Fe-Doped g-C3N4 for Enhanced Photocatalytic Degradation of Brilliant Blue Dye

Brilliant blue, as a pigment food additive, has all the characteristics of printing and dyeing wastewater and belongs to persistent and refractory organic compounds. The photocatalysis–Fenton reaction system consists of two parts: photocatalytic reaction and Fenton reaction. Electrons promote the decomposition of H2O2 to produce •OH. In addition, the effective separation of e- and h+ by light strengthens the direct oxidation of h+, and h+ reacts directly with OH− to produce •OH, which can further promote the removal of organic pollutants. In this paper, g-C3N4 and Fe/g-C3N4 photocatalysts were prepared by the thermal polycondensation method. Fe/g-C3N4 of 15 wt% can reach 98.59% under the best degradation environment, and the degradation rate of g-C3N4 is only 7.6% under the same conditions. The photocatalytic activity of the catalysts was further studied. Through active species capture experiments, it is known that •OH and •O2− are the main active species in the system, and the action intensity of •OH is greater than that of •O2−. The degradation reaction mechanism is that H2O2 combines with Fe2+ in Fe/g-C3N4 to generate a large amount of •OH and Fe3+, and the combination of Fe-N bonds accelerates the cycle of Fe3+/Fe2+ and promotes the formation of •OH, thereby accelerating the degradation of target pollutants. •O2− can reduce Fe3+ to Fe2+, Fe2+ reacts with H2O2 to produce •OH, which promotes degradation, and •O2− itself also plays a role in degradation. In addition, under the optimal experimental conditions obtained by response surface experiments, the fitting degree of first-order reaction kinetics is 0.96642, and the fitting degree of second-order reaction kinetics is 0.57884. Therefore, this reaction is more in line with first-order reaction kinetics. The adsorption rate is only proportional to the concentration of Fe/g-C3N4.