Elsevier

Applied Surface Science

Volume 317, 30 October 2014, Pages 672-681
Applied Surface Science

Controllable electrodeposition of ZnO nanorod arrays on flexible stainless steel mesh substrate for photocatalytic degradation of Rhodamine B

https://doi.org/10.1016/j.apsusc.2014.08.153Get rights and content

Highlights

  • ZnO nanorod arrays (ZNRAs) were prepared by electrodeposition method.

  • Flexible stainless steel mesh (SSM) was first used for electrodeposition of ZNRAs.

  • The morphology, average diameter and density of ZNRAs can be controlled to some extent.

  • The ZNRAs prepared with more electrodeposition times showed enhanced photocatalytic performance.

Abstract

Well-aligned single-crystalline ZnO nanorod arrays (ZNRAs) were prepared on flexible stainless steel mesh (SSM) substrate in large-scale by using a direct electrodeposition method. The effects of electrochemical parameters, such as applied potential, applied nucleation potential time, substrate pretreatment, electrodeposition duration and times, on the orientation, morphology and density of ZNRAs were systematically studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM) and the selected area electron diffraction (SAED). The results showed that ZNRAs on SSM substrate with [0 0 1] preferred orientation and well crystallization were obtained by controlling the applied potential in the range of −0.9 to −1.1 V. The density of ZNRAs could be increased obviously by applying a nucleation potential (−1.3 V for more than 10 s before deposition) or by means of substrate pretreatment (the SSM immersed in zinc acetate colloid for more than 10 min before deposition), meanwhile, the deposited ZNRAs also had small average diameter (<46 ± 4 nm), narrow size distribution and good orientation. In addition, it was also found that the average diameter of ZNRAs could be increased from 89 to 201 ± 5 nm by extending the electrodeposition duration from 1800 to 7200 s, and the length of rods was from 0.8 to 2.2 ± 0.1 μm when the times of the electrodeposition from one to six times. Furthermore, the band gap energy (Eg) of as-prepared ZNTAs was not closely related to the electrodeposition times (only changed from 3.30 to 3.32 eV). The ZNRAs prepared with more electrodeposition times showed enhanced photocatalytic performance under the UV-lamp for degradation of Rhodamine B. The degradation efficiency of ZNRAs improved from 89.4% to 98.3% with the deposition times from one to six times.

Graphical abstract

Well-aligned single-crystalline ZnO nanorod arrays were first prepared on flexible stainless steel mesh substrate in large-scale by using a direct electrodeposition method and showed enhanced photocatalytic performance.

