Electrospun TiO2 Nanofibers Research Articles

Harnessing the potential of electrospun TiO2 nanofibers and nanoparticles enriched with natural dyes: a path towards affordable aolutions for low-cost electronic devices

Abstract This study evaluates the morphological effects of TiO2 nanoparticles, nanofibers, and a bilayer configuration on electronic devices, such as Dye-Sensitized Solar Cells (DSSCs) and UV sensors. Cost-efficient natural dyes—curcumin, coffee beans, and banana peel—were used as sensitizers for nanomaterial films. TiO2 nanoparticles were synthesized using the sol–gel technique, while nanofibers were produced via electrospinning. Characterization techniques, including Scanning Electron Microscopy (SEM), Energy Dispersive x-ray Spectroscopy (EDS), and x-ray Diffraction (XRD), confirmed the formation and dimensions of the TiO2 nanostructures. UV–visible spectroscopy was used to determine the optical properties of the samples. TiO2 nanofibers and nanoparticles exhibited high surface-area-to-volume ratios, with nanofibers having a diameter of 20 nm and particles measuring 50 nm. A binder-free, low-temperature paste was prepared using TiO2 nanoparticles and nanofibers to develop thin films. The turmeric dye showed peak absorption at 470 nm with a band gap energy of 2.06 eV when loaded on a TiO2 bilayer film. This study aims to develop electronic devices that reduce costs and enhance performance by using low-cost, efficient, and economically viable dyes. TiO2 nanofiber and nanoparticle films show promise for cost-effective and high-performance electronic devices.

High-strength TiO2/TPU composite fiber based textiles for organic pollutant removal

Effective integration of nanostructured photocatalysts into polymer matrices is crucial for the broad practical application of fiber-based photocatalytic composite textiles. Herein, highly durable TiO2/TPU composite fibers with high TiO2 content (>30 wt. %) were prepared through wet spinning using 1D electrospun TiO2 nanofibers (TNFs). Due to the fiber reinforcement principle, the TNF/TPU composite fibers exhibited superior mechanical properties compared with pure TPU fibers. Furthermore, the TNF/TPU composite fibers with a ratio of 1:2 process impressive degradation efficiency for rhodamine B (RhB). The orientation of 1D TNFs and stronger interface between TNF and TPU matrices not only enable the excellent load sharing and transfer effects following fiber pullout and crack bridging mechanisms, but also improve photogenerated charge transfer efficiency, resulting in high strength and high photocatalytic activity. In addition, enhanced TNF exposure on the fiber is due to the hollow and porous structures of composite fibers, which is advantageous for photocatalytic degradation. Notably, when the RhB concentration exceeded 15 ppm, the TNF/TPU composite fibers exhibited higher degradation efficiency than the TNF powder. Therefore, TNF/TPU composite fiber–based textiles with high photocatalytic activity and strength are promising for overcoming the separation and recovery issues of nanostructured catalysts in practical wastewater treatment applications.

Photo-annealed electrospun TiO2 nanofibers as ion-storage layer for self-rechargeable Zn-based electrochromic energy storage device

Developing a self-rechargeable transparent electrochromic energy storage device (EESD) is highly demanding for advancing electrochromic technology and energy harvesting capabilities. In this study, we introduce a room-temperature photo-annealing method to fabricate electrospun titanium oxide (TiO2) nanofibers, serving as an ion-storage layer (ISL) on the counter electrode. By monitoring the composition and morphology of the precursor before and after ultraviolet/ozone irradiation, we confirm the formation of oxide nanostructures in electrospun TiO2 nanofibers, which enhances ion transport in the fabricated EESDs. The structural and surface properties of the photo-annealed ISL are comprehensively analyzed using various characterization techniques. Enhanced electrochromic performances are evidenced through cyclic voltammetry, spectroelectrochemical measurements, and charge storage assessments. The Zn-based EESDs with ISL (ISL Zn-EESDs) display rapid electrochemical kinetics, high charge-storing capacities, and long lifespans, with open-circuit potential of 1.2 V, optical contrast of 77 %, discharge capacity of 92 mA h/g, coloration efficiency of 58.63 cm2/C, and 99.9 % efficiency retention up to 250 cycles in both flat and bent states. Furthermore, the practical viability of the ISL Zn-EESDs is demonstrated by powering an LED lamp for several minutes. This approach highlights the potential of ISL Zn-EESDs for developing flexible smart windows, opening up a range of promising applications.

