Thermal oxidation etching process of g-C3N4 nanosheets 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.