Resorcinol Formaldehyde Resin-Modified Carbon Nitride as Metal-free Photocatalyst for Water Treatment

Metal-free catalysts are considered a new strategy for environmental application since they do not release any additional hazardous compounds when employed for an extended period. Carbon-based materials and carbon nitride have drawn a lot of interest owing to their physical and optical properties.  Herein, we reported a new way to modify carbon nitride with resorcinol-formaldehyde resins, a member of phenolic resins, to enhance their photocatalytic activity. The length of time to polymerize resorcinol-formaldehyde resins was investigated as it had a great impact on the characteristic features as well as the photocatalytic performance of the resulting materials. SEM images revealed that RF resins appeared as nano-fragments and were deposited densely on the surface of carbon nitride. On the other hand, the deposition of RF on the surface of carbon nitride had a great influence on the BET surface area values. For photocatalytic performance, all the modified samples exhibited significantly improved photocatalytic activity towards Methylene Blue (MB). The optimal sample was RF@CN10, which the reflux time was 10 hours. This sample has a more broaden absorption spectrum and a narrower bandgap energy (2.66 eV) than the pure carbon nitride.  With regard to photocatalytic activity, this sample could completely degrade MB in the solution within 40 minutes, but it had poor efficiency when visible light was absent. Additionally, the catalyst could work effectively in neutral and alkaline conditions and could be reused for 5 cycles. Finally, the hypothesis for RF-carbon nitride cross-linking and the synergistic effect in the catalyst had been proposed.