Brominated Pd-on-Au Nanostructures Enable Reductive Relay Isomerization of Alkynes to E-alkenes.

Over the past few decades, metallic nanoparticles (NPs) have been of great interest due to their unique properties which distinguish them from those of bulk metals. Many attempts have been conducted to investigate the characteristics of NPs and their applications. However, the sintering process which converts metallic NPs to conductive film was not established yet. In this study, the microstructure evolution of Au NPs after sintering under different thermal condition was examined and the film quality was studied based on densification, organic residues and electrical resistivity. Au NP ink dispersed in a toluene were spin coated on Ni-plated FCCL or Si substrates and thermally treated in a furnace under different sintering profiles under various types of flows such as air, nitrogen (N2), or reducing atmosphere of formic acid (FA). The Au ink was consisted of Au NPs coated with an organic capping molecule. The capping molecules not only help NPs to disperse but prevent aggregation and precipitation of NPs out of solution. When the NPs are treated by thermal process, the surface ligands from capping molecule start to decompose and necking and melting of NPs occur producing the film with the electrical conductivity. The diameter of Au NPs was approximately between 5-7 nm with spherical shape. The Au film sintered under air showed only necking between neighboring Au NPs without further grain growth. When Au NPs films were sintered under N2 atmosphere, NPs fused together in clusters. Under sintering with flows of FA, a larger area of pores due to the volume shrinkage of the film was observed since an agglomeration and melting of NPs were considerably progressed compared to the film sintered under N2. Sintering with a flow of a single gas such as air or N2 showed organic residues in the film indicated by C-H or C-O stretch peaks. However, when mixed flows of FA and N2 were applied, there was no IR peaks from organic substances observed in the film. It is assumed that the organic capping molecules surrounding the Au NPs were removed significantly with sintering with two flows of FA and N2. The microstructure showed less pore distribution and lower level of organic residues compared to those sintered under air, N2, or FA atmospheres. The electrical resistivity was about twice of bulk value of 2.44 μΩ -cm. Overall Au NPs film sintered under FA and N2 resulted in a better sintering effect based on densification of the film and level of residual organics, translating into a relatively high electrical conductivity.

Nanocomposite materials of the Au nanoparticles (Au/PDDA-G) and the bimetallic PtAu nanoparticles on poly-(diallyldimethylammonium chloride) (PDDA)-modified graphene sheets (PtAu/PDDA-G) were prepared with hydrothermal method at 90 °C for 24 h. The composite materials Au/PDDA-G and PtAu/PDDA-G were evaluated by transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and thermogravimetric analysis (TGA) for exploring the structural characterization for the electrochemical catalysis. According to TEM results, the diameter of Au and bimetallic PtAu nanoparticles is about 20–50 and 5–10 nm, respectively. X-ray diffraction (XRD) results indicate that both of PtAu and Au nanoparticles exhibit the crystalline plane of (111), (200), (210), and (311). Furthermore, XRD data also show the 2°–3° difference between pristine graphene sheets and the PDDA-modified graphene sheets. For the catalytic activity tests of Au/PDDA-G and PtAu/PDDA-G, the mixture of 0.5 M aqueous H2SO4 and 0.5 M aqueous formic acid was used as model to evaluate the electrochemical characterizations. The catalytic activities of the novel bimetallic PtAu/graphene electrocatalyst would be anticipated to be superior to the previous electrocatalyst of the cubic Pt/graphene.

Gold (Au) nanoparticles (NPs) are widely used in nanomedical applications as a carrier for molecules designed for different functionalities. Previous findings suggested that biological molecules, including amino acids, could contribute to the dissolution of Au NPs in physiological environments and that this phenomenon was size-dependent. We, therefore, investigated the interactions of L-cysteine with 5-nm Au NPs by means of time-of-flight secondary ion mass spectrometry (ToF-SIMS). This was achieved by loading Au NPs on a clean aluminum (Al) foil and immersing it in an aqueous solution containing L-cysteine. Upon rinsing off the excessive cysteine molecules, ToF-SIMS confirmed the formation of gold cysteine thiolate via the detection of not only the Au-S bond but also the hydrogenated gold cysteine thiolate molecular ion. The presence of NaCl or a 2-(N-morpholino)ethanesulfonic acid buffer disabled the detection of Au NPs on the Al foil. The detection of larger (50-nm) Au NPs was possible but resulted in weaker cysteine and gold signals, and no detected gold cysteine thiolate signals. Nano-gold specific adsorption of L-cysteine was also demonstrated by cyclic voltammetry using paraffine-impregnated graphite electrodes with deposited Au NPs. We demonstrate that the superior chemical selectivity and surface sensitivity of ToF-SIMS, via detection of elemental and molecular species, provide a unique ability to identify the adsorption of cysteine and formation of gold-cysteine bonds on Au NPs.

