Iron-doped TiO2 Research Articles

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.

Synthesis of iron-doped TiO2 for degradation of reactive Orange16

In this study the optimum conditions for preparing the iron-doped TiO2 nanoparticles were investigated. Samples were synthesized by sol–gel impregnation method. Three effective parameters were optimized using Taguchi method, consisted of: (i) atomic ratios of Fe to Ti; (ii) sintering temperature; (iii) sintering time. The characterization of samples was determined using X-ray diffraction, BET- specific surface area, UV- Vis reflectance spectra (DRS) and scanning electron microscope (SEM). The XRD patterns of the samples indicated the existence of anatase crystal phase in structure. UV- Vis reflectance spectra showed an enhancement in light absorbance in the visible region (wavelength > 400 nm) for iron-doped samples. The photocatalytic activity of samples was investigated by the degradation of RO 16 (RO 16) dye under UV irradiation. The results illustrated that the photocatalytic activity of iron-doped TiO2 was more than pure TiO2, because of the smaller crystal size, grater BET surface area and higher light absorption ability.

Influence of iron leaching and oxidizing agent employed on solar photodegradation of phenol over nanostructured iron-doped titania catalysts

Iron-doped TiO2 catalysts with two different iron contents (0.7 and 3.5wt.%) as well as the corresponding undoped system, prepared by a combined sol–gel/microemulsion method and calcined at 600°C, have been examined with respect to their behaviour for photocatalytic degradation of aqueous phenol with H2O2 under solar light. The activity results are complemented with structural/morphological and electronic characterization analysis achieved by XRD, TEM, Raman, SBET, UV–vis DRS and XPS techniques. A detrimental effect of the presence of iron on the photoactivity is detected for the sample with 0.7wt.% iron. In contrast, some activity enhancement is produced for the sample with highest iron loading. Such irregular catalytic behaviour with respect to iron loading is analyzed on the basis of the presence of additional catalytic contributions from new photoactive species. These are created as a consequence of surface modifications produced under reaction conditions related to the existence of phenomena of iron leaching from the catalysts. Differences in the specific nanostructure present in each case can also play a role on explaining the differences observed in the photoactivity. Finally, an analysis of the photoactivity as a function of the oxidizing agent employed, either H2O2 or oxygen from air, is also performed.

Phase Transformation and Charge Transfer in Heavily Iron Ion Doped Titanium Oxide and Oxynitride Nanocolloids

Porous sol–gel generated TiO2 nanocolloids and their corresponding oxynitrides TiO2–xNx are investigated to evaluate the effects that accompany doping with iron (FeII) ions at high doping concentrations. The introduction of FeII at higher concentrations leads to an anatase-to-rutile conversion at room temperature for the seeded oxynitride nanocolloids and to a less crystalline state in the subsurface and bulk as suggested by Raman spectroscopy. Combinations of core level and valence band photoelectron spectroscopy are correlated with the results of density functional theory (DFT) calculations to demonstrate a facile charge transfer from FeII to TiIV, producing TiIII and FeIII, and subsequently the transformation of FeII + TiIII to FeIII + TiII. This process is associated with the detectable formation of Ti(III) and Ti(II) at the surface of the titania-based nanoparticles. With significant visible light absorption, the photocatalytic activities of the iron-seeded titania systems are comparable to that of the iron-doped oxynitride TiO2–xNx as a function of doping concentration. The observations reported herein suggest that the anatase-to-rutile phase transformation and the enhancement of electron transfer can control the visible-light catalytic activity within the doped nanoparticles to form FeII/FeIII-codoped TiO2 nanocolloids.

Preparation of Iron-Doped Titania from Flocculated Sludge with Iron-Titanium Composite Coagulant

The main drawback of flocculation process with dye wastewater is the large amount of unrecyclable sludge which needs disposal. A novel process using Ti-salt flocculation to purify wastewater was developed to produced sludge that can be calcined to produce titania. In this study, iron-doped TiO2 nanomaterial was successfully produced from sludge obtained by the flocculation of dye wastewater with a composite floculant including TiCl4 and FeSO4. The titania was characterised using scanning electron microscopy (SEM/EDX), transmission electron microscopy (TEM), X-ray diffraction (XRD), and the photodecomposition of acetaldehyde. The XDR results showed that the anatase and rutile structures were found after sludge calcination at 550 degrees C and 640 degrees C respectively. The elemental analyses were carried out using EDX. The rutile titania sample consisted of Ti (35.7 wt.%), Fe (14.7 wt.%), O (42.3 wt.%), P (2.6 wt.%) and Ca (4.7 wt.%). The photocatalytic activity was monitored for the photodecomposition of gas acetaldehyde. Iron-doped titania seems to play an important role in increasing the photocatalytic activity under UV light irradiation.

