Photocatalytic property of TiO2 loaded with SnO2 nanoparticles

2.5 nm-sized SnO₂ nanoparticles in rutile phase were loaded on the surface of 25 nm-sized TiO₂ (Degussa P-25) to form SnO₂/TiO₂ nano-composite structure. Up to 10 mol%, the loaded SnO₂ nanoparticles were well-dispersed on the surface of TiO₂ without mutual agglomeration. The SnO₂/TiO₂ with 1 mol% of SnO₂ demonstrated 1.5–1.7 times of photocatalytic activity compared to the pure TiO₂ in decomposing gaseous 2-propanol and in evolving CO₂. The role of SnO₂ nanoparticles on TiO₂ surface is considered to be retardation of recombination rate between electrons and holes by trapping the photo-excited electrons from the conduction band of TiO₂.     

Selective Gas Detection of SnO2-TiO2 Gas Sensors

The composite, consisting of two materials with different sensing temperatures, may show the selectivity for a particular gas. In this study, the microstructural and compositional effects on the electrical conductivity and the CO and the H₂ gas sensing properties of SnO₂-TiO₂ composites were examined. SnO₂-TiO₂ composites in entire (0–100 mol%) composition range were fabricated in the form of porous pellet by sintering at 800C for 3 h. The effects of CuO-coating (or doping) on the electrical conductivity and the sensing properties to 200 ppm CO and H₂ gases were examined.With CuO-coating, SnO₂-TiO₂ composites showed the increased sensitivity to CO gas and a large difference in the sensing temperatures between CO and H₂ gases. As a result, CuO-coated SnO₂-TiO₂ composites showed the selectivity for CO gas between 100C and 190C and the selectivity for H₂ gas between 280C and 380C.     

Low operating temperature CO sensor prepared using SnO<Subscript>2</Subscript> nanoparticles

A low operating temperature CO (carbon monoxide) sensor was fabricated from a nanometer-scale SnO₂ (tin oxide) powder. The SnO₂ nanoparticles in a size range 10–20 nm were synthesized as a function of surfactant (tri-n-octylamine, TOA) addition (0–1.5 mol%) via a simple thermal decomposition method. The resulting SnO₂ nanoparticles were first screen-printed onto an electrode patterned substrate to be a thick film. Subsequently, the composite film was heat-treated to be a device for sensing CO gas. The thermal decomposed powders were characterized by field-emission scanning electron microscopy (FESEM), X-ray diffractometry (XRD), and surface area measurements (BET). The CO-sensing performance of all the sensors was investigated. The experimental results showed that the TOA addition significantly decreased the particle size of the resulting SnO₂ nanoparticle. However, the structure of the powder coating was crucial to their sensing performance. After heat-treatment, the smaller particle tended to cause the formation of agglomeration, resulting in the decline of surface area and reducing the reaction site during sensing. However, the paths for the sensed gas entering between the agglomerated structure may influence the sensing performance. As a CO sensing material, the SnO₂ nanoparticle (~12 nm in diameter) prepared with 1.25 mol% TOA addition exhibited most stable electrical performance. The SnO₂ coating with TOA addition >0.75 mol% exhibited sensor response at a relatively low temperature of <50°C.     

SnO2 nanocrystallines decorated g-C3N4 composites with enhanced visible-light photocatalytic activity

Abstract

A series of SnO₂ nanocrystallines decorated g-C₃N₄ architectures were synthesized using a facile solvothermal method. The structural, morphological, and optical properties of the as-prepared nanocomposites were characterized in detail, indicating that SnO₂ nanocrystallines with diameter ～ 4?nm were well-dispersed on the surface of g-C₃N_4. The photocatalytic activity of the composites was investigated by degrading rhodamine B (RhB) under visible light irradiation. The CNS2 heterostructure exhibits enhanced photocatalytic activity than bare SnO₂ and g-C₃N₄. Kinetic study revealed a promising degradation rate constant of 0.0593?min^?1 for the CNS2, which is 118 and 7 times higher than that of pure SnO₂ and g-C₃N₄, respectively. What’s more, the CNS2 still retained the photocatalytic activity after three cycle measurements. The enhanced photocatalytic performances of the nanocomposite may be due to its large surface area (116.2 m²/g), appropriate ratio of SnO₂/g-C₃N₄ and the compact structure of the junction between the SnO₂ nanocrystallines and the g-C₃N₄, which inhibits the recombination of photogenerated electrons and holes.     

