A comparison study of photocatalytic performance of g-C3N4 prepared from different precursors for the activation of different peroxides

In this study, g-C3N4 catalysts were prepared from six different precursors including urea, melamine and its hydrochloride, dicyandiamide, thiourea, trithiocyanuric acid to compare their photocatalytic performance and the activation of three commonly seen peroxides, i.e., H2O2, peroxymonosulfate (PMS), and peroxydisulfate (PDS) under visible light irradiation. The structural and photoelectric properties were analyzed systematically. Results showed that the g-C3N4 synthesized from trithiocyanuric acid (TCA-CN) showed the largest SSA (56.59 m2/g), the narrowest band gap (2.621 eV), and lowest carriers' recombination rate, which correspondingly exhibited the best photocatalytic performance for the degradation of bisphenol A (BPA). Moreover, the g-C3N4 synthesized by urea (U-CN) demonstrating the strongest photoelectron density, widest band gap (2.790 eV) and the most positive VB potential showed the highest activating efficiencies of all three oxidants. In general, persulfates were more competent to enhance the degradation of BPA than H2O2, and PMS showed the highest activity. The dominant reactive oxidation species (ROS) depended more on the type of peroxides than on the catalyst precursors. The effective activation of PDS by U-CN was primarily resulting from the photoelectrons to produce extra •OH to enhance compounds degradation, and high yield of 1O2 could be achieved by PMS activation through h+ oxidation, leading to the most significant enhancement of BPA removal. The N–C3 and NHx of U-CN were likely the sites for PMS activation. Moreover, the U-CN/LED/PMS process showed the strong adaptability to the complex water environment. This work may provide new insights into selecting highly efficient g-C3N4-based advanced oxidation processes for water remediation.