α-Fe2O3 Nanocrystals Research Articles

High-concentrated synthesis of surface modified iron oxide nanoparticles using ethanol-enhanced supercritical CO2 media

In the synthesis of surface modified metal oxide nanoparticles (NPs), supercritical CO2 is an attractive medium to achieve a simple and green chemistry approach without waster liquor. However, the mass production of surface-modified NPs is still a serious challenge for their industrial utilization. In this work, we aimed to demonstrate the high-concentrated synthesis of surface-modified iron oxide NPs in ethanol-enhanced supercritical CO2. The synthesis and phase observation were performed at 30.0 ± 0.8 MPa of CO2, 100 °C and 18 h, while changing the total concentration of iron(Ⅲ) acetylacetonate, water and oleic acid and ethanol ratio. As a result, lower total concentration gave single nano-sized α-Fe2O3 nanocrystal under uniform phase while higher one gave aggregated α-FeOOH under ununiform phase. However, ethanol entrainer successfully homogenized the reaction field by drastically raising the solubilities of components, allowing the high-concentrated synthesis of single nano-sized α-Fe2O3 nanocrystal. Furthermore, synthesized nanocrystal had chemically and densely modified surface, showing the unimodal size distribution in cyclohexane. These results conclusively show that supercritical CO2 with ethanol entrainer is a promising medium to allow the mass production of densely modified nanocrystal and subsequent their industrial utilization in thin film fabrication and drug delivery system.

Deciphering the facet-dependent scavenging potential of α-Fe2O3 nanocrystals for U(VI) and Eu(III) from aqueous phase

The utilization of biocompatible and inexpensive adsorbents for the effective scavenging of U(VI) and Eu(III) from wastewater is still an open challenge in nuclear waste management. Herein, three kinds of α-Fe2O3 nanocrystals with different morphologies, i.e., α-Fe2O3 nanospheres (HNSs), nanoplates (HNPs) and nanorods (HNRs), which were exposed (102), (001), and (110) facet, respectively, was used to scavenge U(VI) and Eu(III) from aqueous solutions via an adsorption procedure. Various techniques of N2 adsorption–desorption, FT-IR, XRD, XPS, TEM, SEM and EDS were applied to characterize these adsorbents before or after adsorption. The results indicated that the adsorption capacity of U(VI) and Eu(III) was in the order of HNPs (001) > HNRs (110) > HNSs (102), namely, α-Fe2O3 nanoplates was proved to be a good adsorbents, with removal capacity of 221 mg/g and 131 mg/g for U(VI) and Eu(III) scavenged on HNPs, respectively. The kinetics of U(VI) and Eu(III) scavenging agreed with the pseudo second order kinetic model, suggesting that chemical interaction is mainly responsible for U(VI) and Eu(III) scavenging on these materials. Furthermore, the Freundlich model fit the best for adsorption isotherms of U(VI) and Eu(III). The present study demonstrated that these α-Fe2O3 nanocrystals are promising materials in nuclear waste management.

Regular polyhedron α-Fe2O3 nanocrystals prepared from hot rolled sludge for photocatalytic degradation of organic pollutants: Optimization and mechanism

Herein, a photocatalyst with the micromorphology of regular polyhedron (RP-α-Fe2O3 nanocrystals) was prepared via hot rolled sludge (HRS), and its preparation mechanism was investigated. The optical property test and DFT calculations exhibited the RP-α-Fe2O3 nanocrystals has strong visible light absorption and small electrochemical impedance, which indicated that it has excellent catalytic performance under visible light. The degradation efficiency of 100 mg/L Rhodamine B (RhB) solution could reach 99.2% within 60 min. Furthermore, the RP-α-Fe2O3 nanocrystals exhibited excellent reusability and stability. Meanwhile, hydroxyl radicals (·OH), superoxide radicals (·O2−) and photogenerated holes (h+) were the most significant active substances that affect the photocatalytic efficiency, due to they would synergically degrade RhB in the photocatalytic reaction system. Particularly, the diffraction peak of N1s was detected in the RP-α-Fe2O3 nanocrystals after reaction, and the intensity of CO and CO peaks increased, which proved that the photocatalyst has adsorption for RhB.

