BiVO₄-TiO₂Composite-Based Zinc Phosphate Coating for High NIR Reflectance and Sustainable Energy-Saving Applications

A near-infrared (NIR) reflective BiVO4-TiO2 composite pigment was synthesized using a combined precipitation-sol-gel process and successfully assimilated to a zinc phosphate conversion coating on a hot-dip zinc-coated steel sheet. The combination of BiVO4 with TiO2 resulted in reducing crystallite size and band gap, which improved the NIR reflectance. The BiVO4-TiO2 composite-based zinc phosphate coating presented a compact hierarchical structure with a high degree of crystalline coverage. The coating with enhanced yellow coloration exhibited good NIR solar reflectance (80.72%) with long-term NIR reflectivity and thermal durability. The composite-based zinc phosphate coating presented excellent corrosion resistance to the hot-dip coated mild steel with high charge transfer resistance (90.86 kω cm2) and low corrosion current density (0.33 μA/cm2). The coating presented high durability during aggressive salt spray exposure and bend tests. The present coating formulation has a high potential for energy-saving applications in automobiles and buildings to reduce heat buildup.