From lignocellulosic biomass to activated carbon: Impact of composition, structure and activation on the adsorption of organic pollutants

• Activated Carbon derived of Straws from Durum Wheat, Soft Wheat, and Barley. • The activated carbon was chemically activated by impregnating H 3 PO 4 . • Methylene blue's toxicity is a significant environmental concern. • AC derived from straws of durum wheat showed a high adsorption capacity of 57.07 mg/g. • Freundlich model provides the best fit for all three activated carbons • DFT and MD simulations contributed to understanding MB molecule adsorption. Amid growing environmental and economic pressures, the demand for sustainable alternatives to conventional activated carbons—typically sourced from wood and coal—has surged. This study explores the conversion of agricultural by-products, specifically straw from durum wheat, soft wheat, and barley, into activated carbon using phosphoric acid (H₃PO₄) as an affordable chemical activating agent. Prior to activation, the raw biomass underwent structural, compositional, and proximate analysis to assess its suitability as a carbon precursor. The resulting activated carbons were thoroughly characterized through FTIR spectroscopy, SEM imaging, and XRD analysis, confirming well-developed porous networks favourable for adsorbing organic pollutants. Because the three cereal straws exhibit similar lignocellulosic compositions and were subjected to the same H₃PO₄ activation protocol, they developed comparable porous structures, with porosity values reaching approximately 65%. This high level of porosity enhanced the accessibility of adsorption sites, leading to a high methylene blue removal efficiency of up to 95%. Methylene blue was employed as a model contaminant to evaluate adsorption efficiency, with key parameters such as pH, contact duration, temperature, adsorbent dosage, and initial dye concentration systematically analysed. To better understand the adsorption behaviour, kinetic, isotherm, and thermodynamic analyses were conducted. The adsorption kinetics were best described by the pseudo-second-order model, the adsorption isotherms showed a better fit to the Freundlich model, and thermodynamic parameters indicated a spontaneous adsorption process (ΔG° < 0). Additionally, density functional theory (DFT) simulations provided molecular-level insights into the interactions between dye molecules and the adsorbent surface. Overall, this research demonstrates the potential of cereal straws as low-cost, environmentally friendly feedstocks for the production of efficient activated carbons aimed at water purification applications.