Natural polyphenol tannic acid in membrane science: A comprehensive review on interactions, functional modifications, and challenges

Over the coming years, the synthesis of polymeric materials is expected to be mainly based on renewable raw materials, with fossil-derived substances being limited strictly to recycled sources to achieve long-term environmental sustainability. The growing demand for sustainable and eco-friendly materials has made tannic acid (TA), a natural polyphenol, an important focus in polymer science and membrane engineering. Due to its unique structural features, inherent biodegradability, and broad natural abundance, tannic acid represents a promising bio-based candidate for replacing fossil-derived aromatic polymers. This review examines the key and innovative strategies for synthesizing polymers from tannic acid, with a focus on recent progress in chemical modification and polymerization methods. TA has attracted considerable attention as a green crosslinking and polymer-modifying agent, owing to its multiple functional groups and ability to engage in various interactions, including hydrogen bonding, hydrophobic forces, electrostatic attractions, and covalent bonding. The review also explores the fundamental chemistry and interaction mechanisms of TA, including metal–phenolic network formation, surface polymerization processes, and its ability to form both covalent and non-covalent bonds. This ability leads to diverse applications in polymer membrane technologies, including nanoparticle coating, membrane surface modification, metal coordination, and the development of natural polymer composites. Despite significant progress, TA-based systems still face challenges in terms of stability, scalability, and compatibility with different membrane substrates. Overall, this review underscores the multifunctional nature of tannic acid while offering critical insights into its current limitations and its future potential for advancing sustainable polymeric membrane design.