Physicochemical Characterization and Diclofenac Adsorption on Biocarbon Derived from Corn Digestate

The valorization of digestate from agricultural biogas plants into functional carbon adsorbents offers a route to combine waste management with water purification. Herein, corn digestate was converted into physically activated biocarbon by carbonization at 773.15-973.15 K, followed by CO₂ activation at 1073.15 K, and the relationship between preparation temperature, surface chemistry, porous structure, and diclofenac adsorption was examined. The obtained materials exhibited comparable specific surface areas of 576-578 m²/g but differed in pore volume, iodine number, oxygen-containing surface groups, and adsorption efficiency. Among the tested samples, CD_6_8 showed the best overall performance, reaching a maximum diclofenac adsorption capacity of 226-227 mg/g. The adsorption behavior was best described by the Langmuir isotherm and pseudo-second-order kinetic model, while pH-dependent adsorption and point of zero charg (pH_pzc) analysis indicated that diclofenac uptake is controlled by a combination of pore filling, π-π interactions, hydrogen bonding, hydrophobic interactions, and electrostatic effects. The study demonstrates that corn digestate can be transformed into an efficient adsorbent for pharmaceutical contaminants and identifies the physicochemical features responsible for the superior performance of the material carbonized at 873.15 K. Remaining challenges include performance verification in complex water matrices, regeneration, and long-term stability under realistic treatment conditions.