Polythiophene-coated Fe3O4 superparamagnetic nanocomposite: Synthesis and application as a new sorbent for solid-phase extraction

In the present work, a novel type of superparamagnetic nanosorbent, polythiophene-coated Fe₃O₄ nanoparticles (Fe₃O₄@PTh NPs), have been successfully synthesized. The synthesized NPs were characterized by scanning electron microscopy (SEM), Fourier transform-infrared (FT-IR) spectroscopy, and thermal gravimetric analysis (TGA). The synthesized Fe₃O₄@PTh NPs were applied as an efficient sorbent for extraction and preconcentration of several typical plasticizer compounds (di-n-butyl phthalate (DBP), di-(2-ethylhexyl) phthalate (DEHP), and dioctyl adipate (DOA)) from environmental water samples. Separation of Fe₃O₄@PTh NPs from the aqueous solution was simply achieved by applying external magnetic field. Separation and determination of the extracted plasticizers was performed by gas chromatography–flame ionization detection (GC–FID). Several variables affecting the extraction efficiency of the analytes i.e., amount of NPs sorbent, salt concentration, extraction time, and desorption conditions were investigated and optimized. The best working conditions were as follows: amount of sorbent, 100 mg; NaCl concentration, 30% (w/v); sample volume, 45 mL; extraction time, 10 min; and 100 μL of ethyl acetate for desorption of the analytes within 2 min. Under optimized conditions, preconcentration factors for DBP, DEHP, and DOA were obtained as 86, 194, and 213, respectively. The calibration curves were linear (R² > 0.998) in the concentration range of 0.4–100 μg L⁻¹ for both DEHP and DOA and 0.7–100 μg L⁻¹ for DBP. The limits of detection (LODs) were obtained in the range of 0.2–0.4 μg L⁻¹. The intra-day relative standard deviations (RSDs%) based on four replicates were obtained in the range of 4.0–12.3%. The proposed procedure was applied to analysis of water samples including river water, bottled mineral water, and boiling water exposed to polyethylene container (after cooling) and recoveries between 85 and 99% and RSDs lower than 12.8% were obtained.     

Magnetically assisted solid phase extraction using Fe3O4 nanoparticles combined with enhanced spectrofluorimetric detection for aflatoxin M1 determination in milk samples

A novel, facile and inexpensive solid phase extraction (SPE) method using ethylene glycol bis-mercaptoacetate modified 3-(trimethoxysilyl)-1-propanethiol grafted Fe₃O₄ nanoparticles coupled with spectrofluorimetric detection was proposed for determination of aflatoxin M1 (AFM1) in liquid milk samples. The method uses the advantage fluorescence enhancement by β-cyclodexterin complexation of AFM1 in 12% (v/v) acetonitrile–water and the remarkable properties of Fe₃O₄ nanoparticles namely high surface area and strong magnetization were utilized to achieve high enrichment factor (57) and satisfactory extraction recoveries (91–102%) using only 100 mg of magnetic adsorbent. Furthermore, fast separation time of about 15 min avoids many time-consuming column-passing procedures of conventional SPE. The main factors affecting extraction efficiency including pH value, desorption conditions, extraction/desorption time, sample volume, and adsorbent amount were evaluated and optimized. Under the optimal conditions, a wide linear range of 0.04–8 ng mL⁻¹ with a low detection limit of 0.015 ng mL⁻¹ was obtained. The developed method was applied for extraction and preconcentration of AFM1 in three commercially available milk samples and the results were compared with the official AOAC method.     

