H2O Precursor Research Articles

Precursor-based synthesis and electrochemical performance of LiMnPO4

Olivine-like LiMnPO4 was prepared from the NH4MnPO4·H2O precursor precipitated from the aqueous solution. Different morphologies of the LiMnPO4 were obtained by the solid-state reaction of the precursor with LiOH (granular, 100–300 nm) and by ion-exchange reaction with eutectic mixture LiCl–LiNO3 (flake-like crystallites up to 10 μm). The morphology and size distribution of the precursor NH4MnPO4·H2O is preserved during ion-exchange, establishing a new preparation route for nanosized LiMnPO4. After ball-milling with carbon black the granular material delivers 30% of the theoretical capacity at C/5. The rate capabilities of the obtained materials are compared with the results from sol–gel synthesis in the light of particle size effect.

Toward to branched platinum nanoparticles by polyol reduction: A role of poly(vinylpyrrolidone) molecules

Branched Pt nanoparticles with nanometer sizes have been successfully synthesized by reduction of H2PtCl6·6H2O precursor in ethylene glycol (EG) in the presence of small amounts of NaNO3 and PVP. Morphologies of the Pt nanoparticles can be systematically evolved from regular octahedron, and triangular plate via tri-pod, penta-pod, and octa-pod to multi-pod needle-like shapes only by decreasing concentrations of H2PtCl6·6H2O and NaNO3 at a constant NaNO3/H2PtCl6·6H2O molar ratio and the same PVP concentration. To the best of knowledge, this is the first report for the synthesis of Pt penta-pod. High resolution transmission electron microscope (TEM) observation of the Pt nanoparticles demonstrates that the Pt branches actually extendedly grow out from certain angles of triangular plates, octahedrons, and decahedrons, respectively. Multi-branched needle-like Pt nanocrystals are believed probably to originate from further anisotropic growth of the Pt octa-pods or overlap of small branched Pt nanoparticles. PVP molecules have been found to play an important role in controlling morphologies of the branch-like Pt nanoparticles besides NaNO3. It probably is the cooperated kinetic adsorption and desorption of PVP molecules and various anions on particle surfaces that influence the growth of the Pt nanoparticles. A reasonable growth mechanism has been suggested to explain the evolution of the Pt branches, in which the difference among growth rates along various crystallographic directions of face-centered cubic Pt crystal probably determines final morphologies of the Pt nanocrystals.

Nucleation of HfO2 atomic layer deposition films on chemical oxide and H-terminated Si

HfO 2 thin films have been deposited by an atomic layer deposition (ALD) process using alternating pulses of tetrakis-ethylmethylamino hafnium and H2O precursors at 250 °C. The as-deposited films are mainly amorphous and nearly stoichiometric HfO2 (O/Hf ratio ∼1.9) with low bonded carbon content (∼3 at. %). A comparison of the nucleation stage of the films on OH- and H-terminated Si(100) surfaces has been performed using Rutherford backscattering spectrometry, x-ray photoelectron spectroscopy (XPS), and spectroscopic ellipsometry (SE). We find for the initial 5–7 process cycles that the film nucleates more efficiently on the OH-terminated surface. However, after the 7th cycle both surfaces exhibit similar surface coverage, which takes about 40 cycles to reach a steady growth rate per cycle. Angle resolved XPS measurements reveal the formation of a ∼6 Å interfacial layer after four ALD cycles on the H-terminated surface and the thickness of the interfacial layer does not change substantially between the 4th and the 50th process cycles as shown by transmission electron microscopy. Although the surface coverage is comparable for both starting surfaces, film measurements performed by SE suggest that thick films deposited on H-terminated Si are ∼5% thicker than similar films on the chemical oxide surface. Atomic force microscopy (AFM) measurements reveal higher surface roughness for the films deposited in the H-terminated surface. The SE and the AFM data are consistent with higher porosity for the films on H-terminated surfaces.

