Electrospun TiO2 Research Articles

Improved Conversion Efficiency in Dye-Sensitized Solar Cells Based on Electrospun TiCl4-Treated TiO2 Nanorod Electrodes

Electrospun TiO2 nanofibers were prepared by electrospinning of the polymeric sol containing a titanium precursor and Poly(vinyl acetate) in acetic acid-dimethyl formamide mixture and subsequent sintering of the nanofibers at 500°C. The resultant continuous, polycrystalline porous nanofibers contained TiO2 grains of 15--20 nm sizes. The continuous TiO2 nanofibers were broken down into nanorice grains via mechanical grinding. Morphology and crystal structure of the resulting nanofibers and nanorice grains were characterized by scanning electron microscopy (SEM) and X-ray diffraction analysis (XRD), respectively. Photovoltaic properties of dye-sensitized solar cells (DSSC) fabricated from the nanofibers and nanorice grains, showed superior performance with the latter.

Titania nanofiber photoanodes for dye-sensitized solar cells

The porous structure of electrospun TiO2 nanofibers was characterized in-depth and the best performing nanofiber structure for application in dye sensitized solar cell was identified. Four types of TiO2 nanofibers were investigated (electrospun from polyvinylpyrrolidone (PVP) and hydroxypropylcellulose (HPC) as templates) with diameters 100–280nm and surface areas 9–100m2/g. Mesoporous TiO2 films were prepared by supramolecular templating with a block copolymer Pluronic P123. For the preparation of composite nanofiber mesoporous films, 2% or 15% of electrospun nanofibers were added. Incorporation of nanofibers into the mesoporous film results in a decrease in dye N719 adsorption but at the same time in an increase of roughness factor. Solar efficiency of composite mesoporous films increases (unlike for pure mesoporous films) even for layer thickness higher than 2.3μm. Thus we developed a simplified method for the preparation of thick mesoporous nanofiber electrodes with improved solar efficiency of 5.51% which outperforms that of pure mesoporous film (4.96%).

Optimization of electrospun TiO2 nanofibers photoanode film for dye‐sensitized solar cells through interfacial pre‐treatment, controllable calcination, and surface post‐treatment

Dye‐sensitized solar cells (DSSCs) are generally viewed as next generation photovoltaic devices. Electrospun TiO2 nanofibers (NFs) film can be used to construct photoanode for DSSCs. A systematic strategy to optimize such a novel photoanode material of DSSCs was elaborated in this paper. A main drawback of NFs photoanode is the poor adhesion of ceramic NFs film to its conductive glass substrate. This problem can be well solved by sandwiching a transition layer between the overlaid NFs film and the underlaid glass substrate through an interfacial spin‐coating pre‐treatment. After electrospinning, a controllable calcination is also indispensable for obtaining an ideal nanofibrous mat with good morphology and adhesion. The choice of calcination parameters including temperature, holding time, and heating rate was discussed in detail. In addition, a surface TiCl4 post‐treatment can further improve adhesion as well as strength for the NFs photoanode film. And the performance of the resulting DSSCs will benefit from the TiCl4 post‐treatment. Copyright © 2013 John Wiley & Sons, Ltd.

Hybrid solar cells based on poly(3-hexylthiophene) and electrospun TiO2 nanofibers modified with CdS nanoparticles

Organic–inorganic hybrid solar cells based on poly(3-hexylthiophene) and electrospun TiO2 nanofibers were fabricated by solution process. The efficiency of the device was improved by modifying CdS nanoparticles on the surface of TiO2 by electrochemical method. The CdS layer can lead to the increase of both open circuit voltage and short circuit current of the device, which are attributed to enhanced exciton dissociation and light absorption and suppressed carrier recombination by CdS at the heterojunction. However, too thick CdS layer led to increased series resistance and decreased efficiency of the device. Therefore, the optimum condition of the CdS deposition was obtained, which increased the power conversion efficiency of the device for about 50%. Our results indicate that the surface modification on the inorganic semiconductor layer is an effect way to improve the performance of the hybrid solar cells.

