Titanate Nanofibers Research Articles

Investigation of Change in Surface Area and Grain Size of Cadmium Titanate Nanofibers upon Annealing and Their Effect on Oxygen Sensing

We have investigated the phase changes in CdTiO3 nanofibers as the annealing temperature of nanofibers was increased from 600 to 1200 °C. The nanofibers annealed at 600 °C were ilmenite with a very small amount of CdO. Upon annealing at 950 °C, CdO was completely removed. Annealing at 1000 °C yielded pure perovskite nanofibers, and at temperatures above 1100 °C rutile TiO2 nanofibers were obtained. Brunauer-Emmett-Teller (BET) analysis showed that with increase in annealing temperature the surface area of nanofibers was decreased. The nanofibers annealed at 600 °C have the higher surface area of ∼9.41 m(2)/g. Then oxygen sensors using CdTiO3 nanofibers annealed at 600 °C (ilmenite) and 1000 °C (perovskite) were fabricated. The sensitivity of the ilmenite nanofibers sensor was 2 times than that of the perovskite nanofibers sensor. The response and recovery times were 120 and 23 s, respectively, for the ilmenite nanofibers sensor, whereas response and recovery times were 156 and 50 s, respectively, for the perovskite nanofibers sensor. Better oxygen characteristics of ilmenite nanofibers are attributed to their large surface area and porosity. Therefore, we believe that ilmenite CdTiO3 nanofibers are potential candidates to develop practical oxygen sensors.

Growth Morphologies of Nanostructured Rutile TiO2

The morphological and structural characteristics of nanostructure rutile TiO2 were investigated by using x-ray diffraction, scanning electron microscopy, electron diffraction, conventional and high resolution transmission electron microscopy. As a product of the precursor template of hydrogen titanate nanofibers, rutile could exhibit forms like tree, sheaf, or bundle. Both the branch and trunk of tree-like rutile have the same growth axis of [001]. The sheaf-like rutile forms while it grows along both [001] and [ $$ 00\bar{1} $$ ] directions. The bundle-like rutile grows along only one [001] direction. Tree-like morphology of nanocrystals rutile is revealed to be controlled by (101) twin structure. Twin formation is a possible mechanism to decrease the density of defects and reduce the system energy as the crystal grows.

N-doped titanate nanostructures on gradient surface layer of one dimensional nanofibers synthesized on Ti electrode by chemical and thermal treatments

TiO2 nanostructures have attracted much attention due to their semi-conductivity and photocatalytic properties, but are rarely used as functional electrodes for water electrolysis that requires high electrical conductivity. Compared to TiO2, a high doping level of N into titanates is expected due to their layered structure, which was attempted to improve the conductivity. Here, a surface layer of one dimensional hydrogen titanate (H-titanate) nanofibers with high surface area and poor crystallinity was synthesized on the surface of Ti metal by mild NaOH and HCl treatments, as compared to the commonly used severe hydrothermal treatments. The poorly crystallized structure of the layered H-titanate allowed the incorporation of a large amount of N into its surface layer by thermal treatments at 700 °C or more, thereby transforming it into Ti-oxynitrides with high electrical conductivity while retaining the high surface area of the treated layer. The depth profile analyses of the chemically and thermally treated Ti metal revealed that the concentration of O and H was the highest at the top surface of the surface layer. With increasing depth, the concentration of O and H decreased gradually whereas the concentration of N increased gradually, indicating gradients in the structures of the treated nanofibrous surface layer. The dense region below the nanofibrous surface layer was composed of Ti2N, whose amount increased with increasing temperature. This kind of gradient surface layer of N-doped titanate nanofibers without well-defined interfaces was synthesized on the surface of the Ti electrode by our unique chemical and thermal treatments and was modeled with varying depths. The specific objective of the present work is to characterize and study the mechanism of formation of the N-doped structures in a one dimensional gradient surface layer of H-titanate nanofibers synthesized on the treated Ti electrode. The treated one dimensional nanofibrous surface layer on a Ti electrode can be potentially used for the electro-splitting of water after fixation of molecular catalysts on its surface.

