Adsorption of methylene blue solution by hydrothermal carbonization of unmodified rapeseed straw

In recent years, the energy crisis has worsened, prompting increased attention to new clean energy sources for sustainable development. This study investigates the adsorption of methylene blue (MB) by rapeseed straw biochar (RSB) produced <i>via</i> hydrothermal treatment at 120 °C. The results show that RSB120 has superior MB adsorption capabilities, with a maximum adsorption capacity of 212 mg/g. The adsorption process fits both the Langmuir (R² = 0.9677) and Freundlich (R² = 0.9493) models, indicating both monolayer and multilayer adsorption mechanisms. Additionally, the adsorption kinetics of MB on RSB120 are well described by the quasi-first-order (R² = 0.9973) and quasi-second-order kinetic models (R² = 0.9999), suggesting that RSB120 is an effective material for MB removal from wastewater. In this paper, biochar (RSB120) was synthesized using a hydrothermal method with rapeseed straw as the raw material. The adsorption of methylene blue was achieved with high efficiency, demonstrating a maximum adsorption capacity of 212 mg/g. The effects of temperature, pH, and other factors were systematically investigated. The adsorption mechanism was elucidated by integrating the Langmuir and Freundlich models, while the pore structure and functional groups were characterized using scanning electron microscopy (SEM) and Fourier-transform infrared spectroscopy (FTIR). The hydrothermal method is characterized by low temperature and high efficiency, and the utilization of straw resources is both environmentally friendly and economical. This approach offers a novel solution for the treatment of dye wastewater, combining innovation with practical application.