Adsorption behavior of norfloxacin and site energy distribution based on the Dubinin-Astakhov isotherm

Abstract

Concerns about the water resources contaminated by fluoroquinolone antibiotics have prompted research on effective and efficient treatment technologies. In this work, adsorbents based on barley straw were characterized on morphology, surface functional groups, and charge states for the adsorption of norfloxacin, a representative of fluoroquinolone antibiotics, from aqueous solutions. The effects of solution pH were studied, and high norfloxacin adsorption capacities of pretreated barley straw were achieved in a wide pH range (2.90–10.50), which were much higher than those of raw barley straw. The adsorbent was also able to remove norfloxacin from low to high concentration range, demonstrating its capability for norfloxacin removal from water bodies. The electron-donor-acceptor interactions were proposed as one of the main adsorption mechanisms. The adsorption kinetic data achieved at a range of concentrations were well described by the pseudo-second-order kinetic model. The adsorption equilibrium data were reasonably well-fitted by the Dubinin-Astakhov model, and a site energy distribution function based on the Dubinin-Astakhov model was determined. With higher site energies, the pretreated barley straw demonstrated a much stronger adsorption affinity for norfloxacin than raw barley straw.