Charge and size selective thin film composite membranes having tannic acid – Ferric ion network as selective layer

Selective membranes that can distinguish between solutes of different physicochemical properties are highly desirable for membrane applications such as nanofiltration. Rapid coordination complex formation of metals and polyphenols triggered the development of thin film composite membranes in the last decade through a green synthesis procedure, eliminating the use of toxic organic solvents. In this work, thin film composite membranes with high selectivity between organic solutes were prepared. They contain a selective layer based on a metal-polyphenol network (tannic acid – ferric ion (TA-Fe3+)) with a thickness of approximately 10 nm thickness. The thin layer was obtained by coating aqueous solutions of the two components on top of a microporous polyacrylonitrile support in a sequential mode. The morphological, chemical and physical properties of the membranes were investigated. The results demonstrate that hydrophilicity, surface charge, and pore size of the membranes can be fine-tuned by varying the TA/Fe3+ ratio of the casting solutions. The separation performance of the membranes was further analyzed by filtration tests. For instance, selectivities in the range of 3.2–20.6 were achieved between uncharged(0)/(−)charged dyes of comparable molecular size, while exhibiting a good selectivity, reaching up to 3 times, between monovalent to trivalent negatively charged dyes. This work paves a way to eco-friendly membrane synthesis for diverse applications in water and wastewater treatment.