Elsevier

Catalysis Today

Volume 281, Part 3, 1 March 2017, Pages 621-629
Catalysis Today

Fabrication of Au/TiO2 nanowires@carbon fiber paper ternary composite for visible-light photocatalytic degradation of gaseous styrene

https://doi.org/10.1016/j.cattod.2016.06.026Get rights and content

Highlights

  • Au/TiO2 NWs@CFP ternary composite photocatalyst was fabricated.

  • The formation process was investigated through time-dependent experiments.

  • Au/TiO2 NWs@CFP exhibited excellent photoactivity under visible light irradiation.

  • Au/TiO2 NWs@CFP possesses high photocatalytic stability to degrade gaseous styrene.

  • High photocatalytic activity is due to the synergistic effect of 3 components.

Abstract

In this work, Au nanoparticles decorated TiO2 nanowires onto hierarchically porous carbon fiber paper (Au/TiO2NWs@CFP) ternary composite was synthesized using a combining approach of wet coating, hydrothermal growth and photoreduction. Characterization revealed that the 3D network of CFP was homogeneously encapsulated by Au nanoparticles (1.8 nm in diameter) decorated anatase TiO2 NWs with diameter of 15–30 nm and length of several microns. The formation of the Au/TiO2NWs@CFP composite undergoes the following three key-steps: formation of TiO2 islands on CFP, in-situ growth of TiO2 NWs on the TiO2 islands and deposition of Au NPs onto TiO2 NWs. Photocatalytic degradation of gaseous styrene showed that Au/TiO2NWs@CFP exhibited the excellent photoactivity and photostability under visible light irradiation. It is attributed to the synergistic effect of the three components (TiO2 NWs, CFP and Au nanoparticles), which can enhance visible light absorption intensity, reduce the recombination of photogenerated charges and holes, as well as improve the adsorption of organic pollutants. The present strategy would offer an effective way for the synthesis of ternary composite photocatalyst and its application to air purification under visible light irradiation.

Introduction

Heterogeneous photocatalysis of TiO2 can be initiated by UV light at room temperature and organic molecules adsorbed on the TiO2 surfaces can be oxidized to non-toxic substances such as CO2 and H2O [1], [2]. However, bare TiO2 materials show poor absorption of visible light, which limits the efficient utilization of solar energy [3], [4]. The fast recombination of excited electrons and holes on TiO2 also decrease its photocatalytic activity [5], [6]. Therefore, various strategies have been attempted to improve the solar light photocatalytic efficiency of TiO2. Incorporation of additional components such as metals and carbonaceous materials in the TiO2 structures has been verified as one of the most promising methods [4]. Recently, the deposition of noble metal (e.g., Au, Ag, Pt) nanoparticles (NPs) on TiO2 materials also showed an enhancement of the photocatalytic properties of the semiconductor [7], [8]. Especially, coupling Au NPs with TiO2, to form Au/TiO2 nanocomposites, is considered as an efficient way to extend the spectral response of photocatalysts to the visible light region. This is due to the strong surface plasmon resonance of Au NPs derived from the collective oscillation of conductive electrons [9], [10]. Under visible light irradiation, metal particles can absorb photons due to their surface plasmon resonance [11], [12]. Then the excited electrons were transferred to the conduction band of TiO2, leaving the positive holes on the metal particles. With the help of those photogenerated charges, reactive oxygen species can form and be beneficial for the photocatalysis using TiO2-metal nanoparticles composite under visible light irradiation [13]. However, both TiO2 and metal nanoparticles are kinetically unstable and they tend to aggregate into larger structures, which will decrease the photocatalysis efficiency [14], [15].

On the other hand, due to the unique and controllable structural as well as electrical properties, porous carbonaceous materials such as activated carbon, carbon nanotubes and fullerene become great interest for the structural support and photocatalytic enhancement of TiO2-based systems [16], [17], [18]. Firstly, these porous carbonaceous materials could provide high-surface area for the adsorption of organic reactants and increase active sites for photocatalysis [18], [19], [20]. Secondly, carbon structures can act as the catalyst support which is beneficial for the dispersion of TiO2 particles [21], [22]. Thirdly, the carbon species exhibiting high electrical conductivity and electron storage capacity may accept photongenerated electrons from TiO2, thus hindering the recombination of electron-hole pairs and facilitating the reactive oxygen species formation [23]. However, the visible-light catalytic activity of carbon-TiO2 composites is not high.