High yield design of mesoporous tetrakaidecahedron-like α-Fe2O3 nanocrystals with enhanced supercapacitive performance

High yield design of mesoporous tetrakaidecahedron-like α-Fe2O3 nanocrystals with enhanced supercapacitive performance

Clay-derived Synthesis of Supported α-Fe2O3 Nanoparticles: Shape, Adsorption, and Photo-catalysis

Background: This paper reports a versatile bentonite clay-mediated growth method for selectively synthesizing zero-dimensional α-Fe2O3 nanoparticles and one-dimensional α-Fe2O3 nanorods. Method: In such a growth process without any other surfactant or additive, the bentonite clay is not only used as the supporter, but also as a shape mediator for α-Fe2O3 nanocrystals. The products were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Results: The as-prepared products were used to investigate their promising adsorptive and photocatalytic applications in water treatment. According to the Langmuir equation, the maximum adsorption capacity of the α-Fe2O3/bentonite composite for Congo red (CR) is calculated to be 96.9 mg·g-1. Furthermore, the α-Fe2O3/bentonite nanocomposites also show an excellent photocatalytic property in the degradation of methyl orange (MO). Conclusion: This facile and novel synthesis method has the potential to be applied to prepare the low-cost α-Fe2O3/bentonite nanocomposite for the removal of CR and MO.

A dimethyl disulfide gas sensor based on nanosized Pt-loaded tetrakaidecahedral α-Fe2O3 nanocrystals

Surface modification by employing precious metals is one of the most effective ways to improve the gas-sensing performance of metal oxide semiconductors. Pure α-Fe2O3 nanoparticles and Pt-modified α-Fe2O3 nanoparticles were prepared sequentially using a rather simple hydrothermal synthesis and impregnation method. Compared with the original α-Fe2O3 nanomaterials, the Pt-α-Fe2O3 nanocomposite sensor shows a higher response value (R a/R g = 58.6) and a shorter response/recovery time (1 s/168 s) to 100 ppm dimethyl disulfide (DMDS) gas at 375 °C. In addition, it has better selectivity to DMDS gas with the value of more than 9 times higher than the other target gases at 375 °C. This study indicates that the Pt-α-Fe2O3 nanoparticle sensor has good prospects and can be used as a low-cost and effective DMDS gas sensor.

From Himba indigenous knowledge to engineered Fe2O3 UV-blocking green nanocosmetics

This contribution reports on the physical properties of the natural Namibian red Ochre used by the Himba Community in a form of a formulation, so called Otjize as a skin protective and beauty cream. The morphological and crystallographic studies of this red ochre validated its nano-scaled dominating phase of rhombohedral α-Fe2O3 nanocrystals with an additional hydrolized oxide component in a form of γ-FeOOH. The optical investigations showed that such a red ochre exhibits an exceptional UV filtration and a significant IR reflectivity substantiating its effectiveness as an effective UV-blocking & solar heat IR reflector in support of the low skin cancer rate within the Namibian Himba community. In addition, such nanocrystals exhibited a non-negligible antibacterial response against E. Coli & S. Aurus. This study seems confirming the effectiveness of the indigenous Otjize as an effective skin UV protection cream with a sound antimicrobial efficacy against e-Coli & S-Aurus.

Crystal-Phase Control of Ternary Metal Oxides by Solid-State Synthesis with Nanocrystals.

Ternary metal oxides are materials of interest for many applications, from batteries to catalysis. Their crystalline structure and composition determine their properties, and thus it is important to achieve control over these features. Here, we demonstrate that solid-state chemistry among nanocrystalline precursors is a promising approach for their synthesis. We show that the crystalline phase of nanocrystal precursors direct that of the ternary reaction product. The combination of X-ray and electron microscopy techniques reveals that the spinel and rhombohedral phases of copper iron oxide are obtained by reacting copper nanocrystals with spinel γ-Fe2O3 and corundum α-Fe2O3 nanocrystals, respectively. Considering the available library of nanocrystals with tunable crystal phases, this discovery opens up an alternative pathway toward the synthesis of a wide variety of ternary and quaternary materials, including those with metastable phases.

