Synthesis and Characterization of SnO2 Nanopowder Prepared by Precipitation Method

Tetragonal SnO₂ nanopowder of the range ～8 nm has been successfully synthesized by precipitation method. The prepared powder was characterized by thermogravimetry analysis (TGA), x-ray diffraction (XRD), transmission electron microscopy (TEM), Infrared spectroscopy (FTIR), x-ray photoelectron spectroscopy (XPS), diffuse reflectance spectroscopy (DRS), and room temperature photoluminescence (PL) spectroscopy. Experimental results show that the prepared powder was phase pure SnO₂ of tetragonal rutile structure without any impurities. The optical band gap was determined to be 4.26 eV, using diffuse reflectance technique with the aid of Kubelka-Munk relation. The blue shift of the band gap was attributed to the quantum size confinement effect.     

CTAB-assisted synthesis of mesoporous F-N-codoped TiO2 powders with high visible-light-driven catalytic activity and adsorption capacity

This article describes the preparation of mesoporous rod-like F-N-codoped TiO₂ powder photocatalysts with anatase phase via a sol-gel route at the temperature of 373 K, using cetyltrimethyl ammonium bromide (CTAB) as surfactant. The as-prepared photocatalysts were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and UV-visible diffuse reflectance spectra (UV-vis DRS). The results showed that the photocatalysts possessed a homogeneous pore diameter and a high surface area of 106.3-160.7 m³ g⁻¹. The increasing CTAB reactive concentration extended the visible-light absorption up to 600 nm. The F-N-codoped TiO₂ powders exhibited significant higher adsorption capacity for methyl orange (MO) than that of Degussa P25 and showed more than 6 times higher visible-light-induced catalytic degradation for MO than that of P25.     

Hierarchical chlorine-doped rutile TiO2 spherical clusters of nanorods: Large-scale synthesis and high photocatalytic activity

In this study, we report the synthesis of hierarchical chlorine-doped rutile TiO₂ spherical clusters of nanorods photocatalyst on a large scale via a soft interface approach. This catalyst showed much higher photocatalytic activity than the famous commercial titania (Degussa P25) under visible light (λ>420 nm). The resulting sample was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution TEM (HRTEM), nitrogen adsorption, X-ray photoelectron spectroscopy (XPS), UV-vis diffuse reflectance spectroscopy, ¹H solid magic-angle spinning nuclear magnetic resonance (MAS-NMR) and photoluminescence spectroscopy. On the basis of characterization results, we found that the doping of chlorine resulted in red shift of absorption and higher surface acidity as well as crystal defects in the photocatalyst, which were the reasons for high photocatalytic activity of chlorine-doped TiO₂ under visible light (λ>420 nm). These hierarchical chlorine-doped rutile TiO₂ spherical clusters of nanorods are very attractive in the fields of environmental pollutants removal and solar cell because of their easy separation and high activity.     

Double-Layer TiO2 Electrodes with Controlled Phase Composition and Morphology for Efficient Light Management in Dye-Sensitized Solar Cells

The light-scattering effect in the dye-sensitized solar cells (DSCs) was studied by controlling TiO₂ phase composition and morphology by fabrication of double-layer cells with different arrangement modes. The starting material for preparation of TiO₂ cells was synthesized by an aqueous sol–gel process. X-ray diffraction and field emission scanning electron microscopic analyses revealed that TiO₂ nanoparticles had particle size ranging between 18 and 44 nm. The optical property and band gap energy of TiO₂ nanoparticles were studied through UV–Vis absorption. The indirect optical band gap energy of anatase and rutile nanoparticles was found to be 3.47 and 3.41 eV, respectively. The double-layer DSC made of nanostructured TiO₂ film with phase composition of 78 % anatase and 22 % rutile as the under-layer and mixtures of anatase-nanoparticles and anatase-microparticles as the over-layer (i.e., NM solar cell) was shown the highest power conversion efficiency (PCE) of 6.04 % and open circuit voltage of 795 mV. This was achieved due to the optimal balance between the light scattering effect and dye sensitization parameters. Optimum light scattering of photoanode led to improve the PCE of NM double-layer solar cell which was demonstrated by diffuse reflectance spectroscopy.     