Structure and activity of iron-doped TiO2-anatase nanomaterials for gas-phase toluene photo-oxidation

The structural (from local to long range order) and electronic evolution of Fe-doped anatase nanomaterials is evaluated using in situ synchrotron based X-ray total scattering/diffraction and absorption techniques and Raman spectroscopy. These methods are combined with UV-visible spectroscopy and infrared diffuse reflectance (DRIFTS) to maximize the level of structural and morphological information regarding these materials. Fe doping of anatase nanomaterials generates solids having Fe at substitutional positions of the structure, and anion vacancies as charge neutrality entities. These structural modifications lead to materials with decreasing band gap energy as a function of Fe content. Concomitantly, mid-gap electronic states are observed to appear. At the same time, the presence of Fe alters the primary particle shape of the anatase without changing significantly the primary particle size. In contrast with previous results, analysis of the combined results strongly indicates that UV and visible photocatalytic activity are here dominated by morphological rather than structural/electronic issues.

Iron-doped TiO2 nanotubes with high photocatalytic activity under visible light synthesized by an ultrasonic-assisted sol-hydrothermal method

Abstract A series of iron-doped anatase TiO2 nanotubes (Fe/TiO2 NTs) catalysts with iron concentrations ranging from 0.88 to 7.00 wt% were prepared by an ultrasonic-assisted sol-hydrothermal process. The structures and the properties of the fabricated Fe/TiO2 NTs were characterized in detail and photocatalytic activity was examined using a reactive brilliant red X-3B aqueous solution as pollutant under visible light. The lengths of the NTs were determined to range from 20 nm to 100 nm. The incorporation of the iron ions (Fe3+) into the TiO2 nanotubes shifted the photon absorbing zone from the ultraviolet (UV) to the visible wavelengths, reducing the band gap energy from 3.2 to 2.75 eV. The photocatalytic activity of the Fe/TiO2 NTs was 2–4 times higher than the values measured for the pure TiO2 nanotubes.

Iron Insertion and Hematite Segregation on Fe-Doped TiO2Nanoparticles Obtained from Sol–Gel and Hydrothermal Methods

Iron-doped TiO(2) (Fe:TiO(2)) nanoparticles were synthesized by the sol-gel method (with Fe/Ti molar ratio corresponding to 1, 3, and 5%), followed by hydrothermal treatment, drying, and annealing. A similar methodology was used to synthesize TiO(2) and α-Fe(2)O(3) nanoparticles. For comparison, a mixture hematite/titania, with Fe/Ti = 4% was also investigated. Characterization of the samples using Rietveld refinement of X-ray diffraction data revealed that TiO(2) consisted of 82% anatase and 18% brookite; for Fe:TiO(2), brookite increased to 30% and hematite was also identified (0.5, 1.0, and 1.2 wt % for samples prepared with 1, 3, and 5% of Fe/Ti). For hematite/titania mixture, Fe/Ti was estimated as 4.4%, indicating the Rietveld method reliability for estimation of phase composition. Because the band gap energy, estimated as 3.2 eV for TiO(2), gradually ranged from 3.0 to 2.7 eV with increasing Fe content at Fe:TiO(2), it can be assumed that a Fe fraction was also inserted as dopant in the TiO(2) lattice. Extended X-ray absorption fine structure spectra obtained for the Ti K-edge and Fe K-edge indicated that absorbing Fe occupied a Ti site in the TiO(2) lattice, but hematite features were not observed. Hematite particles also could not be identified in the images obtained by transmission electron microscopy, in spite of iron identification by elemental mapping, suggesting that hematite can be segregated at the grain boundaries of Fe:TiO(2).