Boosting room-temperature ppb-level NO2 sensing over reduced graphene oxide by co-decoration of α-Fe2O3 and SnO2 nanocrystals

As promising sensing materials, reduced graphene oxide (RGO)-based nanomaterials have drawn considerable attention in the fields of gas monitoring owing to their low operating temperature. However, constructing RGO-based room-temperature gas sensors possessing ppb-level limit of detection with high sensitivity remains challenging. In this work, a series of highly sensitive NO2 sensors were fabricated using α-Fe2O3 and SnO2 co-decorated RGO hybrids (designated as α-Fe2O3/SnO2-RGO) as sensing materials. They were rationally synthesized by a one-pot hydrothermal method. Compared to SnO2 modified RGO hybrids (SnO2-RGO with bandgap of 3.88 eV), the bandgap energy of α-Fe2O3/SnO2-RGO hybrids (3.53 eV) was reduced by adding α-Fe2O3; the narrower bandgap facilitated the sensing materials to release more electrons and form more oxygen ions at room temperature. Besides, the high carrier migration of RGO, which served as continuous phase, identical structure with ultrasmall particle size of α-Fe2O3 and SnO2 (about 3–6 nm), and abundant chemisorbed oxygen species on the surface (20.8%) of the sensing materials, as well as their suitable bandgap (3.53 eV) in the sensing materials, significantly improved NO2 response at room temperature. Among the sensors fabricated, α-Fe2O3/SnO2-RGO-15-based NO2 sensor had the highest response of 7.4 with a short response time of 59 s towards 1 ppm NO2; it could even reach a response of 2.6 towards 100 ppb NO2. Notably, α-Fe2O3/SnO2-RGO-15 sample has excellent capability to recognize NO2, where the response value (7.4) towards 1 ppm NO2 is about 7 times higher than that of 100 ppm ammonia and common volatile organic compounds (formaldehyde, toluene, ethanol and acetone). Such NO2 sensor has superior repeatability with negligible response deviation towards 1 ppm NO2 for four reversible cycles. This makes it to have a great potential application in the field of NO2 detection.

Facilitating Catalytic Purification of Auto-Exhaust Carbon Particles via the Fe2O3{113} Facet-dependent Effect in Pt/Fe2O3 Catalysts.

The purification efficiency of auto-exhaust carbon particles in the catalytic aftertreatment system of vehicle exhaust is strongly dependent on the interface nanostructure between the noble metal component and oxide supports. Herein, we have elaborately synthesized the catalysts (Pt/Fe2O3-R) of Pt nanoparticles decorated on the hexagonal bipyramid α-Fe2O3 nanocrystals with co-exposed twelve {113} and six {104} facets. The area ratios (R) of co-exposed {113} to {104} facets in α-Fe2O3 nanocrystals were adjusted by the fluoride ion concentration in the hydrothermal method. The strong Pt-Fe2O3{113} facet interaction boosts the formation of coordination unsaturated ferric sites for enhancing adsorption/activation of O2 and NO. Pt/Fe2O3-R catalysts exhibited the Fe2O3{113} facet-dependent performance during catalytic purification of soot particles in the presence of H2O. Among the catalysts, the Pt/Fe2O3-19 catalyst exhibits the highest catalytic activities (T50 = 365 °C, TOF = 0.13 h-1), the lowest apparent activation energy (69 kJ mol-1), and excellent catalytic stability during soot purification. Combined with the results of characterizations and density functional theory calculations, the catalytic mechanism is proposed: the active sites located at the Pt-Fe2O3{113} interface can boost the key step of NO oxidation to NO2. The crystal facet engineering is an effective strategy to obtain efficient catalysts for soot purification in practical applications.