Microporous titanate nanofibers for highly efficient UV-protective transparent coating

Interzeolite conversion was applied to convert a layered titanate into a microporous titanate nanofiber, which hardly showed photocatalytic activity and exhibited extremely low refractive index and then could be used as a UV absorber embedded in commodity organic polymer coatings.

Centrifugal jet spinning for highly efficient and large-scale fabrication of barium titanate nanofibers

The centrifugal jet spinning (CJS) method has been developed to enable large-scale synthesis of barium titanate nanofibers. Barium titanate nanofibers with fiber diameters down to 50nm and grain sizes around 25nm were prepared with CJS by spinning a sol–gel solution of barium titanate and poly(vinylpyrrolidone) with subsequent heat treatment at 850°C. XRD and FTIR analyses demonstrated high purity and tetragonal perovskite structured barium titanate nanofibers. SEM and TEM images confirm the continuous high aspect ratio structure of barium titanate nanofibers after heat treatment. It is demonstrated that the CJS technique offers a highly efficient method for large-scale fabrication of ceramic nanofibers at production rates of up to 0.3g/min.

Electrospun SrTiO3 nanofibers for photocatalytic hydrogen generation

Abstract

New hybrid titanate elongated nanostructures through organic dye molecules sensitization

This study reports on a novel chemical route to synthesize new elongated titanates nanostructured hybrid materials by the combination of titanate nanofibers (TNFs) with organic dye molecules. The influence of the sodium/proton replacement on the adsorption and intercalation characteristics of the TNFs materials was analysed. Depending on the sodium/proton content, materials with surface areas in the 21.08–38.90 m2/g range were obtained. Due to their molecule size and shape, and anticipating their intercalation between the TiO6 layers, the cationic molecules chosen for this study were thionine, methylene blue, crystal violet and rhodamine 6G. The sample with the highest sodium content was the best material on up taking dyes from aqueous media. The amount of the immobilized dyes was higher than the one predictable for the formation of a monolayer in an adsorption process. The intercalation of thionine, methylene blue and crystal violet between the TiO6 layers was accomplished. The characterisation results obtained by adsorption, XRD and FTIR are in agreement with the production of these new hybrid structures, with the organic molecules located within the TiO6 layers. The results also demonstrate that only the thionine was incorporated in the protonated titanate structure, due to the smaller distance between the layers. The optical characterisation of the prepared materials by DRS also indicates that intercalated and adsorbed dyes have strong influence on the optical properties of the new hybrid materials prepared.

Incorporation of cadmium sulfide nanoparticles on the cadmium titanate nanofibers for enhanced organic dye degradation and hydrogen release

Abstract In this study, the effective cadmium sulfide NPs were successfully encapsulated on cadmium titanate electrospun nanofibers. Calcination of electrospun nanofiber mats composed of titanium isopropoxide, poly (vinyl pyrrolidone) (PVP) and cadmium acetate dihydrate with few drops of ammonium sulfide in air at 600 °C led to the production of good morphology of CdS decorated cadmium titanate nanofibers. The morphology and structure of as-synthesized nanocomposites were characterized by field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD). As-synthesized nanocomposites exhibited a strong photocatalytic activity for decomposition of methylene blue (MB) under visible light and showed good hydrogen release from hydrolysis of the ammonia–borane complex. The perfect recovery of catalyst after reaction and its unchanged efficiency for cyclic use showed that it will be an economically and environmentally friendly photocatalyst. The results indicated that the CdS/CdTiO 3 photocatalysts possess improved photocatalytic activity than that of CdTiO 3 alone.

