Fe-doped ZrO2 Research Articles

The efficacy of Fe-doped ZrO2 nanoparticles as a supplement in polysulfone membranes for toxic dye removal

ZrO2 nanoparticles fine-tuned with iron doping (5%Fe-ZrO2) were incorporated by the phase inversion method as a supplement in polysulfone (PSf) membrane medium for dye rejection. The prepared nanocomposite membranes were examined using a variety of characterisation techniques. The findings showed that adding 5%Fe-ZrO2 nanoparticles into the membrane matrix improved its permeability by reducing the contact angle and increasing hydrophilicity. The PSf nanocomposite membrane containing 1 wt% of 5%Fe-ZrO2 (M2) was found to exhibit a dye rejection efficiency of 99% for Eriochrome black-T (EBT) and 98% for Methylene blue (MB), with a flux of 10.2 ±1 LMH. The manufactured membranes can reject dyes and offer commendable productivity and selectivity, making them a popular choice for membrane applications.

Anodic oxidation of Zr-5Fe alloy in ethylene glycol/fluoride electrolyte for Cr(VI) removal under sunlight

In this work, Fe-doped ZrO2 nanotubes (Fe-ZNTs) were synthesized by anodization of Zr-5 wt% Fe alloy in fluoride-containing ethylene glycol (EG)/8 vol% H2O electrolyte at varying ammonium fluoride (NH4F) concentrations (0.1, 0.3 and 0.5 wt%) at 40 V for 3 h. The morphology and crystal structure of as-anodized Fe-ZNTs were analyzed by Field-emission scanning electron microscopy (FESEM) and X-ray diffraction (XRD), respectively. The as-anodized Fe-ZNTs were annealed at 500 °C for 3 h in a tube furnace for crystallization of the oxide film. The crystal structure, surface functional groups, and surface chemistry of annealed Fe-ZNTs were analyzed by XRD, Fourier transform infrared (FTIR), and X-ray photoelectron spectroscopy (XPS), respectively. From the FESEM results, large inner diameter (79 nm) with short nanotubes (1.9 µm) were grown in 0.5 wt% NH4F due to enhanced chemical dissolution of Fe-ZNTs in high fluoride content. XRD result of as-anodized Fe-ZNTs indicate the enhanced intensity of tetragonal-ZrO2 peaks with increasing fluoride content from 0.1 to 0.3 wt% NH4F. The cubic-ZrO2 started to emerge at 0.5 wt% NH4F. For annealed Fe-ZNTs, pure monoclinic-ZrO2 was observed in 0.1 wt% NH4F, while tetragonal-ZrO2 + monoclinic-ZrO2, and cubic-ZrO2 + monoclinic-ZrO2 were co-existed in 0.3 wt% NH4F and 0.5 wt% NH4F, respectively. Cr(VI) photoreduction under sunlight indicates 93 % Cr(VI) removal efficiency over annealed Fe-ZNTs synthesized in 0.3 wt% NH4F which ascribed to high Cr(VI) adsorption and high photocatalytic activity of tetragonal-ZrO2.

Formation of Fe-doped ZrO2 nanotube arrays in glycerol/formamide at varying fluoride content for Cr(VI) photoreduction

Fe-doped ZrO2 nanotubes (Fe-ZNTs) were produced by anodizing a Zr-5 wt% Fe (Zr-5Fe) alloy in a mixture of fluoride-containing glycerol/formamide (FA) (1:1 ratio)/1 vol% H2O at 50 V for 3 h in different concentrations of ammonium fluoride (NH4F) (0.3, 0.5, and 1.0 wt%). These materials were synthesized to serve as photocatalysts for the removal of hexavalent chromium, Cr(VI) ions by photoreduction. To crystallize the oxide film, the as-anodized Fe-ZNTs were subjected to annealing at 500 ℃ for 3 h in a tube furnace. The morphology and crystal structure of the annealed Fe-ZNTs were analyzed using Field-emission scanning electron microscopy (FESEM) and X-ray diffraction (XRD), respectively. The surface functional groups and surface chemical of the samples were analyzed by Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS), respectively. The formation of hollow structure of the Fe-ZNT was validated by High-resolution transmission electron microscopy (HRTEM). The dimensions of the Fe-ZNTs were measured using Image J. UV–Visible spectroscopy was used to determine the Cr(VI) concentration remaining in the sample after photoreduction. From the FESEM micrographs, the diameter of the Fe-ZNTs was enlarged with higher fluoride content, while the length abruptly decreased due to excessive etching of the oxide film at oxide|electrolyte interface. The XRD results indicate the high intensity of tetragonal-ZrO2 in high fluoride content after annealing. From the photocatalytic results of 30 ppm Cr(VI) under sunlight, the Fe-ZNTs synthesized in 1.0 wt% NH4F exhibited the highest Cr(VI) removal efficiency with 100 % after 5 h due to enhanced Cr(VI) adsorption and high photoactivity of tetragonal-ZrO2.

