Modification of nanostructured ZnO surfaces with curcumin: fluorescence-based sensing for arsenic and improving arsenic removal by ZnO

Applying a simple aqueous phase chemistry method, nanostructured zinc oxide surfaces have been modified with curcumin, here referred to as Zn(cur)O. The morphology of these Zn(cur)O nanostructured materials is a grain-like wurtzite hexagonal crystal structure with good crystalline quality. Doping of curcumin fills the defects of ZnO that are visible luminescence centers and prolongs electron-hole recombination, resulting, respectively, in quenching of visible luminescence and an enhancement in the exciton emission of ZnO. The photoluminescence of ZnO is insensitive to arsenic concentration in water, but the photoluminescence of a Zn(cur)O colloidal solution at an excitation wavelength of 425 nm can sensitively sense arsenic in the concentration range 100 to 3000 ppb. At the same time Zn(cur)O can significantly improve the efficient removal of arsenic contamination from water below the maximum contaminant level (MCL) within 30 minutes and almost to zero in 3 h without oxidation and/or pH adjustment. The adsorption kinetics during arsenic removal by Zn(cur)O obeys a pseudo-second order model with exceptional adsorption rates compared to ZnO, reflecting the high affinity of Zn(cur)O nanomaterials to arsenic due to improvement in adsorption.