Effect of Calcinations Temperature on Structural Properties, Phase Transformation and Photocatalytic Activity of Electrospun TiO2 Nanofibers

TiO2 nanofibers were fabricated via an electrospinning method. Titanium (IV) isopropoxide (TIP) and poly (viny pyrrolidone) (PVP) were used as a starting precursor. The electrospun TiO2 nanofibers were obtained by injecting the precursor through a needle under a strong electrical field. As-spunfibers were calcined at 500, 600, 700, 800 and 900 °C for 2 h. The structural of properties of the nanofibers were characterized using X-ray diffraction (XRD) and Scanning electron microscope (SEM). XRD results indicated that the crystallinity of TiO2 nanofibers corresponds to rutile and anatase phase of TiO2 depending on calcinations temperature. SEM results indicated that the surface morphology and size TiO2 nanofibers. The photocatalytic degradation of RhB may be attributed to significant absorption enhancement in visible region by phase transformation of TiO2 nanofibers and fiber size dependence active surface areas.

Photocatalytic degradation of Rhodamine B using electrospun TiO2 and ZnO nanofibers: a comparative study

TiO2 and ZnO nanofibers were fabricated through a facile electrospinning method. The obtained nanofibers were characterized by a variety of analytical means including FESEM, TEM, SAED, XRD, UV–Vis, and PL. Compared with nanoparticles, nanofibers can be recycled more easily when they are used as photocatalysts. The photocatalytic activities of these two nanofibers were investigated and compared by evaluating the photodegradation of hazardous dye Rhodamine B. Although, ZnO nanofibrous photocatalyst exhibits better initial activity than TiO2 nanofibrous counterpart, its photocatalytic performance is inferior to that of the latter on the whole. The photo-instability arising from photocorrosion may be responsible for its rapid deterioration in activity. The difference in the photocatalytic properties between TiO2 and ZnO nanofibers was discussed, and a possible photodegradation mechanism of organic dyes in the presence of the nanofibrous photocatalyst was proposed. This work offers a direct insight into the comparison of photocatalysis of electrospun TiO2 and ZnO nanofibers.

Nanosilver‐Decorated TiO2 Nanofibers Coated with a SiO2 Layer for Enhanced Light Scattering and Localized Surface Plasmons in Dye‐Sensitized Solar Cells

Enhanced harvesting of visible light is vital to the development of highly efficient dye-sensitized solar cells (DSSCs). Nanosilver-decorated TiO2 nanofibers (Ag@TiO2 NFs) were synthesized by depositing chemically reduced Ag ions onto the surface of electrospun TiO2 nanofibers (TiO2 NFs). The prepared Ag@TiO2 NFs were coated with SiO2 (SiO2@Ag@TiO2 NFs) by using PVP as coupling agent for protecting corrosion of Ag nanoparticle by I(-)/I3(-) solution. The fabricated SiO2@Ag@TiO2 NFs demonstrated a synergistic effect of light scattering and surface plasmons, leading to an enhanced light absorption. Moreover, an anode consisting of SiO2@Ag@TiO2 NFs incorporating TiO2 nanoparticles (NPs) increased light harvesting without substantially sacrificing dye attachment. The power conversion efficiency increased from 6.8 to 8.7 % for a thick film (10 μm), that is, 28 %. These results suggest that SiO2@Ag@TiO2 NFs are promising materials for enhanced light absorption in dye-sensitized solar cells.

Preparation of smart nano-engineered electrospun membranes for methanol gas-phase photoxidation

Nano-engineered membranes obtained by electro-hydrodynamic technologies have been proposed as a good candidate for active filtration. The present work reports some results on the development, production and characterization of three different nanostructured membranes based on: electrospun TiO2 inorganic nanofibers, nanocomposite structures of polymer nanofibers with TiO2 embedded nanoparticles and multilayered structures of polymer nanofibers and electrosprayed TiO2 nanoparticles. Their catalytic activity on volatile organic compounds (VOCs) decomposition has been explored in a photo-reactor properly design for this purpose and a comparison among their performance will be extensively discussed. Multilayered membranes showed a complete degradation of methanol in gas phase and the photo-catalytic activity has been found to be affected from the catalyst content and morphology, by means that there is a critical concentration of catalyst over which its increase results on worse photo-oxidation performance. Inorganic TiO2 based membranes revealed the same activity as the nanocomposite membranes, in terms of methanol reacted per gram of catalyst, but their poor mechanical properties makes them not suitable for a potential scale up.

