Aqueous Precursor Solution Research Articles

Hierarchical Carbon Foams with Independently Tunable Mesopore and Macropore Size Distributions

Hierarchical carbon foams with independently tunable mesopore and macropore size distributions were formed in a high internal phase emulsion (HIPE) template. The HIPE consists of an internal oil phase that controls the macropore dimensions and an aqueous resorcinol-formaldehyde precursor solution external phase that directs the mesopore size distribution. Once the emulsion is formed, the precursor solution is cured, fluid elements are extracted from the monolith via solvent exchange, and then the sample is pyrolyzed to create a hierarchical open-cell foam consisting of macropores with mesoporous carbon xerogel walls. Both mesopore and macropore size distributions may be independently tuned by changing the synthesis parameters. These samples have a peak in the mesopore size distribution that may be tuned to between 5 and 8 nm and macropore average diameters that may be tuned to between 0.7 and 2.1 microm. Furthermore, the 0.7 and 2.1 microm average diameter macropores have 0.18 and 0.53 microm diameter macropore windows between adjacent pores, respectively. Pore volumes up to 5.26 cm(3)/g and electrical conductivities as high as 0.34 S/cm are observed after 1200 degrees C carbonization of the framework. These foams may have potential applications as 3-D current collectors in batteries and as fuel cell catalyst supports.

Preparation and characterization of active Ni/MgO in oxidative steam reforming of n-C 4H 10

Oxidative steam reforming of n-C 4H 10 over MgO-supported Ni catalysts is described. The Ni/MgO catalysts were prepared by the impregnation method from aqueous Ni(NO 3) 2 precursor solutions at two pH values. Ni/MgO prepared at pH 7 exhibited considerably higher activity than Ni/MgO prepared from a conventional acidic aqueous precursor solution (pH 3.5). The H 2 formation rate for the modified Ni/MgO was up to 2.3 times that for conventional Ni/MgO under a high space velocity of 1660 L(h g) −1. Furthermore, after reduction at high temperature (1273 K), the modified Ni/MgO showed a higher H 2 formation rate than did Rh/MgO. The superior performance of the modified Ni/MgO was ascribed to stronger resistance to oxidation of Ni 0 due to the formation of relatively large Ni 0 particles.

Electrocatalytic Activity of Platinum Nanoparticles Supported on Nanosilicon

AbstractPlatinum (Pt) nanocatalysts were deposited on/inside of nanostructured silicon (nanoSi) matrix using physico‐chemical methods, i.e. E‐beam high vacuum Pt thin film and, respectively, chemically loaded Pt nanoparticles from hexachloroplatinic acid aqueous or alcoholic precursor solutions. High resolution morphological characterisations, completed by microstructural and compositional analyses have been performed to characterise the nanoSi catalyst support and to investigate the Pt thin film nanostructuration as well as the nanoparticle attachment and clustering processes, evidencing the controlling factors and conditions of the size, morphology and distribution. Furthermore, the experimental structures have been subjected to different electrochemical tests and it was revealed that significant improvement of the long term catalyst stability was achieved when the metal‐porous Si nanoassemblies is formed, which represents a step closer to the realisation of the monolithic integrated Si‐based microfabricated fuel cell.

Carbon nanotube supported platinum nanoparticles for the voltammetric sensing of hydrazine

Electrochemical sensing of hydrazine using a highly sensitive platform based on nanosized Pt (nPt) particles is described. The sensing platform is developed by the pre-organization of metal precursor on multiwalled carbon nanotubes (MCNT) modified conducting substrate and subsequent chemical reduction of the precursor in aqueous solution. The Pt nanoparticles are characterized by transmission electron microscope, X-ray diffraction (XRD), spectral and electrochemical measurements. The nPt on MCNT modified electrode has spherical shape with 5–10 nm size. XRD and selected area electron diffraction pattern reveal the existence of (1 1 1), (2 0 0) and (2 2 0) planes of face centered cubic structure. The electrocatalytic activity of nPt on the MCNT modified electrode toward oxidation of hydrazine is examined. The nPt on the MCNT modified electrode exhibit significantly high electrocatalytic activity with respect to the polycrystalline Pt electrode. The nanoparticle coverage on the electrode has strong influence on the electrocatalytic activity. Gradual negative shift in the oxidation peak potential and increase in the peak current are observed while increasing the particle coverage. The nanoparticle-based electrode is highly stable and sensitive and it can sense as low as 0.5 nM hydrazine sulfate at the potential of −0.35 V without any redox mediator. The co-existence of hydrazine derivative N,N-dimethylhydrazine does not interfere the electrochemical sensing of hydrazine.