Role of active oxygen species in Fe-doped ZrO2 catalyst during CO2 assisted ethane dehydrogenation reaction

CO2 assisted ethane dehydrogenation provides a promising route for the utilization of shale gas and greenhouse gas. This study investigates the role and evolution of active oxygen species over Fe-doped ZrO2 catalysts in distinct dehydrogenation reactions via Mars-van Krevelen mechanism. Fe doping led to an increase in active oxygen species (from 12.9% to 23.4%) benefitted from the phase transformation of ZrO2. This enhancement significantly boosted ethane dehydrogenation activity from 5.0 to 16.1 mmolEthene/gCat/h. In the absence of CO2, the ethane conversions rapidly decreased with a deactivation rate constant (kd) of 0.930 h−1 due to the irreversible oxygen species loss and coke deposition. Although the catalytic stability of the optimal catalyst was greatly improved (kd = 0.006 h−1) after CO2 introduction, a decrease in ethane conversion occurred when CO2 could not supplement oxygen species due to the formation of coke layers. A simple O2 oxidation can effectively restore stable activity during 5 reaction-regeneration cycles for 3600 mins.

Synthesis of transition metal ions doped-ZrO2 nanoparticles supported g-C3N4 hybrids for solar light-induced photocatalytic removal of methyl orange and tetracycline pollutants

Photodegradation is an eco-friendly degradation process routinely employed for the removal of various pollutants produced by pharmaceutical and textile industries. In this work, g-C3N4 sheets (g-CN) supported with Fe-doped ZrO2 nanoparticles have been prepared via a facile hydrothermal method as photocatalysts for the effective photodegradation of methyl orange (MO) and tetracycline (TC). The as-prepared photocatalysts were characterized by using a wide range of techniques to understand the origin of their superior photodegradation performance. Structurally, Fe-doped ZrO2 nanoparticles were found to be uniformly superficially distributed on g-C3N4. The addition of Fe-doped ZrO2 nanoparticles was also found to improve the surface area and light absorption capacity of pure g-CN. It was further revealed that the development of heterojunctions between g-C3N4 and Fe-doped ZrO2 nanoparticles effectively reduced the recombination rate of electron and hole pairs within the photocatalyst system, resulting in improved photocatalytic activity. Previous studies have pointed at the superoxide radical anions (˙O2−) and (OH·) as being primarily responsible for the degradation of MO and TC species, leading us to hypothesize that the g-FZ composite works via a possible free-radical based catalytic mechanism to support the photodegradation process.

Fe-doped zirconia nanoparticles with highly negative conduction band potential for enhancing visible light photocatalytic performance

Maintaining a highly negative value of conduction band (CB) potential of photocatalysts through metal doping has been a great challenge. Herein, we investigated the effects of Fe-doping on the crystal structures and electronic structures of zirconia (ZrO2) in detail by combining experiments and Density Functional Theory (DFT). It was revealed that the Fe-doping obviously triggered the formation of tetragonal phase ZrO2 and induced a defect states in the bandgap of Fe-doped ZrO2. Due to the coherent effect between the electrons of the Fe 3d orbitals and ZrO2 intrinsic electronic states, the defect states expanded the light absorption edge of ZrO2 and Fe-doped ZrO2 showed a small bandgap with maintaining a highly negative value of the CB potential. Meanwhile, Fe-doping significantly enhanced photoelectrochemical properties, the efficiency separation of electron-hole pairs and photocatalytic activity in comparison with the pristine ZrO2. We also found that 0.5%Fe-ZrO2 exhibited the optimum photocatalytic performance, and reached 96% for degradation of Rhodamine B (RhB) within 150 min under visible light irradiation. This work elucidated the mechanism of the photocatalytic degradation of RhB over Fe-doped ZrO2 and provided a promising approach in designing highly negative CB potential of ZrO2 via Fe doping toward sustainable environmental remediation.

