Adsorption of amoxicillin and tetracycline on activated carbon prepared from durian shell in single and binary systems: Experimental study and modeling analysis

The adsorption mechanism of two antibiotics, namely amoxicillin (AMX) and tetracycline (TCN), on durian shell activated carbon (AC) was investigated in single and binary systems. Adsorption isotherms were determined under the same experimental conditions and they showed that the adsorption capacities of AMX were higher than those of TCN at all tested temperatures suggesting that this adsorbent preferred to remove AMX from the aqueous solution. It was also observed that all adsorption capacities decreased from single to binary systems, which was reasonably explained by an antagonistic adsorption between AMX and TCN on the active sites of AC creating an inhibition effect between these adsorbates. Monolayer and competitive monolayer models were developed via statistical physics theory and they were applied to explain and understand the adsorption mechanism of AMX and TCN via steric and energetic parameters. Results suggested that the parallel and non-parallel orientations of both antibiotics on the adsorbent surface of AC could be possible at tested experimental conditions. Modeling results demonstrated that the numbers of accepted antibiotic molecules per active site of AC varied with linear and inverse trends in single and binary systems, respectively, at all tested temperatures thus corroborating the adsorption inhibition effect caused by both adsorbates. An estimation of adsorption energies was also performed to describe and characterize the interactions between both antibiotics and AC surface. The assessment of the parameters of statistical physics models contributed to the explanation of the single and binary adsorption mechanisms of these water pollutants.