One-dimensional hierarchical heterostructures of In2S3 nanosheets on electrospun TiO2 nanofibers with enhanced visible photocatalytic activity

In2S3 nanosheets were assembled on electrospun TiO2 nanofibers template by a hydrothermal technique. For the obtained one-dimensional In2S3/TiO2 hierarchical heterostructures (1D In2S3/TiO2 H-HSs), the density and size of the secondary In2S3 nanosheets could be controlled by adjusting the reactant concentrations for the preparation of In2S3 in the hydrothermal process. The 1D In2S3/TiO2 H-HSs exhibited higher visible-light photocatalytic activity for the degradation of Methyl orange (MO) and the reduction of Cr(VI), as compared with the pure TiO2 nanofibers and pure In2S3 nanosheets. The enhanced visible light photocatalytic activity might be attributed to the extended absorption in the visible light region from the narrow band-gap In2S3, the effective photogenerated electron–hole separation by the photosynergistic effects of the In2S3/TiO2 H-HSs and quick electron-transfer in the 1D TiO2 nanofibers. Meanwhile, the 1D In2S3/TiO2 H-HSs could be recycled easily by sedimentation due to their nanofibrous nonwoven web structure. Moreover, the mechanisms of photodegradation of MO and photoreduction of Cr(VI) were proposed through systematical investigations. This work provided new insights into utilizing 1D In2S3/TiO2 H-HSs as high efficiency visible-light-driven photocatalysts for environmental remediation and energy conversion.

DEPENDENCE OF ORGANIC/INORGANIC PHOTOVOLTAIC DEVICE PERFORMANCE ON PRECURSOR'S CONCENTRATION USED FOR ELECTROSPUN TiO2 NANOFIBERS

Electrospun TiO2 nanofibers were synthesized by optimizing various electrospinning conditions. The effect of the precursor's concentration present in sol used for electrospinning was studied for the performance of hybrid photovoltaic devices. The synthesized nanofibers were characterized by XRD and UV-Vis absorption spectroscopy and morphology of the fibers were investigated by FE-SEM. The surface of fibers was modified, and these modified fibers were applied to P3HT/ TiO2 / N719 composite nanofibers photovoltaic devices. The device performance was investigated by analysis of the incident photon to current conversion efficiency and a J– V characteristic under 1. 5G illuminations, which show that efficiency of the devices, can be improved from 0.13% to 0.83% by introducing TiO2 nanofibers synthesized by optimum precursor's concentration.

Fabrication and evaluation of dye-sensitized solar cells with photoanodes based on electrospun TiO2 nanotubes

Two types of electrospun TiO2 nanotubes were prepared by the technique of co-axial electrospinning followed by pyrolysis of electrospun core–shell nanofibers at 500°C. The SEM/TEM images showed that both types of TiO2 nanotubes were polycrystalline with diameters of ~400–500nm and crystallite/grain sizes of ~10nm. The XRD results indicated that the TiO2 nanotubes possessed the anatase crystalline phase/structure. Upon sonication, both types of TiO2 nanotubes could be shortened; whereas the average lengths were different (i.e., shorter and longer TiO2 nanotubes). The dye-sensitized solar cell (DSSC) with photoanode based on the shorter TiO2 nanotubes had higher short-circuit current density and device efficiency while lower open-circuit voltage than the DSSC with photoanode based on the longer TiO2 nanotubes. The results are discussed in terms of dye loading amount and electron recombination lifetime.

