Fe-doped TiO2 Powders Research Articles

Improved electrocatalytic activity of Pt supported onto Fe-doped TiO2 toward ethanol oxidation in acid media

The low stability of Pt-based catalysts due to severe corrosion of carbon support is one of the most critical technical issues hindering the widespread application of proton exchange membrane fuel cells. Here, we report the successful deposition of Pt nanoparticles on both pure titanium dioxide (TiO2) and Fe-doped TiO2 powder by chemical reduction using formic acid and their performance toward ethanol oxidation in acid media. First, the supported TiO2 was synthesized by the sol–gel method, and its physical-chemical properties were modified by the incorporation of iron (5.0 and 10.0 wt% Fe) into the structure of TiO2. The supports and catalysts were characterized by photoacoustic spectroscopy (PAS), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and transmission electron microscopy (TEM). The PAS data show that the doping of TiO2 with iron ions (III) decreases the band gap from 2.95 eV (undoped TiO2) to lower values depending on the iron content in the support (1.97 eV and 1.90 eV for 5Fe–TiO2 and 10Fe–TiO2, respectively). The XRD and TEM results indicate the presence of small-sized (around 3.5 nm) Pt nanostructures deposited onto the supports. The XPS analyses reveal surfaces rich in metallic Pt and oxygen species (O2− species, OH− and O atoms) in the vicinity of oxygen vacancies, as well as strong interactions between Pt nanoparticles and the Fe–TiO2 support. The Pt/Fe–TiO2 electrocatalyst exhibits higher catalytic activity toward ethanol oxidation than Pt/TiO2 and commercial Pt/C electrocatalysts (used as reference). The efficiency of Pt utilization increases with the Fe content. The sample with 10 wt% (mol/mol) of iron is then the most active catalyst. The enhanced activity and stability of the Pt/Fe–TiO2 catalyst can be attributed to the synergic and electronic effect of the compounds, Pt, and Fe–TiO2.

Sol–Gel Synthesis of Fe-Doped TiO2 Nanocrystals

Fe-doped TiO2 powders were synthesized by the sol–gel method using titanium (IV) isopropoxide (TTIP) as the starting material, ethanol as solvent, and ethylene glycol (EG) as stabilizer. These prepared samples were characterized by x-ray diffractometer (XRD), field emission scanning electron microscope (FESEM), Fourier-transform infrared (FTIR) spectroscopy, diffuse reflection spectroscopy (DRS), energy-dispersive x-ray spectroscopy (EDX), and photoluminescence (PL) analyses to study their structure, morphology, and optical properties. The particle size of Fe-doped TiO2 was in the range of 18–39 nm and the minimum crystallite size was achieved for 4 mol.% of Fe. The XRD result of the samples that were doped with Fe showed a tetragonal structure. It also revealed the coexistence of the anatase and rutile phases, and showed that their ratio changed with various molar concentrations of Fe dopant. FTIR spectroscopy showed the presence of the Ti-O vibration band in the samples. PL analysis revealed the PL property in the UV region. Visible irradiation and the intensity of PL spectra were both reduced by doping TiO2 with 3 mol.% of Fe as compared to the pure variety. The spectra from the DRS showed a red shift and a reduction of 2.6 eV in the band gap energy for 4 mol.% Fe-doped TiO2. The optimum level of impurity (4 mol.%) for Fe-doped TiO2 nanoparticles (NPs), which improve the optical and electrical properties by using new precursors and can be used in solar cells and electronic devices, was determined. The novelty of this work consists of: the Fe/TiO2 NPs are synthesized by new precursors from sol–gel synthesis of iron and TTIP using acetic acid-catalyzed solvolysis (original idea) and the optical properties optimized with a mixture of phases (anatase/rutile) of Fe-doped TiO2 by this facile method.

