Enhanced photocatalytic decolorization of methyl orange by gallium-doped α-Fe2O3

Gallium (Ga)-doped hematite (α-Fe₂O₃) with different molar ratios of Ga/Fe (1%, 2%, 3% and 4%) was prepared by a facile parallel flow co-precipitation method. The photocatalysts prepared were characterized by the Brunauer–Emmett–Teller method, X-ray diffraction, UV/vis diffuse reflectance spectroscopy, and scanning electron microscope. The photo-generated charges separation efficiency of different photocatalysts was investigated using benzoquinone as scavenger. The formation rate of OH radicals produced during the photocatalytic reaction process was studied by a terephthalic acid photoluminescence probing technique. Doping Ga³⁺ into α-Fe₂O₃ increases the specific surface area and the separation efficiency of photo-induced charges. The catalytic activity of the photocatalysts for decolorization of methyl orange aqueous solution was investigated. The results show that α-Fe₂O₃ doped with 3% Ga possesses the best photocatalytic activity. The underlying mechanism is suggested.     

Hydrothermal synthesis and characterization of α-Fe2O3 nanoparticles

Iron oxide (Fe₂O₃) nanoparticles were synthesized by a simple hydrothermal synthesis method using only Fe(NO₃)₃·9H₂O and NH₃·H₂O as raw materials. The effect of reaction temperature and time on the crystalline phase and morphology of Fe₂O₃ products was investigated. The products were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and Fourier transform infrared (FTIR) spectroscopy. The XRD and TEM results show that reaction temperature and time play an important role in the formation of the crystalline phase and morphology of the products. With increasing reaction temperature and time, the diffraction peaks of α-Fe₂O₃ become stronger and sharper, and the morphologies of the samples have an obvious change from floccules to nanoparticles. FTIR peaks show that α-Fe₂O₃ nanoparticles have about a 25 cm^?1 shift to higher frequency compared with those of α-Fe₂O₃ with other morphologies.     

Dzyaloshinskii-Moriya Torque-Driven Resonance in Antiferromagnetic α-Fe2O3

The high-frequency optical mode of α-Fe₂O₃ is examined, and it is reported that Dzyaloshinskii−Moriya (DM) interaction generates a new type of torque on the magnetic resonance. Using a continuous-wave terahertz interferometer, the optical mode spectra is measured, where the asymmetric absorption with a large amplitude and broad linewidth is observed near the magnetic transition point, Morin temperature (T_M ≈ 254.3 K). Based on the spin wave model, the spectral anomaly is attributed to the DM interaction-induced torque, enabling to extract the strength of DM interaction field of 4 T. This work opens a new avenue to characterize the spin resonance behaviors at an antiferromagnetic singular point for next-generation and high-frequency spin-based information technologies.     

Study of sensitivity and selectivity of α-Fe2O3 thin films for different toxic gases and alcohols

This paper presents a detailed study on the sensitivity and selectivity of α-Fe₂O₃ thin films produced by deposition of Fe and post-deposition annealed at two temperatures of 600 °C and 800 °C with flow of oxygen for application as a sensor for toxic gases including CO, H₂S, NH₃ and NO₂ and alcohols such as C₃H₇OH, CH₃OH, and C₂H₅OH. The crystallographic structure of the samples was studied by X-ray diffraction (XRD) method while an atomic force microscope (AFM) was employed for surface morphology investigation. The electrical response of the films was measured while they were exposed to various toxic gases and alcohols in the temperature range of 50–300 °C. The sample annealed at higher temperature showed higher response for different gases and alcohols tested in this work which can be due to the higher resistance of this sample. Results also indicated that the α-Fe₂O₃ thin films show higher selectivity to NO₂ gas relative to the other gases and alcohols while the best sensitivity is obtained at 200 °C. The α-Fe₂O₃ thin film post-deposition annealed at 800 °C also showed a good stability and reproducibility and a detection limit of 10 ppm for NO₂ gas at the operating temperature of 200 °C.     

