Interplay between O2 and SnO2: oxygen ionosorption and spectroscopic evidence for adsorbed oxygen.

Tin dioxide is the most commonly used material in commercial gas sensors based on semiconducting metal oxides. Despite intensive efforts, the mechanism responsible for gas-sensing effects on SnO(2) is not fully understood. The key step is the understanding of the electronic response of SnO(2) in the presence of background oxygen. For a long time, oxygen interaction with SnO(2) has been treated within the framework of the "ionosorption theory". The adsorbed oxygen species have been regarded as free oxygen ions electrostatically stabilized on the surface (with no local chemical bond formation). A contradiction, however, arises when connecting this scenario to spectroscopic findings. Despite trying for a long time, there has not been any convincing spectroscopic evidence for "ionosorbed" oxygen species. Neither superoxide ions O(2)(-), nor charged atomic oxygen O,(-) nor peroxide ions O(2)(2-) have been observed on SnO(2) under the real working conditions of sensors. Moreover, several findings show that the superoxide ion does not undergo transformations into charged atomic oxygen at the surface, and represents a dead-end form of low-temperature oxygen adsorption on reduced metal oxide.     

一维Ga2O3/SnO2纳米纤维的制备及其气敏性能

通过静电纺丝法制备了一维Ga2O3/SnO2纳米纤维,采用X射线衍射(XRD)、扫描电镜(SEM)、紫外可见漫反射光谱(UV-Vis DRS)等方法对材料进行了表征,测试了不同Ga2O3质量分数(0、40%、50%、60%、70%、100%)的Ga2O3/SnO2纳米纤维(650℃,5 h)对应元件对三甲胺、丙酮、乙醛、乙酸、氨气、乙醇、甲醛7种气体的气敏性能。结果表明:在室温(25℃)时,60%(w/w)Ga2O3-40%(w/w)SnO2纳米纤维对三甲胺气体具有较高的灵敏度和较短的响应/恢复时间。对1000μL·L^-1三甲胺的灵敏度达到51;检出限达到0.8μL·L^-1,其灵敏度为1.3。     

Application of specific ion interaction theory and parabolic models for the molybdenum(VI) and tungsten(VI) complexes with NTA and IDA at different ionic strengths

The interaction of nitrilotriacetic acid (NTA) and iminodiacetic acid (IDA) with tungsten(VI) (pH 7.5) and molybdenum(VI) (pH 6.00) has been studied in aqueous solutions at 25 ℃, and different ionic strengths (0.1 相似文献   

Metal ions binding onto a lignocellulosic substrate extracted from wheat bran: a NICA-Donnan approach

In this study ion binding to solid organic matter was investigated. We used the NICA-Donnan model to describe the interaction between Cu(II), Pb(II), and Cd(II) ions and a lignocellulosic substrate extracted from wheat bran. Such a material represents a very cheap and flexible substrate, which can be used as a natural filter to remove toxic metal ions from industrial effluents or applied in the decontamination and rehabilitation of abandoned industrial sites. Moreover, such a material also represents a very simple model of natural organic matter derived from lignin and cellulose, for which there is now a lack of thermodynamic data as far as their interaction with toxic metal ions is concerned. Experimental results were obtained in various conditions of pH and ionic strength. In our modeling, we used the acidity constants and the concentration of sites that were determined in a previous work. The parameters deduced from the NICA-Donnan model were also compared to thermodynamic data available for other cases of natural organic matter, mainly humic substances.     

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).     

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.     

