Synthesis and characterizations of hierarchical biomorphic titania oxide by a bio-inspired bottom-up assembly solution technique

As a representative semiconductor metal oxide, hierarchical biomorphic mesoporous TiO₂ with interwoven meshwork conformation was successfully prepared using eggshell membrane (ESM) as a biotemplate by an aqueous soakage technique followed by calcination treatment. The synthesis conditions were systematically investigated by controlling the concentration, the pH value of the precursor impregnant, and so on. The nucleation, growth, and assembly into ESM-biomorphic TiO₂ in our work depended more on the functions of ESM biomacromolecules as well as the processing conditions. As-prepared TiO₂ meshwork exhibiting hierarchical porous structure with the pore size from 2 nm up to 4 μm, was composed of intersectant fibers assembled by nanocrystallites at three dimensions. Based on the researches into the N₂ adsorption-desorption isothermal and corresponding BJH pore-size distribution, the biomorphic TiO₂ would arose interesting applications in some fields such as photocatalysis, gas sensors, antistatic coating, dye-sensitized solar cells, etc. This mild method and the relevant ideas offer a feasible path to synthesize a new family of functional materials by integrating material science, chemistry, and biotechnology.     

Hierarchical Mesoporous SnO Microspheres as High Capacity Anode Materials for Sodium‐Ion Batteries

Mesoporous SnO microspheres were synthesised by a hydrothermal method using NaSO₄ as the morphology directing agent. Field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and high‐resolution transmission electron microscopy (HRTEM) analyses showed that SnO microspheres consist of nanosheets with a thickness of about 20 nm. Each nanosheet contains a mesoporous structure with a pore size of approximately 5 nm. When applied as anode materials in Na‐ion batteries, SnO microspheres exhibited high reversible sodium storage capacity, good cyclability and a satisfactory high rate performance. Through ex situ XRD analysis, it was found that Na⁺ ions first insert themselves into SnO crystals, and then react with SnO to generate crystalline Sn, followed by Na–Sn alloying with the formation of crystalline NaSn₂ phase. During the charge process, there are two slopes corresponding to the de‐alloying of Na–Sn compounds and oxidisation of Sn, respectively. The high sodium storage capacity and good electrochemical performance could be ascribed to the unique hierarchical mesoporous architecture of SnO microspheres.     

CdO－SnO_2复合氧化物的组成与性能

通过控制共沉淀时溶液中Ｃｄ／Ｓｎ摩尔比的方法，合成了物相组成不同的ＣｄＯ－ＳｎＯ２复合氧化物粉料，探讨了相组成与材料电导及气敏性能之间的关系。     

生物模板法制备纳米氧化锌及其表征

本文以油菜花粉为生物模板,硝酸锌为锌源制备了一种分级多孔结构的纳米氧化锌。采用SEM、TEM、XRD和 FTIR等技术手段对其进行了表征。实验结果表明,采用油菜花粉为生物模板制备的氧化锌纳米材料为六方纤锌矿结构,较好的复制了花粉的分级多孔结构。同时,研究了制备条件诸如煅烧温度和反应物浓度对产物结构、形貌和尺度的影响。     

Tin oxide dependence of the CO2 reduction efficiency on tin electrodes and enhanced activity for tin/tin oxide thin-film catalysts

The importance of tin oxide (SnO(x)) to the efficiency of CO(2) reduction on Sn was evaluated by comparing the activity of Sn electrodes that had been subjected to different pre-electrolysis treatments. In aqueous NaHCO(3) solution saturated with CO(2), a Sn electrode with a native SnO(x) layer exhibited potential-dependent CO(2) reduction activity consistent with previously reported activity. In contrast, an electrode etched to expose fresh Sn(0) surface exhibited higher overall current densities but almost exclusive H(2) evolution over the entire 0.5 V range of potentials examined. Subsequently, a thin-film catalyst was prepared by simultaneous electrodeposition of Sn(0) and SnO(x) on a Ti electrode. This catalyst exhibited up to 8-fold higher partial current density and 4-fold higher faradaic efficiency for CO(2) reduction than a Sn electrode with a native SnO(x) layer. Our results implicate the participation of SnO(x) in the CO(2) reduction pathway on Sn electrodes and suggest that metal/metal oxide composite materials are promising catalysts for sustainable fuel synthesis.     

