Enhanced photocatalytic degradation of methyl orange by coconut shell-derived biochar composites under visible LED light irradiation.

The conversion of carbon-rich biomass into valuable material is an environmental-friendly approach for its reutilization. In this study, coconut shell-derived biochar, graphitic carbon nitride (g-C ₃ N ₄ ), g-C ₃ N ₄ /biochar, titanium dioxide (TiO ₂ )/biochar, zinc oxide (ZnO)/biochar, and ferric oxide (Fe ₂ O ₃ )/biochar were synthesized and characterized by using scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM-EDX), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), surface area analysis, UV-Vis diffuse reflectance spectroscopy (DRS), and zeta potential analysis. The g-C ₃ N ₄ or metal oxide particles were found to be well-distributed on the coconut shell-derived biochar with the improvement in thermal stability and enlargement of specific surface area. A great reduction in band gap energy was observed in the composite materials after incorporating with the biochar. Among different biochar composites, g-C ₃ N ₄ /biochar was found to have the highest photocatalytic activity. The interactive effect of parameters such as catalyst dosage, peroxymonosulfate (PMS) oxidant dosage, and solution pH on the photocatalytic degradation of methyl orange was investigated using the response surface methodology (RSM). The highest photocatalytic degradation efficiency (96.63%) was achieved at catalyst dosage of 0.75 g/L, oxidant dosage of 0.6 mM, and solution pH 3 after 30 min.