UNUSUAL REACTIVITY OF METAL OXIDES WITH AQUEOUS VANADYL IONS: A PROMISING METHOD FOR THE SYNTHESIS OF TERNARY METAL VANADIUM OXIDES

Abstract

Abstract: Unusual reactivity of aqueous vanadyl sulfate solutions towards a wide variety of metal oxides was discovered. The reaction of solid La2O3 with a refluxing aqueous solution of VOSO4 results in the incorporation of vanadium into the solid that is accompanied by the release of lanthanum ions into solution. With excess VOSO4, the reaction produces the mineral duttonite, VO(OH)2 and aqueous lanthanum sulfate. With lower ratios of VOSO4 to La2O3, hydrated bimetallic phases are formed. For example, the reaction of 0.5 molar equivalent of VO2+ per lanthanum ion in La2O3 produced a product with the approximate formula of La0.36VO0.64O1.18(OH)1.28 (H2O)0.42. There are no stable phases for lanthanum vanadium oxides with a ratio of lanthanum to vanadium larger than one (i.e., LaVO4), so dehydroxylation and dehydration of this solid at 600˚C produced a phase separated LaVO4/V2O5 composite. Pure LaVO4 could be produced using a proper choice of reactant ratios. It was determined that this novel reaction also occurs between vanadyl sulfate and Y2O3, AlOOH, Al2O3, Fe2O3, NiO, and ZrO2. The synthesis of a desired metal vandium oxide phase requires a judicious choice of reactant but it is possible to achieve the synthesis of specific phases. It is also possible to produce metal vanadate/vanadium pentoxide composites that have promising applications as catalysts. Furthermore, the V2O5 can easily be washed from composite using aqueous sodium or potassium hydroxide to yield nanocrystals or crystals of pure metal vanadium oxides. Overall, the research reported in this dissertation has developed a novel, extremely promising, method for the preparation of metal vanadates, metal vanadate/metal oxide composites, and metal vanadate/V2O5 composites, VO(OH)2 and V2O4(OH2)2 that can be employed in a myriad of areas in chemistry. This novel synthetic pathway for ternary vanadium oxides is expected to be helpful for the preparation of catalysts, sensors, and phosphors.