Controllable Synthesis Of WO3·0.33H₂O Nanonetwork And Investigation Of Their Enhanced Properties

Based on the special physical and chemical properties, nanomateials have wideapplications in the areas as new energy, biomedicine, information technology,environmental protection, which is showing some great advantages. Tungsten trioxide（WO₃） is a kind of semiconductor with great importance. It has attracted broad attentiondue to its wide-ranging applications in photocatalysts, electrochromic devices, gassensors etc. Researches have demonstrated that the property of materials is profoundlydependent on their morphologies. It is important to transform the structures andmorphologies purposely, characterize the transformation process and investigate theinfluence of the transformation to the properties. Therefore, it is valuable synthesizingdifferent nanostructures of WO₃（hydrate） and investigating their properties. The maincontents of our work can be summarized as follows:1. WO₃·0.33H₂O with numerous morphologies like nanowire/rod, flake, networkand pompon were synthesized by an induced hydrothermal method. Experiment showedthat the effect of diverse salt on the morphology of the product was gigantic different.The as-synthesized products were characterized by XRD and SEM to analyze theirphase and structure. According to the experiment results, a possible inducingmechanism concerning electrostatic adsorption was proposed: cations may selectivelyadsorb onto the facets of the nanocrystal and restrain the growth of these planes.Meanwhile, anions tend to adsorb onto the crystal facets perpendicular to those factesadsorbed by cations and at the same time lower the growth rate of these facets.Furthermore, ions with higher valence state may have stronger adsorption capabilitiesonto the crystal facets, which would more efficiently restrain the growth of these crystalfacets. In addition, novel WO₃·0.33H₂O networks were synthesized by controlling pHvalue of the reaction system with the assistance of Na2SO4. Besides the ionicinducement, analysis indicated that the etching effect of HNO3also contributed a lot inthe growth process of the network squares.2. WO₃·0.33H₂O nanonetworks and nanoplates have been prepared in the presenceof CaCl2and Na2SO4respectively. To explore the photocatalysis originated fromnanonetwork hierarchical structure, the photodegradation of methylene blue was carriedout under simulated sunlight irradiation. The photocatalytic activity of theWO₃·0.33H₂O nanonetworks was compared with that of the nanoplates, and the former showed a higher photocatalytic activity. The results may be owing to its novelhierarchical structure, which possesses higher specific surface area and can promotesunlight absorption. On the other hand, the unique hierarchical structure can increasethe reaction active site in the solution and provide microchannels for reactant andproduct diffusion, which is benificial to the degration of dye.3. The WO₃·0.33H₂O nanonetworks were used as the3D frame for loading Ptnanoparticles and electrocatalytic properties of the Pt/WO₃·0.33H₂O composites for themethanol and ethanol oxidation were investigated. To prove the superiority ofnetwork-structure, Pt/WO₃·0.33H₂O （rod） and Pt/C have been introduced to inveistigatetheir electrocatalytic properties toward methanol and ethanol oxidation. XRD, FESEMand TEM were employed to characterize the sample. Electrocatalytic activity foreletrooxidation of methanol and ethanol were studied by cyclic voltammetry,chronoamperometry, linear scan voltammetry curves, electrochemical impedancespectroscopy and Tafel plots. The electrochemical studies reveal that thePt/WO₃·0.33H₂O network-shaped catalyst shows much higher electrocatalytic activitythan that of the other two electrocatalysts as a result of its specific morphology thatprovides multidimensional active sites and decrease CO poisoning of Pt catalyst.4. Ag2O/WO₃·0.33H₂O heterostructures composite were prepared with differentmolar ratio of WO₃·0.33H₂O to Ag₂O via a simple chemical precipitatation method.FESEM showed that Ag₂O nanoparticles were distributed uniformly in theWO₃·0.33H₂O networks. To explore the photocatalysis of the heterostructures, thephotodegradation of methylene blue was carried out under simulated sunlight irradiation.Photocatalytic activity was enhanced by loading Ag₂O nanoparticles on theWO₃·0.33H₂O networks and the optimum molar ratio of WO₃·0.33H₂O to Ag₂O is1:2.Then the photocatalysis decreased with the excessive amount of Ag2O, which may beattributed to the recombination of electrons form WO₃·0.33H₂O and holes from Ag2O.The Ag2O/WO₃·0.33H₂O heterostructures composite exhitited excellent photocatalyticactivity and stability by recycle four times.