Effect of Fe-doped TiO2 photocatalysts on the degradation of acid orange 7

ABSTRACTThe purpose of the research was to determine the photocatalytic degradation efficiency of acid orange 7 (AO7) using 2 mol% Fe-doped TiO2 as photocatalysts under UV irradiation. Fe-doped TiO2 powder synthesized by solid-reaction technique reveals the average particle size of 0.91 μm, BET surface area of 11.6 m2/g, a wide pore-size distribution with the average pore diameter of 3.2 nm and pore volume of 0.035 cm3/g. Within the experiment, AO7 was prepared as a synthetic textile wastewater at the initial concentration of 34 mg/L along with using various doses of Fe-doped TiO2 photocatalysts. The results indicated that Fe-doped TiO2 with dose of 0.100 g in 100 mL of AO7 reached the highest removal efficiency about 88.7%.

Influence of Fe catalytic doping on the properties of TiO2 nanoparticles synthesized by microwave method

The present work focus on the development of an effective process for undoped and Fe doped TiO2 powders production by microwave technique. The influence of Fe doping on the structure, phase, vibrational bands and optical properties of TiO2 were discussed. The X-ray diffraction patterns of nanoparticles revealed a preferentially oriented (101) anatase phase for TiO2 and transforms to rutile TiO2 with Fe doping. Fourier transform infrared spectra analysis confirmed the phase transformation from anatase to rutile TiO2 with Fe doping. The UV–visible spectra showed the increase in absorption band with Fe doping when compared with undoped TiO2 nano particles, and optical band gap decreased slightly with Fe doping. SEM micrographs revealed spherical shaped grains of TiO2 with high homogeneity, with a subsequent reduction in the agglomeration of particles with Fe doping suggesting its potential application for better photo catalytic activity.

Synthesis of iron-doped TiO2 nanoparticles by ball-milling process: the influence of process parameters on the structural, optical, magnetic, and photocatalytic properties

Titanium dioxide (TiO2) absorbs only a small fraction of incoming sunlight in the visible region thus limiting its photocatalytic efficiency and concomitant photocatalytic ability. The large-scale application of TiO2 nanoparticles has been limited due to the need of using an ultraviolet excitation source to achieve high photocatalytic activity. The inclusion of foreign chemical elements in the TiO2 lattice can tune its band gap resulting in an absorption edge red-shifted to lower energies enhancing the photocatalytic performance in the visible region of the electromagnetic spectrum. In this research work, TiO2 nanoparticles were doped with iron powder in a planetary ball-milling system using stainless steel balls. The correlation between milling rotation speeds with structural and morphologic characteristics, optical and magnetic properties, and photocatalytic abilities of bare and Fe-doped TiO2 powders was studied and discussed.

Preparation and characterization of Fe-doped TiO2 powders for solar light response and photocatalytic applications

Different amounts of Fe-doped TiO2 (with 0.1 to 10 wt.% Fe) powders were prepared at temperatures in the range of 400 and 800?C following a conventional co-precipitation technique and were thoroughly characterized by means of X-ray diffraction (XRD), Fourier-transform infrared (FT-IR), Fourier-transform Raman (FT-Raman), diffuse reflectance spectroscopy (DRS), BET surface area, zeta potential and flat band potential measurements. Photocatalytic ability of Fe-doped TiO2 powders was evaluated by means of methylene blue (MB) degradation experiments conducted under the irradiation of simulated solar light. Characterization results suggested that as a dopant Fe stabilized TiO2 in the form of anatase phase, reduced its band gap energy and adjusted its flat band potentials in such a way that these powders can be employed for photoelectrolysis of water into hydrogen and oxygen in photoelectrochemical (PEC) cells. The 0.1 wt.% Fe-doped TiO2 exhibited highest activity in the photocatalytic degradation of MB. The kinetic studies revealed that the MB degradation reaction follows the Langmuir-Hinshelwood first order reaction rate.

