Site-Engineered Corundum-Structured Aesthetic Composites for Alleviating Heat Accumulation to Mitigate Urban Heat...

Urban heat islands have become a global issue, as they severely impact several key factors, including elevated energy consumption, increased air pollution and greenhouse gas emissions, compromised human health and comfort, and reduced water quality. This escalating issue has become a concern and requires strategic technology deployment to address the threat. In this view, the present work deals with the synthesis of corundum-structured and octahedral site-engineered Mg_{3- x}A_xTeO₆ (A = Fe, and Co; x = 0.05-0.25 wt.%) pigments with brilliant colors via a solution combustion route. The designed corundum-structured Mg_{3- x}A_xTeO₆ pigments exhibit an isostructural geometry with a centrosymmetric space group ( $\overline{R_3}$ ). The prepared pigments exhibit aesthetically pleasing and vibrant brown and purple hues through the engineering of site-specific (Mg/Fe/Co)O₆ octahedral positions within the corundum-structured Mg₃TeO₆ lattice. The colors of the pigments were manipulated (i.e., from absolute white to brown and purple colors) by integrating specific concentrations of transition-metal chromophores. The prepared best-performing Mg_2.85Fe_0.15TeO₆ and Mg_2.85Co_0.15TeO₆ pigments showcase their capability of delivering exceptional average reflectance properties in the near-infrared region (800-2500 nm) of ∼86%. The integration of transition-metal ions into corundum-structured Mg₃TeO₆ could effectively modulate its electronic structure through hybridization between O(p) and Fe(d)/Co(d) states, thereby enhancing the near-infrared reflectance of the pigments. The prepared pigments delivered a low thermal conductivity of about 0.06 and 0.08 W/m.K, which signifies their candidacy in cooling systems over traditional roofing materials. The cooling pigments demonstrated their stability against acid/alkali treatment, photo-resistivity, and thermal stability. The deficient electricity demand as compared to bare cement and TiO₂-mica pearlescent pigment coating was evidently witnessed when the prepared pigments were used as cool coatings in an energy simulation. All clarifies the suitability of pigments in real-time implementation.