Achieving stereoselective alkyne semi‐hydrogenation to E ‐alkenes remains a persistent challenge due to inherent limitations of conventional catalysts in controlling stereochemistry and suppressing over‐hydrogenation. Herein, we resolve this fundamental dilemma through a rationally designed brominated Pd‐on‐Au nanocatalyst (Pd 0.03 ‐Br 1 ^Au/TiO 2 ) featuring spatially segregated active sites operating via reductive relay isomerization. This sophisticated architecture enables unprecedentedly efficient E ‐alkene synthesis (>96% selectivity for trans ‐stilbene at near‐quantitative conversion). Fabricated by sequentially depositing Au nanoparticles on TiO 2 , with tiny Pd loading on Au, and controlled surface bromination, the catalyst leverages synergistic cooperativity: The TiO 2 –Au interface primarily activates formic acid (FA) to generate reactive surface‐bound hydride species (H*) while minimizing unproductive H 2 formation; concurrently, atomically dispersed Pd 1 sites on Au nanoparticles exclusively mediate rapid Z ‐to‐ E isomerization, whereas bromide‐capped Pd nanoclusters kinetically regulate FA dissociation kinetics at TiO 2 –Au interface and sterically block overhydrogenation adsorption geometries. This spatially orchestrated multisite system decisively overcomes classical activity–selectivity trade‐offs, establishing a universally applicable framework for decoupling and optimizing individual catalytic functions in heterogeneous design. Our work delivers both a sustainable strategy for scalable trans ‐alkene production and fundamental mechanistic insights into complex cooperative reaction networks.

Surface metallization of silicon (Si) substrates, that is, adhesive metal films formation on Si is important for obtaining infallible electrical contacts in various devices such as solar cells and power devices. Autocatalytic electroless deposition, which is a conventional method to metallize non-conductive substrates, has several advantages like simplicity of process, uniformity of deposited films, and the covering of complicated structures. The autocatalytic electroless deposition is expected to replace sputtering process of back metal of power devices and screen printing process of electrodes of solar cells. This process requires surface-activation pretreatment of non-conductive substrates (1). Adhesion of metal films obtained by using conventional pretreatments is much lower than that is necessary for the electrical contacts. We recently developed a new surface-activation process for the direct electroless deposition of adhesive metal films on Si substrates (2, 3). The process consists of two steps: Step 1) formation of gold (Au) nanoparticles by electroless displacement deposition; and Step 2) metal films formation on the Si surface by autocatalytic electroless deposition. In previous study, we found that Au nanoparticles have an excellent ability to bind metal films to Si surfaces. In this study, we have investigated the effect of interfacial structure of Au and Si. At the first step of the two-step process, Au nanoparticles were deposited on a p-Si(100) substrate by electroless displacement deposition using a HAuCl4 solution containing HF. At the second step, the nickel-phosphorus alloy (Ni-P) film was electrolessly formed on the Si substrates by using NiSO4 as a metal salt and NaPH2O2as a reducing agent. The adhesion of the electrolessly deposited Ni-P films on Si substrates was examined by a tape test based on Japanese Industrial Standard JIS H8504 corresponding to ISO 2819. The adhesion was evaluated by maximum Ni-P film thickness that occurred no peeling by the tape test. We analyzed the interfacial structure of Au/Si by X-ray diffraction (XRD, Rigaku Ultima IV) and transmission electron microscopy (TEM, JEOL JEM-2100). Figure 1 shows the XRD patterns of Au nanoparticles on p-Si(100) substrates. Only Au(200) diffraction line was obtained for the sample immersed in the Au-deposition-solution for 120 s (Fig.1 (a)). The cross-sectional TEM observation of Si wafer Au-nanoparticle-deposited for 210 s revealed that Au nanoparticles epitaxially grew on Si and each particle was single crystalline. At the interface between Au and Si, Au-Si alloy formation was observed by TEM and XPS (3). Farther deposition yielded Au(200) and (111) diffraction lines such as Fig.1 (b) for immersion deposition time of 240 s. Figure 2 shows the maximum film thickness (adhesion) of electrolessly deposited Ni-P alloy films on Si substrates as a function of Au nanoparticle deposition time. The maximum film thickness increased with deposition time of Au nanoparticles, reached maximum at 120 ~ 210 s, and decreased afterwards. This result indicates that the electrolessly deposited Ni-P films have high adhesion in case that the Au nanoparticles epitaxially deposited on Si substrates. The growth of polycrystalline Au on epitaxially deposited Au nanoparticles on Si decreases the adhesion of the electrolessly deposited Ni-P films. In conclusion, it was revealed that single crystalline Au nanoparticles epitaxially grown on Si substrates yield high adhesion of electrolessly deposited metal films. ACKNOWLEDGEMENTS The present work was partly supported by KAKENHI (26289276) from JSPS. REFERENCES M. Paunovic and M. Schlesinger, Fundamentals of Electrochemical Deposition, 2nd ed., Wiley, NY (2006).S. Yae, M. Enomoto, H. Atsushiba, A. Hasegawa,N. Fukumuro, S. Sakamoto, and H. Matsuda., ECS Trans., 53 (6), 99 (2013).H. Atsushiba, Y. Orita, S. Sakamoto, N. Fukumuro, and S. Yae; ECS Trans., 61(10), 9 (2014). Figure 1

