Environmental applications of S-doped g-C₃N₄ in photocatalytic degradation of Congo Red dyes under solar light Irradiation

Background: Today, researchers are focusing on preparing photoactive semiconductor materials doped with non-metals; such semiconductors may be considered a prospective route to resolving the worldwide water crisis by degrading organic dyes present in wastewater from the textile industry.

Methodology, results, and conclusions: Herein, we report a facile route to synthesise S-doped graphitic carbon nitride (S-GCN) from thiourea via thermal polymerisation methods. The crystalline nature of the synthesised photocatalyst was examined by utilising X-ray diffraction (XRD), with the peak positions at Bragg angles (2θ) of 13.07° and 27.42°, which correspond to Miller indices of (100) and (002), respectively; however, their functional group purity was evaluated through Fourier transform spectroscopy (FT-IR), and the presence of three distinct bands appearing at 3153 and 1636-1240 indicates the presence of N-H and O-H stretching modes of heterocyclic S-doped g-C-N, whereas the region between 805 and 812 cm⁻¹ represents the tri-s-triazine unit of S-GCN. All these results indicated that the synthesised photocatalyst exhibited good crystallinity and purity. To examine the photocatalytic activity, 0.2 g/L of synthesised S-GCN was immersed in 100 mL of 10 ppm Congo red dye solution, stirred for 25 minutes, and kept in the dark to establish adsorption–desorption equilibrium followed by open sunlight irradiation. During irradiation, a 3 mL suspension was taken out at intervals of 25 minutes; absorbance was measured, which decreased with time. Moreover, the S-doped GCN displayed good photocatalytic activity in 150 min of sunlight exposure. The degradation of dyes followed pseudo-first-order kinetics.