Facile microwave-assisted synthesis of Cr2O3 nanoparticles with high near-infrared reflection for roof-top cooling applications

摘要： Microwave-assisted solution synthesis was employed for the preparation of Cr2O3 nanoparticles using Cr(acac)3 and ethylene glycol. The optimum conditions for the completion of the reaction forming a green precipitate (yield-95%) were: irradiation for 40e60 min at 220 (cid:1)C solution temperature. The as-prepared sample was barely crystalline; annealing in air at above 300 (cid:1)C formed nanocrystalline Cr2O3, as shown by X-ray diffraction (XRD). High-resolution transmission electron microscopy (HRTEM) of the “700 (cid:1)C sample” con?rmed the well-crystallised Cr2O3 formation with ~37 nm average size. The as-prepared powder (bluish-green) showed high near-infrared (NIR) re?ectance, whereas the annealed samples showed bright-green re?ectance, whose International Commission on Illumination L*a*b* (CIE L*a*b*) values shifted towards the green region. The higher Dq/B value (3.76), suggested that Cr3t lies in a strong crystal ?eld. Stainless steel blocks covered with the as-prepared (intermediate) material reduced heating under sunlight by 5 (cid:1)C, indicating its suitability as an easily prepared tile coating for roof-top applications. The annealed samples are found suitable as an anti-dazzling coating for automobile windscreens and rear-view mirrors.