Carbon and silica interlayer influence for the photocatalytic performances of spindle-like α-Fe2O3/Bi2O3 p–n heterostructures

The p–n heterojunction is an effective structure to suppress the recombination of photogenerated charge carriers due to the built-in internal electric field. Herein, we successfully synthesize a spindle-like α-Fe₂O₃/Bi₂O₃ core–shell heterostructure, in which α-Fe₂O₃ is an n-type semiconductor and Bi₂O₃ is a p-type semiconductor. In comparison with pure α-Fe₂O₃ seeds, the α-Fe₂O₃/Bi₂O₃ p–n heterojunction photocatalyst exhibits tremendous photocatalytic performance on the degradation of Rhodamine B (RhB) under illumination of visible light. In addition, we insert an interlayer between p–n heterostructure, similar to p–i–n heterostructure. The silicon oxide and carbon are selected as the interlayer due to its different conductivity. The as-obtained α-Fe₂O₃/C/Bi₂O₃ exhibits higher degradation rate than α-Fe₂O₃/SiO₂/Bi₂O₃. The reason is attributed to the mesoporous structure of carbon layer and its high conductivity so that the photogenerated electrons can be easily transferred from the conduction band of α-Fe₂O₃ to the conduction band of Bi₂O₃ thereby promoting an effective separation of photogenerated electrons and holes. However, the introduction of interlayer reduces the photocatalytic activity due to the alteration of internal built-in electric field in the heterojunction. We envision that these results have potential applications for designing the heterostructural photocatalysts.     

Sn-doped α-Fe2O3 patulous nanotubes for high performance formaldehyde sensing

SnO₂-doped α-Fe₂O₃ patulous microtubes (SFPNs) are synthesized by an electrospinning method. The as-synthesized materials are characterized by scanning electron microscope, X-ray powder diffraction and energy dispersive spectroscopy. The gas sensing results show SFPNs possess an excellent sensing property to formaldehyde. The response value of SFPNs gas sensor to 50 ppm formaldehyde is 25.4 at 220 ℃. The lowest detecting limit of 1 ppm formaldehyde is 3.2. Response and recovery characteristic curves of SFPNs gas sensors to 1, 2, 3, 5, 5, 3, 2 and 1 ppm formaldehyde are also tested. The results show a good reversibility and repeatability of SFPNs gas sensors. The sensor exhibits a high selectivity in the presence of acetone, ethanol, toluene, ammonia, hydrogen, carbon monoxide and butane. Moreover, the sensor has a good long-time stability.     

Optical properties and photoinduced superparamagnetism of γ-Fe2O3 nanoparticles formed in dendrimer

We are presenting the joint investigation of the optical and photoinduced superparamagnetic properties of a single-domain γ-Fe₂O₃ nanoparticles (NPs) formed in poly(propylene imine) (PPI)-dendrimer. The optical absorption studies indicated direct allowed transition with the band gap (4.5 eV), which is "blue"-shift with respect to the value of the bulk material. The influence of pulsed laser irradiation on the superparamagnetic properties of γ-Fe₂O₃ NPs was studied by Electron paramagnetic resonance (EPR) spectroscopy. It has been shown that irradiation of the sample in vacuo and cooled in zero magnetic field to 6.9 K leads to the appearance of a new EPR signal, which decays immediately after the irradiation is stopped. We suppose that the generation of conduction band electrons by irradiation into the band gap of the γ-Fe₂O₃ changes the superparamagnetic properties of NPs.     

Ni3N–CeO2 Heterostructure Bifunctional Catalysts for Electrochemical Water Splitting

Developing low-cost and high-efficient bifunctional catalysts for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is greatly significant for water electrolysis. Here, Ni₃N-CeO₂/NF heterostructure is synthesized on the nickel foam, and it exhibits excellent HER and OER performance. As a result, the water electrolyzer based on Ni₃N-CeO₂/NF bifunctional catalyst only needs 1.515 V@10 mA cm⁻², significantly better than that of Pt/C||IrO₂ catalysts. In situ characterizations unveil that CeO₂ plays completely different roles in HER and OER processes. In situ infrared spectroscopy and density functional theory calculations indicate that the introduction of CeO₂ can optimizes the structure of interface water, and the synergistic effect of Ni₃N and CeO₂ improve the HER activity significantly, while the in situ Raman spectra reveal that CeO₂ accelerates the reconstruction of O_V (oxygen vacancy)-rich NiOOH for boosting OER. This study clearly unlocks the different catalytic mechanisms of CeO₂ for boosting the HER and OER activity of Ni₃N for water splitting, which provides the useful guidance for designing the high-performance bifunctional catalysts for water splitting.     

