Experimental and modelling study of adsorption isotherms of amoxicillin, ampicillin and doripenem on bentonite-chitosan composite

Abstract

The occurrence of antibiotic pollution has become a concerning issue to public health, where the adsorption of antibiotics on bentonite-based adsorbent represents an attractive solution to reduce the antibiotic residue in wastewater. In this work, the bentonite-chitosan composite was synthesised and the adsorption isotherms of amoxicillin, ampicillin, and doripenem were investigated experimentally at temperatures between 303.15 and 323.15 K. The bentonite-chitosan composite was characterised by scanning electron microscope, electron dispersive X-ray spectrophotometer, surface area and porosity analyser, powder X-ray diffractometer, Fourier transform infrared spectrometer, and thermogravimetric analyser to examine the structure of the synthesised adsorbent. The experimental data were also correlated with models of Langmuir, Freundlich, Toth, and Dubinin-Radushkevich. The experimental results showed an enhanced adsorption of all antibiotics on the bentonite-chitosan composite compared with raw bentonite despite having a much smaller BET surface area and pore volume. On the other hand, the Toth model provided the best estimates on the adsorption isotherms, though Langmuir constants were mostly recovered particularly in the lower temperature range. From the fitting results, the adsorptions of all antibiotics were implied to be endothermic and associated with monolayer formation. Within the tested temperatures, the adsorption capacities of the bentonite-chitosan composite computed by Toth model were found to be 51.9–86.1 mg g−1 for amoxicillin, 66.1–83.3 mg g−1 for ampicillin, and 78.4–96.0 mg g−1 for doripenem.

Keywords

• Bentonite
• Chitosan
• Amoxicillin
• Ampicillin
• Doripenem
• Adsorption isotherm