Facile, low-cost, and environment-friendly method for preparing peanut shell-based activated carbon: application to dichloromethane removal

Solid adsorption effectively removes hazardous air pollutants like dichloromethane (DCM), thereby mitigating serious environmental problems. In this study, activated carbon (AC) was innovatively prepared from peanut shells using a single-step physical-chemical activation technique involving CO₂ and potassium oxalate monohydrate (POM). The synthesis focused on properties, cost, and environmental impact. Optimization of AC preparation conditions employed central composite circumscribed design (CCCD) to maximize specific surface area (<i>S</i> _BET) and production yield (<i>Y</i> _AC). Two quadratic models described the relationship between synthesis variables: activation temperature (<i>T</i> _act., °C), impregnation ratio (IR, g g^-1), and CO₂ gas flow rate (L h^-1) for each response. The optimized activated carbon (POMCO₂-AC) exhibited an <i>S</i> _BET of 1100 m² g^-1 and a <i>Y</i> _AC of 21%, matching predicted values. Characterization tests indicated minimized macropores, high porosity with 83% micropore distribution, and appropriate surface chemistry. Column adsorption tests demonstrated that POMCO₂-AC efficiently eliminates DCM from a contaminated gas stream. Langmuir, Freundlich, and Langmuir-Freundlich models were employed for adsorption isotherm analysis. The evaluation of adsorption kinetics data was conducted using pseudo-first-order, pseudo-second-order, and intraparticle diffusion models. The results indicated that the Langmuir isotherm and pseudo-first-order models described the experimental data more accurately than other models. The maximum adsorption capacity (<i>q</i> _max) was determined to be 298 mg g^-1 at 273 K. The adsorption mechanism was found to be governed by intraparticle diffusion in combination with the film diffusion. The study reveals that the applied preparation method effectively converts agricultural wastes, such as peanut shells, into an efficient and low-cost adsorbent for removing pollutants, making it suitable for industrial-scale air purification.