Sol-gel preparation of Fe-doped mixed crystal TiO2 powder and its photocatalytic activity for degradation of azo fuchsine under visible light irradiation

In this work, the Fe-doped mixed crystal TiO2 photocatalyst which can utilize visible light was prepared by sol-gel and heat-treated methods. During heat-treatment, the phase transformation of Fe-doped TiO2 powder occurs and the process is characterized by XRD and TG-DTA technologies. Otherwise, the sizes and shapes of Fe-doped and undoped TiO2 powders were also compared using TEM images. The azo fuchsine in aqueous solutions, as a model compound, was treated under visible light irradiation using Fe-doped mixed crystal TiO2 powders as photocatalyst. The results showed that, under visible light irradiation, the (0.25%) Fe-doped mixed crystal TiO2 powder heat-treated at 600°C for 3.0 h behaved very high photocatalytic activities for degradation of azo fuchsine. The remarkable improvement of the photocatalytic activity of TiO2 powder was elucidated through the cooperative effects of iron doping and phase transformation. The iron doping can restrain the recombination of photogenerated electron-hole pairs and the phase transformation can enhance the absorption of visible light. Furthermore, other influence factors such as azo fuchsine concentration, solution acidity, Fe3+ ion content and irradiation time were also studied. Thus, this method is applicable for the treatment of wastewater.

Photocatalytic Degradation of Organic Dyes by a High Efficient TiO2-Based Catalysts Under Solar Light Irradiation

In this work, the Er3+:YAlO3/Fe-doped TiO2 composite, a high efficient TiO2-based photocatalyst, was synthesized by ultrasonic dispersion and liquid boil methods. Among which, the Er3+:YAlO3 is a kind of upconversion luminescence agent, which was prepared by nitrate-citric acid method. It can emit ultraviolet light under visible light excitation. The Er3+:YAlO3/Fe-doped TiO2 composite was characterized by X-ray diffraction and UV–vis spectral techniques. The degradation of Acid Red B dye was used to evaluate the photocatalytic activity of the Er3+:YAlO3/Fe-doped TiO2 composite under solar light irradiation. It was found that the photocatalytic activity of Er3+:YAlO3/Fe-doped TiO2 composite was much higher than that for the similar system with only Fe-doped TiO2. And the influencing factors, such as Er3+:YAlO3 content, irradiation time, initial concentration of Acid Red B, addition amount of Er3+:YAlO3/Fe-doped TiO2 and NaCl, on the photocatalytic degradation were also investigated. The Er3+:YAlO3 as upconversion luminescence agent can elevate the photocatalytic activity of Fe-doped TiO2 powder. Moreover, the Fe2+ ion can restrain the recombination of photogenerated electrons and holes. Thus, this Er3+:YAlO3/Fe-doped TiO2 composite is a useful material for the detoxification of wastewater because it can efficiently utilize solar light by converting visible light into ultraviolet light.

Preparation of nanocrystalline Fe-doped TiO2 powders as a visible-light-responsive photocatalyst

Nanocrystalline Fe-doped TiO2 powders were prepared using TiOSO4, urea, and Fe(NO3)3 · 9H2O as precursors through a hydrothermal method. The as-synthesized yellowish-colored powders are composed of anatase TiO2, identified by X-ray diffraction (XRD). The grain size ranged from 9.7 to 12.1 nm, calculated by Scherrer’s method. The specific surface area ranged from 141 to 170 m2/g, obtained by the Brunauer–Emmett–Teller (BET) method. The transmission electron microscopy (TEM) micrograph of the sample shows that the diameter of the grains is uniformly distributed at about 10 nm, which is consistent with that calculated by Scherrer’s method. Fe3+ and Fe2+ have been detected on the surface of TiO2 powders by X-ray photoelectron spectroscopy (XPS). The UV–Vis diffuse reflection spectra indicate that the light absorption thresholds of the Fe-doped TiO2 powders have been red-shifted into the visible light region. The photocatalytic activity of the Fe-doped TiO2 was evaluated through the degradation of methylene blue (MB) under visible light irradiation. The Fe-doped TiO2 powders have shown good visible-light photocatalytic activities and the maximum degradation ratio is achieved within 4.5 h.

