Short CommunicationNovel one-step preparation of tungsten loaded TiO2 nanotube arrays with enhanced photoelectrocatalytic activity for pollutant degradation and hydrogen production
Graphical abstract
Introduction
TiO2 nanotube arrays (TiO2NTs) are subject to extensive research in photocatalysis and photoelectrocatalysis because of their special properties, including a large surface area, high regulation, prominent controllability, and superior electron transport rate [1]. Anodization represents one of the most promising approaches among all the methods for TiO2NT synthesis [2]. The different types of electrolytes and the desired anodization time can be used to fabricate NTs with adjustable shapes and sizes. However, given its high band gap, TiO2 is a UV-driven photocatalyst [3], [4], which severely limits the applicability of TiO2NTs under visible light.
The doping of NTs with either metal or non-metal elements [5], [6], [7], [8] is a proven effective method of synthesizing efficient photocatalysts in the visible light range. A great deal of research has been directed towards using tungsten (W) to modify TiO2 in the form of nanopowder [9], film [10], and core-shell [11] because the W ion is considered one of best elements for narrowing the band gap of TiO2 [12], [13]. Despite the variety of synthetic methods and products reported, these methods have certain shortcomings. Lewera [14] fixed TiO2 with WO3, but the catalyst was easily lost during photocatalysis. Lai [15] utilized the plasma electrolytic method to fabricate W-loaded TiO2 nanotubes; however, special equipment was required to achieve the spluttering coating. Other researchers [16] achieved W-doped TiO2 nanotubes using alloys but encountered difficulty in adjusting the dopant concentration. Therefore, a simple, facile, and inexpensive method of synthesizing W-doped TiO2NTs is necessary.
In the present study, we report a controllable approach to fabricating W-doped TiO2NTs through the electrochemical oxidation of a Ti substrate in glycerol/fluoride electrolyte containing sodium tungstate. The high efficiency of the photoelectrochemical (PEC) properties of W-doped TiO2 can be prepared by doping different sodium tungstate concentrations in the electrolyte. The PEC properties of W-doped TiO2 can also be controlled by annealing the electrode at various temperatures to obtain the anatase crystal phase. The high photocatalytic activities of W-doped TiO2 were evaluated through the PEC degradation of Rhodamine B (RhB) and hydrogen generation.
Section snippets
Reagents
Ti foil (0.5 mm thick, 99% purity) was purchased from Baoji Titanium Industry Co., Ltd, China. Sodium tungstate (Na2WO4 · 2H2O), HF, HNO3, Na2SO4, glycerol, ethanol and RhB were obtained from Sinopharm Chemical Reagent Co., Ltd, China. Na2S and Na2SO3 were purchased from Sigmal. All chemicals were of analytical grade without further purifying before experiment and solutions were prepared with deionized water.
Preparation of W-TiO2NTs
The highly ordered W-TiO2NTs were synthesized by anodic oxidation in a mixture
Results and discussion
The as-prepared W-TiO2NTs exhibited regular arrays with a uniform size distribution of around 35 nm, as shown in Fig. 1A. The inset of Fig. 1A presents the nanotube profile at ~ 850 nm. The morphology of the W-TiO2NTs is similar to those reported in previous studies [18], [19], indicating that the W-doping process does not influence the morphologies of the TiO2NT samples. Fig. 1B shows the XRD patterns of W-TiO2NTs doped with different concentrations annealed at 400 °C. The W-TiO2NTs consist of a
Conclusion
In summary, we successfully prepared highly ordered W-TiO2NTs with an exclusive anatase phase utilizing a facile and novel anodization process on a Ti sheet. The morphology, crystal phase, chemical composition, and photoelectrocatalytic activity of the prepared samples were evaluated using various characterization techniques. XPS analysis showed that W atoms were successfully incorporated into the TiO2 lattice in the form of W6 + ions, which resulted in the high photoelectrocatalytic activity of
Acknowledgements
This work was supported by the National Natural Science Foundation of China (Grant No. 20977037). The authors thank the Analytical and Testing Center of HUST for the use of SEM and XRD equipment.
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