Durian peel–seed biochar for efficient methylene blue removal from water: synthesis, characterization, and adsorption performance

Dye contamination in wastewater represents a significant environmental challenge because of the toxic nature and poor biodegradability of these compounds. Developing cost-effective, environmentally friendly adsorbent materials derived from agricultural waste is essential for enhancing wastewater treatment efficiency at a reasonable cost. This study investigated the adsorption capability of methylene blue (MB) from aqueous solutions using activated carbon synthesized from durian shells and seeds (BDSS). The adsorbent was prepared <i>via</i> pyrolysis at 500 °C combined with a subsequent hydrothermal treatment. Adsorption experiments were conducted to evaluate key influencing factors and adsorption characteristics. The results revealed that BDSS exhibited a high specific surface area (441.71 m² g^-1), a porous structure, an iodine number of 589 mg g^-1, and a point of zero charge (pH_pzc) of 6.47. The adsorption of MB onto BDSS followed the Langmuir isotherm model, achieving a maximum adsorption capacity of 136.99 mg g^-1. The process adhered to pseudo-second-order kinetics and was identified as a spontaneous and endothermic reaction. Adsorption was observed to occur on both homogeneous and heterogeneous surface sites through a combination of physical and chemical mechanisms, including electrostatic interactions, hydrogen bonding, π-π interactions, electron donor-acceptor interactions, and pore filling. In addition, an artificial neural network (ANN) model was well established to predict BDSS adsorption performance under varying conditions. The optimal ANN with five input variables, one hidden layer of 11 neurons, and one output neuron showed excellent predictive accuracy (<i>R</i> > 0.99). Initial MB concentration had the most pronounced effect, followed by temperature, adsorbent dosage, contact time, and pH. The method is beneficial for process optimization and engineering applications. Furthermore, BDSS maintained 53.74% of its adsorption capacity after three reuse cycles, demonstrating good reusability. Overall, the findings suggest that BDSS-derived activated carbon is a promising, eco-friendly adsorbent with potential applications in the treatment of dye-contaminated wastewater.