Comparison of the photocatalytic efficiencies of bare and doped rutile and anatase TiO2 photocatalysts under visible light for phenol degradation and E. coli inactivation

This study aimed at comparing the photocatalytic efficiencies of various TiO2 based photocatalysts for phenol degradation and bacteria inactivation under illumination with visible light. Commercial undoped anatase and rutile (both from Aldrich), Aeroxide P25 (Evonik Industries), nitrogen-doped anatase (Sumitomo TP-S201, Sumitomo Chemical Inc.), nitrogen and sulphur co-doped anatase (Kronos VLP7000, Kronos Titan GmbH), and our custom-synthesized nitrogen- and iron-doped TiO2, as well as nitrogen and sulphur co-doped Aeroxide P25 and silver- and gold-deposited Aeroxide P25 were studied. The photocatalytic efficiency of different types of titanium dioxide based photocatalysts was determined by inactivation of Escherichia coli K12 bacteria and by phenol decomposition. Electron spin resonance (ESR) in combination with spin trapping was used to get insight into the reactive oxygen species (ROS)-mediated photocatalytic processes in the presence of TiO2-based photocatalysts. ESR results confirmed that titanias which generated OH radicals were efficient in E. coli disinfection, whereas titanias that were unable to produce OH radicals did not reveal significant bactericidal action. Three of our home-made titanias (iron-, nitrogen-, nitrogen/sulphur) as well as the commercial nitrogen/sulphur codoped Kronos VLP7000 TiO2 showed higher efficiency of phenol degradation than the well-established reference photocatalyst, Aeroxide P25, but showed much lower (if any) activity for bacteria inactivation, including Kronos VLP7000, which revealed extremely high efficiency for phenol decomposition. Interestingly undoped Aldrich rutile (with large particles - 100–700nm) had the highest efficiency for inactivation of E. coli and also had fairly high activity of phenol degradation.

Structural refinement and photocatalytic activity of Fe-doped anatase TiO2 nanoparticles

Colloidal iron-doped (0.0–3.0mol%) TiO2 nanoparticles have been synthesized using sol–gel method and characterized by thermogravimetric analysis, powder XRD, IR spectroscopy, Raman spectroscopy, and transmission electron microscopy (TEM). The characteristic features of nanocrystalline TiO2 in tetragonal anatase phase were confirmed by powder XRD studies with Rietveld refinement. Rietveld refinement data gave 2.59, 3.21 value of RB for pure TiO2 and 3.0mol% Fe:TiO2 nanoparticles, respectively. Raman bands at 639cm−1, 517cm−1, and 395cm−1 further confirmed the pure anatase phase in all samples. TEM pictures revealed the non-spherical nanoparticles having sizes in between 7 and 14nm. Surface area and pore volume for the samples were in the range of 150–87m2/g and 0.35–0.21cm3/g, respectively. The magnetic and optical properties of the nanoparticles were investigated by using SQUID magnetometer and UV–vis spectroscopy. The undoped titania nanoparticles were diamagnetic; whereas all doped titania samples were paramagnetic. The optical band gap of titania nanoparticles were found to decrease with the increase in iron content in host lattice. The photocatalytic performance of the iron-doped TiO2 nanoparticles for the conversions of p-nitrobenzaldehyde to p-nitrobenzoic acid as well as photodegradation of Rhodamine 6G was also investigated.

TiO2 Based Photo Catalysts: Evidence for Electron Transfer by Iron

Photocatalysts hold great potential for using sunlight to drive oxidations. Among photocatalysts, TiO2 is one of the most promising due to the strong oxidizing potential of the valence band; the strong oxidizing potential results in mineralization of a wide range of pollutants found in water. Developing a practical material requires improving the photo catalyst in two ways: narrowing the band gap and improving the quantum efficiency. Progress for improving TiO2 is hampered by apparently inconsistent literature reports for the effect of doping on efficiency. The basic source of the apparent inconsistencies is that charge transfer occurs at the catalyst surface and is thus affected by seemingly small differences in catalyst generation. This report contains results from 2.4 nm diameter particles; the small size results in improved consistency enabling comparison of modified and unmodified particles. Results suggest that batch-to-batch variation in grain boundaries and defects are a source of the apparent inconsistencies in the literature. The specific results reported here for iron doping support a model in which low-level iron doping enhances efficiency by acting as an electron transfer agent to molecular oxygen. Iron doping also modifies surface adsorption of methanol, the test molecule, and water. This contribution concludes with suggestions for future directions in developing iron-doped TiO2 photocatalysts. Keywords: Charge transfer, iron doped, oxygen activation, photocatalyst, remediation, TiO2, Fe(II), LVD, SFG, specification

Effect of Iron (III)-Doping on the Photocatalytic Activity of Titanium Dioxide Catalysts for Methylene Blue Degradation

