Polyol Technique Research Articles

Selective CO Methanation Over Ru Supported on Carbon Spheres: The Effect of Carbon Functionalization on the Reverse Water Gas Shift Reaction

Mesoporous carbon spheres (CSs-H) were hydrothermally synthesised using sugar as carbon source. The as-synthesized CSs-H was microporous but after thermal treatment at 900 °C for 4 h it became mesoporous (surface area of 463 m2 g−1). Further treatment of the annealed CSs-H with HNO3 gave a functionalized CSs-H with a high defect content in the carbon matrix which resulted in an increase in surface area (509 m2 g−1). The functionalized and un-functionalized CSs-H were used to support nano Ru particles for CO, CO2 and selective CO methanation reactions. The Ru supported catalysts were prepared using both impregnation and microwave polyol synthesis methods. It was evident from the reduction studies that the functional groups on the surface of the CSs-H influenced the reduction of the RuO2 to Ru. The catalyst with smaller and well dispersed RuO2 particles (d = 2.7 nm) (prepared by the microwave polyol technique) gave a high activity in both CO and selective CO methanation studies. The larger Ru particles observed on the un-functionalized CSs-H showed poor activity for CO and selective CO methanation reactions and also did not promote the reverse water gas shift reaction.

Positron Annihilation Studies on Chemically Synthesized FeCo Alloy

Equiatomic flower-like FeCo magnetic nanoparticles are synthesized through a modified one-pot polyol technique. The as-prepared samples are annealed at 700 and 800 °C under reducing atmosphere. The saturation magnetization and coercivity of the flower-like FeCo are found to be 198 (1) emu/g and 243 (10) Oe respectively. The magnetic properties of FeCo approach the bulk behavior with annealing. Positron lifetime studies on the chemically synthesized equiatomic FeCo magnetic nanoparticles with flower-like morphology are reported and compared with Fe, Co and FeCo annealed at various temperatures. The FeCo is characterized by different lifetime components corresponding to positron annihilation events in vacancies and various open volume defects due to their unique morphology. The studies suggest defects arising out of cluster vacancies and interpetal gap that reduce on annealing. The average pore size obtained from positron annihilation studies closely matches with the interpetal distance obtained from the electron microscopic analysis for the flower-like FeCo.

Application of microwave synthesized Ag-Rh nanoparticles in cyclohexane dehydrogenation for enhanced H2 delivery

The catalytic dehydrogenation of liquid organic hydrides (LOH) is a promising route to deliver H2 for various mobile and stationary applications. However, an efficient and low-cost dehydrogenation catalyst, as an alternative to Pt, is a key for the success of LOH-based H2 supply. In a quest for such catalysts, we synthesized stable Ag-Rh bimetallic nanoparticles (BNP) supported on activated carbon cloth (ACC) and Y2O3 using the microwave-assisted polyol technique. The performance of these catalysts during dehydrogenation of LOH viz., cyclohexane, was evaluated at 300 °C using an advanced spray-pulse reactor system. The Ag:Rh ratio was optimized to maximize the cyclohexane conversion and H2 evolution. The effect of Ag:Rh ratio, catalyst support, and synthesis method was investigated, too. The most stable H2 evolution performance was exhibited by microwave-synthesized 1:4 Ag-Rh/Y2O3 catalyst with the cyclohexane conversion, dehydrogenation rate and H2 evolution rate of 35.8%, 17.2 mmol/gMet/min and 400 mmol/gMet/min, respectively. Finally, the performance of catalysts used in this study was compared with the Pt-based catalysts.