Effect of Sn/Zn ratio on structure and photoluminescence properties of SnO2@ZnO composites

ABSTRACT

The SnO₂@ZnO composites, with Sn/Zn molar ratio (Sn/Zn–ratio) from 4:1 to 8:1, were successfully prepared via two–step hydrothermal method. The microstructure and morphology of the as–prepared Sn/Zn–ratio–dependence SnO₂@ZnO composites were investigated. Furthermore, a reasonable growth mechanism of SnO₂@ZnO composites was proposed and the results indicated that the dispersity of SnO₂ nanowires on the ZnO nanorods surface was obviously influenced by the Sn/Zn–ratio. The photoluminescence (PL) properties of the Sn/Zn–ratio–dependence SnO₂@ZnO composites were investigated. The results showed the opposite intensity change of ultraviolet (UV) and visible emission while the Sn/Zn–ratio increased. In addition, the possible emission mechanisms were also discussed that the UV emission is attributed to free–exciton recombination at the near–band edge and the potential difference between SnO₂ and ZnO result in the visible emission.     

Study of PEDOT:PSS-SnO2 nanocomposite film as an anode for polymer electronics

Poly(3,4-ethylenedioxythiophene) oxidized with poly(4-styrenesulfonate)(PEDOT:PSS) is a candidate material for applications in molecular electronics, such as organic field effect devices, organic photovoltaics, and organic light emitting devices. The properties of 3.5–4.0 nm sized SnO₂ nanoparticles doped PEDOT:PSS films were investigated for anode application. Sheet resistance was decreased and rms roughness was slightly increased with the incorporation of SnO₂ nanoparticles. However, the connectivity of conducting grains was improved by the plasticizing effect of surface –OH groups of SnO₂ nanoparticle. Using photoemission spectroscopy and near edge X-ray absorption fine structure (NEXAFS), the electronic structure of the films is studied comparatively on the C 1s NEXAFS, secondary electron emission cut off, and valence band spectra. The start of electron emission retarded and valence band maximum was increased in the PEDOT:PSS-SnO₂ nanocomposite films. These changes in the electronic structure resulted from emitted electron screening of core-hole in the PEDOT:PSS energy band and electron donation of SnO₂ nanoparticles.     

Poly(Butylene Terephthalate) Filled with Sb2O3 Nanoparticles: Effects of Particle Surface Treatment,Particle Size,Particle Morphology and Particle Loading on Mechanical Properties of Composites

Abstract

Poor dispersion of nanoparticles in polymer matrix would limit the development and application of particulate-filled polymer composites. Therefore, the Sb₂O₃ nanoparticles were functionalized by a combination of cetyltrimethyl ammonium bromide (CTAB) and silane coupling agent KH-560 via water bath modification method so as to improve the dispersion of Sb₂O₃ nanoparticles in poly(butylene terephthalate) (PBT) matrix and enhance the interfacial adhesion between nanoparticles and polymer matrix. Besides, the coating efficiency of compound modifiers on the surface of Sb₂O₃ nanoparticles was characterized by Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA). The Sb₂O₃ nanoparticles with different morphologies were systemically measured using transmission electron microscopy and dynamic light scattering measurement. The effects of particle surface treatment, particle size, particle morphology and particle loading on mechanical properties of composites were studied by the X-ray diffraction (XRD), tensile test machine and impact strength machine. The tensile strength of nanocomposites gradually increases with decreasing the particle size at the same amount of Sb₂O₃ nanoparticle fillers, which is attributed to improvement of interfacial contact area and stronger interfacial adhesion between Sb₂O₃ nanoparticles and PBT matrix. And the compound modified Sb₂O₃ nanoparticles are homogeneously dispersed in PBT matrix and play an important role in the properties enhancement. Moreover, taking consideration of the tensile and impact strengths, the optimal loading is 3?wt%.     

