Solvation enabled highly efficient gradient assembly creates robust metal-phenolic coatings

Metal-phenolic networks (MPNs) are supramolecular materials that have received interest in various fields, including biomedicine, separations, environmental remediation, and catalysis. Despite recent advances, the construction of thick and robust MPN coatings that withstand harsh conditions (e.g., acidic, alkaline) remains challenging. In addition, the interfacial assembly of MPNs in mixed solvents (e.g., water and nonaqueous solvents) has not been investigated. Herein, a solvent-regulated (water/ethylene glycol) gradient assembly strategy that can regulate the coordination kinetics of MPNs to realize thick (up to 1.5 μm) and robust MPN coatings on various substrates is presented. Through mediating interactions between polyphenols, a balance is achieved between the aggregation, precipitation, and continuous assembly of well-dispersed precursors. The gradient assembly of polyphenols and metal ions results in lateral and longitudinal cross-linking leading to the formation of robust MPN coatings. The potential application of the coatings in oil/water separation is demonstrated by their excellent performance (oil intrusion pressure of 2.0 kPa and water flux of 2.59 × 10⁵ L m^-2h^-1), long-term stability, tolerance to various harsh conditions, and thick oil fouling. This study provides further insight into the assembly mechanism of MPNs.