Direct formation of SiO<Subscript>2</Subscript>/SnO<Subscript>2</Subscript> composite nanoparticles with high surface area and high thermal stability by sol–gel-hydrothermal process

SnO₂/SiO₂ composite nanoparticles were prepared by sol–gel-hydrothermal process and their physico-chemical structure and photocatalytic property were investigated. The results of XRD, TEM and FT-IR indicated that SnO₂ crystallites with the tetragonal rutile structure were well-developed directly during hydrothermal process. The SnO₂/SiO₂ composite nanoparticles owned narrow size distribution, large specific surface area, and good thermal stability. As the presence of 25.0 wt% SiO₂, the SnO₂ nanoparticles were about 4.0 nm in diameter and the specific surface area was 259.0 m²/g. After calcination at 800 °C, the crystalline grain size maintained 16.2 nm and the surface area still remained 132.6 m²/g. The SnO₂/SiO₂ composite nanoparticles showed better photocatalytic activity than pure SnO₂ nanoparticles.     

Mesoporous organo-silica nanoarray for energy storage media

A SnO₂–mesoporous organo-silica nanoarray (MOSN) composite was prepared by surfactant mediated synthesis combined with a sol–gel vacuum suction method in which SnO₂ has been successfully incorporated inside the periodic nanoholes in the MOSN or coated on its surface. The MOSN with a high aspect ratio of length to width could not only maintain its structure but also effectively accommodate the volume expansion of the SnO₂ during electrochemical reactions with Li⁺. The SnO₂–MOSN composite showed a higher reversible capacity of 420 mA h g⁻¹ with greatly improved capacity retention and lower initial irreversible capacity compared to SnO₂ powder. This interesting anodic performance of SnO₂–MOSN composite supports the potential use of MOSN for lithium ion batteries.     

单分散SnO2中空微纳米球的制备和性质

模板法是制备无机中空微纳米球的重要方法之一. 本文以苯乙烯为单体, 通过乳液聚合得到粒径约为620 nm的单分散聚苯乙烯(PS)微球. 以磺化后的聚苯乙烯(PSS)微球为模板, 利用阴阳离子静电吸附作用, 将PSS与前驱体SnSO₄中的Sn²⁺结合. 通过Sn²⁺在乙醇-水介质中的水解作用得到核-壳复合结构, 再经高温煅烧, 得到SnO₂中空微纳米球. 实验对前驱体的浓度、表面活性剂的用量、反应时间及模板选择等方面做了研究,通过扫描电镜(SEM)、X 射线衍射(XRD)、红外(IR) 光谱、热重分析(TGA)、H₂ 程序升温还原(H₂-TPR)、Brunauer-Emmett-Teller (BET)比表面积等技术深入探究SnO₂中空微纳米球的结构, 并对比中空SnO₂与实心粒子的氧化还原特性. BET和H₂-TPR显示将SnO₂制备成微纳米空心球后其比表面积增大, 表面氧空位明显增多, 氧化活性明显提高. 从IR 及XRD推断核-壳结构形成机理, 进而优化出简单合理的实验方案, 获得表面光滑、结构致密, 包覆厚度可控的SnO₂中空微纳米球.     

Synthesis of mesoporous SnO2 nanomaterials with selective gas-sensing properties

Using SBA-15/KIT-5/KIT-6 as the hard templates, the mesoporous SnO₂ nanomaterials with different structures were synthesized by nanocasting. X-ray diffraction, transmission electron microscopy, and nitrogen adsorption isotherms were used to testify their structure characteristics. These mesoporous SnO₂ nanomaterials showed high specific surface areas (57–96 m² g^?1) and pore volume (0.17–0.27 cm³ g^?1). The nanopore of these templates makes the nanosize particle of the final mesoporous SnO₂ nanomaterials (4–9 nm) at last. The sensing properties of acetone, ethyl alcohol and methyl alcohol were investigated. The response of SnO₂-15, SnO₂-5, and SnO₂-6 are 17.0, 19.5, and 16.1, respectively as the concentration of ethyl alcohol on 200 ppm. The sensitivity of SnO₂-5 is 28.2 as the concentration of acetone was increased to 200 ppm. With the large surface area, high pore volume, and nanosized particles (close to 2 L = 6 nm of SnO₂), the SnO₂-5 show four fold enhancement in sensitivity compared to commercial SnO₂ powder and low detection limit (even at 200 ppb). The surface area and particle size play a significant party in the gas response. With the large surface area and smallest particle size, SnO₂-5 shows the highest sensitivity of all. These mesoporous nanomaterials show well potential application on the gas response.     

