Template-Mediated Engineering of Functional Metal–Phenolic Complex Coatings

The ability of polyphenols to complex a range of metals leads to a broad selection of functional, thin metal–phenolic network (MPN) coatings, which can be readily deposited onto surfaces (or templates) of diverse shapes, sizes, and compositions. These templates can be selectively dissolved to yield free-standing MPN films including capsules, which have various applications including drug delivery, antibiofouling, biomedical imaging, enzyme immobilization, catalysis, and heavy metal ion removal. Furthermore, MPN thin film coatings (~10 nm thickness) can be generated via a rapid process, whereby the polyphenols simultaneously adsorb and are crosslinked by a metal ion. This method is inexpensive, requires minimal energy input, and is environmentally sustainable when using plant-derived polyphenols such as tannic acid and gallic acid. The film thickness and other film properties can be tailored by modifying the assembly methods or using different assembly techniques. These assembly methods have emerged as robust, reproducible, and efficient for preparing MPNs. Herein, the various template-mediated assembly methods used to date to prepare MPNs, as well as their respective mechanisms and influence on properties are detailed. Finally, the potential for scale-up and the various engineering considerations required to facilitate high-volume preparation of MPNs are highlighted.