Preparation of carbon coated Fe3O4 nanoparticles and their application for solid-phase extraction of polycyclic aromatic hydrocarbons from environmental water samples

The carbon coated Fe₃O₄ nanoparticles (Fe₃O₄/C) were synthesized by a simple hydrothermal reaction and applied as solid-phase extraction (SPE) sorbents to extract trace polycyclic aromatic hydrocarbons (PAHs) from environmental water samples. The Fe₃O₄/C sorbents possess high adsorption capacity and extraction efficiency due to strong adsorption ability of carbon materials and large surface area of nanoparticles, and only 50 mg of sorbents are required to extract PAHs from 1000 mL water samples. The adsorption attains equilibrium rapidly and analytes are eluted with acetonitrile readily. Salinity and solution pH have no obvious effect on the recoveries of PAHs, which avoids fussy adjustment to water sample before extraction. Under optimized conditions, the detection limits of PAHs are in the range of 0.2–0.6 ng L⁻¹. The accuracy of the method was evaluated by the recoveries of spiked samples. Good recoveries (76–110%) with low relative standard deviations from 0.8% to 9.7% are achieved. This new SPE method provides several advantages, such as high extraction efficiency, high breakthrough volumes, convenient extraction procedure, and short analysis times. To our knowledge, this is the first time that Fe₃O₄/C nanoparticles are used for the pretreatment of environmental water samples.     

In-tube magnetic solid phase microextraction of some fluoroquinolones based on the use of sodium dodecyl sulfate coated Fe3O4 nanoparticles packed tube

In-tube magnetic solid phase microextraction (in-tube MSPME) of fluoroquinolones from water and urine samples based on the use of sodium dodecyl sulfate (SDS) coated Fe₃O₄ nanoparticles packed tube has been reported. After the preparation of Fe₃O₄ nanoparticles (NPs) by a batch synthesis, these NPs were introduced into a stainless steel tube by a syringe and then a strong magnet was placed around the tube, so that the Fe₃O₄ NPs were remained in the tube and the tube was used in the in-tube SPME-HPLC/UV for the analysis of fluoroquinolones in water and urine samples. Plackett–Burman design was employed for screening the variables significantly affecting the extraction efficiency. Then, the significant factors were more investigated by Box–Behnken design. Calibration curves were linear (R² > 0.990) in the range of 0.1–1000 μg L⁻¹ for ciprofloxacin (CIP) and 0.5–500 μg L⁻¹ for enrofloxacin (ENR) and ofloxacin (OFL), respectively. LODs for all studied fluoroquinolones ranged from 0.01 to 0.05 μg L⁻¹. The main advantages of this method were rapid and easy automation and analysis, short extraction time, high sensitivity, possibility of fully sorbent collection after analysis, wide linear range and no need to organic solvents in extraction.     

Fabrication of graphene/Fe3O4@polythiophene nanocomposite and its application in the magnetic solid-phase extraction of polycyclic aromatic hydrocarbons from environmental water samples

Polythiophene (PT) was used as a surface modifier of graphene/Fe₃O₄ (G/Fe₃O₄) composite to increase merit of it, and also overcome some limitations and disadvantages of using G/Fe₃O₄ alone as solid phase extraction (SPE) sorbent. An in-situ chemical polymerization method was employed to prepare G/Fe₃O₄@PT nanocomposites. Application of this newly designed material in the magnetic SPE (MSPE) of polycyclic aromatic hydrocarbons (PAHs), as model analytes, in the environmental water samples was investigated. The characterization of the hybrid material was performed using transmission electron microscopy, scanning electron microscopy, energy-dispersive X-ray analysis, Fourier transform-infrared (FT-IR) spectroscopy and vibrating sample magnetometry. Seven important parameters, affecting the extraction efficiency of PAHs, including: amount of adsorbent, adsorption and desorption times, type and volume of the eluent solvent, initial sample volume and salt content of the sample were evaluated. The optimum extraction conditions were obtained as: 4 min for extraction time, 20 mg for sorbent amount, 100 mL for initial sample volume, toluene as desorption solvent, 0.6 mL for desorption solvent volume, 6 min for desorption time and 30% (w/v) for NaCl concentration. Good performance data were obtained at the optimized conditions. Detection limits were in the range of 0.009–0.020 μg L⁻¹ in the real matrix. The calibration curves were linear over the concentration ranges from 0.03 to 80 μg L⁻¹ with correlation coefficients (R²) between 0.995 and 0.998 for all the analytes. Relative standard deviations were ranged from 4.3 to 6.3%. Appropriate recovery values, in the range of 83–107%, were also obtained for the real sample analysis.     