Opal and inverse opal photonic crystals: Fabrication and characterization

Three-dimensional photonic crystals made of close-packed polymethylmethacrylate (PMMA) spheres or air spheres in silica, titania and ceria matrices have been fabricated and characterized using SEM, XRD, Raman spectroscopy and UV–Vis transmittance measurements. The PMMA colloidal crystals (opals) were grown by self-assembly from aqueous suspensions of monodisperse PMMA spheres with diameters between 280 and 415 nm. SEM confirmed the PMMA spheres crystallized uniformly in a face-centred cubic (fcc) array, and UV–Vis measurements show that the colloidal crystals possess pseudo photonic band gaps in the visible and near-IR regions. Inverse opals were prepared by depositing silica (SiO₂), titania (TiO₂) or ceria (CeO₂) in the voids of the PMMA colloidal crystals using sol-gel procedures, then calcining the resulting structure at 550 °C to remove the polymer template. The resulting macroporous materials showed fcc ordering of air spheres separated by thin frameworks of amorphous silica, nanocrystalline titania or nanocrystalline ceria particles, respectively. Optical measurements confirmed the photonic nature of the inverse opal arrays. UV–Vis data collected for the opals and inverse opals obeyed a modified Bragg’s law expression that considers both diffraction and refraction of light by the photonic crystal architectures. The versatility of the colloidal crystal template approach for the fabrication of macroporous oxide structures is demonstrated.     

High‐Loading Nano‐SnO2 Encapsulated in situ in Three‐Dimensional Rigid Porous Carbon for Superior Lithium‐Ion Batteries

Tin oxide nanoparticles (SnO₂ NPs) have been encapsulated in situ in a three‐dimensional ordered space structure. Within this composite, ordered mesoporous carbon (OMC) acts as a carbon framework showing a desirable ordered mesoporous structure with an average pore size (≈6 nm) and a high surface area (470.3 m² g^?1), and the SnO₂ NPs (≈10 nm) are highly loaded (up to 80 wt %) and homogeneously distributed within the OMC matrix. As an anode material for lithium‐ion batteries, a SnO₂@OMC composite material can deliver an initial charge capacity of 943 mAh g^?1 and retain 68.9 % of the initial capacity after 50 cycles at a current density of 50 mA g^?1, even exhibit a capacity of 503 mA h g^?1 after 100 cycles at 160 mA g^?1. In situ encapsulation of the SnO₂ NPs within an OMC framework contributes to a higher capacity and a better cycling stability and rate capability in comparison with bare OMC and OMC ex situ loaded with SnO₂ particles (SnO₂/OMC). The significantly improved electrochemical performance of the SnO₂@OMC composite can be attributed to the multifunctional OMC matrix, which can facilitate electrolyte infiltration, accelerate charge transfer, and lithium‐ion diffusion, and act as a favorable buffer to release reaction strains for lithiation/delithiation of the SnO₂ NPs.     

Highly efficient dye-sensitized SnO2 solar cells having sufficient electron diffusion length

Dye-sensitized solar cells (DSCs) were fabricated from mesoporous SnO₂ electrodes, which were prepared from nano-sized SnO₂ particles. Current–voltage characteristics of the DSCs were compared with DSCs prepared from conventional TiO₂ electrodes, which have similar amount of adsorbed dye with the SnO₂. As a result, short-circuit current of the SnO₂DSC were comparable with that of the TiO₂DSCs, and more than 15 mA/cm² was obtained with the SnO₂ at the thickness of 10 μm under one sun conditions. Electron diffusion coefficients and lifetimes in the SnO₂ and TiO₂ electrodes were measured, showing slower diffusion and longer lifetime in the SnO₂DSC than in the TiO₂. The results imply that the electron transport and transfer dynamics in such electrodes is dominated by the influence of intra-band charge traps, and the control of the trap conditions would be the key strategy to employ various metal oxides for such solar cells.     

