Highly solar-reflective calcium phosphate biomaterials through wet chemical precipitation

Calcium phosphate compounds are critical to an expansive collection of applications within the medical field. In addition, calcium phosphates have been recently exemplified as strong candidates for solar reflective materials, supporting the realization of future sustainability goals. In any of these valuable use cases, an accurate understanding of the composition, morphology, and optical properties is critical to design calcium phosphate materials for target applications. In this work, we present compositional and morphological characterizations for a wide variety of calcium phosphate compounds synthesized through varying the parameters of a wet chemical synthesis method. The influence of reactant pH, reaction temperature, and calcination temperature choices are discussed with respect to the resulting microscale and nanoscale feature sizes as well as the abundance of different calcium phosphate phases. Further, the synthesized calcium phosphates are exemplified as high-performance broadband solar reflectance materials, with normalized reflectance values ranging from 0.93 to 0.98. This feature is enabled by the synergy between their optical properties and morphologies, which produces an efficient dispersion of scattering behaviors throughout the entire solar wavelength regime. The influence of the chosen synthesis parameters on reflectance performance is discussed in detail. This provides key takeaways for sustainable applications, especially the development of passive radiative cooling coatings and paints.