Doped TiO2 Nanofibers Research Articles

Efficiency enhancement of dye-sensitized solar cells by use of ZrO2-doped TiO2 nanofibers photoanode

Due to the good stability and convenient optical properties, TiO2 nanostructures still the prominent photoanode materials in the Dye Sensitized Solar Cells (DSCs). However, the well-known low bandgap energy and weak adsorption affinity for the dye distinctly constrain the wide application. This work discusses the impact of Zr-doping and nanofibrous morphology on the performance and physicochemical properties of TiO2. Zr-doped TiO2 nanofibers (NFs), with various zirconia content (0, 0.5, 1, 1.5 and 2wt%) were prepared by calcination of electrospun mats composed of polyvinyl acetate, titanium isopropoxyl and zirconium n-propoxyl. For all formulations, the results have shown that the prepared materials are continuous, randomly oriented, and good morphology nanofibers. The average diameter decreased from 353.85nm to 210.78nm after calcination without a considerable influence on the nanofibrous structure regardless the zirconia content. XRD result shows that there is no Rutile nor Brookite phases in the obtained material and the average crystallite size of the sample is affected by the presence of Zr-doping and changed from 23.01nm to 37.63nm for TiO2 and Zr-doped TiO2, respectively. Optical studies have shown Zr-doped TiO2 NFs have more absorbance in the visible region than that of pristine TiO2 NFs; the maximum absorbance is corresponding to the NFs having 1wt% zirconia. The improved spectra of Zr-doped TiO2 in the visible region is attributed to the heterostructure composition resulting from Zr-doping. The absorption bandgaps were calculated using Tauc model as 3.202 and 3.217 for pristine and Zr (1wt%)-doped TiO2 NFs, respectively. Furthermore, in Dye-sensitized Solar Cells, utilizing Zr (1wt%)-doped TiO2 nanofibers achieved higher efficiency of 4.51% compared to the 1.61% obtained from the pristine TiO2 NFs.

Investigation of structural, electronic and optical properties of pure and Ag‐doped TiO2 nanofibers fabricated by electrospinning

Pure and 1, 2, and 3 wt% Ag doped TiO2 nanofibers were prepared by electrospinning method at different applied voltages and heights at a constant flow rate of 2 mL/h. Characterization of the prepared samples was performed by x‐ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microcopy (AFM),four point probe method (FPPM), the differential scanning calorimetry/the thermal gravimetric analysis (DSC/TGA), ultraviolet/visible spectrometry (UV/VIS), and energy dispersive X‐ray spectrometer (EDX). It was found that the thermally untreated pure TiO2 nanofibers and thermally treated (at 500 °C) samples have the crystalline phase of anatase (A), and mixed anatase and rutile (A+R) phases, respectively. It was also observed that the content of the silver does not affect the crystal structure, but plays strengthening role in the rutile structure. SEM micrographs showed that all fabricated nanofiber samples have uniform morphologies, and AFM measurements indicated that the nanofibers were formed in three‐dimensional coils. The band gap values of the nanofiber samples obtained from UV/VIS measurements revealed that band gap values of the nanofiber samples decrease while the diameter of the nanofiber increases.

Preparation and application of Sm–Ni oxide doped TiO2 nanofiber as catalyst in hydrogen production from sodium borohydride hydrolysis

Abstract Ternary catalyst system composed of samarium (Sm) and nickel (Ni) oxide doped titanium oxide nanofiber was synthesized for improving hydrogen generation from the hydrolysis of sodium borohydide. The catalytic activities of the fabricated catalyst were compared with the binary system of nickel oxide- and samarium oxide-doped titanium oxide nanofibers. The SEM results of Sm–Ni oxide doped TiO2 nanofibers showed the average diameter of 633 ± 95 nm and 857 ± 33 nm pore diameter with uniform morphology. EDX provided the information about the elements present in nanofibers. Based on BET measurements, the surface area of Sm–Ni oxide doped TiO2 nanofibers system shows higher value when compared with those results obtained for pure Ni oxide- and pure Sm oxide-doped titanium oxide nanofibers. The hydrogen production results show that Sm–Ni oxide doped TiO2 nanofiber can efficiently be used as catalyst with greater catalytic activity as compared to the nickel doped titania and Sm2O3 doped TiO2 nanofibers. The hydrogen generation for the Sm-Ni oxide doped TiO2 can reach up to 650 mL in 160 min at 45 °C. The doping of Sm–Ni oxide on TiO2 can improve the surface area and cationic as well as electronic defect in oxide which can help to increase the diffusion rate of reactants. Furthermore, the Sm–Ni oxide doped catalyst showed superior recyclability with almost similar catalytic activity for repetitive five cycles.

