Polyol Process Research Articles

Improved electrocatalytic kinetics of nickel hydroxide nanoparticles on Vulcan XC-72R carbon black towards alkaline urea oxidation reaction

Nickel hydroxide nanoparticles were fabricated on Vulcan XC-72R carbon black using various reducing agents through assisted microwave polyol process. The formed electrocatalysts using sodium borohydride [Ni(OH)2/C–NB], ethylene glycol [Ni(OH)2/C–EG] and a mixture of them [Ni(OH)2/C–EGNB] displayed an electrocatalytic activity towards urea oxidation in NaOH solution. The oxidation peak potential and current density values were greatly influenced by the employed reducing agent. Lower onset and peak potential values were measured at Ni(OH)2/C–EGNB, while Ni(OH)2/C–EG exhibited the highest oxidation current density during urea oxidation reaction. Electroactive surface area measurements revealed that the number of available active sites for the oxidation reaction was arranged in an ascending order as Ni(OH)2/C–NB < Ni(OH)2/C–EGNB < Ni(OH)2/C–EG. The diffusion coefficient of urea molecules at Ni(OH)2/C–EG and Ni(OH)2/C–EGNB was 14.69 and 5.90 times higher than that at Ni(OH)2/C–NB. Stable performance was measured at all studied electrocatalysts over prolonged operation suggesting their valuable application as efficient anode materials in direct urea oxidation fuel cells.

Synthesis of uniform Prussian blue nanoparticles by a polyol process using a polyethylene glycol aqueous solution.

A polyol process was applied to the synthesis of Prussian blue nanoparticles that have a narrow size distribution. Potassium hexacyanidoferrate(iii) and iron(iii) nitrate aqueous solutions were introduced into a 50% polyethylene glycol (PEG) aqueous solution under magnetic stirring at 50 °C and reacted for 48 h. The shape of the so-obtained particles was cubic with somewhat rounded edges and the mean size was 70 nm. In the formation process, nanoparticles of Prussian green, which is a partially oxidized state of Prussian blue, were firstly generated via reduction of the precursors by PEG molecules. The Prussian green nanoparticles were then reduced subsequently to Prussian blue nanoparticles. Rate constants for both the reduction steps have been estimated using the time evolution of absorbance.

Impregnated Electroreduced Pt on Ru/C as an Anode Catalyst for Direct Methanol Fuel Cells

Direct methanol fuel cells (DMFC) have attracted considerable attention as an alternative energy source for portable devices due to their advantages of relatively higher energy densities and easy fuel storage. The successful commercialization of DMFC depends heavily on the activity and durability of the electrocatalysts. Pt-Ru nanoparticles supported on carbon are a well-studied anode electrocatalyst for DMFC due to their efficient CO removal ability. In this work, we propose a method for synthesizing Pt on ruthenium-on-carbon support (Pt/RuC) by combining the polyol and impregnation-electroreduction methods. First, ruthenium-on-carbon support (Ru/C) with varying Ru weight percentages (viz. 8, 17, and 30 wt%) was synthesized via the polyol process using ethylene glycol as a reducing agent. Second, Pt was impregnated on Ru/C-coated carbon paper and subsequently electroreduced using square wave pulse deposition. Using this synthesis method produced a smaller and more uniform Pt particle size distribution compared to the conventional electroreduction method. Of the various compositions of the Pt/RuC catalyst synthesized, Pt deposited on 30 wt% Ru/C revealed the highest electrochemical surface area and increased mass activity for methanol oxidation reaction. The anode catalyst, when tested in a DMFC, showed the highest peak power density of 80 mW cm−2 at 80°C. Additionally, a short-term stability test carried out at 100 mA cm−2 for 10 h revealed the superior stability of the electrocatalyst.

Growth mechanism of SnC2H4O2 nanowires prepared by the polyol process as SnO2 precursor nanowires.

Tin oxide (SnO2) nanowires are produced by the calcination of tin glycolate (SnC2H4O2) nanowires, which are synthesized with tin oxalate (SnC2O4) and ethylene glycol via the so-called polyol process. In this study, the growth mechanism of SnC2H4O2 nanowires was investigated by monitoring the synthesis using scanning and transmission electron microscopy. The length and diameter of the nanowires were 9.25 μm and 0.37 μm, respectively; the former increased at a rate of 1.85 μm h−1 but the latter did not increase over time. Fourier-transform IR spectroscopy showed that the nanowires were composed of SnC2H4O2 instead of SnC2O4. Changes in the components of the reaction solution were also confirmed by 1H NMR, 13C NMR, and high-performance liquid chromatography. SnC2H4O2 was formed by the substitution of the oxalate coordinated to tin by ethylene glycolate, which was produced by the deprotonation of ethylene glycol. In this reaction, oxalate gradually changed to formic acid and carbon dioxide, and SnC2H4O2 grew as a nanowire through O–Sn–O bond formation. In addition, when ethylene glycol was mixed with 1,2-propanediol, branched SnC2H4O2 nanowires were formed. The branching was due to the interference of the methyl group of 1,2-propanediol with the growth of bundle-type nanowires. The branched nanowires had a higher surface area-to-mass ratio than the bundled ones based on dispersion measurements. Knowledge of the growth mechanism and reaction conditions that affect morphology would be valuable in modifying the physical and electrical properties of metal oxide nanowires.

