Polyol Synthesis Method Research Articles

Synthesis of different copper nanostructures by the use of polyol technique

Self-seeding polyol synthesis method, without additives, was employed for the fabrication of different copper nanostructures. The pertinent parameters including temperature, copper concentration and molar ratio of poly(vinylpyrrolidone) (PVP) to copper were assessed for achieving different size and morphology of copper nanos- tructures, i.e., nanowire, nanosphere and nanocube. It was found that PVP-to-copper molar ratio has the most signif- icant effect on the geometry of the copper nanostructures. Graphical Abstract

Magneto-optical properties of Mn3+ substituted Fe3O4 nanoparticles

MnxFe3−xO4 (0.0≤x≤1.0) nanoparticles were synthesized by the polyol synthesis method and the effect of Mn3+ substitution on structural, magnetic and optical properties of Fe3O4 was studied. X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), UV–visible spectroscopy and vibrating sample magnetometer (VSM) were used to study the physical properties. The crystallite (from XRD) and particle sizes (from TEM and SEM) are in close agreement with each other. Lattice parameter increases with increasing Mn3+ concentration, due to the respective larger ionic radius of Mn3+ ion compared with the Fe3+ ion. The magnetic hysteresis (M–H) curves revealed superparamagnetic characteristics of the products. The extrapolated specific saturation magnetization (σs) values decreased from maximum value of 47.3emu/g to the minimum value of 25.6emu/g by increasing Mn composition. The particle size dependent Langevin function was applied to determine the magnetic particle dimensions (Dmag) around 15nm. The observed magnetic moments of NPs are in range of (1.06–1.96)µB and significantly less than 4µB of bulk Fe3O4. Magnetic anisotropy was offered as uniaxial and calculated effective anisotropy constants (Keff) are between 34.47×104Erg/g and 21.83×104Erg/g. The size-dependent saturation magnetization suggests the existence of a magnetically inactive layer as 1.638nm on FeMnxFe2−xO4 NPs. The UV–vis diffuse reflectance spectroscopy (DRS) and Kubelka−Munk theory were applied to determine the optical properties. The estimated optical band gap (Eg) values dropped almost linearly from 2.05eV to 1.17eV with increasing Mn composition.

Electrocatalytic activity of Vulcan-XC-72 supported Pd, Rh and PdxRhy toward HOR and ORR

Carbon-supported (Vulcan XC-72) Pd, Rh, and PdxRhy (20wt%, x:y=1:1, 3:1, 1:3) electrocatalysts are prepared according a modified pulse-microwave assisted polyol synthesis method and their electrocatalytic activity toward hydrogen electrooxidation (HOR) and oxygen reduction (ORR) reactions is investigated.The as-prepared electrocatalysts are physicochemically characterized by transmission electron microscopy (TEM) and X-ray diffraction (XRD). Their electrochemical characterization is carried out by the aid of cyclic voltammetry (CV), rotating disk electrode (RDE) and chronoamperometry (CA) techniques.It is found that among the as-prepared catalysts, PdRh3 exhibits the highest HOR (ik=7.6mAcm−2) and ORR (ik=5.20mAcm−2) electrocatalytic activity. It is also found that the addition even of small amount of Rh (Pd3Rh-2.7μgcm−2) enhances both Pd’s HOR and ORR electrocatalytic activity by 33% and by 53%, respectively.For the as prepared electrocatalysts, the HOR activity order, in terms of kinetic current density, is found to be as follows: PdRh3≈PdRh>Rh>Pd3Rh>Pd, while a similar trend was found for ORR activity: PdRh3>PdRh>Rh>Pd3Rh>Pd.

