Interfacial Transformation and Durability of Graphitic Carbon Nitride Photocatalytic Coatings Consolidated by a Siloxane Binder

Graphitic carbon nitride (GCN) is an attractive metal-free photocatalyst; however, its application in immobilized form is often limited by insufficient mechanical stability and poor adhesion of catalyst layers. Here, we report the fabrication and surface-science investigation of durable photocatalytic coatings composed of submicron GCN flakes consolidated by an oligomeric siloxane binder undergoing in-situ mineralization under UV irradiation. The photocatalytic activity of GCN induces oxidative transformation of the siloxane binder into an amorphous silica-like network, leading to pronounced changes in surface chemistry, wettability, and coating cohesion. The interfacial transformation of the binder and its impact on coating properties are elucidated using X-ray photoelectron spectroscopy, infrared spectroscopy, contact-angle measurements, and electron microscopy. Mechanochemical wet milling enables the preparation of submicron GCN flakes suitable for uniform coating formation while preserving their crystalline structure. A systematic optimization of the catalyst-to-binder ratio reveals a balance between coating porosity, mechanical durability, and photocatalytic performance. The optimized coatings exhibit stable and reproducible photocatalytic activity during repeated degradation of model organic pollutants and pharmaceutical contaminants. Their durability is further demonstrated under high hydrodynamic stress in a slit-type photomicroreactor. The results provide insight into interfacial mineralization processes in hybrid photocatalytic coatings and demonstrate a surface-engineered strategy for producing mechanically robust and functionally efficient GCN-based photocatalytic surfaces.