Correlation between XPS, Raman and TEM measurements and the gas sensitivity of Pt and Pd doped SnO2 based gas sensors

Nanocrystalline thick-film SnO₂ sensors with different dopants were fabricated by an optimized screen printing process and subsequent annealing. Powders were used as starting materials which were prepared by a wet chemical process from SnCl₄. Microanalysis was performed of both, the precursors and the final sensor materials with their different annealing conditions. Gas sensing tests with CO, CH₄ and NO₂ in air with controlled humidity were correlated with results from X-ray photoemission spectroscopy (XPS), Raman spectroscopy and transmission electron microscopy (TEM). As an interesting result, the distribution of the transition metal dopants Pd and Pt (as deduced from TEM and XPS data) rules out the existence of metallic clusters or even atoms in the metallic state at the surface. This finding does not allow to explain the sensor effects on SnO₂ based materials as usually done by means of spill-over effects or Fermi energy control.     

Photocatalytic performance of Ag doped SnO2 nanoparticles modified with curcumin

Visible light active Ag doped SnO₂ nanoparticles modified with curcumin (Cur–Ag–SnO₂) have been prepared by a combined precipitation and chemical impregnation route. The optical properties, phase structures and morphologies of the as-prepared nanoparticles were characterized using UV–visible diffuse reflectance spectra (UV–vis-DRS), X-ray powder diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). The surface area was measured by Brunauer. Emmett. Teller (B.E.T) analysis. Compared to bare SnO₂, the surface modified photocatalysts (Ag–SnO₂ and Cur–Ag–SnO₂) showed a red shift in the visible region. The photocatalytic activity was monitored via the degradation of rose bengal (RB) dye and the results revealed that Cur–Ag–SnO₂ shows better photocatalytic activity than that of Ag–SnO₂ and SnO₂. The superior photocatalytic activity of Cur–Ag–SnO₂ could be attributed to the effective electron-hole separation by surface modification. The effect of photocatalyst concentration, initial dye concentration and electron scavenger on the photocatalytic activity was examined in detail. Furthermore, the antifungal activity of the photocatalysts and the reusability of Cur–Ag–SnO₂ were tested.     

Dopants in nanocrystalline tin dioxide

The review surveys studies aimed at constructing new materials for gas sensors based on nanocrystalline tin dioxide. The influence of doping with various impurities (Pt, Pd, Ru, Rh, Cu, Ni, or Fe) on the composition, microstructure, and electrophysical and sensor properties of nanocrystalline SnO₂ was discussed. The conditions for the preparation of powders and thick and thin SnO₂ films by the wet chemical method and aerosol pyrolysis of organometallic compounds are reported. The mechanism of interaction of pure and doped nanocrystalline SnO₂ with a gas phase was analyzed based on the data from Mossbauer, Auger electron, and X-ray photoelectron spectroscopy and the results of in situ Raman spectroscopy, XANES, and conductivity measurements.     

Size-controlled synthesis and characterization of quantum-size SnO2 nanocrystallites by a solvothermal route

By using ethylenediamine as both an alkali and ligand, quantum size SnO₂ nanocrystallites were synthesized with a solvothermal route. The transmission electron micrographs (TEM) were employed to characterize the morphologies of the products. The crystal sizes of the as-synthesized SnO₂ were ranged form 2.5 to 3.6 nm. The crystal structure and optical properties of the products were investigated by X-ray diffraction, Fourier transform infrared spectroscopy, optical absorption spectra, photoluminescence and Raman spectra. Anisotropic growth of the SnO₂ nanocrystallites was observed by altering the solvent from water to ethanol. The SnO₂ nanocrystal showed apparent quantum confinement effects. Finally, the mechanism for the formation of quantum size SnO₂ was also discussed.     

Correlation between XPS, Raman and TEM measurements and the gas sensitivity of Pt and Pd doped SnO2 based gas sensors

Nanocrystalline thick-film SnO₂ sensors with different dopants were fabricated by an optimized screen printing process and subsequent annealing. Powders were used as starting materials which were prepared by a wet chemical process from SnCl₄. Microanalysis was performed of both, the precursors and the final sensor materials with their different annealing conditions. Gas sensing tests with CO, CH₄ and NO₂ in air with controlled humidity were correlated with results from X-ray photoemission spectroscopy (XPS), Raman spectroscopy and transmission electron microscopy (TEM). As an interesting result, the distribution of the transition metal dopants Pd and Pt (as deduced from TEM and XPS data) rules out the existence of metallic clusters or even atoms in the metallic state at the surface. This finding does not allow to explain the sensor effects on SnO₂ based materials as usually done by means of spill-over effects or Fermi energy control. Received: 8 August 1997 / Revised: 24 October 1997 / Accepted: 31 October 1997     

