Modified carbon nitride incorporating Keggin-type potassium phosphotungstate enhances photocatalytic degradation of imidacloprid under visible light

Abstract

Despite the significant research efforts that have been dedicated to the applications of graphite carbon nitride (g-C3N4) in the flied of photocatalysis, there is still a significant challenge in terms of its efficiency under visible light conditions. In this study, potassium phosphotungstate (KPW), phosphotungstic acid (HPW), and ammonium phosphotungstate (NHPW) were used to synthesize composite photocatalysts with g-C3N4 by a post-impregnation activation method, and the synthesized g-C3N4/KPW-0.2 exhibited excellent photocatalytic performance. When illuminated by visible light for a duration of 3 h, g-C3N4/KPW-0.2 demonstrated an outstanding degradation rate of 91.72 % for the imidacloprid, with a photocatalytic degradation rate constant of 0.0134 min−1, which is 2.8 times higher than that of g-C3N4. Notably, g-C3N4/KPW-0.2 shows better performance compared to g-C3N4/HPW-0.5 and g-C3N4/NHPW-1.2 prepared using the same procedure. Experimental results have established that KPW forms a strong interaction with g-C3N4, facilitating the migration of electrons, the KPW acting as an electron mediator, enabling increased absorption of visible light, and reducing electron-hole recombination. These synergistic effects significantly improve the photocatalytic activity of g-C3N4. Additionally, g-C3N4/KPW-0.2 showed excellent stability, retaining its high photocatalytic activity even after five cycles of use. From the results of electron spin resonance measurements and radical quenching experiments, photogenerated holes (h+) and superoxide radicals (·O2−) are the keys to the photocatalytic degradation process. The work presented here provides valuable insights into the effective compound of POMs with g-C3N4 in photocatalytic degradation technology. This research can inspire future applications of photocatalytic technology in the treatment of chemical substances in wastewater.