Enhanced photocatalytic activity of electrospun TiO2/ZnO nanofibers with optimal anatase/rutile ratio

The photocatalytic characteristics of the TiO₂/ZnO nanofibers synthesized by electrospinning followed by calcinating at different temperatures to alter the anatase-to-rutile ratio are investigated. The results demonstrate that the photocatalytic activity of TiO₂/ZnO nanofibers is enhanced by optimizing the anatase/rutile ratio among the trade-off effects of the band-gap energy, the electron/hole recombination rate, and the surface area. When calcined at 650 °C, the TiO₂/ZnO nanofibers with optimal anatase/rutile ratio (48:52) balancing these trade-off effects have the highest photocatalytic efficiency both in the degradation of RhB in liquid and conversion of NO gas.     

Preparation of ordered TiO2 nanofibers/nanotubes by magnetic field assisted electrospinning and the study of their photocatalytic properties

Ordered-and-oriented TiO₂ nanofibers and nanotubes were prepared by magnetic field-assisted electrospinning, and photocatalytic properties of all samples were analyzed under UV–Vis shine. TiO₂ nanofibers/nanotubes prepared by magnetic field-assisted electrospinning showed better degradation effect on rhodamine B, reduced the band gap, increased the contact area of organic pollutants with the sample and higher photocatalytic activity than TiO₂ nanofibers/nanotubes prepared by classical electrospinning. The product obtained after high temperature annealing was a mixed phase of rutile phase and anatase phase and could be advantageous to the segregate of photogenic electron hole pairs and enhance the high dye absorption capacity; Surface roughness could increase more active sites and accelerate the reaction rate of photocatalytic activity; the addition of magnetic field regulated the morphology of TiO₂, and narrowed the band gap to favor photocatalytic performance. The magnetic field-assisted electrospinning study prepared in this paper was an easy-to-use and versatile method for the preparation of ordered TiO₂ nanomaterials, which could be easily extended to practical applications or other materials for photocatalysis and water cleavage.     

TiO2 nanofibers doped with rare earth elements and their photocatalytic activity

In the present study rare earth doped (Ln³⁺–TiO₂, Ln = La, Ce and Nd) TiO₂ nanofibers were prepared by the sol–gel electrospinning method and characterized by XRD, SEM, EDX, TEM, and UV-DRS. The photocatalytic activity of the samples was evaluated by Rhodamine 6G (R6G) dye degradation under UV light irradiation. XRD analysis showed that all the synthesized pure and doped titania nanofibers contain pure anatase phase at 500 °C but at 700 °C it shows both anatase and rutile phase. XRD result also shows that Ln³⁺-doped titania probably inhibits the phase transformation. The diameter of nanofibers for all samples ranges from 200 to 700 nm. It was also observed that the presence of rare-earth oxides in the host TiO₂ could decrease the band gap and accelerate the separation of photogenerated electron–hole pairs, which eventually led to higher photocatalytic activity. To sum up, our study demonstrates that Ln³⁺-doped TiO₂ samples exhibit higher photocatalytic activity than pure TiO₂ whereas Nd³⁺-doped TiO₂ catalyst showed the highest photocatalytic activity among the rare earth doped samples.     

Photocatalytic degradation of dyestuff wastewater under visible light irradiation using micron‐sized mixed crystal TiO2 powders

A phase transformation of micron‐sized TiO₂ powder from anatase to rutile was attempted by heat‐treatment in order to generate a new mixed crystal TiO₂ with high associated photocatalytic activity. Heat‐treated micron‐sized TiO₂ powders at different transition stages were characterized by X‐ray diffraction analysis (XRD), Fourier transform infrared spectroscopy (FT‐IR) and transmission electron microscopy (TEM) methods. The tests of photocatalytic activity of the heat‐treated micron‐sized TiO₂ powders were conducted by the photocatalytic degradation of Rhodamine B and Acid Red B under visible light irradiation. The results indicate that mixed crystal TiO₂ photocatalyst heat‐treated at 400 °C for 60 min shows the highest photocatalytic activity. It can effectively decompose the Rhodamine B and Acid Red B in aqueous solution after 6 h visible light irradiation. A remarkable improvement in photocatalytic activity of TiO₂ is caused by the formation of combined rutile–anatase phases and separation of photogenerated electron–hole pairs. Copyright © 2007 Society of Chemical Industry     