3D monolithic composites TiO2/HKUST-1/RGO@melamine foam with improved surface mass transfer for efficient photocatalytic degradation of toluene gas

Currently, photocatalytic technology mostly uses powdered TiO2 catalysts, which are not conducive to recycling, limit the contact between volatile organic compounds (VOCs) and the photocatalyst, and result in lower mass transfer efficiency in gas-solid reactions. Meanwhile, TiO2 catalysts including the electrospun TiO2 nanofibers with hydrophilic surfaces are not favorable for the infiltration and adsorption of non-polar VOCs. To solve these problems, in this work, the monolithic composites TiO2/HKUST-1/RGO@melamine foam (named MRTH) with improved surface mass transfer composed of metal-organic framework (HKUST-1), graphene oxide (GO) and electrospun TiO2 nanofibers was designed. The metal-organic framework HKUST-1 plays a role in promoting the adsorption of toluene, while the reduced graphene oxide (RGO) facilitates the infiltration of non-polar molecules on the surface of the composite and has better electron transport capability. A type II heterojunction between the electrospun TiO2 nanofibers and HKUST-1 formed in the monolithic composites suppresses the recombination of electron-hole pairs and extends their lifespan. Comparing with the bare electrospun TiO2 nanofibers, the MRTH foam composites exhibit a wider light absorption range, hydrophilic and oleophobic properties and a higher separation efficiency of photogenerated carriers. In 90 min of dark adsorption, the removal rate of toluene over MRTH-8 was 52.32 %, while under irradiation by xenon lamp for 150 min, the removal rate over MRTH-8 reached 90.15 %. The amount of monolithic foam composites can also be easily adjusted in the reactor to achieve the best possible removal of the contaminant. The prepared composite materials have been characterized in detail, and the possible mechanisms have also been discussed. The foam composites prepared in this work have high catalytic activity and gas-solid reaction mass transfer efficiency, so they have wide practical application prospects in the field of VOCs abatement.

Review of the recent advances on the fabrication, modification and application of electrospun TiO2 and ZnO nanofibers for the treatment of organic pollutants in wastewater

The heightened occurrence of emerging organic pollutants (EOPs) in aquatic bodies has been the subject of global apprehension due to the toxicity they pose to the environment, humans and animals alike. The presence of EOPs has soared due to industrialization and is further exacerbated by human activities like the overuse and poor disposal of dyes, pesticides, pharmaceuticals, surfactants, personal care products and food additives. The complete treatment and removal of EOPs from industrial wastewater and sewage has remained a challenge because of their pseudo-persistence and resistance to degradation. Due to their impressive light absorption properties, high surface-area-to-volume ratio, high porosity, superior mechanical strength, electrospun titanium dioxide (TiO2) and zinc oxide (ZnO) nanofibers have been proposed for the photocatalytic treatment of EOPs. Therefore, this review first highlights the fabrication and modification methods of TiO2 and ZnO nanofibers. A systematic survey of the latest progress in the application of TiO2 and ZnO nanofibers for the degradation of EOPs is then elaborated. Thus, the main goal is to shed light and give insight to researchers on the possibilities surrounding the elimination of EOPs by applying electrospun TiO2 and ZnO semiconductor materials. In addition, the loopholes associated with fabrication and modification processes are discussed with the aim of encouraging innovation for prospective technology advancement and commercialization, as well as to enhance research efforts in wastewater treatment and environmental sustainability.