Combined X-ray diffraction and diffuse reflectance analysis of nanocrystalline mixed Sn(II) and Sn(IV) oxide powders

Nanocrystalline mixtures of Sn(II) and Sn(IV) oxide powders, potential gas sensor materials, are synthesized via a simple precipitation route using SnCl(2) as the precursor. Materials are characterized by powder X-ray diffraction, thermogravimetric analysis, UV-visible diffuse reflectance spectroscopy (DRS), and Fourier transform infrared spectroscopy. The ratio of Sn(II)/Sn(IV) in powders precipitated at room temperature, as well as the identity of the primary Sn(II) product (SnO or Sn(6)O(4)(OH)(4)), can be varied by adjusting aging time and washing procedures. The identity of the initial Sn(II) product influences the subsequent phase composition and degree of disorder in the tetragonal SnO(2) phase obtained following sintering in air. Analysis of the DRS absorption edge and long-wavelength (Urbach) absorption tail is used to determine the SnO(2) optical band gap and extent of disorder. SnO(2) obtained by heating the SnO/SnO(2) mixture at 600 or 800 degrees C has a smaller optical band gap and a broader Urbach tail than the analogous sample obtained from heating Sn(6)O(4)(OH)(4), indicating a more disordered material.     

Zn_2SnO_4纳米材料制备及光致发光特性

以ZnO、SnO2和活性炭的混合物为原料,通过碳热还原热蒸发法无催化剂成功制备出Zn2SnO4纳米材料.借助X射线衍射仪(XRD)、拉曼光谱和扫描电子显微镜(SEM)对样品物相和形貌进行了表征,结果显示样品为面心立方结构的Zn2SnO4纳米链状棒,同时含有少量的ZnO物相.利用X射线光电子能谱(XPS)对Zn2SnO4样品表面各元素的化学状态及相互作用方式进行了测试,结果表明:样品中Zn和Sn分别是以+2价和+4价氧化态形式存在,其中Zn2p3/2电子有两个结合能,分别来自ZnO和Zn2SnO4,Zn2SnO4中Sn4+占据不同的格点位置.室温下光致发光谱(PL)结果显示,样品在紫外区域(320-450nm)和可见区域存在很强的发光带,其中紫外区域的宽发光带,经过高斯拟合可分为358和385nm两个发光峰,与同条件下制备得到的纯ZnO纳米材料发光谱比较,确认358nm发光峰是来自于Zn2SnO4的近带边复合发光.     

CO oxidation on nanostructured SnO(x)/Pt(111) surfaces: unique properties of reduced SnO(x)

We have investigated surface CO oxidation on "inverse catalysts" composed of SnO(x) nanostructures supported on Pt(111) using X-ray photoelectron spectroscopy (XPS), low-energy ion scattering spectroscopy (LEISS) and temperature-programmed desorption (TPD). Nanostructures of SnO(x) were prepared by depositing Sn on Pt(111) pre-covered by NO(2) layers at low temperatures. XPS data show that the SnO(x) nanoparticles are highly reduced with Sn(II)O being the dominant oxide species, but the relative concentration of Sn(II) in the SnO(x) nanoparticles decreases with increasing Sn coverage. We find that the most active SnO(x)/Pt(111) surface for CO oxidation has smallest SnO(x) coverage. Increasing the surface coverage of SnO(x) reduces CO oxidation activity and eventually suppresses it altogether. The study suggests that reduced Sn(II)O, rather than Sn(IV)O(2), is responsible for surface CO oxidation. The occurrence of a non-CO oxidation reaction path involving reduced Sn(II)O species at higher SnO(x) coverages accounts for the decreased CO oxidation activity. From these results, we conclude that the efficacy of CO oxidation is strongly dependent on the availability of reduced tin oxide sites at the Pt-SnO(x) interface, as well as unique chemical properties of the SnO(x) nanoparticles.     

