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J Nanopart Res (2014) 16:2385 DOI 10.1007/s11051-014-2385-3
RESEARCH PAPER
Effect of titanium doping on the structure and reducibility of nanoparticle molybdenum dioxide
Qian He Oscar Marin-Flores Shuozhen Hu
Louis Scudiero Su Ha M. Grant Norton
Received: 31 January 2014 / Accepted: 21 March 2014 / Published online: 8 April 2014 Springer Science+Business Media Dordrecht 2014
Abstract Molybdenum dioxide (MoO2) has potential not only in heterogeneous catalysis, but also as an electrode material in lithium-ion batteries and fuel cells. However, the reduction tendency to molybdenum metal is a limiting factor in the use of this oxide. In the present work, MoO2 was doped with Titanium (Ti4?) to increase the stability to reduction in a hydrogen-rich environment. Rather than using a conventional high-temperature solid-state reaction, a novel solution-based synthesis method followed by hydrothermal reduction was used. Nano-sized Ti-doped MoO2 particles with Ti/Mo atomic ratios of 0,0.03, and 0.05 were prepared and characterized. X-ray and time-of-ight neutron powder diffraction (XRD and NPD) conrmed the presence of only the MoO2 phase. Transmission electron microscopy showed that the nanoparticles had an acicular morphology with
particle sizes in the long dimension between 30 and 50 nm. Elemental mapping obtained by scanning electron microscopy with energy dispersive spectroscopy showed homogenous distribution of the dopant. Attenuated total reectance-Fourier transform infrared spectroscopy revealed that the solubility limit of the synthesized Ti-doped MoO2 was reached at a
Ti/Mo ratio of 0.05. This observation indicates that the bulk thermodynamic solubility limit can be exceeded at the nanoscale. X-ray photoelectron spectroscopy performed on 0.03 Ti-doped MoO2 samples showed that the Ti dopant is present as Ti4? and the depth prole analysis indicated the presence of this species even in the bulk of the sample. This agrees with the data obtained from Rietveld renement of the XRD and NPD results, which showed changes in the lattice parameters and MoMo interatomic distance upon doping, suggesting a substitution of Mo4? by Ti4?. The effect of Ti doping on the reducibility of MoO2 was demonstrated by in situ XRD in a hydrogen-rich environment.
Keywords Nanoparticle molybdenum dioxide
Ti-doped Rietveld renement Reducibility
Introduction
Molybdenum dioxide (MoO2) is a transition metal oxide with unusual metallic-like electrical conductivity (88 lX cm at 300 K), which is attributed to the
Q. He (&) O. Marin-Flores...