Effect of yttrium on the formation of nanostructured mesoporous CeO<Subscript>2</Subscript>

Mesoporous CeO₂ and yttrium doped CeO₂ (YDC) were prepared by a sol–gel process and characterized by a variety of techniques. XRD patterns showed that the undoped and doped samples had a cubic fluorite structure. The grain size decreased from 24.8 to 6.1 nm at 500 °C for pure CeO₂ and YDC, respectively. N₂ adsorption–desorption isotherms showed that the samples possessed typical mesopore characteristics. The BET specific surface area of the samples increased from 23.04 to 151.49 m²/g for 300 °C calcination after mesoporous CeO₂ was doped with Y. It is found that the introduction of Y can inhibit the grain growth, and the presence of the pores also can be related to this obstacle to grain growth. These results are of great significance for the control of porous microstructure, crystallinity, and applications for the development of nanostructured mesoporous materials.     

Optical and electrical conducting properties of Polyaniline/Tin oxide nanocomposite

Polyaniline(PANI)/Tin oxide (SnO₂) hybrid nanocomposite with a diameter 20–30 nm was prepared by co-precipitation process of SnO₂ through in situ chemical polymerization of aniline using ammonium persulphate as an oxidizing agent. The resulting nanocomposite material was characterized by different techniques, such as X-ray diffraction (XRD), Transmission Electron Microscopy (TEM), Fourier Transform Infrared spectroscopy (FT-IR) and Ultraviolet–Visible spectroscopy (UV–Vis), which offered the information about the chemical structure of polymer, whereas electron microscopy images provided information regarding the morphology of the nanocomposite materials and the distribution of the metal particles in the nanocomposite material. SEM observation showed that the prepared SnO₂ nanoparticles were uniformly dispersed and highly stabilized throughout the macromolecular chain that formed a uniform metal-polymer nanocomposite material. UV–Vis absorption spectra of PANI/SnO₂ nanocomposites were studied to explore the optical behavior after doping of nanoparticles into PANI matrix. The incorporation of SnO₂ nanoparticles gives rise to the red shift of π–π¹ transition of polyaniline. Thermal stability of PANI and PANI/SnO₂ nanocomposite was investigated by thermogravimetric analysis (TGA). PANI/SnO₂ nanocomposite observed maximum conductivity (6.4 × 10^?3 scm^?1) was found 9 wt% loading of PANI in SnO₂.     

Preparation of a large Mesoporous CeO2 with crystalline walls using PMMA colloidal crystal templates

Inverse opals of crystalline CeO₂ were synthesized by using close-packed poly(methyl methacrylate) (PMMA) latex spheres of various sizes as templates, resulting in pore sizes, which could be scaled down even to the mesopore region (30–40 nm). The latex spheres were synthesized by emulsion polymerization, and the PMMA particle size could be substantially decreased by addition of sodium dodecyl sulfate (SDS) as surfactant. Owing to the larger pore wall thickness, the CeO₂ with large mesopores preserves an intact porosity to higher temperatures than previously reported mesoporous CeO₂ obtained from surfactant templates. The porosity and crystallinity were studied by microscopic techniques, wide angle X-ray diffraction (XRD), N₂ sorption, and Hg porosimetry. The evolution of crystallinity (crystallite size and lattice parameters) was determined for different annealing temperatures by means of Rietveld refinements of the XRD data. Thereby, our study allowed getting general insights into the crystallization behavior of sol–gel derived porous CeO₂ frameworks.     

Synthesis of hierarchical shell-core SnO2 microspheres and their gas sensing properties

Using SnSO₄, d-glucose, urea and water, hierarchical shell-core SnO₂ microspheres were successfully synthesized via a simple hydrothermal method. The characterization results showed that the sizes of as-prepared SnO₂ microspheres were 0.6–1 μm, with shell thicknesses of 40−60 nm. The shell and large core of the SnO₂ microspheres were all comprised of the same basic rice-like nanoparticles with diameters of 16−25 nm and lengths of 16−45 nm. Further investigaton showed that the glucose and urea served as structural guiding agents, and urea facilitated the formation of the hierarchical structure. The as-prepared SnO₂ nanomaterials were used to fabricate a gas sensor with an electrode blade used for the gas sensitivity tests. The hierarchical shell-core SnO₂ microspheres exhibited high sensitivity and selectivity toward ethanol, with a responsivity of 63.8 for 50 ppm ethanol at 250 °C, while the response and recovery time were 7 s and 28 s respectively. Moreover, the responsivity of the materials showed good linearity at ethanol concentrations from 500 ppb to 10 ppm. The simple synthetic method, environmentally-friendly raw materials, and excellent gas sensitivity demonstrate that the as-prepared SnO₂ nanomaterial has great potential applications for the sensing of ethanol gas.     