Probing into the crystal plane effect on the reduction of α-Fe2O3 in CO by Operando Raman spectroscopy

For the Fe-based catalysts in Fischer-Tropsch synthesis, the reduction and activation process of α-Fe2O3 precursor has a significant effect on the catalytic performance. As a crystalline material, the reduction and activation of α-Fe2O3 is assuredly influenced by the exposed crystal plane; however, there is a lack of necessary research in this regard. In this work, α-Fe2O3 nanocrystals of three different morphologies, viz., pseudo-cubic, hexagonal-plate and rhombohedra, were synthesized, which mainly expose the crystal planes of (102), (001) and (104), respectively. The evolution of α-Fe2O3 crystal structure was then investigated in CO atmosphere by using the Operando Raman spectroscopy (ORS). The results show that the α-Fe2O3 (001) plane has a better reductive activity in comparison to the (104) and (102) planes. The SEM, TEM, XPS and XRD characterization and DFT calculation results reveal that CO2 desorption is a decisive step for the reduction of α-Fe2O3; owing to the weak binding ability of (001) crystal plane to oxygen atoms, the desorption of CO2 on the (001) crystal plane is much easier, which can promote the reduction process.

Facile synthesis of porous waist drum-like α-Fe2O3 nanocrystals as electrode materials for supercapacitor application

Facile synthesis of porous waist drum-like α-Fe2O3 nanocrystals as electrode materials for supercapacitor application

High-Voltage Cathode α-Fe2O3 Nanoceramics for Rechargeable Sodium-Ion Batteries.

Previously, α-Fe2O3 nanocrystals are recognized as anode materials owing to their high capacity and multiple properties. Now, this work provides high-voltage α-Fe2O3 nanoceramics cathodes fabricated by the solvothermal and calcination processes for sodium-ion batteries (SIBs). Then, their structure and electrical conductivity were investigated by the first-principles calculations. Also, the SIB with the α-Fe2O3 nanoceramics cathode exhibits a high initial charge-specific capacity of 692.5 mA h g–1 from 2.0 to 4.5 V at a current density of 25 mA g–1. After 800 cycles, the discharge capacity is still 201.8 mA h g–1, well exceeding the one associated with the present-state high-voltage SIB. Furthermore, the effect of the porous structure of the α-Fe2O3 nanoceramics on sodium ion transport and cyclability is investigated. This reveals that α-Fe2O3 nanoceramics will be a remarkably promising low-cost and pollution-free high-voltage cathode candidate for high-voltage SIBs.

Fe3C nanocrystals encapsulated in N-doped carbon nanofibers as high-efficient microwave absorbers with superior oxidation/corrosion resistance

In addition to the demand of thin, lightweight, broadband and high-efficient characteristics, exploring microwave absorbents with superior resistance to oxidation and corrosion is urgently need for practical applications. Herein, carbon nanofibers embedded by α-Fe2O3, Fe or Fe3C nanocrystals are prepared through electrospinning technique followed by carbonization in different atmospheres. The one-dimensional structures can intertwine into three-dimensional conductive network, which is favored for energy dissipation. The Fe3C/N-doped carbon nanofibers show boosting microwave absorption properties compared to the bare carbon, α-Fe2O3/C and Fe/C nanofibers. The Fe3C/N-doped carbon nanofibers show an optimal reflection loss of −57.9 dB at 5.8 GHz with a thickness of 4.1 mm. Meanwhile, a reflection loss of −54.5 dB can be achieved at 17.8 GHz, when the absorber thickness is only 1.5 mm. The superior microwave absorption properties are attributed to the dipole polarization, interfacial polarization and ferromagnetic resonance, induced by the synergistic effect of Fe3C nanocrystals and carbon nanofibers. Moreover, acid-soaking and air-annealing treatments reveal that the Fe3C/N-doped carbon nanofibers show remarkable corrosion and oxidation resistance. This work suggests that encapsulating magnetic nanocrystals in dielectric carbon-based materials is an efficient strategy to construct high-efficient lightweight microwave absorbents with oxidation/corrosion resistance.

