Insights into mechanisms, kinetics and pathway of continuous visible-light photodegradation of PPCPs via porous g-C3N4 with highly dispersed Fe(III) active sites

Pharmaceuticals and personal care products (PPCPs) are emerging pollutants leading to harmful toxicological consequences. In this study, hybrid polymeric carbon nitride nanosheets (PCN) with highly dispersed Fe(III) active sites (denoted as Fe-UCN, which UCN stands for PCN with urea as precursor) was synthesized to degrade PPCPs, and Fe-UCN was further entrapped (denoted as CAlg/Fe-UCN) to serve as a fixed-bed reactor to increase the treatment scale and achieve continuous photo-oxidization under white LED light. The Fe-UCN possessed the 2D layered nanosheet, and abundant Fe(III) species interacted with the unsaturated coordination N atom as the active sites. When compared to pristine UCN, the Fe-UCN had higher oxidizing ability to sulfamethoxazole due to the increasing visible-light sensitivity, boosted charge carrier concentration and high separation efficiency of the electron-hole pairs without leakage of Fe(III) species from Fe-UCN. The degradation pathway mainly included S-N breakage, hydroxyl substitution and oxazole ring opening processes. The Fe-UCN could also achieve simultaneous removal of sulfamethoxazole, acetaminophen and trimethoprim with 1 mg L−1 of initial concentration, respectively, and the continuous-flow fixed-bed photoreactor containing CAlg/Fe-UCN could remove 2 mg L−1 of sulfamethoxazole. The photodegradation of PPCPs by the system under LED light without supplement of H2O2 and long-term reusability suggest the great potential of the developed photocatalysts for wastewater treatment.