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Introduction

Photocatalytic degradation has attracted much attention since it has a great potential to contribute to organic pollutants in wastewater. By contrast with the classified conventional approach, it has the advantages of fast reaction, degradation of pollutants, mild reaction conditions and easy operation. Till now, various semiconductor nanopowders including TiO2 [1], [2], [3], SnO2 [4], WO3 [5] and ZnO [6], [7] are deemed to be effective photocatalysts for wastewater treatment due to its high specific surface area and suitable energy band gap. It is worth noting that ZnO has much-higher electron diffusivity and it also absorbs over a larger fraction of solar spectrum than TiO2 [8], indicating that ZnO may be the most suitable alternative for photocatalytic degradation. However, some issues in the practical applications need to deal with, for examples, nanoparticles can easily form aggregates to decrease the photodegredation efficiency, and it is difficult to separate nanoparticles from treated water, which may cause the loss of the photocatalyst and bring about secondary pollution [9]. In view of this, the substrate supported photocatalysts may improve the recovery rate of the catalyst and prevent the loss, and more importantly, the support may interact with the catalyst to inhibit the electron–hole recombination and enhance the adsorption capacity of the reactants to improve the photocatalytic activity. Therefore, the supported ZnO nanostructures are expected to have better safety and stability. To date, various kinds of methods and technologies are applied to fabricate ZnO films with different micro morphologies [10], [11], [12], [13], [14] on substrates such as the sol–gel [15], hydrothermal [16], template [17], chemical vapor deposition (CVD) [18] and electrodeposition methods [19], [20]. As a reason of simple process, lower deposition temperature and pressure, higher growth efficiency and better film adhesion to the substrate, electrodeposition method is considered as one of the promising routes. Till now, many efforts have been taken on electrodeposition of ZnO nanostructures on different substrates including ITO/FTO transparent conducting glasses, metal plates, and conducting polymer films. Generally, the use of glass substrates implicates restrictions related to fragility, massive and shape limitations. Meanwhile, the small specific surface area of the glass support may result in less catalyst load, and the relatively poor adhesion properties. The metal plates are opaque resulting in a shortage of illumination and the catalyst on their surfaces is not easy to be loaded due to the smooth surface, which is similar to the glass substrate. Replacement of the substrates with plastic materials or organic polymer coated with indium doped tin oxide, the following calcination stage with a high temperature (above 300 °C) would break the structure of materials and limit their applications. On the basis of this principle, flexible stainless steel mesh (SSM) has attracted wide interest because of their many properties including a light weight, good flexibility, low cost and well–conducting properties for electrodeposition. Most importantly, the flexible SSM with a lacunose and double-faced structure has large specific surface area to load the ZnO nanostructure and high light-admitting quality to harvest the light. Till now, few efforts have focused on preparation of ZnO on stainless steel wire mesh only by hydrothermal method. In 2011, Yong et al. [21] reported that flower-like CuO–ZnO heterostructured nanowires were fabricated on the SSM by using a hydrothermal method and the photocatalytic activity of CuO–ZnO were also investigated. In 2013, Marbán [22], [23] indicated that the ZnO nanoparticles deposited on the wire mesh had enhanced catalytic activity than that of P25. Therefore, how to realize controllable preparation of ZnO nanorod arrays (ZNRAs) on the flexible SSM by electrodeposition method still remains the big challenge.

In this paper, the flexible SSM was successfully used as substrate to prepare ZNRAs by electrodeposition route. Effects of electrodeposition parameters such as substrate pretreatment, applied potential, electrodeposition duration and times on the morphology of ZNRAs were systematically investigated. Moreover, it was demonstrated that the photocatalytic activity of prepared ZnO nanocrystals under UV radiation for the oxidation of Rhodamine B dyes in aqueous solutions could be effectively controlled by electrodeposition times.

Section snippets

Materials

All of the chemical reagents were of analytical grade and were not subjected to additional purification. All the aqueous solutions were prepared with deionized water. The SSM (99.5% purity, provided by Beijing DOTRUST Co., Ltd. with a wire diameter of 35 μm and a screen opening of 45 μm) was used as substrate and tailored into rectangular shape with dimensions of 1 cm× 2.5 cm. Before electrodeposition, the SSM was immersed in diluted hydrochloric acid (0.0001 mol dm−3) for 10 s to remove the rust, then

Structural and morphological characterization of ZNRAs on flexible SSM

The large-area views of the SSM substrate and as-synthesized ZNRAs were observed by scanning electron microscope (SEM). From Fig. 1(a), it can be seen that the diameter of the metal wire was about 35 μm and the width of square mesh was about 45 μm. The surface of the mesh was smooth and no impurity could be found. Fig. 1(b) exhibited the nanorod structure of ZnO on the SSM. The hexagonal nanorod arrays uniformly covered the entire surface of the SSM and grew vertically to the substrate. Fig. 1(c)

Conclusion

In this paper, by using an electrodeposition approach, ZNRAs with high density, small size and well orientation on SSM could be obtained. The influences of electrodeposition parameters on preparation of ZNRAs were investigated in detail. The suitable applied potential was the key factor for formation of aligned ZNRAs on SSM. In addition, by applying a nucleation potential or by means of substrate pretreatment could both lead to relatively higher density, smaller average diameter, narrower size

Acknowledgements

The work is supported by the National Nature Science Foundation of China (No. 51272025 and 50872011), and 973 Program of China (No. 2014CB643401).

References (30)

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