Phase composition and magnetic properties of niobium-iron codoped TiO2 nanoparticles synthesized in Ar/O2 radio-frequency thermal plasma

Nanoparticles of Nb⁵⁺-Fe³⁺ codoped TiO₂ with various Nb⁵⁺ concentrations (Nb/(Ti+Fe+Nb)=0-10.0 at%) and Fe³⁺ (Fe/(Ti+Fe+Nb)=0-2.0 at%) were synthesized using Ar/O₂ thermal plasma. Dopant content, chemical valence, phase identification, morphology and magnetic properties were determined using several characterization techniques, including inductively coupled plasma-optical emission spectrometer, X-ray photoelectron spectroscopy, X-ray diffraction, UV-vis diffuse reflectance spectrometer, field-emission scanning electron microscopy, transmission electron microscopy and SQUID commercial instrument. The XRD revealed that all the plasma-synthesized powders were exclusively composed of anatase as major phase and rutile. The rutile weight fraction was increased by the substitution of Fe³⁺ for Ti⁴⁺ whereas it was reduced by the Nb⁵⁺ doping. The plasma-synthesized Nb⁵⁺-Fe³⁺ codoped TiO₂ powders had intrinsic magnetic properties of strongly paramagnetic and feebly ferromagnetic at room temperature. The ferromagnetic properties gradually deteriorated as the Fe³⁺ concentration was decreased, suggesting that the ferromagnetism was predominated by the phase composition as a carrier-mediated exchange.     

Effect of annealing temperatures and of high content of the iron ion (Fe<Superscript>3+</Superscript>)-doping on transition anatase–rutile phase of nanocrystalline TiO<Subscript>2</Subscript> thin films prepared by sol–gel spin coating

Titanium dioxide doped with iron (III) was prepared by sol–gel Spin Coating method. The phase structures, morphologies, particle size of the doped TiO₂ have been characterized by X-ray diffraction (XRD), Raman spectroscopy, atomic force microscopy (AFM) and ultraviolet–visible (UV–Vis) spectrophotometer. The XRD and Raman results show that the 10% Fe³⁺-doped TiO₂ thin films crystallize in anatase phase between 600 and 800 °C, and into the anatase–rutile phase at 1,000 °C, and further into the rutile phase when the content of Fe³⁺ increases (20%). The grain size calculated from XRD patterns shows that the crystallinity of the obtained anatase particles increased from 39.4 to 43.4 nm as the temperature of annealing increase, whereas the size of rutile crystallites increases, with increasing Fe³⁺ concentrations from 36.9 to 38.1 nm. The AFM surface morphology results confirmed that the particle size increases by increasing the annealing temperature and also with an increasing of Fe³⁺ content. The optical band gap (E _g) of the films was determined by the UV–Vis spectrophotometer. We have found that the optical band gap decreased with an increasing of annealing temperatures and also with an increasing of Fe³⁺ content.     

Evolution of titania nanotubes-supported WOx species by in situ thermo-Raman spectroscopy, X-ray diffraction and high resolution transmission electron microscopy