Structure Evolution and Associated Catalytic Properties of PtSn Bimetallic Nanoparticles

Bimetallic nanoparticles (NPs) often show new catalytic properties that are different from those of the parent metals. Carefully exploring the structures of bimetallic NPs is a prerequisite for understanding the structure‐associated properties. Herein, binary Pt?Sn NPs with tunable composition are prepared in a controllable manner. X‐ray characterizations reveal that their structures evolve from SnO_2?x‐patched PtSn alloys to SnO_2?x‐patched Pt clusters when more tin is incorporated. An obvious composition‐dependent catalytic performance is observed for the hydrogenation of α,β‐unsaturated aldehydes: the selectivity to unsaturated alcohol increases substantially at high tin content, whereas the reaction rate follows a volcano shape. Furthermore, Pt sites are responsible for hydrogen dissociation, whereas oxygen vacancy (O_vac) sites, provided by SnO_2?x, drastically enhance the adsorption of carbonyl group.     

The morphological,optical and electrical properties of SnO2:F thin films prepared by spray pyrolysis

Combining the spray pyrolysis and the sol–gel techniques gives the possibility to produce Fluorine doped Tin oxide (SnO₂:F) thin films. Transparent conducting SnO₂:F thin films have been deposited on glass substrates by the spray pyrolysis technique. This technique for the fabrication of SnO₂:F filmsby combining sol–gel process and the spray pyrolysis technique ispresented in this paper. The Sol–gel precursors have been successfully prepared using SnCl₂·5H₂O and (Ac)F₃. The structural, electrical, and optical properties of these films were investigated. The high resolution transmission electron microscopy (HRTEM) and selected area diffraction (SAD) patterns of SnO₂:F films show that the gel films lead to a tetragonal structure. The X‐ray diffraction pattern of the films deposited at substrate temperature 530° , the orientation of the films was predominantly [110]. In addition, the surface chemical components were also examined by X‐ray photoelectron spectroscopy (XPS) showing the SnO₂:F deposited with the atomic concentration ratios Sn/F 1.82:1. The minimum sheet resistance was 50 Ω and average transmission in the visible wavelength range of 300 to 800 nm was 87.25%. Copyright © 2008 John Wiley & Sons, Ltd.     

不同载体对负载型氧化钨催化剂在己二酸合成反应中的结构及性能影响

以SBA-15、六角介孔二氧化硅（HMS）和SnO₂为载体,通过浸渍法合成了含钨负载型催化剂,并考察了三种催化剂在环氧环己烷选择氧化制备己二酸反应中的催化性能. 通过X射线衍射（XRD）,透射电镜/场发射透射电镜（TEM/FETEM）,紫外-可见漫反射光谱（UV-Vis DRS）,拉曼（Raman）光谱,X射线光电子能谱（XPS）以及傅里叶变换红外（FTIR）光谱等手段对各种催化剂的结构进行表征. 结果表明,载体与催化剂的性能有密切的关系. 以SnO₂为载体的WO₃/SnO₂催化剂活性最高,其次是WO₃/HMS催化剂,WO₃/SBA-15 催化剂的活性最差.XRD 分析显示WO₃/SnO₂催化剂中氧化钨物种的晶化程度最低,TEM 和XPS 结果表明氧化钨物种在WO₃/SnO₂催化剂表面高度分散并且粒径尺寸很小（约2 nm）,UV-Vis DRS结果表明在WO₃/SnO₂催化剂中存在孤立[WO₄]四面体和低聚态的钨物种,这些物种的存在可能是WO₃/SnO₂催化剂具有高活性的主要原因. 此外,WO₃/SnO₂催化剂可以重复使用多次,6 次反应后己二酸（AA）得率仍然保持在80%以上,说明氧化钨物种与SnO₂载体间存在强烈的相互作用,从而提高了催化剂的稳定性.     

Effects of oxygen vacancy on the magnetic properties of Cr-doped SnO2: Density functional investigation

Magnetic properties of Cr-doped SnO₂ and the effects of oxygen vacancy (V_O) on the magnetic properties are examined to understand the origin of ferromagnetism in Cr-doped SnO₂ and explain the observed discrepant phenomena. Cr-doped SnO₂ shows a p-d hopping ferromagnetic interaction that decreases gradually with the increase in Cr-Cr distance. In Cr-doped SnO₂ with V_O, ferromagnetic interaction is obviously weakened. Exchange constants indicate that the ferromagnetic exchange interaction in Cr-doped SnO₂ is similar to that in Co-doped SnO₂, while it is similar to that in Fe-doped SnO₂ and/or undoped SnO₂ with tin vacancy (V_Sn) in the presence of V_O.     

