Understanding the solid-liquid equilibria between paracetamol and activated carbon: Thermodynamic approach of the interactions adsorbent-adsorbate using equilibrium, kinetic and calorimetry data

Abstract

In this work, we presented the paracetamol-activated carbon interactions and their effect on the adsorption capacity. We evaluated kinetic, equilibrium, and calorimetric data using different solvents (water, HCl 0.1 M, and NaCl 0.1 M) to evaluate the changes in the adsorbent-adsorbate interaction. In addition, the commercial activated carbon (AC) was modified through thermal (ACTT) and chemical (ACNA) methods to change the physicochemical properties of the adsorbents. The relative kinetic constants decrease with the content of basic groups on the activated carbon, indicating a lower influence of diffusion on the adsorption rate when the chemical interactions increase (0.1 _ACNA >0.09 _AC >0.03 _ACTT mmol g^-1). The adsorption capacity for AC at acidic pH increases slightly compared to tests carried out in the water. Under this condition, the adsorbed amount of paracetamol was 1.31 mmol g^-1. However, the maximum adsorption capacity was achieved on ACTT using water as solvent (1.57 mmol g^-1). The paracetamol adsorbed decreases in NaCl (osmotic, ionic strength) on all activated carbons by around 20%. The interaction enthalpy of the paracetamol-activated carbon interaction presents values between - 18.0 and 2.3 J per molecule adsorbed. The Gibbs energy released during the adsorption process is between - 33.1 and - 29.8 kJ mol^-1.

Keywords: Adsorption; Gibbs energy; Immersion enthalpy; Interaction enthalpy; Oxidation; Surface chemistry.