高溶解性盐水体系热力学模型预测能力的比较研究I: 二元体系

用原始Pitzer模型、扩展的Pitzer模型、Pitzer-Simonson-Clegg模型、S-MSA模型和BET模型分别对LiCl-H2O, LiBr-H2O, CaCl2-H2O, Mg(NO3)2-H2O, MnCl2-H2O和Mn(NO3)2-H2O等六种不同体系的热力学性质进行描述, 考察了各种模型的预测能力. 结果表明原始Pitzer模型不能准确描述高浓电解质溶液的性质; 扩展的Pitzer模型虽然能较准确地描述某些体系高浓度的热力学性质, 但预测能力不足; Pitzer-Simonson-Clegg模型对高浓盐水体系热力学性质具有一定的预测能力, 但拟合参数所用的最大浓度与溶解度相差很大时, 外推饱和点的热力学性质则会出现较大偏差; S-MSA模型虽然可以将拟合参数的浓度范围扩大到饱和, 但没有外推能力, 而且需要溶液的密度数据, 这限制了该模型的广泛应用; BET模型对这六种体系均体现出很强的预测能力, 预测结果准确, 且模型参数少, 物理意义明确, 该模型可用于熔盐水化物相变储能材料的设计.     

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.     

Thermodynamic aspects of ion intercalation in KhFek[Fe(CN)6]l*mH2O compounds: application to the Everit's Salt/Prussian blue transition

The K(+) reversible processes for ion exchange in K(h)Fe(k)[Fe(CN)(6)](l)*mH(2)O host compounds (Prussian Blue) were thermodynamically analyzed. A thermodynamic approach was established and developed based on the consideration of a lattice-gas model where the electronic contribution to the chemical potential is neglected and the ion-host interaction is not considered. The occupation fraction of the intercalation process was calculated from the kinetic parameters obtained through ac-electrogravimetry in a previous paper. In this way, the mass potential transfer function introduces a new way to evaluate the thermodynamic aspect of intercalation. Finally, based on the thermodynamic approach, the energy used to put each K(+) ion into the host material was calculated. The values were shown to be in good agreement with the values obtained through transient techniques, for example, cyclic voltammetry. As a result, this agreement between theory and experimental data validates the thermodynamic approach considered here, and for the first time, the thermodynamic aspects of insertion were considered for mixed valence materials.     

Deuterium structural effects in inorganic and bioinorganic aggregates

Deuterium kinetic isotope effects are widely used in chemical and biological research. Deuterium thermodynamic effects on the aqueous synthesis of inorganic materials, however, seem not to have been recognized. Here we report that the simple replacement of H(2)O with D(2)O in the synthesis of a solid-state manganese complex results in a new structurally and magnetically distinct phase. When iron oxides are synthesized, the relative amount of the mineral phases obtained in H(2)O vs D(2)O is different. The morphology and magnetic properties of the iron core of the iron storage protein ferritin are likewise different when mineralization is carried out in heavy water. The formation of extra inorganic solids, change in the ratio of two phases or alteration of a single phase morphology in D(2)O suggest that new inorganic and bioinorganic metal complexes might be obtained by using the thermodynamic isotope effect.     

Intercalation synthesis of functional hybrid materials based on layered simple hydroxide hosts and ionic liquid guests--a pathway towards multifunctional ionogels without a silica matrix?

Functional hybrid materials on the basis of inorganic hosts and ionic liquids (ILs) as guests hold promise for a virtually unlimited number of applications. In particular, the interaction and the combination of properties of a defined inorganic matrix and a specific IL could lead to synergistic effects in property selection and tuning. Such hybrid materials, generally termed ionogels, are thus an emerging topic in hybrid materials research. The current article addresses some of the recent developments and focuses on the question why silica is currently the dominating matrix used for (inorganic) ionogel fabrication. In comparison to silica, matrix materials such as layered simple hydroxides, layered double hydroxides, clay-type substances, magnetic or catalytically active solids, and many other compounds could be much more interesting because they themselves may carry useful functionalities, which could also be exploited for multifunctional hybrid materials synthesis. The current article combines experimental results with some arguments as to how new, advanced functional hybrid materials can be generated and which obstacles will need to be overcome to successfully achieve the synthesis of a desired target material.     