Flexible piezoelectric nanofiber composite membranes as high performance acoustic emission sensors

A flexible acoustic emission (AE) sensor based on lead zirconate titanate (PZT) nanofiber composite membrane is described. The PZT nanofibers, with diameters varying from 50nm to 120nm, were electrospun and aligned across interdigitated electrodes. After being packaged in a flexible polymer structure with a thickness of ∼5μm, this small scale AE sensor can bend freely to follow curved surfaces or embedded into structures. High piezoelectric voltage constant, flexibility and mechanical strength of PZT nanfibers result in a high performance of the demonstrated AE sensor. Fundamental characterization indicates a spontaneous polarization of the PZT nanofibers without any polarization treatment. The electromechanical coupling effect was increased up to 370% after 90min of polarization under an external electric field of ∼3V/μm. The anisotropic sensitivity, which can reduce the required number of sensors to indentify the location of the AE source, was observed from the attenuation maps. The small scale, flexible and highly sensitive PZT nanofiber AE sensor opens up new applications for monitoring small scale structures, curved surfaces and even living cells.

Effect of calcination temperature on structural and photocatalyst properties of nanofibers prepared from low-cost natural ilmenite mineral by simple hydrothermal method

Titanate nanofibers were synthesized via the hydrothermal method (120°C for 72h) using natural ilmenite mineral (FeTiO3) as the starting material. The samples were characterized by X-ray diffraction (XRD), X-ray fluorescent (XRF), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Brunauer–Emmett–Teller (BET) for specific surface area. The nanofibers were 20–90nm in diameter and 2–7μm in length. The as-synthesized nanofibers calcined at 300–400°C showed TiO2 (B) whereas the nanofibers calcined at 500°C revealed a mixture of two phases of TiO2 (B) and anatase. The nanofibers calcined at high temperature of 600–1000°C showed a mixture of tri-crystalline of anatase, rutile, and Fe2O3. The rutile phase increased with increasing calcination temperature. The nanofibers calcined at 300–700°C maintained their structure while the morphology of the nanofibers calcined at 800–1000°C transformed into submicron rod-like structure. This increase of calcination temperature led to the phase transformation from thermodynamically metastable anatase to the most stable form of rutile phase. The crystallite size of prepared samples increased with increasing calcination temperature. Interestingly, with increasing calcination temperature, the absorption edge of the prepared samples shows an obvious shift to visible light region due to the change of crystallite phase and increased crystallite size. Therefore, the band gap energy of the prepared samples became narrower with increasing calcination temperature. Furthermore, the photocatalytic activity of the nanofibers calcined at 400°C for 2h was found to be not merely higher than those of the commercially available TiO2 nanoparticles powders (P-25, JRC-01, and JRC-03) but also the highest of all the samples in this study.

Ultrafast Response Humidity Sensor Based on Electrospun Porous BaTiO<sub>3</sub> Nanofibers

Nanocrystalline and porous barium titanate (BaTiO3) nanofibers with diameter 200-400 nm were synthesized via electrospinning and followed calcinations. The morphology and microstructure of the nanofibers were characterized using field emission scanning electron microscope, X-ray diffractometer and transmission electron microscope, respectively. And the electrical and humidity sensing properties of the nanofibers were also measured. The results reveal that the BaTiO3 nanofibers have a conductivity of about 0.3 S/cm, and show an ultrafast response time (~0.7 s) and a recovery time (~0.4 s) to humidity at room temperature. In addition, the sensing mechanism was also discussed briefly based on its nanocrystalline and porous microstructure of the electrospun material.

Preparation and characterization of Lepidocrocite titanate nanofibers

——————————— *Corresponding author. E-mail: yukf@jlu.edu.cn Received November 2, 2012; accepted December 25, 2012. Supported by the Open Fund of the State Key Laboratory of Inorganic Synthesis and Preparative Chemistry of China(No. 2013-27). © Jilin University, The Editorial Department of Chemical Research in Chinese Universities and Springer-Verlag GmbH Preparation and Characterization of Lepidocrocite Titanate Nanofibers

Adsorption and photocatalytic degradation of methylene blue over hydrogen–titanate nanofibres produced by a peroxide method

