Synthesis of Cr2O3/TNTs nanocomposite and its photocatalytic hydrogen generation under visible light irradiation

doi:10.1016/j.apsusc.2009.07.080

Applied Surface Science

Volume 255, Issue 23, 15 September 2009, Pages 9508-9511

https://doi.org/10.1016/j.apsusc.2009.07.080 Get rights and content

Abstract

A novel Cr₂O₃/TNTs nanocomposite was prepared by loaded suitable amount of amorphous Cr₂O₃ on titanate nanotubes (TNTs) via hydrothermal reaction and impregnation process. XRD, SEM and TEM results demonstrated that the amorphous Cr₂O₃ nanoparticles were homogeneously dispersed on the surface of TNTs. The diffuse reflectance UV–visible absorption spectra exhibited that the spectral response of TNTs was extended to visible light region by coupled with Cr₂O₃. The 2.5Cr₂O₃/TNTs nanocomposite showed the highest activity of hydrogen generation by photocatalytic water-splitting under visible light irradiation (λ > 400 nm). The high activity of H₂ evolution for Cr₂O₃/TNTs nanocomposites was associated with the donor level in the forbidden band of TNTs semiconductor provided by dopant Cr³⁺ and a probably photocatalytic mechanism was proposed.

Introduction

TiO₂-based nanotubes (TO₂NTs) with one-dimensional nanostructure have been received considerable attention due to its peculiar chemical and physical behaviors in recent years. However, the TO₂NTs as a photoresponse material only strongly absorb UV light due to its relatively large band gap energy of about 3.2 eV. Some approaches have been paid to extend its photoresponse and improve its photoactivity [1], [2], [3], [4]. One of the best ways is to doped Cr³⁺ into TiO₂NTs by means of hydrothermal route [5], ion implantation [6], sol–gel route associated with hydrothermal process to synthesize Cr-doped TiO₂NTs for degradation of organic pollutant [7], and spreading a viscous Cr-doped TiO₂ dispersion onto a conducting glass substrate to obtain Cr-doped TiO₂ films for test of its photocurrent induced by the water-splitting [8].

In the paper, we reported a novel Cr₂O₃/titanate nanotubes (TNTs) nanocomposite was prepared by loaded amorphous Cr₂O₃ on titanate nanotubes via hydrothermal synthesis and impregnation technique. The purpose of the present work expects: (1) to design one kind of nanocomposite by one-dimensional TNTs coupled with zero-dimensional Cr₂O₃ nanoparticles, (2) extend optical response of TNTs to visible region, (3) improve the separation efficiency of photogenerated electron–hole pairs and (4) enhance the photocatalytic activity. To seek a new application, the Cr₂O₃/TNTs composite is firstly used as a photocatalytic material for generation of hydrogen by photocatalytic water-splitting under visible light irradiation and the results show that the Cr₂O₃/TNTs nanocomposites have much higher activity than that of pure TNTs.

Section snippets

Preparation of Cr₂O₃/TNTs nanocomposites

The titanate nanotubes were synthesized by hydrothermal method as our previous work reported [4]. The Cr₂O₃/TNTs nanocomposites were prepared by impregnation route. In a typical experiment, 0.0658 g of Cr(NO₃)₃·9H₂O was dissolved in 4 mL anhydrous ethanol with ultrasonic-assistant dispersion to give a clear dark blue solution, and then 5 g of TNTs powder was impregnated in it overnight. The impregnant was volatilized at 70 °C and then calcined at 300 °C for 2 h. The nanocomposite by loading Cr³⁺ at

Doping of Cr³⁺ into TNTs

Fig. 1 shows the XRD patterns of samples. Fig. 1a is the pattern of sample synthesized by hydrothermal method in a concentrated NaOH solution without post-treatment washing. The diffraction pattern occurred at 10.5°, 25.3°, 29.9°, 34.3°, 35.6°, 38.5°, 48.1°, 52.7°, 54.4° and 60.9° corresponding to (0 0 1), (0 1 1), (3 0 0), (−2 0 3), (1 0 3), (−3 1 0), (0 2 0), (−4 1 3), (5 0 1) and (1 2 3) crystal planes is assigned to be monoclinic sodium trititanate nanotubes (Na₂Ti₃O₇) (JCPDS No. 31-1329). Some authors [12],

Conclusions

A series of Cr₂O₃/TNTs nanocomposites were prepared by hydrothermal and impregnating methods. XRD and TEM results revealed that the nanocomposites are composed of Na₂Ti₃O₇ and Na_0.8H_1.2Ti₃O₇ titanate nanotubes with average outer tubular diameter of ca.10 nm coupled with non-crystal Cr₂O₃ nanoparticles less than 4 nm. The absorption edge of TNTs can be extended to visible region and is gradually bathochromic shift with increasing the content of Cr₂O₃. The activity of H₂ evolution for Cr₂O₃/TNTs

Acknowledgment

The authors gratefully acknowledge the Project Supported by Natural Science Basic Research Plan in Shaanxi Province of China (No. SJ08E106).

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Citation Excerpt :
Likely only chromia films above some critical thickness will be effective for exchange bias applications, even without electric/voltage controlled switching. There has been a long standing interest in chromia, which also extends to possible applications as a catalyst or photo-catalyst [13–37], leading to a very rich literature of the interface properties of this material. There have been a number of studies of successful chromia thin film growth on a variety of substrates, including Cr(110) [13–17,29,33–35,38–42], W(100) [43,44], Re(0001) [45], Rh [36], Pt(111) [46,47], Pd(111) [48], Pt [49], Cu(110) [50], Cu(100) [51], Cu(111) [52], Ag(111) [53], Au(111) [54], Fe(100) [55], Fe(110) [56], polycrystalline Fe [57], polycrystalline Co [57], polycrystalline Ni80Fe20 [57], NiAl2O4 [58], Fe2O3 [20,59–61], CrO2 [62,63], and on sapphire or Al2O3(0001) [12,20–24,60,64–66].
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Synthesis of Cr2O3/TNTs nanocomposite and its photocatalytic hydrogen generation under visible light irradiation

Abstract

Introduction

Section snippets

Preparation of Cr2O3/TNTs nanocomposites

Doping of Cr3+ into TNTs

Conclusions

Acknowledgment

Mater. Res. Bull.

Sep. Purif. Technol.

J. Solid State Chem.

Mater. Lett.

Chem. Phys. Lett.

Appl. Surf. Sci.

J. Non-Cryst. Solids