High-Efficiency Degradation of Orange II by Co78Si8B14/g-C3N4 Composite Catalyst in a Visible-Light-Assisted Peroxymonosulfate Activation System

Peroxynitrite-based advanced oxidation technology has gradually become a research hotspot for degrading dye wastewater due to its high efficiency and environmentally friendly features. Transition metal elements, which are commonly used as catalysts for the activation of persulfates, suffer from problems such as easy deactivation and leaching of metal ions, which limit their practical application. In this study, Co78Si8B14/g-C3N4 composite catalysts were prepared by wet milling and ball milling methods to investigate their degradation of Orange II dyes by assisting the activation of peroxynitrite under visible light, and the effects of the catalyst ratio, light intensity, and the dosage of catalysts on the degradation performance were investigated. It was shown that the optimum ratio of Co78Si8B14 to g-C3N4 was 1:3, and the reaction rate constants for the degradation of orange dye by Co78Si8B14/g-C3N4 + PMS + VIS were 4.3 and 5.37 times higher than those of single g-C3N4 + PMS and Co78Si8B14 + PMS, respectively. Meanwhile, the composite catalyst also showed good degradation performance for rhodamine B, methyl orange, and methylene blue dyes, and the degradation effect could reach more than 75%. Cyclic stability tests showed that the catalyst maintained a high degradation efficiency of more than 94% over multiple cycles with low ion dissolution concentration. Its high catalytic activity is attributed to the lowest adsorption energy of the composite catalyst to PMS (Eads = −1.97 eV), which facilitates the degradation reaction, while the synergistic effect of g-C3N4 and Co78Si8B14 promotes the production of ·SO4, ·OH, and ·O2−. This study provides new ideas for the development of stable and efficient catalysts to expand the synergy between PMS-based and other advanced oxidation technologies.