Nanocomposites and nanomaterials

La,Ce-doped TiO2 nanostructured films for determination of Pb (II) concentration in liquids by inversion electrochemical methods
Garashchenko A.Yu.1, Vorobets V.S.2, Fomaniuk S.S.2, Medyk I.A.1, Kolbasov G.Ya.2, Karpenko S.V.2, Oblovatna S.Ya.2, Antonyuk N.G.1
1 Department of Chemistry, National University of „Kyiv-Mohyla Academy”. Skovoroda str., 2, Kyiv-04070, Ukraine.     E-mail: vorobetsvs@i.ua
2 Department of electrochemistry and photo-electrochemistry of non-metallic systems, Vernadsky Institute of General and Inorganic Chemistry of the NAS of Ukraine. Acad. Palladin Str., 32/34, Kyiv-03142, Ukraine.

Electrode materials based on La,Ce-doped TiO2 nanostructured films, synthesized by sol-gel method, were used to determine the concentration of Pb (II) in liquids by stripping voltammetry (SV) method and inversion spectral photoelectrochemical (ISP) method.
Determination of Pb (II) on La,Ce-doped TiO2 electrodes by SV method was done using background solutions based on acetate buffer (pH = 5.0). The solution was stirred during the preliminary electrolysis at a potential of -1400 mV (vs Ag/AgCl electrode) for 120 s and then potential was scanned from -1200 mV to + 100 mV. It is determined that the value of analytical signal of lead in acetate buffer is proportional to the concentration of Pb (II) in solution. By SV method it is possible to determine the concentration of Pb (II) within (0,1-5,3) mg.l-1. To increase the sensitivity of La,Ce-doped TiO2 electrodes to lead concentrations in solutions, an ISP method was used, the essence of which is to concentrate the analyte at the anode and to compare the value of photoelectrochemical current before and after concentration in different parts of the spectral range. It has been shown that at concentration potential of -1.4 V (vs Ag/AgCl) in acetate buffer (pH = 5), the deposition of metallic lead from the buffer 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, even with small amounts of lead. Analysis of the photocurrent spectral characteristics at different concentrations of Pb (II) showed that the dependence of photocurrent quantum yield on Pb (II) concentration is straight-line at СPb(II) <0.3 mg/l.  The sensitivity of ISP method to Pb (II) on La,Ce-doped TiO2 electrodes was 0.01 mg / l, which corresponds to the maximum allowable concentration for lead in water.