Effect of Different Solvents on the Synthesis of Resorcinol–Formaldehyde and g-C3N4 Composite as Photocatalyst for Degradation of Methylene Blue

Carbon nitride, a hot spot in metal-free material, has been widely studied for various fields of application. Various efforts have been made to improve the photocatalytic activity of carbon nitride, including cross-linking with other kinds of polymers. In this study, Resorcinol – Formaldehyde (RF) resins were chosen to modify carbon nitride because they can act as a sacrificial agent to create the Z-scheme catalytic system with carbon nitride. The novelty of this study is using polyol solvents to synthesize nano-fragments Resorcinol–Formaldehyde. The goal of this work was to study the influence of polyol solvents on the formation of RF polymer and the photocatalytic performance of RF-modified carbon nitride. Scanning electron microscope (SEM) images suggested that nano-fragments RF resins that were synthesized in ethylene glycol and glycerol were able to deposit densely on the surface and in pores of carbon nitride as nano-fragments, while RF obtained from hydrothermal had the morphology of microspheres and only anchored on the surface of carbon nitride. In terms of BET (Brunauer–Emmett–Teller) surface area, E-RFCN had the largest value in four samples (72.3 m2 g−1) and was the only sample that had the BET value higher than that of pristine carbon nitride (26.9 m2 g−1). Regarding the photocatalytic activity, E-RFCN was the optimal sample that could completely remove MB in the solution within 40 min in H2O2/visible light conditions. Furthermore, the catalyst could work effectively in a wide pH range from 5 to 9, and could be reused for 4 cycles. By conducting radical scavenging experiments, it was founded that •OH, photoinduced holes (h +) and •O2− contributed to MB decomposition by the order: h + > •OH > •O2−. Finally, the hypothesis for the effect of polyol solvents on the polymerization of RF and the RF-carbon nitride cross-linking had been proposed.