Preliminary Study of Photoelectrochemical Properties of Electrosyntetized Cerium Dioxide (CeO₂) to Pollutant Treatment

Abstract

1. Introduction In this work a systematic procedure to synthetize of cerium dioxide and evaluation and its photoelectrochemical properties for dye degradation in aqueous media is shown. First, electrochemical synthesis of CeO 2 methodology is presented as function of annealing temeprature and concentration of Ce 3+ precursors in the plating. Next, Raman spectra and FTIR analysis were presented to evaluate structural properties of films. Lineal sweep voltammetry (LSV) and chronoamperometry (CA) results are shown to evaluate the photocurrent and its stability of CeO 2 and finally all the results were analyzed in function of excitons production, charge separation and recombination phenomena. 2. Methodology 2.1. Electrochemical synthesis of CeO2 First, cerium hydroxide (Ce(OH) 3 ) was obtained from a CeCl 3 .7H 2 O solution (5 and 25 mM) with 0,05 M of NaNO 3 as support electrolyte by applying of a constant potential of -1,2 V vs AgCl during 300 s to an FTO electrode (1,3 x 0,6 cm). A reference electrode (Ag/AgCl 3,0 M and a Pt wire as a counter electrode were used in the electrochemical cell connected to a potenciostat-galvanostat AUTOLAB N65 Series. After deposition of cerium hydroxide form, the FTO substrates were alienated at different temperatures (200 – 700 o C) for 1 hour to obtain the oxide cerium form. Finally, FTO photoelectrodes were dried with air and stored at room temperature. 2.2 . Photoelectrochemical characterization of CeO 2 films LSV and CA were used to evaluate the photo-response and stability of produced photocurrent of CeO 2 photoanodes. In the LSV experiment, a range of potential from +0,5 V to 1,2 V was used with a sweep of 10 mV/s. Meanwhile, a bias potential of +1,2 V during 300 s with light-dark cycles of 30 s was used in CA experiments. A system of three electrode (FTO-CeO 2 as a working electrode, Ag/AgCl 3,0 M and a Pt wire) were used in an electrochemical with a quartz window. The cell was irradiated with a light source of 100 mW/cm 2 . The solution of the electrochemical cell was Na 2 SO 4 0,1 M. 3. Results Electrochemical measurements show that there is a great influence in the temperature treatment to obtain high photocurrent using CeO 2 photoanodes. Besides, CeO 2 increase its photoelectroactivity when small concentration of Ce 3+ precursor is used in the electrochemical formation of hydroxide. This could be attributed to a decrease of size particle and therefore a favorable change of band gap of CeO 2 . Stability of photocurrent of CeO 2 photoelectrode changes slowly across the time this process could be product of electronic saturation in the process of charge separation or structural changes during the photoelectrocatalytic process due to applying of potential bias. 4. REFERENCES (1) Ma, R.; Zhang, S.; Wen, T.; Gu, P.; Li, L.; Zhao, G.; Niu, F.; Huang, Q.; Tang, Z.; Wang, X. A Critical Review on Visible-Light-Response CeO2-Based Photocatalysts with Enhanced Photooxidation of Organic Pollutants. Catalysis Today 2019 , 335 , 20–30. https://doi.org/10.1016/j.cattod.2018.11.016. (2) Liu, Z.; Guo, S.; Hong, C.; Xia, Z. Synthesis and Photocatalytic Properties of CeO2 Nanocubes. Journal of Materials Science: Materials in Electronics 2016 , 27 (2), 2146–2150. https://doi.org/10.1007/s10854-015-4004-1. (3) Muñoz-Batista, M. J.; Gómez-Cerezo, M. N.; Kubacka, A.; Tudela, D.; Fernández-García, M. Role of Interface Contact in CeO2-TiO2 Photocatalytic Composite Materials. ACS Catalysis 2014 , 4 (1), 63–72. https://doi.org/10.1021/cs400878b.