ZIF-8 derived nano-SnO2@ZnO as anode for Zn/Ni secondary batteries

SnO₂@ZnO was synthesized by a new method involving the immobilization of Sn onto zeolitic imidazolate framework-8 (ZIF-8) followed by calcination. The synthesized nanoparticles were characterized as 20–30 nm spherical ZnO particles uniformly dotted with SnO₂. When SnO₂@ZnO were used as anode material for Zn/Ni batteries, the average specific capacity was approximately 600 mAh g^− 1 and remained stable after 150 cycles at a rate of 1 C.     

Polyaniline(PANI) coated Zn2SnO4 cube as anode materials for lithium batteries

Zn₂SnO₄@PANI composites were synthesized via a micro emulsion polymerization method. The outer surfaces of monodispersed cubes are covered with amorphous aggregated PANI. The addition of PANI can create a buffering structure for Zn₂SnO₄ cubes. Compared with Zn₂SnO₄ cubes, Zn₂SnO₄@PANI composites show an improved electrochemical performance (491.0 mAh g^?1 at a current density of 600 mAg^?1 after 50 cycles). It is believed that PANI coating is a simple and effective way to improve the cycling performance for lithium batteries.     

Compressibility and structural behavior of pure and Fe-doped SnO2 nanocrystals

We have performed high-pressure synchrotron X-ray diffraction experiments on nanoparticles of pure tin dioxide (particle size ∼30 nm) and 10 mol % Fe-doped tin dioxide (particle size ∼18 nm). The structural behavior of undoped tin dioxide nanoparticles has been studied up to 32 GPa, while the Fe-doped tin dioxide nanoparticles have been studied only up to 19 GPa. We have found that both samples present at ∼13 GPa a second-order structural phase transition from the ambient pressure tetragonal rutile-type structure (P4₂/mnm) to an orthorhombic CaCl₂-type structure (space group Pnnm). No phase coexistence was observed for this transition. Additionally, pure SnO₂ presents a phase transition to a cubic structure at ∼24 GPa. The evolution of the lattice parameters with pressure and the room-temperature equations of state are reported for the different phases. The reported results suggest that the partial substitution of Sn by Fe induces an enhancement of the bulk modulus of SnO₂. Results are compared with previous studies on bulk and nanocrystalline SnO₂. The effects of pressure on Sn-O bonds are also analyzed.     

Structural and electrochemical properties of a porous nanostructured SnO2 film electrode for lithium-ion batteries

A B₂O₃-doped SnO₂ thin film was prepared by a novel experimental procedure combining the electrodeposition and the hydrothermal treatment, and its structure and electrochemical properties were investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) analysis, energy dispersive X-ray (EDX) spectroscopy and galvanostatic charge–discharge tests. It was found that the as-prepared modified SnO₂ film shows a porous network structure with large specific surface area and high crystallinity. The results of electrochemical tests showed that the modified SnO₂ electrode presents the largest reversible capacity of 676 mAh g^?1 at the fourth cycle, close to the theoretical capacity of SnO₂ (790 mAh g^?1); and it still delivers a reversible Li storage capacity of 524 mAh g^?1 after 50 cycles. The reasons that the modified SnO₂ film electrode shows excellent electrochemical properties were also discussed.     

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.     

Effect of synthesis conditions on the structure and sorption properties of films based on mesoporous tin dioxide

We have conducted a comparative study of the synthesis conditions for mesoporous materials and films based on tin dioxide in the presence of different types of templates, and we have studied their thermal stability and sorption properties. We demonstrate the advantage of using alcoholic reaction media and nonionic templates (triblock copolymers Pluronic-123 and Pluronic-127) to obtain thin films of mesoporous SnO₂ with relatively high parameters for the porous structure (V_meso = 0.15 cm³/g, S_BET = 147 m²/g) and cassiterite crystallite sizes down to 2.7 nm, significantly smaller than the thickness of the walls.     

