Effect of Zinc Ions Doping on High Near-infrared (NIR) Reflectance Black Pigments of Ca2MnO4

Near-infrared (NIR) reflective pigments have attracted increasing attention in environmental research due to their potential to reduce building energy consumption. In this study, Zn-doped Ca 2 MnO 4 black pigments were synthesized to enhance both NIR reflectance and color performance. The effects of Zn doping on the crystal structure and optical properties were systematically investigated using X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and UV-Vis-NIR diffuse reflectance spectroscopy. The optimal composition, Ca 2 Mn 0.96 Zn 0.04 O 4 , exhibited excellent optical characteristics (L*= 40.43, a* = 0.53, b* = 0.10) and a high NIR solar reflectance of approximately 66%. Compared to conventional dark high-reflectance pigments (e.g., Black-10G996), the Zn-doped sample showed significantly improved NIR reflectance (△R* ≥ 20%) and enhanced chromatic properties. The NIR reflectance enhancement was attributed to an increased concentration of oxygen vacancy introduced by Zn doping. Furthermore, thermal simulation experiments under xenon lamp irradiation demonstrated that a model room using Ca 2 Mn 0.96 Zn 0.04 O 4 as the roofing material maintained a temperature 6.5 °C lower than one using a commercial pigment, indicating superior thermal management capability. In addition, the Zn-doped pigments exhibited lower toxicity, offering an environmentally friendly alternative to traditional black pigments.