(337f) Endogenous Hormones Degradation Using Nanotubular Oxide Layer Grown On Tiw Alloy By Electrochemical Anodization

Advanced Oxidative Processes (AOP) are a significant green technology for application in water purification and organic pollutant degradation. The main mechanism of AOPs is the generation of highly reactive free radicals, such as the hydroxyl radical (•OH). Among different available AOPs, heterogeneous photocatalysis seems to be one of the most popular technologies for wastewater treatment. This process uses semiconductor materials as catalysts and UV light. The efficiency of the electrochemical and photoelectrochemical treatment is strongly dependent on the choice of the anode material and its morphology. The manufacture of Ti and Ti alloys oxide nanotube arrays by electrochemical methods has attracted a great deal of attention for applications in environmental photocatalysis due to its photoinduced reactivity¹. In this work it is proposed the degradation of endogenous hormones, estrone (E1) and 17α-ethinylestradiol (EE2) by photoelectrocatalysis process using self-organized oxide semiconductor nanotubes on a titanium/tungsten alloy applying an anodization process. The growth of self-organized oxide semiconductor nanotubes on a Ti-x%W alloy (x= 0.5, 2.5 and 5.0% wt) was investigated as a function of the applied potential, electrolytic solution (aqueous or organic) and anodization time. The titanium alloy was prepared in an arc melting furnace using a non-consumable tungsten electrode and water-cooled copper crucible in a high purity argon atmosphere. The samples were solidified in an ingot form that was submitted to a rolling process to manufacture the alloy sheet X-ray fluorescence was used to determine the chemical composition of the alloy. The anodization experiments were carried out with a DC power supply and an acrylic electrochemical cell, with a platinum cathode and the Ti alloy anode separated by 2.5 cm. An aqueous solution of 0.2 M HF and two types of ethylene glycol solutions (0.2 M NH₄F and 0.2 M HF) were used as electrolyte solution. All the anodization experiments were carried out at 120 V, with applied time that varied between 5 to 120 minutes. SEM-FEG was used to characterize the nanotubes and X-ray fluorescence results confirmed that the composition of the alloys was as required. The best results of anodization were obtained when 0.2 M HF with ethylene glycol solution was used with the Ti-0.5w%W electrode, with an anodization time of 60 minutes at 120 V. Under these conditions the oxide nanotubular layer was homogeneous and continuous through the surface. After anodization, the nanotubular oxides on Ti0.5%W were annealed at temperature greater than 450°C in air atmosphere for 2 hours and then, cooled back to room temperature in a box furnace to obtain a crystalline structure. X-ray diffraction was used to characterize the crystallization behavior of oxide layer. The degradation of endogenous hormones was carried out in a photoelectrochemical cell. A Ni screen was used as a cathode, and the self-organized oxide nanotube on titanium alloy produced were used as anode. The efficiency of these treatment processes was monitored by following the TOC (Total Organic Carbon) and the E1 and EE2 concentration decay by HPLC technique (High Performance Liquid Chromatography). UV lamp was positioned to illuminate the anode electrode in order to induce the photodegradation of the organic compounds. The percentage of degradation and total organic carbon removal, and the energy consumed per volume of effluent treated were investigated during electrolysis in photoelectrochemical cell.

Acknowledgments:

CNPq (Proc. 483285/2011-0), Fapesp (Proc. 2011/51226-3), LNLS and UNICAMP

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