Evaluation of the charge carriers’ transportation through the grown MgFe2O4 on the nanotextured silicon surface in the presence of hydrogen gases

Here, we report, for the first time, the solution growth of n-type MgFe2O4 spinel ferrite nanoparticles on nano-textured p-type silicon (100) substrate. Water soluble MgFe2O4 spinel ferrite nanoparticles are prepared by polyol technique. The MgFe2O4 spinel ferrite nanoparticles were characterized by transmission electron microscopy both at low and high resolution, selected area electron diffraction, energy dispersive spectroscopy, and Raman spectroscopy. The texturing of the surface of the Si(100) substrate to create well-organized nanopillar-like shapes was carried out by a nanosecond laser lithography technique. The water soluble MgFe2O4 spinel ferrite nanoparticles were deposited on the textured Si(100) substrate. The sample was characterized by scanning electron microscopy and X-ray diffraction. The charge carriers transport mechanism was discussed in terms of the variation of the barrier height under the exposure to various gases. A comparison between the MgFe2O4 spinel ferrite nanoparticles grown on planar and textured p-type Si(100) surfaces showed that the latter demonstrated an improvement of gas sensitivity and accelerated response time. These two characteristics, combined with high performance stability, make these sensors promising for practical applications.

Polyol technique synthesis of Nb2O5 coated on LiFePO4 cathode materials for Li-ion storage

A novel approach has been made to tailor Niobium pentoxide (Nb2O5) as a coating material on the surface of lithium iron phosphate (LiFePO4) via a facile polyol technique. The coating content was optimized at 1 wt%. The superficial coating demonstrated superior discharge capacity than the pristine LiFePO4. However, increasing the coating content further would result in a capacity loss. This may be due to the electrochemical inactiveness that increases with the content of the coating material, and 1 wt% of Nb2O5-coated LiFePO4 sample exhibits initial discharge capacity of 163 mAh g−1 at a current of 0.1 C and retains a stable discharge capacity of 143 mAh g−1 up to 400 cycles at 1 C rate with a coulombic efficiency of 98%.

Microwave-assisted polyol method rapid synthesis of high quality and yield Ag nanowires

In this study, high quality and yield Ag nanowires (NWs) have been fabricated via a microwave-assisted polyol technique by adding sodium bromide (NaBr) into the solution. In our experiments, the Ag NWs with diameters from 45 to 200nm are rapidly prepared in 3min. The fabrication parameters, such as the powers of microwave, concentration of NaBr solution, molar ratio of PVP:AgNO3, and the time of microwave, have been investigated in detail. Ag NWs with adjustable diameters can be obtained by adjusting the microwave powers and the NaBr solution concentration. The different microwave powers can provide different reaction energy, result in different reaction rate during the ultrafast nucleation and growth process. The Br− ions can enhance oxidative etching effect and decrease the diameters of the Ag NWs. Our works provide a new and facile approach for the large scale synthesis of Ag NWs with adjustable diameters by simply adjusting microwave powers and the NaBr solution concentration.

Investigation of Nanostructured SnO2 Synthesized with Polyol Technique for CO Gas Sensor Applications

In the development of gas sensors, many material based on Metal Oxide Semiconductor is often used, one of them is Tin Oxide (SnO2). SnO2is widely used for CO gas sensor because of several advantages including long life expectancy, relatively stable, high durability, resistance to corrosive gases, and good mechanical resistance. Performance improvement of CO gas sensor has been carried out by synthesizing SnO2 by polyol technique to produce nanostructured powder followed by deposition on alumina substrate using doctor blade coating technique. In order to determine the performance of the sensor material, the sample was characterized using x-ray diffraction, scanning electron microscopy, and BETcalculation of N2 adsorption-desorption. The XRD analysis showed the tetragonal crystal phase of SnO2, and BET analysis result in 24,53 m2/g surface area. Furthermore, SEM image showed the nanorod shape of SnO2 morphology with diameter 50nm–2 μm. Sensor characterization with 30 ppm CO gas showed that the sample can work in 150oC working temperature with sensitivity of 52.84%.

