A sustainable and fast methodology based on magnetic activated carbon for removal of imidacloprid from aqueous solution

Abstract

The occurrence of neonicotinoid insecticides in environmental waters represents a potential risk for the ecosystems and human health. Herein, an efficient procedure based on an activated carbon/magnetite (AC/Fe3O4) mixture adsorbent is proposed for fast removal of imidacloprid (IMI) as target molecule. The effects of contact time, adsorbent dosage and presence of inorganic salts on the adsorption characteristics of IMI on AC/Fe3O4 were evaluated by using a simple flow-system. Under optimal conditions, IMI was satisfactorily removed in only 10 min using AC/Fe3O4 (90:10 mass:mass ratio) at pH 7.0. The adsorption capacity was 192 mg g−1 at 25 °C. IMI only adsorbed on AC, but Fe3O4 was necessary to impart magnetic properties to AC. A comparative analysis of adsorption isotherms of several carbon-based adsorbents for IMI demonstrates that not only the maximum adsorption capacity of the adsorbent but also the affinity of the surface for the insecticide (given by the adsorption constant) needs to be considered when choosing an adsorbent. Materials with high maximum adsorption capacities are good for concentrated solutions, such as wastewaters; materials with high adsorption constants are especially good for more dilute solutions, such as environmental samples. Desorption of IMI was also tested under different pH conditions and effective desorption was achieved at pH 11.5 (25 °C), allowing the reuse of the material for subsequent adsorption runs without losing its capacity. Thus, an efficient, sustainable and low-cost adsorption procedure is proposed for fast removal of IMI from aqueous solution. These results demonstrate the potential applications of the studied mixture as adsorbent for developing alternative water cleaning technologies and analytical systems.