Improved photoelectrochemical detection of mercury (II) with a TiO 2-modified composite photoelectrode

Abstract

The spectrophotometric change of a mercury (II) (Hg 2+) selective small molecule chemosensor has been successfully converted into a photovoltaic response upon ligating Hg 2+. The photon excitation was followed by charge separation facilitated by TiO 2 and polyaniline (PANI), resulting in an electron transfer to an electrical back contact. The photoresponse of the Hg 2+ selective chromophore was converted to an electron current equivalent to the amount of Hg 2+ in solution. The favourable properties of a Hg 2+ sensitive chemosensor was combined with the semiconductor capabilities of TiO 2 to construct a sensor that is capable of generating a current in the presence of Hg 2+ under illumination. A composite of the fluorescent chemosensor rhodamine 6G hydrozone derivative (RS) and PANI was immobilized on indium tin oxide (ITO) plates coated with TiO 2 and subjected to photovoltammetric measurements. The photovoltammetric responses of the coated layers were investigated to determine the sensitivity and selectivity of the immobilized sensor to Hg 2+ in the presence of background ions. The photo-response increased linearly with increasing Hg 2+ concentration from 10 to 200 μg L −1 with a limit of quantification (LOQ) of 4 μg L −1. The pH independence for the photoresponse was limited by the TiO 2 layer and was optimal between pH 6 and 7.