Solution-synthesis And Photochromic Property Studies Of Molybdenum Based Oxides

With the rapid development of science and technology, the research and application ofallochroic materials brought us fresh colorful world. Inorganic photochromic materialsbased on molybdenum trioxide (MoO3) have obtained more and more attention becauseof their unique structures and photochromic properties.In this thesis, a series of micro/nano molybdenum based oxides, including metastablehexagonal molybdenum trioxide (h-MoO3), triclinic molybdenum trioxide (t-MoO3·H2O)and Mo/W-oxides, were prepared via a simple liquid-phase crystallization. Crystalstructure and morphology of molybdenum based oxides can be adjusted by changingthe reaction temperature and acidity, thus, the photochromic properties were alsoadjusted. The obtained main results are given as follows:1. Metastable h-MoO3microstructures (such as hexagonal microrods andbranch-structure) and t-MoO3·H2O fiber-structured nanomaterials were obtained byacidification of (NH4)6Mo7O24·4H2O at90oC. Control experiments demonstrated thath-MoO3was synthesized in a wide range of acidic solution. And t-MoO3·H2O waspreferentially obtained under strongly acidic condition, and2. Metastable h-MoO3hexagonal microrods and assembled microspheres weresuccessfully prepared by the induction of poly(vinyl pyrrolidone)(PVP) asstructure-directing agent at40–50oC, which made low-temperature synthesis ofh-MoO3achieved. Without PVP induction, h-MoO3precipitates could not be obtainedeven after tens of hours’ reaction. The PVP-induced mechanism was discussed: groupsthat in the side chains of PVP can be easily protonated to be positively charged ascations, thus the protonated PVP would interact with molybdate anions throughprotonated atoms along the main chains of PVP. With reaction of molybdenumprecursors along the chain, PVP directed the crystals to form as1D hexagonal structure,and some of PVP molecules were trapped in tunnels to stabilize h-MoO3crystals. Othersurfactants with distinguished functional groups were chosen for paralleled preparation.As expected, cationic surfactants (CTAB) or nonionic surfactants which can beprotonated to be cationic (PVP, PEG etc.) have indispensable effects on directing thecrystal growth of h-MoO3at low temperatures..3. A series of Mo/W-oxides were synthesized with different ratio of W to Mo bysimple aqueous method. In order to improve the photochromic response of molybdenum based oxides under visible light, The as-prepared samples were Mo0.5W0.5O3nanoparticles in100-200nm with some impurities including h-MoO3and H2WO4·H2Oetc. The UV-Vis spectra of the prepared samples showed enhanced absorbance ofMo/W-oxides in visible range.4. The photochromic properties of prepared molybdenum based oxides were studied.Metastable h-MoO3showed good photochromic property under natural sunlightirradiation. h-MoO3microspheres had better photochromic property than microrods,and the photochromic property got better as the assemble degree increased. Moreover,part of samples can achieved reversible photochromic process many times, but slowerreversible photochromic process of was still an unsolved problem. t-MoO3·H2Oexhibited better photochromic property than h-MoO3under natural sunlight irradiation,but its discoloring rate is slower than that of h-MoO3. Mo/W-oxides had bestphotochromic property under natural sunlight irradiation in these materials, however,its decoloring property is poor.