Epoxidized natural rubber (ENR-50) stabilized gold and platinum organosols
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Date
2006
Authors
Teoh, Cheng Hoon
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Abstract
Gold and platinum metal organosols were synthesized in-situ in the presence of
ENR-50 via chemical reduction method by employing 2-propanol as the reducing
agent. A similar organosols was also prepared via water to toluene phase transfer
technique of the preformed particles in aqueous solution by sodium borohydride
(NaBH4) reduction of metal ions. For the in-situ preparation, the finest gold and
platinum nanoparticles in terms of size, dispersability and stability can be obtained by
varying the metal ions concentrations and reaction temperatures. The size of gold
nanoparticles decreased with decreasing gold ions concentrations and at higher
(reflux) temperature affording the smallest particles of 9.6 nm while the size of platinum
nanoparticles decreases with increasing platinum ions concentration and moderate
temperature (ca. 80oC) with 1.7 nm particle size obtained. Changes in the reaction
temperatures will influence the rate of reduction of metal ions and the hydrodynamic
volume of ENR, forming gold particles in the size range of 9.6 to 45.6 nm and for
platinum ranging from 1.7 to 173.6 nm. However, for platinum at different
concentrations, the smallest particles is only possible when the ENR chain experience
partial opening of epoxide ring which occurs at high platinum metal ion concentration
thus creating accessibility for the metal to the C=C sites in the ENR chain.
Nonetheless, the different affinity of gold and platinum towards C=C contributes to the
different size trends obtained for these metals in the in-situ preparation. Smaller gold
and platinum nanoparticles in the size range of 4.0 to 7.2 nm with very narrow size
distribution can be prepared through the liquid-liquid phase transfer technique. The
transfer of the metal nanoparticles from aqueous to organic phase was highly efficient
and with very little variation on the size of the nanoparticles before and after transfer.
The metals transferred were stabilized by the nano-void exist in the ENR interchains
and the stability was further enhanced by the metal complexation to the C=C and
epoxide ring of ENR. There is evidence that the metal particles are stripped of the initial
stabilizer, citrate, during transfer from aqueous to organic phase due to the better
stabilizing capability of ENR compared to citrate in the organic phase. Various
morphologies of gold and platinum nanoparticles formed via both methods can be
evaluated in terms of the known models. From this research, ENR was a capable
stabilizer for gold or platinum nanoparticles obtained from both the in-situ and phase
transfer method regardless of the changed in the structure of ENR.
Description
Master
Keywords
Chemical science , Epoxidized natural rubber , Platinum organosols