수산화코발트의 초음파 폴리올 합성과 자성 선별법을 이용한 코발트 나노 분말의 제조

In this study, cobalt nanopowder is fabricated by sonochemical polyol synthesis and magnetic separation method. First, sonochemical polyol synthesis is carried out at 220oC for up to 120 minutes in diethylene glycol (C4H10O3). As a result, when sonochemical polyol synthesis is performed for 50 minutes, most of the cobalt precursor (Co(OH)2) is reduced to spherical cobalt nanopowder of approximately 100 nm. In particular, aggregation and growth of cobalt particles are effectively suppressed as compared to common polyol synthesis. Furthermore, in order to obtain finer cobalt nanopowder, magnetic separation method using magnetic property of cobalt is introduced at an early reduction stage of sonochemical polyol synthesis when cobalt and cobalt precursor coexist. Finally, spherical cobalt nanopowder having an average particle size of 22 nm is successfully separated.

Synthesis of CuNi/C and CuNi/γ-Al2O3Catalysts for the Reverse Water Gas Shift Reaction

A new polyol synthesis method is described in which CuNi nanoparticles of different Cu/Ni atomic ratios were supported on both carbon and gamma-alumina and compared with Pt catalysts using the reverse water gas shift, RWGS, reaction. All catalysts were highly selective for CO formation. The concentration of CH4was less than the detection limit. Cu was the most abundant metal on the CuNi alloy surfaces, as determined by X-ray photoelectron spectroscopy, XPS, measurements. Only one CuNi alloy catalyst, Cu50Ni50/C, appeared to be as thermally stable as the Pt/C catalysts. After three temperature cycles, from 400 to 700°C, the CO yield at 700°C obtained using the Cu50Ni50/C catalyst was comparable to that obtained using a Pt/C catalyst.

Insight into the Effect of Sn on CO and Formic Acid Oxidation at PtSn Catalysts

The role of Sn on the catalytic activity for CO and formic acid oxidation is studied by comparing the activities of differently treated PtSn/C and Pt/C catalysts. The catalysts are prepared by a microwave-assisted polyol synthesis method. As revealed by scanning tunneling and transmission electron microscopic (STM and TEM) characterization, the outcomes of the synthesis procedure for both Pt and PtSn are small particles, ∼1.5 nm in diameter. Upon deposition on the carbon support, the particle size increases to ∼2.5 nm due to sintering. X-ray diffraction (XRD) analysis shows that PtSn/C has a low alloying degree and is mainly composed of Pt and Pt3Sn phases. The remaining Sn is present in the form of very small tin oxide particles. Different surfaces are obtained by double-layer, oxide, and CO annealing of the Pt/C and PtSn/C catalysts and by modifying the CO-annealed surfaces with irreversibly adsorbed tin, Snirr. The presence of Sn in any form (oxide, alloyed, or Snirr) on the surface shifts the onset po...

Preparation of SnO<sub>2</sub> Powders by Modified Polyol Synthesis Using 1,2-Propanediol and Calcination

SnO2 powders were prepared using a modified polyol synthesis method and subsequent calcinations. Well-dispersed spherical 2SnO∙(H2O) particles could be synthesized at room temperature through the modified polyol method using tin (II) 2-ethylhexanoate as the precusor, 1,2-propanediol as the solvent, PVP as the capping agent, and sodium borohydride as the reducing agent. The 2SnO∙(H2O) nanoparticles agglomerated to form larger particles during the drying step, and most of these larger nanoparticles coalesced with one another. Finally, these 2SnO∙(H2O) nanoparticles were successfully transformed into the SnO2 phase by calcination for 1 h at 500 °C.

Pulse microwave-assisted synthesis of Pt nanoparticles onto carbon nanotubes as electrocatalysts for proton exchange membrane fuel cells

This study represents a comprehensive pulse microwave-assisted polyol synthesis method to deposit Pt catalysts onto multi-walled carbon nanotubes (CNTs). Three electrocatalysts have been prepared using different microwave pulse (MP=ton/toff) configurations, namely, CAT 3-1 (MP=3), CAT 2-1 (MP=2), and CAT 3-2 (MP=1.5). The experimental results reveal that the CAT 3-2 catalyst possesses the smallest mean particle size of 2.1nm and the most uniform distribution among these catalysts. The CAT 3-2 catalyst also exhibits the highest electrochemical surface area with excellent stability and the best peak power density of 11.4kWgPt−1 (as anode catalyst) and 5.45kWg−1 (as cathode catalyst) at 80°C. On the basis of the experimental results, the well-dispersed Pt particles over the CNT support by the microwave-assisted deposition deliver an improved catalytic activity and excellent stability not only for hydrogen oxidation reaction but also oxygen reduction reaction kinetics.