Studies on the sensing behaviour of nanocrystalline CuGa2O4 towards hydrogen, liquefied petroleum gas and ammonia

In the present article, the gas sensing behaviour of nanocrystalline CuGa(2)O(4) towards H(2), liquefied petroleum gas (LPG) and NH(3) has been reported for the first time. Nanocrystalline powders of CuGa(2)O(4) having average particle sizes in the range of 30-60nm have been prepared through thermal decomposition of an aqueous precursor solution comprising copper nitrate, gallium nitrate and triethanol amine (TEA), followed by calcination at 750 degrees C for 2h. The synthesized nanocrystalline CuGa(2)O(4) powders have been characterised through X-ray diffraction (XRD), transmission electron microscopy (TEM), field-emission scanning electron microscopy (FESEM) study, energy dispersive X-ray (EDX) analysis and BET (Brunauer-Emmett-Teller) surface area measurement. The synthesized CuGa(2)O(4) having spinel structure with specific surface area of 40m(2)/g exhibits maximum sensitivity towards H(2), LPG, and NH(3) at 350 degrees C.

Synthesis and gas-sensing properties of nano- and meso-porous MoO 3-doped SnO 2

Nano- and meso-porous SnO 2 powders doped with and without 1–10 wt% MoO 3 have been synthesized by an ultrasonic spray-pyrolysis method employing a precursor aqueous solution containing tin (IV) chloride pentahydrate (SnCl 4·5H 2O), ammonium heptamolybdate and polymethylmethacrylate (PMMA) microspheres as a template, and the effects of MoO 3-doping and the addition of PMMA microspheres on the structural, morphological and gas-sensing properties of SnO 2 were investigated in this study. It is confirmed that control of the amounts of PMMA microspheres in the precursor solution was effective in realizing well-developed nano- and meso-porous structures of SnO 2 by X-ray diffraction analysis, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, and the measurement of specific surface area and pore size distribution using a N 2 adsorption isotherm. Gas-sensing properties of their thick films (about 50 μm thick), which were fabricated by screen-printing to various gases (NO 2, C 2H 5OH and H 2) were tested in ambient air. The doped thick films showed a high response and selectivity to 5 ppm NO 2 gas in the case of 10 wt% MoO 3-doping in both nano- and meso-porous structures of SnO 2. We observed that the presence of Mo species in SnO 2 lattice can improve the sensor response and selectivity towards NO 2 gas. The effect of the MoO 3-doping on the sensing characteristics of these films towards NO 2 was discussed.

Mesoporous Ferromagnetic MPt@Silica/Carbon (M = Fe, Co, Ni) Composites As Advanced Bifunctional Catalysts

Ferromagnetic MPt (Fe, Co, Ni) nanocomposites were obtained by infiltration of aqueous and chloroform precursor solutions into ordered mesoporous SBA-15 and CMK-3. Channel-confined crystallization of the intermetallic phases was achieved under a reductive and inert atmosphere in a temperature range from 673 to 1073 K using conventional and ultrafast IR furnace heating. The proper choice of mesoporous matrix allows one to tailor crystallite size and to affect the phase transformation rate into ordered face-centered tetragonal (fct) MPt alloys. XRD and TEM techniques were used to monitor the structural evolution in the system. Physisorption methods reveal degradation of the mesoporous carbon matrix for MPt@CMK-3 composites while SBA-15 templated structures stay intact. SQUID investigations were carried out, demonstrating a strong dependence of magnetic properties on the intermetallic system, matrix, and treatment conditions. Especially for fct FePt@carbon, very high room-temperature coercivities up to 28.4 kOe were observed. The materials are efficient catalysts for acetylene to ethylene hydrogenation. Structure-sensitive selectivity of FePt is reported for the first time, demonstrating a higher selectivity of fct FePt composites as compared to the disordered face-centered cubic (fcc) phase.