Structural and photochemical properties of Fe-doped ZrO2 and their application as photocatalysts with TiO2 for chromate reduction

In this work, we are interested by the photocatalytic activity under sunlight irradiation of Fe-doped ZrO2 prepared by co-precipitation. The structural and photophysical properties of the catalysts have been characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), BET method and UV–Vis diffuse reflectance. The results show that Fe-doped ZrO2 exhibits higher photocatalytic activity than that of both ZrO2 and commercial TiO2 P25. The best photocatalytic activity is obtained with the 50 mol% Fe-content calcined at 600 °C/ 3 h. A total photoreduction of Cr(VI) is achieved within 90 min under solar light with the new hetero-junction Fe-ZrO2/TiO2. The kinetic of Cr(VI) photoreduction is well described by the Langmuir-Hinshelwood (LH) model which obeys to pseudo-first-order kinetics with a rate constant of 0.031 min−1. On the basis of the energy band positions of the hetero-junction Fe-ZrO2/TiO2, the detailed reaction mechanism of reduction of inorganic pollutant has been discussed.

Comparative study on the catalytic activity of Fe-doped ZrO2 nanoparticles without significant toxicity through chemical treatment under various pH conditions

Despite advances in the construction of catalysts based on metal oxide nanoparticles (MO NPs) for various industrial, biomedical, and daily-life applications, the biosafety concerns about these NPs still remain. Recently, the need to analyze and improve the safety of MO NPs along with attempts to enhance their catalytic performance has been strongly perceived. Here, we prepared multiple variants of Fe-doped zirconium oxide (Fe@ZrO2) NPs under different pH conditions; then, we assessed their toxicity and finally screened the variant that exhibited the best catalytic performance. To assess the NP toxicity, the prepared NPs were introduced into three types of human cells originally obtained from different body parts likely to be most affected by NPs (skin, lung, and kidney). Experimental results from conventional cellular toxicity assays including recently available live-cell imaging indicated that none of the variants exerted severe negative effects on the viability of the human cells and most NPs were intracellular localized outside of nucleus, by which severe genotoxicity is unexpected. In contrast, Fe@ZrO2 NPs synthesized under a basic condition (pH = 13.0), exhibited the highest catalytic activities for three different reactions; each was biochemical (L-cysteine oxidation) or photochemical one (4-chlorophenol degradation and OH radical formation with benzoic acid). This study demonstrates that catalytic Fe@ZrO2 NPs with enhanced activities and modest or insignificant toxicity can be effectively developed and further suggests a potential for the use of these particles in conventional chemical reactions as well as in recently emerging biomedical and daily-life nanotechnology applications.

Formation of polar phase in Fe-doped ZrO2 epitaxial thin films

The existence of a polar phase in epitaxially grown Fe-doped ZrO2 thin films has been demonstrated. The films were prepared on yttria-stabilized zirconia substrates by ion-beam sputtering and subsequent annealing, where the composition was controlled by changing the FeO1.5-ZrO2 ratio of the sputtering target. The chemical states of elements in the 30 nm-thick xFeO1.5-(1−x)ZrO2 thin films (x = 0, 0.06, 0.10, and 0.14 nominal composition) have been measured by X-ray photoelectron spectroscopy, and the crystal structure has been examined by using X-ray diffraction and scanning transmission electron microscopy. These observations revealed that the undoped ZrO2 thin film (x = 0) is dominated by the monoclinic phase (space group: P21/c), while the films containing Fe exhibit multi-domain structures consisting of monoclinic and orthorhombic (Pbc21) phases, the latter being a polar phase, showing that the orthorhombic phase is stabilized by the addition of Fe. Concurrently, the polarization-electric field loops of the Fe-doped films exhibited hysteresis for the film with x = 0.06.

