Adsorption of ampicillin sodium on activated carbons with different surface chemistries

Abstract

BACKGROUND: The adsorption of ampicillin from aqueous solution by three types of activated carbon was investigated. The first was a commercial activated carbon (AC), the second (AAC) was AC modified by HNO3 oxidation and the third (HAAC) was AAC modified through thermal treatment. The surface properties of the activated carbon samples were characterized and the effects of pH and contact time on the adsorption were determined. The adsorption isotherms, adsorption kinetics and adsorption mechanism are discussed. RESULTS: Compared to AC, HNO3 oxidation increased the number of acid functional groups on the surface of AAC, which hindered the adsorption of ampicillin. For HAAC, thermal treatment removed surface oxygen groups and then improved the adsorption ability. The adsorption processes was greatly affected by pH and acidic conditions were favorable for adsorption. With an initial ampicillin sodium concentration of 200 mg/L, 9 h was needed for adsorption to reach equilibrium. The Langmuir isotherm provides a better fit for the adsorption than the Freundlich isotherm and the maximum adsorption capacities for AC, AAC and HAAC were 90.6, 59.8, 140.9 mg/g, respectively. The sorption kinetics can be described by a pseudo-second order model. CONCLUSION: The functional groups on activated carbon greatly affect its adsorption ability. The adsorption of ampicillin can be improved by increasing the number of basic functional groups on the activated carbon. Chemisorption was the dominant adsorption process and pH was an important factor affecting ampicillin adsorption.