Electrospinning Synthesis and Photoluminescence Properties of SnO2：xEu3＋ Nanofibers

NnO2：xEu3＋（x=O, 1%, 3%, 5%, molar fraction） fibers were synthesized by electrospinning technology. The size of the as-prepared fibers is relatively uniform and the average diameter is about 200 nm with a large draw ratio. The as-prepared Eu3＋ doped SnO2 nanofibers have a rutile structure and consist of crystallitc grains with an average size of about 10 nm. A slight red shift of the A1gand Bag vibration modes and an additional peak at 288 nm were observed in the Raman spectra of the nanofibers. The energies of bandgaps of the SnO2 nanofiber with Eu doping of 1% and 3% are 2.64 eV, and the energy of bandgap is 2.94 eV with Eu doping of 5%（molar fraction）. There is only orange emission（5D0→7F1 magnetic dipole transition） for Eu doped SnO2 nanofibers, and no red emission could be observed. The orange emission upon indirect excitation splits into three peaks and the peak intensity at the excitation wavelength of 275 nm is higher than that at the excitation wavelength of 488 nm.     

Solidification of metallic tin in dispersed phase

Differential scanning calorimetry (DSC) and particle size measurements were carried out on disproportionation products of pure SnO to investigate the fusion and solidification behaviour of Sn droplets and their catalytic nucleation on Sn oxides. If disproportionation reaction takes place at T ≥ 798 K, the products are metallic Sn and SnO₂; but for 523 < T < 798 K, SnO₂ is replaced by an intermediate oxide (IO) Sn_xO_(1+x). On melting, samples with IO show a drop of melting point of metallic tin due to Gibbs–Thomson effect; no lowering of melting point was observed in samples with SnO₂. On the other hand, if solidification occurs in the presence of IO, Tin droplets always displayed three distinct exothermic solidification peaks, but if it takes place in the presence of SnO₂, only one exothermic peak is observed. Undercooling values and contact angles were determined for each of the heterogeneous nucleation processes. The different behaviour of metallic Tin droplets was related to the different lattice symmetry of SnO₂ and IO, which act as nucleation catalysts.     

Structural effects in low temperature radioluminescence of aqueous ionic systems

Structural effects in the radioluminescence spectra of glassy and polycrystalline aqueous solutions of chloride and alkaline ices observed by pulse radiolysis at temperatures 6–110 K are reported. The luminescence efficiency as well as position of λ_max of the emission spectra are dependent on the physical state and temperature of the matrix. For all the investigated aqueous polycrystalline matrices and for H₂O ice, the emission band peaking at about 330 nm, assigned to OH*A²Σ→X²Π transition appears at temperatures below 40 K. This UV band was not observed for glassy matrices. Luminescence bands observable in the visible range of spectrum (400–600 nm) can be associated with the emission of (OH⁻)*, the radiative capture of trapped electrons e⁻_t by metal cations Me⁺(Me²⁺) and trapped atoms H√_t. For polycrystalline chloride matrices a contribution of the emission of (Cl²⁻₂)* must be taken into account.     

One-step Synthesis and Gas Sensing Properties of Hierarchical SnO2 Materials

Hierarchical tin oxide(SnO₂) architectures were synthesized with a facile hydrothermal method. In the hydrothermal synthesis, sodium dodecyl benzene sulfonate(SDBS) surfactant plays an important role as structure-directing reagent. The synthesized samples were characterized by powder X-ray diffraction(XRD), field emission scanning electron microscopy(FESEM), transmission electron microscopy(TEM) and high-resolution transmission electron microscopy(HRTEM). The results clearly reveal that the hierarchical architectures of SnO₂ were composed of aggregated nanosheets with a thickness of about 100 nm. A possible mechanism for the formation of the SnO₂ hierarchical architectures was proposed. In addition, the gas sensing properties of the as-prepared products were investigated and it was found that the sensor based on the special SnO₂ hierarchical architectures exhibited a high response and good selectivity to NO₂ at the optimal working temperature of 160 ℃.     

