Anatase Nanofibers Research Articles

The Use of Iron-Doped Anatase TiO2 Nanofibers for Enhanced Photocatalytic Fenton-like Reaction to Degrade Tylosin.

The removal of antibiotics from wastewater to prevent their environmental accumulation is significant for human health and ecosystems. Herein, iron (Fe)-atom-doped anatase TiO2 nanofibers (Fe-TNs) were manufactured for the photocatalytic Fenton-like decomposition of tylosin (TYL) under LED illumination. Compared with the pristine TiO2 nanofibers (TNs), the optimized Fe-TNs exhibited improved visible-light-driven photocatalytic Fenton-like activity with a TYL degradation efficiency of 98.5% within 4 h. The effective TYL degradation could be attributed to the expanded optical light absorption and accelerated separation and migration of photogenerated electrons and holes after the introduction of Fe. The photogenerated electrons were highly conducive to the generation of active SO4•- radicals as they facilitated Fe(III)/Fe(II) cycles, and to oxidizing TYL. Moreover, the holes could be involved in TYL degradation. Thus, a significant enhancement in TYL degradation could be achieved. This research verifies the use of iron-doped anatase nanofibers as an effective method to synthesize novel photocatalytic Fenton-like catalysts through surface engineering for wastewater remediation.

Fabrication of high‐efficiency anatase TiO2 photocatalysts using electrospinning with ultra‐violet treatment

AbstractIn metal oxide nanofiber fabrication using the electrospinning method, heat treatment is performed at temperatures of 500°C or higher for crystallization and polymer desorption. Therefore, it is difficult to fabricate low‐temperature phase metal oxides that crystallize at low temperatures. TiO2, a representative metal oxide often used as photocatalysts, is known to have higher photocatalytic activity in the low‐temperature phase (anatase structure) than in the high‐temperature phase (rutile structure). Studies on the fabrication of TiO2 anatase nanofibers using conventional electrospinning have reported disadvantages such as the partial expression of rutile structures and low crystallinity. This study developed an anatase TiO2 nanofiber as a high‐efficiency catalyst based on the electrospinning method and a residual organic matter cleaning method that employs ultra‐violet (UV) light. We fabricated nanofibers using the electrospinning method and implemented TiO2 nanofibers with the anatase structure through heat treatment at 260°C. Residual organics remaining after heat treatment of the fabricated crystalized TiO2 nanofibers were removed by exposing them to UV light, thereby improving photocatalytic efficiency. The photocatalytic efficiency of the fabricated TiO2 nanofibers was confirmed through a methylene blue (MB) decomposition experiment under visible light irradiation. The photocatalytic efficiency (time taken for the concentration of the MB solution to reach 50%) of the UV‐treated TiO2 nanofibers was approximately six times higher than of P25 and the heat‐treated nanofibers.

Role of TiO2 Anatase Surface Morphology on Organophosphorus Interfacial Chemistry

Optimization of physicochemical properties of TiO2 anatase for organophosphorus remediation remains challenging. One approach is to use anatase nanofibers, prepared from hydrothermally synthesized titanates. Charge densities and potentials of anatase nanofibers were determined from atomic force microscopy force–curve measurements using the modified Derjaguin, Landau, Verwey, Overbeek theory, which includes roughness and hydration forces, in the pH range 4–9. Calculated values were −0.007 to −0.03 C m–2 and −70 to −150 mV, respectively. In contrast, at neutral pH, the magnitudes of diffuse layer surface charge densities and potentials have a minimum in anatase nanoparticles. These observations and zeta-potential results suggest that nanofiber surfaces are more acidic compared with nanoparticles. This is consistent with nanofibers having ∼3-fold higher adsorption for organophosphorus methyl parathion (pH ≈ 7). The resulting adsorption includes contributions from (1) charge accumulation at local coordination...

