Adsorption of pharmaceutical pollutants on activated carbon: Physicochemical assessment of the adsorption mechanism via advanced modelling

In this work, the adsorption mechanism of two pharmaceutical pollutants, paracetamol (PCM) and nimesulide (NMS), on activated carbon (AC) is elucidated via advanced modelling. Adsorption isotherms of PCM and NMS on a selected AC are obtained in the temperature range of 298–328 K. A physical model is applied to the experimental data set, assuming that the PCM and NMS molecules formed two layers on the AC, through the contribution of two adsorption energies. This theoretical analysis shows that the saturation adsorption capacities decrease with temperature from 259.27 to 211.82 mg/g for NMS and from 114.79 to 73.49 mg/g for PCM. This trend indicates that the tested AC has higher performances in removing NMS than PCM. The analysis of model parameters indicates that the number of molecules bound per active site (n) for the NMS-AC system are greater than unity for all the investigated temperatures, while it results to be equal to unity for PCM-AC system. This result allows concluding that an aggregation occurs during the adsorption of both the compounds, which are removed via interactions with one AC functional group. Different adsorption energies are determined, showing that the adsorption of NMS and PCM occurs via physisorption. Overall, this paper reports new theoretical assessments of PCM and NMS adsorption mechanism onto activated carbon via the adopted statistical physics model.