Enhanced thermoelectric performance of vertically aligned silicon nanowires through the cold spot effect and charge carrier trapping effect of attached gold nanoparticles

The difficulty in patterning the structures at sub-wavelength range leads to employ the bottom-up approach to form nanostructures of metals as well as dielectric components that disperse them in host media. The optical properties of nanoparticles are studied with UV-Vis 750 (lambda) NIR spectroscopy and fit with empirical relations. The refractive index is about the volume fraction of particles. The AuGe nanoparticles demonstrate improved absorbance, lower refractive index, and higher extinction than Au nanoparticles formed with similar thermal process. Surface plasmon resonance (SPR) phenomena are highly sensitive to the bonding between atoms, atomic structure, and the electronic configuration in atoms of the given material. If one takes into account the structure of materials, then the literature on eutectic alloys predicts that alloying gold with germanium (AuGe) with varying compositions will also change the x-ray diffraction peak positions of gold itself. The peak shift can be interpreted as the change in grain size or shift in grain boundaries implying a corresponding change in material’s atomic arrangement within lattice structure. As a result, there will be a change in the charge distribution of free electron cloud in original gold ultimately affecting a change in the plasmon resonance frequency and thereby modulating the various optical phenomena such as absorbance, reflectance, and refractive index. This alloying also brings a change in the dielectric constant of the material such that the plasmonic behavior may shift among different regions (UV, visible, NIR, MWIR, and LWIR). Metal semiconductor eutectic alloy which is widely popular as a soldering material would have scope in futuristic photonic applications due to its tuneable optical properties. In this work, we study the effects of Au and AuGe nanoparticle deposition on GaAs films grown by molecular beam epitaxy (MBE). Au and AuGe thin films (12-nm thick) were annealed in the temperature ranges of 400–800 and 300–700 °C, respectively, to form Au and AuGe nanoparticles. The formation of these nanoparticles was confirmed by scanning electron microscopy (SEM) measurements. Optical absorption spectroscopy measurements showed plasmon resonance peaks at around 670 and 535 nm for the AuGe-deposited 300 °C-annealed sample and Au-deposited 600 °C-annealed sample on sapphire, respectively, thereby confirming the plasmonic effect. Correlation of Raman spectroscopy measurement results with X-ray diffraction measurement results reveal that the transverse optical mode intensity and full width at half maximum of the GaAs (400) peak increased with an increase in annealing temperature, indicating degradation of the crystalline properties of GaAs film at higher annealing temperatures. The highest increments of the photoluminescence (PL) intensities in comparison to that of the bare GaAs film were observed to be 37 and 77% for the Au-deposited 600 °C-annealed and AuGe-deposited 300 °C-annealed samples, respectively. These enhancements of PL spectra are an indication of the significant scattering of photons by Au and AuGe nanoparticles, and they are attributed mainly to the contribution of the local surface plasmon resonance of these nanoparticles. A comparative analysis of PL enhancements revealed that AuGe nanoparticles induced a greater enhancement than Au nanoparticles. The calculated activation energies of the Au-deposited 600 °C-annealed sample, AuGe-deposited 300 °C-annealed sample, and bare GaAs sample were around 18, 24, and 33 meV, respectively. We found one-order increment in peak responsivity of AuGe plasmonic-based trilayer InAs quantum dot detector in comparison to as-grown detector at 80 K. Therefore, this study is expected to be very useful in the realization of high-performance plasmonic-based optoelectronic and sensing devices.