Effect of Precursor Concentration on Physical Properties of Cube-Like Zn2SnO4 Powders Synthesized by Co-Precipitation Method

Cube-like Zinc stannate (Zn₂SnO₄) spinel powders were synthesized by co-precipitation method using chloride starting precursors of zinc and tin. The influence concentration of precursors on relevant physical properties of Zn₂SnO₄ was investigated by increasing concentration of precursor material at 0.1 to 0.4 M (Zn:Sn at ratio 1:1). Structural properties of as-synthesized and Zn₂SnO₄ crystal were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and X-ray absorption spectroscopy (XAS). The results indicate that as-prepared material without calcination process is in cubic symmetry of zinc hydroxy stannate (ZnSn(OH)₆) affirmed by SEM and XRD results. Meanwhile, spinel phase of Zn₂SnO₄ with strong crystalline and eminent cubic structure can be achieved after calcination at 1000°C. Homogenous dispersion, high crystallinity and good cubic structure of Zn₂SnO₄ powders are occurred at higher concentration of precursors. Moreover, the oxidation state of these samples were investigated by the Zn K-edge and Sn L3-edge X-ray absorption near edge structure (XANES) using the synchrotron radiation light source. The analyses of XANES spectra revealed that the oxidation state of Zn was +2 and Sn valence was +4 in all Zn₂SnO₄ samples, which well corresponds to the theoretical values.     

Effect of SnO2 on improvement on the microwave dielectric properties of Ba2Ti9O20

Effect of SnO₂ addition on the crystal structure/microstructure and the related microwave dielectric properties of the Ba₂Ti₉O₂₀ were systematically investigated. Incorporation of SnO₂ markedly stabilized the phase constituent and microstructure for the Ba₂Ti₉O₂₀ such that high quality materials can be obtained in a much wider processing window. The sintered density of the Ba₂Ti₉O₂₀ increased linearly, but the microwave dielectric constant (K) decreased monotonically, with the SnO₂ doping concentration. The quality factor (Qxf) of the materials increased firstly due to the addition of SnO₂, but decreased slightly with further increase in SnO₂ content. The best microwave dielectric properties obtained are K = 38.5 and Qxf = 31,500 GHz, which occurs for the 0.055 mol SnO₂-doped and 1350 °C/4 h sintered samples. These properties are markedly better than those for undoped materials (K = 38.8 and Qxf = 26,500 GHz).     

Sintering and varistor behaviour of SnO2-Zn2SnO4 composite ceramics

Densified SnO₂-Zn₂SnO₄ composite ceramics were prepared by conventional ceramic processing and the sintering, electrical properties were investigated. The X-ray diffraction results and sintering curves showed that the pellets pressed by ZnO and SnO₂ mixed powders began to shrink after Zn₂SnO₄ was synthesized at about 950 °C. The results suggest that the densification of SnO₂-Zn₂SnO₄ composite ceramics cannot be attributed to the oxygen vacancies created by acceptor doping as traditional viewed. The measurement of J-E curves showed that the SnO₂-Zn₂SnO₄ composite ceramics have good nonlinear properties (α?~?3.9–4.5) without any other doping. Another interesting result is that the composite ceramics have low breakdown electrical field (E _B?~?10 V/mm) with high relative dielectric constant (1 kHz, ε _r?~?6?×?10³). Further studies demonstrate that the varistor behavior is also a grain boundary barrier effect and the barrier height is about 0.84 eV.     

Synthesis and Characterization of Bi-Fe-O Amorphous Nanoparticles for Photocatalysis by Sol-Gel Method

Abstract

Bi-Fe-O amorphous nanoparticles were synthesized via a facile sol-gel method using tartaric acid as the chelating agent. The samples were characterized by X-ray diffraction (XRD), transmission electron microscope (TEM) and UV-vis. Photocatalysis of Bi-Fe-O amorphous nanoparticles was further examined by monitoring the degradation of Rhodamine B dye in an aqueous solution under visible light irradiation with H₂O₂. It was proved that Bi-Fe-O amorphous nanoparticles showed higher degradation rate under visible-light irradiation with H₂O₂ than without H₂O₂.     

Preparation of SnO2 whiskers via the decomposition of tin oxalate

A new method for preparing SnO₂ whiskers by the decomposition of SnC₂O₄ is suggested. A Whisker-like morphology of a SnC₂O₄ precipitate was attained via the gradual addition of an oxalic acid solution to a hot SnCl₂ aqueous solution (T > 50^∘C). In comparison, when the solution temperature was either lower than 50^∘C or when ethanol was used as the solvent, the SnC₂O₄ precipitate showed an angular and relatively isotropic morphology. The morphology of the SnC₂O₄ precipitate remained even after its thermal decomposition into SnO₂ at 400^∘C indicating that SnC₂O₄ precipitation is a key step in preparing the whiskers. The formation mechanism of SnO₂ whiskers was explained by the supersaturation during the precipitation of SnC₂O₄.     

