Adsorption of the most common non-steroidal analgesics from aquatic environment on agricultural wastes-based activated carbons; experimental adsorption study supported by molecular modeling

Adsorption experiments and force-field based molecular modeling of analgesics interactions with carbon structures were applied to study the adsorption of diclofenac sodium salt, paracetamol and ibuprofen on activated carbons prepared from six different agro-wastes. Revealing the role of pore size, various carbon structural properties and surface functionalization in analgesic adsorption led to the determination of the affinity of individual analgesics for carbon: diclofenac sodium salt > paracetamol > ibuprofen. Diclofenac sodium salt bonds predominantly via electrostatic attractions, paracetamol and ibuprofen bond via weak hydrogen bonds and pi-pi interactions flat on the carbon graphitic surface. The micropore volume and size play the key role. Diclofenac sodium salt and ibuprofen adsorption is favoured in micropores with size < 1.2 nm, while smaller pores (<0.86 nm) are the most important for paracetamol adsorption. For diclofenac sodium salt adsorption the high surface polarity (COOH groups) is the second most important property. For adsorption of ibuprofen and paracetamol, the high graphitization rate is determining. Diclofenac sodium salt adsorption is preferred on graphitic edges rather than on the flat graphitic surface. The combination of experiment and molecular modeling was found to be a simple but powerful tool for prediction of adsorption properties.