Titanium dioxide nanofibers integrated stainless steel filter for photocatalytic degradation of pharmaceutical compounds

A photocatalytically active stainless steel filter (P-SSF) was prepared by integrating electrospun TiO2 nanofibers on SSF surface through a hot-press process where a poly(vinylidene fluoride) (PVDF) nanofibers interlayer acted as a binder. By quantifying the photocatalytic oxidation of cimetidine under ultraviolet radiation and assessing the stability of TiO2 nanofibers integrated on the P-SSF against sonication, the optimum thickness of the TiO2 and PVDF layer was found to be 29 and 42μm, respectively. At 10L/m2h flux, 40–90% of cimetidine was oxidized when the thickness of TiO2 layer increased from 10 to 29μm; however, no further increase of cimetidine oxidation was observed as its thickness increased to 84μm, maybe due to limited light penetration. At flux conditions of 10, 20, and 50L/m2h, the oxidation efficiencies for cimetidine were found to be 89, 64, and 47%, respectively. This was attributed to reduced contact time of cimetidine within the TiO2 layer. Further, the degradation efficacy of cimetidine was stably maintained for 72h at a flux of 10L/m2h and a trans-filter pressure of 0.1–0.2kPa. Overall, our results showed that it can potentially be employed in the treatment of effluents containing organic micropollutants.

Spray deposition of electrospun TiO2 nanoparticles with self-cleaning and transparent properties onto glass

A self-cleaning and transparent TiO2 nano-structured film coating was fabricated onto a glass substrate by electrospinning. It was found that the addition of diethanolamine (DEA) to the TiO2 precursor solution remarkably changes the microscopic morphology of the resulting TiO2 coating. In that, as the DEA's amount was increased, the resulting coating changed from opaque fibers to transparent nanoparticles under the same electrospinning conditions which was confirmed by Scanning Electron Microscopy (SEM). Meanwhile, the experimental results showed that the DEA/TiO2 coating containing nanoparticles display better optical transmittance, e.g., a maximum transmittance of over 90% was achieved around 600nm when the glass was coated with the nanoparticles at an electrospinning feed rate of 0.18ml/h. The photocatalytic properties of the particle-like TiO2 coating was studied using Congo red decay and silver ion reduction experiments. Together these experiments proved that this novel TiO2 film/coating comprising electrospun nanoparticles possesses excellent photocatalytic activities. Lastly, water contact angle measurements proved that the coating is superhydrophilic.

Comparative Analysis of Ti, Ni, and Au Electrodes on Characteristics of TiO2 Nanofibers for Humidity Sensor Application

The effect of metal (Ti, Ni, and Au) electrodes on humidity sensing properties of electrospun TiO2 nanofibers was investigated in this work. The devices were fabricated by evaporating metal contact ...

The influence of surface treatment on dye-sensitized solar cells based on TiO2 nanofibers

To improve dye adsorption and conversion efficiency of dye-sensitized solar cells (DSSCs) based on electrospun TiO2 nanofibers, surface treatment combining acidification and oxygen plasma treatment has been adopted. TiO2 nanofiber cell with a thickness of ∼50μm gives a conversion efficiency (PCE) of 7.96%. After acidification, PCE is increased to 8.59%. Subsequently O2 plasma treatment further improves the PCE to 9.33%, reflecting a 17% increase compared to the cell without surface treatment.

Synthesis and photocatalytic applications of flower shaped electrospun ZnO–TiO2 mesostructures

We report the synthesis, characterization and photocatalytic application of ZnO–TiO2 electrospun materials. Flower shaped ZnO–TiO2 mesostructures were synthesized using an electrospinning technique, which is a well established and cost effective method for large scale production of 1-D nanomaterials. Calcination of the obtained electrospun ZnO–TiO2 nanofiber membrane was done in a furnace at 500°C. Photodegradation of alizarin red S (ARS) was examined individually using ZnO (NPs), TiO2 (P25) and ZnO–TiO2 flowers. A comparison of the photocatalytic performance of the material with TiO2 (P25) and ZnO (NPs) showed that the nanoflower shaped structures were superior to commercially available P25 and ZnO (NPs). We expected that the material would have wide range of potential applications such as chemosensors, photonic crystals, UV–vis blockers, self-cleaning and organic synthesis.