Microwave-assisted synthesis and photocatalytic properties of sulphur and platinum modified TiO2 nanofibers

In the present work formation of active TiO2 nanofibers in microwave synthesis and their modification with platinum were studied. Mixture of anatase and rutile nanopowder and 10M KOH solution were used as raw materials. Microwave assisted synthesis method permitted to obtain TiO2 nanofibres with a diameter of 10nm and a specific surface area up to 40.2 m2/g. In order to modify TiO2 nanofibers with platinum it was stirred in H2PtCl6 solution and illuminated with UV irradiation or reduced with sodium boronhydride. To modify titania with sulphur and prepare co-doped nanofibers platinum doped samples were extra treated in hydrogen sulphide atmosphere. Photocatalytic activity was determined by degradation of the methylene blue (MB) solution under UV and visible light irradiation. The obtained samples showed higher photocatalytic activity with respect to pure TiO2 nanofibers. The doped TiO2 nanofibers were appropriate for degradation of harmful organic compounds.

Influence of Calcination Temperature on Crystal Structure of Pt-TiO2 Nanofibers.

Platinum (Pt) doped TiO2 nanofibers were prepared by a sol-gel derived electrospinning and subsequent calcination for 3 h at temperatures from 500 degrees C to 700 degrees C in air. The influence of calcination temperature on crystal structure of the Pt-TiO2 nanofibers was investigated by using an X-ray diffractometer (XRD) and a transmission electron microscope (TEM). The fibers possessed both anatase and rutile phases of TiO2 as a function of the calcination temperature. At 500 degrees C, only anatase phase was observed. However, the rutile phase started to grow with increasing the temperature. At 700 degrees C, 47% of rutile phase with a crystallite size of 31 nm was detected. The continuous and smooth Pt-TiO2 fibers with a diameter of 38 nm were changed to the particulate morphology (at 700 degrees C) with increasing the temperature. This result is particularly important because the calcination temperature is attributed to the fiber morphology and the crystal structure.

Cu0- doped TiO2 nanofibers as potential photocatalyst and antimicrobial agent

Cu0 nanoparticles (NPs)-doped TiO2 nanofibers (NFs) were prepared as an effective photodegradation of three azo dyes as well as an antimicrobial agent under visible light. Fabrication of one dimensional zero-valent Cu nanoparticles-doped TiO2 nanofibers with high aspect ratio have been successfully synthesized by simple and low cost; electrospinning technique followed by hydrothermal process. The photocatalytic activity of introduced nanofibers was evaluated by performing of three azo dyes. Catalytic NFs show a superior photodegaradation activity under visible light as well as good antimicrobial activity. Moreover, photocatalyst nanofibers appeared good stability, which was used for three cycles without regeneration.

Preparation and photocatalytic activity of fly ash incorporated TiO2 nanofibers for effective removal of organic pollutants

Materials with photocatalytic and adsorption property, and antibacterial activity have been widely used in waste water treatment. Taking advantages of TiO2 as a well known photocatalyst and antibacterial material, and fly-ash (FA) as an adsorbent, fly ash doped TiO2 nanofibers were prepared by electrospinning process for the removal of organic pollutant and microorganism from water. Calcination of electrospun nanofiber mats composed of titanium tetraisopropoxide, poly(vinylpyrrolidine), and fly ash in air at 600°C led to produce good morphology FA/TiO2 nanofiber. Several analytical techniques, including scanning electron microscopy (SEM), Transmission electron microscopy (TEM), X-ray diffraction (XRD), and photoluminescence spectroscopy (PL) were used to characterize the resulting FA/TiO2 nanocomosites. As-synthesized nanofiber revealed a distinct performance in adsorption and photocatalytic activity for decomposition of methylene blue, and antibacterial activity against Escherichia coli due to combined effect of TiO2 and fly ash. Results indicated that as-synthesized composite nanofibers exhibit great potential for water purification.

