Solution Synthesis Of Transition Metal Tungstate(Molybdate) And Their Catalytic Properties

Recently, tungstate and molybdate materials have attracted increasing attention in catalysis, sensor, electrochemical energy storage and optical materials, because of their good chemical activity and similar crystal structure. To date, synthesis methods for tungstate and molybdate need harsh conditions, commonly requiring high temperature solid state and sol-gel process. Development new method for tungstate and molybdate is of great important for the investigation on relationship between structure and property. This dissertation foucused on the solution synthesis of tungstate and molybdate and probed the relationship between structure and property in these systems.1. Three types of CoWO4 with different morphologies(i.e. nanoplates, nanorods and nano cuboids) were synthesized by one-step solvothermal method. The structure, composition and morphology were determined by various characterizations. Their performances for electrocatalytic oxygen evolution reaction(OER) were tested in alkaline medium. We found that CoWO4 nanoplates exhibited small overpotential, large catalytic current and excellent stability. When the current density reached 10 mA cm-2, the CoWO4 nanoplates yielded the overpotential of 436 mV compared with other CoWO4 nanostructures. Based on the results of the X-ray diffraction(XRD), X-ray photoelectron spectroscopy(XPS) and Raman spectroscopy for the CoWO4 before and after OER, we proposed the possible mechanism of the CoWO4 for catalyzing OER. The CoWO4 nanoplates underwent in situ electrochemical transformation on structure and composition, which may be related to amorphous feature of the CoWO4 nanoplates.2. The MMoO4·nH2O(M = Co, Ni) nanorods with similar morphology were synthesized by a hydrothermal method. Their structure, compostion and morphology were characterized systematically. The performances of MMoO4·nH2O for electrocatalytic oxygen evolution reaction(OER) in 0.1 M KOH solution were studied. Compared with NiMoO4·nH2O, CoMoO4·nH2O afforded small onset potential, small overpotential and long-time stability. By means of XRD and XPS analysis on CoMoO4·nH2O before and after OER and combining a series of electrochemical tests, we attributed the high OER activity of CoMoO4·nH2O to the much more active sites than that of NiMoO4·nH2O.3. The hierarchical structured FeWO4 were synthesized by a solvothermal method, which presented highly efficient peroxidase-like catalytic activity(i.e. peroxidase mimetic activity). In the presence of H2O2, FeWO4 can catalyze 3,3’5,5’-tetramethylbenzidine dihydrochloride(TMB) and o-phenylenediamine(OPD) to produce color reactions. Based on this property, the colorimetric detection method for H2O2 and glucose was established. This method is simple, low cost, high sensitivity activity, exhibiting a wide linear range and low detection limits for H2O2 and glucose.