The effects of atmosphere and calcined temperature on photocatalytic activity of TiO2 nanofibers prepared by electrospinning

TiO₂-based nanofibers were synthesized using a sol–gel method and electrospinning technique. The as-spun composite fibers were heat-treated at different temperatures (500°C, 550°C, 600°C, and 650°C) and atmospheres (ammonia and nitrogen) for 4 h. The fibers had diameters of 50 to 200 nm and mainly featured anatase and rutile phases. The anatase phase decreased and the rutile phase increased with increasing temperature. Different nitrogen conditions exerted minimal effects on the TiO₂ crystalline phase. Different nitriding atmospheres during preservation heating yielded various effects on fibers. The effect of nitrogen in ammonia atmosphere is better than that in nitrogen atmosphere. The fibers heat-treated at 600°C and subjected to preservation heating in NH₃ showed high photocatalytic activity.     

Facile Fabrication of TiO2/SrTiO3 Composite Nanofibers by Electrospinning for High Efficient H2 Generation

Using electrospinning, specially prepared Ti and Sr precursor TiO₂/SrTiO₃ composite nanofibers were successfully fabricated. This would ensure the close and uniform contact between TiO₂ and SrTiO₃, which significantly contributes to the electrons transfer at the interface between the two semiconductors with different band gaps. Meanwhile, the long fibrous structure of TiO₂/SrTiO₃ composite nanofibers would further ease the electron transfer, enlarge the specific surface area, and enhance the light absorption capability thus leading to the improvement of photocatalytic efficiency. Because of the above‐mentioned advantages, the TiO₂/SrTiO₃ composite nanofibers exhibited higher photocatalytic H₂ generation efficiency over bare TiO₂ nanofibers in a water/methanol sacrificial reagent system under the irradiation of UV light.     

Carbon induced phase transformation in electrospun TiO2/multiwall carbon nanotube nanofibers

Nanofibers of titania and composite nanofibers of titania and multiwall carbon nanotubes were synthesized by electrospinning using a sol-gel process combined with activated carbon nanotubes. The relationships of treatment temperature, carbon nanotube content on the crystal phase, fiber morphology, and electric properties are reported. It is found that the rutile phase becomes more prominent at low heat treatment temperatures with an increase of carbon content in nanofibers, be it for higher amount of carbon due to reducing atmosphere or due to an increase in MWCNT. Atmospheric control and lower heat treatment temperatures enable crystalline nanocomposite fibers of anatase where the level of rutile is below the detection limit of XRD or Raman spectroscopy. This work provides a new path to fabricate electrospun TiO₂/MWCNT nanocomposite nanofibers with limited C-induced rutile phase.     

SnO2 nanoparticle embedded TiO2 nanofibers — Highly efficient photocatalyst for the degradation of rhodamine B

SnO₂ nanoparticle embedded TiO₂ nanofibers were fabricated by a simple electrospinning method. The relationship between the SnO₂/TiO₂ weight ratio and photocatalytic efficiency was investigated from the view point of Rhodamine B decomposition. In addition, electron microscopic analysis, energy dispersive analysis, X-ray diffraction analysis, and photoluminescence study demonstrated that SnO₂ nanoparticle was successfully embedded in TiO₂ nanofibers. TiO₂ nanofibers containing SnO₂ nanoparticle provided an enhanced interfacial region between TiO₂ and SnO₂. SnO₂ nanoparticles embedded TiO₂ nanofibers exhibited highly efficient photocatalytic activity under UV light irradiation due to high charge separation of electron–hole pairs.     

