Aqueous Precursor Solution Research Articles

Impact of Relative Humidity during Spin-Deposition of Metal Oxide Thin Films from Aqueous Solution Precursors

Relative humidity during the spin-processing of thin film solution precursors is often not controlled or measured, and its effect on film thickness is generally unappreciated. Herein, we report that the relative humidity during spin-processing has a marked impact on the film thickness of amorphous metal oxide (aluminum oxide and lanthanum zirconium oxide) and hafnium oxide-sulfate (HafSOx) thin films deposited from aqueous precursors. In the humidity range studied [20–95% relative humidity (RH)], film thicknesses varied by a factor of nearly 3, and this effect is independent of the metal precursor identity. Our data suggest that film thickness depends linearly on evaporation rate (100 – RH) for all systems studied, suggesting this effect is predominantly due to the unique characteristics of water as a solvent. In situ X-ray reflectivity studies of HafSOx films deposited under different humidities reveal that, while the thickness varies significantly with humidity, the density of the as-deposited films is ...

A Generalized Method for the Synthesis of Ligand-Free M@SiO2 (M = Ag, Au, Pd, Pt) Yolk-Shell Nanoparticles.

A universal method is reported for the synthesis of ligand free noble metal M@SiO2 (M = Ag, Au, Pd, Pt) yolk-shell nanoparticles (YSNs). Mesoporous hollow silica shells (mHSS) are used as smart nanoreactors for the synthesis of noble metal yolk-shell nanoparticles. The nanocavity of a mHSS and anionic metal ions play a critical role in the formation of yolk-shell nanoparticles. The synthesis mechanism can be tuned by simply varying the pH of the noble metal precursor aqueous solution. A critical pH ≥ 4 is required for the formation of YSNs. The anionic metal ions can pass freely through the mesopores of mHSS and eventually lead to the formation of YSNs, whereas the cationic metal ions can show strong interaction with the surface of mHSS which hinders the formation of YSNs. The syntheses of YSNs are achieved without using any external capping ligands and reducing agents in the reaction.

Templated, Macroporous PEG‐DA Hydrogels and Their Potential Utility as Tissue Engineering Scaffolds

Poly(ethylene glycol) diacrylate (PEG‐DA) hydrogels have been widely utilized to investigate cell–material interactions and as scaffolds for tissue engineering. Traditionally, PEG‐DA hydrogels are prepared via the UV‐cure of aqueous precursor solutions, but afford a limited range of pore size and interconnectivity that is essential for cellular proliferation and neotissue formation. To overcome these limitations, macroporous PEG‐DA hydrogels are prepared in this study using a combination of solvent‐induced phase separation (SIPS) and a fused salt template. PEG‐DA concentration in the organized fabrication solvent (20, 30, and 40 wt%) and average salt particle size (≈180, ≈270, and ≈460 μm) are varied and the resulting hydrated hydrogel morphology, swelling, mechanical properties, and degradation are characterized. These templated SIPS PEG‐DA hydrogels broaden PEG‐DA hydrogel properties and, in some cases, afford a series of compositions whose properties are decoupled. image

Delicate Structural Control of Si-SiOx-C Composite via High-Speed Spray Pyrolysis for Li-Ion Battery Anodes.

Despite the high theoretical capacity, silicon (Si) anodes in lithium-ion batteries have difficulty in meeting the commercial standards in various aspects. In particular, the huge volume change of Si makes it very challenging to simultaneously achieve high initial Coulombic efficiency (ICE) and long-term cycle life. Herein, we report spray pyrolysis to prepare Si-SiOx composite using an aqueous precursor solution containing Si nanoparticles, citric acid, and sodium hydroxide (NaOH). In the precursor solution, Si nanoparticles are etched by NaOH with the production of [SiO4]4-. During the dynamic course of spray pyrolysis, [SiO4]4- transforms to SiOx matrix and citric acid decomposes to carbon surface layer with the assistance of NaOH that serves as a decomposition catalyst. As a result, a Si-SiOx composite, in which Si nanodomains are homogeneously embedded in the SiOx matrix with carbon surface layer, is generated by a one-pot process with a residence time of only 3.5 s in a flow reactor. The optimal composite structure in terms of Si domain size and Si-to-O ratio exhibited excellent electrochemical performance, such as reversible capacity of 1561.9 mAh g-1 at 0.06C rate and ICE of 80.2% and 87.9% capacity retention after 100 cycles at 1C rate.