From Diatom Biomolecules to Bioinspired Syntheses of Silica- and Titania-Based Materials

AbstractAmorphous silica is (next to CaCO3) the second most abundant biologically produced inorganic material. A certain group of photosynthetic microalgae, called diatoms, forms complex 3D silica architectures (frustules) containing regularly arranged nanoscale features (pores, channels, protuberances). Recently, biomolecules involved in diatom silica formation have been characterized, and first insights into their structure-function correlations have been obtained. This has spurred the development of synthetic (bio)polymers capable of directing thein vitroformation of silica and other inorganic materials from aqueous precursor solutions under mild conditions. Here we present a summary of current insight into the mechanism of silica formation by diatom biomolecules and provide examples of synthetic (bio)polymers for the formation of silica and titania materials with complex structures.

An unusual example of morphology controlled periodic mesoporous organosilica single crystals

Morphology and size controlled mesoporous single crystals are of special significance in various applications. In this work, ethane-included PMO single crystals with cubic and truncated-cubic morphologies have been prepared by self-assembling the surfactant and organosilica precursor in aqueous solution. The PMO single crystals are highly uniform in external morphologies and the particle sizes can be trimmed down to less than one micrometre. With the cubic pore structure, the relatively small particle sizes, and the easily-functionalized organic groups embedded in the pore walls, the PMO single crystals may find new applications in various fields.

ZnS Thin Films Deposited by a Spin Successive Ionic Layer Adsorption and Reaction Process

In this article, we reported a spin successive ionic layer adsorption and reaction (SILAR) method for the first time. ZnS thin films were deposited by spin SILAR using ZnCl2 and Na2S aqueous precursor solutions at room temperature and atmosphere pressure. The optical, structural, and morphological characterizations of the films were studied by scanning electron microscopy, atomic force microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, and UV/visible spectroscopy. Smooth (average roughness <3 nm), uniform, and highly transparent ZnS (transmittance of over 90% in the visible band) thin films could be successfully deposited using this technique with shorter cycle time and much less solvent usage.

Properties of Ultrathin High Permittivity ( Nb1 − xTax ) 2O5 Films Prepared by Aqueous Chemical Solution Deposition

Ultrathin films, with thicknesses from , were deposited by chemical solution deposition starting from aqueous precursor solutions. The film’s dielectric properties were characterized by capacitance–voltage and current–voltage measurements. Permittivities ranged from 20 to 31 after annealing at , with the highest value obtained for pure . With increasing Nb content, increasing leakage currents were observed. The crystallization temperature was determined by in situ X-ray diffraction measurement for films with thickness: was crystalline as deposited , while the crystallization temperature of solid solutions increased with increasing Ta content, up to for pure . showed a marked increase in permittivity from 27 to 38 after crystallization anneal at 600 and , respectively. For , no significant difference in permittivity was observed between amorphous and crystalline layers.

Flame Synthesis of Nanosized Cu−Ce−O, Ni−Ce−O, and Fe−Ce−O Catalysts for the Water-Gas Shift (WGS) Reaction