自掺杂TiO2纳米管：液相制备及光催化性能

采用水合肼（N₂H₄·H₂O）作为还原剂,在液相环境中制备了自掺杂TiO₂纳米管阵列（NTs）。利用FE-SEM、EDS、XPS、XRD、Raman、UV-Vis/NIR分光光度法以及半导体特性分析系统（Keithley 4200 SCS）分别对样品的形貌,晶体结构,光学特性以及电学性能进行了表征。结果表明：通过这种方法制备的自掺杂TiO₂NTs在带隙中引入了大量的氧空位,创造了氧空位能级,从而提高了样品的电导率,有效提高光生电子-空穴对的产生、分离和传输。此外,由于氧空位的作用,使得TiO₂NTs的带隙变窄,增强了可见光吸收能力,致使样品具有较高的光催化活性,并通过降解甲基橙溶液对样品的光催化活性进行评估。结果显示当光照150min后,自掺杂TiO₂NTs对甲基橙溶液的降解率达73%,并且这种催化剂便于回收和重复使用。     

Photocatalytic activities of multilayered ZnO-based thin films prepared by sol–gel route: effect of SnO2 heterojunction layer

In present study, ZnO/SnO₂/ZnO/SnO₂/ZnO multi–layer, ZnO/SnO₂/ZnO triple layer and ZnO single layer films have been deposited on glass substrate by sol–gel dip–coating technique. The structural and optical properties of thin films have been investigated by X-ray diffractometer, UV–visible, photoluminescence spectroscopies and scanning electron microscopy. The structural analysis reveals structural inhomogeneities and different crystallite growth processes as function of number of deposited layers. A comparison between photocatalytic activity of zinc oxide samples toward photodegradation of phenol, 4-aminophenol and 4-nitrophenol has been performed under UV light irradiation. Experiments were conducted to study the effects of operational parameters on the degradation rate. Pseudo-first-order photodegradation kinetics was observed on all films and the reaction constants were determined. The results showed that the photocatalytic activity of ZnO multi–layer film was superior to that of the ZnO single- and triple-layer films. Differences in film efficiencies can be attributed to differences in crystallinity, surface morphology, defect concentration of oxygen vacancy and to presence of SnO₂ sublayer that may act as trap for electrons generated in the ZnO layer thus preventing electron–hole recombination. The results reveal that SnO₂ hetrojunction layers improve crystalline quality, optical and photocatalytic properties of ZnO multilayered films.     

一步醇-水热法合成高效的F掺杂BiVO4光催化剂

以NH₄F为掺杂前体,采用简单的一步醇-水热法制备了F掺杂BiVO₄光催化剂。利用X射线衍射（XRD）、扫描电子显微镜（SEM）、X射线光电子能谱（XPS）、紫外-可见漫反射光谱（UV-Vis）和光致发光光谱（PL）表征了这些光催化剂的物理化学性质。在少量H₂O₂存在条件下,以可见光照射下光催化降解苯酚的反应测定了这些光催化剂的催化活性。研究表明,相较于未掺杂的BiVO₄样品而言,F掺杂BiVO₄样品不仅仍保留了单斜结构,而且有更高的结晶度、表面氧空位密度和光生电荷载流子分离效率,更强的光吸收和更低的带隙能。在这些F掺杂BiVO₄样品中,以n_F/n_Bi的理论值为1.0且带隙能为2.43 eV的F掺杂BiVO₄样品的光催化活性最好（90 min内苯酚的降解率可达95%）。这一优良的光催化性能与其具有最高的结晶度、表面氧空位密度和光生电荷载流子分离效率,最强的光吸收和最低的带隙能有关。     

A Novel Approach for Generation of Oxygen Vacancies in Trirutile MnSb2O6 and Their Impact on Photocatalytic Degradation of MO Dye

Visible light-driven photocatalysis has gained much attention due to its light-harnessing characteristics and is extensively used in wastewater remediation. This paper presents a novel oxygen-deficient manganese antimonate, MnSb₂O_6-x, with a trirutile structure as an effective visible-light-driven photocatalyst for dye degradation. The synthesized samples were subjected to XRD, UV-Vis DRS, SEM-EDS, Raman, XPS, and PL analyses to study their physic chemical properties. The influence of sequential or single heating during the preparation method on the generation of oxygen vacancies is evaluated using UV-Vis DRS, XPS, ESR, and Raman techniques. The oxygen-deficient MnSb₂O₆ could achieve up to 85 % of MO degradation in 180 min under visible light irradiation, and its reusability up to six cycles was also investigated. In addition, the mechanism of dye degradation was supported with a scavenger test, and the degradation activities are correlated to the electron-hole pair separation as convinced from the PL spectra. The simple and unique method of oxygen vacancy generation can inspire the development of antimonates with oxygen deficiencies, which have significant scope of application in environmental and energy conservation.     