MEMS-based microheaters integrated gas sensors

Abstract

In the present work efforts have been made to develop microheater integrated gas sensors with low power consumption. The design and simulation of a single-cell microheater is carried out using ANSYS. Low power consumption (<35?mW) platinum micro-heater has been fabricated using bulk micromachining technique on silicon dioxide membrane (1.5?μm thin), which provided improved thermal isolation of the active area of 250?×?250?μm². The micro-heater has achieved a maximum temperature of ～950?°C at an applied dc voltage of 2.5 V. Fabricated mircro-heater has been integrated with SnO₂ based gas sensors for the efficient detection of H₂ and NO₂ gases. The developed sensors were found to yield the maximum sensing response of ～184 and ～2.1 with low power consumption of 29.18 and 34.53?mW towards the detection of 1?ppm of NO₂ gas and 500?ppm of H₂ gas, respectively.     

The fabrication,characterization of honeycomb-type porous Ag/N-TiO2 nanomaterial and its application in SERS study

ABSTRACT

Combined template method with sol-gel method to make the mixed solution including polystyrene microsphere emulsion, TiO₂ sol and NH₃·H₂O aging at room temperature. Annealing at 500 centigrade for 2 hours on mesoporous TiO₂ nano material doped with nitrogen. Wrapped Ag nanoparticles on the surface of mesoporous TiO₂ nano material through redox reaction. The morphology and optical porosities were characterized by Scanning electron microscope (SEM), X-ray diffraction (XRD), BET tester and Surface enhanced Raman scattering (SERS). The results showed this material has excellent surface enhanced Raman effect, optical absorption effect and also has a great specific surface area.     

Effect of Zn2SnO4 on the sintering and electrical properties of SnO2 ceramics

SnO₂ ceramics with relative density about 98 % were obtained based on the addition of Zn₂SnO₄. The shrinkage of the ceramic samples increased sharply and got a saturated value about 13.3 % with doping more than 0.2 mol% Zn₂SnO₄. In the dielectric spectra, no relaxation peaks were observed and no deep trap states could be detected from 50–300 °C and 40–5 M?Hz. Thus, the oxygen vacancies may not be necessary for the densification of SnO₂ ceramics during sintering process. For all the samples, nonlinear electrical properties were observed and the breakdown electrical fields are in good agreement with the barrier height. With increasing Zn₂SnO₄ content, the activation energies E _a for O^? or O^2? adsorbed at grain boundary decreased and the doping of Zn₂SnO₄ may be an important reason for the improve of grain conductivity and formation of Schottky barrier.     

(Gd,Co, Ta)-Doped SnO<Subscript>2</Subscript> Varistor Ceramics

The effect on the microstructure and electrical properties of (Co, Ta)-doped SnO₂ varistors upon the addition of Gd₂O₃ was investigated. The threshold electric field of the SnO₂ based varistors increased significantly from 720 V/mm to 1455 V/mm, the relative dielectric constants of the SnO₂ based varistors decreased greatly from 833 to 330 as Gd₂O₃ concentration was increased up to 1.2 mol%. The significant decrease of the SnO₂ mean grain size, from 3.8 to 1.6 m with increasing Gd₂O₃ concentration over the range of 0 to 1.2 mol%, is the origin for increase in the threshold voltage and decrease of the dielectric constants. The mean grain size reduction is attributed to the segregation of Gd₂O₃ at grain boundaries hindering the SnO₂ grains from conglomerating into large particles. Varistors were found to have superhigh threshold voltage and comparatively large nonlinear coefficient . For 0.8 mol% Gd₂O₃-doped sample, threshold electrical field E and nonlinear coefficient were measured to be 1125 V/mm and 24.0, for 1.2 mol% Gd₂O₃-doped sample, E and were 1355 V/mm and 23.0. Superhigh threshold voltage and large nonlinear coefficient qualify the Gd-doped SnO₂ varistor as an excellent candidate in use for high voltage protection system.     

Influence of Au particles on the photocurrent of TiO2 films

Au/TiO₂ composite films were employed in an attempt to improve the photon-electron conversion efficiency of TiO₂ film in the visible region, using the surface plasma resonance (SPR) of Au nanoparticles. For investigating the relationship between SPR of Au particle and photocurrent of TiO₂ film, a series of Au/TiO₂ films with different Au concentrations were synthesized by sol-gel method. Results of studies on the influence of Au particle size on crystallization of TiO₂ film, UV-vis absorption and photocurrents generated are discussed. It was shown that SPR performance of the Au nanoparticles was not only related to their size, but also to their distribution in the TiO₂ matrix. Even in TiO₂ films with large Au particle sizes (100 nm), SPR in visible region was still observed. However, this SPR performance did not contribute to the photon-electron conversion of TiO₂ film in the visible region. Contrarily, embedded Au nanoparticles depressed the photocurrent generated by the TiO₂ film in UV region. The reason for this decrease is thought to be partly due to the Au simply blocking some of the light and partly because the extent of crystallization of TiO₂ decreased with high Au levels.     

