Elsevier

Materials Letters

Volume 197, 15 June 2017, Pages 67-70
Materials Letters

Significant enhancement of photocatalytic activity of multi-walled carbon nanotubes modified WSe2 composite

https://doi.org/10.1016/j.matlet.2017.03.150Get rights and content

Highlights

  • The CNT/WSe2 composite has been synthesized via a facile solvothermal reaction.

  • The adding of CNTs can provide a highly conductive underlying skeleton for WSe2.

  • The CNT/WSe2 composite has abundant exposed active edges.

  • The CNT/WSe2 composite exhibits superior photocatalytic activity.

Abstract

Flowerlike WSe2 and multi-walled carbon nanotubes modified WSe2 (CNT/WSe2) composite has been successfully synthesized via a facile one-pot solvothermal reaction. The morphologies, structures and photocatalytic activities were characterized by scanning electron microscopy, transmission electron microscope, X-ray diffraction, and UV–vis absorption spectroscopy, respectively. Compared to bare WSe2, the characterization results show that the CNT/WSe2 composite exhibits enhanced photocatalytic activity in photocatalytic degradation of organic dye methyl orange (MO) under visible light irradiation. The enhanced photocatalytic activity is attributed to the CNTs can reduce electron-hole pair recombination and efficiently inhibit the aggregation of WSe2 for fully exposing the active edges. In addition, a possible mechanism of CNT/WSe2 composite for degradation of MO molecules is proposed and discussed.

Introduction

In recent years, the waste water containing toxicity of various kinds of organic pollutants as one of the most severe environmental problems has become increasingly global ones which do serious harm to the life, survival and development of mankind. Thus, how to degrade the diverse hazardous organic pollutants in aqueous media using a simple, economical and environmentally friendly way has attracted great scientific interest. Compared with conventional strategies, semiconductor photocatalytic oxidation of organic dyes using solar light is considered to be a green technology [1].

Recently, layered transition metal dichalcogenides (TMDs), such as MoS2, WS2, MoSe2, etc., have been emerged and demonstrated as potential candidates for photocatalytic degradation of organic dyes due to their remarkable catalytic activities [2], [3], [4]. As a key member of TMDs, tungsten diselenide (WSe2) with a smaller band gap of ∼1.6 eV, which matches well with the solar spectrum, has a great potential for degradation of organic dyes under visible light irradiation [5], [6], [7]. However, to the best of our knowledge, when compared with the intensive research on MoS2, WS2 and MoSe2, the photocatalytic properties of WSe2 have been rarely investigated and reported. These results motivated us to investigate and improve the photocatalytic properties of WSe2. However, similar to MoS2 and MoSe2, the photocatalytic performance of WSe2 is strongly dependent on its density of exposed active edges and conductivity [8]. Therefore, the key factor is how to enlarge the exposed edge sites and improve the low conductivity of WSe2. Recent studies reveal that acid-treated CNTs has been considered as an effective substrate for the nucleation and subsequent growth of nanomaterials in the liquid-phase approach, which can not only provide a highly conductive underlying skeleton for active materials, but also prevent themselves agglomeration [9].

Herein, the CNT/WSe2 composite constructed with WSe2 nanosheets hybridized with highly conductive CNTs network has been synthesized by a facile one-pot solvothermal method. And for the first time, the photocatalytic degradation of organic dye MO by as-obtained CNT/WSe2 composite has been investigated and a possible photocatalytic mechanism was proposed and discussed. The excellent photocatalytic property of CNT/WSe2 composite is attributed to the CNTs can not only provide a highly conductive underlying skeleton for WSe2, but also efficiently inhibit the aggregation of WSe2.

Section snippets

Synthesis of flowerlike WSe2 and CNT/WSe2 composite

In typical synthesis, precisely 0.39 g H2SeO3 and 0.33 g Na2WO4·2H2O was weighed and dissolved in 25 ml of DMF, and then 25 mL (4 mg/mL) acid-treated CNTs DMF solution was added to the mixture solution of H2SeO3 and Na2WO4·2H2O drop by drop. After an hour stirring, the as-prepared precursor solution was transferred into the autoclave, and then heated at 200 °C for 48 h. After cooling down naturally, the product was filtered off and washed with DIW and ethanol for several times, and dried at 60 °C for 24

Results and discussion

X-ray diffraction (XRD) was firstly carried out to determine the crystalline structure and purity of samples. Fig. 1a shows the XRD patterns of CNTs, bare WSe2 and CNT/WSe2 composite, respectively. For bare WSe2, all major observed diffraction peaks match well with the standard values of hexagonal WSe2 (JCPDF card No. 38-1388). Compared with bare WSe2, a small peak of CNT/WSe2 composite appeared at ∼25° can be associated with C(002) peak of CNTs, which indicates the CNT/WSe2 composite has been

Conclusions

In conclusion, visible-light-driven flowerlike WSe2 and CNT/WSe2 composite photocatalysts have been successfully synthesized. The bare flowerlike WSe2 shows a relatively poor photocatalytic activity due to its low conductivity and aggregation. To address such issues, we indicate that the CNTs modified WSe2 composite could greatly promote the separation of pairs of electrons and holes and effectively reduce the recombination of them, resulting in the increase in the number of holes and ̇OH

Acknowledgements

The research was supported by the National Natural Science Foundation of China (Grant No. 51372033), and National High Technology Research and Development Program of China (Grant No. 2015AA034202).

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