Beyond binary composite systems, multicomponent hybrid nanomaterials obtained through integrating carbon materials, noble metals and TiO2 photocatalyst into a composite system are expected to combine the advantages of each respective component, possess multifunctional properties and show superior photocatalytic activities [24], [25]. Various carbon structures, such as carbon nanotube [26], reduced graphene oxide [27] and carbon nanofiber [28] have been used for the ternary photocatalysts fabrication. However, most investigations are mainly focused on the photocatalysts in powder form, which may lead to some limitations in practical application. For instance, the agglomerated particles are willing to form, which does not favor the contact between catalysts and organics and subsequently decrease the photocatalytic efficiency. Further, powder catalysts can be easily blown away in continuous air flow systems, leading to the secondary pollution and potential threat to human health. Thus, for practical application of photocatalysis, particulate semiconductors need to be immobilized on the macroscopic materials such as nickel foam, carbon foam and graphene thin film [29], [30]. Recently, carbon fibers have been made into paper which is called “carbon fiber paper (CFP)”. CFP structures can be a good candidate for catalyst immobilization, which is a porous three-dimensional (3D) network of micro-sized carbon fibers with big holes and large surface area for loading of photocatalytic materials [31], [32]. Therefore, the CFP-supported photocatalysis may be easy to use in application. However, no reports on preparation of the CFP-supported ternary photocatalysts with multifunctional properties for photodegradation of volatile organic compounds can be found.

In this work, Au/TiO2NWs@CFP ternary composite photocatalyst was prepared and its physicochemical properties were characterized in details. The formation mechanism of ternary composite was investigated through time-dependent experiments and the photocatalytic activities of the catalysts were evaluated by degrading gaseous styrene under visible light irradiation. The results suggest that it is a promising approach to exploit highly efficient composite photocatalysts, which offer more opportunities for practical application of photocatalysis in environmental purification.

Section snippets

Materials and chemicals

Carbon fiber paper (CFP, TGP-H-60) was obtained from Toray Group, Japan. Tetrabutyltitanate (TBT) and hydrogen tetrachloroaurate (III) hydrate (HAuCl4·3H2O, 99.9%) were from Sigma-Aldrich, USA. NaOH and absolute ethanol were from Nanjing Chemical Reagent Co., Ltd. Degussa P25 TiO2 was from Germany. All other reagents were analytic grade, and all aqueous solutions were prepared with deionized water.

Preparation of Au/TiO2NWs@CFP composite

One gram of CFP constituted by carbon fibers with the diameter of 8–15 μm was first treated in a 40 

Characterization

The XRD data of the prepared photocatalysts (Fig. 1) are used to identify the crystallographic phases of the products, along with three groups of JCPDS data including anatase TiO2, Au and graphite. The XRD results of the obtained TiO2NWs@CFP and Au/TiO2NWs@CFP composites show that the characteristic diffraction peaks at 2θ = 25.3°, 48.0°, 53.9°, 55.1° and 62.7° can be attributed to the (101), (200), (105), (211) and (204) faces of anatase TiO2 (JCPDF 21-1272) [34]. It reveals that anatase TiO2 is

Conclusions

A novel photocatalyst, Au/TiO2NWs@CFP ternary composite was fabricated using a sequent approach of wet-coating, hydrothermal reaction and photodeposition. Various characterizations showed that the CFP structures were fully covered by TiO2 NWs, on which the Au NPs with size of ∼1.8 nm were uniformly dispersed to form a unique “core-shell” structure. Ascribed to the high adsorptive capacity toward organics and capture ability of photogenerated electrons of CFP, and the excellent visible-light

Acknowledgments

This work was partially supported by the National Nature Science Foundation of China (41373102 and 21307132), NSFC–Guangdong Joint Funds (U1401245), National Natural Science Funds for Distinguished Young Scholars (41425015), Team Project of Natural Science Foundation of Guangdong Province, China (S2012030006604) and China Postdoctoral Science Foundation (2014M552247). This is contribution No. from GIGCAS. Dr. Jiayuan Shi also wants to thank financial support from China Scholarship Council for

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