Iron-doped TiO2 photocatalyst powders were prepared by the sol–gel method and characterized by Brunauer–Emmett–Teller (BET)-specific surface area, scanning electron microscopy (SEM), X-ray diffraction (XRD), and Ultraviolet–Visible (UV-Vis) spectroscopy. Fe3+ doping in the TiO2 decreases the crystal grain size, increases the specific surface areas of powders, extends the absorption to visible light regions (400~500 nm), and lowers the photocatalytic activity for methylene blue (MB) degradation under UV irradiation. The photocatalytic degradation of MB in water was investigated as a function of the Fe3+ content in TiO2. It was found that under the irradiation of visible light, a small amount of Fe3+ dopant in TiO22 powders could obviously enhance the photocatalytic activity. When the Fe3+ content was in the range of 0.03–0.1 mol%, the photocatalytic activity of the samples was higher than that of undoped TiO2. Appropriate content of Fe-doping is an effective means to improve the photocatalytic activity of TiO2 for MB degradation under visible light irradiation.

Solar light assisted photodegradation of phenol with hydrogen peroxide over iron-doped titania catalysts: Role of iron leached/readsorbed species

Nanostructured iron-doped TiO2 catalysts with anatase structure and two different iron contents (0.7 and 3.5wt.%) have been prepared by a combined sol–gel/microemulsion method and examined with respect to their behaviour for photocatalytic degradation of aqueous phenol with H2O2 under solar light. The activity results are compared with those obtained for similarly prepared undoped systems as well as Degussa P25 reference catalyst and have been complemented with structural/morphological and electronic characterization analyses achieved by XRD, TEM, Raman, SBET, UV–vis DRS and XPS techniques. In contrast to typically observed results, the highest photoactivity is obtained for the catalyst with highest iron loading while that with 0.7% Fe displays lower photoactivity than undoped samples. Such unusual behaviour has been attributed to the contribution of new photoactive iron complexes generated on the surface of the catalyst as a consequence of iron leaching and readsorption processes taking place during the course of phenol photodegradation process.

Photocatalytic degradation of methyl orange on arrayed porous iron-doped anatase TiO2

Arrayed porous iron-doped TiO2 was prepared by sol–gel with polystyrene spheres as template and used as photocatalyst for the degradation of methyl orange. The structure and performances of the prepared photocatalyst were characterized with X-ray diffractometer, inductively coupled plasma-atomic emission spectrometer, scanning electron microscope, UV-visible spectrometer, and methyl orange degradation tests. It is found that the iron dopant does not change the crystal phase of TiO2 but affects its lattice constant, optical absorption, electronic conductivity, charge-transfer resistance, and activity toward the degradation of methyl orange. The sample doped with 0.01 wt.% Fe (based on Ti) and with smaller pore size exhibits the better photocatalytic activity. The degradation rate of methyl orange on the sample with a pore size of 190 nm is 2.3 times that on the undoped sample with the same pore size.

Arrayed porous iron-doped TiO 2 as photoelectrocatalyst with controllable pore size

Arrayed porous iron-doped TiO 2 with controllable pore size was prepared by using polystyrene spheres and its structure, morphology, composition and photoelectrochemical properties were characterized with X-ray diffraction, scanning electron microscope, inductively coupled plasma-atomic emission spectrometer and electrochemical methods. It is found that the photoelectrochemical properties of the arrayed porous TiO 2 can be improved by doping adequate amount of iron in the lattice of TiO 2 and the sample doped with 0.01 wt% Fe (based on Ti) exhibits the best photoelectrochemical performance. With doping 0.01 wt% Fe in TiO 2, the photocurrent density of the sample is improved from 2.0 μA cm −2 to 10.0 μA cm −2 and its flat-band potential shifts from −0.38 V to −0.55 V (vs. SCE).

Optimization of H2O2 use during the photocatalytic degradation of ethidium bromide with TiO2 and iron-doped TiO2 catalysts

A series of nanosized iron-doped titania catalysts has been used for the photocatalytic degradation of ethidium bromide (EtBr) with oxygen. The study shows that EtBr surface adsorption is most favored over basic titania surfaces such as those present in undoped TiO2 and Fe–TiO2 with low iron content. This fact is shown to affect strongly the photocatytic mechanism of EtBr degradation. Based on EtBr adsorption and photocatalytic activity analyses, a titania catalyst with an iron content of 0.7wt.% has been selected for subsequent studies using H2O2 as oxidant. Parameters as reaction pH and initial hydrogen peroxide concentration were analyzed to establish optimum operating conditions. It is shown that a new strategy based on dosing H2O2 in a controlled way could minimize radical self-scavenging reactions and improves final EtBr mineralization degree. Finally, the stability and durability of catalyst/activity have been examined through five consecutive cycles of H2O2 dosing. A constant activity level is maintained during at least four consecutive cycles in which total EtBr and 80% of Total Organic Carbon conversion is achieved.