Microtubular α-Fe2O3/Fe2(MoO4)3 heterostructure derived from absorbent cotton for enhanced ppb-level H2S gas-sensing performance

Microtubular α-Fe2O3/Fe2(MoO4)3 heterostructure (FFMO) was massively prepared by facile immersion-calcination method with absorbent cotton being employed as template, which is formed by a great number of cross-linking nanoparticles. In comparison with the pure iron molybdate (FMO) microtubules, the small-sized α-Fe2O3 nanocrystals evenly attached to the surface of FMO particles, increasing the specific surface area of FFMO composites and forming broad hierarchical pores. Gas-sensing measurement indicates that the sensor fabricated from FFMO heterostructure presents response of 12.69 toward 10 ppm H2S, being about 2.2 times larger than that of pure FMO-based sensor. And the working temperature also reduces from 170 °C to 133 °C. In particular, the FFMO composite exhibits the fastest response (Tres = 3 s) and the lowest detection limit (50 ppb) to H2S gas among all reported FMO-based sensors. Such rapid response and highly sensitive to trace H2S are dominantly assigned to the synergism of the inherent properties of multistage-pores microtubule, n-n heterojunction, surface adsorbed oxygen, as well as the generation of metastable iron sulfide induced by lattice oxygen. In addition, the gas-sensing mechanism of the sensor is also studied in detail.

New sol-gel-derived magnetic bioactive glass-ceramics containing superparamagnetic hematite nanocrystals for hyperthermia application

Although the three main phases of iron oxide – hematite, maghemite, and magnetite – exhibit superparamagnetic properties at the nanoscale, only maghemite and magnetite phases have been explored in magnetic bioactive glass-ceramics aimed at applications in cancer treatment by hyperthermia. In this work, it is reported for the first time the superparamagnetic properties of hematite nanocrystals grown in a 58S bioactive glass matrix derived from sol-gel synthesis. The glass-ceramics are based on the (100-x)(58SiO2-33CaO-9P2O5)-xFe2O3 system (x = 10, 20 and 30 wt%). A thermal treatment leads to the growth of hematite (α-Fe2O3) nanocrystals, conferring superparamagnetic properties to the glass-ceramics, which is enough to produce heat under an external alternating magnetic field. Besides, the crystallization does not inhibit materials bioactivity, evidenced by the formation of calcium phosphate onto the glass-ceramic surface upon soaking in simulated body fluid. Moreover, their cytotoxicity is similar to other magnetic bioactive glass-ceramics reported in the literature. Finally, these results suggest that hematite nanocrystals' superparamagnetic properties may be explored in multifunctional glass-ceramics applied in bone cancer treatment by hyperthermia allied to bone regeneration.

In-situ encapsulation of α-Fe2O3 nanoparticles into ZnFe2O4 micro-sized capsules as high-performance lithium-ion battery anodes

Transition metal oxides as anode materials for high-performance lithium-ion batteries suffer from severe capacity decay, originating primarily from particle pulverization upon volume expansion/shrinkage and the intrinsically sluggish electron/ion transport. Herein, in-situ encapsulation of α-Fe2O3 nanoparticles into micro-sized ZnFe2O4 capsules is facilely fulfilled through a co-precipitation process and followed by heat-treatment at optimal calcination temperature. The porous ZnFe2O4 scaffold affords a synergistic confinement effect to suppress the grain growth of α-Fe2O3 nanocrystals during the calcination process and to accommodate the stress generated by volume expansion during the charge/discharge process, leading to an enhanced interfacial conductivity and inhibit electrode pulverization and mechanical failure in the active material. With these merits, the prepared α-Fe2O3/ZnFe2O4 composite delivers prolonged cycling stability and improved rate capability with a higher specific capacity than sole α-Fe2O3 and ZnFe2O4. The discharge capacity is retained at 700 mAh g−1 after 500 cycles at 200 mA g−1 and 940 mAh g−1 after 50 cycles at 100 mA g−1. This work provides a new perspective in designing transition metal oxides for advanced lithium-ion batteries with superior electrochemical properties.

