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Flexible supercapacitors (SCs) are pivotal in the development of wearable and portable electronic devices because of their exceptional power density, high charge/discharge rates, extended cycle life, lightweight, and flexibility. Graphene (G)-based macroscopic materials, such as one-dimensional fibers, two-dimensional films, and three-dimensional aerogels, exhibit a large specific surface area, low mass, excellent flexibility, and high conductivity. These properties make them highly suitable for use as flexible electrode materials in SCs. However, the low energy density of G-based materials hinders their application in certain fields. Iron oxide (Fe 2 O 3) has garnered considerable attention as a negative electrode material because of its low cost, high theoretical capacity, and environmentally friendly nature. However, its practical application is limited because of its poor cycling stability, easy agglomeration, and low electrical conductivity. The combination of G with Fe 2 O 3 to form a composite material not only addresses the issues of volume change and agglomeration associated with Fe 2 O 3 , but also establishes a robust conductive network that improves the electrochemical performance of composite electrodes. Therefore, the construction of SCs using Fe 2 O 3 /G composite electrodes has gained considerable research attention in recent years. We present a comprehensive review of the recent progress in the design of Fe 2 O 3 /G composites as electrode materials for flexible SCs. In addition, we discuss the current challenges and future prospects associated with the use of Fe 2 O 3 /G composites in flexible SCs. [Display omitted] • Recent progress in the design of iron oxide/graphene composites as electrode materials for flexible SCs is reviewed. • The fabrication methods are discussed in depth to provide insight into various development strategies. • The design strategies of iron oxide/graphene composites with different dimensions were comprehensively discussed. • Challenges in iron oxide/graphene composites-based flexible supercapacitors development were described. [ABSTRACT FROM AUTHOR]

We here couple Nb 2 O 5 with Fe 2 O 3 to form visible-light active heterojunctions. The formed heterojunctions are responsive to visible light, and more importantly, photoactive for the mineralization of refractory organic compounds upon exposure to visible light. The sensitizer, Fe 2 O 3 , is found to govern the photocatalytic activity of the heterojunction. Therefore, the local structure of the sensitizer is investigated in-depth with X-ray absorption spectroscopy, including X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS). Results show that the local structure of Fe 2 O 3 is generally insensitive to the Fe 2 O 3 loading amount, as confirmed by EXAFS. The lengths of the Fe–O coordination and Fe–Fe coordination in the heterojunctions are 1.93 and 2.92 Å, respectively, which are shorter than those in bulk Fe 2 O 3. At a Fe 2 O 3 loading amount that is higher than the optimum value, trace amounts of isolated Fe 2 O 3 and bulk Fe 2 O 3 are likely formed at the heterojunction. This is unfavorable for electron-hole separation, and hence, detrimental to the photocatalytic activity. Image 1 • Heterojunctions composed of Nb 2 O 5 as host and Fe 2 O 3 as sensitizer are prepared. • The heterojunctions are visible light active for photomineralization of organics. • Local structure of the sensitizer, Fe 2 O 3 , is examined in-depth by XANES and EXAFS. • Visible light photoactivity of the heterojunctions is proposed based on light-induced IR. [ABSTRACT FROM AUTHOR]

Design of a multifunctional magnetic bionanosystem has become increasingly important towards advancing the future of clinical medicine. While hollow iron oxide nanoparticles with enhanced surface areas allow for more drug molecules to be attached to the particles, their relatively low saturation magnetization (M S) hinders their practicality in medicinal applications such as drug delivery and hyperthermia therapy. We demonstrate that this limitation can be overcome by utilizing 1D magnetic nanotubes that possess both enhanced surface areas and high M S. In this study, highly crystalline, tunable aspect ratio Fe 3 O 4 nanotubes have been successfully synthesized using a hydrothermal method. Magnetic measurements showed a clear Verwey transition (∼120 K) and high M S (∼75 emu/g) at 300 K, confirming the high quality of the synthesized Fe 3 O 4 nanotubes. Calorimetric experiments on randomly dispersed Fe 3 O 4 nanotubes in water with concentration of 1 mg/mL showed a large Specific Absorption Rate (SAR) value of 400 W/g for an AC magnetic field of 800 Oe, which increased to 500 W/g when the nanotubes were aligned parallel to the DC magnetic field and suspended in a 2% agar solution. Our study shows the possibility of using the Fe 3 O 4 nanotubes as a highly effective multifunctional nanoscale tool for targeted hyperthermia and on-demand drug delivery. • Hydrothermal synthesis of highly crystalline, tunable aspect ratio Fe 3 O 4 nanotubes. • Systematic study of the growth mechanism of the nanotubes. • The presence of Verwey transition and high M S (75 emu/g) at 300 K. • Nanotubes exhibited large SAR value compared to their hollow counterparts. • Dual-purpose applications in hyperthermia and on-demand drug delivery. [ABSTRACT FROM AUTHOR]