Synthesis of Highly Ordered Mesoporous Crystalline WS2 and MoS2 via a High-Temperature Reductive Sulfuration Route

A high-temperature reductive sulfuration method is demonstrated to synthesize highly ordered mesoporous metal sulfide crystallites by using mesoporous silica as hard templates. H2S gas is utilized as a sulfuration agent to in situ convert phosphotungstic acid H3PW12O40.6H2O to hexagonal WS2 crystallites in the silica nanochannels at 600 degrees C. Upon etching silica, mesoporous, layered WS2 nanocrystal arrays are produced with a yield as high as 96 wt %. XRD, nitrogen sorption, SEM, and TEM results reveal that the WS2 products replicated from the mesoporous silica SBA-15 hard template possess highly ordered hexagonal mesostructure (space group, p6mm) and rodlike morphology, analogous to the mother template. The S-W-S trilayers of the WS2 nanocrystals are partially oriented, parallel to the mesochannels of the SBA-15 template. This orientation is related with the reduction of the high-energy layer edges in layered metal dichalcogenides and the confinement in anisotropic nanochannels. The mesostructure can be 3-D cubic bicontinuous if KIT-6 (Iad) is used as a hard template. Mesoporous WS2 replicas have large surface areas (105-120 m2/g), pore volumes ( approximately 0.20 cm3/g), and narrow pore size distributions ( approximately 4.8 nm). By one-step nanocasting with the H3PMo12O40.6H2O (PMA) precursor into the mesochannels of SBA-15 or KIT-6 hard template, highly ordered mesoporous MoS2 layered crystallites with the 2-D hexagonal (p6mm) and 3-D bicontinuous cubic (Iad) structures can also be prepared via this high-temperature reductive sulfuration route. When the loading amount of PMA precursor is low, multiwalled MoS2 nanotubes with 5-7 nm in diameter can be obtained. The high-temperature reductive sulfuration method is a general strategy and can be extended to synthesize mesoporous CdS crystals and other metal sulfides.

Atomic Layer Deposition of Hafnium Oxide from Tetrakis(ethylmethylamino)hafnium and Water Precursors

We have calculated the atomistic mechanism for the HfO2 atomic layer deposition (ALD) using Hf(NEtMe)(4) and H2O precursors using density functional theory. On hydroxylated Si surface, our results show overall Hf(NEtMe)(4) half-reaction is exothermic by 1.65 eV with a small activation barrier of 0.10 eV. The activation barriers for water half-reaction are 0.24 and 0.20 eV. This indicates HfO2 ALD with Hf(NEtMe)(4) and H2O has a faster deposition rate than that with HfCl4 and H2O and can be run at relatively low temperature. However, on H-terminated Si surface, the Hf(NEtMe)(4) half-reaction is endothermic by 2.39 eV with high activation barriers. The H2O half-reaction is similar to that on hydroxylated surface which is kinetically favorable. The results suggest that long Hf(NEtMe)(4) pulse time and high deposition temperature is required during the initial stage of ALD on H-terminated surface. Moreover, our calculations indicate the reaction byproduct HNEtMe is likely to be bound to the surface after each half-reaction because of high desorption energy of 0.7-0.9 eV. Thus, long precursor purge time should be used if HNEtMe is needed to be removed completely.

Preparation of solid nickel nanoparticles by large-scale spray pyrolysis of Ni(NO 3) 2·6H 2O precursor: Effect of temperature and nickel acetate on the particle morphology

