A facile method to synthesize small-sized and superior crystalline Cs0.32WO3 nanoparticles for transparent NIR shielding coatings

A simple one-step solvothermal route was developed to fabricate homogenous cesium tungsten bronze (Cs0.32WO3) nanoparticles, and an environmentally friendly aqueous solution was used to prepare transparent NIR shielding coatings. Based on the results, the addition of Cs+ ions promoted the formation of Cs2WOCl5 crystals, which inhibited the hydrolysis process of WCl6 and limited the formation of hexagonal tunnels. Controlled formation of hexagonal tunnels is favorable for Cs+ ions that completely enter the hexagonal vacant tunnels to form the Cs0.32WO3 crystals. Via a controllable formation process, the superior crystalline Cs0.32WO3 nanoparticles with the primary particle size of 30–60 nm were synthesized at the low temperature of 200 °C and short time of 4 h without any other additives. Furthermore, the Cs0.32WO3 nanoparticles were well dispersed in the aqueous solution, and the as-prepared coating exhibited a high SETS value (0.72), which remained constant with an increase in the film thickness. Simulated solar irradiation experiments revealed that the as-prepared film cut off over about 91.6% of radiation. The simulated model of the real environment revealed that compared with the ordinary glass and commercial Cs0.32WO3, the as-prepared Cs0.32WO3 film showed superior NIR shielding performance for practical application.