The adsorption onto other minerals of charged gold nanoparticles, carried by gas ascending from the Earth's interior, is an important component of their transport and deposition in surficial cover such as alluvial, aeolian, and glacial sediments. To simulate the adsorption of these particles, an experiment was conducted in which a flow of air that contained gold nanoparticles was passed upward through a sample of alluvium from the middlelower reaches of the Yangtze River. These experiments showed that gold nanoparticles are adsorbed on kaolinite, halloysite, goethite, and hematite in the alluvial cover. Both the gold nanoparticles and minerals (i.e., kaolinite, halloysite, goethite, and hematite) carry surface charges that provide them with excellent adsorption properties. This study showed that the specific mineral composition of surficial alluvial cover affects the concentration of gold nanoparticles in the ascending gas. This phenomenon may plausibly be used in exploration for concealed gold, copper-gold, and silver-gold deposits in areas of thick alluvial cover.

We report that gold nanoparticles were synthe-sized by reduction of HAuCl4 using halloysites. The synthesized samples were analyzed by a transmission electron microscope. The results show that the gold nanoparticles have strip-like, subcircle, and irregular shape, which are single crystals or polycrystals. Their shaps and sizes are relate to the different halloysites. Reduction of Au 3+ may be related to the surface dangling bonds of halloysite nanotubes. Our research results show that a simple, room-temperature, and green synthesis of the nanocomposite of halloysite nanotubes and gold nanoparticles are possible. The nanocomposite may have the advantages of both the nanocomposite of halloysite nanotubes and gold nanoparticles, which may be widely applied to physical, chemical and biological field.

We found that gold particles, prepared by reduction of HAuCl4 with trisodium citric acid in the solutions of weak acidity, with a diameter of about 17 nm have different ratios between unsmooth surfaces and smooth surfaces. Gold particles with a diameter of about 7 nm have the structure in which amorphous coexist with crystalline. This paper put forward that study on synthesis of the gold particles of partial amorphous structure and growth increase of unsmooth surfaces and growth control of smooth surfaces should be the future developing direction.

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