Wet Chemical Synthesis of Silica Nanosheets via Ethyl Acetate-Mediated Hydrolysis of Silica Precursors and Their Applications.

Freestanding and transferable silica nanosheets with thicknesses of ≈5-7nm are prepared via ethyl acetate-mediated hydrolysis of silica precursors in aqueous solution. The resulting silica nanosheets have shown many potential applications. For example, they can be used as the support film on the finer mesh grids for transmission electron microscopy imaging and as the precursor for the synthesis of silicon nanosheets.

Development of new hydrodesulfurization NiMo catalysts supported on Al2O3-TiSBA-15 hybrid materials

In the present work, a series of NiMo catalysts supported on hybrid materials consisting of mesoporous TiSBA-15 and conventional γ-alumina were prepared. Three hybrid supports were synthesized with 20, 40 and 60wt.% of TiSBA-15 and compared to pure γ-Al2O3 and TiSBA-15 counterparts. NiMo catalysts were prepared by incipient wetness co-impregnation of aqueous solutions of ammonium heptamolybdate and nickel nitrate precursors. Supports and catalysts were characterized by N2 physisorption, XRD, UV–vis DRS, temperature programmed reduction (TPR) and ammonia TPD. The sulfided NiMo catalysts were characterized by HRTEM and evaluated in the simultaneous hydrodesulfurization of dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (4,6-DMDBT). All NiMo catalysts supported on hybrid materials showed better dispersion of the catalytically active MoS2 phase than the reference catalyst supported on the conventional γ-alumina material. Their activity was similar to that of the NiMo/γ-Al2O3 catalyst in HDS of DBT, but substantially higher in HDS of 4,6-DMDBT.

Morphology memory but reconstructing crystal structure: porous hexagonal GeO2 nanorods for rechargeable lithium-ion batteries.

Hexagonal GeO2, with high theoretical reversible capacity and low operating voltage, is regarded as a promising anode material for Li ion batteries. Being similar to other alloy type anode materials, the practical application of GeO2 is confronted with large volume change and fast capacity fading during lithiation/delithiation cycles. Constructing unique GeO2 nanostructures is proposed as an effective strategy to address this issue of fast capacity degradation. However, the controllable synthesis of GeO2 nanomaterials is challenged due to the fast hydrolysis of Ge precursors in aqueous solution. In this work, we report a simple strategy to synthesize GeO2 nanorods by using orthorhombic Ca2Ge7O16 nanorods as the sacrificial template with HNO3 as the etching agent. With the morphology memory of orthorhombic Ca2Ge7O16 nanorods, the as-prepared porous hexagonal GeO2 nanorods exhibit excellent electrochemical performance with a high capacity of 747 mA h g-1 after 50 cycles, which should be attributed to the porous and one dimensional nanostructure of GeO2 nanorods. This facile 'morphology memory but restructuring crystal structure' method could be extended to the controllable preparation of other GeO2 nanostructures, and achieve more efficient anode materials.

Investigation of selenization and various CBD CdS deposition conditions to fabricate high performing spray pyrolysis synthesized Cu(In,Ga)(S,Se)2 solar cells

Semiconducting thin-films of CIGS were deposited by spray pyrolysis of aqueous precursor solutions. The as-sprayed thin films were then selenized at different temperatures and durations to obtain the optimized selenization conditions (500 °C for 10 min). The chemical bath deposition process was used to deposit cadmium sulphide (CdS) using two different cadmium sources (cadmium acetate and cadmium sulphate) at various deposition times followed by post CdS annealing. Solar cells fabricated with CdS as the buffer layer using cadmium acetate show power conversion efficiency of 9.91% owing to its higher transmission and smaller grain size.