Fe-doped TiO2 prepared by mechanical alloying

The effect of different milling conditions on the formation of Fe-doped TiO2 powders by mechanical alloying was investigated by Mossbauer spectrometry. The milling conditions investigated were ball to powder weight ratio, milling time, rotation velocity of supporting disc, and the type of starting reactive iron and its concentration. X-ray diffraction shows that high energy mechanical milling of undoped anatase TiO2 induce the anatase to rutile phase transformation via high pressure srilankite. Mossbauer spectra for the majority of the doped samples were decomposed into one sextet and one or two doublets. The sextets was attributed to the presence of α-Fe or hematite impurities. The doublets were assigned to Fe3 + incorporated in the TiO2 structure, and to the Fe2 + located either at the surface or the interstitial sites of TiO2. A greater incorporation of Fe in the TiO2 structure was observed when samples were prepared from hematite instead of α-Fe.

Mixtures of iron and anatase TiO2 by mechanical alloying

Fe-doped TiO2 powders were obtained by mechanical alloying. The starting materials were anatase TiO2 and metallic iron (α-Fe) or hematite (α-Fe2O3). The influence of different milling conditions such as: ball to powder weight ratio, milling time, rotation velocity of supporting disc, and dopant concentration on the structural and magnetic properties were investigated. All experiments were performed in atmospheric conditions. The milled powders were characterized by X-ray diffraction (XRD) using Rietveld refinement and room temperature Mössbauer spectrometry. The XRD patterns of all samples show the coexistence of both anatase and rutile phases and also the high-pressure srilankite phase. Mössbauer spectra reveal the presence of Fe2+ and Fe3+ states in Fe-doped TiO2 as well as α-Fe or α-Fe2O3 in samples obtained from metallic iron or hematite, respectively. The Fe3+ contribution could be attributed to Fe incorporated in the TiO2 structure and the Fe2+ can be probably assigned to surface ferrous ions in the TiO2.

Fe valence states and ferromagnetism occurring in reduced anatase Ti0.97Fe0.03O2−δ

Fe-doped anatase TiO2 polycrystalline films and powders have been prepared by the sol-gel method. Air-annealed film shows paramagnetic behavior at room temperature. However, when the film is further annealed in a vacuum, the ferromagnetic properties are strongly enhanced with the magnetic moment of 0.42μB∕Fe at 5kOe. Mössbauer spectrum of air-annealed film at 295K shows a single doublet of Fe3+. On the other hand, the absorption spectrum after vacuum annealing exhibits two doublets, in which one is the same component with air-annealed case and the other is a new doublet corresponding to Fe2+ state. The temperature dependence of absorption linewidth and quadrupole splitting for the Fe2+ doublet indicates that Fe2+ ions are not paramagnetic and their magnetic interaction exists also at 295K.

Photocatalytic behaviors and structural characterization of nanocrystalline Fe-doped TiO2 synthesized by mechanical alloying

Nanocrystalline Fe-doped TiO2 powders were synthesized by mechanical alloying (MA) with varying Fe contents from 0 up to 4.8wt.% to shift the absorption threshold into the visible light region. The photocatalytic feasibility of the Fe-doped TiO2 powder was evaluated by quantifying the visible light absorption capacity using ultraviolet and visible (UV-Vis) spectroscopy and photoluminescence spectroscopy. Effects of Fe additions on the crystal structures and the morphologies of the Fe-doped powders were also investigated as a function of the doping content using transmission electron microscopy–electron diffraction pattern (TEM–EDP), X-ray diffraction (XRD) and energy dispersive X-ray (EDAX) and X-ray photoelectron spectroscopy (XPS). The UV-Vis study showed that the UV absorption for the Fe-doped powder moved to a longer wavelength (red shift) and the photoefficiency was enhanced. Based on the analysis of the photoluminescence spectra, the red shift was believed to be induced by localizing the dopant level near the valence band of TiO2. The UV-Vis absorption depended on the Fe concentration. TEM–EDP and XRD investigations showed that the Fe-doped powder had a rutile phase in which the added Fe atoms were dissolved. The rutile phase was composed of spherical particles and chestnut bur shaped particles, resulting in a larger surface area than the spherical P-25 powder.