In Vivo Effect of Copper and Silver on Synthesis of Gold Nanoparticles inside Living Plants

Abstract

Living plants growing on mine waste were assisted to accumulate gold to a concentration greater than 3500 mg kg–1 (0.35%) dry weight. Where Au was the only high-density metal present in the soil at high concentration, discrete biogenic nanoparticles of the metal were observed in preparations of shoot and leaf biomass. Where an equal concentration of silver was additionally present, a nanoalloy of Au and Ag was observed. An equal concentration of copper in the soil had no chemical affect on the Au and/or Ag structures synthesized and did not alloy with Au and/or Ag. However, both Cu and Ag reduced the size of Au nanoparticles, and the presence of Cu and/or Ag also limited the extent to which Au was reduced in plant tissues to Au(0). Ash prepared from Au-only plant material had a visible reflectance spectrum indicative of a Au surface plasmon resonance that was not apparent for the Au/Ag biomass. The Au concentration of the plant ash (3.2–7.2%) was of the same order of magnitude as Au reference catalysts. Therefore, biogenic synthesis is proposed as a valid technique to create high concentration Au structures in a carbon matrix. Our data suggest that such biogenic nanoparticles should be tested in a range of environmental and industrial reactions.

Supported Palladium Nanoparticles Synthesized by Living Plants as a Catalyst for Suzuki-Miyaura Reactions

“… [13] Plants are known to uptake metal salts and are capable of reducing these metal ions to form crystalline nanostructures. [14] Such MNPs in plants have been described for Au, Ag and Cu. [15] – [17] After formation of MNPs, it is common that extraction from biomass is attempted by methods such as freeze-thawing, biomass incineration, and chemical leaching.…”

Phytomining for Artisanal Gold Mine Tailings Management

“…The bioaccumulation factor for silver was 3, leading to a high concentration of silver in plants relative to what is normally expected (less than 0.1 mg/kg). Silver is a toxic metal, and uptake of silver after cyanide treatment of plants has been previously attributed to necrosis of plants and a shutdown of evapotranspiration and metal uptake [21]. The elevated silver concentration in the biomass of this study may, in part, explain the low gold concentration.…”

“…The greater the concentration of gold in soil, the greater the concentration that can be induced into plants. A mean gold concentration in excess of 100 mg/kg has been reported for a gold concentration in soil as low as 2 mg/kg where treatment is optimised for plant uptake [10,21].…”

Future direction of Au agromining on how to solve artisanal and small scale gold mining problems

“…In general, Au into the tissue consists of 1) solubilization of Au of the soil matrix, 2) gold uptake into the root of hyperaccumulator, 3) transport to the shoots, detoxification and sequestration in the tissues of hyperaccumulator (Sheoran et al, 2013). Gold in Brassica juncea is accumulated in the form of biogenic particles in the carbon matrix (Anderson et al, 2013). The mechanism of Au accumulation has not been deep as understanding for mechanisms of Ni or Zn accumulation (Reeves and Adigüdzel, 2008;Deng et al, 2018).…”