Structural evolution of WO_x species on the surface of titania nanotubes was followed by in situ thermo-Raman spectroscopy. A total of 15 wt% of W atoms were loaded on the surface of a hydroxylated titania nanotubes by impregnation with ammonium metatungstate solution and then, the sample was thermally treated in a Linkam cell at different temperatures in nitrogen flow. The band characteristic of the WO bond was observed at 962 cm⁻¹ in the dried sample, which vanished between 300 and 700 °C, and reappear again after annealing at 800 °C, along with a broad band centered at 935 cm⁻¹, attributed to the v₁ vibration of WO in tetrahedral coordination. At 900 and 1000 °C, the broad band decomposed into four bands at 923, 934, 940 and 950 cm⁻¹, corresponding to the symmetric and asymmetric vibration of WO bonds in Na₂WO₄ and Na₂W₂O₇ phases as determined by X-ray diffraction and High resolution transmission electron microscopy (HRTEM). The structure of the nanotubular support was kept at temperatures below 450 °C, thereafter, it transformed into anatase being stabilized at temperatures as high as 900 °C. At 1000 °C, anatase phase partially converted into rutile. After annealing at 1000 °C, a core-shell model material was obtained, with a shell of ca. 5 nm thickness, composed of sodium tungstate nanoclusters, and a core composed mainly of rutile TiO₂ phase.     

Spectroscopic, thermal, magnetic and structural characterization of K3VF6 prepared at room temperature

A straight forward room-temperature synthesis of V(III) containing complex fluoride K₃VF₆, using KF and vanadium(III) acetylacetonate is reported. The pale green colored powder was characterized by chemical analysis, powder X-ray diffraction; diffuse reflectance spectroscopy, infrared spectroscopy, Raman spectroscopy, differential scanning calorimetry, scanning electron microscopy, photoluminescence spectroscopy, magnetic susceptibility measurements and photoluminescence spectroscopy. The powder X-ray diffraction pattern was fitted in P2₁/n space group (monoclinic) with a = 12.106 (1) Å, b = 17.685 (0) Å, c = 11.802 (0) Å, β = 92.23° (1). Differential scanning calorimetry showed phase transitions, occurring at 158 °C and 190 °C. In the FT-IR spectrum, characteristic band for the VF₆³⁻ group was observed at 508 cm⁻¹. The bands observed in the 335-361 cm⁻¹ region and at 504 cm⁻¹ in the room temperature Raman spectrum of K₃VF₆ corresponded to the F_2g and A_1g modes, respectively. The ratio of the frequencies (F_2g/A_1g) observed in the diffuse reflectance spectrum was fitted on the Tanabe-Sugano diagram to determine the Racah parameter B value of 712 cm⁻¹. Magnetic ordering was not observed down to the lowest measured temperature of 5 K.     

A novel orange phosphor of Eu-activated calcium chlorosilicate for white light-emitting diodes

Novel orange phosphor of Eu²⁺-activated calcium chlorosilicate was synthesized at 1273 K by conventional solid-state reactions under reductive atmosphere and investigated by means of photoluminescence excitation, diffuse reflectance and emission spectroscopies. These results show that this phosphor can be efficiently excited by the incident light of 300-450 nm, well matched with the emission band of 395 nm-emitting InGaN chip, and emits an intense orange light peaking at 585 nm. By combining this phosphor with a 395 nm-emitting InGaN chip, an intense orange light-emitting diode (LED) was fabricated. Under 20 mA forward-bias current, its CIE chromaticity coordinates are (0.486, 0.446). The dependence of as-fabricated orange LED on forward-bias current indicates that it shows excellent chromaticity stability and luminance saturation. These results show that this Eu²⁺-activated calcium chlorosilicate is a promising orange-emitting phosphor for near-ultraviolet (UV) InGaN-based white LED.     

均相水解法制备金红石含量可控的纳米TiO2

用均相水解法通过调节对甲苯磺酸的添加量制备了金红石含量线性可控的纳米TiO2粒子,相同条件下,没有加入对甲苯磺酸时,制备的TiO02颗粒为纯锐钛矿晶型．制备的纳米TiO2颗粒,其单晶尺寸为19．5mm(金红石),13．5mm(锐钛矿),比表面积72．7m^2／g,通过公式计算得到了制备的TiO2纳米颗粒带隙能为2．83eV,比P25和纯锐钛矿纳米TiO2颗粒的带隙能均低．     

Synthesis of carbon nanotube/anatase titania composites by a combination of sol-gel and self-assembly at low temperature

