Upcycling Coir Fiber into Polydopamine-Enabled Adsorbents for Efficient Cu(II)/Cd(II) Removal and Effluent Safety

Heavy metal pollution remains a global environmental challenge, calling for sustainable and low-cost sorbents. Here, we upcycle coir fiber into a bioinspired adsorbent by depositing a polydopamine (PDA) coating (PDA/Coir fiber) for efficient Cu(II) and Cd(II) removal from water while improving effluent safety. Scanning electron microscopy (SEM), Fourier transform infrared (FTIR), X-ray photoelectron spectroscopy (XPS), and thermal gravimetric analysis (TGA) confirm successful PDA functionalization and associated structural changes. Compared with pristine coir fiber, PDA/Coir fiber shows 6.84-fold and 12.86-fold higher adsorption capacities for Cu(II) and Cd(II), respectively. Adsorption is well described by the Langmuir isotherm, indicating monolayer-dominated binding. Kinetic analysis shows that the adsorption of both ions follows the pseudo-second-order model. The fiber also exhibits good reusability over four adsorption–desorption cycles. Importantly, cytotoxicity assays of the treated solutions show substantially reduced biotoxicity after metal removal. Overall, PDA/Coir fiber offers a sustainable and low-cost platform for heavy metal removal by integrating efficient adsorption capabilities and safety implications.