We have successfully introduced sugar alcohol (mannitol) onto the surface of iron oxide magnetic nanoparticles and investigated its role on their colloidal stabilization. The mannitol functionalized magnetic nanoparticles (MMNPs) were prepared through co-precipitation of Fe +2 and Fe 3+ ions in basic medium under N 2 atmosphere followed by in-situ coating of D-mannitol. The formation of iron oxide nanoparticles is evident from XRD and TEM analysis. The coating of nanoparticles with mannitol is analyzed by FTIR, TGA, DLS and zeta-potential measurements. It has been observed that the presence of mannitol on the surface of nanoparticles strongly affect their surface potential and colloidal stability. They show room temperature superparamagnetism with optimal magnetization of 60.5 emu/g at 20 kOe and protein resistant behaviour in physiological medium. These MMNPs were employed as drug delivery carrier using anticancer drug, doxorubicin hydrochloride (DOX). The drug molecules were loaded onto the surface of nanoparticles through electrostatic interactions between positively charged DOX and negatively charged MMNPs. A loading efficiency of 60% has been observed at DOX to MMNPs ratio (w/w) of 1:10 and the loaded drug showed pH dependent sustained release characteristics. Further, MMNPs exhibited good self-heating ability under applied AC magnetic field, thus they can be used as efficient heating source for hyperthermia therapy. [ABSTRACT FROM AUTHOR]

Iron oxide, as a promising anode material, has environmental friendliness, high theoretical capacitance, and a wide voltage window. Cobalt-doped iron oxide was loaded on flexible carbon cloth (Co-Fe 2 O 3 @CC) via hydrothermal reaction. Cobalt doping changes the iron oxide's crystal structure and improves the conductivity of the iron oxide. At the same time, it also increases the oxidation state of iron oxide and improves the pseudocapacitance of the electrode material. The reaction conditions were controlled to prepare iron oxide nano-spheres having porous morphology. The porous structure increases the area where the electrode material is reacted. The area-specific capacitance of the Co-Fe 2 O 3 @CC electrode material is 315.6 mF cm−2, which is 137.2% higher than that of pure Fe 2 O 3 @CC(133 mF cm−2). The capacitance is unchanged before and after 200 times of 90° bending. The voltage window of assembled Co-Fe 2 O 3 @CC//Ni-MnO 2 @CC asymmetric supercapacitors is 0–2 V. The energy density is 0.96 mWh cm−3 and the power density is 28.6 mW cm−3, which has excellent electrochemical performance. After 4000 cycles at a current density of 10 mA cm−2, the capacitance is maintained at 85%. Flexible asymmetric supercapacitors have potential applications in the field of flexible wearables. [Display omitted] • Cobalt was doped into Fe 2 O 3 @CC electrode material (Co-Fe 2 O 3 @CC) via hydrothermal reaction. • Co-Fe 2 O 3 formed nanospheres with nanopores inside. • Co-Fe 2 O 3 @CC electrode material had large area capacitance and good flexibility. • Flexible asymmetric supercapacitors had large area specific capacitance and excellent energy density. [ABSTRACT FROM AUTHOR]

