Agricultural Waste for Remediation of Neonicotinoid Pollution: Mechanisms and Environmental Effects of Multi-Site Adsorption of Dinotefuran on Rice Husk Biochar

The increasing contamination of neonicotinoid pesticides in the environment has become a growing concern, and biochar is considered a promising strategy for removing these pollutants. This study converted waste rice husks into biochar (RHB) via pyrolysis at 400–600 °C under anaerobic conditions, using dinotefuran (DIN) as a representative neonicotinoid. The physicochemical properties of RHB and its adsorption mechanisms for DIN were systematically investigated. Results showed that higher pyrolysis temperatures increased the specific surface area, microporosity, and aromaticity of biochar, while altering the distribution of surface functional groups. RHB prepared at 600 °C (RHB600) exhibited the highest adsorption capacity. The adsorption process followed the Sips isotherm and pseudo-second-order kinetic models, indicating a spontaneous and endothermic process involving heterogeneous physic–chemical adsorption. The primary mechanisms included pore filling, π–π interactions, and hydrogen bonding. The sequence of functional group response during DIN adsorption was C–O > C=C > C=O > –OH. Environmental factors such as solution pH and humic acid concentration significantly influenced adsorption, while phosphate ions caused strong competitive inhibition. An artificial neural network model accurately predicted adsorption under multiple interacting factors, and RHB600 demonstrated good regeneration after ethanol elution. This study confirms that RHB is an effective and practical adsorbent, providing a technical reference for agricultural waste valorization and pesticide-polluted water remediation.