Sensing of arsenic using zinc oxide (ZnO) MODIFIED with curcumin

Abstract

Zinc oxide (ZnO) has presented itself as a special material with great potential and has attracted researchers to study this semiconductor in the form of powders, single crystals, thin films etc. ZnO is used for a wide variety of applications such as, transparent conducting electrodes in solar cells, photocatalysts, UV lasers, sensors etc. Arsenic exists in water as two major inorganic species, namely As (III) (arsenite) and As (V) (arsenate). In aerobic or oxidizing conditions arsenates are stable, whereas under anaerobic or mildly reducing conditions arsenites are more stable. Of these two redox states of arsenic, As (III) (arsenite) is the more toxic form than As (V) (arsenate). In this project work, we have applied a simple aqueous phase chemistry method and have modified nanostructured zinc oxide surfaces with the organic compound curcumin (C21H20O6), here referred to as Zn(cur)O. These Zn(cur)O nanostructured materials have the morphology of a grain-like wurtzite hexagonal crystal structure with good crystalline quality. The defects of ZnO, which are visible luminescence centers get filled by doping of curcumin. It in turn prolongs the electron-hole recombination, thereby causing the quenching of visible luminescence and also enhancing the exciton emission of zinc oxide. Now, Zn(cur)O is weak fluorescent. When it comes in contact with arsenic and binds with it, it becomes strongly fluorescent and shows enhanced photoluminescence. The photoluminescence of ZnO is insensitive to arsenic concentration in water. Arsenic can be sensitively sensed in the concentration range of 100 to 3000 ppb by the photoluminescence of a Zn(cur)O colloidal solution at an excitation wavelength of 425 nm.