Deposition of CdS and Au nanoparticles on TiO2(B) spheres towards superior photocatalytic performance

Photocatalytic conversion of biomass is considered an effective, clean, and environmentally friendly route to obtain high-valued chemicals and hydrogen. However, the limited conversion efficiency and poor selectivity are still the main bottlenecks for photocatalytic biomass conversion. Herein, we report the highly selective photocatalytic conversion of glucose solution on holo-symmetrically spherical three-dimensionally ordered macroporous TiO₂-CdSe heterojunction photonic crystal structure (s-TCS). The obtained s-TCS photocatalysts show excellent stability and strong light harvesting, uniform mass diffusion and exchange, and efficient photogenerated electrons/holes separation and utilization. The optimized s-TCS-4 photocatalyst displays the highest photocatalytic performance for glucose oxidation and hydrogen production. The glucose conversion, lactic acid selectivity, and yield on s-TCS-4 are about 95.9%, 94.3%, and 96.4%, respectively. The photocatalytic production of lactic acid for s-TCS-4 (18.5 g/L) is 2.3 times higher than the pure spherical TiO₂ photonic crystal without CdSe (s-TiO₂, 8.1 g/L), and the hydrogen production rate of s-TCS-4 is 9.4 times that of s-TiO₂. For the first time, we reveal that the photocatalytic conversion of glucose to lactic acid is a third-order and four-electron-involved reaction. This work could shed some new light on the efficient photocatalysis conversion of biomass to highly value-added products with high selectivity and yield, and simultaneously sustainable hydrogen evolution.

A Reduced reduced graphene oxide (RGO)-gold (Au) nanoparticle (NP) nanocomposite was synthesized by simultaneously reducing the Au ions and depositing Au NPs on onto the surface surface of the RGOsRGO simultaneously. To facilitate the reduction of Au ions and the generation of oxygen functionalities for anchoring the Au NPs on the RGOsRGO, ultrasound irradiation was applied to the mixture of reactants. The functional groups were investigated with FT-IR spectra. From the Raman and XPS spectra, the oxygen groups were identified as hydroxyl, epoxy, and carboxyl groups, the same as the one from graphene oxide (GO). As a result, the dense and uniform deposition of nanometer-sized Au NPs with nanometer size was observed on the RGO sheets sheet was observed with from the TEM imagesimage. The Oxygen oxygen functional groups that formed on the surface surface of the RGOs RGO seemed to have served serve as links for Au NPs NP attachment, through the electrostatic attraction of Au ions. Hybrid materials could thus be produced in a short time, with a high yield, by via ultrasound application. Besides, it ultrasound application could can readily take goldAu- binding- peptide (GBP)-modified biomolecules, readily implying its possibility in possible biological applications.

Silicon carbide (SiC) is one of the most promising semiconductor materials for a next generation of power devices. Its physical properties such as breakdown electric field and thermal conductivity are higher and more suitable for efficient power devices than those of silicon, which is common semiconductor material for the present devices. The metallization of SiC surfaces is a key technology to use SiC for power devices. The autocatalytic electroless deposition, which is a conventional method to metallize non-conductive substrates, has several advantages, however, cannot produce adhesive metal films directly on SiC. We recently developed a new surface-activation process for the direct electroless deposition of adhesive metal films on silicon substrates (1, 2). This process uses gold (Au) nanoparticles epitacially grown on silicon by an electroless displacement deposition (3, 4). In this study, this process is applied for formation of adhesive metal films on SiC. The single crystalline n-type 4H-SiC (0001) wafers were used as the substrates. Au nanoparticles were deposited on SiC substrates using a HAuCl4 solution containing HF or KOH under photoillumination using a Hg-Xe short arc lamp. Then, nickel-phosphorus alloy (Ni-P) films were electrolessly formed on the SiC substrates by using NiSO4 solution containing NaPH2O2as a reducing agent. The adhesion of the electrolessly deposited Ni-P films on SiC substrates was examined by a tape test based on Japanese Industrial Standard JIS H8504 corresponding to ISO 2819. Figure 1 shows SEM images of Au-nanoparticle-deposited SiC substrates. The size and particle density of Au deposited using the solution containing KOH (Fig. 1 (b)) were larger than that using HF (Fig.1 (a)). The surface of SiC substrates was roughened by the electroless deposition of Au nanoparticles. No photoillumination significantly attenuated the Au deposition. These results indicate that this Au nanoparticle deposition is a photoelectrochemical displacement reaction. The autocatalytic electroless deposition of Ni-P films was initiated on the Au-nanoparticle-deposited SiC substrate. No deposition occurred on a bare SiC substrate. The adhesion of metal films formed on the SiC substrates depended on the deposition time of Au nanoparticles. Immersion of SiC substrates in the Au-deposition solution containing KOH for 15 min obtained high adhesion. No peeling occurred up to 1.3 μm in thickness of Ni-P films by the tape test. This result is similar to that in the case of single crystalline silicon substrates (1 - 4). In conclusion, we successfully formed adhesive metal films directly on single crystalline SiC substrates by using wet processes that are electroless displacement deposition of Au nanoparticles and common autocatalytic electroless deposition of Ni-P alloy films. Acknowledgements The present work was partly supported by KAKENHI (26289276) from JSPS and A-STEP from JST. References 1) S. Yae, M. Enomoto, H. Atsushiba, A. Hasegawa,N. Fukumuro, S. Sakamoto, and H. Matsuda., ECS Trans., 53 (6), 99 (2013). 2) H. Atsushiba, Y. Orita, S. Sakamoto, N. Fukumuro, and S. Yae., ECS Trans., 61(10), 9 (2014). 3) N. Yamada, H. Atsushiba, S. Sakamoto, N. Fukumuro, and S. Yae., ECS Trans., 69(39), 59 (2015).4) N. Yamada, S. Sakamoto, N. Fukumuro, and S. Yae., Symposium Z01 in this meeting (2016). Figure 1