Dual-functional electrochromic supercapacitors with electrospun TiO2 ion storage layer

We have developed dual-functional electrochromic supercapacitors (ECSs) incorporating electrospun TiO2 nanofibers as an ion storage layer (ISL). The prepared ISL-ECSs exhibit excellent integrated electrochromic performances at low driving voltages due to high visible transparency and energy storage capabilities. This study describes direct electrospinning TiO2 on an FTO electrode and fabricating asymmetric electrochromic devices with viologen-based ion gel compositions. The electrospinning technique proved suitable for producing oxide nanostructures that facilitate efficient ion transport. The surface morphology of the fabricated nanoweb was analyzed using SEM and AFM images. The electrochromic performances were evaluated through cyclic voltammetry and spectroelectrochemical measurements, and charge storage properties were examined by galvanostatic charge–discharge curves. The optimized dual-functional devices demonstrated a large transmittance contrast of up to 87 %, high coloration efficiency of 175.7 cm2/C, areal capacitance of 20.53 mF/cm2, and good charging-discharging cyclic stability. Furthermore, the practical feasibility of the ISL-ECSs was demonstrated by evaluating their ability to serve as a power source for illuminating an LED lamp. The findings suggest the potential application of ISL-ECSs for dual-functional smart windows, in which the color intensity visualizes the real-time energy storage status.

Carbon quantum dot modified electrospun TiO2 nanofibers for flexible formaldehyde gas sensor under UV illumination at room temperature

A flexible gas sensor based on carbon quantum dot decorated TiO2 nanofibers (CQD/TiO2) was prepared by hydrothermal and electrostatic spinning methods to detect formaldehyde at room temperature. SEM, TEM, EDS, XRD and XPS were used to analyze the morphology, structure and composition of the composite. The gas sensing test results show that the working temperature of the material is reduced to room temperature by UV excitation, and subsequently, CQD/TiO2 exhibits a lower detection limit and faster response/recovery time for formaldehyde by carbon material modification. The flexibility test of CQD/TiO2 shows that the composite material of metal oxide and carbon material has a certain degree of flexibility. The enhanced sensing performance by UV excitation and CQD modification is attributed mainly to the photogenerated electron transfer and the formation of p-n heterojunctions. The modification of TiO2 with carbon quantum dots provides an experimental reference for the development of room-temperature flexible MOS-based formaldehyde sensors.

Fabrication of Visible Light Sensitive Electrospun TiO2 Nanofibers Using Squaric Acid for Photocatalytic Application

Degradation of organic pollutants using photocatalysts has gained utmost importance, due to the increasing environmental pollution. Despite various attempts to improve the photocatalytic efficiency of well-known photocatalysts such as titanium dioxide (TiO2), by making them visible light active, various issues need to be resolved. In this work, attempts have been made to improve the visible light absorption capacities of the electrospun TiO2 nanofibers by modification using squaric acid (SqA). An interfacial charge transfer complex is formed by the condensation reaction between the hydroxyl groups on the surface of the TiO2 nanofibers and the SqA ligand. Various characterizations confirmed that the modification using SqA had led to the formation of the interfacial charge transfer layer, without affecting the crystallinity or morphology of the TiO2 nanofibers. The modified TiO2 nanofibers showed sensitivity to visible light with red shift in the optical absorption. It exhibited an improved photocatalytic efficiency of 85% against the degradation of tetracycline, compared with 60% for unmodified TiO2 nanofibers. It also showed an increased rate of degradation of 0.21 mg/L/min, when compared with the 0.13 mg/L/min of unmodified TiO2 nanofibers.

