The enhanced visible-light-driven porous O/P-C3N4 for persulfate photoactivation: Enhanced removal of refractory pollutants and lignin valorization

In this research, an enhanced visible light response of oxygen and phosphorus-doped porous g-C3N4 (HAPA-CN) was prepared by thermo-polymerization of urea, hydroxyacetic acid and phytic acid. Its internal structure was verified by solid-state nuclear magnetism (NMR) and secondary ion mass spectrometry (SIMS). The surface electron density on HAPA-CN was enhanced by the inclusion of oxygen and phosphorus. The boosted photocatalytic activity was attributed to the high spectral utilization of sunlight and meliorated charge separation efficiency. The experimental results showed that the 0.05 HAPA-CN/persulfate (PS) system exhibited a higher efficiency in the photodegradation process of bisphenol A (BPA) and 2-mercaptobenzothiazole (MBT). Compared with ordinary g-C3N4, the integration of photocatalysis and persulfate oxidation led to an increase in the removal of BPA and MBT pollutants, which increased by 68.11 and 11.18 times, respectively. 0.05 HAPA-CN also exhibited a certain photodegradation of BPA under long-wavelength light irradiation such as blue, green, and red light. In the photocatalytic conversion of sodium lignosulfonate (SL), the 0.05 HAPA-CN/PS system achieved a maximum yield of 134.34 mg/gSL vanillic acid at 30 min, which was significantly better than that of g-C3N4. Synergistic gas production (H2, CO, CH4, C2H4, C2H6) was also significantly enhanced. Combined with theoretical calculations, the mechanism was also analyzed. This work provides new insights for exploring high efficiency photocatalyst that combine porous structure, oxygen and phosphorus co-doping and PS activation technology for removal of organic pollutants and lignin valorization.