Thermal and photoinduced reduction of ionic Au(III) to elemental Au nanoparticles by dissolved organic matter in water: possible source of naturally occurring Au nanoparticles.Naturally occurring Au nanoparticles (AuNPs) have been widely observed in ore deposits, coal, soil, and environmental water.  Long-time exposure with thermal and photoirradiation induced the further fusion and growth of AuNPs to branched Au nanostructure as precipitation.  These results imply that, besides biological processes, this thermal or photochemical reduction process is another possible source of naturally occurring AuNPs in natural environments, which possibly has critical impacts on the transport and transformation of Au and engineered AuNPs.
THERM