Large-scale synthesis and microstructure of SnO2 nanowires coated with quantum-sized ZnO nanocrystals on a mesh substrate

Large-quantity single-crystal SnO(2) nanowires coated with quantum-sized ZnO nanocrystals (nc-ZnO/SnO(2) nanowires) were directly synthesized by thermal evaporation of SnO powder and a mixture of basic ZnCO(3) and graphite powders. A common stainless steel mesh was used to collect the products. The microstructure and possible growth mechanism of the nc-ZnO/SnO(2) nanowires were investigated. Results showed that tetragonal structured SnO(2) nanowires were obtained, whose surfaces were coated with single-layer ZnO nanocrystals with an average diameter of less than 5 nm. The nanowires had cross-rectangle section with width-to-thickness aspect ratio ranging from 2:1 to 5:1. The lengths of the nanowires were several tens of micrometers. ZnO nanocrystals were single crystalline wurtzite structures, which coated the whole nanowires and distributed uniformly. The possible growth mechanism of the composite nanowires may be enucleated that Zn atoms in the source vapor will replace the Sn atoms on the surface of the formed SnO(2) nanowires due to the higher reducibility of Zn than Sn. Two strong Raman scattering peaks at 626 and 656 cm(-1) appeared in the micro-Raman spectrum of nc-ZnO/SnO(2) nanowires. The origins of the peaks were discussed. Most importantly, the method can be extended to other composite oxide nanowires that are synthesized by oxidizing two kinds of metals, such as high reducibility elements Mg, Al, Zn, and Ti, and low reducibility elements In, Ge, Ga, etc.     

Synthesis, structure, texture, and CO sensing behavior of nanocrystalline tin oxide doped with scandia

Weakly agglomerated nanocrystalline scandia doped tin oxide powders with high surface area (170-220 m(2)/g) and uniform size (3-4 nm) were synthesized for the first time by a two-step hydrothermal process in the presence of urea, followed by the calcination between 500 and 1200 degrees C. The structure and texture of the binary oxide system were characterized by thermogravimetry and differential thermal analysis, Brunauer-Emmett-Teller-specific surface area analysis, transmission electron microscopy, X-ray diffraction, Raman spectroscopy, and X-ray photoelectron spectroscopy. A metastable scandium tin oxide solid solution in tetragonal structure was formed for the scandia content lower than 6 mol % as the samples were calcined at 800 degrees C, and the excess Sc atoms were dispersed at the surface of the crystallites above this limit. The solid solution was metastable, so scandium migrated toward the surface region of the crystallites and produced a second phase of Sc(4)Sn(3)O(12) during calcining at high temperatures over 1000-1200 degrees C. In the case of the samples with higher dopant concentration (>15 mol %), the calcination at the temperature between 500 and 800 degrees C caused the precipitation of Sc(2)O(3), and the calcination over 1000-1200 degrees C led to the formation of more Sc(4)Sn(3)O(12). Textural analysis showed that doping an appropriate amount of Sc(2)O(3) into nanosized SnO(2) could effectively inhibit the grain growth and stabilize the surface area against high-temperature calcinations below 1000 degrees C. CO gas-sensing property measurements revealed that the dispersion of Sc at the surfaces of the SnO(2) nanocrystallites could improve the CO sensitivity significantly, and the pellet sample with scandia content of 10 mol % sintered at 800 degrees C showed the best CO gas-sensing property in the operation temperature range of 300-400 degrees C. On the basis of the structural and textural analysis, the correlation between the structure/texture and the sensitivity to CO for the as-calcined (SnO(2))(1-x)(Sc(2)O(3))(x) nanocrystallites has been established and explained.     

