Water-soluble low-molecular-weight cellulose chains radially oriented on gold nanoparticles

Cellulose chains bearing N-lipoyl group at the reducing-end as a sulfide linker, self-assembled on the surface of gold nanoparticles (CELL2Au, CELL13Au, and CELL41Au with the number average degrees of polymerization (DP_n) of 2, 13, and 41, respectively) were prepared. CELL2Au, CELL13Au, and CELL41Au were obtained via deprotection of the cellulose triacetate (CTA) self-assembled on the surface of gold nanoparticles that are consisting of CTA chains with corresponding DP_n organized in a radial manner with head-to-tail orientation, where a head is the reducing-end, and a tail is the non-reducing-end. CELL2Au and CELL13Au were well-dispersed in water including a trace of methanol, whereas CELL41Au was not. The transmission electron microscopy (TEM) observation of CELLAus deposited on copper grids revealed that the diameters (d) of the gold cores of CELL2Au, CELL13Au, and CELL41Au were 6.1, 6.1, and 11.5 nm, respectively. Wide angle X-ray diffractgram showed that cellulose chains of CELL13Au had quite low crystallinity and exhibited additional faint diffraction pattern of cellulose II. Cellulose chains of CELL41Au were amorphous. The UV–vis measurements revealed that CELL2Au and CELL13Au were well-dispersed in water. The hydrodynamic diameters (D) of CELL2Au and CELL13Au in water were 21.8 and 55.9 nm, respectively, according to dynamic light scattering (DLS) measurements, suggesting that cellulose chains on the gold were organized in a radial manner with head-to-tail orientation. ¹H-NMR measurement revealed that low-molecular-weight cellulose chains (DP_n = 13) on the gold dissolved in water, whereas low-molecular-weight cellulose (DP_n = 13) itself did not.     

Size‐Dependence of the Activity of Gold Nanoparticle‐Loaded Titanium(IV) Oxide Plasmonic Photocatalyst for Water Oxidation

Mesoporous TiO₂ nanocrystalline film was formed on fluorine‐doped tin oxide electrode (TiO₂/FTO) and gold nanoparticles (NPs) of different sizes were loaded onto the surface with the loading amount kept constant (Au/TiO₂/FTO). Visible‐light irradiation (λ>430 nm) of the Au/TiO₂/FTO photoanode in a photoelectrochemical cell with the structure of photoanode|0.1 m NaClO4 aqueous solution|Ag/AgCl (reference electrode)|glassy carbon (cathode) leads to the oxidation of water to oxygen (O₂). We show that the visible‐light activity of the Au/TiO₂/FTO anode increases with a decrease in Au particle size (d) at 2.9≤d≤11.9 nm due to the enhancement of the charge separation and increasing photoelectrocatalytic activity.     

Antibacterial Activity of Light-Activated Silicone Containing Methylene Blue and Gold Nanoparticles of Different Sizes

Methylene Blue and methylene blue-gold nanoparticle mixtures were encapsulated in a silicone polymer using a swell-encapsulation-shrink technique. The antibacterial properties of the materials, when tested against Escherichia coli and Staphylococcus epidermidis, and exposed to laser light (660 nm), were significantly affected by both the presence and size of Au nanoparticles. Bacterial inactivation data were analysed using the Weibull inactivation model. For both E. coli and S. epidermidis the value of the parameter, indicating the time required to achieve the first log₁₀ reduction in the viable count, decreased when Au nanoparticles of ca 2 nm diameter were present. Larger Au nanoparticles (diameters of 5 and 20 nm) in combination with methylene blue were also embedded in silicone. The values of these materials increased with nanoparticle diameter, indicating a reduction in antibacterial activity. In all cases E. coli had higher values than S. epidermidis.     

Thermal behavior of carbon nanotubes decorated with gold nanoparticles

Three different forms of carbon, i.e., multi-walled carbon nanotubes (CNTs), single-walled CNTs, and soot, were decorated with gold nanoparticles by a new method. In this method C₁₀H₈ ⁻ ions transfer electrons to the CNTs or soot. These electrons on the carbon surface can then reduce Au³⁺ species to form supported Au nanoparticles with a narrow particle size distribution. Thermogravimetric/differential thermal analyses (TG/DTA), XRD, Raman, and TEM show that naphthalene molecules remain trapped inside the Au nanoparticles and can only be removed by treatment at ca. 300 °C. Remarkable effect of the Au nanoparticles on the oxidation of carbon by O₂ is also observed by TG/DTA, i.e., on-set oxidation temperature and activation energy (E _a). It is shown that as the Au particle size decreases from 25 to 2 nm a linear decrease of the oxidation temperature is observed. Au particles larger than 25 nm do not produce any significant effect on carbon oxidation. These results are discussed in terms of spillover catalytic effect where Au nanoparticles activate O₂ molecules to produce active oxygen species which oxidize the different carbon supports.     

