The mechanism of metal nanoparticle formation in plants: limits on accumulation |
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Authors: | R G Haverkamp A T Marshall |
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Institution: | (1) School of Engineering and Advanced Technology, Massey University, Palmerston North, 4442, New Zealand |
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Abstract: | Metal nanoparticles have many potential technological applications. Biological routes to the synthesis of these particles
have been proposed including production by vascular plants, known as phytoextraction. While many studies have looked at metal
uptake by plants, particularly with regard to phytoremediation and hyperaccumulation, few have distinguished between metal
deposition and metal salt accumulation. This work describes the uptake of AgNO3, Na3Ag(S2O3)2, and Ag(NH3)2NO3 solutions by hydroponically grown Brassica juncea and the quantitative measurement of the conversion of these salts to silver metal nanoparticles. Using X-ray absorption near
edge spectroscopy (XANES) to determine the metal speciation within the plants, combined with atomic absorption spectroscopy
(AAS) for total Ag, the quantity of reduction of AgI to Ag0 is reported. Transmission electron microscopy (TEM) showed Ag particles of 2–35 nm. The factors controlling the amount of
silver accumulated are revealed. It is found that there is a limit on the amount of metal nanoparticles that may be deposited,
of about 0.35 wt.% Ag on a dry plant basis, and that higher levels of silver are obtained only by the concentration of metal
salts within the plant, not by deposition of metal. The limit on metal nanoparticle accumulation, across a range of metals,
is proposed to be controlled by the total reducing capacity of the plant for the reduction potential of the metal species
and limited to reactions occurring at an electrochemical potential greater than 0 V (verses the standard hydrogen electrode). |
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Keywords: | Silver Nanoparticle Phytomining Phytoremediation XAS XANES EXAFS Nanobiotechnology |
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