Size and shape-controlled nanomaterials based on modified polyol and thermal decomposition approaches. A brief review.

Abstract: Since its inception in 2007, the Colloidal Materials Group, one of the research groups in nanotechnology of the Institute of Chemistry of Sao Carlos (IQSC) at University of Sao Paulo (USP) carries out studies related to the development of syntheses methods of nanoparticles and multifunctional nanostructured systems. Our works search new synthesis methodologies that allow high size and shape control of the individual nanoparticles or that compose the nanostructured systems and has as a principle the synthetic approaches based on the modified polyol and thermal decomposition processes. Systems involving nanoparticles have received extensive attention both in the fundamental research and in several technological applications exploring the unique properties presented in nanomaterials. These properties are strongly size- and shape-dependent of the nanoparticles and a large distribution of size or shape implies in a high response dispersion, justifying the intense research for the so-called nanoparticle monodisperse systems. In this review, we present the main aspects to obtain monodisperse nanoparticulate systems, correlating with the synthesis processes used in our group and some of our results in systems involving nanoparticles with magnetic, optical, and electronic properties, as well as some obtained composite materials for different applications.

Facile Synthesis of Ag/ZnO Photocatalysts on the Degradation of Diuron Herbicide Under Simulated Solar Light and the Investigation of Its Antibacterial Activity for Waste-Water Treatment

Nanocrystalline Ag/ZnO powders have been successfully prepared by a modified polyol process using triethylene-glycol (TEG) as solvent, reducing and stabilizing agent. The synthesis procedure has been conducted without any post-synthesis thermal treatment. The structural and optical properties have been characterized by X-ray diffraction, transmission electron microscopy, N2 adsorption study, inductively coupled plasma optical emission spectroscopy and UV–Vis diffuse reflectance spectroscopy. The photocatalytic activity of Ag/ZnO materials has been studied by analyzing the degradation of an herbicide, diuron, under solar light. Ag/ZnO photocatalysts with optimized x = 0.7% Ag content showed 14 times higher rate of degradation than that of unmodified ZnO. We attribute these observations to the addition of silver nanoparticles allowing interfacial oxide-to-metal electron transfer within the hybrid Ag/ZnO photocatalyst. The inhibitory and bactericidal activities of samples have been tested against Gram-negative bacteria; Escherichia coli, Salmonella typhimurium and gram-positive bacteria; Staphylococcus aureus, Enterococcus faecium and Candida albicans. The results showed that the Ag/ZnO can be used as photocatalysts and antibacterial agents for potential practical applications in the wastewater treatment. Schematic of the proposed photocatalytic and bactericidal mechanism of Ag/ZnO nanostructure.

A facile preparation of MSS@FePt nanocomposites and their application for H2O2 detection

In this report, Platinum iron nanoparticles (FePt NPs) were attached onto Mesoporous silicon spheres (MSS) by a facile polyol process. Based on the prepared nanoparticles, a novel colorimetric sensor for fast and sensitive determination of H2O2 was established. The established colorimetric sensing platform exhibited perfect peroxidase-like activities confirmed by oxidating 4, 4’-Bi-2, 6-xylidine (TMB) with H2O2. After optimizing the reaction conditions, the linearity of H2O2 determination ranged from 40 to 300 μM and the limit of detection (LOD) of 18.27 μM.

One-Dimensional Sb2Se3 Nanorods Synthesized through a Simple Polyol Process for High-Performance Lithium-Ion Batteries

The good crystalline Sb2Se3 nanorods have been successfully synthesized through a simple polyol process. The detailed morphological and structural characterizations reveal that nanorods are composed of Sb2Se3 single crystals oriented along the [120] orientation; the tiny Sb2Se3 nanorods are found to display a higher crystallinity with respect to thick Sb2Se3 nanorods. The nanorods have been applied as anode materials for lithium-ion batteries, with tiny Sb2Se3 nanorod anodes delivering the relatively high discharge capacity of 702 mAh g−1 at 0.1 C and could maintain the capacity of 230 mAh g−1 after 100 cycles. A more stable cycling performance is also demonstrated on tiny Sb2Se3 nanorods, which is ascribed to their more pronounced one-dimensional nanostructure.

