Towards net-zero architecture: Functional coatings from fly ash waste for energy-efficient and hygienic building surfaces

This study reports the development of a sustainable polymeric coating system utilizing fly ash as a raw ingredient, contributing to circular economy goals in the built environment. Hollow ceramic microcores (HCMs) composed of mullite were synthesized from processed fly ash and subsequently functionalised with titanium dioxide (TiO 2 ) to form HCM@TiO 2 core-shell structures. These were embedded into a polyurethane (PU) matrix at an optimal loading of 4 wt% to create a high-performance composite coating. Comprehensive evaluation of the coating's surface, mechanical and biological properties was conducted using Taber abrasion, nanoindentation, electrochemical impedance spectroscopy and microbial assays. The modified coating demonstrated significant improvements in antimicrobial efficacy, demonstrating up to 90 % and 98 % reduction in bacterial and algal growth, respectively, alongside enhanced wear resistance and creep stability. A notable hydrophobic surface transition was also observed (contact angle: 105.8 ± 2°), supporting improved durability in moisture-prone environments. The advanced multifunctionality of this coating system highlights its potential for deployment on building surfaces, infrastructure, and marine structures where resistance to microbial contamination and mechanical degradation is critical. • Fly ash waste was upcycled into core–shell fillers for multifunctional building coatings. • The new coating kills 90 % bacteria and 98 % algae, boosting surface hygiene. • Enhanced hardness, creep resistance, and hydrophobicity (contact angle ∼105.8°. • High corrosion resistance confirmed by impedance ∼6.3 × 10 7 Ω cm 2 . • Supports circular economy and net-zero goals in building applications.