阳极电沉积条件对Ti/SnO2-Sb2O5/PbO2+Nano-Co3O4复合电极组成、形貌和结构的影响

本文在涂有中间层SnO2-Sb2O5的Ti基体上,采用阳极复合电沉积法制备了Ti/SnO2-Sb2O5/PbO2+Nano-Co3O4复合电极材料,借助于X射线衍射（XRD）、X射线光电子能谱（XPS）、扫描电镜（SEM）等分析方法研究了制备条件对该复合电极材料的组成、结构和形貌的影响。结果表明,纳米Co3O4的掺杂可提高PbO2电极表面的粗糙度和空隙率;沉积电位、镀液中Co3O4粒子浓度及有机溶剂的添加均对镀层中Co3O4的嵌入量有很大影响。     

石墨/氧化锡/活性炭锂离子电池负极材料的合成及性能

采用液相法,以SnCl2·2H2O、石墨、活性炭为原料,在油浴中共热合成石墨/氧化锡/活性炭复合材料.通过XRD和电化学测试对材料进行了表征.结果表明,样品中含有石墨和金红石SnO2·这种材料作为锂离子电池负极材料具有良好的充放电循环性能.     

CO gas sensing by ultrathin tin oxide films grown by atomic layer deposition using transmission FTIR spectroscopy

Ultrathin tin oxide films were deposited on SiO2 nanoparticles using atomic layer deposition (ALD) techniques with SnCl4 and H2O2 as the reactants. These SnO(x) films were then exposed to O2 and CO gas pressure at 300 degrees C to measure and understand their ability to serve as CO gas sensors. In situ transmission Fourier transform infrared (FTIR) spectroscopy was used to monitor both the charge conduction in the SnO(x) films and the gas-phase species. The background infrared absorbance measured the electrical conductivity of the SnO(x) films based on Drude-Zener theory. O2 pressure was observed to decrease the SnO(x) film conductivity. Addition of CO pressure then increased the SnO(x) film conductivity. Static experiments also monitored the buildup of gas-phase CO2 reaction products as the CO reacted with oxygen species. These results were consistent with both ionosorption and oxygen-vacancy models for chemiresistant semiconductor gas sensors. Additional experiments demonstrated that O2 pressure was not necessary for the SnO(x) films to detect CO pressure. The background infrared absorbance increased with CO pressure in the absence of O2 pressure. These results indicate that CO can produce oxygen vacancies on the SnO(x) surface that ionize and release electrons that increase the SnO(x) film conductivity, as suggested by the oxygen-vacancy model. The time scale of the response of the SnO(x) films to O2 and CO pressure was also measured by using transient experiments. The ultrathin SnO(x) ALD films with a thickness of approximately 10 A were able to respond to O2 within approximately 100 s and to CO within approximately 10 s. These in situ transmission FTIR spectroscopy help confirm the mechanisms for chemiresistant semiconductor gas sensors.     

Tin oxide (SnO2) nanoparticles/electrospun carbon nanofibers (CNFs) heterostructures: controlled fabrication and high capacitive behavior

Tin oxide (SnO(2))/carbon nanofibers (CNFs) heterostructures were fabricated by combining the versatility of the electrospinning technique and template-free solvent-thermal process. The results revealed that the SnO(2) nanostructures were successfully grown on the primary electrospun carbon nanofibers substrates. And, the coverage density of SnO(2) nanoparticles coating on the surface of the CNFs could be controlled by simply adjusting the mass ratio of CNFs to SnCl(4)·5H(2)O in the precursor during the solvent-thermal process for the fabrication of SnO(2)/CNFs heterostructures. The electrochemical performances of the SnO(2)/CNFs heterostructures as the electrode materials for supercapacitors were evaluated by cyclic voltammetry (CV) and galvanostatic charge-discharge measurement in 1 M H(2)SO(4) solution. At different scan rates, all the samples with different coverage densities of SnO(2) showed excellent capacitance behavior. And, the sample CS2 (the mass ratio of CNFs to SnCl(4)·5H(2)O reached 1:7) exhibited a maximum specific capacitance of 187 F/g at a scan rate of 20 mV/s. Moreover, after 1000 cycles, the specific capacitance retention of this sample was over 95%. The high capacitive behavior could be ascribed to the low resistance of SnO(2)/CNFs heterostructures and rapid transport of the electrolyte ions from bulk solution to the surface of SnO(2).     

