Photocatalytic Functional Coatings at a Turning Point: From High-Activity Materials to Service-Ready Surfaces
Photocatalytic functional coatings are at a pivotal juncture where the primary research focus must transition from intrinsic material activity to a unified framework centered on surface serviceability. Surface serviceability encompasses the ability of a coating to maintain catalytic activity, interfacial integrity, multifunctional performance, safety, and manufacturability under specific service environments over its operational lifetime. Over the past three decades, photocatalytic surfaces have demonstrated potential for degrading organic pollutants, maintaining surface cleanliness, and enabling air purification, with applications in buildings, glass, highways, and infrastructure. However, high intrinsic activity alone does not guarantee stable long-term performance when the photocatalyst is immobilized as a substrate-integrated film. Performance is governed by coupled factors including interfacial adhesion, film structure, environmental aging, and functional durability. Current challenges extend beyond catalytic activity to include long-term deactivation, coating-substrate interfacial stability, trade-offs among multiple functions, adequacy of evaluation methods, and scalability of fabrication. These issues form a progressive service chain: design determines catalyst exposure and adhesion; environmental stresses induce functional or structural failure; multifunctional integration may compromise one function for another. Therefore, application-oriented evaluation is essential. This perspective advocates for a paradigm shift toward service-oriented design, requiring establishment of service-relevant evaluation protocols and development of scalable, repairable fabrication routes. Such efforts will enable photocatalytic coatings to evolve from high-activity laboratory materials into engineering surfaces that are verifiable, comparable, manufacturable, and durable in real-world applications.