Nanoporous of W/WO3 Thin Film Electrode Grown by Electrochemical Anodization Applied in the Photoelectrocatalytic Oxidation of the Basic Red 51 used in Hair Dye

Abstract

Eletrodo nanoporoso auto-organizado de W/WO 3 pode ser obtido através da anodização eletroquímica de placas de W em solução de NaF 0,15 mol L -1 como eletrólito suporte, aplicando uma rampa de potencial de 0,2 V s -1 , até alcançar 60 V, mantendo por 2 h. A forma monoclínica altamente ordenada do WO 3 é majoritária quando calcinado a 450 0 C durante 30 min, obtendo uma maior fotoatividade quando irradiada na luz visível em relação a luz UV. O eletrodo promove a descoloração total do vermelho básico 51, utilizado em tinturas de cabelo, após 60 min de oxidação fotoeletrocatalítica, em densidade de corrente de 1,25 mA cm -2 e irradiação em comprimento de onda 420-630 nm. Nessa condição foi obtido 63% de mineralização. Uma menor eficiência é obtida para o sistema irradiado por comprimento de onda (280-400 nm), quando apenas 40% de remoção de carbono orgânico total é obtida, necessitando de 120 min de tratamento para a descoloração total da solução do vermelho básico 51.Self-organized W/WO 3 nanoporous electrodes can be obtained by simple electrochemical anodization of W foil in 0.15 mol L -1 NaF solution as the supporting electrolyte, applying a ramp potential of 0.2 V s -1 until it reached 60 V, which was maintained for 2 h. The monoclinic form is majority in the highly ordered WO 3 annealed at 450 °C , obtaining a higher photoactivity when irradiated by visible light than by UV light. The electrode promotes complete discoloration of the investigated basic red 51 dye after 60 min of photoelectrocatalytic oxidation, on current density of 1.25 mA cm -2 and irradiation on wavelength of 420-630 nm. In this condition it was obtained 63% of mineralization. Lower efficiency is obtained for the system irradiated by wavelength (280-400 nm) when only 40% of total organic carbon removal is obtained and 120 min is required for complete discoloration.Keywords: W/WO 3 electrodes, electrochemical anodization, photoelectrocatalysis, basic red 51, hair dye IntroductionThe use of TiO 2 as photoanode in photoelectrocatalytic degradation of pollutants is well known in literature. [1][2][3][4][5][6][7][8][9][10] Nevertheless, this material presents band gap energy around 3.2 eV, which is photoexcited only in the ultraviolet region (l ≤ 380 nm).11-14 Tungsten trioxide has been an excellent alternative material, since it presents smaller band gap energy (2.4-2.8 eV) and can be photoexcited in the visible region close to the UV region. [15][16][17][18] 28-34 Although a sol-gel technique is one of the simplest and lowest-cost procedures selected for a wide range of applications, there have been only a few reports on photoelectrochemical characteristics of the WO 3 film prepared by a sol-gel technique. [5][6][7][8] Several techniques for improving photoresponse of thin film electrodes W/WO 3 have already been proposed. The electrodeposited Pt/WO 3 catalysts have improved the oxidation of methanol and formic acid. [35][36][37][38] The WO x films with Pt, Sn, and Ru dopands were used for electrooxidation of acetaldehyde. Some authors have de...

Nanostructured Tungsten Trioxide Thin Films Synthesized for Photoelectrocatalytic Water Oxidation: A review

“…W 2 O 5 þ 2 H þ þ 2 e À ð4Þ Table 1 summarizes the various electrochemical approaches for the synthesis of nanostructured WO 3 thin films through anodization: even when using the electrochemical anodization method alone, different synthesis approaches can be adopted as evidenced by the various pretreatments, electrolytes, applied potentials, and annealing temperatures used. [23] Hahn et al reported the use of a threeelectrode electrochemical cell to prepare WO 3 in an electrolyte containing HClO 4 and NaClO 4 applying a potentials in the ranges from 10-100 V. [24] They concluded that the nanoporous WO 3 structure formed had a uniform surface with an average pore diameter of 40 nm and a pore length of 16 mm. For instance, Fraga et al prepared W/WO 3 thin films by anodization of W foil in a NaF solution by using a conventional two-electrode electrochemical cell.…”

“…For instance, Fraga et al prepared W/WO 3 thin films by anodization of W foil in a NaF solution by using a conventional two-electrode electrochemical cell. [23] They found that the particle size of the nanoporous WO 3 layer formed was around 100 nm and that the thin film had a great uniformity. Moreover, the absorption of the thin films was extended to wavelengths above 480 nm (into the visible light spectrum) and thus, good photoactivity is achieved.…”

Honey-Comb Structured WO3/TiO2Thin Films with Improved Electrochromic Properties

“…After magnetron sputtering deposition, a two electrode system with a platinum cathode was used to anodize the W/Ti thin films in 0.3 M NH 4 F dissolved in ethylene glycol (98% anhydrous, Sigma Aldrich) to which 4 vol.% deionized water had been added. The voltage was ramped up to 10 V at a sweep rate of 0.1 V s −1 and then held for a period of 40 min (Keithley 236 Source Measuring Unit); the use of voltage ramp reduces solvent breakdown in the early stages of oxide growth that can occur if the maximum voltage is applied immediately.…”

Removal of metals using a ZnO/Au composite under visible-light illumination

“…Furthermore, the nanoparticles are attractive for water purification since they are capable of removing biological contaminants, besides of simple chemicals. For instance, it is known that TiO 2 enhances antibacterial effect [2][3][4][5], whereas WO 3 can be efficiently used to eliminate organic pollutants [6][7][8][9].…”