Fe-doped Titania Research Articles

Waste ilmenite sludge-derived low-cost mesoporous Fe-doped TiO2: A versatile photocatalyst for enhanced visible light photocatalysis without a cocatalyst

Ilmenite (FeTiO3), a waste of the titania production industry, is proposed as a potential candidate for visible-light-driven photocatalysis due to its narrow band gap (Eg = 2.01–2.90 eV). However, to date, its photocatalytic performance has been very poor, even significantly lower than TiO2 (Eg = 3.2 eV) due to its high iron content. Herein we report waste ilmenite sludge-derived mesoporous Fe-doped titania (m-FDT) photocatalyst with significantly enhanced activity for a variety of photocatalytic processes, including photocatalytic CO2 reduction, water splitting, and dye-degradation. The m-FDT is developed via a simple hydrothermal process and has desirable properties such as a low band gap (1.72 eV), high surface area (137 m2/g), and lower charge recombination. This can be attributed to the formation of various defects (Fe2+, Fe3+, Ti3+, and O vacancies) due to the doping of Fe in the TiO2 lattice, as confirmed by various experiments and theoretical studies. The champion photocatalyst with an optimal Fe content (1.8 wt%) exhibits high methanol production (86.1 mmol/gcat), which is 100-fold higher than commercial TiO2 without noble metal cocatalyst and sacrificial agent. The designed photocatalyst shows excellent water-splitting activity (55.03 μmol/gcat) and dye degradation ability. This work presents a high-performance, low-cost, versatile photocatalyst for visible light photocatalysis and opens new avenues in semiconductor photocatalysis.

Degradation of methylene blue-ciprofloxacin and hydrogen production simultaneously using combination of electrocoagulation and photocatalytic process with Fe-TiNTAs

The study reported in this paper combines the electrocoagulation and photocatalysis for the simultaneous degradation of methylene blue dyes (MB)-antibiotic ciprofloxacin (CP) and production of hydrogen. The pollutant removal process was conducted by combining adsorption by electrocoagulation and degradation by photocatalysis. Meanwhile, H2 was produced by reducing the H+ on the cathode and the photocatalyst surface in a reactor made of acrylic equipped with aluminum as the anode, stainless steel 316 plates as a cathode, Fe-doped titania nanotube arrays (TiNTAs) as a photocatalyst, and a 250-W mercury lamp as the light source. TiNTAs were synthesized via anodization and followed by the successive ionic layer adsorption and reaction (SILAR) method to incorporate Fe as the dopant. In particular, the effects of Fe loading in the composite photocatalyst are investigated. XRD results showed that TiO2 nanotubes arrays comprise a 100% anatase phase. FESEM, EDX, TEM, and HRTEM analysis confirmed the formation of the nanotubular structure of TiO2 and the presence of Fe deposited on the surface. The UV–Vis DRS indicated that the bandgap of Fe-TiNTAs reduced with Fe introduction, as compared to that of the undoped TiNTAs. The results showed that accumulation of the produced hydrogen from the combination of electrocoagulation-photocatalytic system is greater than that which is obtained using individual electrocoagulation or photocatalytic system. The combined process exhibited an enhanced degradation ability of methylene blue and ciprofloxacin, as well as in the H2 production.

Thin-Film Composite Membranes with a Hybrid Dimensional Titania Interlayer for Ultrapermeable Nanofiltration.

The interfacial properties within a composite structure of membranes play a vital role in the separation properties and application performances. Building an interlayer can facilitate the formation of a highly selective layer as well as improve the interfacial properties of the composite membrane. However, it is difficult for a nanomaterial-based interlayer to increase the flux and retention of nanofiltration membranes simultaneously. Here, we report a nanofiltration membrane with a hybrid dimensional titania interlayer that exhibits excellent separation performance. The interlayer, composed of Fe-doped titania nanosheets and titania nanoparticles, helps the formation of an ultrathin (∼30 nm thick) and defect-free polyamide selective layer with an ideal nanostructure. The hybrid dimensional interlayer endows the membrane with a superior permeability and alleviates flux decline. In addition, the rigid interlayer framework on a PVDF support drastically improves the pressure resistance of nanofiltration membranes and shows negligible flux loss up to 1.5 MPa of pressure.