Ru decorated Pt nanoparticles by a modified polyol process for enhanced catalytic activity for methanol oxidation

Ru decorated Pt nanoparticles on carbon nanotubes (MWCNTs) were prepared by a modified polyol synthesis method for enhanced catalytic activity for methanol oxidation. The characterizations for the electrocatalysts were carried out by transmission electron microscopy (TEM), X-ray diffraction (XRD), cyclic voltammetry (CV) and chronoamperometry (CA). The modified polyol synthesis method promoted position-controlled nucleation and growth of Ru atoms near Pt, and resulted in improved durability against catalyst poisoning compared to PtRu/MWCNTs prepared by common polyol method. This concept also allowed a high loading and dispersion of the catalyst on the carbon supports with few agglomerations of catalyst nanoparticles, resulting in high catalytic activity.

Electron microscopy investigations of the organization of cerium oxide nanocrystallites and polymers developed in polyvinylpyrrolidone-assisted polyol synthesis process

The microstructures and the organization mechanism of cerium oxide (ceria) nanospheres were investigated by transmission electron microscopy. The ceria nanospheres with the diameter of 50–150 nm were produced by the polyol synthesis method with cerium nitrate precursor and with polyvinylpyrrolidone (PVP) used as a protecting agent. Dose-limited observations performed by energy-filtering transmission electron microscopy revealed that the ceria nanospheres were the aggregated products consisting of ceria nanocrystallites ~3 nm in size and PVP-derived polymer products. It was found that the ceria nanocrystallites were oriented within the nanospheres by high-resolution transmission electron microscopy and selected-area electron diffraction. Selective adsorption of PVP on the crystal facets of the ceria nanocrystallites was suggested, and the aggregation of the PVP-adsorbed ceria through cross-linking reaction of PVP causes the crystal orientation.

Structure, morphology and magnetic properties ofMg(x) Zn(1 − x)Fe2O4 ferrites prepared by polyol and aqueous co-precipitation methods: a low-toxicity alternative toNi(x)Zn(1 − x)Fe2O4 ferrites

The synthesis and properties ofMg(x)Zn(1 − x)Fe2O4 spinel ferrites as a low-toxicity alternative to the technologically significantNi(x)Zn(1 − x)Fe2O4 ferrites are reported. Ferrite nanoparticles have been formed through boththe polyol and aqueous co-precipitation methods that can be readilyadapted to industrial scale synthesis to satisfy the demand of a variety ofcommercial applications. The structure, morphology and magnetic properties ofMg(x)Zn(1 − x)Fe2O4 were studied as a function of composition and particle size. Scanning electron microscopy images showparticles synthesised by the aqueous co-precipitation method possess a broad size distribution (i.e. ∼ 80–120 nm) with an average diameter of the order of100 nm ± 20 nm and could be produced in high process yields of up to 25 g l − 1. In contrast, particles synthesised by the polyol-based co-precipitationmethod possess a narrower size distribution with an average diameter in the30 nm ± 5 nm range but are limited to smaller yields of ∼ 6 g l − 1. Furthermore, the polyol synthesis method was shown to control average particle size byvarying the length of the glycol surfactant chain. Particles prepared by both methods arecompared with respect to their phase purity, crystal structure, morphology, magneticproperties and microwave properties.

The pH-Controlled Particle Size Tuning of Nanocrystalline Ni in Polyol Synthesis Method Without Additional Cappant

The pH-Controlled Particle Size Tuning of Nanocrystalline Ni in Polyol Synthesis Method Without Additional Cappant

Synthesis and characterization of phosphate-modified LiMn 2O 4 cathode materials for Li-ion battery

LiMn 2O 4 spinel cathode materials were modified with 2 wt.% Li–M–PO 4 (M = Co, Ni, Mn) by polyol synthesis method. The phosphate surface-modified LiMn 2O 4 cathode materials were physically characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). The charge–discharge test showed that the cycling and rate capacities of LiMn 2O 4 cathode materials were significantly enhanced by stabilizing the electrode surface with phosphate.

