Elsevier

Chemical Physics Letters

Volume 571, 20 May 2013, Pages 49-53
Chemical Physics Letters

A route for the synthesis of Cu-doped TiO2 nanoparticles with a very low band gap

https://doi.org/10.1016/j.cplett.2013.04.007Get rights and content

Highlights

  • A very low band gap energy is obtained for Cu-doped TiO2 nanoparticles synthesized.

  • A methodology to obtain internally Cu-doped TiO2 is introduced.

  • An extensive characterization of the samples has been developed.

  • The nanoparticles can be of great use in photovoltaic and photocatalytic applications.

Abstract

This letter presents a method for the synthesis of copper-doped TiO2 nanoparticles. The semiconductors synthesized were characterized in order to know the composition, crystalline structure, the band gap energy, etc. The nanoparticles obtained have a very low band gap (1.6 eV for 7.5% Cu-doping) compared with the values reported in the literature. The results obtained revealed that internal doping of the TiO2 structure is produced, and that the predominant crystalline phase is anatase. The semiconductors synthesized would be of great use in photocatalytic and photovoltaic applications due to the high specific surface and the low band gap energy values.

Introduction

Because of its commercial availability, optical and electronic properties, chemical stability and low toxicity, TiO2 has been widely studied for use as a heterogeneous catalyst or semiconductor [1]. To improve its applications in these fields, it has been shown that, in general, doped TiO2 improves its properties as a photocatalyst [2] and a semiconductor in photovoltaic applications [3]. For example, the following elements have been used as dopants for photocatalyst applications: iron [4], chromium [4], carbon [5], nitrogen [6], or bismuth [7]. For photovoltaic applications, it is possible to find studies about the use of doped TiO2 as semiconductor in dye-sensitized solar cells, for example, niobium [8], vanadium [9], or ytterbium [10] have been used as dopants.

Moreover, copper has been commonly used as dopant for different applications [3], [11], [12], [13], [14]. The methods found in the literature for obtaining Cu-doped TiO2 can be divided into three main groups: (a) by means of commercial TiO2 and by using the wet impregnation method or variations of this [15], [16], [17], [18], [19], [20], [21], [22], [23], [24], (b) synthesis using one precursor to obtain TiO2 and another for doping (Cu) [12], [25], [26], [27], [28], [29], and (c) deposition methods [30], [31], [32], [33], [34]. For Cu-doped TiO2 samples in the literature, the band gap energy has been reported in some cases. For example, using the wet impregnation method, Karunakaran et al. reported a band gap energy value of 2.83 eV (2 wt.% Cu) [16], Yoong et al. reported a minimum value of 2.40 eV (10 wt.% Cu) [17], Nguyen et al. reported a value of 2.90 eV (0.5 wt.% Cu–0.54 wt.% Fe) [21]; and Slamet et al. obtained a band gap energy of 2.73 eV (3 wt.% Cu) [24]. Moreover, for synthesis using option (b) described before, López et al. reported a value of the band gap energy of 2.81 eV (5 wt.% Cu) [12]; Colon et al. obtained a value of 3.00 eV (1 wt.% Cu) [26]; and López-Ayala and Rincón reported a band gap of 2.75 eV (Cu/Ti (mol/mol) = 0.16) [28]. At last, Wang et al. obtained a value of 2.2 eV, using a metal plasma ion implantation which is the lowest value found in the literature [34]. This letter presents a method for the synthesis of Cu-doped TiO2 based on the low-temperature hydrolysis reaction of titanium n-butoxide, where CuCl2 is the precursor used to introduce the doping agent. Performing this synthesis at a low temperature is an innovation that slows down the formation of TiO2, thus obtaining a small crystallite size for the semiconductors. The band gap energy values obtained for the nanoparticles synthesized are lower than the values reported in the literature for the synthesis of Cu-doped TiO2. The bang gap energy value obtained in this letter leads us to believe that their use in photocatalytic and photovoltaic applications could be of considerable interest.

Section snippets

Synthesis

Cu-doped TiO2 was synthesized using a low temperature hydrolysis reaction using titanium n-butoxide as a precursor. The procedure was as follows: (a) 100 mL of water was cooled at 4 °C; (b) during the cooling process a stoichiometric amount of CuCl2·2H2O (purity 98%, Panreac) was added to get theoretical Cu/TiO2 proportions of 2.5%, 5.0% and 7.5%; (c) 10 mL of titanium n-butoxide (purity 97%, Sigma–Aldrich) was added drop wise under magnetic stirring; (d) when the addition was finished, the

Inductively coupled plasma atomic emission spectroscopy

Inductively coupled plasma atomic emission spectroscopy (ICP-AES) was used to characterize the composition of the samples. The initial quantities of Cu introduced are shown in Table 1 as the percentage of the mass of Cu in relation to the mass of TiO2. This table also shows the values obtained by ICP-AES for the real percentages of Cu versus TiO2 which were introduced in the nanocrystals. In all cases, the percentage of Cu incorporated into the TiO2 structure was around 80% with regard to the

Conclusions

Letter presents a method for the synthesis of copper-doped TiO2 based on the low temperature hydrolysis reaction of a titanium alkoxide. The produced semiconductors synthesized have a very low band gap energy value, reaching 1.6 eV for a doping of 7.5%. This is much lower as compared to the values reported in the literature for levels of doping similar to those in letter. Likewise, the band gap energy decreased as the amount of Cu in the samples increased. The samples were also characterized

Acknowledgements

We thank the Junta de Andalucía of Spain under projects P09-FQM-04938, and FEDER funds.

References (48)

  • A.C. Lee et al.

    Mater. Chem. Phys.

    (2008)
  • F. Han et al.

    Appl. Catal., A

    (2009)
  • R. Dholam et al.

    Int. J. Hydrogen Energy.

    (2009)
  • B. Zhou et al.

    Appl. Catal., B: Environ.

    (2009)
  • T. Sreethawong et al.

    Int. J. Hydrogen Energy

    (2008)
  • R. López et al.

    Catal. Today

    (2009)
  • J. Araña

    J. Mol. Catal. A: Chem.

    (2004)
  • C. Karunakaran et al.

    J. Colloid Interface Sci.

    (2010)
  • L.S. Yoong et al.

    Energy

    (2009)
  • J. Araña et al.

    Appl. Surf. Sci.

    (2004)
  • J. Araña et al.

    Appl. Catal., B: Environ.

    (2008)
  • T.-V. Nguyen et al.

    Catal. Commun.

    (2008)
  • B. Thirupathi et al.

    Appl. Catal., B: Environ.

    (2011)
  • D. Luo et al.

    J. Mol. Struct.

    (2011)
  • Slamet et al.

    Catal. Commun.

    (2005)
  • E. Celik et al.

    Mater. Sci. Eng., B

    (2006)
  • G. Colón et al.

    Appl. Catal., B: Environ.

    (2006)
  • M. Hamadanian et al.

    Appl. Surf. Sci.

    (2010)
  • S. López-Ayala et al.

    J. Photochem. Photobiol., A: Chem.

    (2011)
  • D.A.H. Hanaor et al.

    Surf. Coat. Tech.

    (2011)
  • A. Teleki et al.

    Sens. Actuators, B

    (2008)
  • D.L. Hou et al.

    Thin Solid Films

    (2008)
  • C.E. Rodríguez-Torres et al.

    Phys. B: Condens. Matter

    (2007)
  • D.-Y. Wang et al.

    Thin Solid Films

    (2006)
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