Competitive adsorption of selected non-steroidal anti-inflammatory drugs on activated biochars: Experimental and molecular modeling study

The adsorption of targeted non-steroidal anti-inflammatory drugs: diclofenac (DCF), naproxen (NPX), and ibuprofen (IBP) by two types of activated biochar (N-/O-biochar) was studied in single- and multi-solute adsorption experiments in conjunction with molecular modeling subsequently interpreting the binding energy. The carbonaceous structure of the biochars was elucidated via nuclear magnetic resonance and the intensity of the interactions between the solute and adsorbent was also determined. Using fractions of the carbonaceous functional group on the adsorbent for the single-solute adsorption, the overall binding energies were determined to be in the order of DCF > NPX > IBP (-21.8 > -17.5 > -14.1 kcal/mol for N-biochar and -21.2 > -17.3 > -14.2. kcal/mol for O-biochar), while the maximum adsorption capacities of DCF, NPX, and IBP for N-biochar and O-biochar were 372, 290, 311. mg/g and 214, 228, 286. mg/g, respectively. A strong interaction between the DCF and the adsorbent resulted in the occupation of effective adsorption sites as compared to other solutes, while blocking the pores in which smaller sized NPX and IBP that may have been adsorbed. A weaker adsorption of IBP was observed in the presence of adsorption competitors. More specifically, the presence of adsorption competitors caused lower binding energy due to a combination of lower binding energy, polarity, and π-energy with the adsorbent and electrostatic repulsion from the cosolutes that occupied adsorption sites.