On the asymmetry in molybdenum–oxygen bonding in the MoO3 structure: ETS–NOCV analysis

A combined QTAIM/IRI topological analysis of the effect of axial/equatorial positions of NH2 and CN substituents in the [(PY5Me2)MoO]+ complex

By means of the Interaction Region Indicator (IRI) and Quantum Theory of Atoms in Molecules (QTAIM), the influence exerted by NH₂ (amino) and CN (cyano) as electron donor and electron acceptor substituent groups, respectively, located at para-positions of axial and equatorial pyridine rings of derivatized complexes coming from the [(PY₅Me₂)MoO]⁺ complex during the hydrogen molecular release in the gas phase was analyzed. In any case, a H-H covalent bond is forming at the transition state, with a strengthening of the electron density of 5.5% when the substituent group involved is NH₂ at the para-position of the axial pyridine ring. However, there was no difference between NH₂ and CN when these substituent groups are located at the para-positions of the equatorial pyridine rings. The topological properties of electron densities from the QTAIM are not perturbed by the electron donor and electron acceptor nature of the substituents, even when these substituent groups are located at the axial or equatorial pyridine rings of the Mo-based complex.

Synthesis and defect engineering of molybdenum oxides and their SERS applications

Surface-enhanced Raman scattering (SERS) spectroscopy has been developed into a cross-disciplinary analytical technology through exploring various materials' Raman vibrational modes with ultra-high sensitivity and specificity. Although conventional noble-metal based SERS substrates have achieved great success, oxide-semiconductor-based SERS substrates are attracting researchers' intensive interest due to their merits of facile fabrication, high uniformity and tunable SERS characteristics. Among all the SERS active oxide semiconductors, molybdenum oxides (MoO_x) possess exceptional advantages of high Raman enhancement factor, environmental stability, recyclable detection, etc. More interestingly, the SERS effect of the MoO_x SERS substrates may involve both the electromagnetic enhancement mechanism and the chemical enhancement mechanism, which is determined by the stoichiometry and morphology of the material. Therefore, the focus of this review will be on two critical points: (1) synthesis and material engineering methods of the functional MoO_x material and (2) MoO_x SERS mechanism and performance evaluation. First, we review recent works on the MoO_x preparation and material property tuning approaches. Second, the SERS mechanism and performance of various MoO_x substrates are surveyed. In particular, the performance uniformity, enhancement factor and recyclability are evaluated. In the end, we discuss several challenges and open questions related to further promoting the MoO_x as the SERS substrate for monitoring extremely low trace molecules and the theory for better understanding of the SERS enhancement mechanism.

Direct conversion of multilayer molybdenum trioxide to nanorods as multifunctional electrodes in lithium-ion batteries

In this study we prepared molybdenum trioxide (MoO3) nanorods having average lengths of 0.5-1.5 μm and widths of approximately 100-200 nm through a one-step mechanical break-down process involving favorable fracturing along the crystal direction. We controlled the dimensions of the as-prepared nanorods by applying various imposing times (15-90 min). The nanorods prepared over a reaction time of 90 min were, on average, much shorter and narrower relative to those obtained over 30 min. Evaluations of lithium-ion storage properties revealed that the electrochemical performance of these nanorods was much better than that of bulk materials. As cathodes, the nanorods could deliver a high specific capacity (>315 mA h g(-1)) with losses of less than 2% in the first cycle at a rate of 30 mA g(-1); as anodes, the specific capacity was 800 mA h g(-1) at a rate of 50 mA g(-1). Relative to α-MoO3 microparticles, these nanorods displayed significantly enhanced lithium-ion storage properties with higher reversible capacities and better rate performance, presumably because their much shorter diffusion lengths and higher specific surface areas allowed more-efficient insertion/deinsertion of lithium ions during the charge/discharge process. Accordingly, enhanced physical and/or chemical properties can be obtained through appropriate nanostructuring of materials.