A route for the synthesis of Cu-doped TiO2 nanoparticles with a very low band gap
Graphical abstract
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)
- et al.
Mater. Chem. Phys.
(2008) - et al.
Appl. Catal., A
(2009) - et al.
Int. J. Hydrogen Energy.
(2009) - et al.
Appl. Catal., B: Environ.
(2009) - et al.
Int. J. Hydrogen Energy
(2008) - et al.
Catal. Today
(2009) J. Mol. Catal. A: Chem.
(2004)- et al.
J. Colloid Interface Sci.
(2010) - et al.
Energy
(2009) - et al.
Appl. Surf. Sci.
(2004)
Appl. Catal., B: Environ.
Catal. Commun.
Appl. Catal., B: Environ.
J. Mol. Struct.
Catal. Commun.
Mater. Sci. Eng., B
Appl. Catal., B: Environ.
Appl. Surf. Sci.
J. Photochem. Photobiol., A: Chem.
Surf. Coat. Tech.
Sens. Actuators, B
Thin Solid Films
Phys. B: Condens. Matter
Thin Solid Films
Cited by (126)
Synthesis of Cu@NC nanocube based on Cu<inf>2</inf>O for electrocatalytic nitrogen reduction to ammonia
2022, Materials Today EnergyStructural, optical and electronic properties of copper doped TiO<inf>2</inf>: Combined experimental and DFT study
2022, Inorganic Chemistry CommunicationsOptical and gas sensing properties of TiO<inf>2</inf>/RGO for methanol, ethanol and acetone vapors
2022, Inorganic Chemistry CommunicationsSelected organic dyes (carminic acid, pyrocatechol violet and dithizone) sensitized metal (silver, neodymium) doped TiO<inf>2</inf>/ZnO nanostructured materials: A photoanode for hybrid bulk heterojunction solar cells
2022, Spectrochimica Acta - Part A: Molecular and Biomolecular SpectroscopyUnravelling the role of interface of CuO<inf>x</inf>-TiO<inf>2</inf> hybrid metal oxide in enhancement of oxygen reduction reaction performance
2022, International Journal of Hydrogen Energy