Thermodynamic analysis of acetaminophen and salicylic acid adsorption onto granular activated carbon: Importance of chemical surface and effect of ionic strength

We evaluated the effect of the ionic strength (INaCl  = 0, 0.01 M, 0.1 M) on the adsorption of acetaminophen and salicylic acid on two activated carbons (CAG and CAR1073) from equilibrium data and immersion calorimetry. The adsorption isotherms were adjusted to Langmuir and Freundlich models, and the adsorption capacity in each system was calculate. In the adsorption carried out in water, the adsorption capacities are greater than the systems with change in the ionic strength on both activated carbons. The adsorption capacities in water are QI=0 CAG = 1.83 mmol g−1 and QI=0 CAR1073 = 1.55 mmol g−1 for the salicylic acid and acetaminophen respectively. In the activated carbon CAG the ionic strength (NaCl 0.1 M) decrease the adsorbed amount (Q) for salicylic acid (AcSc) and acetaminophen (ACE) adsorption in a 54 % and 67 % respectively. The thermodynamic analysis were carried out from immersion calorimetry in solutions of salicylic acid or acetaminophen with concentrations between 6.6 × 10−2 and 7.2 mmol L-1. The immersion enthalpies were between −7.63 and −68.1 J g-1. Additionally, the interaction enthalpy, Gibbs energy and entropy change were determinated.