Electrochemical Photocatalytic Degradation of Orange G Using TiO₂Films Prepared by Cathodic Deposition

Abstract

Herein, we report that organic dyes with poor adsorption on photocatalysts (e.g., OG (orange G) on TiO 2 ) can only be significantly degraded via the indirect oxidation process by the electrochemical photocatalytic (EPC) or photo-electro-Fenton (PEF) mechanisms because of their enhanced electron-hole separation for generating H 2 O 2 . The TiO 2 /Ti photo-anodes were prepared by cathodic deposition from a bath containing TiCl 3 , HCl, H 2 O 2 , and NaNO 3 under a two-electrode mode for EPC dye degradation. Effects of the deposition cell voltage, deposition time, and annealing temperature on the photocatalytic activity of TiO 2 films, evaluated by the photocurrent density, are systematically investigated. The surface morphologies and crystalline structure of various TiO 2 films were studied using scanning electron microscopic (SEM) and X-ray diffraction (XRD) analyses. The EPC characteristics of TiO 2 /Ti photo-anodes combined with a graphite cathode toward the OG degradation have also been evaluated. The maximal photocatalytic activity is obtained for the TiO 2 /Ti photo-anode deposited at a cell voltage of 2.6 V for 20 min and annealed at 700 • C in air for 1 hr, which exhibits a photocurrent density of 22.86 μA mg −1 . The order of degradation modes with respect to decreasing the degradation efficiency of OG is: PEF > EPC > PC (photocatalytic) > EC (electrocatalytic) oxidation.In recent years, TiO 2 in various forms (e.g., anatase, rutile, and brookite phases) has been widely recognized as the most popular photocatalyst for photo-electrodes, due to its high photocatalytic activity and chemical stability under ultraviolet light excitation for water and air purifications, 1-3 photocatalysts, 4 gas sensors, 5 electrochromic devices, 6 etc. When TiO 2 was employed as a photo-anode for organic chemicals degradation, its electro-photocatalytic activity, significantly affected by the electron transport rate meanwhile characteristics of recalcitrant organic pollutants mainly depend on the microstructures (e.g., crystalline structure, crystal size, film thickness, etc.) of TiO 2 , substrate, applied potential bias, solution pH, and electrolyte conductivity. 7,8 Fortunately, the microstructure of TiO 2 films can be controlled by varying the preparation methods and parameters.Titanium dioxide films can be prepared by sol-gel method, 9,10 direct oxidation of metallic titanium, 11 chemical vapor deposition (CVD), 12 hydrothermal synthesis, 13 electrospinning, 14 magnetron sputtering, 15,16 anodizing, 17 and electrodeposition. 18-20 Among the above mentioned methods, anodizing and electrodeposition are the most common methods for fabricating TiO 2 photo-anodes for the photo-electrochemical processes (e.g., photo-electro-Fenton (PEF) and photo-electro-catalysis (PEC) reactions). Moreover, electrodeposition is preferred because this process generally provides the advantages such as uniform deposition on substrates of complex shapes and cost effective meanwhile the thickness can also be controlled by varying the charge density....

Highly active and thermo-stable anatase TiO2 photocatalysts synthesized by a microwave-assisted hydrothermal method

“…3a and b, the morphology of T-400 is very similar to that of TU powders although the particulate boundary of the former sample seems to be relatively clearer. A similar phenomenon has been found for TiO 2 NPs prepared by means of cathodic deposition in our previous work [18] and the above result suggests that annealing at relatively low temperatures (e.g., ≤500°C) does not cause significant coalescence of A-TiO 2 primary NPs for crystal growth. On the other hand, primary NPs start to merge into bigger secondary aggregates with ambiguous grain boundaries at about 600°C (see Figs.…”

Carbon textiles electrodes modified with RGO and Pt nanoparticles used for electrochemical treatment of azo dye

“…There is considerable literature published on OG degradation [33][34][35]. However, until now there was no available literature about electrochemical degradation of OG using textile electrodes with reduced graphene oxide-based electrodes coated with dispersed platinum, these electrodes have been named in this work with the abbreviation TC-RGO-Pt, with the objective of decreasing costs and energy consumption.…”

Review—Recent Progress in Low Temperature Synthesis of Crystalline TiO2 Photocatalytic Films by Highly Controllable Electrodeposition

“…This kind of crystallization strategy is already known for decades and a huge number of scientific publications on this issue has been published up to now. 21,[28][29][30][31][32][33][34][35][36][37][38][39][40] The heating step (usually >350 °C) is not only energetically expensive, but makes the usage of temperature-fragile, flexible substrates (e.g., PET, PEN …), synthetic fibres or low-melting-point metals like zinc and tin impossible. Additionally, the concentrations of oxygen deficiencies and Ti interstitials cannot be accurately controlled with these methods.…”