Jianxun Cui

Formation of FeMoO4 hollow microspheres via a chemical conversion-induced Ostwald ripening process

FeMoO4 hollow microspheres were prepared via a template-free hydrothermal method using FeCl2 and Na2MoO4 as the starting reaction reagents and distilled water as the solvent. The crystal structure, morphology and UV-vis reflection property of the as-synthesized products are characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy and UV-vis diffuse reflectance spectroscopy. The hollow microspheres have diameters ranging from 3 to 5 μm, hollow interiors of ∼2.5 μm and the shell is constructed by numerous nanoparticles with sizes of 100–200 nm. The effects of reaction temperature, concentration of reaction reagents and reaction times have been studied. The formation mechanism of the FeMoO4 hollow microspheres is related to the chemical conversion-induced Ostwald ripening process.

Self-supported construction of 3D CdMoO4 hierarchical structures from nanoplates with enhanced photocatalytic properties

Three-dimensional (3D) CdMoO4 hierarchical structures constructed by single-crystalline nanoplates were prepared by a facile hydrothermal route. The obtained samples were systematically characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and UV-Vis spectrophotometry. The morphology modulation of the as-prepared products could be easily tuned by changing the concentration of reactants, reaction temperature, molybdenum source, pH value and reaction time. The formation process of CdMoO4 hierarchical structures was related to the two-step growth, in which CdMoO4 main nanoplates were formed first in the synthesis, followed by self-construction of small nanoplates on both side of the main nanoplates in a regular fashion. The photocatalytic activities of CdMoO4 hierarchical structures and nanoplates for degradation of Rhodamine B (RhB) under ultraviolet (UV) light irradiation were also evaluated. CdMoO4 hierarchical structures constructed by nanoplates have a higher photocatalytic activity toward photo-degradation of RhB than that of CdMoO4 nanoplates, mainly due to their unique morphology and high crystallinity.

Single-crystal Na2Ti6O13 nanorings formed by self-coiling of a nanobelt

We presented, for the first time, the evidence of loop-by-loop self-coiling of a nanobelt to form single-crystal Na2Ti6O13 nanorings with diameters of several micrometres. The winding nanobelts, with thickness of about 15 nm and widths of 100–500 nm, grow along their [010] crystallographic directions, and coherently match at ±(200) crystallographic planes. The driving force of such a coherent match is suggested to be the minimization of local electrostatic energy introduced by the cations and anions. We also discussed the dependence of the nanorings yield on the thickness of the nanobelts, which affects the elastic deformation energy and misfit energy of the rings.

Substrate Effects on Growth of MoS2 Film by Laser Physical Vapor Deposition on Sapphire, Si and Graphene (on Cu)

Molybdenum disulfide (MoS2) films were deposited on sapphire (0001), Si (001) and graphene on Cu by laser physical vapor deposition at 600°C for different time periods to achieve control of thickness. MoS2 film was found to grow on all the substrates in the (0002) orientation. Films are found to be S-deficient and a free Mo peak was observed in the x-ray diffraction. Raman spectroscopy showed the characteristic peaks of MoS2 film with decreasing separation between the A1g and E2g1 peaks for a shorter time of deposition or smaller thickness of the film. MoS2 films on sapphire substrate showed additional peaks due to MoO3 and Mo4O11 phases. Films on Si substrate and graphene on Cu contained only the characteristic peaks. MoS2 films on graphene suppressed the graphene peak as a result of large fluorescence background in the Raman spectrum. Interfacial effects and the presence of an oxygen impurity are considered responsible for the large fluorescence background in the Raman spectrum. X-ray photoelectron spectroscopy indicated substrate interaction with the films on sapphire and Si. Coverage of the film on the substrates is uniform with uniform distribution of the Mo and S as evidenced from the x-ray maps. Atomic force microscopy image revealed the surface of the film on sapphire to be very smooth. Electrical conductance measurements showed the MoS2 film on sapphire is semiconducting but with much lower activation energy compared to the bandgap. The presence of excess Mo in the film is considered responsible for the lower activation energy.