Thermal oxidation etching process of g-c₃n₄nanosheets from their bulk materials and its photocatalytic activity under solar light irradiation

The behaviour of g-C₃N₄ samples under thermal oxidation etching process were investigated. The g-C₃N₄ samples were prepared from melamine powder by following a two-step heating method in a semi-closed system. The effects of different thermal oxidation etching processes were systematically investigated to understand the influence of this process on the g-C₃N₄ properties. The transformation of g-C₃N₄ 3 h (bulk) to g-C₃N₄ 12 h (nanosheets) was confirmed by conducting systematic studies including scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Photoluminescence (PL), Fourier-transform infrared spectroscopy (FTIR), UV-vis diffuse reflectance spectroscopy (UV-vis DRS), Brunauer Emmett Teller (BET) analysis and particle size analysis. Methylene blue (MB) dye was selected as a model organic pollutant to evaluate the photocatalytic activity of the g-C₃N₄ samples. The XPS, UV-vis DRS and FTIR results indicated no major effect of the oxidation etching process on bulk g-C₃N₄ in the first 9 h. However, some variations were observed in XRD, particle size and BET analysis indexing where the etching process was observed to reduce the particles size and lower the number of layers on the g-C₃N₄ backbone. After 12 h of oxidation etching treatment, XPS and FTIR spectra showed some variation in the C-H, CO and N pyridinic structure of g-C₃N₄. MB results showed faster (150 min) degradation by the g-C₃N₄ nanosheets compared to bulk g-C₃N₄ (240 min) under solar irradiation. This can be attributed to other factors such as smaller particle size, rich carbon surface and high surface area exhibited by the g-C₃N₄ nanosheets. Thermal oxidation etching of g-C₃N₄ for 12 h is more effective at enhancing the photocatalytic degradation of organic pollutants under solar irradiation.