Antibacterial activity of photocatalytic electrospun titania nanofiber mats and solution-blown soy protein nanofiber mats decorated with silver nanoparticles

Highly porous photocatalytic titania nanoparticle decorated nanofibers were fabricated by electrospinning nylon 6 nanofibers onto flexible substrates and electrospraying TiO₂ nanoparticles onto them. Film morphology and crystalline phase were measured by SEM and XRD. The titania films showed excellent photokilling capabilities against E. coli colonies and photodegradation of methylene blue under moderately weak UV exposure (≤ 0.6 mW/cm² on a 15-cm illumination distance). In addition, solution blowing was used to form soy protein-containing nanofibers which were decorated with silver nanoparticles. These nanofibers demonstrated significant antibacterial activity against E. coli colonies without exposure to UV light. The nano-textured materials developed in this work can find economically viable applications in water purification technology and in biotechnology. The two methods of nanofiber production employed in this work differ in their rate with electrospinning being much slower than the solution blowing. The electrospun nanofiber mats are denser than the solution-blown ones due to a smaller inter-fiber pore size. The antibacterial activity of the two materials produced (electrospun titania nanoparticle decorated nanofibers and silver-nanoparticle-decorated solution-blown nanofibers) are complimentary, as the materials can be effective with and without UV light, respectively.     

Photocatalytic activities of electrospun tin oxide doped titanium dioxide nanofibers

SnO₂ doped TiO₂ electropsun nanofiber photocatalysts were successfully prepared by means of electrospinning process. The surface morphology, structure and optical properties of the resultant products were characterized by field-emission electron microscopy (FE-SEM), X-ray diffraction (XRD), high-resolution transmission electron microscopy (HR-TEM), X-ray photoelectron spectroscopy (XPS), UV–vis spectroscopy, photoluminescence (PL) and cathodoluminescence (CL) techniques. The utilized physiochemical analyses indicated that the introduced SnO₂ doped TiO₂ nanofibers have a smooth surface and uniform diameters along their lengths. The photocatalytic performance of the composite nanofibers was tested for degradation of methylene blue (MB) and methyl orange (MO) dye solution under ultraviolet (UV) irradiation. Under the UV irradiation, the photocatalytic reaction rate in case of utilizing SnO₂-doped TiO₂ nanofibers was rapidly increased than that of the pristine TiO₂ nanofibers. Overall, this study demonstrates cheap, stable and effective material for photocatalytic degradation at room temperature.     

Fabrication of TiO2 photocatalytic electrode and contamination control with atmospheric pressure O2 plasma jet

In this study, we demonstrate the fabrication of TiO₂ photocatalytic electrode by sol-gel and electrospinning technique. The anatase TiO₂ nanofiber is successfully formed after thermal annealing at 260°C. As-prepared TiO₂ photocatalytic electrode contains surface contamination, which includes a polymer binder such as ethyl cellulose, carbon by carbonization of polyvinylpyrrolidone, and residue polyvinylpyrrolidone. To efficiently remove the surface contaminants from the TiO₂ photocatalytic electrode, we employ an atmospheric-pressure O₂ plasma jet and the exposure time is controlled by the scanning rate. As the results, photodegradation efficiency of methylene blue is significantly enhanced with a scanning rate in the range of 100-500 μm/s and was saturated with a scanning rate in the range of 10-100 μm/s.     

TiO2, TiO2/Ag and TiO2/Au photocatalysts prepared by spray pyrolysis

TiO₂, TiO₂/Ag and TiO₂/Au photocatalysts exhibiting a hollow spherical morphology were prepared by spray pyrolysis of aqueous solutions of titanium citrate complex and titanium oxalate precursors in one-step. Effects of precursor concentration and spray pyrolysis temperature were investigated. By subsequent heat treatment, photocatalysts with phase compositions from 10 to 100% rutile and crystallite sizes from 12 to 120 nm were obtained. A correlation between precursor concentration and size of the hollow spherical agglomerates obtained during spray pyrolysis was established. The anatase to rutile transformation was enhanced with metal incorporations and increased precursor concentration. The photocatalytic activity was evaluated by oxidation of methylene blue under UV-irradiation. As-prepared TiO₂ particles with large amounts of amorphous phase and organic residuals showed similar photocatalytic activity as the commercial Degussa P25. The metal incorporated samples showed comparable photocatalytic activity to the pure TiO₂ photocatalysts.     