Studies on Chemical and Physical Properties of LiFeMPO<sub>4</sub> (M=Cu, La) by Polyol Route

Bare Lithium Iron Phosphate (LiFePO4), Cu, La doped and Cu with La co-doped LiFePO4 composite materials have been prepared via polyol technique without further post heat treatment. The prepared bare and composite materials’ crystalline structure has been indexed an orthorhombic phase olivine structure with space group of Pnma. The functional group vibrations and surface morphology of the prepared materials has been observed using Fourier transfer infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM) with EDX analyses. Magnetization measurements revealed that saturation magnetizations (Ms) of the metal doped samples are gradually increased than that of the pure LiFePO4. All the samples exhibit the spin-glass behaviour of magnetic materials.

Photoluminescence enhancement and energy transfer mechanism of Bismuth added LaGaO3: Eu nanophosphor for display applications

A systematic investigations were carried out on pure LaGaO3, Bi3+ doped-LaGaO3, Eu3+doped-LaGaO3, Bi3+ and Eu3+ co-doped LaGaO3 (LaGaO3:Bi3+, Eu3+) nanophosphors synthesized by low temperature polyol technique for enhanced luminescent properties. Powder x-ray diffraction (PXRD), UV⿿vis spectroscopy, FTIR, and FE-SEM with EDAX measurements were done for the phase identification, energy band gaps, functional group analysis and structural morphology and elemental presence respectively. Photoluminescence (PL) spectra of prepared nanophosphors under near-UV light exhibited a red luminescence corresponding to the electric dipole transition 5D0-7F2 at 616nm. The enhanced PL intensity was observed in LaGaO3:Bi3+, Eu3+ nanophosphor due to strong absorption of excitation energy and effective energy transfer mechanism in between the dopants. The corresponding decay curve was observed with a long life time of 2.13ms. The obtained CIE data indicates these nanophoshors serve as potential candidates for display device industry.

Highly sensitive nanostructure voltammetric sensor employing Pt/CNTs and 1-butyl-3-methylimidazolium hexafluoro phosphate for determination of tryptophan in food and pharmaceutical samples

A novel, sensitive, selective and simple method for the direct and quantitative determination of l-tryptophan (Trp) was proposed in this work. Pt/CNTs nanocompoite made by polyol technique, were used to modify ionic liquid carbon paste electrode (CPE) without any treatment to study the electrochemical behaviors of the Trp using cyclic voltammetry (CV) and chronoamperometry (CA) and square wave voltammetry (SWV) methods. The results demonstrated that the 1-butyl-3-methylimidazolium hexafluoro phosphate (([C4mim]-[PF6])) Pt/CNTs modified carbon paste electrode ([C4mim]-[PF6]/Pt/CNTs/CPE) exhibited high catalytic activity and analytical performance towards the electro-oxidation of Trp. The linear oxidation response range and limit of detection were found to be 0.1–400μM and 0.04μM, respectively. The [C4mim]-[PF6]/Pt/CNTs/CPE was successfully applied for the voltammetric determination of Trp in food and pharmaceutical samples.

Investigation of synthesized nanosized copper by polyol technique with graphite powder

Polyol method is a type of soft chemical method employed to prepare stable fine transition metals (TMs), without using any sophisticated instruments in a normal clean room environment. In the present work, pure nano-sized copper powder was prepared by reduction of copper (II) chloride dehydrate with sodium hydroxide in the glycerol environment at reaction temperature of 160°C for 17min. The Field Emission Scanning Electron Microscopy (FESEM) observation of synthesized copper powder showed the particle dimensions varying from 70 to 400nm. The Energy Dispersive Spectroscopy (EDS) and X-ray Diffraction (XRD) analysis supported the 98.46% purity of synthesized copper powder. The Rietveld analysis confirmed the cubic structure for synthesized copper with cell parameter: a=3.63Å. Whereas the Ultraviolet–Visible Spectroscopy (UV–Vis) revealed damping of surface plasmon resonance due to inactive chloride monolayer at the particle surface. This copper powder heat-treated in carbon environment showed the presence of copper oxalate phase using XRD analysis, noted from the peaks at 36.2° and 46.4° for (120) and (200) planes, respectively; and Fourier Transform Infra Red (FTIR) Spectroscopy backed the presence of copper oxide (Cu2O).