• Oxygen partial pressure influences the crystallization of magnetite by LFZ growth. • Different crystal orientations of iron phases determined by growth atmospheres. • Fibers present a conductor core (Fe 3 O 4) and an insulated shell (Fe 2 O 3) structure. • Electrical conductivity is more influence due to grain boundaries of hematite. The control of the oxidation state represents an important challenge for materials engineering. It is fairly known that iron oxide can be present in several oxidation states each one with unique physical and chemical properties. In the present work the effects of the different oxygen partial pressure on the growth of Fe 3 O 4 fibers, using hematite (Fe 2 O 3) as a precursor material was studied. The fibers were grown by the Laser Floating Zone (LFZ) method at a constant pulling rate (100 mm/h) under different atmospheres (air, vacuum, argon and nitrogen). The structure and morphology of the as-grown fibers were studied by X-ray diffraction, SEM/EDS/EBSD and optical microscopy. The fibers show a core/shell structure, where Fe 3 O 4 is the core and Fe 2 O 3 the shell, putting in evidence that the partial pressure of oxygen is a crucial parameter to control the thickness and grains morphology of the shell. Low oxygen partial pressure increases the width of the Fe 2 O 3 insulating phase shell. The electrical conductivity, of the samples grown under an atmosphere with low oxygen partial pressure, is improved due to the morphology of the grains in the shell. However, no significant changes in the magnetization measurements were detected. From the results, we can conclude that applying an atmosphere during the LFZ growth allows tunning the transport properties envisaging electrical applications of the as-grown material. [ABSTRACT FROM AUTHOR]

• Surface-modified carbon foam (SMCF) was obtained by carbothermal reaction of FeSO 4. • The carbothermal reaction greatly influences the microstructures of carbon foams. • Resulting Fe 2 O 3 particles were embedded into the honeycomb-like surface of SMCF. • High N, O and S contents are beneficial to the electrochemical performance. • The SMCF-1000 has relatively high specific capacitance and excellent cyclability. [Display omitted] This work developed novel surface-modified carbon foams (SMCFs) with high heteroatom contents and a certain amount of iron oxide particles via the carbothermal reduction reaction between iron oxide and the cyanate resin-based carbon foam. The effects of carbothermal reduction of iron oxide on microstructures and electrochemical properties of the carbon foams have been studied systematically using TG, XRD, FESEM, BET, and XPS. Results show that the carbothermal reduction greatly influences the microstructures of carbon foams when the temperature is higher than 600 °C. The generated iron oxide particles were embedded into the surface of carbon foams. With the increase of temperature, the surface became porous and rough with a certain graphitic structure. When the temperature arrives at 1000 °C, the as-prepared SMCF-1000 has a highest specific capacitance of 212.42 F g−1 at 1 A g−1, and the specific capacitance maintains 107% of the initial value after 10,000 charge-discharge cycles. In addition, the SMCF-1000 exhibits a maximum compressive strength of 2.52 MPa, which is expected to be a novel three-dimensional self-supporting electrode material. [ABSTRACT FROM AUTHOR]

Abstract: Thin films of hematite (α-Fe2O3) were deposited by the reactive evaporation of iron in an oxygen atmosphere. The films were deposited on unheated and heated substrates. Structural analysis, using X-ray diffraction, verified the phase of the films and revealed that the films had a polycrystalline structure composed of nano-crystallites. Atomic force microscopy indicated that the films had smooth surfaces, with a lateral grain size that increased substantially by substrate heating. The optical properties of the films, including the refractive index, extinction coefficient, absorption coefficient, and band gap were determined from spectrophotometric measurements. In the wavelength range 600–2000nm, the refractive indices were 1.7–2.2 for the films deposited on unheated substrates, and 2.3–2.9 for the films deposited on heated substrates. The films had direct and indirect band gaps. The direct band gap was 2.18eV, and the indirect band gap was 1.82–1.96eV, depending on the substrate temperature. [Copyright &y& Elsevier]

