H₂O₂ Assisted Hydrothermal Synthesis Of Nanostructured Semiconducting Oxides

Low-dimensional nanostructures, such as nanorods, nanobelts, nanotubes, andnanosheets, have received considerable interest due to their novel physical andchemical properties differing from their bulk counterparts. They have potentialapplications in lithium-ion battery, sensor, laser, and photocatalysis. In recent years,the synthesis of semiconducting oxide nanostructures have been intensively researchedto promote their performance. In this thesis, some typical semiconducting oxidenanostructures, such as MoO₃, TiO₂ and ZnO, have been prepared via a facile H₂O₂assisted hydrothermal method. The influences of reaction parameters on themorphologies and crystal structures have been investigated and the formationmechanism has also been discussed. The main results are as follows:（1） Several kinds of MoO₃ nanostructures have been synthesized by hydrothermaltreating metallic molybdenum powder in H₂O₂ solution without the aid of anytemplates or surfactant. It is found that MoO₃ can evolve from helical nanosheets tocross-like nanostructures to nanobelts with the reaction time increased. The syntheticmethod is environmentally friendly and the products are very pure. As the molar ratioof molybdenum and H₂O₂ is 0.17, helical MoO₃ nanosheets are formed after 6 h at 180℃, cross-like MoO₃ nanoflowers are obtained after 8 h, and then pure MoO₃nanobelts with widths of 100-200 nm, thickness of 10-20 nm, and lengths up toseveral to several tens of micrometers are prepared after 12h. When the molar ratio ofmolybdenum and H₂O₂ decreases to 0.08, only pure MoO₃ nanobelts are fabricated.XRD patterns show that the crystallinity of MoO₃ nanostructures increases as thereaction time increases. When MoO3 nanobelts are used as cathode materials inlithium-ion pattery, the first cycle specific capacity can reach 230 mAh/g. （2） Hollow ZiO₂ structures with controllable morphologies and crystal structureshave been prepared in H₂O₂ solution using different Ti sources by hydrothermalmethod. Anatase hollow TiO₂ microspheres assembled by nanoparticles are obtainedby hydrothermal treating titanium powder-H₂O₂ solution at 180℃using ammonia toadjust pH values. The outer diameters and thickness are 600-900 nm and 80-140 nm,respectively. Hollow TiO2 microbricks with diameters of 2-3μm can be synthesizedwithout adjusting pH values. Ruffle hollow TiO2 microspheres with outer diameters of1-4μm can be formed by hydrothermal treating ZiCl₃-H₂O₂ solution at 120℃. Thesehollow microspheres are composed of nanorods. The diameters and lengths of TiO₂nanorods are in the range of 20-50 nm and 100-200 nm, respectively. The hollowmicrospheres can be ruptured at higher reaction temperature.（3） ZnO nanostructures have been synthesized using zinc powder andZn（NO₃）₂·6H₂O as zinc sources, respectively. When zinc powders are hydrothermaltreated in HEOE-NaOH solution at 180℃, ZnO nanorods with diameters of 100-300nm and with lengths of about ten micrometers are obtained. When the molar ratio ofZn²⁺/OH^- is 1: 20, flower-like ZnO nanostructures consisting the ZnO nanorods withdiameters of 100-300 nm and length up to several micrometers are formed usingZn（NO₃）₂·6H₂O as the zinc source at 180℃. Interestingly, when the molar ratio ofZn²⁺/OH^- increases to 1: 4, ZnO nanosheets with thickness of 10-20 nm are fabricatedat 80℃. The thickness of ZnO nanosheets can increase to 30-40 nm as the reactiontemperature increases to 180℃.