Effect of Nanoparticle Size on Gas-sensing Properties of Tin Dioxide Sensors

Sn(OH)₄ was prepared by the conventional solution precipitate method, followed by supercritical CO₂ drying. The resultant Sn(OH)₄ was divided into three aliquots and calcined at 400, 600 and 800℃, respectively, thus SnO₂ nanoparticles with average crystallite sizes of 5, 10 and 25 nm were obtained. Furthermore, three SnO₂ thick film gas sensors(denoted as sensors S-400, S-600 and S-800) were fabricated from the above SnO₂ nanoparticles. The adhesion of sensing materials on the surface of alumina tube is good. Compared to the sensors S-600 and S-800, sensor S-400 showed a much higher sensitivity to 1000 μL/L ethanol. On the other hand, sensor S-800 showed a much lower intrinsic resistance and improved selectivity to ethanol than sensors S-400 and S-600. X-Ray diffraction(XRD), transmission electron microscopy(TEM) and selective area electron diffraction(SAED) measurements were used to characterize the SnO₂ nanoparticles calcined at different temperatures. The differences in the gas sensing performance of these sensors were analyzed on the basis of scanning electron microscopy(SEM).     

Bi2Sn2O7 nanoparticles attached to SnO2 nanowires and used as catalysts

We introduce a simple method of synthesizing SnO₂ nanowire-Bi₂Sn₂O₇ nanoparticle composites based on the principle that SnO₂ nanowires can be grown by using Bi as catalysts. A mixture of Bi and Sn powders was thermally evaporated, and the effects of growth temperature on the morphology and structure of the products were investigated. We obtained Bi₂Sn₂O₇-tipped SnO₂ nanowires at 700 °C through a vapor–liquid–solid (VLS) process, whereas particle-free SnO₂ nanowires were produced at higher temperatures. We have investigated the oxygen sensing properties of the as-synthesized product.     

掺杂Eu2O3的SrTiO3及SnO2光致发光

用具有大能隙的本征半导体(SrTiO₃及SnO₂)粉末作本体,分别掺杂1%(原子百分数)的Eu₂O₃;所得物质表现出Eu³⁺离子的线发射光谱特性,但相对发光强度及光谱形状有相当大的变化。X射线衍射结构分析显示Eu³⁺在SrTiO₃晶格里是处在间隙位置,而它在SnO₂晶格里则形成新物相Eu₂Sn₂O₇。     

The surface and materials science of tin oxide

The study of tin oxide is motivated by its applications as a solid state gas sensor material, oxidation catalyst, and transparent conductor. This review describes the physical and chemical properties that make tin oxide a suitable material for these purposes. The emphasis is on surface science studies of single crystal surfaces, but selected studies on powder and polycrystalline films are also incorporated in order to provide connecting points between surface science studies with the broader field of materials science of tin oxide. The key for understanding many aspects of SnO₂ surface properties is the dual valency of Sn. The dual valency facilitates a reversible transformation of the surface composition from stoichiometric surfaces with Sn⁴⁺ surface cations into a reduced surface with Sn²⁺ surface cations depending on the oxygen chemical potential of the system. Reduction of the surface modifies the surface electronic structure by formation of Sn 5s derived surface states that lie deep within the band gap and also cause a lowering of the work function. The gas sensing mechanism appears, however, only to be indirectly influenced by the surface composition of SnO₂. Critical for triggering a gas response are not the lattice oxygen concentration but chemisorbed (or ionosorbed) oxygen and other molecules with a net electric charge. Band bending induced by charged molecules cause the increase or decrease in surface conductivity responsible for the gas response signal. In most applications tin oxide is modified by additives to either increase the charge carrier concentration by donor atoms, or to increase the gas sensitivity or the catalytic activity by metal additives. Some of the basic concepts by which additives modify the gas sensing and catalytic properties of SnO₂ are discussed and the few surface science studies of doped SnO₂ are reviewed. Epitaxial SnO₂ films may facilitate the surface science studies of doped films in the future. To this end film growth on titania, alumina, and Pt(1 1 1) is reviewed. Thin films on alumina also make promising test systems for probing gas sensing behavior. Molecular adsorption and reaction studies on SnO₂ surfaces have been hampered by the challenges of preparing well-characterized surfaces. Nevertheless some experimental and theoretical studies have been performed and are reviewed. Of particular interest in these studies was the influence of the surface composition on its chemical properties. Finally, the variety of recently synthesized tin oxide nanoscopic materials is summarized.     