Synthesis of IZTO(Indium Zinc Tin Oxide) particle by spray pyrolysis and post-heat treatment and characterization of deposited IZTO film

The micron-sized indium zinc tin oxide (IZTO) particles were prepared by spray pyrolysis from aqueous precursor solution for indium, zinc, and tin and organic additives such as citric acid (CA) and ethylene glycol (EG) were added to aqueous precursor solution for indium, zinc, and tin. The obtained IZTO particles prepared by spray pyrolysis from the aqueous solution without organic additives had spherical and filled morphologies, whereas the IZTO particles obtained with organic additives had more hollow and porous morphologies. The micron-sized IZTO particles with organic additives were changed fully to nano-sized IZTO particles, whereas the micron-sized IZTO particles without organic additives were not changed fully to nano-sized IZTO particle after post-treatment at 700 °C for 2 hours and wet-ball milling for 24 hours. Surface resistances of micron-sized IZTO’s before post-heat treatment and wet-ball milling were much higher than those of nano-sized IZTO’s after post-heat treatment and wet-ball milling. From IZTO with composition of 80 wt. % In2O3, 10 wt. % ZnO, and 10 wt. % SnO2 which showed a smallest surface resistance IZTO after post-heat treatment and wet-ball milling, thin films were deposited on glass substrates by pulsed DC magnetron sputtering, and the electrical and optical properties were investigated.

Amorphous Mixed-Metal Oxide Thin Films from Aqueous Solution Precursors with Near-Atomic Smoothness.

Thin films with tunable and homogeneous composition are required for many applications. We report the synthesis and characterization of a new class of compositionally homogeneous thin films that are amorphous solid solutions of Al2O3 and transition metal oxides (TMOx) including VOx, CrOx, MnOx, Fe2O3, CoOx, NiO, CuOx, and ZnO. The synthesis is enabled by the rapid decomposition of molecular transition-metal nitrates TM(NO3)x at low temperature along with precondensed oligomeric Al(OH)x(NO3)3-x cluster species, both of which can be processed from aq solution. The films are dense, ultrasmooth (Rrms < 1 nm, near 0.1 nm in many cases), and atomically mixed amorphous metal-oxide alloys over a large composition range. We assess the chemical principles that favor the formation of amorphous homogeneous films over rougher phase-segregated nanocrystalline films. The synthesis is easily extended to other compositions of transition and main-group metal oxides. To demonstrate versatility, we synthesized amorphous V0.1Cr0.1Mn0.1Fe0.1Zn0.1Al0.5Ox and V0.2Cr0.2Fe0.2Al0.4Ox with Rrms ≈ 0.1 nm and uniform composition. The combination of ideal physical properties (dense, smooth, uniform) and broad composition tunability provides a platform for film synthesis that can be used to study fundamental phenomena when the effects of transition metal cation identity, solid-state concentration of d-electrons or d-states, and/or crystallinity need to be controlled. The new platform has broad potential use in controlling interfacial phenomena such as electron transfer in solar-cell contacts or surface reactivity in heterogeneous catalysis.

Facile preparation of egg-shell-type pellet catalysts using immiscibility between hydrophobic solvent and hydrophilic solution: Enhancement of catalytic activity due to position control of metallic nickel inside alumina pellet

Egg-shell-type catalysts, in which active components were selectively located outer region of pellet, have been prepared to effectively utilize catalytically active components in the reactions with high gas-hourly space velocity conditions. We developed a new and facile preparation method for egg-shell catalysts using immiscibility between hydrophobic solvent preoccupied inside pellet and aqueous hydrophilic precursor solution. A series of alcohols, propanol, butanol, pentanol and so on, were used as hydrophobic solvents to retard the penetration of aqueous metal precursor solutions. After drying solvents and proper calcination and reduction, catalytically active components, metallic nickel particles, were selectively located in the outer region of pellet. Owing to the selective deposition of metallic particles, the egg-shell catalysts showed higher conversion of methane in steam methane reforming than homo-type catalysts, which has homogeneous distribution of metal particles on the entire range of pellet, as the space velocity increased from 6000 to 30,000h−1.

Preparation of Magnetic Iron Oxide Nanoparticles (MIONs) with Improved Saturation Magnetization Using Multifunctional Polymer Ligand.