Visible Light-Driven Photocatalytic Activity and Kinetics of Fe-Doped TiO2 Prepared by a Three-Block Copolymer Templating Approach.

Fe-doped titania photocatalysts (with 1, 2.5, and 3.5 wt. % Fe nominal content), showing photocatalytic activity under visible light, were prepared by a soft-template assisted sol–gel approach in the presence of the triblock copolymer Pluronic P123. An undoped TiO2 photocatalyst was also prepared for comparison. The photocatalysts were characterized by means of X-ray powder Diffraction (XRPD), Quantitative Phase Analysis as obtained by Rietveld refinement, Diffuse Reflectance (DR) UV−Vis spectroscopy, N2 adsorption/desorption at −196 °C, electrophoretic mobility in water (ζ-potential), and X-ray photoelectron spectroscopy (XPS). The physico-chemical characterization showed that all the samples were 100% anatase phase and that iron was present both in the bulk and at the surface of the Fe-doped TiO2. Indeed, the band gap energy (Eg) decreases with the Fe content, with Tauc’s plot determined values ranging from 3.35 (undoped TiO2) to 2.70 eV (3.5 wt. % Fe). Notwithstanding the obtained Eg values, the photocatalytic activity results under visible light highlighted that the optimal Fe content was equal to 2.5 wt. % (Tauc’s plot determined Eg = 2.74 eV). With the optimized photocatalyst and in selected operating conditions, under visible light it was possible to achieve 90% AO7 discoloration together with a TOC removal of 40% after 180 min. The kinetic behavior of the photocatalyst was also analyzed. Moreover, the tests in the presence of three different scavengers revealed that the main reactive species are (positive) holes and superoxide species. Finally, the optimized photocatalyst was also able to degrade phenol under visible light.

Synthesis of Fe- and Co-Doped TiO2 with Improved Photocatalytic Activity Under Visible Irradiation Toward Carbamazepine Degradation.

Pure TiO2 and Fe- and Co-doped TiO2 nanoparticles (NPs) as photocatalysts were synthesized using wet chemical methods (sol-gel + precipitation). Their crystalline structure and optical properties were analyzed using X-ray diffraction (XRD), Raman spectroscopy and Fourier-transform infrared (FTIR) spectroscopy, ultraviolet-visible light (UV-Vis) diffuse reflectance spectroscopy (DRS), and photoluminescence (PL) spectroscopy. The photocatalytic activity of the synthesized nanoparticles was evaluated through degradation of carbamazepine (CBZ) under UV-A and visible-light irradiations. The XRD and Raman analyses revealed that all synthesized nanomaterials showed only the anatase phase. The DRS results showed that the absorption edge was blue-shifted for Fe-doped TiO2 NPs. The decrease in charge recombination was evidenced from the PL investigation for both Co-doped and Fe-doped TiO2 nanomaterials. An enhancement in photocatalytic degradation of carbamazepine in aqueous suspension under both UV-A light and visible-light irradiations was observed for Fe-doped Titania NPs by comparison with pure TiO2. These results suggest that the doping cations could suppress the electron/hole recombination. Therefore, the photocatalytic activity of TiO2-based nanomaterials was enhanced.