La-, Mn- and Fe-Doped Zirconia Washcoats Deposited on Monolithic Reactors via Sol-Gel Method: Characterization and Evaluation of their Mass Transfer Phenomena and Kinetics in Trichloroethylene Combustion

Abstract La-, Mn- and Fe-doped ZrO2 was synthesized using the sol-gel method, washcoated on cordierite monoliths and used in trichloroethylene (TCE) combustion. A sol from sol-gel synthesis method was used to obtain the zirconia washcoatings. The washcoatings deposited on the cordierite monolith materials were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy and N2 physisorption measurements, being the crystalline phase determination the most correlate with the catalytic activity. The washcoat properties were correlated to their performance in trichloroethylene combustion. The catalytic washcoatings contained a mixture of crystalline tetragonal ZrO2 and monoclinic ZrO2, and the monoclinic phase exhibited strong interactions with the α-cordierite crystalline phase. For the kinetic tests, the mass transfer into the washcoated monolith channels was evaluated using a recently developed model for the internal mass transfer coefficients for diffusion and reactions in catalytic monoliths. This model involves three resistances. In a plot of the overall resistance as function of the Thiele modulus was determinate that he reaction occurred in the kinetically controlled regime. The kinetic data were fit to two Langmuir–Hinshelwood (LH) models, and the reaction rate was fitted as a function of the trichloroethylene inlet concentration. The adsorption parameters obtained with both LH models were validated based on thermodynamic criteria for the changes in the standard enthalpy of adsorption(${\Delta}H_{ads}^0$) and standard total entropy of adsorption (${\Delta}S_{ads}^0$). It was found that adsorbed TCE and oxygen atoms should be more mobile over the catalyst, which had a higher proportion of tetragonal phase than monoclinic phase of zirconia. The La, Fe-doped catalyst exhibited the highest activity, mainly due the presence of tetragonal zirconia.

Advanced Properties in Fe-Doped Zirconia Nanoparticles

Discrete, well-shaped monoclinic Fe-doped ZrO2 nanoparticles were prepared in the range of nominal compositions Zr1−xFexO2−x/2, being 0 ≤ x ≤ 0.1 by a hydrothermal approach and their optical and chemical properties evaluated for potential application as photocatalysts. Monoclinic Fe-containing ZrO2 nanoparticles sized around 20 nm were obtained straightaway from the reagent mixture through the hydrothermal aging at 140 °C for 3 days. The thermal stability of those mono-clinic Fe–ZrO2 solid solutions was followed by X-ray diffraction, infrared and Raman spectroscopies, and scanning and transmission electron microscopy. Further annealing at 800 °C brought monosized, monoclinic single-phase Fe-containing ZrO2 nanocrystals without significant microstructural changes. On comparing with other not conventional synthetic approaches to zirconia based solid solutions, it is to remark that the present hydrothermal approach lead to monoclinic form of zirconia solid solution. Some preliminary results on potential advanced applications of the prepared monoclinic Fe–ZrO2 solid solutions as photocatalysts will be discussed.

Vapor phase methylation of phenol on Fe-substituted ZrO2 catalyst

Fe-doped ZrO2 compounds were prepared by a co-precipitation method. The compounds were characterized by X-ray diffraction, N2 adsorption-desorption, ultraviolet diffuse reflectance infrared Fourier transform spectroscopy, scanning electron microscopy–energy-dispersive X-ray spectroscopy, transmission electron microscopy, NH3 temperature-programmed desorption, X-ray photoelectron spectroscopy, and in situ Fourier transform infrared spectroscopy. The incorporation of Fe into ZrO2 lattice favored and effectively stabilized the formation of purely ZrO2 tetragonal phase. Subsequently, the catalytic activity of the Fe-doped ZrO2 compounds was evaluated toward vapor phase methylation of phenol. The catalytic activity was governed by Fe content and related to the Lewis acidity of the prepared catalyst.

