Preparation of porous solids composed of layered niobate walls from colloidal mixtures of niobate nanosheets and polystyrene spheres

Macroporous solids with crystalline layered walls were fabricated from colloidal mixtures of size-controlled niobate nanosheets and polystyrene spheres. The macroporous solids, obtained after burning off the spheres, were characterized by scanning electron microscopy and X-ray diffraction. The obtained structures strongly depended on the lateral dimension L of the nanosheets used. When small nanosheets (L=100 nm) were used, partly ordered macroporous solids with interconnected pores were obtained, whereas sponge-like random macroporous structures were obtained with larger nanosheets (L=190 and 270 nm). Peapod-like hollow structures were obtained when we used small (L=190 nm) and very large (L=3 microm) nanosheets at the same time. The microstructure of the pore walls was controllable by changing the calcination conditions. The walls were composed of propylammonium/K(4)Nb(6)O(17) intercalation compound which has a layered structure with exchangeable cations in the interlayer space, stable up to 350 degrees C for 6 h on calcination. The walls were converted to crystalline K(8)Nb(18)O(49) after calcination at 500 degrees C for 6 h.     

X-ray photoelectron spectroscopy study of neodymium niobate and tantalate precursors and thin films

Neodymium niobate NdNbO₄ (NNO) and tantalate NdTaO₄ (NTO) thin films (~100 nm) were prepared by sol-gel/spin-coating process on Al₂O₃ substrate with LaNbO₄/PbZrO₃ interlayer and annealing at 1000°C. Surface chemistry was investigated by X-ray photoelectron spectroscopy (XPS). The core-level XPS studies of sol-gel NNO and NTO were performed for the first time. The binding energy differences Δ(O―Nb) and Δ(O―Ta) were used to characterize average energies of Nb―O bonding in NNO (322.9 eV) and Ta―O bonding in NTO (504.2 eV). The XPS demonstrated single valence state of Nd (Nd³⁺) in precursors. Nd concentration (at. %) decreases from 22% in precursors to 7% in films considering the substrate contains C, Al, Si, Pb, and Zr elements (37%) at Nb or Ta (5%) and O (51%). The X-ray diffraction analyses verified formation of the monoclinic (M-NdNbO₄ or M′-NdTaO₄), orthorhombic (O-NdNbO₄) and tetragonal (T-NdTaO₄) phases in precursors and films. Single valence state of Nd³⁺ was confirmed in these films designed for the application in environmental electrolytic thin film devices.     

Orientation of diamagnetic layered transition metal oxide particles in 1-tesla magnetic fields

The magnetic field-driven orientation of microcrystals of six diamagnetic layered transition metal oxides (HLaNb(2)O(7), HCa(2)Nb(3)O(10)·0.5H(2)O, KNaCa(2)Nb(4)O(13), KTiTaO(5), KTiNbO(5), and H(2.2)K(1.8)Nb(6)O(17)·nH(2)O) suspended in epoxy resins was studied by X-ray diffraction using permanent magnets producing a 0.8 T field. Although the degree of orientation, quantified as the Hermans order parameter, was strongly affected by the particle size distribution, in all cases microcrystals with ～1-2 μm lateral dimensions were found to orient with the magnetic field vector in the layer plane. Control of the orientation of ionically conducting layered oxides is of interest for practical applications in batteries and fuel cells. The consistent direction of orientation of the lamellar oxides studied can be rationalized in the framework of a quantitative bond anisotropy model developed by Uyeda (Phys. Chem. Miner.1993, 20, 77-80). The asymmetry of metal-oxygen bonding at the faces of the octahedral layers results in long and short M-O bonds perpendicular to the plane of the sheets. This distortion of the M-O octahedra, which is a structural feature of almost all layered materials that contain octahedral bonding frameworks, gives rise to the diamagnetic anisotropy and results in an easy axis or plane of magnetization in the plane of the sheets.     