Abstract: Fe2O3 thin films have been prepared by novel chemical successive ionic layer adsorption and reaction (SILAR) method. Further these films were characterized for their structural, morphological and optical properties by means of X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectrum, scanning electron microscopy (SEM), wettability test and optical absorption studies. The XRD pattern showed that the Fe2O3 films exhibit amorphous in nature. Formation of iron oxide compound was confirmed from FTIR studies. The optical absorption showed existence of direct optical band gap of energy 2.2eV. Fe2O3 film surface showed superhydrophilic nature with water contact angle less than 10°. The supercapacitive properties of Fe2O3 thin film investigated in 1M NaOH electrolyte showed supercapacitance of 178Fg−1 at scan rate 5mV/s. [ABSTRACT FROM AUTHOR]

• Halloysite nanotubes were fixed on the surface of graphene sheets or embedded between graphene nanosheets, forming a three-dimensional network structure, which reduced the agglomeration between graphene sheets. • The hybrid of halloysite nanotube and graphene sheet increased the graphene's specific surface area and realized a three-dimensional network porous structure. • The synergistic effect of iron oxide and polyaniline made the composites have larger capacitance, the capacitance reaches 557.6 Fg−1. • After 1000 cycles, the specific capacitance of composites remained 81%. Great progress had been made in the synthesis and application of graphene, graphene oxide (GO) aerogels, and reduced graphene oxide (rGO). However, most of the reported graphene hybrid aerogels reduced the mechanical properties of the obtained materials because of their wide pore size distribution, which limited the recycling of aerogels. Therefore, it was urgent to prepare graphene hybrid aerogels with uniform mesopores or micropores to enhance the structural stability of aerogels. Meanwhile, the mechanical and electrical properties of graphene hybrid aerogels could be further improved. In this paper, halloysite/graphene-polyaniline three-dimensional hybrid aerogel loaded with Fe 3 O 4 (HGA-PANI) was fabricated. The microstructure, mechanical properties, and electrochemical properties of HGA-PANI were characterized by scanning electron microscope (SEM), X-ray Photoelectron Spectroscopy (XPS), N 2 adsorption-desorption tests, universal material testing machine, electrochemical workstation, and so on. Halloysite nanotubes (HNT) were fixed on the surface of graphene sheets or intercalated between graphene nanosheets. The three-dimensional network structure was formed, which reduced the agglomeration between graphene sheets. The hybrid of HNT and graphene sheet increased the graphene's specific surface area and constructed a three-dimensional network porous structure. Through Cyclic voltammetry (CV), Galvanostatic charge-discharge (GCD), Electrochemical impedance spectroscopy (EIS), and cycle stability tests, HGA-PANI had acceptable electrical properties, large capacitance, thin internal resistance, and amazing cyclical stability. [ABSTRACT FROM AUTHOR]

Iron oxide (Fe 2 O 3) is an intriguing anode material of electrochemical energy storage systems such as rechargeable batteries. The rational design of its nanostructure at mild condition to cope with the issues of low reversible capacity and sluggish kinetics is required. Herein, an efficient, facile, and potentially large-scale synthesis approach using the precursor of laminated iron oxychloride@polyaniline heterostructure and mild annealing is developed, yielding unique Fe 2 O 3 @carbon nanocomposites with hematite nanoparticles (∼20 nm) that embedded in nitrogen/chlorine-doped carbon nanodisk (N/Cl–C). Given the benefit of abundant active sites, good chemical contact between carbon and Fe 2 O 3 , and robust composite structure, the as-prepared Fe 2 O 3 @N/Cl–C anode material delivers competent lithium-ion storage properties, including high reversible capacity of 1010 mAh g−1 (based on the mass of the as-prepared nanocomposite) at 0.1 A g−1, decent rate performance upon a rigorous current change, and superior cycling stability with 955 mAh g−1 after 180 cycles as well as a sustained Coulombic efficiency of about 99%. This structural design may provide a new avenue for achieving efficient iron oxide-based materials in chemical and electrochemical applications such as catalysis, lithium-ion batteries, and sodium-ion batteries. Image 1 • Developing a novel, facile and scalable synthesis approach for hematite/carbon nanocomposites. • N/Cl-doped carbon nanodisk-encapsulated hematite anode shows robust structure for Li-ion storage. • High reversible capacity, decent rate capability and superior cycling performance are achieved. [ABSTRACT FROM AUTHOR]