Phase control of yttrium (Y)-doped TiO2 nanofibers and intensive visible photoluminescence

Yttrium (Y)-doped TiO2 nanofibers were successfully fabricated by electrospinning and the subsequent calcination of the as-spun nanofibers. The X-ray diffraction and Raman scattering results showed that the incorporation of Y into TiO2 impedes the rutile-phase growth, facilitates the anatase phase growth. Estimated grain sizes are reduced from 15.71nm to 8.8nm with increasing Y-doping concentration. Raman scattering studies confirm the existence of slight brookite phase in case of Y-doped TiO2 nanofibers. Field emission scanning electron microscope (FESEM) and transmission electron microscope (TEM) images revealed that the nanofibers comprised of nanoparticles and that Y-doping reduced the nanoparticle size. The optical band gap energy increased with increasing Y-doping, which can be ascribed to both quantum confinement effect and pure anatase phase transformation from mixed rutile-anatase phase. Y-doping induced a blue-shift of the broad visible photoluminescence (PL) peak and an increase of PL intensity with the concurrent decrease grain size. For 3at.% Y-doped TiO2 nanofibers PL intensity enormously increased due to defect-related centers on the surface.

Preparation of doped TiO2 nanofiber membranes through electrospinning and their application for photocatalytic degradation of malachite green

Fe3+ doped TiO2 composite nanofiber membranes and pure TiO2 nanofiber membranes were prepared through electrospinning, and were applied to the photocatalytic degradation of malachite green (MG) in aqueous solutions under simulated sunlight. The effects of ferric ion content, initial concentration of MG, photocatalyst loading, and recycling behavior were studied. Microscopic characterization showed that the products have fiber morphology with bent property and favorable continuity. The degradation results showed that TiO2 nanofiber membranes containing 0.8 mol% Fe3+ performed the best photocatalytic activity against MG under identical light irradiation. The TiO2:Fe3+ composite nanofiber membranes maintained their photocatalytic efficiency through seven recycling processes.

Electrospun nanofibers of Er3+-doped TiO2 with photocatalytic activity beyond the absorption edge

Er3+-doped TiO2 nanofibers with different Er3+ contents were prepared via electrospinning and characterized by X-ray diffraction, scanning electron microscopy, ultraviolet–visible diffuse reflectance spectroscopy and photocurrent measurement. Photocatalytic activities of the as-prepared samples were evaluated by the decolorization of methyl orange aqueous solution under simulated solar light irradiation. The results indicated that the photocatalytic activity of Er3+-doped TiO2 nanofibers was much higher than that of the undoped one, and the optimal dosage of Er3+ at 1mol% achieved the highest degradation rate. Moreover, the photocatalytic activity of Er3+-doped TiO2 nanofibers under the irradiation of light with the wavelength beyond the absorption edge of TiO2 was explored by the decolorization of a dye, rhodamine B and the photodegradation of a typical colorless pollutant, phenol. The results further revealed the mechanism of the enhanced photocatalytic activity through Er3+ doping in TiO2 nanofibers.

Preparation and characterization of doped TiO2 nanofibers by coaxial electrospining combined with sol–gel process

Abstract N, Fe, and W doped TiO 2 nanofibers were fabricated by coaxial electrospining and directly annealing polyvinylpyrrolidone (PVP)/Tetrabutyl titanate (TBT) composite nanofibers. The crystal structure, morphology, and surface composition of the doped TiO 2 nanofibers were investigated by the X-ray diffraction (XRD), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS) respectively. The results show that the dopants have different influence on the surface topographies, the crystal structures and the transformation of anatase to rutile of TiO 2 nanofibers. Fe dopant promotes bigger influence on topographies, phase transformation and crystallite growth of TiO 2 nanofibers than that of either N or W dopant.

Rapid degradation of toxic toluene using novel mesoporous SiO2 doped TiO2 nanofibers

Toluene is a typical volatile organic compound (VOC), which is harmful to human. The novel mesoporous TiO2 composite fibers with optimal SiO2 content were fabricated via electrospinning the relevant gel precursor, and were characterized by XRD, SEM, TEM, TG–DTA, UV–vis, and BET surface analysis, respectively. Through photocatalytic degradation of gaseous toluene with these nanostructured fibrous catalysts, it has shown that 10% silica doped TiO2 nanofibers displayed the highest degradation rate among a lot of titania fibers with different silica content, and whose reaction rate is two-fold enhancement than Degussa P25. What is more, it is easy to fix and recycle nanofibrous catalysts. Furthermore, the degradation pathway of cleaning toluene has been verified based on GC–MS detection.