A simple method is described for the synthesis of carbon nanotube/anatase titania composites by a combination of a sol-gel method with a self-assembly technique at 65 °C. This method makes use of polyelectrolyte for wrapping multi-walled carbon nanotube (MWCNT) and providing them with adsorption sites for electrostatically driven TiO₂ nanoparticle deposition. The composites were characterized using X-ray diffraction, transmission electron microscopy, Fourier transform infrared and X-ray photoelectron spectroscopy, and photoluminescence for analyzing their crystal phase, microstructure, particle size, and other physicochemical properties. The results showed that MWCNT were covered with an anatase TiO₂ thin layer or surrounded by an anatase TiO₂ thick coating, which is constructed of TiO₂ particles about 6 nm in size. The composites were rich in surface hydroxyl groups. The excited e⁻ in conduction band of TiO₂ may migrate to MWCNT. Concerning the potential applicability, MWCNT/TiO₂ composites showed excellent photocatalytic activity toward the photodegradation of methyl orange.     

Synthesis,Characterization and Optical Properties of BaMoO<Subscript>4</Subscript> Synthesized by Microwave Induced Plasma Method

BaMoO₄ crystals were synthesized by a 900 W microwave induced plasma process (MIP) for 40, 60, 120 and 140 min. Phase, morphology, vibrational mode and energy gap were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), photoluminescence (PL) spectroscopy, Fourier transform infrared (FTIR) spectroscopy and UV-visible spectroscopy. In this research, the phase and morphology of product were influenced by microwave heating time. The sample processed for 140 min shows spherical particles tetragonal BaMoO₄ phase with size of 200–700 nm in diameter. BaMoO₄ with band gap of 3.35 eV shows a blue emission wavelength at 440 nm.     

Monitoring of potential cytotoxic and inhibitory effects of titanium dioxide using on-line and non-invasive cell-based impedance spectroscopy

Titanium dioxide (TiO₂) nanoparticles (NPs) with different sizes and structures were probed for plausible cytotoxicity using electric cell-substrate impedance sensing (ECIS), a non-invasive and on-line procedure for continuous monitoring of cytotoxicity. For insect cells (Spodoptera frugiperda Sf9), the ECIS₅₀ values, i.e., the concentration required to achieve 50% inhibition of the response, differed depending on the size and shape of the TiO₂ nanostructure. The lowest ECIS₅₀ value (158 ppm) was observed for the needle shaped rutile TiO₂ (10 nm × 40 nm, 15.5 nm nominal particle size), followed by 211 ppm for P-25 (34.1 nm, 80% anatase and 20% rutile), 302 ppm for MTI5 (5.9 nm, 99% anatase) and 417 ppm for Hombitan LW-S bulk TiO₂ (169.5 nm, 99% anatase). Exposure of TiO₂ NPs to UV light at 254 nm or 365 nm exhibited no significant effect on the ECIS₅₀ value due to the aggregation of TiO₂ NPs with diminishing photocatalytic activities. Chinese hamster lung fibroblast V79 cells, exhibited no significant cytotoxicity/inhibition up to 400 ppm with P25, MTI₅ and bulk TiO₂. However, a noticeable inhibitory effect was observed (ECIS₅₀ value of 251 ppm) with rutile TiO₂ as cell spreading on the electrode surface was prevented     

Fabrication and characterization of hexagonal boron nitride powder by spray drying and calcining-nitriding technology

Hexagonal boron nitride (hBN) powder was fabricated prepared by the spray drying and calcining-nitriding technology. The effects of nitrided temperature on the phases, morphology and particle size distribution of hBN powder, were investigated. The synthesized powders were characterized by X-ray diffraction (XRD), field emission scanning electron microscope (FESEM), Fourier transformed infrared spectrum, ultraviolet-visible (UV-vis) spectrum and photoluminescence (PL) spectrum. UV-vis spectrum revealed that the product had one obvious band gap (4.7 eV) and PL spectrum showed that it had a visible emission at 457 nm (λ_ex=230 nm). FESEM image indicated that the particle size of the synthesized hBN was mainly in the range of 0.5-1.5 μm in diameter, and 50-150 nm in thickness. The high-energy ball-milling process following 900 °C calcining process was very helpful to obtain fully crystallized hBN at lower temperature.     

