Photocatalytic and mechanical performance of Ag/ZnO geopolymer composite coatings

Abstract

Coatings support sustainability by prolonging the service life of civil infrastructure. Fly ash geopolymer coatings are recognized for their low carbon footprint and industrial by-product utilization, serving as sustainable alternatives to conventional coatings. In this study, fly ash geopolymer coatings incorporating different Ag/ZnO loadings (0, 5, and 10 wt.%) were prepared and spray-applied onto mortar substrates. The geopolymer coatings with different additions of Ag/ZnO were investigated for their adhesion strength, microstructure, and photocatalytic activity. The apparent degradation of methylene blue (MB) was evaluated by immersing the coated specimens in MB solution under direct natural sunlight. The addition of Ag/ZnO enhanced both mechanical and photocatalytic performance. Notably, the 5 wt.% Ag/ZnO coating achieved the highest adhesion strength (0.95 MPa after 28 days of curing) and the greatest apparent MB removal efficiency (75%), whereas overloading at 10 wt.% caused particle agglomeration and performance deterioration. Consequently, 5 wt.% Ag/ZnO is identified as the optimal formulation, offering an ideal balance between mechanical stability and photocatalytic activity for protective and sustainable self-cleaning infrastructure coatings.