Synthesis and photocatalytic properties of Zn2+ doped anatase TiO2 nanofibers

Zn2+ doped TiO2 nanofibers were prepared by electrospinning followed by calcination. The results of TGA, FE-SEM, XRD and XPS indicated that the obtained nanofibers with diameter in range of 50–150 nm were composed of anatase TiO2 phase and Zn2+ doping in TiO2 did not distort the pristine crystal structure of TiO2. Besides methylene blue (MB) was employed to investigate photocatalytic properties of the obtained samples. The results revealed that Zn2+ doped TiO2 nanofibers had excellent photocatalytic activity, which was symbolized by an optimum photodegradation efficiency of 96.1% under Zn2+ doping concentration of 2 at.%. The photocatalytic efficiency of 2 at.% Zn2+ doped TiO2 nanofibers still exceeded 95% after using for five times.

Electrospun Cu-doped titania nanofibers for photocatalytic hydrolysis of ammonia borane

Among reported hydrogen storage materials, ammonia borane is a promising candidate to be utilized in many industrial applications. The high chemical resistance of the ceramic catalysts makes them one of the most stable classes of catalytic materials. In this study, CuO nanoparticles (NPs) -doped TiO2 nanofibers (NFs) are introduced as a highly effective and reusable catalyst for ammonia borane complex hydrolysis. The incorporation of CuO NPs inside the TiO2 NFs provided distinct advantages for the introduced catalyst; the aggregation problem of the CuO NPs was overcome and a synergistic effect was created as the synthesized CuO NPs-doped TiO2 revealed higher activity compared to the individual components. Typically, after 10min, the obtained hydrogen equivalent was 2.7, 0.9 and 0.95 when CuO NPs-doped TiO2 nanofibers, CuO NPs and pristine TiO2 nanofibers were used as the catalyst, respectively. The catalytic activity of the introduced nanofibers did not change after being used for three successive cycles. Moreover, the catalytic performance was strongly modified when the hydrolysis process was performed under sunlight irradiation because of the photocatalytic activity of the TiO2 and CuO. The introduced nanofibers were prepared by the simple, effective, low cost and high yielding technique of electrospinning. The present study introduces TiO2 nanofibers as a promising catalyst for the ammonia borane complex, as well as an interesting support used for functional materials.

Synthesis, characterization and high natural sunlight photocatalytic performance of cobalt doped TiO2 nanofibers

Co2+ doped TiO2 nanofibers with different doping percentages were successfully synthesized using a nonaqueous sol–gel method. X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), x-ray photoelectrons spectroscopy (XPS), FTIR and UV–vis spectroscopy were used to characterize the crystal structures, chemical states, morphologies and photocatalytic properties of Co doped TiO2 nanofibers. Co2+ doping was found to affect the phase transformation from anatase to rutile. Grain growth activation energy of 17.575kJ/mol was obtained for the TiO2 nanofibers. The photocatalytic activities of the pure and doped nanofibers were investigated with degradation of methyl orange (MO) as a model pollutant. The degradation followed the Langmuir–Hinshelwood (L–H) kinetic model with pseudo-first-order apparent rates of 3.2×10−2, 5.3×10−2, 8.9×10−2 and 7.1×10−2 for Co doped nanofibers of Rt=0.0, 0.0025, 0.005, 0.01 (where Rt is the molar ratio of Co(OAc)2 to Ti(OiPr)4). The result showed that Co2+ doped nanostructure significantly enhanced the photocatalytic degradation of methyl orange under direct sunlight compared to pure TiO2. Rt=0.005 sample showed best sunlight photocatalytic performance among the above samples which is 2.3 times (after 30min) efficient than that of pure nanostructure.

