Solvothermal Synthesis of Tungsten Bronze Compounds

Tungsten bronze compounds are a kind of important inorganic compounds. Tungsten ions in these compounds exist in the mixed valence states of W₆⁺, W₅⁺ and W₄⁺, so that the overall charge of the compounds is balanced. Rich crystal structure, tunneling structure and this special valence state make it have excellent properties, such as electronic and ionic conductivity, superconductivity, optical properties, etc. Its applications in secondary batteries, electrochromic, near infrared absorption and chemical sensors have attracted extensive research interest.

At present, the preparation of tungsten bronze compounds mainly uses wet chemical methods, thermal reduction methods and thermal decomposition methods. Until now, it is not possible to directly obtain pure phase ammonium tungsten bronze nanopowder. Therefore, the obtained micron-sized large particles are usually broken into small particles by ball milling, but such compounds are easily oxidized during ball milling. Inactivation and easy decomposition, accompanied by defects such as decreased crystallinity, so there is no way to directly obtain nano-ammonium tungsten bronze powder.

In view of the above problems existing in the existing technology, some scholars directly synthesized tungsten bronze nano-powder with controllable particle size by solvothermal method, which was carried out in the following steps:

(1)Dissolve 0.01-1g organic tungsten source in 20-40ml organic acid solution, stir to obtain uniform solution, then add 4-30ml organic amine, mix to uniform, move to the reactor, 150-350 ℃ crystallization reaction 0.5-48 hours, after reaction, centrifuge the powder sample, wash, and vacuum drying at 40-250 ℃ for 1-12 hours, that is, obtain powder sample.

The crystal structure and phase of the samples were analyzed by X-ray diffraction and SEM. The morphology and pore structure of the nanoparticles were observed. Under solvothermal conditions, ammonium tungsten bronze nanoparticles were synthesized in one step from organic tungsten source and organic high boiling amine using organic long chain high boiling acid as reaction medium in non-aqueous environment. The remarkable advantage of this method is that the synthesis steps are simple, the yield is high, the particle morphology is uniform, the crystallinity is good, the particle size distribution is narrow, the size is adjustable in a certain range, the chemical valence state is reduced, and the nano-powder is obtained directly without long high temperature process and subsequent ball milling process.

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