Electrocatalytic oxidation of ethylene glycol (EG) on supported Pt and Au catalysts in alkaline media: Reaction pathway investigation in three-electrode cell and fuel cell reactors

Here we describe the size-selective, hydroquinone (HQ)-mediated electrophoretic deposition of 4 and 15 nm diameter citrate-stabilized Au nanoparticles (NPs) onto a glass/indium-tin-oxide (ITO) electrode. Protons liberated from HQ during electrochemical oxidation at the Au NP surface during collisions with the glass/ITO electrode lead to Au NP deposition through neutralization of the citrate stabilizer surrounding the Au NPs, protonation of the glass/ITO electrode, or some combination of the two. Interestingly, the 4 nm Au NPs deposit at about 300-400 mV more negative potential than that of 15 nm diameter Au NPs because of faster HQ oxidation kinetics at the 4 nm NPs, leading to lower overpotentials. This allows for selective deposition of the 4 nm Au NPs over 15 nm Au NPs in a solution containing a mixture of the two by controlling the electrode potential. Controlled pH experiments indicate that significant NP deposition occurs on glass/ITO at a pH of ∼3, giving insight into the local pH needed from HQ oxidation in order to deposit the Au NPs. Experiments performed at different ionic strengths confirm that migration is a major mode of mass transport of the NPs to the glass/ITO. Long deposition times lead to films of densely packed Au NPs that are mostly free from NP-NP contact, indicating that some electrostatic repulsion between the NPs remains during the deposition. This simple method of Au NP deposition may find use for separation of Au NPs and electrode device preparation for a variety of sensor and electrocatalysis applications.

Pt and Au nanoparticles with controlled Pt : Au molar ratios and PtAu nanoparticle loadings were successfully self-assembled onto poly(diallyldimethylammonium chloride) (PDDA)-functionalized graphene (PDDA-G) as highly effective electrocatalysts for formic acid oxidation in direct formic acid fuel cells (DFAFCs). The simultaneously assembled Pt and Au nanoparticles on PDDA-G showed superb electrocatalytic activity for HCOOH oxidation, and the current density associated with the preferred dehydrogenation pathway for the direct formation of CO(2) through HCOOH oxidation on a Pt(1)Au(8)/PDDA-G (i.e., a Pt : Au ratio of 1 : 8) is 32 times higher than on monometallic Pt/PDDA-G. The main function of the Au in the mixed Pt and Au nanoparticles on PDDA-G is to facilitate the first electron transfer from HCOOH to HCOO(ads) and the effective spillover of HCOO(ads) from Au to Pt nanoparticles, where HCOO(ads) is further oxidized to CO(2). The Pt : Au molar ratio and PtAu nanoparticle loading on PDDA-G supports are the two critical factors to achieve excellent electrocatalytic activity of PtAu/PDDA-G catalysts for the HCOOH oxidation reactions.

Lysine-capped gold nanoparticles can be electrostatically assembled on the surface of Bacillus cerius, a Gram-Positive bacterium. The conductivity of the “gold-plated” bacteria assembly immobilized between electrodes is a function of the humidity experienced by the nanoparticles.