Stable Dispersions of PVP-Protected Au/Pt/Ag Trimetallic Nanoparticles as Highly Active Colloidal Catalysts for Aerobic Glucose Oxidation

A simple, effective method has been demonstrated to synthesize Au/Pt/Ag trimetallic nanoparticles (TNPs) with an average diameter of 1.5 nm by reduction of the corresponding ions with rapid injection of NaBH4. The prepared TNPs were characterized by UV–vis, X-ray diffraction, X-ray photoelectron spectroscopy (XPS), high-resolution transmission electron microscopy, and energy dispersion X-ray spectroscopy in high-resolution scanning transmission electron microscopy. The activity of the TNPs is several times higher than that of Au NPs with nearly the same particle size. The high catalytic activities of the Au/Pt/Ag TNPs can be ascribed to the following factors: (1) the small average size, about 1.5 nm in diameter, and (2) the formed negatively charged Au atoms due to electron donation of Ag neighboring atoms and poly(N-vinyl-2-pyrrolidone) acting as catalytically active sites for aerobic glucose oxidation. The presence of the negatively charged Au atoms was supported by XPS measurements and electron density calculation with density functional theory

Fabrication of Liquid Crystal Sol Containing Capped Ag−Pd Bimetallic Nanoparticles and Their Electro-Optic Properties

Liquid crystal molecule-capped Ag−Pd bimetallic nanoparticles (atomic ratio = 1/9, 1/4, 1/1, 4/1, and 9/1) were prepared by photoirradiation of the tetrahydrofuran solution of silver perchlorate and palladium(II) acetate in the presence of liquid crystal molecule, 4′-pentylbiphenyl-4-carbonitrile. (5CB is often used for this compound based on conventional nomenclature 4′-pentyl-4-cyanobipenyl. Thus, 5CB is used in this paper.) The prepared bimetallic nanoparticles had an average diameter of 1.8−3.6 nm. Infrared spectra of carbon monoxide adsorbed on the bimetallic nanoparticles suggested that bimetallic nanoparticles had a random alloy structure. The nanoparticles were dispersed in liquid crystal 5CB to construct novel twisted nematic liquid crystal devices (TN-LCDs). The TN-LCDs containing Ag−Pd bimetallic nanoparticles revealed the electro-optic properties depending on the composition of nanoparticles, especially surface composition of nanoparticles, which was shown to be of importance to control not only the properties but also the stability of nanoparticle-doped LCDs by bimetallization

Novel Formation of Ag/Au Bimetallic Nanoparticles by Physical Mixture of Monometallic Nanoparticles in Dispersions and Their Application to Catalysts for Aerobic Glucose Oxidation

Ag/Au bimetallic nanoparticles (BNPs) with a size less than 2 nm were prepared by physical mixture of colloidal dispersions of Ag and Au nanoparticles (NPs). This provides an example of fabrication of BNPs with self-organization by the reaction between metal NPs. Although Ag/Au BNPs having different structures and compositions are one of the most widely studied bimetallic systems in the literature due to their wide range of uses such as in catalysis, electronics, plasmonics, optical sensing, and surface-enhanced Raman scattering, we first prepared such BNPs by physical mixture and characterized them by UV–vis spectroscopy, SERS, XPS, TEM, and EDS in HR-STEM. The present fabrication method has the advantage of avoiding the unfavorable formation of AgCl precipitates in the reaction process which are always produced when Ag⁺ ions are used as a starting material in combination with a HAuCl₄ precursor. These Ag/Au BNPs showed high catalytic activities for aerobic glucose oxidation, and the highest activity of 11 510 mol of glucose·h^–1·mol of metal^–1 was observed for the BNPs with a Ag/Au atomic ratio of 1/4; the activity value is about 2 times higher than that of Au NPs with nearly the same particle size. XPS and DFT calculation results show that the negatively charged Au atoms due to the electron charge transfer effects from neighboring Ag atoms and poly­(<i>N</i>-vinyl-2-pyrrolidone) act as catalytically active sites and play an important role in the aerobic glucose oxidation

Surfactant-Wrapped n‑Type Organic Thermoelectric Carbon Nanotubes for Long-Term Air Stability and Power Characteristics

