Nanocomposites and nanomaterials

Nanocrystalline Y–TiO2 thin-film electrodes for determination of Pb(II) and oxygen in aqueous medium 
Medyk I.A.1, Vorobets V.S.2, Fomanyuk S.S.2, Kolbasov G.Y.2, Karpenko S.V.2
1Department of Chemistry, National University of „Kyiv-Mohyla Academy”. Skovoroda str., 2, Kyiv-04070, Ukraine.
2Department of electrochemistry and photoelectrochemistry of non-metallic systems, Vernadsky Institute of General and Inorganic Chemistry of the NAS of Ukraine. Acad. Palladin Str., 32/34, Kyiv-03142, Ukraine. 
E-mail: vorobetsvs@i.ua

We present study results of possibility to use electrodes based on nanocrystalline  Y-doped titanium oxide thin films to determine the concentration of Pb2+ ions and O2 by anodic stripping voltammetry (ASV) method and inversion spectral photoelectrochemical (ISP) method. Lead by the ASV method was determined during anodic potential scanning, recording the current of electrodissolution of the reaction products formed on the surface of the indicator electrode after previous cathodic electroconcentration in an electrolyte solution containing lead ions. Oxygen was determined by the oxygen electroreduction current observed during the cathode potential scan. Solutions of 0.1 M hydrochloric acid,  0.4 M formic acid and acetate buffer (pH=5.5) were used as background electrolytes. It is determined that the value of analytical signal of lead in the studied electrolytes is proportional to the concentration of Pb (II) in solution, thus Y-TiO2 electrodes can be used as indicator electrodes for determination of Pb2+ ions by ASV method. The optimum conditions of Pb2+ ions determination are: background solution based on 0.1M hydrochloric acid, electroconcentrating potential -1,4 V; time of electrolysis 120 s, scanning speed of potential  50 mV.s-1. The sensitivity of the ASV method to Pb2+ – 0.1 mg·l-1, to O2 – (3-6)·10-3 mg·l-1.
To increase the sensitivity of Y-doped TiO2 electrodes to lead, an ISP method was used, which consists in concentrating of Pb2+ at the anode and comparing photoelectrochemical current before and after concentrating on different parts of spectral range. It has been shown that at concentrating potential of -1.4 V in acetate buffer, the deposition of metallic lead from the solution occurs. Metallic lead blocks the active centers of the surface, which results in significant decrease in the photocurrent value in the spectral range of  250-350 nm, which corresponds to light absorption by the TiO2 film. The dependence of photocurrent quantum yield on Pb2+ is straight-line at СPb2+ <0.3 mg·l-1. The sensitivity of ISP method to Pb2+on Y-doped TiO2 electrodes was 0.01 mg·l-1.