Synthesis of Lanthanum Tungstate Interconnecting Nanoparticles Using Ammonium Metatungstate

In the past few decades, nanostructured materials has gained more scientific interest owing to their distinctive physical and chemical properties. Lanthanum tungstate (La2(WO4)3) nanoparticles exhibits a monoclinic scheelite-like structure with a space group of C2/c. It has been widely applied in fields such as luminescence, photocatalysis and scintillators due to their unique optical and structural properties.

Lanthanum tungstate-based MPEC membranes as a type of CO2 resistant membranes have attracted great attention in the field of hydrogen separation, which possess protonic and electronic conductivities under H2-containing atmosphere at high temperatures. However its hydrogen permeation performance is limited. In order to enhance the hydrogen permeation flux through lanthanum tungstate membrane, the strategy of doping with metal ions is an effective approach to improve its protonic and electronic conductivities, such as Mo6+, Re7+ and Nb5+.

La2(WO4)3 nanoparticles have ever been synthesized by a combination of electrospinning and high temperature calcination. It is therefore for us to use a mixture of inorganic reagents dissolved in poly(vinyl alcohol) (PVA) to synthesize inorganic–polymeric fibrous composites, which would be transformed into interconnecting-nanoparticles’ fibers by subsequent high temperature calcination. Lanthanum tungstate interconnecting nanoparticles have been synthesized by ammonium metatungstate, The experimental procedures to prepare La2(WO4)3 interconnecting nanoparticles are as following steps:

Basing on the conventional sol–gel process, lanthanum nitrate hexahydrate (99.0% La(NO3)3·6H2O) and ammonium metatungstate hydrate (99.0% H26N6O40W12·H2O) with 2:3 molar ratio of La:W were dissolved in 10 ml of deionized (DI) water. The precursor solution was stirred for 10 min and mixed with 20 ml aqueous PVA (poly(vinyl alcohol), 72,000 MW) solution at a temperature of 70 °C with vigorous stirring. The mixture was electrospun by a 15 kV applied electric voltage. A dense web of PVA/La2(WO4)3 composite fibers was collected on a piece of copper plate placed 15 cm away from the needle tip and divided into several parts. To avoid the undesired oxidation process, each of the parts was then heated in an argon atmosphere (inert gas) at 450, 550, 650 and 750 °C for 3 h, and at 750 °C for 4 and 5 h.

In summary, Lanthanum tungstate interconnecting nanoparticles have been synthesized by ammonium metatungstate, The crystalline monoclinic La2(WO4)3 fibers with 200–700 nm in diameter. At 750 °C and 5 h calcination, the product was composed of nanoparticles joined together shaped like fibers with two main Raman peaks at 945 and 927 cm−1, FTIR stretching vibration modes at 936 and 847 cm−1, 2.02 eV energy gap, and 415–430 nm blue emission—one of the promising materials for different applications.

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