Photocatalytic degradation of clofibric acid by g-C₃N₄/P25 composites under simulated sunlight irradiation: The significant effects of reactive species

Pharmaceutically emerging micropollutants have become an environmental concern in recent years. In the present paper, the reactive species (RSs)-induced degradation mechanism of clofibric acid (CA) was investigated using a newly sunlight-driven g-C₃N₄/P25 photocatalyst. A very low g-C₃N₄ content of 8.0 weight percent resulted in a 3.36 and a 2.29 times faster reaction rate for CA photodegradation than for pristine g-C₃N₄ and P25, respectively. Electron spin resonance and quenching experiments demonstrated the participation of HO, h⁺, e^-, ¹O₂ and O₂^·- in the photocatalytic system, and the contribution rates were calculated to 73.3%, 15.3%, 5.1%, 6.7% and 33.1%, respectively. According to the pulse radiolysis measurements and the competitive kinetics approaches, the bimolecular reaction rate constants for HO, e^-, and ¹O₂ with CA were (8.47 ± 0.33) × 10⁹ M^-1s^-1, (6.41 ± 0.48) × 10⁹ M^-1s^-1 and (6.6 ± 0.37) × 10⁶ M^-1s^-1, respectively. RSs were found to significantly influence the degradation of CA, and the degradation pathways occurred primarily via e^- reduction, HO addition and ¹O₂ attack reactions on the basis of mass spectrometry and theoretical calculations.