Preparation and Characterization of Titania Thin Films from Aqueous Solutions

Dip- or spin-coating and characterization of titania (TiO₂) thin films from various aqueous solutions have been studied. The aqueous titanium solutions mainly used in this study were halogen- and chelate-free solutions with the concentrations up to 1.4 M derived from titanium isopropoxide (TIP) with tetramethylammonium hydroxide (TMAOH) or some alkylamines, while aqueous and alcoholic solutions containing titanium atoms stabilized chelating ligands were examined for comparison. The TiO₂ films prepared from the TIP-TMAOH solution were already crystallized at 350°C to anatase form and those formed at 600°C had high transparency and refractive indices of 2.40. No carbon residue in the film prepared at 400°C was detected by XPS. The pure anatase form was sustained up to 850°C. Interestingly, it was found that the (004) preferentially oriented anatase films were obtained from TIP-lactic acid (LA) system until 700°C. The solutions containing citric acid (CA) or alkanolamines yielded anatase and rutile form fired at the temperatures equal to or higher than 600°C. Carbon residue was detected in the film fired at 400°C. The film thickness monotonically decreased from the upper to the bottom ends of the substrate. However, it was found that the thickness uniformity was drastically improved by an addition of sucrose to the aqueous solutions. The effects of the solution composition and polyhydroxy compounds on the crystal modifications of formed films and the film uniformity are discussed.     

Layer-by-layer assembly and spontaneous flocculation of oppositely charged oxide and hydroxide nanosheets into inorganic sandwich layered materials

Exfoliated oxide nanosheets such as Ti0.91O2 and Ca2Nb3O10 and layered double hydroxide (LDH) nanosheets of Mg2/3Al1/3(OH)2 were restacked into inorganic sandwich layered materials. Sequential adsorption of these oppositely charged nanosheets from their colloidal suspensions yielded multilayer ultrathin films while their simple mixing produced lamellar flocculates. Eliminating carbonate ions from the reaction system was found to be essential for successfully achieving the sandwich structures. The flocculated materials as well as the films were characterized by atomic force microscopy (AFM), UV-visible absorption spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction (XRD), transmission electron microscopy (TEM), and chemical analysis, which all supported the formation of the ordered sandwich structures. AFM observations revealed alternate dense tiling of LDH nanosheets and oxide nanosheets onto a substrate surface. UV-visible absorption spectra exhibited progressive enhancement of optical density due to oxide nanosheets as a function of deposition cycles, providing strong evidence for regular growth of multilayer films. The combinations of Mg2/3Al1/3(OH)2/Ti0.91O2 and Mg2/3Al1/3(OH)2/Ca2Nb3O10 produced XRD Bragg peaks having multilayer spacings of 1.2 and 2.0 nm, respectively. These basal spacing values are compatible with the sum of thickness of LDH nanosheets and corresponding oxide nanosheets. TEM images of flocculated samples displayed lamellar features with two different constituent layers appearing alternately.     

Photoconductive properties of organic-inorganic hybrid films of layered perovskite-type niobate

A hybrid film of layered niobate and an organic amphiphile was prepared by the Langmuir-Blodgett (LB) method. Trimethylammonium-exchanged perovskite-type niobates ((CH(3))(3)NHSr(2)Nb(3)O(10)) were exfoliative to form an aqueous suspension. A monolayer of octadecylamine was produced on such an aqueous dispersion as a template for a hybrid film. A hybrid film was transferred as a Y-type LB film onto a hydrophilic glass plate or an ITO substrate. The structure of a deposited film was investigated with X-ray diffraction (XRD), Fourier transform infrared (FT-IR), and atomic force microscopy (AFM) measurements, indicating a layer-by-layer structure with a single or double sheet of niobate as an inorganic composite. From the cyclic voltammogram on an ITO electrode modified with the Y-type 10 layered film, the lower edge of the conduction band of a niobate layer was determined to be - 0.6 V (vs Ag/AgCl). ac impedance and dc measurements were carried out on 1, 5, and 10-layered LB films (2 mm (electrode spacing) x 8 mm (width)) with aluminum electrodes. The freshly deposited samples behaved as an insulator under the illumination of 280 nm light (2.04 x 10(16) quanta s(-1)). Photoconductivities appeared, however, when they were preirradiated with a 150 W Xe lamp (ca. 2 x 10(18) quanta s(-1)) for 0.5-8.5 h. The process was denoted as photomodification. From the FT-IR and XRD results, it was deduced that the photomodification of LB films caused the decomposition of organic templates (octadecylammonium) accompanied by the collapse of layer-by-layer structures. dc analyses on the 5- and 10-layered films after photomodification also showed that they behaved as a photosemiconductor under UV light illumination.     