Freestanding hematite nanofiber membrane for visible-light-responsive photocatalyst

Freestanding mesoporous hematite (α-Fe₂O₃) nanofiber membranes were successfully fabricated by sol–gel electrospinning process using ferratrane precursor for use as a high-performance material for visible-light-responsive photocatalyst. Non-porous nanofiber membranes spun on the heated collector at 300 °C were crystalline α-Fe₂O₃ phase. Upon calcination, pure mesoporous nanofiber membranes were obtained even at a low temperature of 400 °C. The photocatalytic membrane calcined at 400 °C showed the highest efficiency for methylene blue (MB) degradation under visible-light irradiation. The synergetic effects of higher surface area, pore volume and pore diameter promoted the photocatalytic efficiency for MB degradation under visible light. The utilization of photocatalyst in the form of membrane could not only solve the problems of catalyst separation and recovery, but also produce high photodegradation efficiency for both systems without and with hydrogen peroxide even at a catalyst loading as low as 0.04 g/L. No appreciable loss in photocatalytic activity was observed and structural integrity was retained, even after five cycles of photodegradation, which predicted the stability and reusability of these nanofiber membranes for practical use in environmental applications.     

Electrospinning amorphous SiO2-TiO2 and TiO2 nanofibers using sol-gel chemistry and its thermal conversion into anatase and rutile

SiO₂-TiO₂ nanofibers were electrospun from partially hydrolyzed tetraethyl orthosilicate, and titanium isopropoxide using sol-gel chemistry. SiO₂-TiO₂ sol phase diagrams were created summarizing the role of composition on solution homogeneity and electrospinnability. Inorganic nanofiber spinnability was studied without the addition of any organic polymer, oligomer, gelator, or binder. TiO₂ concentration within SiO₂-TiO₂ fibers ranged from 25 to 100 mol%. SiO₂, SiO₂-TiO₂, and TiO₂ nanofiber structures were investigated using scanning electron microscopy and transmission electron microscopy. Inorganic fiber spinning was highly dependent on sol reaction temperature, time, and solution composition. At high TiO₂ concentrations, twisted and ribbon-like nanofibers with dumbbell-shaped cross-sections were observed. This was attributed to jet branching and splitting during electrospinning. Electrospun fibers were amorphous at room temperature, but thermally converted into crystalline anatase, which underwent additional structural changes at higher temperatures into rutile. This anatase-rutile thermal phase transformation was highly dependent upon TiO₂ concentration. Nanofiber composition, thermal stability, and crystalline structures were characterized by energy-dispersive X-ray spectroscopy; Fourier transform infrared spectroscopy, thermal gravimetric analysis, and wide-angle X-ray diffraction.     

Enhanced photocatalytic degradation of rutile/anatase TiO2 heterojunction nanoflowers

Rutile/anatase TiO₂ heterojunction nanoflowers were prepared via a facile one-step hydrothermal approach using titanium tetrachloride and urea as the raw materials, cetyl trimethyl ammonium bromide (CTAB) as the template. The prepared TiO₂ nanoflowers were characterized by XRD, SEM, TEM and BET analyses. The photocatalytic performance of the as-prepared TiO₂ samples for methyl blue degradation under simulated solar light was investigated. TiO₂ heterojunction nanoflowers with mixed rutile/anatase phase (prepared with 3 mmol CTAB) give the highest photocatalytic activity. In addition, TiO₂ nanoflowers show excellent stability after 9 cycles under the same conditions. These results suggested that the mixed phase anatase/rutile TiO₂ heterojunction nanoflowers have great potential for the future photodegradation of real dye waste water.     

Study of the effect of rutile/anatase TiO2 nanoparticles synthesized by hydrothermal route in electrospun PVA/TiO2 nanocomposites

Mixed rutile–anatase TiO₂ nanoparticles were synthesized by hydrothermal treatment under acidic conditions and incorporated into poly(vinyl alcohol) (PVA). These nanocomposites were electrospun to produce nanofibers of PVA/TiO₂, which were characterized by scanning electron microscopy, transmission electron microscopy, X‐ray diffraction (XRD), UV–vis diffuse reflectance spectroscopy, thermogravimetric analysis, and differential scanning calorimetry. The photocatalytic degradation of Rhodamine B and degradation of the polymer by UV‐C lamps were also investigated. The results showed that TiO₂ nanoparticles did not change the morphology and thermal behavior of the nanofiber polymer, but were effective in modifying the UV absorption of PVA without reducing its stability. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Preparation of Necklace-Structured TiO2/SnO2 Hybrid Nanofibers and Their Photocatalytic Activity

TiO₂/SnO₂ nanonecklace-structured hybrid nanofibers have been prepared via an electrospinning method. These hybrid nanofibers are characterized with SnO₂-rich beads and pure TiO₂ chains. It is found that TiO₂ in the beads shows a rutile structure, and the one in the chains is entirely composed of anatase phase. This novel microstructure enhanced the photocatalytic activity, as well as its ideal recyclable character. We believe that this fire-new type of nanofiber may potentially serve as a new generation photocatalyst in environmental remediation.     