A study on copper(II)-Schiff base-azide coordination complexes: Synthesis, X-ray structure and luminescence properties of [Cu(L)(N3)]X (L = Schiff bases; X = ClO4, PF6)

Two Schiff bases N,N′-(bis(pyridin-2-yl)benzylidene)propane-1,3-diamine (pbpd) and N,N′-(bis(pyridin-2-yl)formylidene)butane-1,4-diamine (pfbd) have been prepared and used to synthesize copper(II) complexes. Four complexes of the type [Cu(L)(N₃)]X (1–4) [L = pbpd; X = ClO₄ (1); L = pbpd; X = PF₆ (2); L = pfbd; X = ClO₄ (3); L = pfbd; X = PF₆ (4)] have been synthesized and characterized on the basis of microanalytical, spectroscopic, magnetic, electrochemical, luminescence and other physicochemical properties. Two representative complexes of the series, 2 and 3, have been characterized by single crystal X-ray diffraction measurements which reveal that in each complex the copper(II) ion assumes a distorted trigonal bipyramidal environment through coordination of the metal centre by two pyridine N atoms and two imine N atoms of the Schiff base with the fifth position occupied by a N atom of a terminal . They display intraligand ¹(π–π^*) fluorescence at room temperature and intraligand ³(π–π^*) phosphorescence in glassy solutions (MeOH at 77 K). A band (492 nm) observed for the complexes in their solid-state emission spectra is an excimeric emission arising due to an aromatic π–π interaction. Electrochemical electron transfer study reveals Cu^II–Cu^I reduction in methanolic solutions.     

PdO,Au, CdO修饰SnO2纳米纤维的制备及其气敏特性

采用静电纺丝的方法制备了SnO₂纳米纤维,并分别用PdO、Au、CdO对该纳米纤维材料进行表面修饰.用X射线衍射(XRD)、扫描电子显微镜(SEM)、X射线能谱(EDX)、X射线光电子能谱(XPS)分析、Brunauer-Emmett-Teller (BET)比表面积测试对材料进行表征.修饰前后, SnO₂纳米纤维都是由约15 nm的纳米颗粒构成的直径约为200 nm的多级结构材料.采用静态测试系统对纯SnO₂及不同物质修饰的SnO₂的气敏特性进行测试,结果表明,未修饰的SnO₂纳米纤维气敏元件对甲醛具有较好的响应.修饰后的SnO₂材料的气敏特性都有明显的改善. CdO修饰的SnO₂气敏元件对甲醛的响应值最高,且响应恢复时间短,选择性好. Au修饰的SnO₂气敏元件对甲醛响应的最佳工作温度从300 ℃降到了200 ℃.经PdO修饰后, SnO₂纳米纤维对甲苯的响应值变得最高.初步分析了经过修饰的SnO₂气敏材料的敏感机理.     

Band fluorescence of xenon

The Xe₂ emission band at 168 nm has been observed during irradiation of xenon gas with the 147 nm resonance line. The band is attributed to Xe₂ molecules formed by reaction between ground-state and metastable (2_u) xenon atoms.     

Rational Fabrication of Size Tunable SnO2 Hollow Microspheres

A designed solution route was developed to fabricate size tunable SnO₂ hollow microspheres based on the sol-gel theory. The hydrolysis of SnSO₄ released protons to form SnO₂ particulates and induced the decrease of pH value. To minimize the high surface energy, the SnO₂ particulates tended to assemble into large particles, the size of which was affected by the electrolyte concentration or pH value. Elevating SnSO₄ content aroused the decrease of the pH value that directed to the shrinkage of the aggregated particle size of SnO₂. Size tunable SnO₂ hollow microspheres were then rationally fabricated under solvothermal conditions via Ostwald ripening by simply adjusting the SnSO₄ concentration. The in situ pH decrease directed to the shrinkage of the particle size from 270 nm to 112 nm. The formation mechanism was confirmed and rationally elucidated by the time dependant morphology evolution. Charge-discharge tests revealed that the reduced particle size aroused an improved lithium ion battery performance.     

