Formation and characterization of tannic acid-based functional nanofilms

Abstract

Tannic acid (TA), a ubiquitous natural polyphenol, is and its derivatives make stable metal-organic coordination complex (MOC) with transition or lanthanide metal ions, especially Fe(Ⅲ), and the MOC nanofilms form rapidly upon mixing of Fe(Ⅲ) and TA solutions. The material-independent universal Fe(Ⅲ)-TA nanocoating has been demonstrated with a multitude of substrates, including planar and particulate ones. Formed Fe(Ⅲ)-TA nanofilms is multifunctional in various sectors, making it possible to control surface properties including anti-fouling, anti-moisture, and antimicrobial coating. Although the Fe(Ⅲ)-TA nanocoating ensures film uniformity for nano/micrometer-sized objects, it is a formidable task to coat bulk or water-floating substrates, because the coating method has been limited to diffusion-driven, supramolecular complex formation in solution. Considering these limitations of immersive nanocoating, we envisioned that spray nanocoating would be a practical and powerful alternative

it has been used to form nanofilms on a variety of substrates, having two-dimensionally textured morphologies or three-dimensionally arbitrary shapes, exemplified by spray coating of layer-by-layer multilayers and polydopamine. In addition, spray coating is much more time-efficient compared with the immersive nanocoating, because spraying and washing steps generally take less than 10 seconds, and the cross-contamination of suspensions is hardly found. Herein, we demonstrate that stable Fe(Ⅲ)-TA-MOC nanofilms by spraying of Fe(Ⅲ) and TA solutions, and apply the developed coating strategy to bulk commodity goods, including fruits such as mandarin orange using antimicrobial property. In addition, as this coating is material-independent and makes hydrophilic surface, we showed that the superhydrophobic surface, which is nanoporous anodic aluminum oxide (AAO), converts into the hydrophilic surface in a short time. We showed also just tannic acid is performed even by plasma treatment.