Electrospun TiO2 Nanofibers in the Presence of Avocado Seed Extract

The electrospinning technique is particularly prominent in membrane production techniques due to its easy applicability and ability to obtain nanofibers in various diameters with high surface area. Titanium dioxide (TiO2) is often used in biomaterial technologies due to their high biocompatibility, high processability and their photocatalytic activities in waste water treatment. In this study, TTIP (Titanium tetra isopropoxide) was used as a TiO2 precursor and PVP polymer was used as a carrier polymer for electrospinning. Avocado seed extract (ASE) which is a new and valuable source of phenolic compounds was used for the coordination and reduction of TTIP. TiO2-PVP-Avocado seed extract (T/P/A) composite nanofibers were produced at different voltages, distances and polymer concentrations. Crystalline TiO2 formation was not observed in as-spun nanofibers, thus selected nanofibers were heat treated at 500oC for 3 h. Smooth and integrated TiO2 nanofibers prepared by using 5 w% PVP, at 15 kV and 15 cm distance with or without ASE were imaged by Scanning Electron Microscopy (SEM). X-ray Diffraction (XRD) patterns of heat-treated TiO2 nanofibers prepared in the presence of ASE were crystallized mainly in anatase form. However, both anatase and rutile phases were obtained in the crystalline structure of TiO2 nanofibers when ASE was not used. Specific IR vibrations of TiO2 were shown by Fourier Transform Infrared Spectroscopy (FTIR). These green synthesized electrospun TiO2 nanofibers may have potential to be used in biomaterial and engineering applications.

Flexible-in-rigid polycrystalline titanium nanofibers: a toughening strategy from a macro-scale to a molecular-scale.

TiO2 nanomaterials, especially one-dimensional TiO2 nanofibers fabricated by electrospinning, have received considerable attention in the past two decades, for a variety of basic applications. However, their safe use and easy recycling are still hampered by the inherently subpar mechanical performance. Here, we toughened polycrystalline TiO2 nanofibers by introducing Al3+-species at the very beginning of electrospinning. The resultant long-and-continuous TiO2 nanofibers achieved a Young's modulus of 653.8 MPa, which is ca. 25-fold higher than that of conventional TiO2 nanofibers. Within each nanofiber, amorphous Al2O3-based oxide effectively hindered the coalescence of TiO2 nanocrystals and potentially repaired the surface groves. The solid-state 17O-NMR spectra further revealed the toughening strategy on a molecular scale, where relatively flexible Ti-O-Al bonds replaced rigid O-Ti-O bonds at the interfaces of TiO2 and Al2O3. Moreover, the modified TiO2 nanofibers exhibited superb sinter-resistance, without cracking over 900 °C, which was dynamically monitored by TEM. Therefore, flexible-in-rigid TiO2 fibrous mats can be facilely folded into 3D sponges through origami art. As a potential showcase, the TiO2 sponges were demonstrated as a duarable and renewable filtrator with a high filtration efficiency of 99.97% toward PM2.5 and 99.99% toward PM10 after working for 300 min. This work provides a rational strategy to produce flexible oxide nanofibers and gives an in-depth understanding of the toughening mechanism from the macro-scale to the molecular-scale.

NiS/Pt loaded on electrospun TiO2 nanofiber with enhanced visible-light-driven photocatalytic hydrogen production

The porous TiO2 nanofiber has been synthesized via facile electrospinning and thermal annealing. Furthermore, the intermediate layer of NiS and Pt nanoparticles can be sequentially deposited on the porous TiO2 nanofiber to form hierarchical core-shell TiO2/NiS/Pt nanofiber through wet-chemical and self-assembly processes. Compared with the TiO2 (16 µmolh−1g−1 L−1) nanofiber and TiO2/NiS nanofiber (54 µmolh−1g−1 L−1), TiO2/NiS/Pt nanofiber (4411 µmolh−1g−1 L−1) revealed remarkably photocatalytic activity for hydrogen evolution from water under visible light excitation. The significant enhancement in photocatalytic activity over the TiO2/NiS/Pt nanofiber could be attributed to enhanced visible light absorption and the separation of photogenerated electrons and holes. Furthermore, reusability experiments prove that TiO2/NiS/Pt nanofiber exhibits excellent stability for the long-term photocatalytic process. In addition, TiO2/NiS/Pt nanofiber can also use photocatalytic hydrogen production under different water bases. Therefore, this study provides a promising strategy to develop a novel heterostructure photocatalyst for highly efficient energy conversion.

Electrochemical Impedance Investigation of Dye-Sensitized Solar Cells Based on Electrospun TiO2 Nanofibers Photoanodes.