Anodic oxidation of formic acid on PdAuIr /C-Sb_2O_5·SnO_2 electrocatalysts prepared by borohydride reduction

PdAuIr/C-Sb2O5·SnO2electrocatalysts with Pd∶Au∶Ir molar ratios of 90∶5∶5,70∶20∶10 and 50∶45∶5 were prepared by borohydride reduction method.These electrocatalysts were characterized by EDX,X-ray diffraction,transmission electron microscopy and the catalytic activity toward formic acid electro-oxidation in acid medium investigated by cyclic voltammetry(CV),chroamperometry(CA)and tests on direct formic acid fuel cell(DFAFC)at 100℃.X-ray diffractograms of PdAuIr/C-Sb2O5·SnO2electrocatalysts showed the presence of Pd fcc phase,Pd-Au fcc alloys,carbon and ATO phases,while Ir phases were not observed.TEM micrographs and histograms indicated that the nanoparticles were not well dispersed on the support and some agglomerates.The cyclic voltammetry and chroamperometry studies showed that PdAuIr/C-Sb2O5·SnO2(50∶45∶5)had superior performance toward formic acid electro-oxidation at 25℃compared to PdAuIr/C-Sb2O5·SnO2(70∶20∶10),PdAuIr/C-Sb2O5·SnO2(90∶5∶5)and Pd/C-Sb2O5·SnO2electrocatalysts.The experiments in a single DFAFC also showed that all PdAuIr/C-Sb2O5·SnO2electrocatalysts exhibited higher performance for formic acid oxidation in comparison with Pd/C-Sb2O5·SnO2electrocatalysts,however PdAuIr/C-Sb2O5·SnO2(90∶5∶5)had superior performance.These results indicated that the addition of Au and Ir to Pd favor the electro-oxidation of formic acid,which could be attributed to the bifunctional mechanism(the presence of ATO,Au and Ir oxides species)associated to the electronic effect(Pd-Au fcc alloys).     

Surface states and resonances in field emission from low-index facets of clean tungsten

The energies, widths, and shapes of features observed in the total energy distributions in field emission from W(1 0 0) and W(1 1 1) are compared with the results of a full-potential LAPW calculation of the surface density of states based on a supercell model of the crystal structure at the metal–vacuum interface. The Swanson hump on W(1 0 0) is attributed to two bands of surface states and surface resonances of d_z² symmetry that are highly localised at , and a second peak observed at lower energy is attributed to a band of surface resonances, also of d_z² symmetry, centred at from along . The energy scale of the calculated total energy distribution is compressed by about 20% relative to the experimental data. The present calculation yields strong evidence that the broad asymmetric peak observed on W(1 1 1) is due to emission from a band of surface resonances. Further calculations for W(1 1 1) are proposed both to test the accuracy of the band model and to take into account the velocity factor that enters in a calculation of the emission current.     

纳米氧化锡在锌-硝基苯电池反应中的电催化

以氯化锡为原料,四丙基溴化铵为表面活性剂水热法制备纳米二氧化锡（SnO₂）催化剂,并以钛网为基材,制备催化电极. 应用SEM,XRD等手段对催化剂进行表征. 考察了反应物浓度、反应温度和反应时间对催化剂形貌的影响. 研究了纳米SnO₂催化剂对锌还原硝基苯原电池反应的电催化性能. 结果表明,当 NaOH浓度为0. 5 mol•L^-1、水热反应温度160 ℃、水热反应时间15 h时,得到的SnO₂催化剂是由纳米片构成的刺球状颗粒,粒径最小,约17 nm. 与平板铂电极相比,制备的催化电极对硝基苯电还原具有更高的催化活性,硝基苯转化率为74%,最大放电功率为21.9 mW•cm^-2,远大于平板铂电极. 硝基苯的主要还原产物为苯胺、对乙氧基苯胺和对氯苯胺.     

电泳法制备的致密氧化锡薄膜及其在高稳定性钙钛矿太阳能电池中的应用

在平面型钙钛矿太阳能电池中常采用SnO₂作为电子传输层材料,相应的SnO₂薄膜常采用溶液旋涂法制备。但是由于前驱液中的纳米颗粒可能会发生部分团聚、基底和溶液难以完全避免灰尘等杂质颗粒混入,且最佳的SnO₂电子传输层的厚度通常仅有约20 nm,所以这种方法制备的电子传输层难以保证严格致密和无纳米针孔。在本工作中,我们报道了一种电泳沉积制备致密SnO₂薄膜的方法,并用其有效地提高了钙钛矿太阳能电池的光电转换效率和工况稳定性。通过电泳法,表面带负电荷的SnO₂纳米颗粒在电场的作用下沉积到氧化铟锡(ITO)阳极表面,这种方法得到的薄膜比旋涂法制备的更为致密。将其应用于n-i-p结构的钙钛矿太阳能电池中,能够使得暗电流降低并抑制载流子的非辐射复合,从而提高电池的短路电流和开路电压,进而实现更高的光电转换效率(从18.17%提高到19.52%),且能消除迟滞效应。更重要的是,长期工况稳定性测试表明基于电泳-旋涂法制备的器件在1个太阳的光照下、最大功率点处连续工作960 h后,仍然能够保持71%的初始效率;然而基于旋涂法制备的器件在工作100 h后即降低到初始效率的70%。本工作提供了一种全新的SnO₂电子传输层的制备方法,显著地提高了器件性能和工况稳定性,后续有望应用于制备大面积器件和电池模组。     