Continuous Production of Nanocrystalline TiO2 Nanofibers

Titanium dioxide in its anatase allotropic modification is well known for its photovoltaic and photocatalytic activity. Through a modification of Nanospider™ device it was achieved a continuous production of nanocrystaline anatase nanofibers. These inorganic fibres have a huge specific surface area due to their fine diameter and structure and thus offer a promising potential in many applications. In this article it is described the device allowing continuous production of inorganic TiO2 nanofibers by the use of electrospinning process and optimization of following calcination process leading to obtaining of almost pure nanocrystaline anatase structure.

Single-Step Synthesis of SnS₂ Nanosheet-Decorated TiO₂ Anatase Nanofibers as Efficient Photocatalysts for the Degradation of Gas-Phase Diethylsulfide.

We report on a facile one-step soft hydrothermal process for synthesizing 1D anatase TiO2 nanofibers decorated with ultrathin SnS2 nanosheets. H-titanate nanofibers were used as preshaped Ti precursor. Under controlled conditions, the H-titanate structure was transformed into anatase maintaining the fibril morphology, while at the same time SnS2 nanosheets were grown in situ on the surface of the nanofibers. The successful formation of SnS2 nanosheets on the TiO2 nanofibers was confirmed by high-resolution TEM, and together with XPS spectroscopy, the tight interface formed between the SnS2 and the anatase TiO2 nanofibers was verified. The 1D SnS2/TiO2 hierarchical nanostructures with semiconductor heterojunction were proven to be very efficient under artificial solar irradiation in the photocatalytic degradation of gaseous diethylsulfide as simulant for live yperite chemical warfare agent as well as model substrate for malodorous organosulfide volatile organic compounds. SnS2 did not operate as a visible light sensitizer for TiO2 but rather as an oxidizing agent and charge-carrier separator. The semiconductor ratio in the heterostructure controlled the photoactivity. Samples with no or high content of SnS2 were less active than those with moderate SnS2 content. Enhanced reactivity was ascribed to an efficient separation of the photogenerated charge carriers driven by the differences in band edge positions and favored by the tight interface within the coupled heterostructure.

Enhanced photodynamic therapy of mixed phase TiO2(B)/anatase nanofibers for killing of HeLa cells

Photodynamic therapy (PDT), which is a procedure that uses photosensitizing drug to apply therapy selectively to target sites, has been proven to be a safe treatment for cancers and conditions that may develop into cancers. Nano-sized TiO2 has been regarded as potential photosensitizer for UV light driven PDT. In this study, four types of TiO2 nanofibers were prepared from proton tri-titanate (H2T3O7) nanofiber. The as-obtained nanofibers were demonstrated as efficient photosensitizers for PDT killing of HeLa cells. MTT assay and flow cytometry (FCM) were carried out to evaluate the biocompatibility, percentage of apoptotic cells, and cell viability. The non-cytotoxicity of the as-prepared TiO2 nanofibers in the absence of UV irradiation has also been demonstrated. Under UV light irradiation, the TiO2 nanofibers, particularly the mixed phase nanofibers, displayed much higher cell-killing efficiency than Pirarubicin (THP), which is a common drug to induce the apoptosis of HeLa cells. We ascribe the high cellkilling efficiency of the mixed phase nanofibers to the bandgap edge match and stable interface between TiO2(B) and anatase phases in a single nanofiber, which can inhibit the recombination of the photogenerated electrons and holes. This promotes the charge separation and transfer processes and can produce more reactive oxygen species (ROS) that are responsible for the killing of HeLa cells.

Versatile Graphene Quantum Dots with Tunable Nitrogen Doping

This paper reports a facile fabrication of N‐doped graphene quantum dots (N‐GQDs) showing controllable chemical properties through a hydrothermal treatment. The N‐GQDs have a uniform size of 3.06 ± 0.78 nm and prefer the equilibrium shapes of circle and ellipse due to the minimization of edge free energy. The N/C atomic ratio in N‐GQDs can be precisely tailored in a range from 8.3 at% to 15.8 at% by simply controlling the concentration of N source (ammonium hydroxide). One order of magnitude quantum yield of 34.5% is achieved by N‐GQDs, compared with the N‐free GQDs, as the substitutional N has an essential role in more effective radiative emission. Excessive N dopants in N‐GQDs can lead to photoluminescence quenching, through nonradiative transition back to the ground state. The N‐GQDs are further found to be suitable as photocurrent conversion materials due to benign energy matching with anatase nanofibers, the ultrafast electron injection at their interface, and efficient electron transfer. This work provides an efficient and inspiring approach to engineering both chemical components and physical properties of N‐GQDs, and will therefore promote their basic research and applications in energy conversion.