Secondary inter­actions in gold(I) complexes with thione ligands. 5. Two ionic compounds of the form bis­(thione)gold(I) bis(4‐halobenzene­sulfon­yl)amide

Bis(1,3‐thia­zolidine‐2‐thione‐κS²)gold(I) bis­(4‐chloro­benzene­sulfonyl)amide, [Au(C₃H₅NS₂)₂](C₁₂H₈Cl₂NS₂O₄), has no imposed symmetry. Classical N—H⋯N and N—H⋯O hydrogen bonds link the residues to form chains parallel to the b axis. Weaker inter­actions involve C—H⋯O, C—H⋯Au and a number of X⋯Cl contacts (X = Cl, S or Au) clustered in the region y ≃ . In bis­(1‐methyl­imidazolidine‐2‐thione‐κS²)gold(I) bis­(4‐iodo­benzene­sulfonyl)amide, [Au(C₄H₈N₂S)₂](C₁₂H₈I₂NS₂O₄), the Au atom of the cation and the N atom of the anion lie on the twofold axis (0, y, ) in the space group C2/c. The formula unit forms a self‐contained ring with two symmetry‐equivalent N—H⋯O hydrogen bonds, and weak C—H⋯X (X = O, I or S), Au⋯I and I⋯I contacts are observed. In both compounds, the anions display extended conformations.     

Functional polysilanes of relevance for the synthesis of Au and Au–Pd nanoparticle assemblies—a study on the role of polymer‐supported thioether side chains

Linear polysilanes, [{PhHSi}_x{Ph(RSCH₂CH₂CH₂)Si}_1?x]_n [R = n‐dodecyl ( 1 ), n‐hexyl ( 2 ), n‐butyl ( 3 )], have been synthesized and their reactivity with HAuCl₄·3H₂O (Polymer:Au = 10:1, RT, toluene) examined to gain an insight into the role of polymer‐supported thioether groups in the stabilization of in situ generated gold nanoparticles (AuNPs). The method allows a simple approach for expeditious synthesis of assemblies of AuNPs comprising of well‐separated individual nanoparticles of average diameter 4.5 ± 1.9 nm. In this regard, polysilane 1 with dodecyl side chains serves as a superior matrix than 2 and 3 and confers long shelf‐life stability to the nanoparticle assembly. The structural attributes are preserved in Au–Pd bimetallic nanoparticles which have been synthesized from the polymer‐gold nanoassembly. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Photothermal Oxidation of Cinnamyl Alcohol with Hydrogen Peroxide Catalyzed by Gold Nanoparticle/Antimony-Doped Tin Oxide Nanocrystals

Gold nanoparticles with different mean sizes were formed on antimony-doped tin oxide nanocrystals by the temperature-varied deposition-precipitation method (Au/ATO NCs). Au/ATO NCs possess strong absorption in the near-infrared region due to Drude excitation in addition to the localized surface plasmon resonance (LSPR) of AuNPs around 530 nm. Au/ATO NCs show thermally activated catalytic activity for the oxidation of cinnamyl alcohol to cinnamaldehyde by hydrogen peroxide. The catalytic activity increases with a decrease in the mean Au particle size (d_Au) at 5.3 nm≤d_Au≤8.2 nm. Light irradiation (λ_ex >660 nm, ∼0.5 sun) of Au/ATO NCs increases the rate of reaction by more than twice with ∼95 % selectivity. Kinetic analyses indicated that the striking enhancement of the reaction stems from the rise in the temperature near the catalyst surface of ∼30 K due to the photothermal effect of the ATO NCs.     

