Fabrication and photocatalytic properties of porous crystalline titanium dioxide film co-doped with Fe and Si by PEO

Abstract

Porous photocatalytic titania film co-doped with Fe and Si was fabricated on carbon steel substrate by plasma electrolytic oxidation (PEO). The microstructure of the film was investigated and the photocatalytic activity of the film was tested by measuring the photodegradation rate of the organic methylene blue (MB). The results revealed that the obtained film was composed of anatase and rutile TiO2 crystalline phases. Fe and Si were co-doped in the film. The film was thick with the thickness of about 25μm. It was double layered with a compact inner layer and loose out layer. The film surface was coarse and porous and was covered with micro pores. The photodegradation rate of MB reached 86% with 3h irradiation of UV, showing a high photocatalytic activity. The method reports a rapid and simple route to fabrication porous crystalline TiO2 film with high photocatalytic activity. Introduction TiO2 film has received much and increasing attention due to its wide applications, among which the photocatalytic ability is one of the significant application. It can be used to degrade organic pollutants under the irradiation of ultraviolet lights [1-2]. This also gain increasing attentions during the situation that more concerns of human are concentrated on the environment and water pollution. Various methods have been developed to fabricated TiO2 films, such as sol-gel methods [3], chemical vapor deposition [4], Sputtering [5]. However, in most cases, a relatively high temperature are usually needed during preparation and the whole substrate are heated, or else amorphous TiO2 films will be often obtained when the temperature is high enough, which will usually decrease the photocatalytic activity。 The present paper reports the fabrication of photocatalytic crystalline TiO2 film in facile room temperature environment by plasma electrolytic oxidation (PEO) [6-8]. PEO is based on conversional anodic oxidization technology and is capable of preparing protective and functional films on metals. It is an eco-friendly technology which is widely used. In order to improve the performance of the TiO2 film, Fe and Si elements were co-doped into the TiO2 film by using Fe as substrate which was also used as Fe source and Na2SiO3 in electrolyte was used as Si source. The microstructure and the photolytic activity of the film were evaluated. Experimental details The conventional bi-electrode PEO system was adopted for preparation of the film. Q235 carbon steels with the dimension of 10 mm × 20 mm × 1.8 mm served as anode and a rectangle stainless steel sheet with the dimension of 20 mm × 200 mm × 1.8 mm was used as the counter electrode. A stainless steel electro-bath was used as the container of the electrolyte which was cooled by running water travelling around. A home-made electrical single-pulse power source was connected to the two electrodes. During PEO process, the parameters were: the current density was kept constant at 12A/dm2; the pulse frequency was kept 1000 Hz; the treatment time was 10 min. The electrolyte 4th International Conference on Mechatronics, Materials, Chemistry and Computer Engineering (ICMMCCE 2015) © 2015. The authors Published by Atlantis Press 2515 was silicate solution made up of some Na2SiO3, some NaH2PO2 and some TiO2 power. The carbon steels substrate was polished and thoroughly washed for The phase composition of the film was detected by X-ray Diffractometer (XRD, D8 ADVANCE, Germany).The surface and cross section morphologies of the film were observed by scanning electron microscopy (SEM, S-3400N, Hitachi, Japan). The diameter distributions of the surface pores was calculated by the software Nana Measurer. The elements composition of the film was detected by the Energy Disperse Spectroscopy (EDS, accessory of SEM, USA). The photocatalytic activity of the film was tested by measuring the photodegradation rate of methylene blue. A beaker of 100ml methylene blue (MB) solution is prepared and the initial concentration is 5 mg/L. TiO2 film sample was immersed into the beaker and was illuminated perpendicularly by a germicidal lamp(40W, 254nm wavelength ) .The whole test lasted for 3h, and the concentration change of MB are measured every 30 minutes. The concentration of MB was determined using a UV spectrophotometer (UV-2450, Shimadz, Japan), by measuring the absorbance at 662 nm, which show a linear and positive relationship with the concentration. The photodegradation rate of MB is measured by removal ratio