Photocatalytic Degradation of Azo Dye Reactive Violet 5 on Fe-Doped Titania Catalysts under Visible Light Irradiation

The presence of azo dyes in textile effluents is an issue of major concern due to their potential impact on the environment and human health. In this study we investigate the photocatalytic degradation under visible light of Reactive Violet 5 (RV5), an azo dye widely used in the textile industry. A preliminary screening of different titania-based catalysts was carried out to identify the best candidate for RV5 removal. The selected catalyst was then tested in a stirred and aerated lab-scale reactor illuminated with a blue light-emitting diode (LED) source emitting in the wavelength range of 460–470 nm. The effects of pH, catalyst load, and hydrogen peroxide additions on the efficiency of dye removal were evaluated. Under the best conditions (pH 10, 3 g/L of catalyst, and 60 mM hydrogen peroxide), the dye solution was completely decolorized in about 2 h. Overall, the results obtained suggest that the proposed process may represent a suitable method for the removal of RV5 from textile effluents.

Structural, optical and photoluminescence studies of sol-gel synthesized pure and iron doped TiO2 photocatalysts

Pure and Iron doped TiO2 nanoparticles were synthesized using the sol-gel method. These materials were characterized by X-ray diffractometer (XRD), high-resolution transmission electron microscope (HR-TEM), scanning electron microscope (SEM), Energy dispersive X-ray (EDX), UV–Vis diffuse reflectance spectroscopy (DRS), Fourier-transform infrared (FTIR), Raman and fluorescence spectrometer. XRD analysis revealed that all the samples were a single phase with anatase nanocrystallite structures. The crystallite size of titania reduced from 9.64 nm to 7 nm with Fe doping. The HRTEM images of the TiO2 and 3% Fe doped TiO2 have revealed that all the particles have a spherical shape with an average particle size of 10 nm and 8 nm respectively. The characteristic peak at 482 cm−1 of the TiO bond stretching vibrations can be evidently observed from FTIR analysis. The Raman blue shift was found in the Fe doped TiO2 samples. Fe-doped TiO2 nanoparticles showed a significant red-shift in band edge as compared with pure TiO2 nanoparticles. The redshift of band gap was detected in Fe doped TiO2 nanoparticles. The photoluminescence (PL) emission intensity of Fe doped TiO2 nanoparticles decreases with an increase in Fe doping concentration. The photocatalytic efficiencies of the Fe-doped TiO2 nanoparticles have shown a strong photocatalytic activity (PCA) response. At constant irradiation time, the Fe-doped titania nanoparticles display more catalytic activity compared to undoped TiO2. The photodegradation efficiencies typically decline with an increase in the concentration of Fe+3 doping for the decolorization of methylene blue (MB) under visible light irradiation.

Photocatalytic properties of TiO2 and Fe-doped TiO2 prepared by metal organic framework-mediated synthesis

The Ti-containing metal organic framework (MOF) MIL-125 has been used as sacrificial precursor to obtain TiO2 materials through the MOF-mediated synthesis route. In this study, Fe3+ was deposited on the surface of MIL-125 after its hydrothermal synthesis. Targeted Fe-doped titania photocatalysts were prepared through the direct calcination in air of Fe/MIL-125 crystals and/or by using a two-step method, including carbonization in inert atmosphere followed by calcination in air. The relationship between the synthesis conditions and the properties of the Fe-doped titania nanopowders, such as Fe content, porosity, phase composition and particle size was investigated. From elemental mapping, X-ray photoelectron spectroscopy, X-ray absorption spectroscopy, UV–Vis absorption spectroscopy and photoluminescence emission spectra, the presence of highly dispersed Fe3+ ions incorporated into the TiO2 crystal lattice was confirmed, which led to a significant red shift of photoresponse towards visible light and reduced the recombination rate of electron-hole pairs at low iron content. By varying the pre-carbonization temperature, both crystal size and phase composition in the final materials were modulated. The performance of Fe-doped titania materials in photocatalytic water-splitting was tested for hydrogen evolution. Optimal photocatalytic performance was found at 0.15 and 0.5 wt% iron concentration and exceeded those of non-doped titania and commercial anatase both under visible and UV light irradiation, respectively, and among the highest reported in literature for these systems.

