Valorization of citrus by-products: A pathway to sustainable lignocellulose-based carbon materials

Citrus processing generates substantial quantities of agro-industrial residues, primarily peels, pomace, and seeds, which are rich in lignocellulosic polymers and bioactive constituents. These by-products are a promising feedstock for developing carbon-based materials within the emerging circular bioeconomy framework. This review examines recent progress in citrus waste valorization with particular emphasis on the synthesis of functional carbon materials, including activated carbon, carbon dots, biochar, and carbon fibers. Various extraction and conversion techniques, such as green solvent extraction, supercritical CO₂ extraction, ultrasound-assisted extraction, and enzymatic treatments, are discussed in relation to their efficiency, scalability, and environmental implications. The review further analyzes the reported applications of citrus-derived carbon materials in environmental remediation, energy storage, catalysis, and biomedical fields, highlighting how precursor composition and processing conditions influence material properties and performance. Key technological challenges associated with feedstock variability, process integration, and large-scale implementation are also discussed. By synthesizing findings across extraction, conversion, and application stages, this review provides a consolidated perspective on the current state of citrus waste valorization for carbon material production and outlines key considerations for future research and industrial development in-context of circular bioeconomy.