A flame synthesis method has been used to prepare nanosized, high-surface-area Cu-Ce-O, Ni-Ce-O, and Fe-Ce-O catalysts from aqueous solutions of metal acetate precursors. The particles were formed by vaporization of the precursors followed by reaction and then gas to particle conversion. The specific surface areas of the synthesized powders ranged from 127 to 163 m(2)/g. High-resolution transmission electron microscope imaging showed that the particle diameters for the ceria materials are in the range of 3-10 nm, and a thin layer of amorphous material was observed on the surface of the particles. The presence and surface enrichment of the transition-metal oxides (CuO, NiO, and Fe(2)O(3)) on the ceria particles were detected using X-ray photoelectron spectroscopy. Electron energy-loss spectroscopic studies suggest the formation of a core-shell structure in the as-prepared particles. Extended X-ray absorption fine structure studies suggest that the dopants in all M-Ce-O systems are almost isostructural with their oxide counterparts, indicating the doping materials form separate oxide phases (CuO, Fe(2)O(3), NiO) within the host matrix (CeO(2)). Etching results confirm that most of the transition-metal oxides are present on the surface of CeO(2), easily dissolved by nitric acid. The performance of the flame-synthesized catalysts was examined toward water-gas shift (WGS) activity for fuel processing applications. The WGS activity of metal ceria catalysts decreases in the order Cu-Ce-O > Ni-Ce-O > Fe-Ce-O > CeO(2) with a feed mixture having a hydrogen to carbon monoxide (H(2)/CO) ratio of 1. There was no methane formation for these catalysts under the tested conditions.

Combustion-Driven Synthesis of Non-Oxide Nanoparticles in a High Temperature Reducing Jet

Copper nanoparticles were synthesized using a new technique that combines thermal decomposition and hydrogen reduction. The technique uses a flame as a source of low-cost energy to initiate particle synthesis. Molar concentration of the aqueous precursor solution, reactor pressure and temperature, and flow rate of combustion gases (hydrogen, oxygen, and nitrogen), were varied to control particle size, size distribution, and morphology. Copper serves here as a prototype for non-oxide materials that are generally difficult to produced in flame-based reactors. This work demonstrates that such materials can be produced in substantial quantities with particle diameters below 50 nm in this process.

Synthesis of highly ordered Fe-containing mesoporous carbon materials using soft templating routes

Highly ordered Fe-containing mesoporous carbon materials were directly synthesized through simple soft templating routes by using resorcinol–formaldehyde (RF) as a carbon precursor, triblock copolymer Pluronic F127 as a template agent and hydrated iron nitrite as an iron source. The main strategy of this approach is to use the acidity self-generated in the aqueous solutions of the iron precursors as the catalyst for RF polymerization and no any additional mineral acid was necessary. The resultant materials were characterized using nitrogen sorption, X-ray diffraction, and transmission electron microscopy. It was found that the final products with a highly ordered mesostructure were obtained when the Fe/R ratio was around 0.1. For those with Fe/R ratios smaller or greater than this value, the ordering decreased. Iron species in the mesoporous carbon matrix existed in two states, metallic Fe and γ-Fe2O3. Metallic Fe nanoparticles are dominantly buried in the walls of the mesoporous carbon while γ-Fe2O3 nanoparticles are mostly located on the surface. The resulting materials with Fe/R ratio of 0.1 (Fe/OMC-0.10) exhibit specific activity for the catalytic wet peroxide oxidation (CWPO) of phenol solution with hydrogen peroxide. The phenol and TOC conversion can reach to 93.0% and 61.7% within 180min at an initial of phenol 247ppm under very mild conditions (P=1atm and T=80°C).

Preparation and Electric Property of Lead-Free KNbO3 Piezoceramics Derived from Citrate Complex Precursor

The synthesis of well-crystalline KNbO 3 nanopowder has been carried out by using citrate complex precursor method. By using this powder as raw materials, dense KNbO 3 ceramics (RD = 98.9%) was successfully prepared, and showed excellent ferroelectric and piezoelectric properties. The effect of starting K/Nb mixture ratio in aqueous precursor solution on the crystallinity and electric properties of derived KNbO 3 ceramics was studied. It was found that an appropriate superfluous addition of the K-souce (K/Nb = 1.05) was required to synthesis excellent KNbO 3 ceramics, because of the existence of residual K+ ions in the aqueous solution without being involved in the formation of the chelating complex.

