Modulating the adsorption performance of tea waste biochar for Rhodamine B via pyrolysis temperature

The tea industry generates a significant amount of waste, leading to environmental issues and creating a need for sustainable waste management strategies. This research aims to evaluate the effect of different pyrolysis temperatures (250, 300, and 350 °C) on the physicochemical characteristics, structural composition, and adsorption capabilities of biochar derived from tea waste. Biochar was produced at varying temperatures and characterized using yield, pH, proximate and ultimate analyses. The surface topography was studied through scanning electron microscopy (SEM), the zeta potential through dynamic light scattering (DLS) and the surface functional groups were analysed qualitatively using Fourier transform infrared spectroscopy. The crystallinity of biochar was determined using X-ray diffraction (XRD), and thermal stability was estimated through thermogravimetric analysis. The results showed that yield, moisture content, volatile content, nitrogen, hydrogen, sulfur, and oxygen decreased, whereas fixed carbon, pH, and carbon content increased. Within the temperature range studied, biochar produced at 300 °C had relatively balanced mineral content, while increasing temperatures enhanced porosity, and surface roughness, significantly altering the crystalline structure, resulting in the highest negative zeta potential. Biochar produced at 350 °C adsorbs the greatest amount of Rhodamine B. Experimental adsorption kinetics followed pseudo-second-order kinetics, and adsorption equilibrium was well described the Freundlich isotherm model, indicating a heterogeneous multilayer adsorption process with Rhodamine B. Intraparticle diffusion analyses revealed that both intraparticle pore diffusion and surface adsorption contributed to overall sorption mechanism of Rhodamine B. In conclusion, biochar produced at 300 °C exhibited relatively higher nutrient content, while biochar produced at 350 °C showed improved performance for Rhodamine B dye removal. Future field trials are recommended to evaluate its application in soil nutrient management and wastewater treatment.