Electrochemical and cycling performance of neodymium (Nd3+) doped LiNiPO4 cathode materials for high voltage lithium-ion batteries

Olivine-type LiNiPO4 and their corresponding Nd3+ doped LiNiPO4 cathode materials were synthesized through polyol process with 1, 2 propane-diol as the medium. The inclusion of Nd3+ to LiNiPO4 significantly enhanced the electronic conductivity by two orders as compared to bare LiNiPO4. The cyclic voltammograms revealed that the rare earth doped LiNiPO4 electrode improved the electrochemical properties. The single cell consisting of 0.07 mol% Nd3+ doped samples showed the highest specific capacity of 95.2 mAh g−1 at low current rate, which makes Nd3+ doped LiNiPO4 a prime candidate for high potential lithium-ion batteries (LIBs).

Observation of n-type behavior in Fe-doped tetrahedrite at low temperature

Tetrahedrite exhibits favorable thermoelectric properties, while also being composed of non-toxic and earth-abundant elements. Although tetrahedrite has been studied extensively as a p-type thermoelectric, n-type behavior in this material has not yet been observed. We report the first findings of n-type conductivity in tetrahedrite observed over a temperature range of 80 to 310 K, with typical p-type conductivity found at higher temperatures. Herein, we characterize electrical and thermal transport properties on these samples from 80 to 673 K. Mechanical alloying and modified polyol synthesis methods were used to synthesize Fe-doped samples (Cu12-xFexSb4S13 with x = 1, 1.3, and 1.5) by solid-state and solution-phase approaches, respectively. Elemental analysis by energy-dispersive X-ray spectroscopy was conducted to investigate the relationship between thermoelectric properties and chemical composition. A maximum ZT = 0.67 at 673 K was obtained for Cu10.5Fe1.5Sb4S13 synthesized by the modified polyol process. Our observation of negative Seebeck coefficient values in the low-temperature regime should serve as a foundation for further study of n-type behavior in tetrahedrite materials.

From nano-structured polycrystalline spheres with Zn1-xCoxO composition to core-shell Zn1-xCoxO@SiO2 as green pigments

ZnO doped with Co2+, a well-known green pigment which is an alternative to the chromium based inorganic pigments, has been prepared by a polyol process and investigated in terms of crystallographic structure and UV–visible properties. Thanks to the obtaining of nanometric crystallite size from our process, the incorporation of a very high concentration of Co2+ in the ZnO matrix is achieved. Thus, different grades of more or less deep green pigments can be produced. Furthermore, the obtaining of spherical aggregates allows the easy preparation of ZnO:Co@SiO2 core-shells, minimizing hence the problems linked to the zinc oxide high solubility into slightly acidic conditions acidic conditions and the metal cation's toxicity.

A general one-pot synthetic strategy to reduced graphene oxide (rGO) and rGO-nanoparticle hybrid materials

There is great interest in new materials that synergistically combine properties of reduced graphene oxide (rGO) with nanoparticles (NP) generating rGO-nanoparticles hybrid materials (NPHM). Based on the modified polyol process (MPP), we developed a new and versatile method to synthesize rGO and rGO-NPHM in one-pot route. rGO sheets with small defects number were reduced from graphene oxide by the MPP, and experimental parameters were varied to evaluate the method robustness, and adjusted to prepare rGO-NPHM, for instance, rGO/Au, rGO/Ag, rGO/CdSe, rGO/FePt and rGO/Fe3O4 inferring the versatility of our methodology. NPHM were evaluated by X-ray diffraction, transmission electron microscopy, vibrating sample magnetometry, and Raman, UV–Vis, and FTIR spectroscopies. All synthesized NPHM shown size-controlled monodisperse-like NP homogeneously distributed onto the rGO sheets, except for the Ag-NP where a bimodal size distribution was observed. Plasmon (rGO/Au and rGO/Ag) and typical absorption and emission (rGO/CdSe) by UV–Vis, whereas paramagnetic-like (rGO/FePt) and superparamagnetic (rGO/Fe3O4) behavior was observed by the magnetic NPHM. The MPP is already efficient for NP preparation and here, we showed that its might successful for rGO and rGO-NPHM synthesis in a simple and versatile one-pot route, which can be scaled up to allow mass production and easily tuned for other NP kinds.