Dy3+离子掺杂的全色荧光粉Ca9La(PO4)7的制备及发光特性

采用高温固相法合成了Ca₉La(PO₄)₇:Dy³⁺发光材料. 荧光粉的晶体结构和微观尺寸由X射线粉末衍射(XRD)仪和扫描电子显微镜(SEM)测定. 光致激发和发射光谱发光揭示了材料的光学特性. 实验结果显示: Ca₉La(PO₄)₇:Dy³⁺能够有效吸收紫外-可见光(300-460 nm)而被激发, 呈现一系列的吸收峰. 样品在350 nm近紫外光激发下, 有较强的蓝光(481 nm)和黄光(573 nm)两个窄带发射, 混合成优质的白光发射, 该白光色坐标在国际照明委员会(CIE)色品图中分布在无色点D65 (0.313, 0329)周围. 随着掺杂Dy³⁺离子的摩尔分数的增加, 两种发射均发生浓度猝灭现象, Dy³⁺离子的最佳掺杂为0.05(摩尔分数), 电偶极-电偶极相互作用是主要的猝灭机理.     

钛基金属氧化物电极制备及其氨氮废水降解性能

采用热分解方法制备了4种电极钛基金属氧化物：Ti/SnO₂+Sb₂O₃、Ti/SnO₂+Sb₂O₃/SnO₂+IrO₂、Ti/SnO₂+Sb₂O₃/SnO₂+RuO₂和Ti/SnO₂+Sb₂O₃/SnO₂+CeO₂. X-射线衍射分析表明Ti/SnO₂+Sb₂O₃/SnO₂+CeO₂电极的CeO₂晶体结构完好,连续工作较长时间电极表面没有明显析氧. 使用该电极电解氧化氨氮模拟废水（降解2 h）,氨氮模拟废水从高浓度（500 mg·L^-1）降解为较低浓度（180 mg·L^-1）,降解效率可达64%,电解活性最佳.     

Highly sensitive detection of transient absorption in dye-doped ultrathin polymer films by the TiO(2)/K(+) composite optical waveguide method upon pulsed laser excitation

A composite optical waveguide (OWG) composed of a 10–18 nm thick titanium dioxide (TiO₂) film sputtered on a conventional K⁺-doped optical waveguide was first applied to detect transient absorption of organic dyes in ultrathin polymer films upon excitation with ns laser. The thickness of the TiO₂ film considerably affected the relative sensitivity of the composite OWG. The composite OWG with 10 nm thick TiO₂ gave much stronger transient absorption for 30–415 nm thick polymer films containing organic dyes than that with 18 nm TiO₂. Transient absorption of phthalocyanine and spiropyran in 20–135 nm thick polymer films was detected 3–20 times more sensitively by the composite OWG with 10 nm TiO₂ than the conventional K⁺-doped OWG which showed a 150-fold sensitivity as compared with the usual normal incidence method. The relative sensitivity of the composite waveguide was also affected by the thickness and refractive index of polymers.     

Matrix isolation and theoretical study of the photochemical reaction of CH3CN with CrO2Cl2 and OVCl3

The matrix isolation technique has been combined with theoretical calculations to identify and characterize the photoproducts in the reactions of CH₃CN with CrCl₂O₂ and OVCl₃. Twin jet co-deposition of these reagents led to the formation of a 1:1 molecular complex which was observed using UV/visible spectroscopy. Irradiation of these matrices with light of λ>300 nm led to the observation of new bands in the infrared spectra, the most intense of which was seen at 1942 cm⁻¹ for the CrCl₂O₂/CH₃CN system. The product bands are assigned to the ²η complexes of acetonitrile n-oxide with CrCl₂O and VCl₃, respectively. Identification of these species was supported by extensive isotopic labeling (²H and ¹⁵N), as well as by B3LYP/6-311++G(d,2p) density functional calculations.