CdSe-sensitized TiO2 nanotube array film fabricated by ultrasonic-assisted electrochemical deposition and subsequently wrapped with TiO2 thin layer for the visible light photoelectrocatalysis
Highlights
► CdSe is electrochemically deposited onto TiO2 nanotube arrays with ultrasonics. ► TiO2 thin layer overcoating on the arrays can protect CdSe from photocorrosion. ► TiO2 nanotube array/CdSe/TiO2 film possesses visible light photocatalytic activity.
Introduction
Heterogeneous photocatalysis is an advanced oxidation process, which can degrade a great variety of organic compounds. Among oxide photocatalysts, titanium dioxide (TiO2) has been proven as one of the most promising candidates due to its high oxidation efficiency, outstanding chemical stability and environmentally friendly nature [[1], [2], [3]]. However, TiO2 has a wide band gap (3.2 eV) and can only be excited by ultraviolet light less than 387 nm. It is of great interest to develop the visible light photocatalysts to extend the absorption wavelength range into visible light region [[4], [5], [6]]. Therefore, numerous studies have been performed, including impurity doping [7], metallization [8], and dye sensitization [9]. In recent years, attempts have been made to use narrow band gap semiconductors such as CdS [10], [11], Bi2S3 [12] and PbS [13] to photosensitize TiO2 for visible light response. However, there are few references on the utilization of CdSe-sensitized TiO2 photocatalyst systems for environmental purification under visible light irradiation [[14], [15], [16]].
Owing to their precisely controlled dimensions and faster charge transport, highly ordered vertically oriented TiO2 nanotube arrays have widely application in the development of sensors [17], quantum-dot-sensitized solar cells [18] and photoelectrocatalysis [19]. Recently, an attempt has been made to prevent CdS nanoparticles from photocorrosion by building a layer of ZnO nanorods on the TiO2 nanotube/CdS surface for photoelectrocatalytic degradation methyl orange [20]. The approach to solving the photocorrosion of sulfur group semiconductors could promote their application in visible light photocatalysis.
Herein, we present an ultrasonic-assisted cyclic voltammetry electrochemical deposition technique to prepare CdSe-sensitized TiO2 nanotube array film which is subsequently wrapped by a TiO2 protection layer via TiCl4 hydrolysis. The typical experimental procedure is schematically illustrated in Fig. 1. And the photoeletrochemical behaviors and photoelectrocatalytic activity are investigated under visible light illustration.
Section snippets
Materials
All reagents were of analytical grade and used without any further purification. Ti foil (250 μm thick, 99.5% purity) was purchased from Shenzhen City Xuguang Titanium Co., LTD. Hydrofluoric acid, nitrate acid and anhydrous ethanol were obtained from Guangzhou Chemical Reagent Factory. Selenium oxide, cadmium sulfate octahydrate, sodium nitrate, titanium tetrachloride, glucose and sulfuric acid were purchased from Guangdong Guanghua Chemical Factory Co., LTD.
Preparation of TiO2 nanotube array film
The ordered TiO2 nanotube arrays (TiO2
Morphologies and structures
It could be clearly observed from Fig. 2 that the self-organized TiO2 nanotube arrays with high aspect ratios have been fabricated on Ti foil by the electrochemical anodization technique. The diameters of these TiO2 nanotubes are in the range from 50 nm to 100 nm, and the wall thickness is approximately 10 nm. The thickness of the anodized TiO2 nanotube array film is around 300 nm [21]. Fig. 3a–d show FESEM images of the TiO2NTA/CdSe films obtained under ultrasonic condition by 20, 50, 60 and 80 CV
Conclusions
A composite structure, TiO2 nanotube array/CdSe nanoparticle/TiO2 layer, was fabricated by inserting CdSe nanoparticles into anodized TiO2 nanotube arrays via ultrasonic-assisted cyclic voltammetry electrochemical deposition and subsequently wrapped with a protection layer of TiO2. Under ultrasonic condition, CdSe nanoparticles are prone to disperse into the nanotube arrays by cyclic voltammetry electrochemical deposition. Increasing CV cycle increases the loading of CdSe on the TiO2 nanotube.
Acknowledgment
The work is supported by the Science & Technology Plan Project of Guangdong Province (No. 2009B030400002), National 973 project of China (No. 2009CB220002) and Knowledge Innovation Program of the Chinese Academy of Sciences (No. KGCX2-YW-343).
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