Acid acting as redispersing agent to form stable colloids from photoactive crystalline aqueous sol–gel TiO2 powder

In this work, the redispersion of three nanocrystalline TiO2 colloids is studied: one pure and two Fe-doped titania. These three colloids are produced by an easy aqueous sol–gel synthesis using precipitation-acidic peptization of Ti precursor. For the two Fe-doped TiO2, one is doped during synthesis (primary doping) and the other is doped after the synthesis (secondary doping). The initial colloids are composed of crystalline TiO2 particles around 7 nm with good photocatalytic properties, tested on PNP degradation under visible light (wavelength >390 nm). The powders obtained by air drying of these three colloids are redispersed in water to produce colloids, which are compared to the initial colloid produced. For each colloid, five cycles of drying redispersion are achieved. The colloids are characterized by dynamic light scattering, zeta potential measurements, inductively coupled plasma–atomic emission spectroscopy, X-ray diffraction, nitrogen adsorption–desorption measurements, Mossbauer spectroscopy, diffuse reflectance spectroscopy, and photocatalytic tests. The results show that similar products are obtained between the cycles, maintaining homologous properties of colloids. This property of redispersion is mainly due to the acid (HNO3, HCl, or H2SO4) which protonates the surface of the TiO2 nanoparticle leading to high-surface charges and electrostatic repulsions between aggregates. This property can be very useful for industrial applications of this synthesis, especially as it allows the volume and weight to be reduced for transportation and storage. Moreover, results show that the pure TiO2 powder can be doped during its redispersion step. The redispersion of the TiO2 developed here is possible without surface functionalization or multiple step processes, contrary to commercial Degussa P25. A 2-year stability study of all the produced colloids has been performed by following the evolution of the macroscopic aspect and the physicochemical properties of these sols. This study showed high stability of the produced colloids.

Effects of Pre-annealing Atmosphere on Microstructure and Photocatalytic Activities of Fe-doped Titania Nanotubes

The nanotubes with an anatase structure were hydrothermally synthesized using the Fe-doped anatase nanopowder precursors that were annealed in air and reductive atmospheres. The microstructure and physicochemical properties of the nanotubes were comparably investigated. Results show that the reductive pre-annealing yields more surface-chemisorbed oxygen by introducing lower valance Fe 2+ and Ti 3+ ions. The specific surface area, methylene blue adsorption and photoabsorption threshold of the nanotubes are greatly enhanced by the reductive annealing when comparing with annealing in air. 1 mol% Fe doping and reductive annealing yield the highest adsorption, photocatalytic efficiency and durability for degradation of MB solution; extreme Fe doping decreases the photocatalytic efficiency. The Fe content of the nanotubes is decreased by the hydrothermal synthesis, especially in the case of annealing in air. Moreover, the action mechanism of the Fe doping and reductive annealing was discussed.

Effect of the structure of Fe-doped titania-based nanocomposites on the photocatalytic activity of polyester fabrics modified by them

We have studied the photochemical activity of polyester fabrics modified with nanocomposites based on Fe-doped titania and evaluated the stability of the photocatalytic effect to external influences during service.

Effects of sintering atmospheres on phase transformation, oxygen vacancy and photoabsorption behaviors of highly Fe-doped titania crystals

Fe-doped TiO2 crystals were successfully prepared using a sol–gel technique in reducing and oxidizing atmospheres. The effects of sintering atmosphere on phase transformation, oxygen vacancy concentration and photoabsorption behaviors were investigated. The results indicate that upon sintering in reducing atmosphere, Ti and Fe ion valences were decreased and highly Fe ions (12 mol%) were entirely dissolved into titania crystals, increasing oxygen vacancy concentration and leading to increased photoabsorption capability. In contrast, sintering in oxidizing atmosphere causes precipitation of the Fe2O3 phase, which is detrimental to the photoabsorption capability. The best photoabsorption performance is obtained by sintering 12 mol% Fe-doped TiO2 in reducing atmosphere, resulting in an absorption edge of approximately 435 nm, which is much higher than that of undoped TiO2 in the oxidizing atmospheres with the absorption edge 352 nm.