Gold‐loading magnetic core–shell organic/inorganic nanocomposites: facile preparation and multiple properties

Magnetic composite nanospheres (MCS) were first prepared via mini‐emulsion polymerization. Subsequently, the hybrid core–shell nanospheres were used as carriers to support gold nanoparticles. The as‐prepared gold‐loading magnetic composite nanospheres (Au‐MCS) had a hydrophobic core embed with γ‐Fe₃O₄ and a hydrophilic shell loaded by gold nanoparticles. Both the content of γ‐Fe₃O₄ and the size of gold nanoparticles could be controlled in our experiments, which resulted in fabricating various materials. On one hand, the Au‐MCS could be used as a T₂ contrast agent with a relaxivity coefficient of 362 mg^?1 ml S^?1 for magnetic resonance imaging. On the other hand, the Au‐MCS exhibited tunable optical‐absorption property over a wavelength range from 530 nm to 800 nm, which attributed to a secondary growth of gold nanoparticles. In addition, dynamic light scattering results of particle sizing and Zeta potential measurements revealed that Au‐MCS had a good stability in an aqueous solution, which would be helpful for further applications. Finally, it showed that the Au‐MCS were efficient catalysts for reductions of hydrophobic nitrobenzene and hydrophilic 4‐nitrophenol that could be reused by a magnetic separation process. Copyright © 2014 John Wiley & Sons, Ltd.     

Comparative toxicity study of Ag, Au, and Ag–Au bimetallic nanoparticles on Daphnia magna

A comparative assessment of the 48-h acute toxicity of aqueous nanoparticles synthesized using the same methodology, including Au, Ag, and Ag–Au bimetallic nanoparticles, was conducted to determine their ecological effect in freshwater environments through the use of Daphnia magna, using their mortality as a toxicological endpoint. D. magna are one of the standard organisms used for ecotoxicity studies due to their sensitivity to chemical toxicants. Particle suspensions used in toxicity testing were well-characterized through a combination of absorbance measurements, atomic force or electron microscopy, flame atomic absorption spectrometry, and dynamic light scattering to determine composition, aggregation state, and particle size. The toxicity of all nanoparticles tested was found to be dose and composition dependent. The concentration of Au nanoparticles that killed 50% of the test organisms (LC₅₀) ranged from 65–75 mg/L. In addition, three different sized Ag nanoparticles (diameters = 36, 52, and 66 nm) were studied to analyze the toxicological effects of particle size on D. magna; however, it was found that toxicity was not a function of size and ranged from 3–4 μg/L for all three sets of Ag nanoparticles tested. This was possibly due to the large degree of aggregation when these nanoparticles were suspended in standard synthetic freshwater. Moreover, the LC₅₀ values for Ag–Au bimetallic nanoparticles were found to be between that of Ag and Au but much closer to that of Ag. The bimetallic particles containing 80% Ag and 20% Au were found to have a significantly lower toxicity to Daphnia (LC₅₀ of 15 μg/L) compared to Ag nanoparticles, while the toxicity of the nanoparticles containing 20% Ag and 80% Au was greater than expected at 12 μg/L. The comparison results confirm that Ag nanoparticles were much more toxic than Au nanoparticles, and that the introduction of gold into silver nanoparticles may lower their environmental impact by lowering the amount of Ag which is bioavailable.     

Supramolecular assembly and solvochromic luminescence of a Au(I) complex containing di(4-pyridylmethyl)aminedithiocarbamate

The di(4-pyridylmethyl)aminedithiocarbamate (DPMACS₂) ligand was used to react with (Me₂S)AuCl to give a dinuclear complex, [Au(DPMACS₂)]₂, which shows both intramolecular Au(I)⋅⋅⋅Au(I) distances of 2.741(9)–2.788(1) Å and intermolecular Au(I)···Au(I) contacts of 2.917(5)–3.047(7) Å, leading to 1-D Au(I) chains in the solid state. In addition, complex [Au(DPMACS₂)]₂ shows the luminescence at 555 nm at room temperature while excited, and almost no energy shift for the luminescence at 553 nm upon grinding has been observed. In this regard, we further examined the solvochromic luminescence upon grinding with various solvents, and the luminescence is within 549–572 nm. It is noted that the solvochromic luminescence for dichloromethane (566 nm) and 1,2-dichloroethane (572 nm) has been observed, and the original luminescence at 555 nm can be restored upon solvent loss. Indeed, such red-shifts for the solvochromic luminescence are most likely due to a decrease in intermolecular Au(I)⋅⋅⋅Au(I) contacts while solvents entering into crystal lattices upon grinding and it is a reversible process upon solvent loss.     

