Synthesis and Characterization of Water-Soluble and Bifunctional ZnO−Au Nanocomposites

Abstract

The ability to synthesize multicomponent nanocomposites (NCs) is important for exploring their functional properties of not only individual single components but also their combinations in technological applications. This paper presents an investigation on the synthesis and characterization of water-soluble and bifunctional ZnO−Au NCs, of which ZnO provides fluorescence and Au is used for organic functionality for bioconjugation. ZnO nanocrystals were employed as seeding material for nucleation and growth of reduced gold by citrate to form the water-soluble ZnO−Au NCs. The morphology and components of the ZnO−Au NCs, characterized by the TEM and XRD, respectively, demonstrate a dumbbell-like shape and crystalline wurtzite ZnO together with face-center-cubic Au nanoparticles. The surface plasmon absorption band of ZnO−Au NCs in aqueous solution is distinctly broadened and red-shifted relative to monometallic Au nanoparticles, and the UV emission intensity is higher by about 1 order of magnitude in ZnO−Au NCs than in pure ZnO nanocrystals; these observations reflect the strong interfacial interaction between ZnO and Au. Moreover, multiphonon Raman scattering of ZnO is also largely enhanced by the strongly localized electromagnetic field of the Au surface plasmon.

Hydrogen-Etched TiO2−x as Efficient Support of Gold Catalysts for Water–Gas Shift Reaction

“…As shown in Figure 10a, since the work function of metal Au (Φm = 4.8 eV) is smaller than that of semiconductor TiO2 (Φs = 5.1 eV) [70], the electrons At first, more surface oxygen vacancies of TiO 2−x -N lead to the fact that gold of Au-TiO 2−x -N mainly exists as metallic Au 0 species (XPS results). As shown in Figure 10a, since the work function of metal Au (Φ m = 4.8 eV) is smaller than that of semiconductor TiO 2 (Φ s = 5.1 eV) [70], the electrons can diffuse from the metal into the semiconductor when the two phases are in contact [71,72]. This electron transfer was called "hot-electron flow" [56,57,[73][74][75] or "chemicurrent" [76][77][78], which usually happened in exothermic catalytic reactions [56,57,[73][74][75] and low-energy reactions [74] or even nonthermal directions [75].…”

“…In addition, the energy bands (E CB and E VB ) of the semiconductor are bent downwards and form their new Fermi levels [56,71,72], which forms the Ohmic barrier (E OB , i.e., energy difference between metal Au and the bent E CB of the semiconductor). As mentioned in the paragraph above, energetic electrons with energy of 98.4-122.7 kJ/mol (1.02-1.27 eV) are enough to move across the Ohmic barrier (E OB = 1.1 eV, Figure 10), suggesting that the electrons can transfer to the conduction band of the semiconductor TiO 2 to form hot-electron flow.…”

Effects of Au layer thickness and number of bilayers on the properties of Au/ZnO multilayers

“…A very similar evolution versus the ordinal number are reported in Raman measurements on ZnO particles with diameters of 4-5 nm close to the ZnO layer thickness in our multilayers. 29 The frequency detected at 335 cm À1 is much lower than the A1 (TO) mode reported at 380 cm À1 . Note that a frequency of 332 cm À1 was detected by Raman spectroscopy corresponding to the difference between the E2-low and E2-high modes, 28 yet these modes are not IR active.…”

“…6 Overtones in ZnO have been calculated and their presence confirmed mainly by Raman spectroscopy. 25,28,29 The contribution at 416 cm À1 is close to the E1 (TO) mode, actually slightly larger, which corresponds to atoms moving perpendicular to the c axis of the wurtzite structure (Ref. 7 and references therein).…”

Hollow, Branched and Multifunctional Nanoparticles: Synthesis, Properties and Applications

“…In an analogous reaction, Au nanoparticles have been grown on ZnO nanoparticles again using an organic amine as the reducing agent. 135 …”