This work investigates an electrochemical impedance analysis based on synthesized TiO2 nanofibers (NFs) photoanodes, which were fabricated via electrospinning and calcination. The investigated photoanode substrate NFs were studied in terms of physicochemical tools to investigate their morphological character, crystallinity, and chemical contents via scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD) analyses. As a result, the studied photoanode substrate NFs were applied to fabricate dye-sensitized solar cells (DSCs), and the electrochemical impedance analysis (EIS) was studied in terms of equivalent circuit fitting and impacts of N-doping, the latter of which was approved via XPS analysis. N-doping has a considerable role in the enhancement of charge transfers, which could be due to the strong interactions between active-site N atoms and the used photosensitizer.

Synergistic effect of interstitial C doping and oxygen vacancies on the photoreactivity of TiO2 nanofibers towards CO2 reduction

TiO2 nanofiber membranes were prepared by calcinating the electrospun TiO2 nanofibers precursor. Sample calcined at 400 °C (T400) exhibited high CO2 to CH4 conversion efficiency (55.17 μmol·g−1·h−1) and electron selectivity (98.3%) under simulated sunlight. In-situ DRIFTS and the calculated Gibbs free energy revealed CO* to be a major intermediate with the formation of COH* intermediate being the rate-limiting step. The considerable CO2 photoreduction behavior obtained on T400 sample can be attributed to the following causes: (1) the existence of surface OVs gives the change in electronic structure by upshifting CB position to be capable of CO2 photoreduction; (2) the surface Ti terminals acted as reaction sites, resulting in the accumulation of CO* intermediates to continually produce CH4 with the support of sufficient electrons. These results lay the foundation for advancing the mechanistic insight on CO2 photoreduction and its selectivity to CO2 to CH4.

Structural and optical characterization of electrospun TiO2 nanofibers using titanium tetrabutoxide and titanium isopropoxide as precursors for photocatalytic applications

The structural and optical characterization of TiO2 nanofibers (TiO2-NF’s) synthesised from two different chemical precursors, titanium tetrabutoxide (TNBT) and titanium isopropoxide (TTIP), obtained by electrospinning technique with controlled morphology and crystalline phase, is presented. Varying the distance between the needle tip and the collector called "air gap", it was possible to control the diameter and the formation of the fibers within the nanometric scale. The crystalline phase (CP) of the TiO2-NFs was controlled through thermal treatment (TT) at 450 °C for 3 h, anatase phase. The chemical composition of the annealed electrospun TiO2-NF was estimated by EDS, finding there is an excess of titanium that causes oxygen vacancies, which stimulate the CP transformation, from amorphous to anatase. By means of scanning electron microscopy (SEM) and transmission electron microscopy (TEM) was possible to corroborate the formation of TiO2-NFs with a smooth morphology and well-defined shape. FTIR spectroscopy and Raman scattering results of electrospun TiO2-NFs demonstrated changes in structural and optical properties caused by TT. By Raman scattering was found that the annealed TiO2-NFs showed the anatase CP, which was corroborated by X-ray diffraction. At first sight, the surface morphology of the electrospun fibers was not affected by the choice of precursor; however, on closer review, the fibers prepared with the TTIP precursor showed a smaller crystal size of 8.51 nm and band gap energy of 3.38 eV, while the samples prepared with TNBT showed a smaller bandgap energy of 3.06 eV and a nanocrystal size of 10.98 nm. With both precursors at a working distance of 15 cm, homogeneous fibers are obtained, with a smaller diameter without the presence of morphological defects, called beds, and a better size distribution.