Reprint of: Extraction of fluoxetine from aquatic and urine samples using sodium dodecyl sulfate-coated iron oxide magnetic nanoparticles followed by spectrofluorimetric determination

A new method based on the combination of magnetic solid phase extraction (MSPE) and spectrofluorimetric determination was developed for isolation and preconcentration of fluoxetine form aquatic and biological samples using sodium dodecyl sulfate (SDS) coated Fe₃O₄ nanoparticles (NPs) as a sorbent. The unique properties of Fe₃O₄ NPs including high surface area and strong magnetism were utilized effectively in the MSPE process. Effect of different parameters influencing the extraction efficiency of fluoxetine including the amount of Fe₃O₄ and SDS, pH value, sample volume, extraction time, desorption solvent and time were optimized. Under optimized condition, the method was successfully applied to the extraction of fluoxetine from water and urine samples and absolute recovery amount of 85%, detection limit of 20 μg L⁻¹ and a relative standard deviation (RSD) of 1.4% were obtained. The method linear response was over a range of 50–1000 μg L⁻¹ with R² = 0.9968. The relative recovery in different aquatic and urine matrices were investigated and values of 80% to 104% were obtained. The whole procedure showed to be conveniently fast, efficient and economical for extraction of fluoxetine from environmental and biological samples.     

Preparation of Fe3O4 nanoparticle enclosure hydroxylated multi-walled carbon nanotubes for the determination of aconitines in human serum samples

A magnetic carbon nanomaterial for Fe₃O₄ enclosure hydroxylated multi-walled carbon nanotubes (Fe₃O₄-EC-MWCNTs-OH) was prepared by the aggregating effect of Fe₃O₄ nanoparticle on MWCNTs-OH, and combined with high-performance liquid chromatography (HPLC)/diode array detection (DAD) to determine the aconitines (aconitine, hypaconitine and mesaconitine) in human serum samples. Compared with other extraction modes investigated in experiment, Fe₃O₄-EC-MWCNTs-OH sorbents showed a good affinity to target analytes. Some important parameters that could influence extraction efficiency of aconitines, including the extraction mode, amounts of Fe₃O₄-EC-MWCNTs-OH, pH of sample solution, extraction time, desorption solvent and desorption time, were optimized. Under optimal conditions, the recoveries of spiked serum samples were between 98.0% and 103.0%; relative standard deviations (RSDs) ranged from 0.9% to 6.2%. The correlation coefficients varied from 0.9996 to 0.9998. The limits of detection ranged from 3.1 ng mL⁻¹ to 4.1 ng mL⁻¹ at a signal-to-noise ratio of 3. The experimental results showed that the proposed method was feasible for the analysis of aconitines in serum samples.     

纳米Fe3O4-TiO2靶向光动力疗法对肝癌细胞的杀伤效应

光动力疗法(PDT)作为一种迅速发展的传统替代疗法,在抗癌治疗中显示出巨大的潜力.为增强靶向性和提高光催化杀伤效率,本研究设计了一种新型光敏剂Fe₃O₄-TiO₂磁性纳米粒.在不同外磁场下,考察其在可见光和紫外光激发下对肝癌细胞的杀伤效应.同时利用流式细胞术检测纳米Fe₃O₄-TiO₂对肝癌细胞凋亡率、细胞周期和线粒体膜电位的影响.根据纳米Fe₃O₄-TiO₂和肝癌细胞的作用方式探讨其抗癌机制.结果表明,可见光激发纳米Fe₃O₄-TiO₂可以杀伤癌细胞,且其杀伤效率与紫外光激发下无明显差别.此外,Fe₃O₄-TiO₂比TiO₂具有更高的细胞摄取率,从而使其具有更高的选择性和光催化杀伤效率.其作用机制是光催化纳米Fe₃O₄-TiO₂产生活性氧ROS抑制癌细胞,然后通过阻滞细胞周期G₀/G₁期,降低线粒体膜电位,线粒体去极化,最终诱导细胞凋亡.     

