Solution-Based Chemical Synthesis And Magnetic Properties Of Tungstate Functional Nanomaterials

In this dissertation,soft solution-based routes were developed to synthesize functional metal tungstate nanomaterials which contain magnetic ions such as Mn²⁺ and Fe²⁺ and their magnetic properties were studied.It was found that the magnetic properties of such hierarchically assembled MnWO₄ and FeWO₄ architectures were different from their corresponding bulk materials,which may give us the chance to realize the application of such sample on magnetic nano device.The photocatalytic property of hierarchically assembled FeWO₄ microcrystals have been firstly studied, therefore it is an effective method to develop a novel environment friendly material which is anti-acid and anti-alkali.In addition,the discharge ability of Co₉S₈ hollow microspheres as Li battery cathode materials and their magnetic property as well as their catalytic property in electrocatalysis of Oxygen Reduction Reaction(ORR) were also studied.The main results can be summarized as follows.1.Three dimensional(3D) urchin-like MnWO₄ microspheres assembled by nanorods have been fabricated by a cationic surfactant cetyltrimethyl ammonium bromide(CTAB) assisted hydrothermal method.The results indicated that CTAB played an important role as a soft template in directing growth and self-assembly of urchin-like MnWO₄ microspheres.In addition,suitable pH values and reaction temperature are also essential for the formation of urchin-like microspheres.Magnetic measurement indicates that urchin-like MnWO₄ microspheres show a weak ferromagnetic ordering at low temperature due to spin-canting and surface spins of microspheres,while much shorter MnWO₄ nanorods show antiferromagnetism at low temperature.2.Highly hierarchical plate-like FeWO₄ microcrystals have been synthesized by a simple solvothermal route,where ethylene glycol(EG) plays an important role as a capping agent in directing growth and self-assemble of such unique structures.In addition,a certain amount of NaAc was necessary for the formation of such unique FeWO₄ microstructures.The photocatalytic property of as-synthesized hierarchical FeWO₄ microcrystals has been firstly studied,which shows excellent photocatalytic activity for degradation of rhodamine-B(RhB) under UV and visible light irradiation (modeling sunlight).Moreover,magnetic measurement indicates that hexangular FeWO₄ plate-like microcrystals show a small ferromagnetic ordering at low temperature due to spin-canting of antiferromagnetic materials and surface spins of FeWO₄ nanoparticles.3.Highly hierarchical hollow Co₉S₈ microspheres have been synthesized by a simple solvothermal route,the morphology characterization of products obtained by different reaction time shows that the formation process of such hollow architecture was according to Ostwald Ripening mechanism,and appropriate volume ratio of triethylenetetramine(TETA) and H₂O is necessary to precipitation of hollow Co₉S₈ microspheres.Firstly,the discharge ability of such sample as Li batteries cathode materials and their catalytic property in electrocatalysis of Oxygen Reduction Reaction(ORR) was studied and analyzed,it was found that the discharge capacity of hollow Co₉S₈ microspheres at the initial discharge stage of Li battery cathode materials is higher than nanosized Co₉S₈ particles,then the RDE measurement shows that the reversible potential of Co₉S₈ hollow microspheres is approaching to the calculated value by theory simulation which validated the accordance between experiment and theory of reversible eversible potential of Co₉S₈ sulfide.In addition, the magnetic properties of Co₉S₈ hollow microspheres were also studied and it shows that the main magnetic properties of sample is paramagnetic and the sample also contains anti-ferromagnetic properties.