This paper describes the preparation of ultra-small magnetic iron oxide (Fe3O4) nanoparticles (MIONs) coated with water-soluble thioether end-functionalized polymer ligand pentaerythritol tetrakis 3-mercaptopropionate-polymethacrylic acid (PTMP-PMAA). The MIONs were prepared by co-precipitation of aqueous iron precursor solution at a high temperature. The polymer modified MIONs were characterized by dynamic light scattering (DLS), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), X-ray powder diffraction (XRD), thermogravimetric analysis (TGA), and vibrating sample magnetometery (VSM). It was found that these MIONs were successfully modified by this water-soluble polymer ligand with a fairly uniform size and narrow size distribution. The dried powder of MIONs could be stored for a long time and re-dispersed well in water without any significant change. Additionally, the polymer concentration showed a significant effect on size and magnetic properties of the MIONs. The saturation magnetization was increased by optimizing the polymer concentration. Furthermore, the 3-(4,5-dimethylthiazol-2-yl)-2-5-diphenyltetrazolium bromide (MTT)-assay demonstrated that these MIONs were highly biocompatible and they could be successfully coupled with fluorescent dye Rhodamine due to the formation of amide bond between carboxylic acid groups of MIONs and amine groups of dye. The obtained results indicated that these multifunctional MIONs with rich surface chemistry exhibit admirable potential in biomedical applications.

Sensitive, Selective, and Fast Detection of ppb-Level H2S Gas Boosted by ZnO-CuO Mesocrystal.

ZnO-CuO mesocrystal was prepared via topotactic transformation using one-step direct annealing of aqueous precursor solution and assembled into a H2S sensor. The ZnO-CuO mesocrystal-based sensor possesses good linearity and high sensitivity in the low-concentration range (10–200 ppb). Compared to pure CuO, the as-prepared ZnO-CuO mesocrystal sensor exhibited superior H2S sensing performance with a response ranging from 8.6 to 152 % towards H2S concentrations from 10 ppb to 10 ppm when applied at the optimized working temperature of 125 °C. The sensor showed excellent repeatability and good selectivity towards H2S gas even at a concentration four orders of magnitude lower than the interfering gases, such as H2, CO2, CO, NO2, acetone, and NH3. The improved sensitivity could be attributed partially to the effective diffusion of analyte gas through the mesocrystal surface and the abundant accessible active sites. Moreover, the nanoscale p-n junctions within the mesocrystal, which could effectively manipulate the local charge carrier concentration, are also beneficial to boost the sensing performance.Electronic supplementary materialThe online version of this article (doi:10.1186/s11671-016-1688-y) contains supplementary material, which is available to authorized users.

Influence of Water in the Photogeneration and Properties of a Bifunctional Quinone Methide.

Quinone methides (QM) are crucial reactive species in molecular biology and organic chemistry, with little known regarding the mechanism(s) for the generation of short-lived reactive QM intermediates from relevant precursors in aqueous solutions. In this study, several time-resolved spectroscopy methods were used to directly examine the photophysics and photochemical pathways of 1,1'-(2,2'-dihydroxy-1,1'-binaphthyl-6,6'-diyl)bis(N,N,N-trimethylmethanaminium) bromide (BQMP-b) from initial photoexcitation to the generation of the key reactive binol QM intermediate (BQM) in aqueous solution. The fluorescence of BQMP-b is effectively quenched with a small amount of water, which suggests an excited state intramolecular proton transfer (ESIPT) occurs. The kinetics isotope effects observed in femtosecond and nanosecond time-resolved transient absorption experiments provide evidence for the participation of water molecules in the BQMP-b singlet excited state ESIPT process and in the subsequent -HNMe3+ group release and ground state intramolecular proton transfer that give rise to production of the reactive BQM intermediate. Nanosecond time-resolved resonance Raman (ns-TR3) measurements were also employed to investigate the structure and properties of several intermediates, including the key reactive BQM in aqueous solution. The ns-TR3 and density functional theory (DFT) computational results were compared, and this indicates the binol moiety and water molecules both have important roles in the characteristics and structure of the key reactive BQM intermediate produced from BQMP-b. The results presented here also provide new benchmark characterization of bifunctional quinone methide intermediates that can be utilized to guide direct time-resolved spectroscopic study of the alkylation and interstrand cross-linking reactions of quinone methides with DNA in the future.

