A black pigment that shows strong near-infrared reflectivity for solar heat control

Abstract

Solar thermal energy regulation is important for sustainable development, comfortable housing, and living. Black compounds are usually considered as an absorber of solar heat. This work reports a series of black near-infrared reflective pigments, Ca2-yMgyMn(1)1-xMn(2)xO4 (x = 0–1, y = 0–0.5), which show strong near-infrared (NIR) reflectivity. Comprehensive analyses were carried out to characterize the obtained pigments including X-ray diffraction, scanning electron microscopy, Raman spectroscopy, and UV–Vis–NIR spectrophotometry. Through the substitution of MnO2 with Mn2O3, NIR solar reflectance of the black pigment can be enhanced by 13%, which might be mainly attributed to differences in particle size and lattice parameters. Meanwhile, through Mg doping, the obtained pigment Ca1.8Mg0.2MnO4 shows excellent color performances (L* = 43, a* = 0.36, b* = −0.37) and NIR solar reflectance (R*, ∼60%). EnergyPlus simulation results show that for a warm city (Haikou), using the Ca1.8Mg0.2MnO4 coating (L* = 25, R* = 51%) can reduce annual cooling energy consumption by 21%.