Green synthesis of 1–2 nm gold nanoparticles stabilized by amine-terminated ionic liquid and their electrocatalytic activity in oxygen reduction

Abstract

Stable gold nanoparticles with average size 1.7 nm synthesized by an amine-terminated ionic liquid showed enhanced electrocatalytic activity and high stability.Electrocatalytically active gold nanoparticles are enjoying increasing applications in electrochemistry, electroanalysis and bioelectronics. 1 Catalytic activity has been shown to depend strongly on the gold oxidation state, nanoparticle size and surface properties. 2 For example, 1.3 nm gold nanoparticles exhibited superior activity in catalysis of aerobic alcohol, relative to larger (9.5 nm) particles. 3 An established method for generating 1-3 nm gold nanoparticles is reduction of AuCl 4 − by sodium borohydride in the presence of an alkanethiol in water-toluene biphasic reaction systems. 4 While the resulting nanoparticles are very stable, the reagents are hazardous. A "greener" route, reduction by citrate in water, yields particles of only limited stability. 5 In general, preparation of gold particles with narrow size distribution in the 1-3 nm range and long-term electrocatalytic activity is difficult, and reports of suitable novel syntheses are few. 6-8Room-temperature ionic liquids (RTILs) seem well positioned to address the challenge of preparing stable, active gold nanoparticles, due to their high chemical and thermal stability, negligible vapor pressure, recyclability, high conductivity and wide electrochemical window. 9 Moreover, low interfacial tensions result in high nucleation rates, allowing formation of very small particles because Ostwald ripening occurs only weakly. 10 RTILs have been successfully employed in "green" preparations of Cu 2 O crystals, 9 gold nanosheets, 11 and nanoparticles of silver, gold or platinum. 12-14 In this work, a functionalized RTIL, 1-(3-aminopropyl)-3-methylimidazolium bromide (IL-NH 2 ), 15 was applied to simultaneously reduce aqueous HAuCl 4 and stabilize the resulting gold nanoparticles, which had an average diameter 1.7 nm and retained long-term stability without special protection. These IL-stabilized gold nanoparticles (Au-IL) showed better electrocatalytic activity in reduction of oxygen

Rapid room-temperature synthesis of hierarchical porous zeolitic imidazolate frameworks with high space-time yield

“…The lattice fringes can be clearly observed in high-resolution TEM (HR-TEM) images (Fig. 3d, f), confirming that these materials have high crystallinity [30]. These results indicate that the entire particle is crystalline with well-ordered mesopores penetrating through the microporous framework [31].…”

Enhanced catalytic application of Au@polyphenol-metal nanocomposites synthesized by a facile and green method

“…[3][4][5] However, Au NPs in catalytic reactions oen show a strong tendency to aggregate because of their high surface energies, leading to the loss of their initial activities. 6 Hence, core-shell architectures with a noble metal core preserved by an outer shell have recently attracted a great deal of attention for catalysis due to the following structural advantages: (a) the shell can hinder the aggregation of neighboring cores 7,8 and (b) remarkable catalytic activity may be achieved due to the unique identity of the shell or the interaction of the shell and the core.…”

Ionic Liquids as Designer Solvents for the Synthesis of Metal Nanoparticles

“…Additionally, Au nanoparticles were stabilized by using a zwitterionic imidazolium sulfonate-terminated thiol (Tatumi & Fujihara, 2005), and Au nanoparticles and Pd nanowires could be prepared by using a thiol functionalized IL, 1-methyl-3-(2'-mercaptoacetoxyethyl) imidazolium chloride . Similarly, nitrile-functionalized (Zhao et al, 2004;Chiappe et al, 2006;Fei et al, 2007) and amine-functionalized (Wang et al, 2008) ILs were also used towards metal nanoparticles stabilization, and superior ability of nitrile-functionalized ILs over nonfunctionalized ILs was demonstrated in this particular context (Zhao et al, 2004;Chiappe et al, 2006;Fei et al, 2007). Since synthesis of thiol-and nitrile-functionalized ILs usually involves hazardous and odorous raw materials and multiple synthesis steps, other functionalized ILs such as N-(2-hydroxyethyl)-N-methylmorpholinium) tetrafluoroborate {[HEMMor] [BF 4 ]} were prepared using more environmentally-benign synthesis and utilized for the synthesis of 4.3 nm Au nanoparticles .…”