Nanoengineering with residual catalyst from CNT templates

We investigate how residual catalyst from carbon nanotube (CNT) templates can be used to engineer novel functional nanomaterials. CNTs, produced via continuous flow chemical vapour deposition, typically contain catalyst residues in the form of encapsulated metal clusters or of iron oxide nanoparticles attached to the outside of the CNTs. These CNTs are used as sacrificial templates for TiO 2 coatings using benzyl alcohol as a linking agent. Upon oxidation of the CNTs, the encapsulated iron particles dissolve into the TiO 2 lattice and form iron-doped TiO 2 nanotubes without the formation of secondary phases, while the iron oxide particles merely attach to the outer surface. The materials show extended light absorption into the visible range, a requirement for visible-light photocatalyst.

Surface properties of doped and undoped TiO 2 thin films deposited by magnetron sputtering

In this work, transparent titanium dioxide (TiO 2) thin films were deposited onto microscope glass slides by means of the d.c. reactive magnetron sputtering method. The films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), UV–visible spectroscopy (UV) and contact angle analysis using the Owens–Wendt method for the surface energy calculation. The photocatalytic activity of the films was tested by measuring the photodegradation of Rhodamine-B ( RhB) dye under radiation of UV light. Iron-doped TiO 2 films were also prepared in order to study the Fe-doping effect on TiO 2 photocatalytic activity. The influences of different iron concentrations on the contact angle of the series of Fe-doped TiO 2 thin films, were investigated. The influences of total sputtering pressures on TiO 2 photocatalytic activity were also investigated. It was observed that the photocatalytic activity of the TiO 2 thin films was slightly improved by increasing the total sputtering pressure. Moreover, it was also observed that in general, iron-doping was detrimental for photocatalytic activity, nevertheless the films with low iron concentrations showed better photocatalytic activity than those with high iron concentrations. It was found that iron-doping has changed the wettability appetency of TiO 2 coated surfaces.

Evaluation of the adsorption potential of titanium dioxide nanoparticles for arsenic removal

The adsorption potential of titanium dioxide (TiO 2) nanoparticles for removing arsenic from drinking water was evaluated. Pure and iron-doped TiO 2 particles are synthesized via sol-gel method. The synthesized TiO 2 nanoparticles were then immobilized on ordinary sand for adsorption studies. Adsorption isotherms were conducted on the synthesized nanoparticles as well as the sand coated with TiO 2 nanoparticles under varying conditions of air and light, namely, the air-sunlight (A-SL), air-light (AL), air-dark (AD) and nitrogen-dark (ND). X-ray diffraction (XRD) analysis showed that the pure and iron-doped TiO 2 nanoparticles were in 100% anatase crystalline phase with crystal sizes of 108 and 65 nm, respectively. Adsorption of arsenic on the three adsorbents was non-linear that could be described by the Freundlich and Langmuir adsorption models. Iron doping enhanced the adsorption capacity of TiO 2 nanoparticles by arresting the grain growth and making it visible light responsive resulting in a higher affinity for arsenic. Similarly, the arsenic removal by adsorption on the sand coated with TiO 2 nanoparticles was the highest among the three types of sand used. In all cases, As(V) was adsorbed more compared with As(III). The solution pH appeared to be the most important factor in controlling the amount of arsenic adsorbed.

Synthesis, structural characterization, and photocatalytic properties of iron-doped TiO2 aerogels

Fe(III)-doped TiO2 aerogels are prepared by acid catalyzed sol–gel method followed by supercritical drying, and then heat treatment. Raman spectra together with X-ray diffraction (XRD) and selected area electron diffraction (SAED) patterns of the iron-doped TiO2 aerogel samples revealed the existence of both anatase and brookite crystalline phases. It was found that the brookite phase formation is favored by the increase of the iron content in the dried samples. XRD measurements show that the lattice constant c of anatase phase decreases with the dopant addition, while the value of a remains essentially unchanged. The microstructure of the investigated samples is relatively compact with small mesopores as revealed from transmission electron microscopy (TEM). The most enhanced photocatalytic activity was exhibited by the TiO2 aerogel sample with 1.8 at.% Fe(III) whose apparent rate constant of the salicylic acid photodegradation was found to be of almost six times higher than that of Degussa P25.