A low-temperature synthesis of ultraviolet-light-emitting ZnO nanotubes and tubular whiskers

We have successfully synthesized single-crystal ZnO nanotubes and tubular whiskers by employing Zn(NO₃)₂·6H₂O, NH₃·H₂O as the starting materials in the presence of polyethylene glycol (PEG, M_w=2000) at ambient pressure and low temperature (70 °C). Characterizations are carried out by X-ray powder diffraction (XRD), X-ray energy dispersive spectroscopy (EDS), scanning electron microscopy (SEM), transmission electron microscopy (TEM, HRTEM) and photoluminescence (PL) measurement. The results show that the as-prepared ZnO are tubular textures, which have average cross-sectional dimensions of 200-300 nm, lengths of 2-3.5 μm, and wall thickness of 80 nm. These tubular products demonstrate a sharp ultraviolet excitonic emission peak centered at 385 nm at room temperature. A possible growth mechanism and the influence of the reaction temperature on the formation of crystalline ZnO are presented.     

Preparation and characterization of SiO2/TiO2 composite microspheres with microporous SiO2 core/mesoporous TiO2 shell

SiO₂/TiO₂ composite microspheres with microporous SiO₂ core/mesoporous TiO₂ shell structures were prepared by hydrolysis of titanium tetrabutylorthotitanate (TTBT) in the presence of microporous silica microspheres using hydroxypropyl cellulose (HPC) as a surface esterification agent and porous template, and then dried and calcined at different temperatures. The as-prepared products were characterized with differential thermal analysis and thermogravimetric (DTA/TG), scanning electron microscopy (SEM), X-ray diffraction (XRD), nitrogen adsorption. The results showed that composite particles were about 1.8 μm in diameter, and had a spherical morphology and a narrow size distribution. Uniform mesoporous titania coatings on the surfaces of microporous silica microspheres could be obtained by adjusting the HPC concentration to an optimal concentration of about 3.2 mmol L⁻¹. The anatase and rutile phase in the SiO₂/TiO₂ composite microspheres began to form at 700 and 900 °C, respectively. At 700 °C, the specific surface area and pore volume of the SiO₂/TiO₂ composite microspheres were 552 and 0.652 mL g⁻¹, respectively. However, at 900 °C, the specific surface area and pore volume significantly decreased due to the phase transformation from anatase to rutile.     

Low temperature design of titanium dioxide anatase materials decorated with cyanuric acid for formic acid photodegradation

The influence of cyanuric acid (CA) on the structural, textural, electronic, morphological properties and the photocatalytic activity of titanium dioxide materials (TNCA) were herein evaluated. TNCAs samples were prepared through the sol gel method. The novelty of this work that cyanuric acid; the so far most recalcitrant molecule, is used here as reservoir of nitrogen. The synthesis of TNCAs nanomaterials are performed at low temperature in presence of quaternary ammonium as co-catalyst for anatase growth. Samples were characterized by means of nitrogen adsorption-desorption isotherms at 77 K, X-ray diffraction (XRD), Infrared (ATR), Raman, diffuse reflectance ultraviolet-visible, photoluminescence (PL) and electron paramagnetic resonance (EPR) spectroscopies, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The photocatalytic activities of TNCAs and their free counterpart nanomaterials were then evaluated in the photocatalytic degradation of formic acid (FA) as model molecule under UV.X-ray and Raman show success of anatase phase formation at low temperature without any post-calcination. IR-ATR analysis confirms CA grafting onto TiO₂ identified by formation of vibration band between Ti and triazine. SEM mapping shows that C, O, Ti, and N are homogeneously distributed in the nanomaterial. Nitrogen adsorption-desorption measurements at 77 K show developed textural properties; the heat of N₂ adsorption seems to be affected by CA loading. PL and UV-visible spectroscopies show simultaneously (i) electron trapping by the oxygen vacancy identified by Raman spectroscopy by redshift of Eg1 mode and (ii) the hole is confined by nitrogen. Therefore, the excited electron can move from TiO₂ VB to the new sublevels initiated by the introduction of nitrogen which results in quenching of the photoluminescence intensity. The photocatalytic activity of the various TNCAs nanomaterials increases versus CA loading. The highest k_LH of TNCA2 (5 wt%) could be explained by short migration time conjugated with lower bulk recombination of the photogenerated electron hole.     