Effect of TiO2 rutile nanorods on the photoelectrodes of dye-sensitized solar cells

In order to enhance the electron transport on the photoelectrodes of dye-sensitized solar cells, one-dimensional rutile nanorods were prepared using electrospun TiO2 nanofibers. The grain size of the nanorods increased with increasing temperature. Electrochemical impedance spectroscopy measurements revealed reduced interface resistance of the cells with the one-dimensional rutile nanorods due to the improved electron transport and the enhanced electrolyte penetration. Intensity-modulated photocurrent/photovoltage spectroscopy showed that the one-dimensional rutile nanorods provided the electrons with a moving pathway and suppressed the recombination of photogenerated electrons. However, an excessive quantity of rutile nanorods created an obstacle to the electrons moving in the TiO2 thin film. The photoelectrode with 7 wt.% rutile nanorods optimized the performance of the dye-sensitized solar cells.

Electron Transport and Recombination in Photoanode of Electrospun TiO2 Nanotubes for Dye-Sensitized Solar Cells

The technique of coaxial electrospinning has been adopted to prepare the TiO2 nanotubes with average inner diameter of ∼275 nm and wall thickness of ∼115 nm. The electrospun TiO2 nanotubes possess the anatase type of crystalline structure, well-defined tubular morphology, and large aspect ratio. The dye-sensitized solar cell (DSSC) based on the TiO2 nanotubes alone has an efficiency of 3.33% with open-circuit voltage (Voc) of 800 mV, short-circuit current (Jsc) of 6.01 mA cm–2, and fill factor (FF) of 68.5%. Intriguingly, the addition of 20 wt % TiO2 nanoparticles in the TiO2 nanotubes improves the DSSC efficiency significantly. The charge transport and recombination in the fabricated DSSCs are characterized by the dark current, photovoltage as a function of light intensity, and transient photovoltage and photocurrent measurements. The results indicate that electrospun TiO2 nanotubes have large diffusion coefficient and slow recombination compared to the mesoporous film of TiO2 nanoparticles. The enhanced...

Fabrication of stable electrospun TiO2 nanorods for high-performance dye-sensitized solar cells

TiO2 multi-electrodes composed of nanoparticles and nanorods were prepared for use as electrodes in dye-sensitized solar cells (DSSC) in an effort to improve the light-to-electricity conversion efficiency. TiO2 nanorods have been successfully prepared via electrospinning methods using a solution containing titanium isopropoxide (TIP). Acetic acid is generally used as a catalyst in sol-gel processes involving TIP; however, acetic acid induces rapid solidification of the sol solution, resulting in clogging of the nozzle during electrospinning, thereby hindering the mass production of TiO2 nanorods. In this work, we introduced acetyl acetone as a new catalyst and optimized the electrospinning conditions of TiO2 nanofibers. The use of acetyl acetone catalysts dramatically extended the solidification time of the TIP sol solution. The DSSC efficiency was improved through the use of TiO2 multi-electrodes. Open image in new window

The influence of anatase-rutile mixed phase and ZnO blocking layer on dye-sensitized solar cells based on TiO2nanofiberphotoanodes

High performance is expected in dye-sensitized solar cells (DSSCs) that utilize one-dimensional (1-D) TiO2 nanostructures owing to the effective electron transport. However, due to the low dye adsorption, mainly because of their smooth surfaces, 1-D TiO2 DSSCs show relatively lower efficiencies than nanoparticle-based ones. Herein, we demonstrate a very simple approach using thick TiO2 electrospun nanofiber films as photoanodes to obtain high conversion efficiency. To improve the performance of the DSCCs, anatase-rutile mixed-phase TiO2 nanofibers are achieved by increasing sintering temperature above 500°C, and very thin ZnO films are deposited by atomic layer deposition (ALD) method as blocking layers. With approximately 40-μm-thick mixed-phase (approximately 15.6 wt.% rutile) TiO2 nanofiber as photoanode and 15-nm-thick compact ZnO film as a blocking layer in DSSC, the photoelectric conversion efficiency and short-circuit current are measured as 8.01% and 17.3 mA cm−2, respectively. Intensity-modulated photocurrent spectroscopy and intensity-modulated photovoltage spectroscopy measurements reveal that extremely large electron diffusion length is the key point to support the usage of thick TiO2 nanofibers as photoanodes with very thin ZnO blocking layers to obtain high photocurrents and high conversion efficiencies.