高聚物固体电解质聚氧化乙烯－溴化铜复阻抗谱及介电常数的静水压效应

采用分子量５００万的聚氧化乙烯和无水溴化铜，通过混溶蒸发法制备成高聚物固体电解质Ｐ（ＥＯ）ｎ－ＣｕＢｒ２薄膜，并在０．１～３００ＭＰａ范围不同的流体静水压下详细测量其复平面阻抗谱，分别得到在不同压力下离子电导率和介电常数与测量频率的关系．进一步解谱准确地求出Ｐ（ＥＯ）ｎ－ＣｕＢｒ２（ｎ＝１２、１６）薄膜离子电导率和介电常数的静水压效应，并结合Ｘ－光物相分析，根据离子迁移通道的物理图象和高聚物的极化机构进行了初步的讨论．添加２０％的增塑剂碳酸丙烯酯，较大改进了压力下的导电性．１２０～３００ＭＰａ的离子电导率提高一个数量级     

Kinetics and mechanism of the interaction of thioglycolic acid with [(H2O)(tap)2RuORu(tap)2(H2O)]2+ ion at physiological pH

The interaction of thioglycolic acid (tgaH₂) with the title complex has been studied spectrophotometrically in aqueous medium as a function of [substrate complex], [ligand], pH and temperature at constant ionic strength. The reactivity of different donor centers [e.g., (N), (N,O) and (O,O) are compared]. In the studied pH range the reaction is a two-step ligand dependent process. The thermodynamic and activation parameters are reported and compared with other systems studied earlier. As no study on this system is available in the literature, it is not possible to compare with reports from other groups.     

The nonmonotonic concentration dependence of the mean activity coefficient of electrolytes is a result of a balance between solvation and ion-ion correlations

We propose a simple model to explain the nonmonotonic concentration dependence of the mean activity coefficient of simple electrolytes without using any adjustable parameters. The primitive model of electrolytes is used to describe the interaction between ions computed by the adaptive grand canonical Monte Carlo method. For the dielectric constant of the electrolyte, we use experimental concentration dependent values. This is included through a solvation term in our treatment to describe the interaction between ions and water that changes as the dielectric constant changes with concentration. This term is computed by a Born-treatment fitted to experimental hydration energies. Our results for LiCl, NaCl, KCl, CsCl, NaBr, NaI, MgCl(2), CaCl(2), SrCl(2), and BaCl(2) demonstrate that the principal reason of the nonmonotonic behavior of the activity coefficient is a balance between the solvation and ion-ion correlation terms. This conclusion differs from previous studies that assumed that it is the balance of hard sphere repulsion and electrostatic attraction that produces the nonmonotonic behavior. Our results indicate that the earlier assumption that solvation can be taken into account by a larger, "solvated" ionic radius should be reconsidered. To explain second order effects (such as dependence on ionic size), we conclude that explicit water models are needed.     

反尖晶石结构的Mg2SnO4系长余辉材料的研究进展及应用

Mg2SnO4具有典型的反尖晶石结构,由于存在大量缺陷,非常适合作为长余辉材料的基质材料,而且其成本低,结构稳定光学性能优异,应用前景非常广泛。通过在反尖晶石结构的Mg2SnO4材料中掺杂不同离子可以制备出不同性质的长余辉材料。本文主要介绍了Mg2SnO4系长余辉材料的常用的制备工艺方法和发光机理,从离子掺杂的角度分析其性能,并对反尖晶石结构的Mg2SnO4系长余辉材料在防伪、信息存储、成像等方面的应用现状进行了综述和展望。