Efficient Self‐Cleaning and Anti‐Bacterial Behavior Realized by Hierarchical Structure in Hybrid Waterborne Polyurethane Coatings Containing Photocatalyst

ABSTRACT Waterborne polyurethane (WPU) hybrid coatings with a hierarchical structure show efficient self‐cleaning and anti‐bacterial properties. The hierarchical structure is constructed by combining directional freezing polymerization, the addition of carbon nitride (g‐C ₃ N ₄ ) nanosheets, thermoplastic molding, and acid treatment. The WPU hybrid coatings feature numerous papillae structures on the micrometer scale, derived from WPU, and a tubular structure on the nanometer scale, originating from the g‐C ₃ N ₄ nanosheets. This hierarchical structure considerably increases the specific surface area and generates more photocatalytic sites. After 1 h of visible light exposure, over 90% of the methylene blue (MB) is efficiently degraded. For common daily stains, such as tomato juice, the photodegradation rate can also reach 66.6% after 1 h of visible‐light irradiation, which is 41.7% faster than that without a hierarchical structure. In addition, the WPU hybrid coatings with a hierarchical structure also exhibit good anti‐bacterial behavior due to the photogeneration of reactive oxygen species. Based on the more active sites for photocatalysis provided by the additional hierarchical structure, the coatings exhibit a 99.6% inactivation of S. aureus and a complete elimination of E. coli after 2 h of visible‐light exposure, rendering them very promising for indoor applications, particularly in furniture and automotive interiors.