Advances in electrospun TiO2 nanofibers: Design, construction, and applications

• Structure control of electrospun TiO 2 NFs through various strategies was summarized. • Mechanical flexibility adjusting of electrospun TiO 2 NFs and related deformation mechanism were discussed. • Multifunctional applications of electrospun TiO 2 NFs in environment, energy, and sensors were introduced. • Current challenges and future perspectives on the development of electrospun TiO 2 NFs were proposed. One dimensional (1D) TiO 2 nanomaterials, as one of the most important semiconductor materials, which have attracted much attention due to their unique structural feature, outstanding optical or electronic properties. Electrospinning is one of the most facile and highly versatile approaches to fabricate 1D TiO 2 nanofibers (NFs) with high porosity, controllable dimensions, designed structures, and adjustable mechanics, which hold great promise in many areas including photocatalytic degradation, solar cells, lithium-ion batteries, water splitting, sensors, and catalyst supports. In this review, progress in structure/mechanics design, fabrication and multifunctional applications of electrospun TiO 2 NFs are presented. The strategies to prepare electrospun TiO 2 NFs with diverse structures involving porous, hollow, hierarchical, aligned, and 3D self-assembled nanostructures are introduced and analyzed. Moreover, the recent breakthrough in the construction of flexible TiO 2 nanofibrous materials and corresponding deformation mechanism have been concerned. Furthermore, some achievements associated with the potential applications of electrospun TiO 2 NFs in the areas of environmental remediation, energy, and sensors are discussed. Finally, a straightforward summary, main challenges and future outlooks about electrospun TiO 2 NFs are proposed. It is anticipated that this review could provide guidelines for designing and constructing novel TiO 2 -based nanofibrous materials for advanced applications.

Plasmonic Active "Hot Spots"-Confined Photocatalytic CO2 Reduction with High Selectivity for CH4 Production.

Plasmonic nanostructures have tremendous potential to be applied in photocatalytic CO2 reduction, since their localized surface plasmon resonance can collect low-energy-photons to derive energetic "hot electrons" for reducing the CO2 activation-barrier. However, the hot electron-driven CO2 reduction is usually limited by poor efficiency and low selectivity for producing kinetically unfavorable hydrocarbons. Here, a new idea of plasmonic active "hot spot"-confined photocatalysis is proposed to overcome this drawback. W18 O49 nanowires on the outer surface of Au nanoparticles-embedded TiO2 electrospun nanofibers are assembled to obtain lots of Au/TiO2 /W18 O49 sandwich-like substructures in the formed plasmonic heterostructure. The short distance (< 10nm) between Au and adjacent W18 O49 can induce an intense plasmon-coupling to form the active "hot spots" in the substructures. These active "hot spots" are capable of not only gathering the incident light to enhance "hot electrons" generation and migration, but also capturing protons and CO through the dual-hetero-active-sites (Au-O-Ti and W-O-Ti) at the Au/TiO2 /W18 O49 interface, as evidenced by systematic experiments and simulation analyses. Thus, during photocatalytic CO2 reduction at 43± 2 °C,these active "hot spots" enriched in the well-designed Au/TiO2 /W18 O49 plasmonic heterostructure can synergistically confine the hot-electron, proton, and CO intermediates for resulting in the CH4 and CO production-rates at ≈35.55 and ≈2.57µmol g-1 h-1 , respectively, and the CH4 -product selectivity at ≈93.3%.

In-situ synthesis of phthalocyanines on electrospun TiO2 nanofiber by solvothermal process for photocatalytic degradation of methylene blue.

Titanium dioxide/phthalocyanine (TiO2/Pc), TiO2/fluor containing phthalocyanine (TiO2/FPc), and TiO2/fluor containing cobalt phthalocyanine (TiO2/FCoPc) had been successfully fabricated by a simple combination of phthalocyanines obtained by in-situ synthesis on the surface of TiO2 nanofibers prepared by electrospinning. Scanning electron microscopy micrographs and X-ray diffraction analysis indicated that the phthalocyanines uniformly immobilized on the surface of TiO2 nanofibers. Photocatalytic activity of TiO2, TiO2/Pc, TiO2/FPc, TiO2/FCoPc nanofibers for methylene blue in water was comparatively investigated firstly by ultraviolet-visible absorption measurements with time, and kinetic parameters were calculated. Results indicated that the obtained TiO2/Pc, TiO2/ FPc and TiO2/FCoPc exhibited high photocatalytic activity for the degradation of methylene blue and TiO2/FCoPc was found the best. It showed similar or higher activities than related studies and can be suggested as a promising candidate for environmental and energy applications.