Nb2O5·nH2O-PtRu/C的制备及其对甲醇氧化的催化作用

采用沉淀法制备了甲醇氧化电催化剂10%Nb2O5 nH2O-20%Pt10%Ru/C,并在Ar气氛下对它进行了热处理.用X射线衍射(XRD),透射电子显微镜(TEM)和X射线光电子谱(XPS)研究了热处理对催化剂的结构和形貌的影响,用循环伏安法和计时电流法研究了热处理对催化剂的电化学性能的影响.结果表明:催化剂中看不到Ru的衍射峰存在,Pt晶粒以面心立方体结构存在,Nb2O5 nH2O对Pt的结合能基本无影响;与20%Pt10%Ru/C相比,同温度热处理的条件下,10%Nb2O5 nH2O-20%Pt10%Ru/C催化剂中Pt,Ru合金化程度较差,活性组分颗粒较小、分散均匀,而且催化甲醇氧化性能和抗"CO"毒化性能较好,700℃热处理的10%Nb2O5 nH2O-20%Pt10%Ru/C的性能最好.Nb2O5 nH2O不仅能抑制热处理过程中活性颗粒的长大和Pt,Ru的合金化,还能促进氢离子的传递,提供活性"-OH",使甲醇及其氧化中间体更容易吸附-脱附.     

Humidity-dependent reversible aggregation of rhodamine 6G dye immobilized within layered niobate K4Nb6O17

The spectroscopic behavior of rhodamine 6G (R6G) dye intercalated in layered hexaniobate K4Nb6O17 was investigated. R6G cations were intercalated into the niobate through displacement of preintercalated alkylammonium ions. Powder X-ray diffraction and elemental analysis indicated that the dye molecules were densely accommodated in the interlayer spaces of niobate. The spectroscopic behavior of intercalated R6G was characterized by humidity-dependent aggregation at room temperature. The dye molecules were present dominantly as monomers under humid conditions (93% relative humidity (RH)), while they formed dimers under relatively dry conditions (20% RH). The aggregation-deaggregation of dye occurred reversibly depending on the humidity. The reversible aggregation was not accompanied by a large alteration of the interlayer structure of the sample, because only a small amount of water was adsorbed/desorbed with a small change in the basal spacing of the intercalation compound during the humidity change.     

Novel soft chemical method for optically transparent Ru(bpy)3-K4Nb6O17 thin film

A unique guest-guest ion exchange method was developed for preparing a thin film of a nano-layered K(4)Nb(6)O(17).3H(2)O that possesses both (1) optical transparency and (2) ion-exchangeability under ambient conditions without calcination at high temperature. An optically transparent Ru(bpy)(3)(2+)-K(4)Nb(6)O(17) hybrid thin film, a photoresponsive electrode, was successfully prepared by the guest-guest exchange method by use of the intercalation compound MV(2+)-K(4)Nb(6)O(17) as a precursor. The optically transparent Ru(bpy)(3)(2+)-K(4)Nb(6)O(17) hybrid thin films have been characterized by X-ray diffraction, SEM, AFM, IR, and UV spectroscopies, as well as elemental analysis. The electrochemical behavior of the ITO/Ru(bpy)(3)(2+)-K(4)Nb(6)O(17) hybrid thin film electrode was studied; it also exhibits swift photoresponse in the visible region.     

Soft‐Chemical Exfoliation Route to Layered Cobalt Oxide Monolayers and Its Application for Film Deposition and Nanoparticle Synthesis

A colloidal suspension of exfoliated, layered cobalt oxide nanosheets has been synthesized through the intercalation of quaternary tetramethylammonium ions into protonated lithium cobalt oxide. According to atomic force microscopy, exfoliated nanosheets of layered cobalt oxide show a plateau‐like height profile with nanometer‐level height, underscoring the formation of unilamellar 2D nanosheets. The exfoliation of layered cobalt oxide was cross‐confirmed by X‐ray diffraction, UV/Vis spectroscopy, and transmission electron microscopy. The maintenance of the hexagonal in‐plane structure of the cobalt oxide lattice after the exfoliation process was evidenced by selected‐area electron diffraction and Co K‐edge X‐ray absorption near‐edge structure analysis. The zeta‐potential measurements clearly demonstrated the negative surface charge of cobalt oxide nanosheets. Adopting the nanosheets of layered cobalt oxide as a precursor, we were able to prepare the monodisperse CoO nanocrystals with a particle size of ≈10 nm as well as the heterolayered film composed of cobalt oxide monolayer and polycation.     

