Preparation of hollow glass microspheres@ZnS x Se1− x or copper-/indium-co-doped ZnS x Se1− x composite color pigments with enhanced near-infrared reflectance

To improve the near-infrared (NIR) solar reflectance of ZnS_xSe_1−x or copper-/indium-co-doped ZnS_xSe_1−x (ZnS_xSe_1−x:Cu/In) pigment with various colors, hollow glass microspheres (HGMs)@ZnS_xSe_1−x or ZnS_xSe_1−x:Cu/In composite pigments with a litchis-like core-shell structure were prepared with HGMs dispersed and surface-corroded in an alkali-solution under ultrasound and ZnS_xSe_1−x or ZnS_xSe_1−x:Cu/In particles deposited on HGMs surface via in-situ co-precipitation and subsequent sintering. The structure, particle size, morphology, color properties and thermal performance of the composite pigments were investigated by X-ray diffraction (XRD), Fourier transfer infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), laser diffraction particle size analysis, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), nitrogen gas adsorption method (BET), ultraviolet-visible-near-infrared (UV-VIS-NIR) spectroscopy and infrared irradiation image analysis. The results show that ultrasound can promote the corrosion of HGMs surface in alkali solution and form a mesh-pore structure, thus providing some heterogeneous nucleation sites on HGMs surface and favoring the nucleation of pigment precursors on HGMs surface in subsequent in-situ co-precipitation reaction. Compared to ZnS_xSe_1−x or ZnS_xSe_1−x:Cu/In pigments, HGMs@ZnS_xSe_1−x or ZnS_xSe_1−x:Cu/In composite pigments have a higher solar reflectance since the multiple layer reflections occur at the interface between the pigment particles and HGMs, thus leading to a better heat-reflective property. The NIR solar reflectance of HGMs@ZnS_xSe_1−x or ZnS_xSe_1−x:Cu/In composite pigments is 90.61 ± 0.052% or 73.13 ± 0.046%. The surface temperature of aluminum plate coated with HGMs@ZnS_xSe_1−x composite yellow pigment is 3.4 ± 0.2 °C or 9.6 ± 0.2 °C lower than that of aluminum plate coated or uncoated with ZnS_xSe_1−x pigment. This approach may shed a light on a promising composite structure design for high-performance solar reflective 'cool materials'.