Decontamination of used transformer oil containing polychlorinated biphenyls using biochar: molecular computational study and adsorption performance evaluation

Polychlorinated biphenyls (PCBs) are hazardous synthetic organic compounds once widely used in transformer oils due to their insulating and thermal stability. This study uses combined computational and experimental approaches to investigate coconut fiber-derived biochar as a sustainable adsorbent for PCB remediation. Density functional theory (DFT) calculations compared pure biochar (PB), sulfuric acid-activated biochar (BSA), and sodium hydroxide-activated biochar (BSH), with BSH exhibiting the strongest interaction energy with PCB congeners. Laboratory adsorption tests using 0.5 g of BSH in 50 mL of contaminated transformer oil achieved an equilibrium capacity of 24.8 mg/g and 52% removal efficiency at 70 °C. Thermodynamic evaluation indicated an activation energy of 9.88 kJ/mol, confirming the process was endothermic. Material characterization further revealed that BSH possessed the largest average pore diameter (3.60 nm) and a pore volume of 0.15 cc/g, supporting enhanced uptake. These findings demonstrate that BSH is an effective and eco-friendly adsorbent, with adsorption performance governed by favorable pore structure and surface interactions. This work illustrates the value of integrating computational screening with experimental validation to guide the design of biochar-based materials for PCB-contaminated oil treatment.