Nanostructured SnO2-ZnO heterojunction photocatalysts showing enhanced photocatalytic activity for the degradation of organic dyes

Nanoporous SnO(2)-ZnO heterojunction nanocatalyst was prepared by a straightforward two-step procedure involving, first, the synthesis of nanosized SnO(2) particles by homogeneous precipitation combined with a hydrothermal treatment and, second, the reaction of the as-prepared SnO(2) particles with zinc acetate followed by calcination at 500 °C. The resulting nanocatalysts were characterized by X-ray diffraction (XRD), FTIR, Raman, X-ray photoelectron spectroscopy (XPS), nitrogen adsorption-desorption analyses, transmission electron microscopy (TEM), and UV-vis diffuse reflectance spectroscopy. The SnO(2)-ZnO photocatalyst was made of a mesoporous network of aggregated wurtzite ZnO and cassiterite SnO(2) nanocrystallites, the size of which was estimated to be 27 and 4.5 nm, respectively, after calcination. According to UV-visible diffuse reflectance spectroscopy, the evident energy band gap value of the SnO(2)-ZnO photocatalyst was estimated to be 3.23 eV to be compared with those of pure SnO(2), that is, 3.7 eV, and ZnO, that is, 3.2 eV, analogues. The energy band diagram of the SnO(2)-ZnO heterostructure was directly determined by combining XPS and the energy band gap values. The valence band and conduction band offsets were calculated to be 0.70 ± 0.05 eV and 0.20 ± 0.05 eV, respectively, which revealed a type-II band alignment. Moreover, the heterostructure SnO(2)-ZnO photocatalyst showed much higher photocatalytic activities for the degradation of methylene blue than those of individual SnO(2) and ZnO nanomaterials. This behavior was rationalized in terms of better charge separation and the suppression of charge recombination in the SnO(2)-ZnO photocatalyst because of the energy difference between the conduction band edges of SnO(2) and ZnO as evidenced by the band alignment determination. Finally, this mesoporous SnO(2)-ZnO heterojunction nanocatalyst was stable and could be easily recycled several times opening new avenues for potential industrial applications.     

Growth and structure evolution of novel tin oxide diskettes

The novel SnO diskettes have been synthesized by evaporating either SnO or SnO(2) powders at elevated temperature. Disregard the source material being SnO or SnO(2), the SnO diskettes are formed at a low-temperature region of 200-400 degrees C. Two types of diskette shapes have been identified: the solid-wheel shape with a drop center rim (type I) and the diskette with cone peak(s) and spiral steps (type II). The diskettes are determined to be tetragonal SnO structure (P4/nmm), with their flat surfaces being (001). The formation of the SnO diskettes is suggested to result from a solidification process. The structural evolution from SnO diskettes to SnO(2) diskettes has been investigated by oxidizing at different temperatures. The result shows that the phase transformation from SnO to SnO(2) occurs in two processes of decomposition and oxidization, and the decomposition process consists of two steps: first from SnO to Sn(3)O(4) and then from Sn(3)O(4) to SnO(2).     

The effect of the surface of SnO2 nanoribbons on their luminescence using x-ray absorption and luminescence spectroscopy

X-ray excited optical luminescence (XEOL) and x-ray absorption near-edge structure in total electron, x-ray fluorescence, and photoluminescence yields at Sn M5,4-, O K-, and Sn K-edges have been used to study the luminescence from SnO2 nanoribbons. The effect of the surface on the luminescence from SnO2 nanoribbons was studied by preferential excitation of the ions in the near-surface region and at the normal lattice positions, respectively. No noticeable change of luminescence from SnO2 nanoribbons was observed if the Sn ions in the near-surface region were excited selectively, while the luminescence intensity changes markedly when Sn or O ions at the normal lattice positions were excited across the corresponding edges. Based on the experimental results, we show that the luminescence from SnO2 nanoribbons is dominated by energy transfer from the excitation of the whole SnO2 lattice to the surface states. Surface site specificity is not observable due to its low concentration and weak absorption coefficient although the surface plays an important role in the emission as a luminescence center. The energy transfer and site specificity of the XEOL or the lack of the site specificity from a single-phase sample is discussed.     