Effect of chemisorbed carbon monoxide on Pt/C electrode on the mechanism of the hydrogen oxidation reaction

The influence of poisoning of Pt catalyst by CO on the kinetics and mechanism of H 2 oxidation reaction (HOR) at Pt/C electrode in 0.5 mol dm −3 HClO 4, saturated with H 2 containing 100 ppm CO, was examined with rotating disc electrode (RDE) at 22 °C. Commercial carbon black, Vulcan XC-72 was used as support, while Pt/C catalyst was prepared by modified polyol synthesis method in an ethylene glycol (EG) solution. The kinetically controlled current ( I k) for the HOR at Pt/C decreases significantly at CO coverage ( Θ CO) > 0.6. For Θ CO < 0.6 the HOR takes place through Tafel–Volmer mechanism with Tafel reaction as rate-determining step at the low CO coverage, while Volmer step controls the overall reaction rate at the medium CO coverage. When CO coverage is higher then 0.6, Heyrovsky–Volmer mechanism is operative for the HOR with Heyrovsky as the rate-determining step (rds).

Silver nanostructures with well-controlled shapes: synthesis, characterization and growth mechanisms

This paper describes a poly(vinylpyrollidone)-directed polyol synthesis method for the fabrication of silver (Ag) nanostructures with well-controlled shapes (such as nanorods and nanocubes) by adjusting the synthesizing parameters. The structure characterizations suggest that the Ag nanorods grow from the five-fold twinned decahedral crystal nuclei. The nature of the {1 1 1} planes of Ag crystal and the highly selective poly(vinylpyrollidone) adsorption on the {100} planes of Ag crystal nuclei are favourable for the formation of Ag nanorods and Ag nanowires. The single crystalline Ag nanocubes obtained at optimum conditions are perfect in shape and are enclosed by the {1 0 0} facets. The optical properties of the Ag nanostructures show an attractive plasma resonance, displaying a considerable dependence on the shape and size. The formation of the Ag nanostructures with well-defined shapes is probably due to the fact that the nanostructures are controlled thermodynamically and kinetically. The ability to generate shape-controlled Ag nanostructures also provides an opportunity to experimentally and systematically study the relationship between their properties and geometric shapes.

Pulse-microwave assisted polyol synthesis of highly dispersed high loading Pt/C electrocatalyst for oxygen reduction reaction

In the present investigation, a high loading Pt/C up to 50% (weight ratio) was prepared by a pulse-microwave assisted polyol synthesis method, in which the metal reduction can be accomplished in 2 min. X-ray diffraction (XRD) and transmission electron microscopy (TEM) results showed that the Pt particles were highly dispersed on the support and had a narrow particle distribution with a mean particle size of about 2.7 nm. Based on the electrochemical properties characterized by cyclic voltammetry and rotating disk electrode techniques, it was found that the as-prepared 50% Pt/C exhibited a comparable activity for oxygen reduction reaction with respect to the commercial one.

Characterization of a surface modified carbon cryogel and a carbon supported pt catalyst

A carbon cryogel, synthesized by carbonization of a resorcinol/formaldehyde cryogel and oxidized in nitric acid, was used as catalyst support for Pt nanoparticles. The Pt/C catalyst was prepared by a modified polyol synthesis method in an ethylene glycol (EG) solution. Characterization by nitrogen adsorption showed that the carbon cryogel support and the Pt/C catalyst were mesoporous materials with high specific surface areas (Sbet&gt;400 m2 g-1) and large mesoporous volumes. X-Ray diffraction of the catalyst demonstrated the successful reduction of the Pt precursor to metallic form. TEM Images of the Pt/C catalyst and Pt particle size distribution showed that the mean Pt particle size was about 3.3 nm. Cyclic voltammetry (CV) experiments at various scan rates (from 2 to 200 mV s-1) were performed in 0.5 mol dm-3 HClO4 solution. The large capacitance of the oxidized carbon cryogel electrode, which arises from a combination of the double-layer capacitance and pseudocapacitance, associated with the participation of surface redox-type reactions was demonstrated. For the oxidized carbon cryogel, the total specific capacitance determined by 1/C vs. v0.5 extrapolation method was found to be 386 F g-1. The hydrogen oxidation reaction at the investigated Pt/C catalyst proceeded as an electrochemically reversible, two-electron direct discharge reaction. .

