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An investigation into transition metal ion binding properties of silk fibers and particles using radioisotopes
Author(s) -
Rajkhowa Rangam,
Naik Radhika,
Wang Lijing,
Smith Suzanne V.,
Wang Xungai
Publication year - 2010
Publication title -
journal of applied polymer science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.575
H-Index - 166
eISSN - 1097-4628
pISSN - 0021-8995
DOI - 10.1002/app.33059
Subject(s) - silk , metal , metal ions in aqueous solution , ion , absorption (acoustics) , fiber , ion exchange , materials science , chemistry , transition metal , nuclear chemistry , composite material , organic chemistry , metallurgy , catalysis
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, 64 Cu 2+ , 109 Cd 2+ , and 57 Co 2+ were used to study the absorption of their respective stable metal ions Cu 2+ , Cd 2+ , and Co 2+ 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: Cu 2+ > Cd 2+ > 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 Cu 2+ bound was found to be higher than theoretically predicted values based on known specific Cu 2+ binding sites (AHGGYSGY), suggesting that additional (new) sites for transition metal ion binding sites are present in silk fibers. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011