The Application of Electrospun Titania Nanofibers in Dye-sensitized Solar Cells

Titania nanofibers were fabricated using the industrial Nanospider(TM) technology. The preparative protocol was optimized by screening various precursor materials to get pure anatase nanofibers. Composite films were prepared by mixing a commercial paste of nanocrystalline anatase particles with the electrospun nanofibers, which were shortened by milling. The composite films were sensitized by Ru-bipyridine dye (coded C106) and the solar conversion efficiency was tested in a dye-sensitized solar cell filled with iodide-based electrolyte solution (coded Z960). The solar conversion efficiency of a solar cell with the optimized composite electrode (η = 7.53% at AM 1.5 irradiation) outperforms that of a solar cell with pure nanoparticle film (η = 5.44%). Still larger improvement was found for lower light intensities. At 10% sun illumination, the best composite electrode showed η = 7.04%, referenced to that of pure nanoparticle film (η = 4.69%). There are non-monotonic relations between the film's surface area, dye sorption capacity and solar performance of nanofiber-containing composite films, but the beneficial effect of the nanofiber morphology for enhancement of the solar efficiency has been demonstrated.

Synthesis and Photocatalytic Performance of Titanium Dioxide Nanofibers and the Fabrication of Flexible Composite Films from Nanofibers

Titanium dioxide nanofibers were synthesized and applied in flexible composite films that are easy to handle and recycle after use. The nanofibers were obtained in a multi-step procedure. First, sodium titanate nanofibers were prepared from TiO2 nanoparticles through the alkali hydrothermal method. In the next step, sodium hydrogen titanate nanofibers were made by washing the sodium titanate nanofibers in HCl solution. Finally, the sodium hydrogen titanate nanofibers were transformed to TiO2 anatase nanofibers by calcination in air. The photocatalytic activity of TiO2 anatase nanofibers were evaluated and compared to a TiO2 nanoparticle catalyst by decomposing methyl orange dye in aqueous solutions. The achieved reaction rate constant of TiO2 anatase nanofibers was comparable to that of Degussa P25. Paper-like flexible composite films were prepared by co-filtrating aqueous dispersions of TiO2 catalyst materials and cellulose. The composite films made from the nanofibers exhibit better mechanical integrity than those of the nanoparticle-cellulose composites.

Physical properties of individual anatase TiO2 nanowires investigated by field emission in a transmission electron microscope

The authors present studies on the field emission (FE) mechanism and the FE-induced transformation of individual anatase TiO2 nanowires (NWs). The NWs were synthesized by electrospinning followed by calcination at 500 °C which produces polycrystalline anatase nanofibers as determined by Raman spectroscopy and transmission electron microscopy (TEM) characterization. Nanowires of ∼100 nm in diameter were individually mounted at the apexes of tungsten tips for further physical characterization. The FE experiments were carried out in a TEM which allows the measurement of the FE current while simultaneously observing structural modifications leading to the NW’s destruction. For low currents (below 100 nA), we observe reproducible FE Fowler-Nordheim I/V characteristics. Higher currents (up to 1 μA) can be obtained but sudden destruction of the NW may take place. Our observations show that a thermally-activated transition occurs and leads to rapid re-crystallization phenomena and a variation of the FE characteristics. If not controlled, this transition leads to thermal runaway and sample destruction. The understanding of the destruction phenomena is a key parameter to further improve the FE performance of such nanowire cathodes.

