Light Strikes Gold to Create Better Catalysts

The Science

Gold nanocrystals are industrial catalysts and are also widely used in diagnostic assays and therapeutics. A recent study revealed a photochemical strategy that enables synthesis of gold nanocrystals with desirable properties.

The Impact

The study reveals a key role for a surfactant called polyvinylpyrrolidone (PVP) in the growth of gold nanocrystals upon exposure to visible light. The findings could be used to optimize properties of gold nanocrystals for specific industrial and medical applications.

Summary

Gold is highly stable and has other attractive features suitable for various industrial and medical applications, but controlling the size and shape of single-crystal nanostructures has been difficult. In a recent study, a team of researchers from the University of Florida, Department of Energy’s (DOE) Environmental Molecular Sciences Laboratory (EMSL), and Brookhaven National Laboratory (BNL) revealed a photochemical strategy that enables growth of gold nanocrystals with controlled properties. The researchers found that a high yield of hexagonal or triangular gold nanoprisms can be obtained by mixing organic polymer PVP in an aqueous solution containing gold nanocrystal seeds and tetrachloroauric acid (HAuCl₄). To understand the underlying mechanisms, the researchers probed the spatial distribution of PVP molecules on individual gold nanoprisms using nanoscale secondary ion mass spectrometry at EMSL, a DOE Office of Science user facility. They also used EMSL’s scanning probe atomic force microscope (AFM) compound microscope as well as the dynamic force AFM. Surprisingly, the results revealed PVP preferentially adsorbs onto defects along the perimeter of the gold nanocrystals instead of the top and bottom facets as previously suggested. Upon exposure to visible light, the adsorbed PVP directed photo-excited electrons as they reduced aqueous HAuCl₄^– ions to add metal to the growing nanocrystal. This study broadens the applicability of this photochemical strategy beyond synthesis of silver-based nanostructures and reveals novel insights into the molecular mechanisms driving the growth of gold nanocrystals. The findings could be used to tailor the shape and size of gold nanocrystals for specific industrial and medical applications.

Principal Investigator(s)

Wei David Wei
University of Florida
[email protected]

Zilua Zhu
EMSL
[email protected]

Funding

This work was supported by DOE’s Office of Science (Offices of Biological and Environmental Research and Basic Energy Sciences), including support of EMSL and BNL’s Center for Functional Nanomaterials, both of which are DOE Office of Science user facilities. Additional support was provided by the U.S. Air Force, National Science Foundation’s CCI Center for Nanostructured Electronic Materials, and University of Florida.

References

Zhai, Y., J. S. DuChene, Y.-C. Wang, J. Qiu, A. C. Johnston-Peck, B. You, W. Guo, B. DiCiaccio, K. Qian, E. W. Zhao, F. Ooi, D. Hu, D. Su, E.A. Stach, Z. Zhu and W.D. Wei. 2016. “Polyvinylpyrrolidone-Induced Anisotropic Growth of Gold Nanoprisms in Plasmon-Driven Synthesis,” Nature Materials 15, 889-95. DOI:10.1038/nmat4683.