Removal of ronidazole and sulfamethoxazole from water solutions by adsorption on granular activated carbon: equilibrium and intraparticle diffusion mechanisms

The equilibrium and intraparticle diffusion of ronidazole (RNZ) and sulfamethoxazole (SMX) during the adsorption on granular activated carbon (GAC) from aqueous solution was investigated in this work. The solution pH, temperature, ionic strength and water matrix affected the adsorption capacity of GAC towards SMX, but no effect was observed for the adsorption of RNZ. This behavior was due to the different mechanism involved in the adsorption of both antibiotics. The adsorption capacity of GAC towards RNZ was greater than that towards SMX. Molecular computation allowed the estimation of the binding free energy and confirmed that the adsorption of RNZ was more favorable than the adsorption of SMX. The adsorption mechanism of both antibiotics is governed by pi-pi dispersive interactions, and molecular simulation demonstrated that the coulombic interactions did not affect, but the solvation and nonpolar interactions play a significant role on the adsorption of both antibiotics. The application of diffusional models revealed that the overall adsorption rate of both antibiotics is controlled by intraparticle diffusion. Moreover, the surface diffusion was more predominant than the pore volume diffusion. Besides, surface diffusion coefficient, D-s, for RNZ was not a function of the aqueous matrix, whereas D-s for SMX was highly dependent on the water matrix.