Adsorption of Cd2+, Cu2+, and Ni2+ with Modified Silk Fabric

In this study, silk fabric was modified by polydopamine (PDA), and the removal of Cd2+, Cu2+, and Ni2+ ions from aqueous solutions by adsorption into PDA-coated silk fabric (PDA-SF) was investigated under various conditions. The effects of initial metal concentration, adsorbent dosage, and contact time on adsorption were investigated, and the optimal conditions for adsorbing Cd2+, Cu2+, and Ni2+ with the modified silk fabric were as follows: 60 mg/l of Cd2+, Cu2+, and Ni2+ solution, PDA-SF (0.4 g for Cd2+ and 0.6 g for Cu2+ and Ni2+), and absorption under shaking for 10 min. The corresponding metal adsorption amounts reached 100 %, 99 %, and 93 % in 10 min. Under the same conditions, the modified silk fabric had a better absorption effect than untreated silk fabric. Additionally, the adsorption isotherm data were better fitted with the Langmuir equation than the Freundlich equation. Furthermore, the adsorption kinetics indicated that the PDA-SF data were better fitted by the pseudo-second-order model than the pseudo-first-order model. The absorbed metal ions on PDA-SF could be mostly desorbed within 5 min. This work provides a basis for waste silk application in heavy metal ion removal.