Nanocomposites of Ag₂S and Noble Metals

Abstract

Besides the more conventional hybrid nanomaterials, for example, core-shell, [1][2][3][4] alloy, [5][6][7] and bimetallic heterostructures, [8][9][10][11] there has been increasing interest devoted towards the development of semiconductor-metal nanocomposites that consist of different classes of materials with coherent interfaces. This type of nanostructure combines materials with distinctly different physical and chemical properties to yield a unique hybrid nanosystem with multifunctional capabilities and tunable or enhanced properties that may not be attainable otherwise. [12] The early studies of semiconductor-metal nanocomposites involved different metals (e.g. gold, silver, and platinum) deposited on or doped in TiO 2 powders for photocatalytic applications. [13][14][15][16][17][18][19] In these structures, the metal domain induces the charge equilibrium in photoexcited TiO 2 nanocrystals, thus affecting the energetics of the nanocomposites by shifting the Fermi level to more negative potentials. The shift in Fermi level is indicative of improved charge separation in TiO 2 -metal systems and is effective towards enhancing the efficiency of photocatalysis. [20,21] In 2004, Banin and co-workers made a breakthrough in semiconductor-metal nanocomposites.[22] They demonstrated a solution synthesis for nanohybrids by the selective growth of gold tips on the apexes of hexagonal-phase CdSe nanorods at room temperature. The novel nanostructures displayed modified optical properties arising from the strong coupling between the gold and semiconductor components. The gold tips showed increased conductivity and selective chemical affinity for forming self-assembled chains of rods. The architecture of these nanostructures was qualitatively similar to bifunctional molecules such as dithiols, which provide twosided chemical connectivity for self-assembly and for electrical devices and contacting points for colloidal nanorods and tetrapods. These researchers later reported the synthesis of asymmetric semiconductor-metal heterostructures in which gold was grown on one side of CdSe nanocrystalline rods and dots. Theoretical modeling and experimental analysis showed that the one-sided nanocomposites were transformed from the two-sided architectures through a ripening process. [23] Subsequently, various approaches were developed for the synthesis of semiconductor-metal nanocomposites (e.g. ZnO-Ag, [24,25] CdS-Au, [26,27] InAs-Au, [28] TiO 2 -Co, [29] PbSAu, [30][31][32][33][34] Ag 2 S-Au, [35] and semiconductor-Pt systems [36][37][38][39] ) by anisotropic growth of metals on semiconductors through reduction, physical deposition, or photochemistry.We recently presented a general protocol for transferring the transition-metal ions from water to an organic medium using an ethanol-mediated method, which was extended to synthesize a wide variety of heterogeneous semiconductornoble-metal nanocomposites. [40] In another study, we synthesized three different types of semiconductor-Au nanocomposites (CdS-Au, CdSe-Au, and PbS-Au), which d...

Влияние Температуры На Размер Частиц И Рекристаллизацию Нанопорошков Сульфида Серебра

“…Их действие основано на восстановлении катионов Ag + сульфида серебра до атомов металлического серебра Ag, превращении акантита α-Ag 2 S в аргентит β-Ag 2 S и возникнове-нии проводящего канала из серебра Ag и аргентита β-Ag 2 S [6][7][8]. Гибридные гетеронаноструктуры Ag 2 S/Ag обнаруживают повышенную эффективность в фотоката-лизе [9].…”

Pt-Containing Ag2S-Noble Metal Nanocomposites as Highly Active Electrocatalysts for the Oxidation of Formic Acid

“…The different features of Au and Pt deposition on Ag 2 S nanocrystal could be further employed to integrate Au, Pt, and Ag 2 S into a single nanosystem. Different from the successive synthesis reported previously [13], the ternary Ag 2 S-Au-Pt nanocomposites were prepared by co-reduction of HAuCl 4 and H 2 PtCl 6 metal precursors using citrate in the presence of preformed Ag 2 S nanocrystals (Fig. 2(c)).…”

“…The syntheses of Ag 2 S nanocrystals and Ag 2 S-noble metal nanocomposites followed a protocol reported previously with modifications [13]. In a typical synthesis of a hydrosol of monoclinic Ag 2 S nanocrystals, 600 mg of BSPP was added to 300 mL of aqueous AgNO 3 solution (1 mM).…”

“…Our recent work demonstrated that the integration of Pt with a suitable semiconductor might be an effective way to improve the catalytic property of Pt for PEMFC reactions [13,14]. For example, in the Ag 2 S-noble metal nanomaterials reports recently, the Pt-containing nanocomposites were found to display excellent catalytic activity for methanol oxidation, due to electron donation from the semiconductor domains to the ultrafine Pt crystallites [13].…”

“…For example, in the Ag 2 S-noble metal nanomaterials reports recently, the Pt-containing nanocomposites were found to display excellent catalytic activity for methanol oxidation, due to electron donation from the semiconductor domains to the ultrafine Pt crystallites [13]. In addition, in core-shell structured CdSe-Pt nanocomposites were obtained by reducing platinum precursors by sodium citrate in the presence of previously formed CdSe nanocrystals, and the compressive strain effect imposed from the CdSe core on the deposited Pt shell results in an appropriate downshift of the d band center of Pt catalysts, which leads to the enhancement of the core-shell structured nanocomposites for catalyzing the oxygen reduction and methanol oxidation in direct methanol fuel cells [14].…”