A new 2212-type stair like structure: Bi14Sr21Fe12O61, m=5 member of the generic [Bi2Sr3Fe2O9]m[Bi4Sr6Fe2O16] family

A new oxide, Bi₁₄Sr₂₁Fe₁₂O_61, with a layered structure derived from the 2212 modulated type structure Bi₂Sr₃Fe₂O₉, was isolated. It crystallizes in the I2 space group, with the following parameters: a=16.58(3) Å, b=5.496(1) Å, c=35.27(2) Å and β=90.62°. The single crystal X-ray structure determination, coupled with electron microscopy, shows that this ferrite is the m=5 member of the [Bi₂Sr₃Fe₂O₉]_m[Bi₄Sr₆Fe₂O₁₆] collapsed family. This new collapsed structure can be described as slices of 2212 structure of five bismuth polyhedra thick along , shifted with respect to each other and interconnected by means of [Bi₄Sr₆Fe₂O₁₆] slices. The latter are the place of numerous defects like iron or strontium for bismuth substitution; they can be correlated to intergrowth defects with other members of the family.     

Synthesis of Fe3O4\SiO2\Ag nanoparticles and its application in surface-enhanced Raman scattering

To obtain a recyclable surface-enhanced Raman scattering (SERS) material, we developed a composite of Fe₃O₄\SiO₂\Ag with core\shell\particles structure. The designed particles were synthesized via an ultrasonic route. The Raman scattering signal of Fe₃O₄ could be shielded by increasing the thickness of the SiO₂ layer to 60 nm. Dye rhodamine B (RB) was chosen as probe molecule to test the SERS effect of the synthesized Fe₃O₄\SiO₂\Ag particles. On the synthesized Fe₃O₄\SiO₂\Ag particles, the characteristic Raman bands of RB could be observed when the RB solution was diluted to 5 ppm (1×10⁻⁵ M). Furthermore, the synthesized particles could keep their efficiency till four cycles.     

Preparation, crystal structure, and magnetic studies of Na3Fe2Mo5O16, a new oxide containing Mo3O13 clusters

The complex oxide Na₃Fe₂Mo₅O₁₆ has been synthesized, and its crystal structure was determined by single-crystal X-ray diffraction (space group (SG) P-3m1; a=5.7366(6) Å, c=22.038(3) Å; Z=2). The compound can be considered as a new structure type containing Mo₃O₁₃ cluster units, which can be derived from the Na₂In₂Mo₅O₁₆ structure model by doubling of the cell along the c-axis. Na₃Fe₂Mo₅O₁₆ crystallizes in centrosymmetric SG (P-3m1) and the positions of the sodium atoms are fully occupied in contrast to the proposed Na₂In₂Mo₅O₁₆ model SG (P3m1). Magnetic properties of Na₃Fe₂Mo₅O₁₆ were studied by superconducting quantum interference device measurements, revealing antiferromagnetic ordering below Tχ_max=10(1) K. Thermal stability in air was investigated by in situ high-temperature X-ray powder diffraction. Structural relationships to Na₂In₂Mo₅O₁₆ and NaFe(MoO₄)₂ are discussed.     

Mixed hemimicelles solid-phase extraction based on cetyltrimethylammonium bromide-coated nano-magnets Fe3O4 for the determination of chlorophenols in environmental water samples coupled with liquid chromatography/spectrophotometry detection