Rutile TiO 2 nanowires on anatase TiO 2 nanofibers: A branched heterostructured photocatalysts via interface-assisted fabrication approach

A water–dichloromethane interface-assisted hydrothermal method was employed to grow rutile TiO 2 nanowires (NWs) on electrospun anatase TiO 2 nanofibers (NFs), using highly reactive TiCl 4 as precursor. The water–dichloromethane interface inhibited the formation of rutile NWs in water phase, but promoted the selective radial growth of densely packed rutile NWs on anatase NFs to form a branched heterojunction. The density and length of rutile NWs could be readily controlled by varying reaction parameters. A formation mechanism for the branched heterojunction was proposed which involved (1) the entrapment of rutile precursor nanoparticles at water–dichloromethane interface, (2) the growth of rutile NWs on anatase NFs via Ostwald ripening through the scavengering of interface-entrapped rutile nanoparticles. The heterojunction formed at anatase NF and rutile NW enhanced the charge separation of both under ultraviolet excitation, as evidenced by photoluminescence and surface photovoltage spectra. The branched TiO 2 heterostructures showed higher photocatalytic activity in degradation of rodamine B dye solution than anatase NFs, and the mixture of anatase NFs, and P25 powders, which was discussed in terms of the synergistic effect of enhanced charge separation by anatase–rutile heterojunction, high activity of rutile NWs, and increased specific area of branched heterostructures.

Nitrogen-Doped Anatase Nanofibers Decorated with Noble Metal Nanoparticles for Photocatalytic Production of Hydrogen

We report the synthesis of N-doped TiO(2) nanofibers and high photocatalytic efficiency in generating hydrogen from ethanol-water mixtures under UV-A and UV-B irradiation. Titanate nanofibers synthesized by hydrothermal method are annealed in air and/or ammonia to achieve N-doped anatase fibers. Depending on the synthesis route, either interstitial N atoms or new N-Ti bonds appear in the lattice, resulting in slight lattice expansion as shown by XPS and HR-TEM analysis, respectively. These nanofibers were then used as support for Pd and Pt nanoparticles deposited with wet impregnation followed by calcination and reduction. In the hydrogen generation tests, the N-doped samples were clearly outperforming their undoped counterparts, showing remarkable efficiency not only under UV-B but also with UV-A illumination. When 100 mg of catalyst (N-doped TiO(2) nanofiber decorated with Pt nanoparticles) was applied to 1 L of water-ethanol mixture, the H(2) evolution rates were as high as 700 μmol/h (UV-A) and 2250 μmol/h (UV-B) corresponding to photo energy conversion percentages of ∼3.6 and ∼12.3%, respectively.

Growth of hierarchical TiO2 nanostructures on anatase nanofibers and their application in photocatalytic activity

Three-dimensional hierarchical nanostructures of TiO2, consisting of high density nanorods on nanofibers, were synthesized by the combination of electrospinning, thermal annealing and hydrothermal methods. The morphologies, crystal structures, surface area, band gap and photocatalytic activity of the hierarchical nanostructures were characterized by Raman microscopy, X-ray diffraction, UV-vis spectroscopy, scanning electron microscopy, transmission electron microscopy and surface area analysis. The results revealed that the nanofibers, synthesized by the electrospinning method followed by the thermal annealing, were of anatase phase. Similarly, the TiO2 nanorods grown on the anatase nanofibers by hydrothermal reaction in Ti-HCl solution were of rutile phase, with tetragonal shape, and had top square facet morphologies. The diameter and the length of these rutile nanorods could be varied over the range, 10 nm to 400 nm, and 20 nm to 1 um, respectively, by changing the parameters of the hydrothermal reaction. The growth mechanisms of these rutile rods are discussed on the basis of (i) surface roughness of the anatase nanofibers, (ii) presence of the twin planes of anatase layer with structure similar to rutile phase and (iii) Cl/Ti ratio in the solution. The estimated band gap energies of the nanofibers and nanorods were close to 3.2 eV and 3.0 eV. The total surface area of the hierarchical nanostructures could reach up to ∼20.41 m2 g−1; while, the pure the anatase nanofibers surface area is ∼19.79 m2 g−1. For the first time, such TiO2 hierarchical nanostructures, rutile nanorods on anatase nanofibers, have been synthesized. The photocatalytic activity of the TiO2 hierarchical nanostructures was found to be superior to that of pure anatase nanofibers.