In this study, Degussa P25 TiO2 was partially dissolved in a mixture of hydrogen peroxide and sodium hydroxide at high pH. The fabrication of nanofibres proceeded by the hydrothermal treatment of the solution at 80 °C. This was followed by acid wash in HCl at pH 2 for 60 min, which resulted in the formation of hydrogen–titanate nanofibres. The nanofibres were annealed at 550 °C for 6 h to produce crystalline anatase nanofibres. The nanofibres were characterised for physico-chemical modifications and tested for the adsorption and photocatalytic degradation of methylene blue as a model water pollutant. An average specific surface area of 31.54 m2/g, average pore volume of 0.10 cm3/g and average pore size of 50 Å were recorded. The nanofibres were effective adsorbents of the model pollutant and adsorbents and good photocatalysts under simulated solar light illumination. No reduction in photocatalytic activity was observed over three complete treatment cycles, and the effective separation of nanofibres was achieved by gravity settling resulting in low residual solution turbidity.

Tuning the Surface Structure of Nitrogen-Doped TiO2Nanofibres-An Effective Method to Enhance Photocatalytic Activities of Visible-Light-Driven Green Synthesis and Degradation

Nitrogen-doped TiO2 nanofibres of anatase and TiO2(B) phases were synthesised by a reaction between titanate nanofibres of a layered structure and gaseous NH3 at 400-700 °C, following a different mechanism than that for the direct nitrogen doping from TiO2. The surface of the N-doped TiO2 nanofibres can be tuned by facial calcination in air to remove the surface-bonded N species, whereas the core remains N doped. N-Doped TiO2 nanofibres, only after calcination in air, became effective photocatalysts for the decomposition of sulforhodamine B under visible-light irradiation. The surface-oxidised surface layer was proven to be very effective for organic molecule adsorption, and the activation of oxygen molecules, whereas the remaining N-doped interior of the fibres strongly absorbed visible light, resulting in the generation of electrons and holes. The N-doped nanofibres were also used as supports of gold nanoparticle (Au NP) photocatalysts for visible-light-driven hydroamination of phenylacetylene with aniline. Phenylacetylene was activated on the N-doped surface of the nanofibres and aniline on the Au NPs. The Au NPs adsorbed on N-doped TiO2(B) nanofibres exhibited much better conversion (80 % of phenylacetylene) than when adsorbed on undoped fibres (46 %) at 40 °C and 95 % of the product is the desired imine. The surface N species can prevent the adsorption of O2 that is unfavourable for the hydroamination reaction, and thus, improve the photocatalytic activity. Removal of the surface N species resulted in a sharp decrease of the photocatalytic activity. These photocatalysts are feasible for practical applications, because they can be easily dispersed into solution and separated from a liquid by filtration, sedimentation or centrifugation due to their fibril morphology.

Temperature dependent transport and dielectric properties of cadmium titanate nanofiber mats

We investigate electrical and dielectric properties of cadmium titanate (CdTiO3) nanofiber mats prepared by electrospinning. The nanofibers were polycrystalline having diameter ∼50 nm-200 nm, average length ∼100 μm and crystallite size ∼25 nm. Alternating current impedance measurements were carried out from 318 K – 498 K. The frequency of ac signal was varied from 2 – 105 Hz. The complex impedance plots revealed two depressed semicircular arcs indicating the bulk and interface contribution to overall electrical behavior of nanofiber mats. The bulk resistance was found to increase with decrease in temperature exhibiting typical semiconductor like behavior. The modulus analysis shows the non-Debye type conductivity relaxation in nanofiber mats. The ac conductivity spectrum obeyed the Jonscher power law. Analysis of frequency dependent ac conductivity revealed presence of the correlated barrier hopping (CBH) in nanofiber mats over the entire temperature range.

Ferroelectric characterization of aligned barium titanate nanofibres

We report the synthesis, structural and ferroelectric characterization of continuous well-aligned nanofibres of barium titanate produced by the electrospinning technique. The fibres with average diameter of 150–400 nm consist of connected nanoparticles of BaTiO3 stacked together to form the shape of a long filament. The tetragonal phase in the obtained nanofibres was revealed by the x-ray diffraction and Raman spectroscopy and has been also confirmed by the second harmonic generation (SHG) and piezoresponse force microscopy (PFM). The temperature dependence of the SHG in the vicinity of the paraelectric–ferroelectric phase transition suggests that barium titanate nanofibres are indeed ferroelectric with an apparent glass-like state caused by metastable polar nanoregions. The existence of domain structure and local switching studied by PFM present clear evidence of the polar phase at room temperature.