Exhaled VOCs sensing properties of WO3 nanofibers functionalized by Pt and IrO2 nanoparticles for diagnosis of diabetes and halitosis

This work presents a simple synthetic route to produce WO₃ nanofibers functionalized by catalytic Pt and IrO₂ nanoparticles and their superior acetone and H₂S sensing characteristics, demonstrating the potential use of Pt and IrO₂ nanoparticles in applications as sensors of biomarkers of diabetes and halitosis, respectively, in exhaled breath. The individual WO₃ fiber, calcined at 500 °C, was composed of small nanoparticles with a size distribution in the range of 30?C100?nm. Networks of WO₃ fibers exhibited a high surface-to-volume ratio and unique morphologies, thus facilitating efficient gas transport into the entire fiber layers. Pt (4?C7?nm) and Ir (4?C8?nm) nanoparticles were synthesized by polyol methods and were used as additives to decorate the surface of the WO₃ fibers. After a heat treatment, those catalyst particles were partially or fully oxidized to Pt/PtO_x and IrO₂, respectively. To investigate the advantages of Pt-decorated WO₃ fibers (Pt-WO₃) and IrO₂-decorated WO₃ (IrO₂-WO₃) fibers as acetone (CH₃COCH₃) and H₂S sensing materials, respectively, we carried out gas-sensing measurements in a highly humid atmosphere (RH 75?%) similar to that of an oral cavity. The Pt-WO₃ fibers showed a high acetone response (R_air/R_gas?=?8.7 at 5?ppm) at 350?°C and a superior H₂S response (R_air/R_gas?=?166.8 at 5?ppm) at 350?°C. Interestingly, IrO₂-WO₃ fibers showed no response to acetone, while the gas response to H₂S exhibited temperature-insensitivity, which has never been reported in any other work. Thus, the highly selective cross-response between H₂S and acetone was successfully achieved via the combination of IrO₂ particles on WO₃ fibers. This work demonstrates that accurate diagnosis of diabetes and halitosis by sensing exhaled breath can be realized through the use of electrospun WO₃ fibers decorated with Pt and IrO₂ catalysts.     

WO3/BTO heterostructures based NO2 sensor with enhanced response characteristics

Abstract

In the present work, an efficient NO₂ gas sensor has been realised using single phase Barium titanate, BaTiO₃, (BTO) thin film, grown by chemical solution deposition technique (CSD). The gas sensing characteristics of BTO thin film were enhanced by integrating WO₃ modifier in the form of uniformly distributed circular nano-clusters and continuous overlayer. The WO₃ nanoclusters/BTO sensing element exhibited enhanced sensor response (～156) with fast response speed (16?s) at a relatively low operating temperature (140?°C) towards 50?ppm NO₂ gas. An attempt has been made to explain the sensing mechanism involving the twin effect of “Fermi-level exchange mechanism” and “spill over mechanism” upon interaction with target NO₂ gas. The obtained results in the present work are encouraging for the realization of hand-held NO₂ gas sensor.     

Synthesis and Characterization of Zn-Doped TiO2 Nanoparticles via Sonochemical Method

Zn-doped TiO₂ nanoparticles were successfully fabricated using sonochemical method accompanying post calcination process. Titanium isopropoxide (Ti[OC₃H₇]₄) and Zinc chloride (ZnCl₂) were used as starting precursors for Ti and Zn sources, respectively. The homogeneous mixing solution of different Zn (0–1 mol%) and Ti ratio were irradiated in high intensity ultrasound sonometer (750 W 20 kHz) for 30 min at room temperature to obtain as-synthesized Zn-doped TiO₂ nanoparticles followed by calcination at 400–700°C. To evaluate the structure and phase identification of prepared powders, the X-ray diffraction (XRD) and Raman spectroscopy were employed. The results reveal that the as-synthesized Zn-doped TiO₂ nanoparticles are in anatase phase and their crystallinity increases with increasing calcined temperature. The morphology of as-synthesized powders was investigated by transmission electron microscope (TEM). The effect of Zn content and calcinations temperature on TiO₂ properties was also discussed.