Hydrothermal Synthesis of Molybdenum Oxide Based Materials: Strategy and Structural Chemistry

Heterogeneous catalysis with an organic–inorganic hybrid based on MoO3 chains decorated with 2,2′-biimidazole ligands

Polymeric [MoO₃(2,2′-biimidazole)]·H₂O outperforms other one-dimensional MoO₃-ligand hybrid materials as a heterogeneous and recyclable catalyst for (bio)olefin epoxidation and sulfoxidation.

Rapid synthesis of vertically aligned α-MoO3 nanostructures on substrates

We report a new procedure for large scale, reproducible and fast synthesis of polycrystalline, dense, vertically aligned α-MoO3 nanostructures on conducting (FTO) and non-conducting substrates (Si/SiO2) by using a simple, low-cost hydrothermal technique. The synthesis method consists of two steps, firstly formation of a thermally evaporated Cr/MoO3 seed layer, and secondly growth of the nanostructures in a highly acidic precursor solution. In this report, we document a growth process of vertically aligned α-MoO3 nanostructures with varying growth parameters, such as pH and precursor concentration influencing the resulting structure. Vertically aligned MoO3 nanostructures are valuable for different applications such as electrode material for organic and dye-sensitized solar cells, as a photocatalyst, and in Li-ion batteries, display devices and memory devices due to their high surface area.

Al2O3-Supported W–V–O bronze catalysts for oxidative dehydrogenation of ethane

Vanadium-containing hexagonal tungsten bronze (HTB) structures supported on Al₂O₃ are more selective to ethylene during ethane ODH than supported vanadium oxides.

Template conversion of MoO3 to MoS2 nanoribbons: synthesis and electrochemical properties

Electrochromic α-MoO₃ nanoribbons were prepared by a hydrothermal method and converted to MoS₂ with the same morphology.

A unique fluoride nanocontainer: porous molecular capsules can accommodate an unusually high number of "rather labile" fluoride anions

The present work refers to the challenging issue of fluoride anion recognition/binding in water by taking advantage of the unique possibilities offered by the porous molecular nanocontainers of the {Mo132} Keplerate type allowing the study of a variety of new phenomena. Reaction of the highly reactive carbonate-type capsule with aqueous HF results in the release of carbon dioxide and integration of an unprecedentedly large number of fluoride anions--partly as coordinated ligands at both the pentagonal units and the linkers, partly as a disordered water/fluoride assembly inside the cavity. The internal assembly and some of the fluoride ligands are easily released, which provides interesting options for future studies regarding coordination chemistry and catalysis under confined conditions.

Crystal facet tailoring arts in perovskite oxides

This review highlights various facet tailoring arts in perovskite structure oxides.

Solution-based synthesis and design of late transition metal chalcogenide materials for oxygen reduction reaction (ORR)

Late transition metal chalcogenide (LTMC) nanomaterials have been introduced as a promising Pt-free oxygen reduction reaction (ORR) electrocatalysts because of their low cost, good ORR activity, high methanol tolerance, and facile synthesis. Herein, an overview on the design and synthesis of LTMC nanomaterials by solution-based strategies is presented along with their ORR performances. Current solution-based synthetic approaches towards LTMC nanomaterials include a hydrothermal/solvothermal approach, single-source precursor approach, hot-injection approach, template-directed soft synthesis, and Kirkendall-effect-induced soft synthesis. Although the ORR activity and stability of LTMC nanomaterials are still far from what is needed for practical fuel-cell applications, much enhanced electrocatalytic performance can be expected. Recent advances have emphasized that decorating the surface of the LTMC nanostructures with other functional nanoparticles can lead to much better ORR catalytic activity. It is believed that new synthesis approaches to LTMCs, modification techniques of LTMCs, and LTMCs with desirable morphology, size, composition, and structures are expected to be developed in the future to satisfy the requirements of commercial fuel cells.