Mixed hemimicelles solid-phase extraction (SPE) based on cetyltrimethylammonium bromide (CTAB)-coated nano-magnets Fe3O4 was investigated for the preconcentration of four chlorophenols (CPs) in environmental water samples prior to HPLC-spectrophotometry determination in this paper. By the rapid isolating (about 5 min) of Fe3O4 nanoparticles (NPs) through placing a Nd-Fe-B strong magnet on the bottom of beaker, the time-consuming preconcentration process of loading large volume sample in conversional SPE method with a column can be avoided. The unique properties of Fe3O4 NPs such as high surface area and strong magnetism were utilized adequately in the SPE process. This novel separation method produced a high preconcentration rate and factor. A comprehensive study of the adsorption conditions such as the Fe3O4 NPs zeta-potential, CTAB added amounts, pH value, standing time and maximal extraction volume was also presented. Under optimized conditions, four analytes of 2-chlorophenol (2-CP), 2,4-dichlorophenol (2,4-DCP), 2,4,6-trichlorophenol (TCP) and pentachlorophenol (PCP) were quantitatively extracted. The method was then used to determine four CPs in five real environmental water samples. High concentration factors (700) were achieved for each of the analytes, with observed detection limits ranging between 0.11 and 0.15 microg L(-1). The accuracy of method was evaluated by recovery measurements on spiked samples. Good recovery results (83-98%) with satisfactory relative standard deviation (RSD) were achieved. It is important to note that satisfactory preconcentration factors and extraction recoveries for the four CPs were obtained with only a little amount of Fe3O4 NPs (0.1g) and CTAB (60 mg). To the best of our knowledge, this was the first time a mixed hemimicelles SPE method based on Fe3O4 NPs magnetic separation had been used for the pretreatment of environmental water samples.     

Photodegradation of 2,4-D over PdO/Al2O3-Nd2O3 photocatalysts prepared by the sol-gel method

The photocatalytic activity of 1.0 wt% PdO supported on Al₂O₃-Nd₂O₃ binary oxides prepared by the sol-gel method was studied in the photodegradation of 2,4-dichlorophenoxyacetic acid (2,4-D). The photocatalysts were characterized by N₂ physisorption, XRD and UV-vis spectroscopy. PdO supported on γ-Al₂O₃ photo-degrades the 2,4-D, however the addition of Nd₂O₃ to γ-Al₂O₃ notably improves the photocatalytic activity. As the concentration of Nd₂O₃ in the binary oxide increases from 2 to 10 wt%, the photodegradation of 2,4-D is highly enhanced. The catalytic test for PdO supported on pure Nd₂O₃ showed scarce photocatalytic activity. Total organic carbon (TOC) analysis showed that the 2,4-D has been completely destroyed on the PdO/Al₂O₃-Nd₂O₃ photocatalysts after 6 h under irradiation.     

Sol-gel synthesized semiconducting LaCo0.8Fe0.2O3-based powder for thick film NH3 gas sensor

Perovskite type LaCo_xFe_1−xO₃ nanoparticles was synthesized by a sol-gel citrate method. The structural, electrical and sensing characteristics of the LaCo_xFe_1−xO₃ system were investigated. The structural characteristics were performed by using X-ray diffraction (XRD) and transmission electron microscopy (TEM) to examine the phase and morphology of the resultant powder. The XRD pattern shows nanocrystalline solid solution of LaCo_xFe_1−xO₃ with perovskite phase. Electrical properties of synthesized nanoparticles are studied by DC conductivity measurement. The sensor shows high response towards ammonia gas in spite of other reducing gases when x = 0.8. The effect of 0.3 wt.% Pd-doped LaCo_0.8Fe_0.2O₃ on the response and a recovery time was also addressed.     

High performance liquid chromatography determination of chlorophenols in water samples after preconcentration by continuous flow liquid membrane extraction on-line coupled with a precolumn

A continuous flow liquid membrane extraction (CFLME)-C₁₈ precolumn-liquid chromatography system was developed for preconcentration and determination of chlorinated phenols (CPs). After preconcentration by CFLME, which is based on the combination of continuous flow liquid-liquid extraction and supported liquid membrane, CPs were enriched in 960 μl of 0.5 mol l⁻¹ NaOH used as acceptor. This acceptor was on-line neutralized and transported onto the C₁₈ precolumn where analytes were absorbed and focused. Then the focused analytes were injected onto the C₁₈ analytical column for separation and detected at 215 nm with a diode array detector. CFLME related parameters such as flow rates, pH of donor and acceptor concentration were optimized. The proposed method presents detection limits of 0.02-0.09 μg l⁻¹ (S/N=3) when 100 ml samples were enriched. The proposed method was successfully applied to determine CPs in tap water and river water samples with spiked recoveries in the range of 70-121%.     

