Study On The Synthesis Of Nanometer MoO₃Via Solution Approach At Low Temperature

With its special layered structure and properties,nanometer MoO₃has broadapplication prospects in smoke suppression filling,sensors，battery electrodes，displaydevices and catalysts etc.As the morphology of nanometer MoO₃has important effectson its properties，the research work on the preparation of MoO₃to obtain the nanometerproduct which has different morphologies and well dispersed particles will besignificant in exerting its good properties.In this thesis，sodium molybdate and secondary ammonium molybdate were usedrespectively as starting reagents to form MoO₃sol by ion exchange method，then thenanometer MoO₃was synthesized from MoO₃sol by ultrasonic method andhydrothermal method respectively.The samples were characterized by methods ofX-ray diffraction （XRD），scanning electron microscope （SEM） and X-ray energyspectrum （EDS）；the influences of the preparation parameters on the crystallinity，purityand the morphology of the products were investigated，which include the density of thestarting materials, the treatment time in ultrasound field, calcination temperature，thetemperature and time for hydrothermal reaction. The main research results are asfollows:Using sodium molybdate as starting reagents，the ion exchange method wasapplied to prepare the stable MoO₃sol，from which the MoO₃nanobelts weresynthesized in ultrasonic field with no catalyst or template，and the optimal parametersare as follows：0.3mol/L for concentration of the reactant，180min for the treatmenttime in ultrasonic field and400℃for calcination temperature；in addition the MoO₃nanobelts were synthesized from the MoO₃sol by hydrothermal method withtemperature of220℃and reaction time of12h；Then the principle for the preparation of the namometer MoO₃by hydrothermal method was discussed.Using ammonium molybdate as starting reagents, the hexagonal MoO₃nanorodswere synthesized via the ultrasonic method from the MoO₃sol, the optimal preparationparameters being0.05mol/L for concentration of the reactant and400℃for calcinationtemperature；Similarly, the MoO₃nanobelts were prepared from the MoO₃sol in aself-made reactor.The results show that in the process of preparing nanometer MoO₃，change in thereactant concentration results in the change of the specific surface area and surface freeenergy of the particles，which have influences on the size and dispersion condition ofthe product；the calcination temperature has influence on the crystal structure and themorphology of the product; the cavitation effect produced by the ultrasonic wave canlower the surface free energy of the particle，and the microjet and shockwave producedby the ultrasonic wave can break the as formed aggregates，hence the agglomeration ofparticles during the preparation of nano material can be solved effetively.