Synthesis of porous yttria-stabilized zirconia microspheres by ultrasonic spray pyrolysis

High yield synthesis of yttria-stabilized zirconia (YSZ) porous microspheres can enable application in advanced thermal barrier coatings, exploiting reflective properties originated from high temperature photonics. The complexity of typical wet-chemistry processes utilized in microspheres manufacturing limits yield and can hardly deliver stable porous structures. Here, ultrasonic spray pyrolysis was utilized to produce high quantities of porous YSZ. Droplets of an aqueous precursor solution were dragged with continuous air flow into a furnace kept at temperatures varying from 700 to 1200°C. Spherical fully cubic zirconia particles were obtained in all processing conditions, and the sizes of the spheres decreased as a function of the processing temperature, ranging from 484 to 373nm (average diameters), while their crystallite sizes had an inverse trend, ranging from 4.9 to 25.2nm. This was attributed to higher temperatures activating coarsening of the spheres.

Improved photo-catalytic activity of novel nano-dimension Ce/Zn composite oxides deposited on flat-glass surface for removal of Acid Black 4BN dye pollution

In this research, we studied an easy method to prepare pure cerium oxide nano particle (CeONP), pure zinc oxide nano particle (ZnONP) and Ce/Zn nano composite (Ce/ZnONP) coupled oxide by one pot reaction of cerium and zinc nitrate as precursors in aqueous solution using a Teflon-lined stainless autoclave at 120 °C for 12 h. Model water pollutant Acid Black 4BN as a di-azo textile dye was used to compare the photo-catalytic activity of (CeONP), (ZnONP) and (CeZnONP) deposited on flat-glass surface to overcome the problem of nano catalyst separation from suspension. Thermal, structural and spectral characterization of nano-structures were studied by thermo-gravimetric analysis, X-ray diffraction method, field emission scanning electron microscopy, Fourier transform infrared spectroscopy, energy dispersive X-ray spectroscopy. The elemental analysis using energy dispersive X-ray spectroscopy proved the existence of cerium and zinc in immobilized nano-structures Ce/Zn oxides. The X-ray diffraction result of the composite showed high crystalline cubic cerium oxide and hexagonal wurtzite zinc oxide. The photo-catalytic activity of Ce/Zn nano composite oxide coated on flat-glass surface for degradation dia-azo dye was enhanced compared to their single oxide counterparts. This heterogeneous photo-catalytic degradation of dia-azo dye can be applied as an alternative to suspended oxide powders and over-come drawbacks of filtration of photo-catalysts. This study for the first time showed the potential application of Ce/Zn nano composite for removal of organic pollutant from water.

CoP As an Acid-Stable Electrocatalysts for the Hydrogen-Evolution Reaction: Synchrotron-Based Operando Oxidation-State Determinations

Electrochemical water splitting is an important component of several developing clean-energy technologies that aim to be sustainable, renewable, and carbon-neutral. In order to carry out this process efficiently, catalysts for the cathodic half reaction (hydrogen evolution, HER) and anodic half reaction (oxygen evolution, OER) are essential. Currently, earth-abundant, low-cost materials are being vigorously sought for these purposes. Here we report a facile electrochemical method for the synthesis of a cobalt phosphide film that displays both excellent HER activity and stability during operation in acidic media. CoP films were synthesized electrochemically via cathodic deposition from oxidized precursors in aqueous solution at room temperature. The as-deposited films required an overpotential of only 85 mV to drive a current density of 10 mA cm−2 in 0.5M H2SO4. Over 24 h of galvanostatic electrolysis at 10 mA cm-2 resulted in an overpotential increased of less than 20 mV. X-ray photoelectron spectroscopic examination of the film surface after electrocatalysis revealed that the phosphorus existed in both reduced (phosphide) and oxidized states (orthophosphate). In order to determine the surface character during electrocatalysis operando X-ray absorption and Raman spectroscopic analysis were performed. Such analysis directly confirmed that the catalyst existed solely in the reduced state (phosphide) during catalysis.