Spherical nickel nanoparticles were prepared by a large-scale spray pyrolysis process with two continuous reactors and were investigated in terms of particle-formation mechanism, surface property, particle shape, and size with changing the temperature of two continuous reactors and the type of precursor. When nickel nitrate was used as a precursor and the second reactor temperature was over 1200 °C, solid Ni particles were obtained, but many ultra-fine particles of less than tens nanometer were simultaneously formed via a gas-to-particle conversion mechanism. The formation of such ultra-fine particles was reduced by making hollow particles in the first reactor at 500 °C and thereafter densifying them in the second reactor at 1400 °C, but could not completely prevent. The addition of about 5–10 mol% nickel acetate instead nitrate precursor was found to be very effective to avoid the formation of such ultra-fine particles as well as producing solid particles with clean and smooth surface. On the basis of the results obtained, a mechanism of particle formation in the large-scale spray pyrolysis was proposed. Finally, spherical and solid nickel nanoparticles, which had clean surface and high density (larger than 8.4 g/cm 3), were prepared from the mixed precursor (nitrate/acetate) at a residence time of about 3 s without any chemical additive.

Precursor induced synthesis of hierarchical nanostructured ZnO

As-synthesized ZnO nanostructures with a bladed bundle-likearchitecture have been fabricated from a flower-like precursorZnO·0.33ZnBr2·1.74H2O via a mechanism of dissolution–recrystallization. Experimental conditions, such as initial reactantsand reaction time, are examined. The results show that no bladed bundle-like ZnO hierarchicalnanostructures can be obtained by using the same molar amount of other zinc salts, such asZnBr2, instead ofthe flower-like ZnO·0.33ZnBr2·1.74H2O precursor, and keeping other conditions unchanged. The products werecharacterized by field emission scanning electron microscopy (FE-SEM) andtransmission electron microscopy (TEM). The ZnO nanostructures are mainlycomposed of nanowires with a diameter around 40–50 nm and length up to1.5–2.5 µm. Meanwhile, ZnO nanoflakes with a thickness of about 4–5 nm attached to the surface ofZnO nanowires with a preferred radially aligned orientation. Furthermore, thephotoluminescence (PL) measurements exhibited the unique white-light-emittingcharacteristic of hierarchical ZnO nanostructures. The emission spectra cover the wholevisible region from 380 to 700 nm.

Synthesis of hollow ZnO microspheres by an integrated autoclave and pyrolysisprocess

Hollow zinc oxide microspheres have been synthesized from a microZnBr2·2H2O precursor obtained by an autoclave process in bromoform steam at220 °C /2.5 MPa. Field-emission scanning electron microscropy (FE-SEM) andtransmission electron microscopy (TEM) show that the products are about1.0 µm single crystal spherical particles with hollow interiors, partly open surfaces and wallsself-assembled by ZnO nanoparticles. X-ray diffraction (XRD) analysis shows that theas-prepared ZnO hollow spheres are of a hexagonal phase structure. A possible formationmechanism is suggested on the basis of the shape evolution of ZnO nanostructures observedby SEM and TEM. The room-temperature photoluminescence (PL) spectrumshows UV emission around 386 nm and weak green emission peaks indicatingthat there are few defects in the single crystal grains of the ZnO microspheres.

Tin Dioxide Nanodimensional Film Based H2 sensor

AbstractPaper presents results of investigation aimed at the development of tin dioxide nanodimensional film gas sensors (NDFGS) with high sensitivity to hydrogen. Specifics of the performed research consist in the approach based on the combination of utilization nanodimensional metal oxide film, as gas sensitive element of device, and group electron technology methods that allows to arranging from small to large scale manufacturing of given NDFGS.Gas sensitive nanodimensional film (NDF) had been formatted by means of chemical spray pyrolysis method on the both ceramic substrate for study and optimization of electrophysical and gas sensitive characteristics and “chip” of gas sensor (GS) preliminarily produced through group electron technology. Films were deposited at the temperatures in interval 400-500°C from water solutions of SnCl4.5H2O precursor. The thickness of SnO2 films was varied in the range 40-80 nm.Study of electrophysical characteristics of obtained layers has shown that the last one possess resistance on the level 105-106 Ohm/ at the working temperatures of GS. Gas sensitivity was determined as ratio of SnO2 film resistance in the pure air and in the presence of gas impurity in atmosphere (S=Rgas/Rair). Values of R were determined through Van-der-Pauw method.X-ray and SEM investigation has allowed establishing the interconnection between technologic parameters, nanostructure and gas sensitive characteristics of obtained films.Gas sensitivity S of the deposited undoped films has amounted 9-10 relative units to the 100 ppm of hydrogen in air. Modification of gas sensitive properties of tin dioxide NDF through bulk and surface doping with Pd has allowed to increasing hydrogen sensitivity up to almost 104 rel. units, providing the detection of hydrogen at the concentration on the level 1 ppm and shift of the sensitivity maximum from 350°C (in the case of undoped films) to 150°C (Pd doped NDF).Performed sensor chip thermal regimes modeling has allowed developing of the NDFGS topology with reduced power consumption (< 30 mW).