Controlled synthesis of α-Fe2O3@rGO core–shell nanocomposites as anode for lithium ion batteries

The fine shape control of metal oxides nanocrystal and component are the key for the preparation of high-performance metal oxides/graphene nanocomposites. Herein, a simpler and practicable in situ one-pot approach was used to synthetize α-Fe2O3@reduced graphene oxide (rGO) core–shell nanocomposites. By controlling the amount of hydrazine hydrate and GO in reaction system, the shape of α-Fe2O3 nanocrystals can be tailored from spindle gradually to ellipsoid and quasi-sphere, and the thickness of enwrapped rGO can also be finely controlled. The as-prepared α-Fe2O3@rGO core–shell composites showed much better lithium storage performance than bare α-Fe2O3 nanocrystals. Owing to the core–shell structure and the high conductivity and stability of rGO nanosheet, the quasi-sphere-α-Fe2O3@rGO composites delivered a high reversible specific capacity up to 971 mAh g−1 at the current density of 0.2 A g−1, retaining 530 mA h g−1 at 2 A g−1 and 361 mA h g−1 at 5 A g−1 after 800 cycles with only 0.05% decay per-cycle. Moreover, the facile approach can provide a new strategy for the fabrication of other shape-size dependent, functional, and multicomponent graphene-based composites.

Removal of Heavy Metals from Wastewater using α-Fe2O3 Nanocrystals

In this work, α-Fe2O3 nanocrystals are synthesized by co-precipitation method and used as adsorbent to remove Cr6+, Cd2+, and Pb2+ from wastewater at room temperature. The prepared sample is evaluated by XRD, BET surface area, and FESEM for structural and morphological characteristics. XRD patterns confirm the formation of a pure hematite structure of average particle size of ~ 40 nm, which is further supported by the FESEM images of the nanocrystals. The nanocrystals are found to have BET specific surface area of ~ 39.18 m2 g−1. Adsorption experiments are carried out for the different values of pH of the solutions, contact time, and initial concentration of metal ions. High efficiency Cr6+, Cd2+, and Pb2+ removal occur at pH 3, 7, and 5.5, respectively. Equilibrium study reveals that the heavy metal ion adsorption of the α-Fe2O3 nanocrystals followed Langmuir and Freundlich isotherm models. The Cr6+, Cd2+, and Pb2+ adsorption equilibrium data are best fitted to the Langmuir model. The maximum adsorption capacities of α-Fe2O3 nanocrystals related to Cr6+, Cd2+, and Pb2+ are found to be 15.15, 11.63, and 20 mg g−1, respectively. These results clearly suggest that the synthesized α-Fe2O3 nanocrystals can be considered as potential nano-adsorbents for future environmental and health related applications.

Morphology-Controlled Synthesis of α–Fe2O3 Nanocrystals Impregnated on g-C3N4–SO3H with Ultrafast Charge Separation for Photoreduction of Cr (VI) Under Visible Light

Surface functionalization and shape modifications are the key strategies being utilized to overcome the limitations of semiconductors in advanced oxidation processes (AOP). Herein, the uniform α-Fe2O3 nanocrystals (α-Fe2O3–NCs) were effectively synthesized via a simple solvothermal route. Meanwhile, the sulfonic acid functionalization (SAF) and the impregnation of α-Fe2O3–NCs on g-C3N4 (α-Fe2O3–NCs@CN-SAF) were achieved through complete solvent evaporation technique. The surface functionalization of the sulfonic acid group on g-C3N4 accelerates the faster migration of electrons to the surface owing to robust electronegativity. The incorporation of α-Fe2O3–NCs with CN-SAF significantly enhances the optoelectronic properties, ultrafast spatial charge separation, and rapid charge transportation. The α-Fe2O3-HPs@CN-SAF and α-Fe2O3-NPs@CN-SAF nanocomposites attained 97.41% and 93.64% of Cr (VI) photoreduction in 10 min, respectively. The photocatalytic efficiency of α-Fe2O3–NCs@CN-SAF nanocomposite is 2.4 and 2.1 times higher than that of pure g-C3N4 and α-Fe2O3, respectively. Besides, the XPS, PEC and recycling experiments confirm the excellent photo-induced charge separation via Z-scheme heterostructure and cyclic stability of α-Fe2O3–NCs@CN-SAF nanocomposites.