Highly stable PtRuTiO x/C anode electrocatalyst for direct methanol fuel cells

In the present investigation, PtRuTiO x /C electrocatalyst was prepared by a modified polyol synthesis method and the as-prepared electrocatalyst was treated under the reductive atmosphere (30 vol% H 2 in Ar) at 500 °C for 2 h (denoted as PtRuTiO x /C-500) to enhance the interaction between the metal particles and the support. For comparison, the commercial PtRu/C electrocatalyst was also treated by the same procedure as PtRuTiO x /C (denoted as PtRu/C-500). Transmission electron microscopy results indicated that PtRuTiO x /C electrocatalyst exhibited not only a uniform dispersion and narrow size distribution with a smaller particle size, but also excellent stability during the thermal treatment. In contrast, the commercial PtRu/C electrocatalyst is not stable during the thermal treatment and the metal particles greatly agglomerated. The results of CO-stripping voltammetry, single direct methanol fuel cell tests and life-time test jointly showed that PtRuTiO x /C-500 had better durability than commercial PtRu/C while keeping a desirable activity toward methanol electro-oxidation, which may be attributed to the addition of titanium oxide that improved the interaction between noble metal particles and the support.

Specificity of the UPD of H to the structure of highly dispersed Pt on carbon support

Home-made carbon cryogel synthesized by sol–gel polycondensation and freeze-drying is used as support for preparation of highly dispersed Pt catalyst that is made by a modified polyol synthesis method in an ethylene glycol (EG) solution. Specific surface area of carbon support and Pt/C catalyst is determined from nitrogen adsorption isotherm. The adsorption isotherm demonstrates a significant mesoporosity of carbon support. Specific surface area of the carbon support, calculated by the BET equation, is found to be 573 m 2 g - 1 . X-ray diffraction (XRD) results demonstrate a successful reduction of the Pt precursor to its metallic form, and transmission electron microscopy (TEM) images show very uniform Pt particle size distribution with mean particle size of about 2.7 ± 0.7 nm of the catalyst. Potentiodynamic studies of the underpotential deposition of hydrogen ( H upd ) on Pt/C electrode in 0.5 mol dm - 3 HClO 4 aqueous solution in the temperature range from 274 to 318 K are made, and thermodynamic state functions for the hydrogen adsorption are determined. The experimental results are analyzed assuming linear variation of the Gibbs energy of adsorption versus θ H upd on the basis of the surface heterogeneity. The increase of Δ G H upd θ with the surface coverage indicates the repulsive interactions between H upd adatoms. From the temperature dependence of the Gibbs energy of adsorption, the enthalpy and the entropy of adsorption are calculated. The values of these functions are determined to be Δ H H upd θ = 0 = - 5.6 kJ mol - 1 and Δ S H upd θ = 0 = 69.1 J mol - 1 K - 1 . The value of Δ H H upd θ allows determinations of the bond energy between electrode surface and H upd that is found to be E Pt – H = 223 kJ mol - 1 for θ = 0 .

Oxygen Reduction on Carbon Cryogel-Supported Pt Nanoparticles in Acid Media

The kinetics of oxygen reduction (ORR) on carbon cryogel supported Pt nanoparticles (Pt / C) in acid solution was studied using the rotating disk electrode technique. This electrocatalyst was prepared by a modified polyol synthesis method and characterized by transmission electron microscopies. The kinetics of ORR shows a significant enhancement at Pt nanoparticle surfaces as compared with the same reaction on polycrystalline Pt surface. The four-electron reduction, with a first-charge transfer-rate determining step, has been found to be operative. However, the specific activity of the Pt / C is similar to that of the polycrystalline Pt electrocatalyst.