Gd-N共掺杂SrTiO3/TiO2复合纳米纤维制备及光催化性能

以静电纺丝技术制备的TiO_2纳米纤维为基质和反应物,结合一步水热法制得Gd-N共掺杂SrTiO_3/TiO_2复合纳米纤维光催化剂。利用X射线衍射(XRD)、扫描电子显微镜(SEM)、高分辨透射电镜(HRTEM)、X射线光电子能谱(XPS)、紫外-可见漫反射(UV-Vis DRS)和荧光光谱(PL)等方法对其微观结构、形貌和光学性能进行表征。结果表明:SrTiO_3和TiO_2形成异质结能够使光生电子和空穴得到很好的分离,而Gd-N共掺杂产生新带隙,可以拓宽光谱响应范围至可见光区,并引起晶格缺陷,成为光生电子-空穴对的浅势捕获阱。Gd-N共掺杂与异质结的协同作用有效提高了SrTiO_3/TiO_2复合纳米纤维的可见光催化活性。     

Effect of Hg2+doping and of the annealing temperature on the nanostructural properties of TiO2 thin films obtained by sol–gel method

This work is a study of Hg²⁺-doped TiO₂ thin films deposited on silicon substrates prepared by sol–gel method and treated at temperatures ranging between 600 to 1000 °C for 2 h. The structural and optical properties of thin films have been studied using different techniques. We analyzed the vibrations of the chemical bands by Fourier transform infrared (FTIR) spectroscopy and the optical properties by UV–Visible spectrophotometry (reflection mode) and photoluminescence (PL). The X-ray diffraction and Raman spectra of TiO₂ thin films confirmed the crystallization of the structure under the form of anatase, rutile, mercury titanate (HgTiO₃) as a function of the annealing temperature. The observation by scanning electron microscopy (SEM) showed the changing morphology, with respect to nanostructures, nanosheets, nanotubes, with the annealing temperature. The diameters of nanotubes ranged from 50 nm to 400 nm. The photoluminescence and reflectance spectra indicated that these structures should enhance photocatalytic activity.     

Enhanced photocatalytic activity for titanium dioxide by co-modification with copper and iron

A copper(II) and iron(III) co-modified titanium dioxide nano material was prepared by a simple sol–gel process using titanium(IV) isopropoxide plus copper(II) and iron(III) nitrates as raw materials. The as-prepared nanocomposites were characterized by X-ray diffraction (XRD), diffuse reflectance spectroscopy and photoluminescence spectra. The XRD results showed that the undoped TiO₂ nanoparticles mainly include anatase phase while the Cu, Fe-codoped TiO₂ nanoparticles showed a mixture of anatase phase with a small fraction of rutile phase displaying higher activity than the pure anatase phase. Optical characterization showed that the codoping with copper(II) and iron(III) resulted in a red shift of adsorption and lower recombination probability between electrons and holes, which were associated with high photocatalytic activity of the Cu, Fe-codoped TiO₂ nanoparticles under visible light (λ > 400 nm). The photocatalytic activity of the samples was tested by aqueous methyl orange degradation. The capability of the codoped catalyst was much higher than that of the pure TiO₂ catalyst under visible irradiation. A mechanism is proposed in order to account for the enhanced catalytic activity.