Molecular adsorption of hydrogen peroxide on N- and Fe-doped titania nanoclusters

Titanium dioxide (titania) nanoparticles have been extensively investigated for photocatalytic applications such as the decomposition and adsorption of pollutant and undesirable compound in air and waste water. In this context, the present article reports the molecular adsorption of hydrogen peroxide on the surface of doped titania clusters. Density functional theory calculations were performed to investigate the structures and electronic properties of two nanoscale (TiO2)n clusters (n=5,6) modified by nitrogen and iron dopants. The relative stability of all possible N-doped and Fe-doped isomers has been compared with each other and with the parent cluster. It was found that the Fe-doped clusters are in general more stable than the N-doped counterparts. Moreover, after N/Fe doping an enhanced in the magnetization of the clusters is observed. In the second part, we have investigated different modes of H2O2 adsorption on the lowest-energy isomers of doped clusters. In almost all the cases, the adsorptions on the doped clusters are found to be less exothermic than on the corresponding undoped parent cluster. Our results highlight the essential role of charge transfer into the interaction between H2O2 and doped (TiO2)n clusters, especially for Fe-doped clusters.

Structural, optical and photodegradation properties of pure and Fe-doped titania nanoparticles probed using simulated Solar light

We report the successful, low temperature synthesis of pure and Fe-doped titania nanoparticle (NP) powders, using organic Ti- and Fe-precursors. The properties of the synthesized titania based materials were obtained using XRD, UV/vis and EPR spectroscopy and BET measurements. The doping of TiO2 induced a shift in the absorption threshold towards the visible spectral range, compared to pure titania. The process of annealing induced an increase in crystallinity and particle sizes in the obtained materials. The photocatalytic activity, using simulated Solar light (Vitalux lamp), of our samples was checked by following the photodegradation reaction of Rhodamine B and trichlorophenole as model compounds.

Direct microwave–hydrothermal synthesis of Fe-doped titania with extended visible-light response and enhanced H2-production performance

Fe-doped TiO2 photocatalysts were synthesized rapidly and directly by the microwave–hydrothermal method and evaluated for hydrogen production by water splitting under UV–vis irradiation. The photocatalysts were characterized by X-ray diffraction, transmission electron microscopy, N2 adsorption–desorption isotherms, inductively coupled plasma atomic emission spectroscopy, UV–vis spectroscopy, X-ray photoelectron spectra and photoelectrochemical experiments. The results showed that Fe-doped TiO2 photocatalysts synthesized by the microwave–hydrothermal method exhibited a smaller crystallite size and higher specific surface area than TiO2 photocatalysts. The microwave–hydrothermal method was a feasible way to increase the Fe doping concentration with enhanced electron–hole separation and electron transfer efficiency. It was also observed by first-principles density functional theory calculations that Fe can induce the formation of impurity levels near the valence band, leading to the reduction of the band gap and the improvement of photocatalytic activity. The highest photoactivity was achieved for TiO2 doped with 0.5% Fe with a hydrogen production rate of 10.95μmolh−1.

Mercury Removal from Flue Gas with Fe-Doped Titania Photocatalyst

The titanium-based nanocatalysts were prepared and used to photocatalytically oxidize Hg0 to remove it in the simulated flue gas in this paper .The modified commercial degussa P25 and Fe3+ doped TiO2 photocatalyst prepared with sol-gel method were applied to conduct the experimenent on self-built experimental platform to test their photocatalytically oxidation performance on mercury in the simulated flue gas.By designing different ratios of Fe2O3/TiO2, comparison experiments under UV(ultra violet) irradiation, it was compared with the result of the experiment and reference documents to verify the rationality of the experimental results and the accuracy. The best catalyst modification conditions were determined and analyzed the Fe-doped TiO2 photocatalytic mechanism to guarantee high or higher mercury removal from flue gas.

Preparation of Fe-doped TiO2 nanotube arrays and their room-temperature ferromagnetic properties.