氧化锡和氧化锌双层薄膜的XPS研究

用XPS法研究了SnO2 /ZnO及ZnO/SnO2 双层膜中锌和锡的扩散情况 ,结果表明 :锌在SnO2中的扩散比锡在ZnO中的扩散更容易。讨论了锌在SnO2 层中的扩散方式和扩散的结果。在ZnO层留下了较多的氧 ,并使部分的SnO2 还原为SnO。     

负载Pd密偶催化剂的载体效应

采用尿素水解法或吸附沉淀法制备了金属氧化物载体,并用浸渍法负载0.5%Pd制得了Pd/Sn0.4Zr0.6O2,Pd/ZrO2,Pd/SnO2,Pd/SnO2-Al2O3和Pd/Al2O3催化剂.采用原位漫反射红外光谱、拉曼光谱、X射线光电子能谱和程序升温还原等方法对催化剂结构进行了表征,探讨了不同载体对表面PdOx物种化学吸附性质和氧化还原性能的影响,并与样品的丙烷氧化活性相关联.漫反射红外光谱表明,在Pd/SnO2-Al2O3中,Sn对Al2O3表面的Pd原子簇起到稀释作用,促进了Pd的分散,使得其CO线式吸附强度明显高于Pd/Al2O3,但Pd过高的分散度不仅减少了表面Pd-PdO活性位对的数目,而且使反应中间物种Pd-OH之间脱水困难,因而阻塞了活性位,降低了其循环氧化还原活性;而在Sn0.4Zr0.6O2复合氧化物载体中,SnO2有效地阻止了四方晶相ZrO2向稳态单斜晶相转变,且复合载体的比表面积较ZrO2和SnO2有所增加,其表面PdOx物种的分散度适中.此外,Sn0.4Zr0.6O2复合氧化物负载的Pd的价态介于Pd0与Pd2 之间,表面氧空位较多,促进了丙烷中C-H键的活化,使比表面积较低的Pd/Sn0.4Zr0.6O2具有最好的催化丙烷氧化能力,相反比表面积较高的Pd/SnO2-Al2O3活性很差,说明分散度适中且具有较低氧化态的PdOx(0相似文献   

New Polymer Syntheses, 108. Controlled Degradation and In‐Situ Functionalization of Polycarbonates by Means of Bu2SnO

It was found that diphenyl carbonate reacts with Bu₂SnO above 140°C yielding CO₂ and Bu₂Sn(OPh)₂. This insertion reaction was also successfully applied to a polycarbonate prepared from polytetrahydrofuran diol‐1000 and Bu₂SnO containing macrocyclic polyTHF dioxides. Bu₂SnO reacted analogously with poly(bisphenol A) carbonates yielding tin‐containing rapidly crystallizing cyclic oligocarbonates. Their treatment with 1,2‐ethanedithiol gave linear oligocarbonates having two OH end groups. Bu₂Sn‐containing macrocyclic oligocarbonates reacted in‐situ with several carboxylic acid chlorides, forming telechelic oligocarbonates with functional ester end groups. Bu₂Sn‐containing macrocycles also reacted in‐situ with terephthaloyl chlorides yielding a poly(ester carbonate).     

