New correlations between the composition of the surface layer of carbon and its physicochemical properties exposed while paracetamol is adsorbed at different temperatures and pH

The series of previously characterized commercial activated carbons D43/1 with almost the same porosity, however differing in the composition of the surface layer, was characterized using some additional methods of porosity and of surface chemistry description (DFT method, electrochemical studies, acid-base site distribution, pH(PZC), and resistance measurements). On these carbons adsorption isotherms of paracetamol (as well as kinetic curves) were measured at acidic pH (1.50) and at three temperatures 300, 3 10, and 320 K. The measurements of the enthalpy of immersion in HCl and paracetamol solutions were also performed at 310 K. Diffusion coefficients and the energies of diffusion were calculated. The results of measurements at acidic pH are compared with those measured for adsorption at the neutral pH. Some new correlations between the constants describing the chemical properties of the surface layer are given. Moreover, the properties of the surface are correlated with the constants characterizing the process of paracetamol adsorption. The mechanism of adsorption at both pH values is elaborated, the importance of surface carbonyls and basic groups is emphasized, and the product of polymerization of paracetamol adsorbed at acidic pH is determined using FTIR and UV-vis measurements. (C) 2003 Elsevier Science (USA). All rights reserved.