Nanocomposites and nanomaterials

Determination of Cd(II) and oxygen in aqueous medium on nanocrystalline Ce-TiO2 thin film electrodes 
V. Vorobets, S. Fomanyuk, G. Kolbasov, S. Karpenko
 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. 
E-mail: vorobetsvs@i.ua

Pollution of the environment with harmful substances, in particular heavy metal ions, is one of the global problems of our time, which requires constant monitoring of toxic elements in the human habitat. Along with the measurements of toxic elements, the determination of the concentration of dissolved oxygen is also of current interest, especially for medicine in the context of the COVID-19 pandemic, when it is necessary to diagnose and treat diseases caused by coronavirus infection. We present study results of possibility to use electrodes based on nanocrystalline  Ce-doped titanium oxide thin films to determine the concentration of Cd2+ ions and O2 by anodic stripping voltammetry (ASV) method. This method consists in preliminary electroconcentrating of Cd2+ ions in cathodic potential range and subsequent electrodissolution of electrodeposition products at anode potential scan. Herewith the oxygen concentration is determined in the cathode potential range. Thin films of nanocrystalline Ce-modified titanium dioxide were obtained on Ti-substrate by sol-gel method from titanium isopropoxide, followed by annealing at 500°C. The average size of nanoparticles calculated from the Scherrer equation was 7- 11 nm. 
Determination of Cd2+ ions was carried out using background solutions based on 0.35 M formic acid, 0.1 M hydrochloric acid and acetate buffer (pH=5.0) using standard addition method with potential scanning speed of 20–50 mV·s-1. The solution was stirred during the preliminary electroconcentrating at potential of –(1200–1600) mV (vs silver-chloride reference electrode) for 60–180 s and then the potential was scanned from -1600 to +200 mV. It is shown that Ce-TiO2 electrodes can be used as indicator electrodes for determination of Cd2+ ions by anodic stripping voltammetry method. It was found that the   optimum conditions of Cd2+ ions determination are:  background solution is acetate buffer (pH=5.0), electroconcentrating potential -1,4 V; time of electrolysis 120 s, scanning speed of potential  50 mV.s-1. It was found that the sensitivity of the ASV method to Cd2+ was 0.01 mg·l-1, to dissolved oxygen was (3-6)·10-3 mg·l-1, measurement accuracy 4 ÷ 5%.