Sustainable functionalization of crayfish shell waste: Progress and perspectives

Crayfish shell waste, generated in large quantities from the processing of Procambarus clarkii , represents an underutilized biogenic resource rich in chitin, chitosan precursors, calcium carbonate, proteins, pigments, and naturally doped heteroatoms. Its conversion into functional materials provides a promising route for waste valorization, although the environmental and economic advantages of different strategies still require critical evaluation. This review summarizes recent progress in the extraction, conversion, modification, and application of crayfish shell-derived materials, with emphasis on the links between processing routes, material structures, interfacial mechanisms, and practical performance. Conventional acid–alkali extraction, deep eutectic solvent-assisted methods, enzymatic hydrolysis, microbial fermentation, pyrolysis, and activation strategies are compared in terms of efficiency, product quality, scalability, and environmental trade-offs. Functionalization approaches, including heteroatom self-doping, metal or metal oxide coupling, magnetic modification, and hierarchical porous structure construction, are discussed in relation to specific application scenarios. Particular attention is given to micro-interfacial mechanisms governing pollutant removal and catalytic reactions, such as precipitation, ion exchange, surface complexation, electrostatic interaction, hydrogen bonding, π–π interaction, redox transformation, electron transfer, and reactive oxygen species generation. Current applications span water and soil remediation, adsorption, catalysis, energy storage, food packaging, sensing, bioactive compounds, and biomedical materials. Finally, key challenges are identified, including feedstock heterogeneity, seasonal supply, storage-related degradation, contaminant risks, limited life-cycle and techno-economic assessments, insufficient comparison with other crustacean wastes, and regulatory barriers. This review highlights knowledge gaps and future directions for advancing crayfish shell waste from laboratory-scale valorization toward and scalable functional materials.