Synthesis and electrochemical characterization of olivine-type lithium iron phosphate cathode materials via different techniques

High-potential, eco-friendly LiFePO4 cathode materials were synthesized by polyol, hydrothermal, and solid-state reaction methods. The polyol technique was carried out without any special atmosphere and postheat treatment. The synthesized samples were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscope (SEM) with energy dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectrometry (XPS), and charge-discharge and cyclic voltammetry tests. The LiFePO4 prepared via polyol technique exhibits good electrochemical performance than other method samples do.

Development of polyol method for the synthesis of concentrated colloids of PVP-stabilised Ru nanoparticles

In the current work narrowly distributed and stable Ru nanoparticles (NPs) with mean diameters within 1.7 to 2.8 nm interval were prepared by reduction of RuCl3 with ethylene glycol (EG) as a solvent and a reducing agent as well as polyvinylpyrrolidone (PVP) as a stabiliser in the temperature range from 170°C to 198°C. Besides a typical polyol technique, Ru NPs synthesis using microwaves as well as sodium borohydride reduction at room temperature was applied as an effective alternative approach. The effect of heating conditions, Ru/PVP ratio, reducing agent and metal precursor concentrations on the particle size was studied. Microstructure of Ru NPs was characterised by UV Vis, XPS and HRTEM. Higher PVP/Ru ratios and reduction temperature gave slightly smaller nanoparticles with narrower size distributions, while no clear effect was observed when the initial ruthenium concentration was varied.

Bimetallic Pd–Rh nanoparticles onto reduced graphene oxide nanosheets as electrocatalysts for methanol oxidation

Abstract An advanced electrode for methanol oxidation in alkali medium, comprising Pd–Rh nanoparticles and reduced graphene oxide (r-GO) sheets, has been successfully synthesized by pulse microwave polyol (MP) technique. The MP technique is capable of depositing Pd–Rh nanoparticles on the surface of r-GO sheets under microwave irradiation. The atomic ratio of Pd:Rh is chosen as a crucial factor to examine the catalytic activity toward H adsorption/desorption and methanol oxidation. The Pd–Rh catalyst (with Pd:Rh ratio = 75:25) displays the highest alloying degree (~ 41.5%), favoring the formation of Pd–Rh pairs in the binary crystals. On the Pd–Rh catalyst, the Pd site acts as major contributor toward hydrogen adsorption and methanol oxidation, whereas the neighboring Rh site serves as a promoting center to strip oxygenate species (e.g., Pd − (CO) ads sites). The enhanced catalytic activity on the Pd–Rh catalyst is attributed to the fact that the binary catalyst possesses a high alloying degree, leading to high catalytic coverage, high-level of CO tolerance, and superior cyclic durability. The Tafel slope of as-made Pd–Rh catalyst could reach as low as 63 mV dec − 1 among the electrodes, based on the analysis of Tafel plots. The Pd–Rh catalyst also exhibits both lower equivalent diffusion resistance and equivalent series resistance, as compared with pure Pd one.

Enhanced rate performance of multiwalled carbon nanotube encrusted olivine type composite cathode material using polyol technique

Olivine type multi-walled carbon nanotube encrusted LiFePO4/C composites have been prepared using economic and energy efficient simple polyol technique without any subsequent heat treatment. The prepared material has an olivine type orthorhombic phase. Also, the iron oxidation state is 2+, which is identified by X-ray diffraction and X-ray photoelectron spectroscopy. It is possible to attain the discharge capacity almost close to theoretical capacity of LiFePO4 as in high temperature methods with ∼100% coulombic efficiency. The specific surface area has been increased upon encrusting multi walled carbon nano tube on LiFePO4/C, which results in enhanced reversible capacity upto 166 mAh g−1 at C/10. Also, it exhibits 89 mAh g−1 even at 30 C rate. This is due to the formation of conductive networks by carbon nanotube, and excellent attachment of LiFePO4/C composite particles on multi-walled carbon nanotube, which induced the kinetics during intercalation/deintercalation process. Multi-walled carbon nanotube acts as the electro-conductive filler on the LiFePO4 surface. The direct addition of MWCNT would result better performances than blending the MWCNT with LiFePO4/C.

