Browsing by Author "Naik, R"

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    An investigation into transition metal ion binding properties of silk fibers and particles using radioisotopes
    (Wiley-Blackwell, 2011-03-15) Rajkhowa, R; Naik, R; Wang, L; Smith, SV; Wang, XG
    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+ > Co2+. 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. © 2011, Wiley-Blackwell.
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    Metal ion binding properties of novel wool powders
    (Wiley-Blackwell, 2010-02-05) Naik, R; Wen, G; Dharmaprakash, MS; Hureau, S; Uedono, A; Wang, XG; Liu, XG; Cookson, PG; Smith, SV
    Wool fibres have shown potential for the removal and recovery of toxic chemical and metal ions; however, their slow kinetics of binding has limited their widespread application. In this study three wool powders have been prepared from chopped wool fibre using various milling operations. Brunauer, Emmett, Teller analysis (BET) showed negligible change in surface area and Positron annihilation lifetime spectroscopy indicated no change in nanoporosity of the powders on processing. Binding of the transition metal ions, Co2+, Cu2+, and Cd2+ was investigated over the pH range 3-9 at ambient temperature (23°C) using their respective radioisotopes (i.e. 57Co, 64Cu, or 109Cd). The optimum pH for binding of Cu2+ and Cd2+ was in the range 6-8, while Co2+ absorption peak was sharp at pH 8. The rate of uptake of Cu2+ for each of the wool powder was dramatically faster (42 fold) than that of the wool fibre. In comparison with commercial cation exchange resins, the wool powders showed significantly higher (two to nine fold) metal ion loading capacity. Selective binding of the metal ions could be enhanced by varying pH and/or incubation times. The use of radioisotopes to monitor the metal ion binding allowed the development of a highly sensitive and rapid high-throughput analysis method for assessing wool powder binding properties. The ability to produce large quantities of wool powders and their ease of handling indicate that they have potential for application in separation and recovery of metal ions from industrial effluents and environmental waterways. © 2010, Wiley-Blackwell. The definitive version is available at www3.interscience.wiley.com
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    Wool powders used as sorbents to remove Co2+ ions from aqueous solution
    (Elsevier, 2010-01-25) Wen, G; Naik, R; Cookson, PG; Smith, SV; Liu, XG; Wang, XG
    The Co2+ sorption of two wool powders was investigated using its radioisotope 57Co (T1/2 = 271.8 days and γ = 122.1 and 136.5 keV) as a tracer. The effects of the type of buffer, the pH value, the contact time and the initial concentration of Co2+ on the sorption behaviour of wool powders were studied. The Co2+ releasing ability of wool powders and the re-use of wool powders to sorb Co2+ were also examined. The optimum sorption of Co2+ by the powders occurred at pH 8 in phosphate buffer and pH 10 in ammonium sulphate buffer. Fourier-transform infrared spectroscopy (FTIR) was used to study the changes in chemical structure of the wool after exposure to both buffer solutions. Compared to the untreated wool fibre, the fine wool powders showed rapid sorption rates and high sorption capacities for Co2+. Co2+ ions were recovered after exposing the Co2+ loaded wool to HCl (0.1 M) and buffer at pH 3 (glycine/sodium chloride). After releasing Co2+ ions from wool powders, the efficiency of wool powders re-used to sorb Co2+ was 80% of that of the fresh wool powders. It is concluded from this study that wool powder can be used as an efficient sorbent to remove and release Co2+ from solution. © 2010, Elsevier Ltd.