A facile method to synthesize small-sized and superior crystalline CsWO nanoparticles for transparent NIR shielding coatings

A simple one-step solvothermal route was developed to fabricate homogenous cesium tungsten bronze (Cs 0.32 WO 3 ) 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 Cs 2 WOCl 5 crystals, which inhibited the hydrolysis process of WCl 6 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 Cs 0.32 WO 3 crystals. Via a controllable formation process, the superior crystalline Cs 0.32 WO 3 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 Cs 0.32 WO 3 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 Cs 0.32 WO 3 , the as-prepared Cs 0.32 WO 3 film showed superior NIR shielding performance for practical application. Small-sized and superior crystalline Cs 0.32 WO 3 nanoparticles used for NIR-shielding were developed by tailoring the molar ratio of Cs/W.