Synthesis and crystal structure of the A6B5O18 perovskite-like compounds

New members of the A_nB_n−1O_3n perovskite-like family (Ba₅KNb₅O₁₈ and Sr₆Nb₄SnO₁₈ compounds) with n = 6 have been synthesized and studied by the X-ray powder diffraction. Their crystal structures were found to belong to the Ba₆Nb₄TiO₁₈-type with a = 0.57840(7) nm, c = 4.2532(5) nm and a = 0.5661(1) nm, c = 4.186(1) nm for Ba₅KNb₅O₁₈ and Sr₆Nb₄SnO₁₈, respectively. It was shown that Ba and K (A-atoms) are completely disordered in the crystal structure of Ba₅KNb₅O₁₈ compound. But Nb and Sn atoms (B-atoms) in the crystal structure of the Sr₆Nb₄SnO₁₈ compound are quite ordered with the preferred Sn⁺⁴ and Nb⁵⁺ cations localization in the center of perovskite-like block and on the boundaries of these blocks, respectively. Temperature and frequency dependencies of the real components of electric conductivity σ^I and dielectric permeability ɛ^I; specific electric conductivity at the direct current σ_dc have been obtained by the impedance spectroscopy method for Sr₆Nb₄SnO₁₈.     

Combination of microspheres and sol-gel electrophoresis for the formation of large-area ordered macroporous SiO2

A simple and effective fabrication scheme involving sequential electrophoretic depositions of polystyrene (PS) microspheres (500 nm and 1 μm in diameter) and SiO₂ sols (~ 5 nm in diameter) to produce large-area ordered macroporous SiO₂ inverse opals (2 × 2 cm²) on ITO substrates is demonstrated. The zeta potentials for PS microsphere suspension and SiO₂ sols are measured to determine an optimized processing window in which both samples carry negative surface charges and sol-gel transformation can be properly implemented. Our approach entails the electrophoresis of PS microspheres to render a colloidal crystal with negligible defects. Afterward, SiO₂ sols are infiltrated to the interstitial voids among the closely-packed PS microspheres via another electrophoresis process, followed by an oxidation treatment to remove the PS colloidal template and complete the densification of SiO₂ gels. The resulting SiO₂ inverse opals reveal impressive surface uniformity and structural integrity. Fourier transform infrared spectroscopy confirms the complete removal of PS microspheres, leaving an intact SiO₂ skeleton, whereas X-ray diffraction pattern indicates its amorphous nature.     

Mesoporous and nanocrystalline sol–gel derived NiTiO3 at the low temperature: Controlling the structure,size and surface area by Ni:Ti molar ratio

Nanocrystalline nickel titanate (NiTiO₃) thin films and powders with mesoporous structure were produced at the low temperature of 500 °C by a straightforward particulate sol–gel route. The sols were prepared in various Ni:Ti molar ratios. X-ray diffraction and Fourier transform infrared spectroscopy revealed that the powders contained mixtures of the NiTiO₃ and NiO phases, as well as the anatase-TiO₂ and the rutile-TiO₂ depending on the annealing temperature and Ni:Ti molar ratio. Moreover, it was found that Ni:Ti molar ratio influences the preferable orientation growth of the nickel titanate, being on (202) planes for the nickel dominant powders (Ni:Ti ≥ 75:25) and on (104) planes for the rest of the powders (Ni:Ti: ≤ 50:50). The average crystallite size of the powders annealed at 500 °C was in the range 1.5–2.4 nm and a gradual increase occurred up to 8 nm by heat treatment at 800 °C. The activation energy of crystal growth decreased with an increase of Ni:Ti molar ratio, calculated in the range 24.93–37.17 kJ/mol. Field emission scanning electron microscope analysis revealed that the deposited thin films had mesoporous and nanocrystalline structure with the average grain size of 20–35 nm. Moreover, atomic force microscope images presented that the thin films had a hill-valley like morphology with roughness mean square in the range 41–57 nm. Based on Brunauer–Emmett–Taylor analysis, the synthesized powders showed mesoporous structure containing pores with needle and plate like shapes. The mesoporous structure of the powders was stable at high annealing temperatures and one of the highest surface areas (i.e., 156 m²/g) reported in the literature was obtained for the powder containing Ni:Ti = 50:50 at 500 °C.