Eletrodos porosos contendo TiO2 e WO3 : propriedades eletroquímicas e atividade fotocatalítica para remoção do corante Rodamina 6G e do hormônio 17 a-etinilestradiol em solução aquosa / Porous electrodes containig TiO2 and WO3 : eletroctrochemical properties and photocatalytic activity for removal of Rodhamine 6G dye and 17 alfa -ethynylestradiol

AUTOR(ES)
FONTE

IBICT - Instituto Brasileiro de Informação em Ciência e Tecnologia

DATA DE PUBLICAÇÃO

02/07/2012

RESUMO

Porous films electrodes containing TiO2 and WO3 were deposited on SnO2:F (FTO) conducting glass from aqueous suspensions with TiO2 Degussa P25®, WO3 precursors and polyethylene glycol, followed by heating (450°C, 30 min). The maximum absorption was respectively observed at 390 and 480 nm for TiO2 and WO3 samples; intermediate values were obtained for the mixtures. The TiO2 films, ca. 4.5 mm, consisted of interconnected spherical particles (25 nm), resulting in a porous surface and excellent substrate coverage. Adding H2WO4 on the TiO2 suspension resulted in the TiO2/WO3 film, with comparable morphology but less porous. The WO3 electrode exhibited a non-uniform surface coverage with disk shaped particles (0.1-1mm). The morphology of the bilayer WO3-TiO2, obtained from the deposition of a TiO2 film on the top of a WO3 electrode, was similar to that observed for TiO2. The electrochemical properties were investigated in Na2SO4 aqueous solution, in the dark and under polychromatic irradiation. The electrodes exhibited an n-type semiconductor behavior, with negative photopotential and anodic photocurrent; higher photocurrent was observed for electrodes containing WO3. The electrodes were used for remediation of Rhodamine 6G dye aqueous solution (10 mmol L) using the configurations for heterogeneous photocatalysis (HP) and electro assisted-HP by polarization at 0.7 V (EHP). Under irradiation, at the initial 3 h, a pseudo first order kinetics was observed for the dye solution bleaching; in HP configuration, the WO3, TiO2 and WO3-TiO2 electrodes promoted respectively 8, 34 and 38 % of dye removal (apparent rate constants of 0.37x10; 2.3x10 and 2.8x10 min) and, without photocatalysts, only 4 %. Higher efficiency was observed under EHP configuration; for WO3-TiO2, 44 % of dye was removed (3.2x10 min). Also, the electrodes were used for treatment of aqueous solution containing the 17 a-ethynylestradiol hormone (34 mmol L); after 4 h in HP and EHP configurations, the remediation with TiO2 resulted in degradation of 38 and 48 % of the hormone, and the TiO2/WO3 electrode promoted 45 and 54 %. HP and EHP configuration resulted in similar mineralization for both electrodes, 15 and 19 %, respectively; without the photocatalyst, 10 % of degradation was observed (4 % of mineralization). The dye and hormone photocatalytic oxidation by these electrodes was discussed considering energy diagrams; for the electrodes containing WO3, the better harvesting of visible radiation, as well as, the favorable relative position of valence and conduction band of these semiconductors, promotes the separation of photogenerated charges, which minimizes their recombination, improving the efficiency of organic compounds oxidation.

ASSUNTO(S)

tio2 wo3 fotocatálise heterogênea rodamina 6g estradiol tio2 wo3 heterogeneous photocatalysis rhodamine 6g estradiol

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