Research On Preparation And Properties Of ZnWO₄Nanocrystallites Prepared With A Microwave Hydrothermal Process

The Wolframite Zinc tungstate is a kind of optical material, belongs to themonoclinic structure. They are widely used as scintillation materials,photoluminescence and catalyzer. In this paper, the ZnWO4nanorods can beprepared by a microwave hydrothermal method in the low temperature. On thisbasis, we also developed a complexing microwave hydrothermal method toprepare the six petal flat flower-like ZnWO4and flower-like ZnWO4, whichadopted the complexing agent to complexing reactions in the microwavehydrothermal process. And, using template assisted microwave hydrothermalmethod to prepare PVA-ZnWO4composite nanocrystallites. The products werecharacterized by X-ray diffraction analysis (XRD), scanning electron microscope(SEM), transmission electron microscopy (TEM) and photolumicescencespectroscopy (PL), infrared spectroscopy (FT-IR), UV-visible spectrum (UV-Vis),and the test of photocatalysis.The ZnWO4nanorods were prepared by a facile, template-free microwavehydrothermal method using Na2WO4·2H2O and Zn(COOCH3)2·2H2O as startmaterials, and investigated effect technological factors on synthesis of ZnWO4nanorods, including time, temperature, and pH. Results indicate that ZnWO4nanorods have a preferential orientation growth along the direction of [100]. Thediameter is about20nm, and the length is60nm-80nm. An intense blue PLemission with a460nm wavelength is observed when the as-prepared ZnWO4nanorods are excited by a295nm wavelength, and they show a strong absorptionin the ultraviolet region. The band gap of ZnWO4nanorods is3.6-3.9eV, thedifferent photocatalysis of the ZnWO4nanorods are caused by the differentroutes.On the basis of microwave hydrothermal method, the six petal flatflower-like ZnWO4and flower-like ZnWO4can be prepared by complexing microwave hydrothermal method, using Zn(COOCH3)2and ZnSO4as the zincsource and Na2WO4as the tungsten source, and CTAB were used as thecomplexing agent. ZnWO4can be prepared by Zn(COOCH3)2and ZnSO4as thezinc source, whatever with or without CTAB, the size of ZnWO4is3-5μm.Using Zn(COOCH3)2as zinc source, if without CTAB, the sample is sphericalZnWO4; if with CTAB, the sample is the six petal flat flower-like ZnWO4. UsingZnSO4as zinc source, whatever with or without CTAB, the both of the samplesare flower-like ZnWO4.PVA-ZnWO4composite nanocrystallites can be prepared by the templateassisted microwave hydrothermal method, and the zinc source wasZn(COOCH3)2, the tungsten source was Na2WO4, and PVA were used as thetemplate. Results indicate that the length of PVA-ZnWO4composite nano-crystallites is30-40nm，the width of ZnWO4nanocrystallites is10-20nm, andthe sample grows along the direction of [001], and has photocatalysis. PVA-ZnWO4composite nanocrystallites are prepared in the condition of Zn2+: WO2-4:PVA (mol)=1:1:1, the both of the concentration of Zn2+and WO2-4are0.2mol/L,which have the best photocatalysis, when the time of photocatalysis is15min,the photocatalysis degradation rate of RhB could reach70%.