Citric acid-induced hydrothermal synthesis of cesium tungsten bronze (CTO, Cs0.33WO3).
According to the chemical formula of CsxWO3 (0 < x < 0.33), the valence state of tungsten in the CsxWO3 system is in a reduced state, and with the increase of cesium ions, the number of low-valent tungsten ions increases, which shows that a certain reducing atmosphere is required for the synthesis of CsxWO3, and As the doping amount of cesium ions increases, the requirement for the reducibility of the reducing atmosphere becomes higher. In the citric acid-induced hydrothermal synthesis method, citric acid and ethanol are used as reducing agents. The carboxyl or hydroxyl groups in citric acid and ethanol can be oxidized to carbon dioxide or carboxyl at higher temperature and pressure, and W6+ is reduced to W4+ at the same time. Or W5+, cesium ions doped into the tungsten bronze structure to generate CsxWO3. Specific steps are as follows:
- Preparation of CsxWO3 powder
(1) Using analytically pure sodium tungstate Na2WO4•2H2O as raw material, prepare a sodium tungstate solution with a concentration of 0.5 mol/L.
(2) To obtain tungstic acid sol by cationic resin exchange, add citric acid (analytical pure) solution with a concentration of 1 mol/L or 2 mol/L and cesium carbonate Cs2WO3 (analytical pure) solution with a concentration of 0.3 mol/L, and stir Uniformly, the precursor liquid of hydrothermal reaction is obtained.
(3) Put the precursor solution in an autoclave, react at 190 °C for 3 days, and then wash with ultrasonic water, wash with alcohol, centrifuge, and dry to obtain CsxWO3 powder.
- Preparation of CsxWO3 thin film
After fully grinding the CsxWO3 powder, ultrasonically disperse it in a citric acid solution for 1 h, then add it to a 0.1 g/mL polyvinyl alcohol (PVA) solution, stir in a water bath at 80 °C for 30 min, and age for 1 d to obtain a film to be coated Latex, CsxWO3 films were prepared on glass slides by the dip-pull method.
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