SnO2水溶胶气-液界面纳米胶粒成膜过程

采用胶体化学法制得稳定的ＳｎＯ２纳米粒子溶胶。在ＬＢ膜槽内，用膜天平考察了溶胶在陈化和均速压缩过程中，气－液界面表面压力的变化。，并用布儒斯特色显微镜，直接观察了陈化过程中界面胶体粒子的片面成膜过程，和均速压缩过程中界面胶体粒子的压缩成膜过程。     

纳米SnO2／TiO2的制备及光催化臭氧化活性

用沉积-沉淀法制备了一系列不同Sn/Ti比例的纳米催化剂SnO2/TiO2, 以糖蜜酒精废水的脱色降解为探针反应, 研究了在紫外光条件下Sn/Ti比和焙烧温度对其臭氧化活性的影响. 结果表明, 在Sn掺杂量为5%(mol)时, 焙烧温度773K时, SnO2/TiO2催化活性最好. XRD、TPR显示, 部分Sn4+可能掺入到TiO2的晶格之中, 形成了Sn-O-Ti键. 紫外漫反射光谱显示, 复合SnO2/TiO2对光的吸收明显增加, 催化活性的提高应归因于SnO2/TiO2表面的臭氧吸附. SnO2/TiO2光催化臭氧化降解糖蜜酒精废水的活性与臭氧在催化剂表面的吸附分解有很大的关系, 光的作用只是强化催化臭氧化的氧化效果.     

Effects of Cr2O3 modification on the performance of SnO2 electrodes in DSSCs

In this paper, we demonstrate that Cr(2)O(3), a visible absorbing insulator, can be used as an efficient blocking layer material for the anode of dye-sensitized solar cells (DSSCs). We prepared SnO(2) electrodes surface-modified with Cr(2)O(3) with various Cr/Sn ratios and studied the effect of the modification on the performance of DSSCs. DSSCs with Cr/Sn ratios 0.02, 0.05, and 0.10 showed increased overall photon-to-electricity conversion efficiency from that of pure SnO(2). Especially, the DSSC with the Cr/Sn ratio 0.02 showed a remarkably large increase by 55%. The electrode materials were analyzed by powder X-ray diffraction, transmission electron microscopy, N(2) adsorption studies, and UV-Vis diffuse reflectance spectroscopy. The Cr-containing species appears to be Cr(2)O(3) nanoparticles, spread evenly on the SnO(2) nanoparticles and filling the gap space between SnO(2) particles. The electrochemical properties of the electrodes were characterized by Mott-Schottky plots and electrochemical impedance spectroscopy. As the Cr-content increases, the flat-band potential is negatively shifted. The impedance spectroscopy data show that Cr/Sn = 0.02 and 0.05 samples have lower charge transport resistance at the electrode, which can be explained by the rise of the conduction level due to the charge transfer from the more basic Cr(2)O(3) nanoparticles to SnO(2) nanoparticles. These observations corroborate with the trends of the short-circuit current and the open-circuit voltage of the DSSCs.     

不同形态SnO2纳米晶的制备

In this paper, we report our research on morphologically selective synthesis of nanocrystalline SnO2 by the combination of hydrothermal preparation and calcinated process. We firstly prepared SnO2 nanocrystals by the hydrothermal method at 140 ℃ for 3 h, using SnCI4 as the reactant. With the initial pH of 1.8 or 1.34, we prepared uniform and well-dispersed SnO2(tetragonal) nanocrystals, with similar size of about 3 nm, as determined by TEM. However, after being calcinated at 500 ℃ for 2 h, specimen 1 prepared at pH＝1.8 showed the rod-like shape with an average size of 5 nm×20 nm, while the other one(specimen 2)prepaed at pH＝1.34 showed a granular shape with an average size of 10 nm. XRD experiments showed that specimen 1 had a new diffraction peak after calcination, which was contributed by the (023) face of orthorhombic SnO2. The experiment results indicated that the morpholgy of SnO2 nanocrystals after calcination was closely related to the initial acidity of the reaction solution, possibly due to the difference in surface properties, e.g. the difference in crystalline faces exposed to the surface of particals, under different hydrothermal conditions.