Removal of copper (Cu), and cadmium (Cd) from binary system using eco-friendly cellulose nanocrystals gels derived from orange peels

The large-scale disposal of citrus peels from the fruit processing industry poses significant environmental challenges, while simultaneously representing an underutilised source of renewable biopolymers. In this study, eco-friendly cellulose nanocrystal (CNC) gels were synthesised from citrus peels and applied for the simultaneous removal of copper (Cu²⁺) and cadmium (Cd²⁺) ions from a binary aqueous system. Cellulose was extracted through alkaline treatment followed by bleaching, and CNCs were obtained via acid hydrolysis. The resulting CNCs were formulated into gel structures to enhance stability and adsorption performance. Structural and functional characterisation was carried out using Fourier Transform Infrared Spectroscopy (FTIR) and Scanning Electron Microscopy (SEM). FTIR analysis confirmed the preservation of the cellulose backbone, with characteristic hydroxyl stretching vibrations observed at 3333 cm⁻¹ and 3329 cm⁻¹ for purified cellulose and CNCs, respectively, indicating successful removal of hemicellulose and lignin during chemical treatment. SEM images revealed a nanoscale morphology with a high surface area favourable for metal ion adsorption. Batch adsorption studies demonstrated that the CNC gels exhibited effective and simultaneous removal of Cu²⁺ and Cd²⁺ from the binary system, attributed to abundant surface hydroxyl groups and enhanced interaction between the gel matrix and metal ions. The results highlight the potential of citrus-peel-derived CNC gels as sustainable, low-cost, and efficient bio-adsorbents for heavy metal remediation, while simultaneously contributing to agricultural waste valorisation and environmental protection.