Removal of heavy metals from aqueous solutions by modified waste silk

In order to reuse the waste fabric and develop a novel textile-based adsorbent for heavy metal removal, the waste silk fabric was modified by tannic acid (TA) and the prepared adsorbents were characterized using Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS) analysis. The removal of Cd(II), Cu(II), and Ni(II) ions from aqueous solutions was investigated using the modified silk fabric (TA-SF) under various conditions and the adsorption behavior of heavy metal ions was compared with the original silk fabric. The results showed that the maximum metal adsorption amounts reached 100% in 10 min. The adsorption isotherm models were demonstrated using Langmuir, Freundlich, and Temkin isotherm models, and the adsorption of TA-SF to Cd(II), Cu(II), and Ni(II) were well fitted with Langmuir isotherm than Freundlich and Temkin isotherm model. Moreover, the adsorption kinetics was well fitted with to the pseudo-first-order and pseudo-second-order kinetic models, and adsorption kinetics indicated that the former model was better suited than the latter. For 60 mg/L initial concentrations of Cd(II), Cu(II), and Ni(II) at pH 9.0, the adsorbents' maximum adsorption capacity was 8.03 mg g(-1), 7.42 mg g(-1), and 7.47 mg g(-1), respectively. Within 5 min, the absorbed metal ions on TA-SF could mostly be desorbed. Moreover, TA-SF can adsorb heavy metal ions from dyeing aqueous solution, showing its capability of simultaneous removal of heavy metal and waste dyes. The results suggest that the lower-cost TA-SF could be an effective adsorbent for removing heavy metals from industrial wastewater.