Nanocables composed of anatase nanofibers wrapped in UV-light reduced graphene oxide and their enhancement of photoinduced electron transfer in photoanodes

This paper reports a facile method for fabricating a new nanocable structure consisting of reduced graphene oxide (RGO) wrapped anatase TiO2 nanofibers by UV-light photocatalytic reduction. The nanocable was prepared by injecting 0.8 g L−1 aqueous graphene oxide colloid into 0.8 g L−1 electrospun TiO2 nanofibers in ethanol, followed by a mild UV light irradiation for 20 h. The conformal wrapping of RGO is a result of noncovalent interactions (van der Waals and electrostatics). The RGO walls of the nanocables exhibited a uniform thickness of ∼5 nm. Half of the oxygen groups were removed and the partially reduced RGO was favored to be well dispersed in water. The invariability of the ID/IG ratio of the D to G bands in Raman spectra proposed the presence of a “defect-repair” process in the reduction. We further demonstrated the enhancement of photoinduced electron transfer and depression of electron combination by integrating the RGO/TiO2 nanocables into TiO2 photoanodes, proving our nanocables are good candidates for photovoltaic devices.

Formation of Inorganic Nanofibers from Preformed TiO2 Nanoparticles via Electrospinning

The study demonstrates that mesoporous anatase nanofibers can be prepared via electrospinning of preformed TiO2 nanoparticles in an adequate solvent mixture without the use of any surfactant. A systematic study of several parameters influencing the fiber formation, that is, solvent composition, molecular weight of the polymer, TiO2 source, and humidity, was conducted to investigate the underlying physicochemical principles that determine the formation of the porous structure. The porosity of the fibers was characterized by nitrogen physisorption and SEM investigations with consistent results. It is proposed that the microphase separation of nanoparticles from the polymer produces a mesoscopic hybrid, resulting in pronounced mesoporosity after calcination. We believe that our study thus presents a general methodology to generate nonwovens of metal oxides with intrinsic mesoporosity based on electrospinning of preformed nanoparticles.

Perpendicular rutile nanosheets on anatase nanofibers: Heterostructured TiO 2 nanocomposites via a mild solvothermal method

A novel hierarchically heterostructured TiO 2 nanocomposite, which consists of rutile nanosheets perpendicular standing on anatase nanofibers, is successfully created through a two-step approach. Firstly, the fibrous anatase TiO 2 framework is fabricated by a facile electrospinning method, then a layer of relative uniform rutile nanosheets grow on the fibers after a mild solvothermal reaction process. This work provides a convenient and effective route for fabricating desired three-dimensional nanocomposite and should be easily extended through to many other materials system.

Hierarchical nanostructures of K-birnessite nanoplates on anatase nanofibers and their application for decoloration of dye solution

This paper reports a simple method for fabricating hierarchical nanostructures consisting of K-birnessite (KxMnO2) nanoplates on anatase (TiO2) nanofibers. The nanofibers were prepared in the form of a composite by electrospinning, followed by calcination at 500 °C in air for 2 h. The nanofibers were then immersed in a sulfuric acid solution containing KMnO4 at 90 °C for 20 min to deposit the KxMnO2 nanoplates. The nanoplates had a thickness of ∼5 nm and an edge length of ∼150 nm, and were oriented perpendicular to the nanofibers. They were confirmed as K-birnessite by XRD and EDX measurements. The density of the KxMnO2 nanoplates could be controlled by simply adjusting the concentration of KMnO4 and/or the deposition time. We also investigated the growth mechanism in light of surface roughness for the nanofibers and spatial confinement for the plates. We further demonstrated the potential use of these hierarchical nanostructures for waste water treatment by removing congo red from an aqueous solution. They exhibited good performance in both batch and continuous flow studies.