Electrochemical and structural characterization of sputter-deposited Mg–Nb and Mg–Nb–Al–Zn alloy films

Nanocrystalline Mg–Nb and Mg–Nb–Al–Zn alloy films were deposited by dc magnetron sputtering on glass and quartz substrates in a wide range of niobium concentrations from 6 to 80 at.%. Structural, electrochemical and corrosion properties of the films were studied by X-ray diffraction, dc voltammetry, electrochemical impedance spectroscopy and electrochemical quartz crystal microbalance. Development of body-centred cubic Nb structure in the Mg–Nb alloy matrix yielded the effects of lattice contraction, grain refining and electrochemical passivity. The measurements showed high corrosion resistance of the films in alkaline solutions when niobium content was one third or more. An increased corrosion resistance was achieved by introducing minor amounts of Al (ca. 2 at.%). In particular, such Al effect was pronounced at lower Nb concentrations (20 to 30 at.%). Semiconductor properties of spontaneously formed oxide on Mg–Nb alloy were studied by Mott–Schottky plots, which indicated highly doped n-type oxide structures on Mg–Nb surface. The paper fills some gap in understanding of niobium–magnesium systems, which show potential for applications in hydrogen storage, switchable mirrors and corrosion protection.     

Nb2O5·nH2O as a heterogeneous catalyst with water-tolerant Lewis acid sites

Niobic acid, Nb(2)O(5)·nH(2)O, has been studied as a heterogeneous Lewis acid catalyst. NbO(4) tetrahedra, Lewis acid sites, on Nb(2)O(5)·nH(2)O surface immediately form NbO(4)-H(2)O adducts in the presence of water. However, a part of the adducts can still function as effective Lewis acid sites, catalyzing the allylation of benzaldehyde with tetraallyl tin and the conversion of glucose into 5-(hydroxymethyl)furfural in water.     

Orientation of tungsten trioxide thin films fabricated by sol–gel method using aqueous sols of colloidal layered tungstates

Oriented monoclinic WO₃ thin films were fabricated by sol–gel method using aqueous sols of colloidal layered tungstates. The colloidal tungstate sols were prepared by reacting different alkylamines with layered tungstic acid H₂WO₄ in water. With decreasing the alkyl chain length of the alkylamines, the colloidal layered tungstate became smaller. Alkylamines with a short alkyl chain provided transparent aqueous sols. Furthermore, the WO₃ thin films fabricated from the obtained aqueous sols had a high (100)-orientation. However, upon annealing H₂WO₄ crystals applied on a glass substrate with the tungstate layers parallel to the substrate, highly (001)-oriented WO₃ layers were obtained. Since both of the A- and C-planes of WO₃ have a similar structure to the layers of H₂WO₄, the orientation of the WO₃ thin films and layers probably resulted from the topotactic structural conversion of the tungstates. Interestingly, the preferential orientation of the thin films was dependent on the presence or absence of interlayer alkylamines in the tungstates.     

Oxidation and nitridation of niobium films by rapid thermal processing

The oxidation and nitridation processes of niobium films in a rapid thermal processing (RTP) – system were investigated. 200 and 500 nm niobium films were deposited via sputtering on sapphire-(1-102)-substrate. At first niobium films were oxidized in molecular oxygen at temperatures ranging from 350 to 500 °C and for times of 1, 2 and 5 min and then nitridated in ammonia at 1000 °C for 1 min using an RTP system. For characterisation of the niobium films complementary analytical methods were used: X-ray diffraction (XRD) for phase analysis, secondary ion mass spectrometry (SIMS) for determining the elemental depth profiles of the films, scanning electron microscopy (SEM) and atomic force microscopy (AFM) for characterisation of the surface morphology of the films. The influence of the substrate, single crystalline sapphire, on the reactivity of the niobium films was studied in dependence of temperature, time of reaction and film thickness. The possibility of existence of niobium oxynitride phase was investigated. According to XRD and SIMS data, there is evidence that an oxynitride phase is formed after oxidation and subsequent nitridation in the bulk of some Nb films. In some of the experiments crack formation in the films or even delamination of the Nb films from the substrates was observed.     