Unveiling temperature-modified electrospun TiO2 nanofibers with size-driven microstructure evolution and enhanced photocatalytic effect

Tailoring the properties and functionalities of TiO2 nanofibers (NFs) via controlling the surface morphology, size, and compositions has attracted tremendous attention in the last few decades. Nevertheless, the development of an efficient and stable nanostructured TiO2 NFs photocatalyst remains a challenge. Here, a heat treatment temperature-driven appearance on the microstructural evolution of TiO2 NFs and the corresponding impact on the photodegradation of organic dye were reported based on the precursor decomposition, crystallization, surface structure and active radicals. Systematic TG/DSC curves, IR spectra, X-ray diffraction, SEM and TEM images, XPS and PL spectra illustrated the impact of temperature on thermal decomposition, microstructure, morphologies and surface structure. Anatase TiO2 NFs at 900 °C with better morphological thermal stability, crystallite size and crystallinity possessed highest photocatalytic activities due to low electron-hole recombination and high production of •OH and O2•-. With the addition of radical scavengers, the results illustrated O2•- and •OH acted as the main radicals on the process of photocatalytic activities. The results of this work may provide valuable information to design and produce new highly efficient TiO2 NFs materials for wastewater treatment applications.

Tailored fabrication of TiO2/In2O3 hybrid mesoporous nanofibers towards enhanced photocatalytic performance

In present work, we report the fabrication of mesoporous TiO2/In2O3 nanofibers photocatalyst via the combination of electrospinning and hydrothermal method, in which In2O3 were uniformly grown on electrospun TiO2 nanofibers. The mass loading of In2O3 nanostructures and mesoporous nanostructure could be easily controlled by adjusting raw materials weight of In2O3 within the hydrothermal solutions. The as-prepared photocatalyst were also employed to study their photocatalytic performance for organic decomposition. It is found that TiO2/In2O3 composites showed significantly enhanced photocatalytic efficiency as compared to that of pristine TiO2 and In2O3 photocatalysts for RhB degradation. The enhanced performance could be attributed to the combined effects of the extended visible-light response range, efficient separation of photo-excited charge carriers and increased reaction active sites.

Controlled synthesis of electrospun TiO2 nanofibers and their photocatalytic application in the decolouration of Remazol Black B azo dye

The obtaining of monocrystalline TiO2 nanofibers with high specific surface area synthesized by the electrospinning technique with controlled crystalline structure and morphology is reported. The nanofibers were annealed at 500, 700 and 900 °C in a controlled atmosphere in the presence of air for two hours to achieve crystalline phase transformation. By means of TEM, it was possible to clearly corroborate the presence of solid nanofibers with a well-defined shape, a smooth surface and without the presence of interconnections and defects called beads. The chemical stoichiometry of electrospun TiO2 nanofibers was estimated by EDS, finding that at low annealing temperatures excess of oxygen was detected and at high temperatures excess of titanium that originates oxygen vacancies. By Raman scattering was found that the TiO2 nanofibers showed a crystalline phase transformation from pure anatase, mixed anatase-rutile and pure rutile as the annealing temperature is increased, caused by the generation of oxygen vacancies, which was corroborated by X-ray diffraction. The band gap energy (Eg), obtained from optical absorption spectra, decreases as the temperature is increased, which is ranged in 2.42 ≤ Eg≤ 3.27 eV, caused by the anatase→rutile crystalline phase transformation. Photoluminescence shows that the radiative bands -present a gradual red shift as the temperature increases due to the Eg reduction. In addition, the photocatalytic properties of the annealed TiO2 nanofibers were evaluated in the decolouration of the Remazol Black B azo dye. Changes in absorption spectra were noticeable as the measurement time increases. Absorbance spectra showed a decrease in the intensity of the main absorption band at 589 nm, which gradually decreases until it completely disappears, indicating that the decomposition of the organic compound is complete, while physically there is an absence of color from the solution. The anatase crystalline phase was the one with the highest specific surface area and the highest photocatalytic activity.