A review on eggshell membrane: Structure, functionalization, and its emerging role in bioproduct separation and biorefinery applications

Eggshell membrane (ESM) is a sustainable and cost-effective bio-waste material with a wide range of applications in biorefinery, environmental remediation, and energy storage. The natural protein membrane accounts for around 3.5 % of an egg's composition. It is mostly made up of densely connected collagen fibers with functional groups such as -COOH, -NH₂, and OH. These groups allow for a variety of surface alterations and applications. ESM's unique structure consists of interwoven microporous networks with fiber diameters ranging from 0.1 to 7 μm. This type of structure makes excellent substrates for producing nanostructures and possesses significant adsorption properties. This review focuses on ESM's physical and chemical properties, separation methods, and approaches to improve its functions. It emphasizes its growing importance in energy storage, environmental remediation, and biomedical applications. Recent advances in ESM-based supercapacitors demonstrate specific capacitances that exceed 800 F g⁻¹. Furthermore, in catalytic applications, ESM shows outstanding efficiency in breaking down contaminants, with clearance rates exceeding 90 %. Using ESM in bio-waste valorisation promotes circular bioeconomy principles by providing sustainable alternatives to traditional materials. This review also highlights important hurdles, such as scaling difficulties, the necessity for standards, and regulatory concerns. It recommends future research directions that may aid in commercial application and incorporation into sustainable biorefinery processes.