A highly efficient Cu/ZnO/Al2O3 catalyst via gel-coprecipitation of oxalate precursors for low-temperature steam reforming of methanol

The impact of preparation methods on the structure and catalytic behavior of Cu/ZnO/Al2O3 catalysts for H2 production from steam reforming of methanol (SRM) has been reported. The results show that the nanostructured Cu/ZnO/Al2O3 catalyst obtained by a novel gel-coprecipitation of oxalate precursors has a high specific surface area and high component dispersion, exhibiting much higher activity in the SRM reaction as compared to the catalysts prepared by conventional coprecipitation techniques. It is suggested that the superior catalytic performance of the oxalate gel-coprecipitation-derived Cu/ZnO/Al2O3 catalyst could be attributed to the generation of “catalytically active” copper material with a much higher metallic copper specific surface as well as a stronger Cu–Zn interaction due to an easier incorporation of zinc species into CuC2O4 · x H2O precursors as a consequence of isomorphous substitution between copper and zinc in the oxalate gel-precursors.

Atomic-Scale Study of in Situ Metal Nanoparticle Synthesis in a Ni/TiO2 System

The nucleation and evolution of Ni nanoparticles during reduction of a Ni(NO3)2.6H2O precursor supported on a commercial titania substrate have been studied in situ at atomic resolution using environmental transmission electron microscopy. An incipient wetness technique was used to prepare the starting unreduced material (10 wt % Ni precursor on titania). The Ni precursor, before reduction, shows a nonuniform distribution over the titania support. It is observed that upon reduction, the initial Ni "seed" crystal nucleates within the precursor patch. The distribution and size of the Ni nanoparticles thus generated are influenced by the distribution and size of the precursor patches. In this system, we see no evidence of preferential nucleation of Ni particles on anatase or rutile. At 350 degrees C with CO as the reducing agent, the {111} surface facets of the Ni nanoparticles are predominant during the initial stage of nucleation and growth. However, the {111} facets are partially consumed with time, indicating that they are not thermodynamically favored in the CO atmosphere. In CO and H2 atmospheres, Ni particles show a nonwetting morphology on titania, while in a mild oxidizing environment, a thin layer of NiOx is formed, thus giving rise to a morphology that is indicative of wetting of the support. This work provides fundamental information on understanding and controlling the important parameters involved in the preparation of a well-designed supported Ni catalyst using the incipient wetness technique.

Compositional stability of hafnium aluminates thin films deposited on Si by atomic layer deposition

We have used nuclear reaction analyses and Rutherford backscattering spectrometry to investigate quantitatively the compositional stability of hafnium aluminate thin films deposited on Si(001) by atomic layer deposition using HfCl4∕H2O and Al(CH3)3∕H2O precursors. It was found that increasing Al∕Hf deposition cycles ratio leads to increasing oxygen deficiency in the as-deposited films as well as to increasing metal losses (up to ∼15%) from the films after rapid thermal annealing at 1000 °C. Furthermore, isotopic substitution experiments, showed that incorporation of oxygen from the gas phase is eased in the cases where deposition conditions failed to supply enough oxygen to complete oxides stoichiometry.

