Unraveling the mechanisms of methylene blue adsorption onto biochar: a robust and sustainable approach for water remediation

Biochar has emerged as a cost-effective adsorbent for the removal of diverse pollutants. In this investigation, six different biochar variants were derived from oat hull and pea hull, generated at varying pyrolysis temperatures spanning 500°C–700°C. Different methods were employed to characterize these biochars, which were subsequently utilized as adsorbents for the removal of methylene blue (MB) from aqueous solutions. The adsorption performance of the biochar samples is closely linked to the temperature at which pyrolysis was conducted. Significantly, biochar produced at higher temperatures demonstrates markedly enhanced adsorption capabilities compared to those from lower temperatures, with a surface area exceeding 250 m²/g. Adsorption data is best fitted with Sips isotherm Notably, oat hull biochar exhibits a higher maximum adsorption capacity than pea hull biochar, with capacities of 183.4 mg/g and 145.5 mg/g, respectively, and removal efficiencies of 97% and 91%. An exploration of the adsorption mechanism reveals that MB adsorption is influenced not solely by Lewis’s acid–base interactions but also by π–π interactions entailing the biochar’s surface. The adsorption of methylene blue by biochar offers a sustainable and cost-effective solution for wastewater treatment, contributing to environmental remediation and resource utilization.