The low air stability and unfavorable power properties of n-type carbon nanotubes (CNTs) limit the development of flexible electronics and organic transistors. Hence, determining an optimal n-dopant remains crucial. We propose the high surface coverage of adsorbed surfactant layers on nanotubes to maintain a continuous carrier stability and preserve the organic thermoelectric properties of n-type materials. Aqueous solutions of gemini surfactants with a tail length of 8 or 12 C atoms (8-3-8 and 12-3-12) were used as dispersants for the nanotubes. The gemini surfactants facilitated the enhanced dispersion of nanotubes to a greater degree than single-chain surfactants, ultimately improving the thermoelectric performance of films. An in-plane dimensionless figure-of-merit value of 6.04 × 10–3 was recorded for the optimized 12-3-12/CNTs, which was comparable to that of oil-soluble dopants. In addition, the n-type thermoelectric characteristics had not been previously investigated beyond 100 d in conventional systems because of a significant drop in the power factor, which was caused by a decrease in the negative Seebeck coefficient. We therefore evaluated the air stabilities of CNTs fabricated using 8-3-8 and 12-3-12, observing that gemini surfactants extended the lifetimes and enhanced the thermoelectric performances of n-type carriers to a greater extent than single-chain surfactants. Approximately 83% of the initial power characteristics were retained for 12-3-12/CNTs after 120 d under air, which was attributed to the high surface area of the adsorbed gemini surfactant on the nanotubes. The low specific surface areas of the bare nanotubes reduced the oxygen-accessible area, suppressing hole doping caused by atmospheric oxygen and improving the stabilities and power characteristics of n-type CNTs. The future design of surfactants to control the form of cationic molecular adsorption is therefore essential to achieve sustained air stabilities and favorable output properties for n-type materials

Long-Alkyl-Chain Phosphonium Surfactant Molecular Wrapping to Block Oxygen Impurities in n‑Type Carbon Nanotubes for Thermoelectric Applications

In several electronics applications, the instability of components containing n-type carbon nanotubes (CNTs) to atmospheric oxidation in harsh environments or high temperatures is a significant concern. Here, we reported that a dense molecular wrapping of n-type CNTs with phosphonium salts reduced the exposed CNT surface by 79% and suppressed the electrophilic reaction of oxygen on the CNT surface. After aging at 353 K for 28 days, 89% of its initial thermoelectric power factor was retained (290.3 μW m–1 K–2). This opens new avenues for the use of n-type materials in high-temperature electronics

Pd–Rh Alloyed Nanoparticles on Zeolite Imidazolide Framework-67 for Methyl Orange Degradation

Bimetallic or alloyed nanoparticles (NPs) are important materials that often exhibit chemical properties different from those of their monometallic counterparts. However, access to uniformly alloyed bimetallic particles, particularly in the Pd–Rh system, is difficult because of the thermodynamic immiscibility of the individual metals. Herein, we propose a method for accumulating Pd–Rh alloy particles on the surface of zeolite imidazolide framework-67 (ZIF-67), a chemically stable metal–organic framework, under mild conditions at 25 °C. The degradation of methyl orange was used to test the applicability of the resultant material as a heterogeneous catalyst. A turnover frequency of 38.5 h–1 was recorded for Pd0.12Rh0.88/ZIF-67, which is higher than that of catalysts with either Pd (17.2 h–1) or Rh (16.5 h–1). The acceleration of methyl orange decomposition was attributed to electron transfer from Pd to Rh in the alloy particles due to the differences in Pauling electronegativity and an increase in metallic Rh on the catalyst surface. No metal leakage or structural degradation of the ZIF-67 support was observed during the catalytic reaction. Pd0.12Rh0.88/ZIF-67 could actively degrade methyl orange, Congo red, and methylene blue. The structure of the catalyst remained intact even when a mixed solution of all three dyes was circulated for 60 min in a fixed-bed system, and the catalyst conversion rate exceeded 99.7%. Our results collectively demonstrate the successful preparation of Pd–Rh-supported catalysts and their application to the continuous reduction of multicomponent dye mixtures. The metal NP-MOF composites prepared using the proposed approach are free from MOF pore damage and can maintain their specific surface area. Therefore, this strategy could give impetus to research on catalytic applications of NP-MOF composites