Enzyme biosensor based on the immobilization of HRP on SiO<Subscript>2</Subscript>/BSA/Au composite nanoparticles

In this work, an enzyme biosensor based on the immobilization of horseradish peroxidase (HRP) on SiO₂/BSA/Au/thionine/nafion-modified gold electrode was fabricated successfully. Firstly, nafion was dropped on the surface of the gold electrode to form a nafion film followed by chemisorption of thionine (Thi) as an electron mediator via the ion-exchange interaction between the Thi and nafion. Subsequently, the SiO₂/BSA/Au composite nanoparticles were assembled onto Thi film through the covalent bounding with the amino groups of Thi. Finally, HRP was immobilized on the SiO₂/BSA/Au composite nanoparticles due to the covalent conjugation to construct an enzyme biosensor. The surface topographies of the SiO₂/BSA/Au composite nanoparticles were investigated by using scanning electronic microscopy. The stepwise self-assemble procedure of the biosensor was further characterized by means of cyclic voltammetry and chronoamperometry. The enzyme biosensor showed high sensitivity, good stability and selectivity, a wide linear response to hydrogen peroxide (H₂O₂) in the range of 8.0 × 10^-6 ∼ 3.72 × 10^-3 mol/L, with a detection limit of 2.0 × 10^-6 mol/L. The Michaelies-Menten constant K_M^app K_M^{app} value was estimated to be 2.3 mM.     

Visible‐Light‐Induced Electron Transport from Small to Large Nanoparticles in Bimodal Gold Nanoparticle‐Loaded Titanium(IV) Oxide

A key to realizing the sustainable society is to develop highly active photocatalysts for selective organic synthesis effectively using sunlight as the energy source. Recently, metal‐oxide‐supported gold nanoparticles (NPs) have emerged as a new type of visible‐light photocatalysts driven by the excitation of localized surface plasmon resonance of Au NPs. Here we show that visible‐light irradiation (λ>430 nm) of TiO₂‐supported Au NPs with a bimodal size distribution (BM‐Au/TiO₂) gives rise to the long‐range (>40 nm) electron transport from about 14 small (ca. 2 nm) Au NPs to one large (ca. 9 nm) Au NP through the conduction band of TiO₂. As a result of the enhancement of charge separation, BM‐Au/TiO₂ exhibits a high level of visible‐light activity for the one‐step synthesis of azobenzenes from nitrobenzenes at 25 °C with a yield greater than 95 % and a selectivity greater than 99 %, whereas unimodal Au/TiO₂ (UM‐Au/TiO₂) is photocatalytically inactive.     

Adduct effects on structure and luminescence in a series of new dithiocarbamatogold(I) complexes

Reaction of [AuCl(SMe₂)] with NaL·H₂O (L = ethyl(pyridine-4-yl methyl)dithiocarbamate (epdtc) or methyl(2-(pyridin-2-yl)ethyl)dithiocarbamate (mpdtc)) affords a series of neutral dinuclear gold(I) complexes bridged by each dithiocarbamate ligand, [Au(L)]₂. The successive reaction of [Au(L)]₂ with organic acids such as isophthalic acid (m-pa) and maleic acid (ma) produces 1:1 adducts, [Au(L)]₂·(organic acid). The crystal structure of [Au(L)]₂·(m-pa) is a 1D polymer formed via hydrogen bonds between the free pyridyl and the carboxylic acid moiety. For the dinuclear moiety, strong intradinuclear aurophilic interactions (Au(I)–Au(I) = 2.7783(8) Å and 2.7525(7) Å) exist, but interdinuclear interactions are weak (3.2551(8)–3.2733(8) Å). The dinuclear gold(I) complexes, [Au(epdtc)]₂ and [Au(mpdtc)]₂, show a bright luminescence at 562.5 and 552.0 nm in solid state, respectively, but their organic acid adducts, [Au(L)]₂·(organic acid), have no luminescent properties. This dramatic difference in properties between the gold(I) complexes and their adducts may be ascribed to the weakness of the internuclear Au(I)–Au(I) interaction including crystal packing.     

EXAFS studies on gold nanoparticles over novel catalytic materials

Novel nanogold catalytic systems made up of gold nanoparticles (∼2–6 nm) supported on niobium, ytterbium, lanthanum and cerium oxide materials were synthesized. XAS is uniquely suited for studying catalytic systems with low metal and high metal dispersion. Au L₃ edge X-ray absorption spectroscopic measurements were carried out over a series of supported gold nanoparticles. The interesting results obtained from EXAFS and XANES confirms the typical characteristics and structure of gold nanoparticles in these materials.     