Application of Electrochemically Deposited Cobalt Films in a Hydrogen Evolution Reaction

Hydrogen gas production is a rapidly growing field of research due to its desirable properties from a sustainability viewpoint. The burning of hydrogen gas provides an environmental incentive as well, due to the lack of carbon-based byproducts [1-2]. Hydrogen gas is often evolved from water but is an energy intensive process. Solid chemical storage has been implemented through the use of metal hydrides, such as sodium borohydride. The oxidation reaction of sodium borohydride in water slowly evolves 4 moles of hydrogen gas. While a slow reaction is favorable for reduction, the use of NaBH4to produce hydrogen gas necessitates the use of catalysis to accelerate the reaction to an appreciable rate. A great deal of research has been conducted searching for catalysts of such reactions, often finding noble metals to be the most efficient. While less efficient than noble metals, cobalt materials have also demonstrated catalytic properties in a variety of hydrogen evolution reactions. Cobalt is more abundant in the earth’s crust than the noble metals, which makes it an arguably more attractive catalytic material due to a relatively lower cost and easier scalability [3-5]. Cobalt films deposited from aqueous (H2O/CoCl) and non-aqueous precursor (Ch:Ch/EG/CoCl) solutions were tested for catalytic activity in the hydrogen evolution reaction of aqueous NaBH4. The evolved gas was measured through the use of a water-displacement system, Ohaus microbalance, and mass logging software. The non-aqueously deposited films initially showed a higher reaction rate, but voids in the surface could prevent disassociation of the hydrogen, reducing the catalytic surface. The aqueously deposited films were largely amorphous, providing better active sites for the reaction than its non-aqueous counterpart. Both Co films outperformed the copper substrate (Cu). Catalytic Surface Rate Constant (10-3 min-1) Aqueous Co Deposition 4.9 Non-aqueous Co Deposition 4.6 Original Copper Substrate 3.3

Impact of Precursor Compositions on the Structural and Photovoltaic Properties of Spray-Deposited Cu2 ZnSnS4 Thin Films.

Pure sulfide Cu2 ZnSnS4 thin films were fabricated on Mo-coated glass substrates by facile spray deposition of aqueous precursor solutions containing Cu(NO3 )2 , Zn(NO3 )2 , Sn(CH3 SO3 )2 , and thiourea followed by annealing at 600 °C. When a precursor solution containing a stoichiometric composition of Cu, Zn, and Sn was used, the resulting Cu2 ZnSnS4 thin film contained a Cu2-x S impurity phase owing to the evaporation of Sn components during the annealing process. The Cu2-x S impurity in the Cu2 ZnSnS4 thin film was removed by reducing the concentration of Cu in the precursor solution. This resulted in an improvement of the structural features (i.e., grain sizes and compactness) as well as the electric properties such as acceptor densities, the nature of the acceptor defects, and carrier lifetimes. A solar cell based on the Cu2 ZnSnS4 film with an empirically optimal composition showed conversion efficiency of 8.1 %. The value achieved was one of the best efficiencies of Cu2 ZnSnS4 -based cells derived from a non-vacuum process.

Ultrasonic-assisted synthesis of ZrO2 nanoparticles and their application to improve the chemical stability of Nafion membrane in proton exchange membrane (PEM) fuel cells

Zirconium dioxide (ZrO2) nanoparticles were fabricated successfully via ultrasonic-assisted method using ZrO(NO3)2·H2O, ethylenediamine and hydrazine as precursors in aqueous solution. Morphology, structure and composition of the obtained products were characterized by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), dynamic light scattering (DLS), Fourier transform infrared spectroscopy (FT-IR) and diffuse reflectance spectroscopy (DRS). Then, the synthesized nanoparticles were used to prepare Nafion/ZrO2 nanocomposite membranes. The properties of the membranes were studied by ion exchange capacity (IEC) proton conductivity (σ), thermal stability and water uptake measurements. The ex-situ Fenton’s test was used to investigate the chemical stability of the membranes. From our results, compared with Nafion membrane, the nanocomposite membrane exhibited lower fluoride release and weight loss. Therefore, it can concluded that Nafion/ZrO2 nanocomposite exhibit more chemical stability than the pure Nafion membrane. ATR-FTIR spectra and SEM surface images of membranes also confirm these results.