Fluorine incorporation into SnO2 nanoparticles by co-milling with polyvinylidene fluoride

Fluorine was incorporated into SnO₂ nanoparticles from polyvinylidene fluoride (PVdF) by co-milling. The incorporation process was triggered by an oxidative partial decomposition of PVdF due to the abstraction of oxygen atoms, and began soon after milling with a simultaneous decrease in the crystallite size of SnO₂ from 56 nm to 19 nm, and increase in the lattice strain by a factor 7. Appearance of D and G Raman peaks indicated that the decomposition of PVdF was accompanied by the formation of nanometric carbon species. Decomposing processes of PVdF were accompanied by the continuous change in the states of F, with a decrease of C–F in PVdF and increase in Sn–F. This indicates the gradual incorporation of F into SnO₂, by replacing a part of oxygen in the oxide with fluorine. These serial mechanochemical reaction processes were discussed on the basis of X-ray diffractometry, FT-IR, Raman and UV–Vis diffuse reflectance spectroscopy, transmission electron microscopy, F1s, Sn3d and C1s X-ray photoelectron spectroscopy and Auger electron spectra, as well as magic angle spinning NMR spectroscopy of ¹⁹F and ¹¹⁹Sn. The present findings serve as an initial stage of incorporating fluorine into SnO₂ via a solvent-free solid-state process, toward the rational fabrication of fluorine doped SnO₂ powders.     

Correlations between structure and properties of materials. X. Anomalous optical properties and Raman spectra of glassy ternary B2O3–BaTiO3–Na2O materials

The anomalous behavior of refractive index and density in the glassy ternary B₂O₃–BaTiO₃–Na₂O materials is presented and discussed in terms of Raman spectroscopy results. The slope change in the optical properties as a function of composition takes place within the same range of composition in which the Raman spectra suggest a transition from a bridging type of attack on the glassy matrix by the oxygen present in the basic oxide, to a nonbridging type. The structural modifications of the materials at different compositions are inferred from a detailed analysis of the Raman spectra.     

High visible light-driven photocatalytic activity of large surface area Cu doped SnO<Subscript>2</Subscript> nanorods synthesized by novel one-step microwave irradiation method

The paper investigates the structural, optical and photocatalytic activity of large surface area single crystalline copper (Cu) doped SnO₂ nanorods (NRs) synthesized by a novel one-step microwave irradiation method. Powder X-ray diffraction (XRD) analysis confirms that both pure and Cu doped SnO₂ are tetragonal rutile type structure (space group P42/mnm) formed during the microwave process within 10 min without any post annealing treatment. Transmission electron microscopy (TEM) reveals that the as synthesized Cu doped SnO₂ samples exhibited rod-like shape and the length was less than 80 nm and diameter was about few nanometers. Typical selected-area electron diffraction (SAED) pattern indicates that, the growth direction of Cu–SnO₂ nanorod is along [110] direction. The variety of phonon interaction in the pure and Cu doped SnO₂ is observed by Raman spectroscopy. Electron paramagnetic resonance and X-ray photoelectron spectroscopy (XPS) confirms that the presence of copper and tin as Cu²⁺ and Sn⁴⁺ in state, respectively. The photocatalytic activity was monitored via the degradation of methylene blue (MB) and Rhodamine B (RhB) dyes and the Cu–SnO₂ showed better photocatalytic activity than that of pure SnO₂. This could be attributed to the effective electron–hole separation by surface modification.     

CFTS-3/In2S3/SnO2:F heterojunction structure as eco-friendly photocatalytic candidate for removing organic pollutants