Facile synthesis of multifunctional attapulgite/Fe3O4/polyaniline nanocomposites for magnetic dispersive solid phase extraction of benzoylurea insecticides in environmental water samples

In this study, the superparamagnetic attapulgite/Fe₃O₄/polyaniline (ATP/Fe₃O₄/PANI) nanocomposites were successfully synthesized by a one-pot method. Fe (III) was applied as both the oxidant for the oxidative polymerization of aniline and the single iron source of Fe₃O₄ formed by the redox reaction between aniline and Fe (III). The ATP/Fe₃O₄/PANI was used as sorbent for magnetic dispersive solid phase extraction (MDSPE) of benzoylurea insecticides (BUs) in environmental water samples. The as-prepared nanocomposite sorbents were characterized by Fourier transform infrared spectra (FT-IR), X Ray diffraction (XRD), scanning electron microscopy(SEM), transmission electron microscopy (TEM), and vibrating sample magnetometry. Various experimental parameters affecting the ATP/Fe₃O₄/PANI-based MDSPE procedure, including the composition of the nanocomposite sorbents, amount of ATP/Fe₃O₄/PANI nanocomposites, vortex time, pH, and desorption conditions were investigated. Under the optimal conditions, a good linearity was observed for all target analytes, with correlation coefficients (r²) ranging from 0.9985 to 0.9997; the limits of detection (LOD) were in the range of 0.02–0.43 μg L⁻¹, and the recoveries of analytes using the proposed method ranged between 77.37% and 103.69%. The sorbents exhibited an excellent reproducibility in the range of 1.52–5.27% in extracting the five target analytes. In addition, the intra-day and inter-day precision values were found to be in the range of 0.78–6.86% and 1.66–8.41%, respectively. Finally, the proposed ATP/Fe₃O₄/PANI-based MDSPE method was successfully applied to analyze river water samples by rapid preconcentration of BUs.     

Effect of capping and particle size on Raman laser-induced degradation of γ-Fe2O3 nanoparticles

Diol capped γ-Fe₂O₃ nanoparticles are prepared from ferric nitrate by refluxing in 1,4-butanediol (9.5 nm) and 1,5-pentanediol (15 nm) and uncapped particles are prepared by refluxing in 1,2-propanediol followed by sintering the alkoxide formed. X-ray diffraction (XRD) shows that all the samples have the spinel phase. Raman spectroscopy shows that the samples prepared in 1,4-butanediol and 1,5-pentanediol and 1,2-propanediol (sintered at 573 and 673 K) are γ-Fe₂O₃ and the 773 K-sintered sample is Fe₃O₄. Raman laser studies carried out at various laser powers show that all the samples undergo laser-induced degradation to α-Fe₂O₃ at higher laser power. The capped samples are however, found more stable to degradation than the uncapped samples. The stability of γ-Fe₂O₃ sample with large particle size (15.4 nm) is more than the sample with small particle size (10.2 nm). Fe₃O₄ having a particle size of 48 nm is however less stable than the smaller γ-Fe₂O₃ nanoparticles.     