脉冲激光沉积LiNi0.5Mn0.5O2薄膜正极性能

高能量密度、功率密度和高温度稳定性的全固态薄膜锂离子电池是微电子器件的理想电源.开发新型的大比容量正极薄膜材料是解决问题的关键之一.与LiCoO2正极相比,层状结构的LiNi0.5Mn0.5O2有更高的可逆比容量和结构稳定性.本文应用脉冲激光沉积法制备LiNi0.5Mn0.5O2沉积薄膜,研究了衬底材料、温度对薄膜的微观结构、表面形貌及组分的影响.由LiNi0.5Mn0.5O2电极组装半电池,研究了薄膜的电化学性能与晶体结构、表面形貌及组分间的关系,表征了LiNi0.5Mn0.5O2沉积薄膜于不同充电截止电压的循环稳定性及倍率性能,并讨论了LiNi0.5Mn0.5O2薄膜的结构特点.     

Preparation, characterization, and growth mechanism of a novel aligned nanosquare anatase in large quantities in the presence of TMAOH

Monodispersed and well-aligned samples of TiO(2) nanosquares were synthesized in large quantities in the presence of tetramethylammonium hydroxide (TMAOH) for the first time. These nanosquares were single crystals characterized by slightly truncated shape bounded by {101} facets. XRD, AFM, FT-IR, Raman scattering, TEM and HRTEM were employed to characterize the as-prepared samples. The possible microreaction mechanism was discussed. As a result, TMAOH accelerates the formation of crystalline anatase and plays a structural template role to modify the particle shape to nanosquare. Moreover, TMAOH reacted with hydrolysates and formed layered structural complex compound.     

Water-based ferrofluids from FexPt1-x nanoparticles synthesized in organic media

This paper describes an effective method to transfer oleic acid/oleylamine-capped colloidal FePt nanoparticles dispersed in hexane into water, using tetramethylammonium hydroxide (TMAOH) as a phase transfer agent. FexPt1-x nanoparticles with different compositions (x = 0.32, 0.40, 0.48, 0.60, 0.66, 0.69) in the size range of 2-4 nm were synthesized by a high-temperature organometallic route with oleic acid and oleylamine as stabilizers. The surface of such nanoparticles was modified through removal of the organic, hydrophobic layer and adsorption of TMAOH, which provides the nanoparticles with sufficient surface charge so that an electrostatic double layer builds up, and the FePt nanoparticles can be fully redispersed in aqueous solution, even with high concentrations. The water-dispersible FePt nanoparticles were characterized by transmission electron microscopy, electrophoretic mobility, X-ray diffraction, and Fourier transform infrared spectroscopy.     

TiO2 *nH2 O凝胶预处理对水热合成SrTiO3 粉的影响

以TiCl4为钛源, 首先制备TiO2 * nH2O凝胶, 然后在80℃的水热条件下制备了SrTiO3粉.利用X射线衍射(XRD)、透射电子显微镜(TEM)和红外光谱(FTIR)研究了TiO2 * nH2O凝胶水洗方式、阴离子(Cl-和NO3-)以及TiO2 * nH2O热处理对SrTiO3粉性能的影响.结果表明, 水洗和热处理都能使TiO2 * nH2O凝胶产生晶化; TiO2 * nH2O的晶化程度对产物SrTiO3颗粒的粒度和粒度分布有很大影响,以非晶质TiO2 * nH2O为钛源制备的SrTiO3颗粒粒度大且粒度分布宽.以结晶TiO2 * nH2O为钛源制备的SrTiO3颗粒粒度小且粒度分布窄,而且可以得到纳米颗粒.水热反应液相中存在Cl-或NO3-能使产物SrTiO3颗粒粒度稍有增大.综合以上结果, TiO2 * nH2O凝胶水洗对产物颗粒的影响主要是由于使凝胶产生了晶化,而由阴离子脱除产生的影响很小.因此,在不考虑阴离子对其它工程化影响(如设备腐蚀等)的前提下,可采用热处理代替水洗.     

Stable liquid crystalline phases of colloidally dispersed exfoliated layered niobates

Colloidally dispersed niobium oxide nanosheets obtained by exfoliation of layered niobates HNb(3)O(8) and HTiNbO(5) formed stable liquid crystalline phases; their liquid crystallinity was dependent on the niobate species exfoliated.     

三维骨加{[Cu（1,2—pn）2]4[V18O42（H2O）]}n·8nH2O化合物的水热合成和晶体结构

物材多孔材料广泛应用于吸附、形状和尺寸选择性的多相催化和离子交换．利用有机胺分子的模板和结构导向作用已设计合成了许多沸石分子筛、中孔MCM－41和非致密过渡金属磷酸盐等多孔性氧化料[’－“．过渡金属氧簇结构中普遍存在金属－金属键,业已证明金属氧簇合物具有催化活