Synthesis and Characterization of Vanadyl Hydrogen Phosphite Hydrate

A novel method for the preparation of vanadyl hydrogen phosphite hydrates is described. The reaction of V2O5, H3PO3, and 1-propanol in the absence of water at 150 °C led to the formation of VOHPO3·1.5H2O with high surface area (ca. 50 m2/g), whereas in the presence of water VOHPO3·H2O was the unique product. The materials were characterized using a combination of techniques including elemental analysis, thermogravimetric analysis, powder X-ray diffraction, laser Raman spectroscopy, and infrared spectroscopy. On heating the sample in flowing nitrogen at 750 °C, it was found that the vanadyl(IV) hydrogen phosphite(III) hydrates transformed into vanadium(III) phosphate(V), VPO4, via an internal oxidation−reduction process between V(IV) and P(III), wherein V(IV) was reduced to V(III) and P(III) was oxidized to P(V). Whereas, heating the vanadyl hydrogen phosphite hydrates in flowing hydrogen can inhibit the phase transformation from vanadyl hydrogen phosphite to VPO4. The catalytic performance for the selective oxidation of n-butane to maleic anhydride using the final catalysts prepared by in situ activation under the reaction conditions was contrasted. It was found that the catalyst derived from the VOHPO3·H2O precursor shows a higher intrinsic activity for the production of maleic anhydride than that derived from VOHPO3·1.5H2O.

Effects of Precursor and Support Variation in the Genesis of Uranium Oxide Catalysts for CO Oxidation and Selective Reduction of NO: Synthesis and Characterization

A range of uranium oxide-based catalysts, derived from UO2(NO3)2.6H2O and UCl4 precursors, and supported on gamma-Al2O3, SiO2 and mesoporous H1SiO2, have been synthesized and then characterized using the following methods: isothermal nitrogen adsorption/desorption measurements, diffuse reflectance infrared spectroscopy (DRIFTS), gas titration of surface hydroxyl groups using Grignard reagents, U L(III) extended X-ray absorption fine structure (EXAFS), powder X-ray diffraction (PXRD), and thermogravimetric and differential thermal analysis. Brij76-templated H1SiO2 mesoporous silicas are found to be essentially stable under flowing oxygen after 16 h at 1073 K. At temperatures above this, however, extensive structural collapse, together with extensive dehydroxylation, ensues. Titration of the accessible hydroxyl group concentrations shows that in these materials the density of OH groups is considerably lower than in their amorphous counterparts. The adsorption of uranyl nitrate onto these dispersants results in a supported, and partially dehydrated, phase of the parent molecule with little obvious structural distortion; however, the adsorption of UCl4 leads to a complex adstructure which may best be described as U(O)2Cl2. The subsequent formation of the uranium oxide phase, nominally active for the oxidation of CO and selective reduction of NO (generally accepted to be U3O8), is found to be a considerable function of both the precursor and support system employed. Calcination of such systems to 1073 K results in extensive extrusion of the supported uranium phase from mesoporous supports, resulting in the formation of very large orthorhombic U3O8 domains. PXRD, however, shows that on amorphous SiO2 and gamma-Al2O3 similar treatment results in the formation of a hexagonal phase of U3O8. The formation of U3O8 is found to be promoted in mesoporous systems and by the presence of Cl in the catalyst make up. Some evidence is also found that suggests that a persistence of Cl limits the growth of U3O8 domains.