磁性纳米Pd/Fe3O4催化剂的制备及其在Heck反应中的应用

通过使用聚乙烯吡咯烷酮作为稳定剂,合成了磁性Pd/Fe₃O₄纳米颗粒催化剂。对该催化剂进行粉末X射线衍射、透射电子显微镜、感应耦合等离子体和磁性表征。将Pd/Fe₃O₄催化剂用于Heck反应,检测其催化性能。测试结果表明Pd纳米颗粒负载在Fe₃O₄纳米颗粒上,而且催化剂的尺寸<20 nm,并在Heck反应中表现了极好的催化性能。此外,催化剂可以通过磁场回收利用, 且催化活性没有显著的降低。     

The formation and physicochemical characterization of Al2O3-doped manganese ferrites

Mn/Fe mixed oxide solids doped with Al₂O₃ (0.32-1.27 wt.%) were prepared by impregnation of manganese nitrate with finely powdered ferric oxide, then treated with different amounts of aluminum nitrate. The obtained samples were calcined in air at 700-1000 °C for 6 h. The specific surface area (S_BET) and the catalytic activity of pure and doped precalcined at 700-1000 °C have been measured by using N₂ adsorption isotherms and CO oxidation by O₂. The structure and the phase changes were characterized by DTA and XRD techniques. The obtained results revealed that Mn₂O₃ interacted readily with Fe₂O₃ to produce well-crystallized manganese ferrite (MnFe₂O₄) at temperatures of 800 °C and above. The degree of propagation of this reaction increased by Al₂O₃-doping and also by increasing the heating temperature. The treatment with 1.27 wt.% Al₂O₃ followed by heating at 1000 °C resulted in complete conversion of Mn/Fe oxides into the corresponding ferrite phase. The catalytic activity and S_BET of pure and doped solids were found to decrease, by increasing both the calcination temperature and the amount of Al₂O₃ added, due to the enhanced formation of MnFe₂O₄ phase which is less reactive than the free oxides (Mn₂O₃ and Fe₂O₃). The activation energy of formation (ΔE) of MnFe₂O₄ was determined for pure and doped solids. The promotion effect of aluminum in formation of MnFe₂O₄ was attributed to an effective increase in the mobility of reacting cations.     

Phase formation, crystal chemistry, and properties in the system Bi2O3-Fe2O3-Nb2O5

Subsolidus phase relations have been determined for the Bi₂O₃-Fe₂O₃-Nb₂O₅ system in air (900-1075 °C). Three new ternary phases were observed—Bi₃Fe_0.5Nb_1.5O₉ with an Aurivillius-type structure, and two phases with approximate stoichiometries Bi₁₇Fe₂Nb₃₁O₁₀₆ and Bi₁₇Fe₃Nb₃₀O₁₀₅ that appear to be structurally related to Bi₈Nb₁₈O₅₇. The fourth ternary phase found in this system is pyrochlore (A₂B₂O₆O′), which forms an extensive solid solution region at Bi-deficient stoichiometries (relative to Bi₂FeNbO₇) suggesting that ≈4-15% of the A-sites are occupied by Fe³⁺. X-ray powder diffraction data confirmed that all Bi-Fe-Nb-O pyrochlores form with positional displacements, as found for analogous pyrochlores with Zn, Mn, or Co instead of Fe. A structural refinement of the pyrochlore 0.4400:0.2700:0.2900 Bi₂O₃:Fe₂O₃:Nb₂O₅ using neutron powder diffraction data is reported with the A cations displaced (0.43 Å) to 96g sites and O′ displaced (0.29 Å) to 32e sites (Bi_1.721Fe_0.190(Fe_0.866Nb_1.134)O₇, Fd3¯m (#227), ). This displacive model is somewhat different from that reported for Bi_1.5Zn_0.92Nb_1.5O_6.92, which exhibits twice the concentration of small B-type cations on the A-sites as the Fe system. Bi-Fe-Nb-O pyrochlores exhibited overall paramagnetic behavior with large negative Curie-Weiss temperature intercepts, slight superparamagnetic effects, and depressed observed moments compared to high-spin, spin-only values. The single-phase pyrochlore with composition Bi_1.657Fe_1.092Nb_1.150O₇ exhibited low-temperature dielectric relaxation similar to that observed for Bi_1.5Zn_0.92Nb_1.5O_6.92; at 1 MHz and 200 K the relative permittivity was 125, and above 350 K conductive effects were observed.