In this paper, quaternary chalcogenide Cu₂FeSnS₄ (CFTS) thin films were synthesized by spray pyrolysis using multilayer deposition technique in which the number (N) of sequential deposition runs (DR) is N = 1, 2, 3 and 4. The delivered volume in each sample is (N × 300 ml). Correspondingly, samples are named CFTS-N. Chemical composition, morphological, structural, optical and electrical properties were characterized using dispersive X-ray spectrometry (EDX), scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectroscopy, spectrophotometer and Hall Effect measurements. XRD and Raman spectroscopy show a purer phase and better crystalline quality of CFTS-3 than other films. Average particle size increases with DR and reaches a maximum value of about 60 nm for N = 3. Optical results show high absorption coefficient value about 10⁵ cm⁻¹ in visible range, with an optical band gap of about 1.47 eV. Electrical resistivity of CFTS-3 equals to 5.82 10⁻³ Ω cm which is the lowest value of these four samples. We have investigated the photocatalysis activity of various thin films by measuring the degradation of methylene blue (MB) and Rhodamine (RhB) as pollutant dyes. In particular we have compared the candidates: CFTS-3/SnO₂:F, CFTS-3/In₂S₃ and CFTS-3/In₂S₃/SnO₂:F. Under sun light irradiation, CFTS-3/In₂S₃/SnO₂:F heterojunction exhibits the best photodegradation rate (96%) of MB dye.     

Preparation of electrospun heterostructured hollow SnO<Subscript>2</Subscript>/CuO nanofibers and their enhanced visible light photocatalytic performance

Heterostructured SnO₂/CuO nanofibers with a hollow morphology were successfully fabricated by a one-step electrospinning method. The electrospun nanofibers were transformed into hollow nanostructures in the presence of camphene after a calcination process, and the obtained samples were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), UV-vis diffuse reflection spectroscopy (DRS), photoluminescence spectra (PL), and photodegradation measurements. The scanning electron microscopy (SEM) images displayed a rough and hollow structure for the obtained nanofibers. X-ray photoelectron spectroscopy (XPS) and energy-dispersive X-ray spectroscopy (EDX) identified the molecular composition and chemical interactions of the nanofibers. Photoluminescent (PL) measurements indicated that a recombination of the photoinduced electrons and holes was further inhibited due to the hollow nanostructure. Furthermore, the photodegradation of methylene blue suggested that the heterostructured SnO₂/CuO hollow nanofibers possessed higher charge separation and photodegradation abilities than those of the other samples under visible light irradiation. This work can be potentially applied to the fabrication of other inorganic oxide photocatalysts with enhanced photodegradation activity in the field of environmental remediation.     

Growth and characterization of ultrathin carbon films on electrodeposited Cu and Ni

Ultrathin carbon films were grown on different types of metallic substrates. Free‐standing foils of Cu and Ni were prepared by electroforming, and a pure Ni film was obtained by galvanic displacement on a Si wafer. Commercial foil of Ni 99.95% was used as a reference substrate. Carbon films were grown on these substrates by chemical vapour deposition in a CH₄‐H₂ atmosphere. Obtained films were characterized by Raman spectroscopy, X‐ray photoelectron spectroscopy (XPS), Auger electron spectroscopy, and ultraviolet photoemission spectroscopy. The XPS at grazing collection angle was used to determine the thickness of carbon films. Depending on the deposition parameters, the films of graphene or graphite were obtained on the different substrates. The uniformity of graphene and its distribution over the sample area were investigated from Raman data, optical images, and XPS chemical maps. The presence of graphene or graphite in the films was determined from the Raman spectra and Auger peak of C KVV. For this purpose, the D parameter, which is a fingerprint of carbon allotropes, was determined from C KVV spectra acquired by using X‐rays and electron beam. A formation of an intermediate layer of metal hydroxide was revealed in the samples with graphene overlayer.     

The effect of Sn dopant on crystal structure and photocatalytic behavior of nanostructured titania thin films

In this study, preparation of Sn doped (0–30 mol % Sn) TiO₂ dip-coated thin films on glazed porcelain substrates via sol–gel process have been investigated. The effects of Sn content on the structural, optical, and photo-catalytic properties of applied thin films have been studied by X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), field emission SEM (FE-SEM), and high resolution transmission electron microscopy (HR-TEM). Surface topography and surface chemical state of thin films were examined by atomic force microscope (AFM) and X-ray photoelectron spectroscopy (XPS). XRD patterns showed an increase in peak intensities of the rutile crystalline phase by increasing the Sn dopant. The prepared Sn-doped TiO₂ photo-catalyst films showed optical absorption edge in the visible light area and exhibited excellent photo-catalytic ability for degradation of methylene blue solution under UV irradiation. The result shows that doping an appropriate amount of Sn can effectively improve the photo-catalytic activity of TiO₂ thin films, and the optimum dopant amount is found to be 15 mol%. The Sn⁴⁺ dopants substituted Ti⁴⁺ in the lattice of TiO₂ and increased surface oxygen vacancies and the surface hydroxyl groups. TEM results showed small increase in planar spacing (was detected by HR-TEM caused by Sn dopants in titania based crystals).