Freeze Drying-Assisted Synthesis And Characterization Of ZnO-based Nanomaterials

Nanosized ZnO with wide band gap(＞3.2eV),high exciton bound engry(60meV)and low threshold value voltage,which makes it the most attracting material in the following fields of UV laser and vacuum fluorescent display field.In the past several decades,the optical properties of nanoscale ZnO have already been researched deeply and extensively.As a special drying method,freeze drying technique posseses the ability to synthesize multicomponent polycrystalline powders with controlled characteristics and less agglomeration.Precipitation method was adopted in this paper,the precursor was dried using freeze drying and common drying,ZnO nanopowder was obtained by calcining the precursor at different temperature(400℃-600℃).The product was characterized through X-Ray diffraction(XRD)and Fourier transformation infrared ray(FT-IR)techniques and so on.The results indicated that:all products are hexagonal wurtzite structure,freeze drying synthesis can lead to less agglomeration of product.Furthermore,we also studied the Ultralviolet-visible(UV-vis)spectra and Photoluminescence (PL)spectra of products at room temperature.Freeze drying process was employed to prepare SnO₂/ZnO nanomaterials with the molar ratio of Sn/Zn=0.5,1 and 2.The phase and crystal size of the as-prepared nanomaterial would change with different thermal temperature and Sn/Zn molar ratio.The UV-vis spectras of products have been investigated,the band gap energy of SnO₂/ZnO nanomaterials are smaller than pure ZnO,indicating that SnO₂/ZnO nanomaterials could enhance the photocatalysis activity of ZnO.Co-doped ZnO nanomaterials have been synthesized by precipitation method and freeze drying technique from Zinc acetate (Zn(CH₃COO)₂·2H₂O)and Cobalt acetate(Co(CH₃COO)₂·2H₂O).When the Co doping concentration is below 6mol%,there was no other phase. Effects of different doping concentration of Co on the crystal size and the energy band gap of the nanomaterial were primarily investigated.The energy band gap of the Co-doped ZnO nanomaterial decreased by increasing the doping concentration of Co.