Recent progress in the synthesis of silver nanowires and their role as conducting materials

Synthesis of silver nanowires got much attention of researchers due to their promising applications in various fields of nanoelectronic devices. Many research articles focusing on silver nanowires synthesis have been reported since past decade. A number of techniques have been applied for successful synthesis of silver nanowires. Solution-based polyol process was proved as a dominant approach to the fabrication of silver nanowires with homogeneity and high aspect ratio. Various inorganic salts have been used in solution-based polyol synthesis of silver nanowires which play a key role in controlling the final morphology of silver nanowires and lead to uniform growth of silver nanowires. The different experimental parameters have been studied, which directly influence the final morphology of silver nanowires. The research on the development of an efficient synthesis approach of silver nanowires is still in progress to accomplish the need of advanced technology for controlled morphology and highest aspect ratio of silver nanowires. Moreover, the unique applications of silver nanowires in conducting polymers composites were discussed.

Fabrication of porous FePt microcapsules for immunosensing techniques.

Porous FePt microcapsules are fabricated for use in bead-based immunoassay technologies, that generally use magnetic spheres to immobilize biomolecules on their surface. The magnetic capsules can be used to carry assay reagents to reduce the time required to perform immunoassay processes, and microsize capsules are easier to manipulate magnetically than nanosize ones. Silica particles of approximately 2.5 μm diameter are used as templates and modified with poly(ethyleneimine) (PEI), which enables FePt nanoparticles to accumulate selectively on the template particles and an FePt shell to be formed by a polyol process. To increase the mechanical stability of the FePt nanoparticle assembly shell, a double-layered FePt nanoparticle assembly is fabricated by repeating the modification process of PEI and the synthesis process of FePt nanoparticles, resulting in the fabrication of magnetic capsules with a three-dimensional structure. We further investigate the ability of magnetic capsules to immobilize antibodies on their surface. Gold nanoparticles are used as linkers between the magnetic microcapsules and antibodies. The antibodies are successfully immobilized on the surface of the developed microsize FePt capsules.

Enhanced coercivity in non-equiatomic CoPt-Cu nanoparticles

Co30Cu10Pt60 nanoparticles were prepared by a simplified polyol process devoid of any surfactants or capping agents. Thermo-magnetic analysis showed that the addition of 10 at.% Cu reduces the Curie temperature of Co40Pt60 from 492 °C to 435 °C. The incorporation of Cu is effective in reducing the threshold ordering temperature for the A1-fcc to L10-fct phase transformation of CoPt, resulting in coercivity enhancement. Coercivity close to 10 kOe at a lower annealing temperature of 600 °C in Co30Cu10Pt60 demonstrates that high coercivity in CoPt can be achieved in non-equiatomic compositions also. Annealing temperature dependent two phase behavior has been understood by δM studies.

The first one-pot synthesis of undoped and Eu doped β-NaYF4 nanocrystals and their evaluation as efficient dyes for nanomedicine

Polygonal-shaped about 75 nm sized and highly crystallized Eu3+-doped β-NaYF4 particles were directly prepared under mild conditions using the polyol process. A set of operating parameters were optimized for such a purpose. A conventional heating under reflux for 30 min of a mixture of Y(III) and Eu(III) acetate, ammonium fluoride, sodium hydroxide and oleic acid (OA) dissolved in ethyleneglycol offered a pertinent material processing route if a large excess of NH4F and an enough amount of OA were used. Typically, the former parameter provides an exclusive stabilization of the desired β allotropic form, while the latter allows a significant size decrease of the particles. Thanks to their coating by a double OA layer, the produced particles exhibited a hydrophilic surface feature when dispersed in water and when excited under UV light they emitted a very intense red photoluminescence. Additionally, they did not evidence any accurate cytotoxicity when incubated with healthy human foreskin fibroblast (BJH) cells for doses as high as 50 μg·mL−1 and contact time as long as 48 h, highlighting the ability of the prepared particles to be used as efficient down-converter light sources for cell labelling.

Highly Transparent and Flexible All-Solid-State Supercapacitors Based on Ultralong Silver Nanowire Conductive Networks.

Ultralong silver nanowires (Ag NWs) are preferred for enabling transparent conductive networks with low sheet resistance, high transparency, and excellent mechanical flexibility, which offer great merits in achieving high-performance and flexible energy storage devices. Herein, a new type of polyol process was proposed for the synthesis of ultralong Ag NWs. Uniform Ag NWs with the average length of 75 μm were obtained. Transparent conductive films (TCFs) based on the as-prepared Ag NWs exhibited low sheet resistance of 15.2 Ω/sq at 84% transmittance with a negligible change in sheet resistance after bending. Flexible all-solid-state supercapacitors based on the resulting Ag NW TCFs showed high transparency (>50%), good mechanical flexibility, and high cyclic stability with only slight areal capacitance decays after 100 times of bending (∼25%) and 5000 charge-discharge cycles (∼15%). The results manifest great potentials of the resulting TCFs based on ultralong Ag NWs for flexible and wearable energy-storage applications.

