Chen Zl

Formation of CdMoO4 porous hollow nanospheres via a self-assembly accompanied with Ostwald ripening process and their photocatalytic performance

A simple direct precipitation process in an aqueous solution at room temperature has been developed for the synthesis of monodispersed CdMoO4 porous hollow nanospheres (PHNs). The obtained CdMoO4 PHNs have an average diameter of ∼500 nm and the shell is constructed from nanoparticles with an average diameter of ∼40 nm. The effects of the concentrations of the reaction reagents, pH value and reaction duration have been systematically studied. The formation mechanism of the CdMoO4 PHNs is related to a self-assembly process accompanied with an Ostwald ripening process, during which the CdMoO4 solid nanospheres are first formed through the self-assembly of CdMoO4 nanoparticles and then gradually developed into porous nanospheres with hollow interiors by an Ostwald ripening process. An optical adsorption investigation shows that the CdMoO4 PHNs exhibit a strong absorption peak in the wavelength of 230–365 nm, centered at 256 nm. The photocatalytic activities of the CdMoO4 samples for the degradation of Rhodamine B (RhB) under UV light were studied. The CdMoO4 PHNs calcined at 300 °C for 2 h exhibit excellent photocatalytic efficiency for the degradation of RhB under UV light, which is up to 97% within 40 minutes. The high photocatalytic performance of the CdMoO4 PHNs is associated with the well-crystallized structure and plenty of nanopores which exist in the spheres, serving as transport paths for small molecules.

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.

Colloidal synthesis and formation mechanism of calcium molybdate notched microspheres

A special structure, calcium molybdate (CaMoO4) notched microspheres, were prepared by a solution-phase rapid-injection-based route using only CaCl2, (NH4)6Mo7O24, and sodium dodecyl sulfate as reagents and ethylene glycol as a solvent. X-ray diffraction, scanning electron microscopy, transmission electronic microscopy and an X-ray energy dispersive spectrometer were used to characterize the obtained samples. The notched microspheres were uniform in size and shape, with each sphere containing one notch on its surface. The results show that the formation process of the CaMoO4 notched microspheres is due to a “two-step” growth process, in which CaSO4 nanorods are formed first and then CaMoO4 microspheres are grown on the surfaces of the CaSO4 nanorods. The reaction intermediate, the CaSO4 nanorods, acts as a self-template for the formation of “CaMoO4 sphere gripped CaSO4 nanorod” structures, and finally produce very special structures – CaMoO4 notched microspheres. The shape and size of the notched CaMoO4 samples can be tuned from ellipses to spheres with diameters in the range of 0.1–1 μm by controlling the reaction conditions.

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.