under both strongly acidic and alkaline conditions. The pseudo-first-order rate constants for p-Cl removal at pH 3, 7, and 11 were 0.0558, 0.0354, and 0.0443 min−1, respectively. Moreover, combining DFT calculations and LC-MS data, analysis on the intermediate products of p-Cl degradation revealed unique characteristics at different pH values, further proving the flexible tunability and providing insights into the practical application of modified carbon nitride.