Studies on graphene enfolded olivine composite electrode material via polyol technique for high rate performance lithium-ion batteries

The graphene enfolded LiFePO4/C composite cathode material has been prepared via low temperature polyol process, followed by a simple chemical reaction method. The low viscous polyol solvent (DEG) (35.7 mPa s at 25°C) and usage of low temperature process (below 245°C) aid the graphene tightly encapsulated on the LiFePO4 surface that plays an important role, especially in the high rate performances over long cycles, efficiently preventing the separation of the graphene and LiFePO4 during the reaction processes, hence realizing the full potential of the active materials. The graphitization on LiFePO4/C remarkably increased the electronic conductivity of LiFePO4. The layered sheets of graphene wrapped on LiFePO4 particles provide void between graphene sheets and LiFePO4 surfaces, which facilitate the diffusion of Li+. This approach opens up a method to attain the theoretical capacity of LiFePO4. The material exhibits a superior electrochemical performance such as initial discharge capacities of 169.6 and 92 mAhg−1 at 0.1 and 30 C rates, respectively. It has an excellent capacity retention and diminutive capacity fading. The nanosize of LiFePO4 particle causes a shorter diffusion path, which reduces the time for Li+ migration between cathode and electrolyte.

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

Synthesis of surface modified LiFePO4 cathode material via polyol technique for high rate lithium secondary battery

The NiO-coated LiFePO4 composite cathode materials were prepared by simple tailored polyol technique, which has orthorhombic olivine structure without NiO phase. It delivers the reverse capacity of 164mAhg−1 at 0.1C at ambient temperature. The material exhibits stable reverse capacity for several cycles even for the higher C-rates. Increasing the rate, the reverse capacity is almost stable over several cycles. Furthermore, at a high rate viz., 10, 20 and 30C, the discharge capacity has been observed for the optimized NiO-coated LFP as 135, 120 and 69mAhg−1, which demonstrates the excellent rate performance that can be useful for high power lithium secondary battery.

Investigations on the rate performance of LiFePO4/CeO2 composite materials via polyol technique for rechargeable lithium batteries

Surface modification of LiFePO4 using CeO2 cathode materials has been prepared by polyol technique with a chemical combination route. CeO2 has been formed as solid solution on LiFePO4 surface, which provides better EC performances.

A facile synthesis and characterization of LiFePO4/C using simple binary reactants with oxalic acid by polyol technique and other high temperature methods

An attempt has been made to synthesize the carbon coated Fe-based phospho-olivine nano-crystalline cathode materials using simple binary sources via polyol method. Also, a curious attempt has been made to compare the material with the high temperature methods, viz., hydrothermal and solid state method with the same binary sources as raw materials and oxalic acid as a carbon source. The thermal behaviour of the mixed raw materials of LiFePO4 and thermal stability of the final prepared materials were characterized by TGA. The prepared materials were confirmed as orthorhombic olivine structure with Pnma space group. LiFePO4/C material prepared by Polyol method exhibits an initial reverse capacity of 150 mAh g−1 at 0.1 C rate under room temperature. Also, stable capacity of 143 mAh g−1 has been observed over 50 cycles at 0.1 C rate at room temperature among the other methods studied. It may be due to the coverage of tiny particles by carbon and it leads to provide better electronic conductivity and thereby provides good electrochemical performances.