Flexible 3D Fe@VO2 core-shell mesh: A highly efficient and easy-recycling catalyst for the removal of organic dyes

https://doi.org/10.1016/j.scitotenv.2018.05.085Get rights and content

Highlights

  • Novel 3D Fe@VO2 mesh was designed and successfully fabricated for the first time.

  • The mesh exhibited high catalytic efficiency across a wide pH range.

  • The mesh is free-standing, flexible with excellent recyclability.

  • This is a new and efficient catalyst beyond powders and films for water purification.

Abstract

Nowadays, it is extremely urgent to search for efficient and effective catalysts for water purification due to the severe worldwide water-contamination crises. Here, 3D Fe@VO2 core-shell mesh, a highly efficient catalyst toward removal of organic dyes with excellent recycling ability in the dark is designed and developed for the first time. This novel core-shell structure is actually 304 stainless steel mesh coated by VO2, fabricated by an electrophoretic deposition method. In such a core-shell structure, Fe as the core allows much easier separation from the water, endowing the catalyst with a flexible property for easy recycling, while VO2 as the shell is highly efficient in degradation of organic dyes with the addition of H2O2. More intriguingly, the 3D Fe@VO2 core-shell mesh exhibits favorable performance across a wide pH range. The 3D Fe@VO2 core-shell mesh can decompose organic dyes both in a light-free condition and under visible irradiation. The possible catalytic oxidation mechanism of Fe@VO2/H2O2 system is also proposed in this work. Considering its facile fabrication, remarkable catalytic efficiency across a wide pH range, and easy recycling characteristic, the 3D Fe@VO2 core-shell mesh is a newly developed high-performance catalyst for addressing the universal water crises.

Introduction

In recent years, worldwide water-contamination crises are aggravated ceaselessly. Organic dyes and phenolic compounds from textiles, dyestuff, dyeing industries etc. are the majority of the colored and uncolored effluents (Chowdhury and Viraraghavan, 2009). Numerous methods have been investigated and developed to tackle this severe environmental issue, such as physical adsorption (Dong et al., 2012; Nadafi et al., 2014; Parasuraman and Serpe, 2011; Zaban et al., 1997), photocatalysis (Higashi et al., 2011; Huang et al., 2017; Li et al., 2013; Pan et al., 2016). Advanced oxidation processes (AOPs) are recognized as an effective and efficient way to decompose synthetic organic contaminants (Chan et al., 2011; Chung and Kim, 2012; Hisaindee et al., 2013; Yao et al., 2013; Zuorro and Lavecchia, 2014). What's more, Fenton-like catalysts are famous materials for AOPs (Garrido-Ramírez et al., 2010). New kinds of Fenton-like catalysts have already drawn a great deal of attention, such as manganese silicate (Nuli et al., 2011; Tušar et al., 2012), carbon-Fe (Ramirez et al., 2007), CeO2 (Xu and Wang, 2012), MnSNT-10 (Hao et al., 2016), Fe3O4/HA (Niu et al., 2011), 3D HPB 1 (Fei et al., 2018), BaNaPW (Fei et al., 2017), two copper (II) Schiff base complexes (Fei et al., 2015) etc. However, despite their excellent efficiency toward decomposing organic contaminants, there are still three main challenging issues needed to be addressed, i.e. facile fabrication, easy recycling and limited pH, preferentially between 2 and 4. Up to now, the actual use of Fenton-like catalysts has been seriously impeded because of their tedious fabrication process. Besides, classical Fenton system (Fe2+/Fe3+/H2O2) and most of the emerging catalysts are in forms of powders or nanoparticles, inevitably leading to undesirable secondary water pollution and undoubtedly making the recycling of catalysts much more difficult. Until now, the separation of the Fenton-like catalysts is seriously under-emphasized (Hou et al., 2008; Jiang et al., 2011; Li et al., 2017; Nutt et al., 2006; Wei et al., 2011; Zheng and Stucky, 2006). More importantly, the pH range of Fenton or Fenton-like reaction is quite narrow and can only perform good catalytic efficiency in strong acid medium (pH 3–5) (Wang, 2008), which usually causes extra cost to regulate pH and undoubtedly restrains the practical use of the catalyst. Herein, we report flexible 3D Fe@VO2 core-shell mesh as a new Fenton-like catalyst with both easy-recycling characteristic and remarkable degradation efficiency in an acid, neutral or alkaline solution.

VO2, a well-known material for the manufacture of optical devices and electronic devices (Becker et al., 1994; Frenzel et al., 2009; Joushaghani et al., 2015; Wall et al., 2013; Whittaker et al., 2011), is rarely investigated for its catalytic function as a Fenton-like catalyst. In this work, for the first time, free-standing and flexible 3D Fe@VO2 core-shell mesh was designed and fabricated successfully by an electrophoretic deposition (EPD) method (Corpuz and Albia, 2014; Nam et al., 2016; Yu and Zhou, 2008; Zhang et al., 1994). Intriguingly, the resultant 3D Fe@VO2 core-shell mesh, along with H2O2, performs an excellent catalytic activity in a dark condition toward the degradation of organic dyes (Andrade et al., 2017). Its free-standing and flexible characteristics make the recycling of the mesh much more convenient. The result of Fenton-like catalysis repeatability demonstrates that it can be reused with a stable catalytic efficiency. What's more, not only can 3D Fe@VO2 core-shell mesh perform great catalytic efficiency under an acid or neutral condition, but also possesses excellent degradation capability of organic dyes in an alkaline solution. The possible catalytic mechanism is also discussed in the work. From the above, this new Fenton-like catalyst is expected to serve as a promising, inexpensive and easy-recycling material for water purification.

Section snippets

Materials and fabrication of 3D Fe@VO2 core-shell mesh

4 g of 99.5% purity V2O5 powder (Baichuan Vanadium Industry) was melted by calcining in air at 850 °C for 10 min. Then, the melted V2O5 was immediately poured into a beaker filled with 200 mL deionized water. After intensive stirring at 600 rpm at room temperature for 30 min and aging for 5 days, the stabilized V2O5 sol was obtained.

A circular plain-woven 304 stainless steel mesh (diameter of 30 mm) was used as a substrate for the electrophoretic deposition (EPD). The substrate was ground,

Characterization of materials

Considering the great challenges of both recycling and secondary pollution faced by the powdery catalysts (Yamashita et al., 1996), free-standing and flexible 3D Fe@VO2 core-shell mesh was designed and fabricated as schematically illustrated in Fig. 1. A clean 304 stainless steel mesh was used as the matrix. Firstly, V2O5 sol was prepared and then homogeneously deposited on the steel mesh surface by EPD. Then, the V2O5 coated steel mesh was dried at 70 °C for 30 min and was subsequently

Conclusions

In summary, 3D Fe@VO2 core-shell mesh was designed and fabricated successfully as a novel and effective Fenton-like catalyst across a wide pH range for the first time. Fine VO2 grains were in situ generated on the steel mesh surface and formed a dense shell wrapping around the steel wire with the thickness of 2 μm. In presence of H2O2, the organic dyes including RhB, Rh6G, MO and CV could be effectively decomposed by the catalyst with addition of H2O2. More intriguingly, Fe@VO2 core-shell

Acknowledgments

This work was supported by the Young Elite Scientists Sponsorship Program by CAST (Grant No. 2017QNRC001) and the National Natural Science Foundation of China (Grant No. 51402116). The authors thank the Analytical and Testing Center of Huazhong University of Science and Technology for support.

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