An investigation into transition metal ion binding properties of silk fibers and particles using radioisotopes

Rangam Rajkhowa, Radhika Naik, Lijing Wang, Suzanne V. Smith, Xungai Wang

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17 Citations (Scopus)


Silk is a structural protein fiber that is stable over a wide pH range making it attractive for use in medical and environmental applications. Variation in amino acid composition has the potential for selective binding for ions under varying conditions. Here we report on the metal ion separation potential of Mulberry and Eri silk fibers and powders over a range of pH. Highly sensitive radiotracer probes, 64Cu2+, 109Cd2+, and 57Co2+ were used to study the absorption of their respective stable metal ions Cu2+, Cd2+, and Co2+ into and from the silk sorbents. The total amount of each metal ion absorbed and time taken to reach equilibrium occurred in the following order: Cu2+ > Cd2+ > Co 2+. In all cases the silk powders absorbed metal ions faster than their respective silk fibers. Intensive degumming of the fibers and powders significantly reduced the time to absorb respective metal ions and the time to reach equilibrium was reduced from hours to 5-15 min at pH 8. Once bound, 45-100% of the metal ions were released from the sorbents after exposure to pH 3 buffer for 30 min. The transition metal ion loading capacity for the silk sorbents was considerably higher than that found for commercial ion exchange resins (AG MP-50 and AG 50W-X2) under similar conditions. Interestingly, total Cu2+ bound was found to be higher than theoretically predicted values based on known specific Cu2+ binding sites (AHGGYSGY), suggesting that additional (new) sites for transition metal ion binding sites are present in silk fibers.

Original languageEnglish
Pages (from-to)3630-3639
Number of pages10
JournalJournal of Applied Polymer Science
Issue number6
Publication statusPublished or Issued - 15 Mar 2011
Externally publishedYes


  • absorption
  • fibers
  • powder
  • separation of metal ions
  • silk

ASJC Scopus subject areas

  • Chemistry(all)
  • Surfaces, Coatings and Films
  • Polymers and Plastics
  • Materials Chemistry

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