Shape-Selective Fabrication of Zinc Phosphate Hexagonal Bipyramids via a Disodium Phosphate-Assisted Sonochemical Route

Via a simple and facile disodium phosphate-assisted sonochemical route, highly uniform zinc phosphate hexagonal bipyramid crystals were selectively synthesized under ambient conditions. All the facets of hexagonal bipyramids are smooth. The average size (from pole to pole) and the standard deviation were 1.437 μm and 562 nm, respectively. The concentration of HPO42− in the aqueous precursor solution is thought to be a key factor in getting hexagonal bipyramidal morphology. This method is simple, fast, economical, and environmentally benign. It is expected that this sonochemical technique can be readily adopted in realizing other forms of various micro/nanostructured materials.

In Situ Controllable Loading of Ultrafine Noble Metal Particles on Titania

Herein we present a novel and facile approach to controllably load ultrafine noble metal nanoparticles on titania through in situ redox reaction between the reductive titanium(III) oxide support and metal salt precursors in aqueous solution. A series of noble metal/TiO(2) nanocomposites with uniform metal dispersion, tunable metal particle size, and narrow metal particle size distribution were obtained.

Probing the Incorporation of Ti(IV) into the BEA Zeolite Framework by XRD, FTIR, NMR, and DR UV−jp810722bis

The method (Dzwigaj, S., et al. Chem. Commun. 1998, 87) proposed earlier to incorporate V(V) ions into the BEA zeolite framework at the solid−liquid interface from V precursors in aqueous solution has been successfully extended to the solid−gas interface and titanium, with TiCl4 vapor as the precursor. The use of TiCl4 vapor has the advantage to restrict the speciation of titanium to this single species and to lead to a significant amount of Ti (∼5 Ti wt %) determined by chemical analysis. The incorporation of Ti into the SiBEA zeolite framework is evidenced by XRD. The reaction of TiCl4 vapor with H-bonded and terminal SiO−H groups of vacant T-atom sites is monitored by FTIR, 29Si MAS NMR, 1H−29Si CP MAS NMR and 1H MAS NMR. The presence of tetrahedral Ti(IV) as the main titanium species is evidenced by diffuse reflectance UV−vis. A possible pathway for the formation of framework tetrahedral Ti(IV) in TiSiBEA is proposed.

Organosilica Monoliths with Multiscale Porosity: Detailed Investigation of the Influence of the Surfactant on Structure Formation

Monolithic inorganic-organic hybrid materials have been synthesized via sol-gel processing of an ethylene glycol-modified ethane-bridged silane precursor in aqueous solution of the non-ionic block copolymer Pluronic™ P123. The influence of different sol compositions on the final gel structure was investigated in detail. The resulting materials consist of macroporous networks comprising periodically arranged mesopores, where the macropore size as well as the morphology of the material can be deliberately tailored by reducing the amount of the block copolymer template. The structure was investigated by small-angle X-ray scattering as well as scanning and transmission electron microscopy. Information on the porosity, surface area and pore size distribution were obtained from BET/BJH analysis and mercury intrusion measurements. For a more detailed insight into mechanism and kinetics of the mesostructure formation, in-situ SAXS experiments were carried out.

Triblock copolymer templated semi-crystalline mesoporous titania films containing emulsion-induced macropores

Triblock copolymer templated synthesis of titania films in water (without ethanol) was demonstrated, which led to the formation of emulsions in the aqueous precursor solutions by adding hydrophobic 1,3,5-triisopropylbenzene (TIPBz). A cubic Im-3m mesoporous anatase film containing emulsion-induced macropores was prepared by spin-coating of an aqueous precursor solution of water-soluble triblock copolymer such as Pluronic F127 through the evaporation-induced self-assembly approach. The addition of TIPBz in the aqueous system also affords pinhole-like macrospaces in the mesostructured film. Expansion of the pinhole-like macrospaces during calcination would offset a tensile stress through shrinkage with the retention of the mesostructure, leading to complete crystallization of the titania framework that is important for effective adsorption of DNA molecules.