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Facet selective etching of Au.microcrystallites

Nano Research 2015年第9期8卷 2925-2934页

作者： gangaiah mettela and giridhar u. kulkarni Thematic u.it of Excellence on Nanochemistry and Chemistry and Physics of Materials u.it Jawaharlal Nehru Centre for AdvancedScientific Research (JNCASR) Jakkur P.O. Bangalore 560 064 India

High-symmetry crystals exhibit isotropic properties. Indu.ing anisotropy, e.g., by facet selective etching, is considered implau.ible in face-centered cu.ic （FCC） metals, particu.arly gold, which, in addition to being an FCC, is noble. We report for the first time the facet selective etching of Au.microcrystals obtained in the form of cu.octahedra and pentagonal rods from the thermolysis of a gold- organic precu.sor. The selective etching of {111} and {100} facets was achieved u.ing a capping method in which tetraoctylammoniu. cations selectively cap the {111} facets while Br- ions protect the {100} facets. The exposed facets are oxidized by O2/C1-, yielding a variety of interesting geometries. The facet selective etching of the Au.microcrystallites is governed only by the natu.e of the facets; the geometry of the microcystallite does not appear to play a significant role. The etched su.faces appear rou.h, bu. a closer examination reveals well-defined corru.ations that are indexable to high hkl valu.s. Su.h su.faces exhibit enhanced Raman activity.

关键词： gold,microcrystallites,facet selective eapping

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Non-FCC rich Au.crystallites exhibiting u.u.u.l catalytic activity

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Nano Research 2017年第7期10卷 2271-2279页

作者： gangaiah mettela Nisha Mammen Joydip Joardar Shobhana Narasimhan giridhar u. kulkarni Thematic u.it of Excellence on Nanochemistry and Chemistry and Physics of Materials u.it Jawaharlal Nehru Centre for Advanced Scientific Research Jakkur Bangalore 560 064 India Theoretical Sciences u.it Jawaharlal Nehru Centre forAdvanced Scientific Research Jakkur Bangalore 560 064 India IntemationalAdvanced Research Centre for Powder Metallu.gy & New Materials Balapur Hyderabad 500 005 India Centre for Nano and Soft Matter Sciences Jalahalli Bangalore 560 013 India

Bipyramidal Au.microcrystallites have been synthesized by thermalizing a Au.organic complex in the presence of Ag（I） ions, the latter acting as a shape- directing agent. With a highly corru.ated morphology leading to strain-indu.ed non-face-centered cu.ic （non-FCC） Au.phases, the non-FCC portion can be tu.ed by varying the Ag/Au.ratio, as verified by diffraction measu.ements. For a Ag/Au.ratio of 0.34, the non-FCC Au.portion was as high as 85%. X-ray microdiffraction and electron diffraction measu.ements reveal that the non-FCC contribu.ion comes primarily from bipyramids, while other microcrystallites, namely, tetrahexahedrons and hexagrams, host non-FCC phases only at the edges and, to an even lesser extent, at the comers. When u.ed as a catalyst for p-nitrophenol redu.tion, the non-FCC microcrystallites exhibit a significantly enhanced activity compared to FCC Au. which shows only negligible activity. These resu.ts are in accordance with trends in the valu.s of two descriptors of reactivity calcu.ated from first principles： The effective coordination nu.ber is fou.d to decrease and the d-band center is fou.d to increase in energy going from the FCC to the non-FCC phases of Au. Ou. findings contradict the general notion that Au.is catalytically active only in nanodimensions and is otherwise inert; in this system, its activity arises from the non-FCC phases.

关键词： Au.microcrystallites non-face-centered cu.ic(non-FCC) phases microbeam X-raydiffraction (XRD) catalysis effective coordinationnu.ber

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