“Click” synthesis of thermally stable au nanoparticles with highly grafted polymer shell and control of their behavior in polymer matrix

Thermally stable core–shell gold nanoparticles (Au NPs) with highly grafted polymer shells were synthesized by combining reversible addition‐fragmentation transfer (RAFT) polymerization and click chemistry of copper‐catalyzed azide‐alkyne cycloaddition (CuAAC). First, alkyne‐terminated poly(4‐benzylchloride‐b‐styrene) (alkyne‐PSCl‐b‐PS) was prepared from the alkyne‐terminated RAFT agent. Then, an alkyne‐PSCl‐b‐PS chain was coupled to azide‐functionalized Au NPs via the CuAAC reaction. Careful characterization using FT‐IR, UV–Vis, and TGA showed that PSCl‐b‐PS chains were successfully grafted onto the Au NP surface with high grafting density. Finally, azide groups were introduced to PSCl‐b‐PS chains on the Au NP surface to produce thermally stable Au NPs with crosslinkable polymer shell ( Au‐PSN₃‐b‐PS 1 ). As the control sample, PS‐b‐PSN₃‐coated Au NPs ( Au‐PSN₃‐b‐PS 2 ) were made by the conventional “grafting to” approach. The grafting density of polymer chains on Au‐PSN₃‐b‐PS 1 was found to be much higher than that on Au‐PSN₃‐b‐PS 2 . To demonstrate the importance of having the highly packed polymer shell on the nanoparticles, Au‐PSN₃‐b‐PS 1 particles were added into the PS and PS‐b‐poly(2‐vinylpyridine) matrix, respectively. Consequently, it was found that Au‐PSN₃‐b‐PS 1 nanoparticles were well dispersed in the PS matrix and PS‐b‐P2VP matrix without any aggregation even after annealing at 220 °C for 2 days. Our simple and powerful approach could be easily extended to design other core–shell inorganic nanoparticles. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Binding forms of gold(III) from solutions by cadmium diethyl dithiocarbamate: Thermal behavior and role of secondary interactions in the supramolecular self-assembly of polymeric complexes ([Au{S2CN(C2H5)2}2][AuCl4]) n and [Au{S2CN(C2H5)2}Cl2] n

The chemisorption interaction between the binuclear cadmium diethyl dithiocarbamate (EDtc), [Cd₂{S₂CN(C₂H₅)₂}₄], (chemisorbent I) and AuCl₃ solutions in 2 M HCl results in the formation of polymeric gold(III) complexes: ([Au{S₂CN(C₂H₅)₂}₂][AuCl₄]) _n (II) and [Au{S₂CN(C₂H₅)₂}Cl₂] _n (III) with the same Au : EDtc : Cl ratio (1 : 1 : 2). The alternating centrosymmetric cations and anions of complex II are structurally self-assembled to form linear polymeric chains: the gold atom in [Au{S₂CN(C₂H₅)₂}₂]⁺ forms secondary Au(1)?Cl(1) bonds (3.7784 Å) with two neighboring [AuCl₄]^? anions. This binding is additionally strengthened by secondary S(1)?Cl(1) interactions (3.4993 Å). The mixed-ligand complex III comprises two structurally non-equivalent molecules [Au{S₂CN(C₂H₅)₂}Cl₂]: A—Au(1) and B—Au(2), each being in contact with two nearest neighbors through pairs of unsymmetrical secondary bonds: Au(1)?S(1)^a/b 3.4361/3.6329; and Au(2)?S(4)^c/d 3.4340/3.6398 Å. At the supramolecular level, this gives rise to independent zigzag-like polymeric chains, (?A?A?A?) _n and (?B?B?B?) _n along which antiparallel isomeric molecules of III alternate. The chemisorption capacity of cadmium diethyl dithiocarbamate calculated from the gold(III) binding reaction is 963.2 mg of gold per 1 g of the sorbent. The recovery conditions for the bound gold were elucidated by simultaneous thermal analysis of II and III. The DSC curves reflect different sets of heat effects, because thermolysis occurs for complex molecules (III) or for cations and anions (II). Nevertheless, the patterns of experimental TG curves are similar despite different structures of the complexes. The final product of thermal transformations is reduced gold.     