Ring‐Like Nanosheets Standing on Spindle‐Like Rods: Unusual ZnO Superstructures Synthesized from a Flakelike Precursor Zn5(OH)8Cl2×H2O.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Ring-Like Nanosheets Standing on Spindle-Like Rods: Unusual ZnO Superstructures Synthesized from a Flakelike Precursor Zn5(OH)8Cl2·H2O

Unusual ZnO superstructures with nanosheets standing on the backbone of spindle-like rods were synthesized for the first time from a flakelike Zn5(OH)8Cl2·H2O precursor under mild solution conditions without using high temperature or any organic molecular templates. The formation of the ring-like nanosheets standing on the spindle is related to the special morphology of the precursor and its solubility, as well as the refluxing reaction conditions. The time dependent shape evolution process and the conductivity measurement of the local reaction solution suggested that the spindle-like ZnO particles were formed at first and then the ring-like nanosheets grew heterogeneously on the backbone of these spindles. The ring-like nanosheets standing on the spindle-like rods was somewhat analogous to nacreous calcium carbonate layers around the columns near the growth tip of a young in red abalone, which could have some implications related with the formation of complex biominerals that exist in nature.

Atomic layer deposition of ZrO2 on W for metal–insulator–metal capacitor application

A metal–insulator–metal (MIM) capacitor using ZrO2 on tungsten (W) metal bottom electrode was demonstrated and characterized in this letter. Both ZrO2 and W metal were synthesized by an atomic layer deposition (ALD) method. High-quality 110∼115 Å ZrO2 films were grown uniformly on ALD W using ZrCl4 and H2O precursors at 300 °C, and polycrystalline ZrO2 in the ALD regime could be obtained. A 13∼14-Å-thick interfacial layer between ZrO2 and W was observed after fabrication, and it was identified as WOx through angle-resolved x-ray photoelectron spectroscopy analysis with wet chemical etching. The apparent equivalent oxide thickness was 20∼21 Å. An effective dielectric constant of 22∼25 including an interfacial WOx layer was obtained by measuring capacitance and thickness of MIM capacitors with Pt top electrodes. High capacitance per area (16∼17 fF/μm2) and low leakage current (10−7 A/cm2 at ±1 V) were achieved.

Collisional quenching of NCO () by some inorganic molecules

Collisional removal of the (0,00,0) level of the A2Σ+ state of the NCO radical has been studied at room temperature (298 K). NCO radicals were produced by laser photolysis of CHBr3 at 266 nm followed by the reaction of CH with N2O, then electronically excited with Nd:YAG laser pumped dye laser. The quenching rate coefficients kq and thermally averaged cross-sections σq were determined by the pressure dependence of the time-resolved fluorescence. Colliders investigated are Ar, N2, O2, CO, NO, N2O, CO2, SO2, H2O and photochemical precursor CHBr3. The quenching rates increase on the whole with the increasing of polarities of the colliders. By comparison with the formation cross-sections of complexes calculated by means of a collision complex model, it is believed that the attractive forces play main roles in the collision quenching processes of NCO (A2Σ+) by the quenchers studied in this work.

The effect of cobalt doping on vanadyl pyrophosphate catalyst

Co-promoted vanadyl pyrophosphate catalyst (Co/V = 2.23 %) was prepared by classical organic method via VOHPO4 .0.5H2O precursor and calcined for 100 h in a mixture of n-butane in air. The synthesised catalyst was characterised by N2 physisorption, ICP, X-ray diffraction, scanning electron microscopy, and temperature-programmed desorption of oxygen.

Considerable enhancement in mechanical strength of trivalent Sc 3+ ion-conducting Sc 2(WO 4) 3 solid electrolyte by germanium dioxide addition

By mixing germanium dioxide with the Sc 3+ ion-conducting Sc 2(WO 4) 3 solid electrolyte, the mechanical strength was greatly enhanced from 40 before mixing to 197 after the addition in Vickers hardness ( H V). The microscopic GeO 2 dispersion in the tungstate electrolyte was successfully accomplished by decomposing the (NH 4) 3HGe 7O 16·6H 2O precursor. The GeO 2 microscopic mixing contributes greatly to precipitate the added GeO 2 as a glassy state in the grain boundaries and makes a superior effect on improving not only the sinterability of the electrolyte ceramics but also a considerable enhancement in the trivalent ion-conducting characteristics.