Hydrothermal Synthesis and Photoluminescence of Pre-Perovskite Lead Titanate Nanofibers

Pre-perovskite PbTiO3 nanofibres were synthesized by hydrothermal method with four butyl titanate ((C4H9O)4Ti) and lead nitrate (Pb (NO3)) as the main precursors and Tetramethylammonium Hydroxide (TMAH) as mineralizer. X-ray diffraction (XRD), Raman, Scanning Electronic Microscopy (SEM), Transmission electron microscopy (TEM), high-resolution TEM (HRTEM), and the corresponding selected area electron diffraction (SEAD) were used to characterize the crystal structure and morphology of the obtained products. The results showed that the nanofibers are of a few to tens micrometer at length size, and 50~300 nm at diameter size. Based on the experimental results, the effect of Tetramethylammonium Hydroxide (TMAH) was simply discussed.

One-pot growth of free-standing CNTs/TiO2 nanofiber membrane for enhanced photocatalysis

We report a one-pot route to the formation of free-standing, large-area CNTs/TiO2 nanofiber membrane with enhanced photocatalytic activity. Tetra-n-butyl titanate was reacted with NaOH to form high-quality titanate nanofibers with diameters below 200nm and longitudinal dimensions of several tens of micrometers. CNTs were condensed with the as-prepared nanofibers and enabled the nanofibers to assemble into a free-standing membrane. It is proposed that the CNTs act as linkers between the nanofibers, and it is crucial for the formation of the membrane under the hydrothermal conditions. Benefiting from the introduction of CNTs, the as-prepared nanofiber membrane exhibited higher photocatalytic activity than pure TiO2 nanofibers.

Silver oxide nanocrystals anchored on titanate nanotubes and nanofibers: promising candidates for entrapment of radioactive iodine anions

Iodine radioisotopes are released into the environment by the nuclear industry and medical research institutions using radioactive materials. The (129)I(-) anion is one of the more mobile radioactive species due to a long half-life, and it is a great challenge to design long-term management solutions for such radioactive waste. In this study, a new adsorbent structure with the potential to efficiently remove radioactive iodine anions (I(-)) from water is devised: silver oxide (Ag2O) nanocrystals firmly anchored on the surface of titanate nanotubes and nanofibers via coherent interfaces between Ag2O and titanate phases. I(-) anions in fluids can easily access the Ag2O nanocrystals and be efficiently trapped by forming AgI precipitate that firmly attaches to the adsorbent. Due to their one-dimensional morphology, the new adsorbents can be readily dispersed in liquids and easily separated after purification; and the adsorption beds loaded with the adsorbents can permit high flux. This significantly enhances the adsorption efficiency and reduces the separation costs. The proposed structure reveals a new direction in developing efficient adsorbents for the removal of radioactive anions from wastewater.

Hydrothermal Synthesis of Nanofibers from Natural Ilmenite Mineral and Their Utilization for Dye-Sensitized Solar Cell

Titanate nanofibers were synthesized by a hydrothermal method using a low-cost ilmenite mineral as the starting material. The crystalline structure of the as-synthesized nanofibers demonstrated titanate structure (H2TixO2x+1). The bi-crystalline mixture consisting of TiO2 (B) and anatase TiO2 nanofibers was obtained by heat treatment at 500°C for 2 h. Dye-sensitized solar cells (DSSCs) with photoanode consisting of the nanocomposite of nanoparticles and nanofibers (5%) rendered a light-to-electricity conversion efficiency (η) of 0.28%. In contrast, the cells with photoanodes consisting of only nanoparticles and nanofibers exhibited η of 0.25% and 0.15%, respectively.