Binding of gold(iii) with silver(i) dipropyldithiocarbamate: supramolecular self-assembly (role of secondary Au…S and Ag…S bonds) and thermal behavior of the ionic-polymer complex ([Au(S2CNPr2)2][AgCl2])n

The double ionic-polymer complex ([Au(S₂CNPr₂)₂][AgCl₂])_n (1) was prepared as an individual fixation form of gold(III) from NaCl solutions with silver(I) dipropyldithiocarbamate and was characterized by single-crystal X-ray diffraction and ¹³C magic-angle spinning (MAS) NMR spectroscopy. The structure of 1 comprises two nonequivalent centrosymmetric complex cations [Au(S₂CNPr₂)₂]⁺ (A and B) and the discrete linear anion [AgCl₂]^–. Gold(III) cations are linked by pairs of unsymmetrical secondary Au…S bonds to form linear supramolecular chains (…A…B…)n. Neighboring cations are additionally linked by [AgCl₂]^– anions via secondary Ag…S and Cl…S bonds, the anions being involved in the overall stabilization of the supramolecular structure. The cation–anion interactions lead to a distortion of the linear configuration of the [AgCl₂]^– anion. The character of thermolysis of 1 accompanied by quantitative regeneration of bound Au and Ag was established by simultaneous thermal analysis.

     

Two thiourea‐containing gold(I) complexes

The crystal structures of two salts of bis­(thio­urea)­gold(I) complexes, namely bis­(thio­urea‐κS)­gold(I) chloride, [Au(CH₄N₂S)₂]Cl, (I), and bis­[bis­(thio­urea‐κS)­gold(I)] sulfate, [Au(CH₄N₂S)₂]₂SO₄, (II), have been determined. The chloride salt, (I), is isomorphous with the corresponding bromide salt, although there are differences in the bonding. The Au^I ion is located on an inversion centre and coordinated by two symmetry‐related thio­urea ligands through the lone pairs on their S atoms [Au—S 2.278 (2) Å and Au—S—C 105.3 (2)°]. The sulfate salt, (II), crystallizes with four independent [Au(CH₄N₂S)₂]⁺ cations per asymmetric unit, all with nearly linear S—Au—S bonding. The cations in (II) have similar conformations to that found for (I). The Au—S distances range from 2.276 (3) to 2.287 (3) Å and the Au—S—C angles from 173.5 (1) to 177.7 (1)°. These data are relevant in interpreting different electrochemical processes where gold–thio­urea species are formed.     

Gold and Silver Chains Supported by Linear Hexaphosphine Ligands

A new linear hexaphosphine, rac‐cis,cis,trans‐ bis{[(diphenylphosphinomethyl)phenylphosphinomethyl]phenylphosphino}methane ( P₆ ), was synthesized and isolated as a pure isomer, confirmed by transforming to the corresponding phosphine sulfide. The methylene‐bridged linear hexaphosphine readily organized flexible gold(I) and silver(I) hexanuclear chains, [M₆(μ‐ P₆ )₂]X₆ (X₆=(OTf)₆, M=Au ( 1 ), Ag ( 2 ); X₆=Cl₂(PF₆)₄, M=Au ( 3 )). The hexaphosphine also supported a tetrasilver(I) complex [Ag₄(μ‐ P₆ )₂](OTf)₄ ( 4 ), which was readily transformed by treatment with AgOTf into 3 , revealing a drastic alternation of the two P₆ arrangement. The hexagold(I) chains exhibited a considerably red‐shifted absorption (～410 nm) and emission (540–580 nm) to ¹[5d_σ*→6p_σ] and from ³[5d_σ*→6p_σ] excited states of the metal centers, respectively. The new linear hexaphosphine could be a useful tool to construct linear metal clusters as subnano building blocks.     

Surface chemical states of gold nanoparticles prepared using the solution-plasma method in a CsCl aqueous solution

In this study, gold nanoparticles (AuNPs) prepared in a 5 mM CsCl aqueous solution using the solution-plasma method are characterized via transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy with synchrotron radiation (SR-XPS). The particle diameter is measured over the process time via TEM. During the solution-plasma process, small particles of 2.1 to 2.2-nm diameter are generated in the CsCl aqueous solution; these particles then enlarge via Ostwald ripening over time until they reach an equilibrium size of ~13 nm after 36 days. In addition, the surface chemical states of the AuNPs are characterized at different depths via SR-XPS. The SR-XPS measurements obtained using incident X-ray energy (hν) of 945.0 eV revealed that Cs─Au, Cl─Au, and Cs─Cl─Au bonds are present 1.2 nm below the surface. The measurements obtained at an incident X-ray energy of 2515.0 eV showed that Cs─Cl─Au bonding is also present 2.5 nm below the surface, indicating that Cs and Cl strongly interact with Au. The TEM and SR-XPS measurements revealed that 2 processes occur cyclically during the growth process via Ostwald ripening: (i) the Cs and Cl in the aqueous solution adsorb on the AuNP surface and (ii) Au atoms subsequently bond to the AuNPs surface.