Fe-doped titania nanotube arrays (NTs) were fabricated by electrochemical anodization on a Ti foil using Fe(NO3)3 · 2H2O as iron source. Their morphology, structure and optical properties were investigated by field emission scanning electron microscopy, X-ray diffraction, UV-visible absorption spectroscopy and photoluminescence spectroscopy. The UV-visible reflection spectrum of the Fe-doped TiO2 NTs showed a red shift in wavelength of absorption and greater reflectivity compared with the undoped sample due to the Fe ion incorportion in TiO2 lattices. The photoluminescence spectrum of the Fe-doped TiO2 NTs shows two strong new peaks centered at 388 nm and 694 nm, besides the UV emission peak owing to the electronic transition mediated by the defect levels such as oxygen vacancies in the band gap. The magnetic property of the Fe-doped TiO2 NTs exhibits a room temperature ferromagnetic characteristic with a saturation magnetization (Ms) of 0.146 x 10(-2) emu/cm3 and a coercive field of 60 Oe. And the cause of the magnetic properties has been discussed in detail.

Improving photovoltaic performance of titanium oxide thin films by integration of iron doping and dye sensitization

Iron-titania thin films derived by sol–gel coating were investigated as anode elements in dye-sensitized solar cells. The Fe-doped titania films were shown more hydrophilic and exhibited a higher dye uptake than the undoped (titania) film. The Fe addition induced chemical shifts of Ti and O atoms as revealed by X-ray photoelectron spectroscopy and caused a positive shift in the flat-band potential of titanium oxide (at low Fe/Ti ratios). The Fe-doped titania electrodes at low Fe concentrations produced higher photocurrents than the undoped (titania) electrode under ultraviolet illumination. Electrochemical impedance and pulsed photocurrent analyses suggest that Fe dopants serve as shallow trap states for charge transition to increase charge collection efficiency. The dye addition improved photocurrent and voltage for the oxide electrodes, because the Fe doping modifies surface and electronic structures to enhance dye adsorption and tune conduction band position for accelerating injection of excited electrons. Mechanistic aspects about the Fe-mediated electron transport and transfer from dye sensitization to promote photovoltaic efficiency are discussed.

Phase transformation of titania gels highly doped with Fe in different sintering atmospheres

The effect of sintering atmosphere on the phase transformation of high contents of Fe-doped titania gels was studied. Experimental results show that the sintering atmosphere has less influence in the transformation temperature of the gel to anatase. Sintering in an oxidizing atmosphere causes precipitation of the Fe2O3 phase while sintering in a reducing atmosphere promotes the transformation of the gel to anatase, causes the Fe ions to dissolve entirely into the titania crystals, and enhances the transformation temperature of anatase to rutile. Fe-doping inhibits the transformation of the gel to anatase while promoting the transformation of anatase to rutile and decreasing the mean crystal size of the titania crystals during sintering in oxidizing or reducing atmospheres. Moreover, the action mechanism of the sintering atmosphere and Fe-doping are discussed in terms of oxygen vacancies, ionic valence and substitutions.

Evaluating the potential of a new titania precursor for the synthesis of mesoporous Fe-doped titania with enhanced photocatalytic activity

Mesoporous Fe (III) doped TiO2 nanoparticles with an anatase phase were prepared by using a stable precursor potassium hexafluorotitanate as Ti source for the first time and its physical as well as photocatalytic properties were compared with that of Fe doped titania prepared from the most common Ti source titanium isopropoxide. FeSO4·7H2O and Fe (NO)3·9H2O were used for doping titania with Fe (III). Physicochemical properties of the samples were characterized by XRD, XPS, FTIR, Raman spectroscopy, N2 adsorption–desorption isotherms, UV–vis diffuse reflectance spectroscopy. EDX confirms the presence of Fe. DRS and TEM reveals that doping has taken place. It was found that Fe-doped nanostructured titania prepared from potassium hexafluorotitanate was much more effective in the photocatalytic decomposition of bromocresol green than undoped nanostructured titania as well as commercial titania.