Interplay between size and crystal structure of molybdenum dioxide nanoparticles--synthesis, growth mechanism, and electrochemical performance

A detailed study is presented on the formation of MoO(2) nanoparticles from the dissolution of the precursor to the final rodlike product, with a focus on the exploration of the inorganic reaction occurring ahead of the nucleation step, and interplay between size and crystal structure of MoO(2). In situ X-ray absorption spectroscopy experiments show that the crystallization and the growth process of MoO(2) nanorods is initiated by rapid reduction of the MoO(2) Cl(2) precursor in benzyl alcohol and acetophenone. This reaction triggers the nucleation of 2 nm MoO(2) particles with spherical shape and hexagonal crystal structure. The transformation from spheres into rods emerges as a complex process driven by oriented attachment. High-resolution transmission electron microscopy and X-ray diffraction results provide evidence that the 2 nm particles first aggregate into 5-20 nm-large oriented assemblies. The increase in particle size induces the phase transition from hexagonal to the less symmetrical monoclinic crystal structure, and finally the transformation into rods. Is it shown that electrodes for lithium-ion batteries based on MoO(2) nanorods have a long-term cycling life. The specific discharge capacity even after 200 cycles at a discharge rate of 1 C is about 300 Ah kg(-1) .

Controllable Layered Structures in Polyoxomolybdate-Surfactant Hybrid Crystals

Inorganic-organic hybrid crystals containing α-octamolybdate (Mo₈) or hexamolybdate (Mo₆) were isolated by using hexadecyltrimethylammonium (C₁₆) surfactant. The packing mode of the inorganic layers depended on a difference in the polyoxomolybdate molecular structure. The structure for both crystals consisted of alternate stacking of C₁₆ organic bilayers and polyoxomolybdate inorganic layers with a periodicity of 24.4–24.6 Å. However, the C₁₆-Mo₈ crystals contained Mo₈ monolayers, while the C₁₆-Mo₆ crystals contained Mo₆ bilayers. These lattice structures for the polyoxometalate/organic hybrid will be designed by the molecular structures of polyoxometalate.

Tetra-ammonium diaqua-diperoxidoocta-molybdate(VI) tetra-hydrate

The title compound (NH₄)₄[Mo₈O₂₄(O₂)₂(H₂O)₂]·4H₂O, consists of an octa­molybdate cluster with a crystallographic centre of symmetry. The clusters pack in a cubic close packing arrangement defining channels containing water mol­ecules and ammonium cations, which exhibit hydrogen bonding with neighbouring clusters. Hydrogen bonding also exists between the coordinated water mol­ecules of one cluster with one of the O atoms of the peroxido fragment in a neighbouring cluster.

Environmentally friendly methodologies of nanostructure synthesis

Environmentally friendly synthetic methodologies have gradually been implemented as viable techniques in the synthesis of a range of nanostructures. In this work, we focus on the application of green-chemistry principles to the synthesis of complex metal oxide and fluoride nanostructures. In particular, we describe advances in the use of the molten-salt synthetic methods, hydrothermal protocols, and template-directed techniques as environmentally sound, socially responsible, and cost-effective methodologies that allow us to generate nanomaterials without the need to sacrifice sample quality, purity, and crystallinity, while allowing control over size, shape, and morphology.

[Mo16O53F2]12-: a New Polyoxofluoromolybdate Anion

Single crystals of a new beta-octamolybdate salt containing protonated 1,4-diazabicyclo[2.2.2]octane cations were prepared under mild hydrothermal conditions. This compound, [C6H13N2]2[C6H14N2][Mo8O26], was then used as a starting material in the synthesis of [C6H13N2]6[Mo16O53F2].4H2O, which contains previously unreported [Mo16O53F2]12- anions. The structure-directing properties of gamma-[Mo8O26]4-, a likely intermediate in this pH-dependent transformation, are responsible for the site selection of the fluoride incorporation. [Mo16O53F2]12-, the largest reported polyoxofluoromolybdate cluster, expands upon the limited number of such anions in the literature. The structures of both compounds were determined using single-crystal X-ray diffraction.