Synthesis of a Recoverable CuS/Fe3O4 Composite Structure with Enhanced Oxidase-Like Activity for Detection of Chromium (VI)

In this study, CuS/Fe3O4 composite structures were prepared in a two-step process. Initially, we used a simple solvothermal method to synthesize CuS nanostructures. Hydrothermal method was employed to form CuS/Fe3O4 composites. We characterized the particles using X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDX). The particles exhibit an oxidase-like activity using the colorless 3,3′,5,5′-tetramethylbenzidine (TMB) as oxidase substrate. The presence of chromium (VI) increases the oxidase-like activity and is dependent on the concentration. The UV/visible absorption intensity of the oxidized TMB (oxTMB) increases with the concentration of chromium (VI) which provides a route to colorimetric determination of chromium (VI). We noticed a limit of detection as small as 60 nM and a wide linear dynamic range of 0–1500 µM. We found a high selectivity of this method for chromium (VI) against potentially interference cations and anions. Its applicability for determination of chromium (VI) in real environmental samples is demonstrated using tap water. This result demonstrates the capability of the method in determination of chromium (VI) in real samples.