Application of H-titanate nanofibers for degradation of Congo Red in an annular slurry photoreactor

Anatase nanofibers (TiO2–N) were synthesized as photocatalyst for the application in an annular slurry photoreactor (ASP). The unique properties of TiO2–N have facilitated its high reactivity and suitability for water treatment. The influence of operational variables: TiO2–N loading, pH, aeration rate and dye concentration on the photo-degradation kinetics and efficiency to remove a model compound of Congo Red (CR) were investigated. The photo-degradation kinetics of CR followed the Langmuir–Hinshelwood regime at lower pH. The Langmuir adsorption constant, KL–H was determined as 7.695 × 102 dm3 mol−1. The optimal photo-degradation rate of 3.47 × 10−2 mol dm−3 min−1 was achieved at 60 ppm CR, pH 3, aeration rate of 5 dm3 min−1 and TiO2–N loading of 4 g dm−3. Batch settling tests based on Kynch's theory revealed that the TiO2–N photocatalysts could produce a settling velocity of 8.38 × 10−4 ms−1. It was expected that these novel TiO2–N particles can deliver a true engineering solution as an industrial process for photocatalytic water treatment.

Effect of Calcination Temperature on the Structure of a Pt/TiO2 (B) Nanofiber and Its Photocatalytic Activity in Generating H2

Hydrogen trititanate (H 2Ti 3O 7) nanofibers were prepared by a hydrothermal method in 10 M NaOH at 403 K, followed by acidic rinsing and drying at 383 K. Calcining H 2Ti 3O 7 nanofibers at 573 K led to the formation of TiO 2 (B) nanofibers. Calcination at 673 K improved the crystallinity of the TiO 2 (B) nanofibers and did not cause any change in the morphology and dimensions of the nanofibers. TiO 2 (B) and H 2Ti 3O 7 nanofibers are 10-20 nm in diameter and several micrometers long, but FE-SEM reveals that several of these nanofibers tend to bind tightly to each other, forming a fiber bundle. Calcination at 773 K transformed TiO 2 (B) nanofibers into a TiO 2 (B)/anatase bicrystalline mixture with their fibrous morphology remaining intact. Upon increasing the calcination temperature to 873 K, most of the TiO 2 (B) nanofibers were converted into anatase nanofibers and small anatase particles with smoother surfaces. In the photocatalytic dehydrogenation of neat ethanol, 1% Pt/TiO 2 (B) nanofiber calcined at 673 K was the most active catalyst and generated about the same amount of H 2 as did 1% Pt/P-25. TPR indicated that the calcination of 1% Pt/TiO 2 (B) nanofiber at 573 K produced a poor Pt dispersion and poor activity. Calcination at a temperature higher than 773 K (in ambient air) resulted in an SMSI effect similar to that observed over TiO 2 in the reductive atmosphere. As suggested by XPS, such an SMSI effect decreased the surface concentration of Pt metal and created Pt (delta) sites, preventing Pt particles from functioning as a Schottky barrier and leading to a lower activity. Because of the synergetic effect between TiO 2 (B) and anatase phases, the bicrystalline mixture, produced by calcining at 773 K, was able to counter negative effects such as the reduction in surface area and the SMSI effect and maintained its photocatalytic activity.

Direct Oxidation of Methanol on Pt Nanostructures Supported on Electrospun Nanofibers of Anatase

This letter reports an electrocatalytic study of electrospun anatase nanofibers decorated with Pt catalysts in the form of nanoparticles or nanowires. We decorated the surface of nanofibers with Pt through a polyol process, in which nanoparticles of 2−5 nm in size were formed with different densities depending on the reaction time. By adding Fe(III) ions to the polyol process, we also obtained Pt nanowires of ∼7 nm in diameter and up to 125 nm in length. We then studied the effects of both the coverage and morphology of the Pt nanostructures on the methanol oxidation reaction. Nanofibers with a submonolayer of Pt nanoparticles were found to display improved catalytic durability over commercial Pt/C as determined by chronoamperometry owing to a synergistic effect of the underlying anatase surface and the Pt nanostructures with well-defined facets. Improvement in catalytic activity and durability were also observed for Pt nanowires, indicating that the additional catalytic facets on the nanowires can enhanc...