Giant Exchange‐Bias in Polyol‐Made CoFe2O4‐CoO Core–Shell Like Nanoparticles

AbstractCobalt ferrite ferrimagnetic nanoparticles (NPs) are prepared and used in this work as seeds to grow a thin antiferromagnetic poly‐ and nanocrystalline CoO shell. The major purpose is to study systematically the characteristics of the as‐produced powders, making emphasis on their internal crystallographic arrangement and their magnetic properties. 57Fe Mössbauer spectrometry evidences an evolution of the cation distribution among the spinel lattice in the cobalt ferrite core during the core–shell NPs processing. High‐resolution transmission electron microscopy shows a perfect epitaxy between the face‐centered cubic lattices of the spinel core and the rock‐salt shell. Finally, the measurements of 7T‐field‐cooled magnetic hysteresis loops at low temperature (5 K) of the composite particles exhibit a strong exchange bias coupling with an exchange field, µ0HE, of 365 mT and an enhanced coercive field, µ0HC, of 1395 mT. These values are very high compared to those of differently prepared CoO‐based oxide composite NPs and for which a giant exchange‐bias is reported. These features are attributed to the favorable material processing conditions offered by the polyol process in terms of crystalline quality, particularly at the interfaces, and for the pinning action exerted by the CoO phase on the magnetization of the CoFe2O4 phase.

Original strategy for facile synthesis of hybrid ‘ZnO–Zn2TiO4’ nanotubes and antimicrobial activity

The necessity of new catalytically active nanomaterials has drawn interest on developing new and emerging hybrid nanomaterials based on nanoparticles and nanocompounds. Furthermore, research work on the synthesis and the study of new hybrid nanomaterials are areas of great curiosity in modern science due to their potential applications in different areas. In the present work, ZnO–Zn2TiO4 hybrid nanotubes (NTs) were synthesized for the first time based on a polyol process. This novel approach allows one to produce ZnO–Zn2TiO4 NTs owing to a modified polyol process that makes use of 1,3 propanediol as a solvent and zinc(II) acetate with Titanium (IV) butoxide as the zinc and titanium precursors. The structural features, crystalline structures, thermal behavior and chemical composition of the resulting ZnO–Zn2TiO4 hybrid NTs were systematically characterized using x-ray diffraction (XRD), Transmission Electron Microscopy (TEM) and Energy Dispersive x-ray spectrometry (EDX). Preparing the hybrid NTs according to this polyol method allows us to obtain ZnO–Zn2TiO4 hybrid nanotubes with a uniform diameter (200–500 nm) along the pore length (3–5 μm) without using any metal catalyst. ZnO–Zn2TiO4 nanoparticle was tested for its antibacterial effect using MIC and MBC technique and has showed a good activity against gram-negative and gram-positive bacteria.

Effect of reducing agent and surfactant on the morphology, structural and magnetic properties of Ni magnetic nanoparticles

ABSTRACTWe report the effect of reducing agent and surfactant on the morphology, structural and magnetic properties of Ni magnetic nanoparticles (MNPs) synthesised by the polyol process. The samples in this work were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM) and vibrating sample magnetometry (VSM). The XRD results indicate that samples synthesised by EG-NaOH and 1.2H-OAm/OAc have a cubic structure with space group Fm-m. The average crystallite sizes of these samples are found to be ∼ 20.7 and 16.2 nm, respectively. The sample synthesised by a combination of EG-OAm/OAc grows in nanorod form, whereas that synthesised by EG-NaOH and 1.2H-OAm/OAc has a spherical shape. The temperature dependence of the magnetisation, (M-T) measurements, indicate that the EG-NaOH sample has a superparamagnetic transition, while the 1.2H-OAm/OAc sample shows ferromagnetic behaviour in the temperature range of 5–380 K. The magnetic anisotropy constants of the EG-NaOH and 1.2H-OAm/OAc samples extracted from the M-T experiments, are 141.3 × 105 and 10.5 × 105 erg/cm3, respectively. In addition, the magnetic hysteresis measurements taken at 5 and 300 K show that the 1.2H-OAm/OAc sample is more stable than the sample synthesised by EG-NaOH. The overall results are important for the use of the Ni MNPs for low- and room-temperature applications in bio- and nano-technology.