Raw <scp>A</scp> lgerian pine cones as a sustainable biosorbent for malachite green removal: Experimental and <scp>DFT</scp> ‐based insights

Abstract The presence of cationic dyes in wastewater represents a serious threat to aquatic ecosystems and public health. This study explores raw powdered Algerian pine cones (PC) as an abundant, low‐cost biosorbent for Malachite Green (MG) removal from aqueous solutions. The material was characterized using FTIR, SEM, TGA, and pHpzc. The adsorption process was examined under different conditions: contact time, pH, initial dye concentration, biosorbent dosage, and temperature. Adsorption followed a pseudo‐second‐order model, achieving a maximum removal efficiency of 86.95% after 30 min. Optimal conditions were pH 10, with 1 g biosorbent, 10 mg/L dye concentration, at 35°C. Thermodynamic parameters (Δ H °, Δ G °, Δ S °) were evaluated to elucidate the adsorption process nature. Results suggest that (MG) adsorption onto biosorbent was an endothermic physisorption process (Δ H ° = +16.12855 KJ/mol). Positive Gibbs free energy change (Δ G ≥ 0) values, between 288 K and 308 K, indicate that the process is not spontaneous within this temperature range. However, at 318 K, energy change Δ G becomes negative (−0.30251 KJ/mol), suggesting a shift toward spontaneity as the temperature increases. The positive (Δ S °) suggests a randomness increase at the solid–liquid interface, which enhances the adsorption efficiency at elevated temperatures. DFT‐based quantum chemistry calculations explored electronic interactions between MG and biosorbent components, mainly cellulose. Results showed the adsorbed molecule is electrically stable and prone to nucleophilic attack, increasing its affinity for hydroxyl‐rich lignocellulosic surfaces. So, unprocessed Algerian pine cones offer an eco‐friendly solution for removing MG from wastewater, with strong potential for dye treatment and local biomass valorization.