Understanding ferromagnetism and optical absorption in 3d transition metal-doped cubic ZrO2 with the modified Becke-Johnson exchange-correlation functional

The electronic structure, magnetic, and optical properties in cubic crystalline phase of Zr1−xTMxO2 (TM = V, Mn, Fe, and Co) at x = 6.25% are studied using density functional theory with the Generalized Gradient Approximation and the modified Becke-Johnson of the exchange-correlation energy and potential. In our calculations, the zirconia is a p-type semiconductor and has a large band gap. We evaluated the possibility of long-range magnetic order for transition metal ions substituting Zr. Our results show that ferromagnetism is the ground state in V, Mn, and Fe-doped ZrO2 and have a high value of energy in Mn-doped ZrO2. However, in Co-doped ZrO2, antiferromagnetic ordering is more stable than the ferromagnetic one. The exchange interaction mechanism has been discussed to explain the responsible of this stability. Moreover, it has been found that the V, Mn, and Fe transition metals provide half-metallic properties considered to be the leading cause, responsible for ferromagnetism. Furthermore, the optical absorption spectra in the TM -doped cubic ZrO2 are investigated.

The origin of magnetism in transition metal-doped ZrO2 thin films: experiment and theory

We have investigated the magnetic properties of Fe/Co/Ni-doped ZrO2 laser ablated thin films in comparison with the known results of Mn-doped ZrO2, which is thought to be a promising material for spintronics applications. It is found that doping with a transition metal can induce room temperature ferromagnetism in ‘fake’ diamond. Theoretical analysis based on density functional theory confirms the experimental measurements, by revealing that the magnetic moments of Mn- and Ni-doped ZrO2 thin films are much larger than that of Fe- or Co-doped ZrO2 thin films. Most importantly, our calculations confirm that Mn- and Ni-doped ZrO2 show a ferromagnetic ground state in comparison to Co- and Fe-doped ZrO2, which favor an antiferromagnetic ground state.

Preparation of Fe-doped ZrO2 nanotube arrays by anodization of Zr–Fe alloy and their magnetic properties

Zr–Fe (Fe: 16.95wt%) alloy was prepared through the vacuum melting method. Fe-doped ZrO2 nanotube arrays have been achieved directly by anodizing the Zr–Fe alloy. Morphologies and structures of the samples were characterized by a scanning electron microscope, a transmission electron microscope and X-ray diffraction. The effects of electrolyte and temperature on the morphologies were studied. Magnetic properties of the samples were studied as well. Results show that the as-prepared sample was amorphous. Pure monoclinic phase was obtained when annealed at 400°C, monoclinic and tetragonal phase coexisted at 500°C and 600°C. Higher value of coercivity (627Oe) was achieved when annealed at 500°C.

Synthesis, characterization and electrochemical properties of iron-zirconia solid solution nanoparticles prepared using a sol–gel technique

The range of compositions and temperatures at which single-phase tetragonal and monoclinic Fe-containing zirconia nanoparticles are stable is reported. Both types of iron-doped zirconia particles were synthesized by annealing dried gels FexZr1-xO2, with nominal compositions in the range 0 ≤ x ≤ 0.15, over the range of temperatures between 400 °C and 1300 °C. Monophasic crystalline specimens of Fe-ZrO2 solid solutions were characterized by different techniques including X-ray powder diffraction (XRD), infrared and Raman spectroscopies (IR and Raman), and transmission electron microscopy (TEM). Energy gaps were estimated from diffuse reflectance ultraviolet-visible spectra (DRUV-Vis) and compared with those obtained from electrochemical data. Upon increasing the amount of iron in both types of iron-containing zirconia-based structures the energy gaps slightly lowered. The electrochemical properties of those solid solutions obtained using the voltammetry of microparticles (VPM) technique indicated the presence of a small portion of iron as Fe(2+) in both types of crystalline Fe-doped ZrO2. Electrochemical data suggest that the monoclinic solid solutions provide a particularly high accessibility for promoting catalytic processes such as electrochemical oxygen reduction.

Stabilization of tetragonal/cubic phase in Fe doped zirconia grown by atomic layer deposition

In this work we investigated the effect of Fe doping on structural properties of ZrO2 grown by atomic layer deposition (ALD) using Zr(TMHD)4 for Zr and Fe(TMHD)3 for Fe precursors (TMHD=2,2,6,6-tetramethyl-3,5-heptanedionate) and ozone as oxygen source. The temperature during the growth process was fixed at 350°C. The ALD process was tuned to obtain Fe-doped ZrO2 films with uniform chemical composition, as seen by the time of flight secondary ion mass spectrometry. The control of Fe content was effectively reached, by controlling the ALD precursor pulse ratio, as checked by X-ray photoemission spectroscopy (XPS) and spectroscopic ellipsometry. From XPS, Fe was found in Fe3+ chemical state, which maximizes the magnetization per atom. We also found, by grazing incidence X-ray diffraction, that the inclusion of Fe impurities in ZrO2 induces amorphization in thin ZrO2 films, while it stabilizes the high temperature crystalline tetragonal/cubic phase after rapid thermal annealing at 600°C.