Fabrication and characterization of metal-doped TiO2 nanofibers for photocatalytic reactions

Metal (Co2+, Ni2+, Cu2+, and Zn2+) doped TiO2 nanofibers were fabricated by a sol–gel method and an electrospinning technique using poly(methyl methacrylate) (PMMA) and titanium isopropoxide as precursors. Co, Ni, and Zn were found to promote the anatase–rutile (A–R) phase transformation, whereas Zn inhibited this process. The as-prepared catalysts were evaluated in the photodecomposition of methylene blue under UV light. Ni- and Zn-doped TiO2 nanofibers were found to be more efficient than pure TiO2 nanofibers in this reaction. The photocatalytic degradation rate fitted a pseudo-first-order equation. Zn-doped TiO2 nanofibers were found to be promising materials for the photocatalytic decomposition of methylene blue with a kinetic constant of 0.0240min−1.

Photo-Kelvin probe force microscopy for photocatalytic performance characterization of single filament of TiO2 nanofiber photocatalysts

This is an in-depth study on the photocatalytic performance characterization for single filament of TiO2 nanofiber photocatalysts by the novel photo-Kelvin probe force microscopy technique (photo-KPFM) and first principles calculations. Three kinds of TiO2 nanofibers: anatase TiO2 nanofibers (anatase TiO2 NFs), nitrogen doped TiO2 nanofibers (N-TiO2 NFs), and nitrogen doped TiO2 nanofibers decorated with platinum nanoparticles (N-TiO2-Pt NFs) were investigated. The N-TiO2-Pt NFs exhibit the largest negative photo surface potential shift (−182 mV) as compared to anatase TiO2 NFs (−29 mV). The first-principles calculations based on density functional theory (CASTEP simulation software) indicate that the significant photo surface potential shift obtained by adding nitrogen and platinum into TiO2 NFs is induced by two mechanisms: (1) enhancement in absorbance to increase exciton generation and (2) decreased charge recombination to increase surface charge. These changes in the photo surface potential of various TiO2 nanofibers are closely correlated with their photocatalytic activity. Thus, this novel photo-KPFM provides a useful technique to easily monitor the photocatalytic capability of materials in the development of high performance photocatalysts.

Preparation of nitrogen doped TiO2 nanofibers by near field electrospinning (NFES) technique for NO2 sensing

Parallel arrays of well aligned crack-free N-doped and undoped TiO2 nanofibers (3–4mm long, 300–500nm diameter) have been deposited by near field electrospinning (NFES) technique on Si3N4 substrates with interdigitated Pt electrodes and annealed at 400°C for 1h. Anatase TiO2 with crystallites’ size of approximately 12nm have been prepared and characterized by XRD, SEM, TEM and XPS techniques. Experimental measurements have been conducted through an ad hoc analog integrated resistive sensor interface, based on an oscillating circuit, fabricated in a 0.35μm standard CMOS technology. Gas response to NO2 in the range 1–10ppm and 100–300°C operating temperature (OT) has shown best practical sensor sensitivity (S=RG/RA) at a relatively low OT (150°C) and detection limits down to 1ppm gas. Nitrogen doping at N:Ti 1:1 atomic ratio has been proposed in order to decrease the intrinsic resistance of TiO2, thus enabling better signal to noise ratio of the electrical response.

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 700nm. 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.

Application of a composite structure of carbon nanoparticles and Nb–TiO2 nanofibers as electrocatalyst support for PEM fuel cells

Platinum catalyst nanoparticles (20wt.%) were deposited on a mixed support, which consisted of 25at.% Nb doped TiO2 nanofibers and carbon agglomerates. XRD analysis revealed that titania was present in the rutile phase. The catalyst was characterized electrochemically with respect to durability and oxygen reduction activity. Based on cyclic voltammetry tests, the Nb–TiO2/C supported catalyst was more stable compared to a commercially available carbon supported Pt catalyst (E-tek) over 1000 cycles. The apparent active Pt area decreased by 5% due to cycling, whereas in the case of Pt/C the decrease was 23%. The oxygen reduction performance was comparable for both cases. For example, during the anodic sweep the mass activity at 0.9V vs. the reversible hydrogen electrode (RHE) was 19AgPt−1 and 20AgPt−1 for the freshly prepared in-house prepared and commercial catalysts, respectively. After the durability experiment both types of catalysts yielded a mass activity of 17AgPt−1. Fuel cell tests with a single cell configuration were also carried out with the Nb–TiO2/C supported catalyst on the cathode side (gas diffusion electrode), yielding a peak power density of 0.34Wcm−2 at 75°C when pure oxygen was supplied on the cathode side.