Mn2O3/TiO2 nanofibers with broad-spectrum antibiotics effect and photocatalytic activity for preliminary stage of water desalination

Composite nanofibers consisting of Mn₂O₃ and TiO₂ were prepared by the electrospinning process, and tested as Gram-class-independent antibacterial agent and photocatalyst for organic pollutants degradation. Initially, electrospinning of a sol–gel consisting of titanium isopropoxide, manganese acetate tetrahydrate and poly(vinyl pyrrolidone) was used to produce hybrid polymeric nanofibers. Calcination of the obtained nanofibers in air at 650 °C led to produce good morphology Mn₂O₃/TiO₂ nanofibers. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were employed to characterize the as-spun nanofibers and the calcined product. X-ray powder diffractometry (XRD) analysis was also used to characterize the chemical composition and the crystallographic structure of the sintered nanofibers. The antibacterial activity of Mn₂O₃/TiO₂ nanofibers against Gram negative and Gram positive bacteria was investigated by calculating the minimum inhibitory concentration after treatment with the nanofibers. Investigations revealed that the lowest concentration of Mn₂O₃/TiO₂ nanofibers solution inhibiting the growth of Staphylococcus aureus ATCC 29231 and Escherichia coli ATCC 52922 strains is 0.4 and 0.8 μg/ml, respectively. Incorporation of Mn₂O₃ significantly improved the photodegradation of methylene blue (MB) dye under the visible light irradiation due to enhancing rutile phase formation in the TiO₂ nanofibers matrix.     

Preparation of Unique TiO2 Nano-particle Photocatalysts by a Multi-gelation Method for Control of the Physicochemical Parameters and Reactivity

A novel multi-gelation method to prepare TiO₂ nano-particle photocatalysts showed good performance in controlling the important parameters determining the photocatalytic reactivity, i.e., the particle size, surface area, crystallinity, pore-volume, pore-diameter as well as the anatase and rutile phase composition of the catalysts. In particular, this method at higher pH swing times could prevent the phase transition from anatase to rutile, leading to higher photocatalytic activity. By adopting variations in the pH swing, the TiO₂ nano-particle photocatalysts showed significantly higher photocatalytic reactivity for the complete oxidation of 2-propanol diluted with water into CO₂ and H₂O. It can be considered a viable alternative method for the preparation of high performance TiO₂ nano-particle photocatalysts for widespread commercial applications.     

Preparation of Highly Active TiO2 Nano-particle Photocatalysts by a Flame Aerosol Method for the Complete Oxidation of 2-Propanol

A flame aerosol method has been employed to prepare spherical TiO₂ nano-particle photocatalysts with controlled anatase/rutile phase ratios without calcination at higher temperatures. This method was found to have important advantages since the main factors in achieving high photocatalytic activity such as the particle size, crystallinity and the anatase/rutile phase ratios could be easily controlled. In particular, the incorporation of small amounts of bimetals, such as Fe and Zn, were found to initiate the formation of well-crystalline, small and uniform spherical nano-size particles with a well-defined anatase/rutile phase ratio of around 60/40, similar to P-25 TiO₂. This suppressed the recombination of the photoformed charge carriers leading to a significant increase in the photocatalytic reactivity of the TiO₂ nano-particles. The incorporation of very small amounts of mono-metals, such as Fe, Cr and Zn (around 1 at.%), within the TiO₂ nano-particles led to a slight increase in the photocatalytic activity of the TiO₂ nano-particle photocatalysts for the complete oxidation of 2-propanol dissolved in water into CO₂ and H₂O as compared with the unincorporated pure TiO₂. The incorporation of bimetals of Fe and Zn within TiO₂ (Fe/Zn–TiO₂) nano-particles, on the other hand, led to a remarkable enhancement in the photocatalytic activity as compared with the unincorporated and mono-metal incorporated TiO₂.