Lightly Reduced

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Science  18 Jul 2003:
Vol. 301, Issue 5631, pp. 279
DOI: 10.1126/science.301.5631.279c

Two component nanoparticles that consist of a core of one metal surrounded by a shell of a second metal have a number of potential applications in optics and catalysis. Unfortunately, the reduction step normally used to create the shell can introduce nucleation sites that allow nanoparticles of the second metal to form. Mandal et al. avoid this problem by exploiting the photoswitchable reducing behavior of Keggin ions, in this case phosphotungstic acid [PTA: H3(PW12O40)], for synthesizing both the core and the shell. Activation of PTA with ultraviolet (UV) light leads to a one-electron reduction. Adding HAuCl4 initiates a reaction in which PTA is reoxidized while the gold is reduced to give a nanoparticle with surface-bound Keggin ions. A second round of UV activation and addition of Ag2SO4 produces the outer silver shell. — PDS

J. Am. Chem. Soc. 10.1021/ja034972t.

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