Mössbauer spectroscopic study of iron-doped zirconia synthesized by microwave route

Zirconium oxide (zirconia) exists in three crystalline forms of monoclinic, tetragonal and cubic structures at atmospheric pressures. The cubic form of zirconia is well known for its mechanical, electrochemical and optical applications. Fe-doped cubic zirconia (high temperature phase) compositions are synthesized by microwave combustion method. Here, we present a Mossbauer investigation of Zr1 − x Fe x O2 composition within a range of Fe (0.03 < x < 0.09). 57Fe Mossbauer spectra were recorded at room temperature and at low temperature (77 K) for all samples. 3% Fe-doped ZrO2 shows doublet and the corresponding 6% and 9% Fe-doped ZrO2 samples show superimposed sextet and doublets. The isomer shift and quadrupole moment indicate, Iron to be in III oxidation state and to occupy different octahedral sites, associated with some amount of disorder. X-ray powder diffraction pattern of Fe-doped ZrO2 samples appear as very well crystalline. The Miller indices refer to the cubic fluorite-type ZrO2 structure. The magnetic behavior shows increase in moment and decrease in coercivity, with increase in Fe concentration. The M vs. H plots of the as-prepared Zr1-x Fe x O2 essentially show typical hysteresis loops, indicating room temperature ferromagnetism. Thus, the introduced microwave combustion route is an effective process to achieve multifunctional Fe-doped Zirconia with coexistent magnetic properties.

Absence of ferromagnetism in Mn- and Fe-stabilized zirconia nanoparticles

In order to experimentally check the recent theoretical prediction regarding the Mn- or Fe-doped cubic ZrO2 as potential spintronic materials and to search for high-temperature ferromagnetic spintronic material, a series of Zr1−xMnxO2 (x=0.15–0.35) and Zr1−xFexO2 (x=0.15–0.40) nanoparticles were prepared by a coprecipitation method. The crystal structure and magnetic properties of the compounds were investigated by means of X-ray diffraction, transmission electron microscopy (TEM) and magnetic measurements. Detailed structural analysis confirmed that single phase of Mn- and Fe-stabilized cubic zirconia was obtained. The solubility limit of Mn (or Fe) in ZrO2 is about x=0.27 (or 0.36). Magnetic measurements showed that all the samples were paramagnetic at room temperature and 5 K. Existence of antiferromagnetic interactions in the samples was inferred from the fitting of magnetization data to the Curie–Weiss law. The absence of ferromagnetism could plausibly be attributed to an excess of oxygen vacancies in the Mn- or Fe-stabilized cubic zirconia.

Fe-Doped Zirconium Oxide Produced by Self-Sustained High-Temperature Synthesis: Evidence for an Fe−Zr Direct Bond

The local structure of iron in Fe-doped cubic ZrO2 produced by combustion synthesis was studied by Mössbauer spectroscopy and Fe-K edge extended x-ray absorption fine structure (EXAFS) and X-ray absorption near edge structure (XANES). Iron was found to be in its II oxidation state and to occupy two different sites of the fluorite ZrO2 structure, both associated with some amount of disorder. One of the sites has been identified with the regular Zr position in 0,0,0, thus giving rise to substitutional (i.e., Fe atoms occupying the regular Zr position, with a net 2−charge, with respect to the lattice) defects, while the other site has been identified with the normally empty position at 1/2, 1/2, 1/2, thus giving rise to interstitial (i.e., Fe atoms occupying an interstitial position, with a net 2+ charge, with respect to the lattice) defects. For this last site, there is a short Fe−Zr distance (2.64 Å). This result, coupled to the quite small value of the Debye−Waller factor for this distance, gives evidence of a direct Zr−Fe metal-to-metal bond.