Synthesis and properties of high near-infrared reflectance BaZn1−xNixSiO4 purple pigments

Abstract

The rapid urbanization has intensified the urban heat island (UHI) effect, increasing cooling energy demand and greenhouse gas emissions, posing a challenge for sustainable, low-carbon development. Cool pigment coatings with high near-infrared (NIR) reflectance offer great potential to mitigate this effect. In this study, a novel purple pigment BaZn_1-xNi_xSiO₄ with high NIR reflectance was synthesized using a high-temperature solid-state method. The as-synthesized BaZn_1-xNi_xSiO₄ solid solution belongs to the P6₃ space group. XPS analysis confirmes that the oxidation state of Ni is +2. The purple color of the solid solution is due to the ³T₁(³F)→³T₁(³P) and ³T₁(³F)→³A₂(³F) transition of Ni²⁺ in the tetrahedral sites. First-principles calculations investigate the effects of Ni doping on the electronic structure and color of BaZnSiO₄, revealing that the introduced states reduce the band gap and result in a purple pigment. Due to the excellent near-infrared solar reflectance (74.8 %) of the pigment, purple coatings with improved solar reflectance were prepared. Moreover, the pigment was successfully introduced into superhydrophobic polymer to fabricate a multifunctional coating, providing a promising candidate with both high solar reflectance and self-clean properties.