Enhanced formaldehyde-sensing properties of mixed Fe2O3–In2O3 nanotubes

Pure In₂O₃ and mixed Fe₂O₃–In₂O₃ nanotubes were prepared by simple electrospinning and subsequent calcination. The as-prepared nanotubes were characterized by scanning electron microscopy, powder X-ray diffraction, and energy-dispersive X-ray spectrometry. Gas sensors were fabricated to investigate the gas-sensing properties of In₂O₃ and Fe₂O₃–In₂O₃ nanotubes. Compared to pure In₂O₃, Fe₂O₃–In₂O₃ nanotubes exhibited better gas-sensing properties for formaldehyde at 250 °C. The response of the Fe₂O₃–In₂O₃ nanotube gas sensor to 100 ppm formaldehyde was approximately 33, which is approximately double the response of the pure In₂O₃ nanotube gas sensor. In both cases the response time was ~5 s and the recovery time was ~25 s.     

Linker Defects in Metal–Organic Frameworks for the Construction of Interfacial Dual Metal Sites with High Oxygen Evolution Activity

Designing efficient electrocatalysts based on metal–organic framework (MOF) nanosheet arrays (MOFNAs) with controlled active heterointerface for the oxygen evolution reaction (OER) is greatly desired yet challenging. Herein, a facile strategy for the synthesis of MOF-based nanosheet arrays (γ-FeOOH/Ni-MOFNA) is developed with abundant heterointerfaces between Ni-MOF and γ-FeOOH nanosheets by introducing linker defects to the former. The experimental and theoretical results show the key role of linker defects in inducing the growth of secondary γ-FeOOH nanosheets onto the surface of Ni-MOFNAs, which further leads to the formation of interfacial Ni/Fe dual sites with high oxygen evolution activity. Notably, the resulting γ-FeOOH/Ni-MOFNA exhibits excellent OER performance with low overpotentials of 193 and 222 mV at 10 and 100 mA cm⁻², respectively. Furthermore, the study of the structure–performance relationship of MOF-based heterostructures reveals that Ni sites at the interface of the γ-FeOOH/Ni-MOFNA have higher activity than those at the interface of NiFe layered double hydroxide and Ni-MOFNA. This study provides a new prospect on heterostructured electrocatalysts with highly active sites for enhanced OER.     

Unraveling the Synergistic Mechanism of Bi-Functional Nickel–Iron Phosphides Catalysts for Overall Water Splitting

Ni–Fe bimetallic electrocatalysts are expected to replace existing precious metal catalysts for water splitting and achieve industrial applications due to their high intrinsic activity and low cost. However, the mechanism by which Ni and Fe species synergistically enhance catalytic activity remains obscure, which still needs further in-depth study. In this study, a highly active bi-functional electrocatalyst of Ni₂P/FeP heterostructures is constructed on Fe foam (Ni₂P/FeP-FF), clearly illustrating the effect of Ni on Fe species for oxygen evolution reaction (OER) and revealing the true catalytic active phase for hydrogen evolution reaction (HER). The Ni₂P/FeP-FF only needs overpotentials of 217 and 42 mV to reach 10 mA cm⁻² for OER and HER, respectively, exhibiting superior bi-functional activity for overall water splitting. The Ni can elevate the strength of Fe O on Ni₂P/FeP-FF surface and promote the formation of high-valence FeOOH phase during OER, thus enhancing OER performance. Based on first-principles calculations and Raman characterizations, the Ni₂P/Ni(OH)₂ heterojunction evolved from Ni₂P/FeP is identified as the real high active phase for HER. This study not only builds a near-commercial bifunctional electrocatalyst for overall water splitting, but also provides a deep insight for synergistic catalytic mechanism of Ni and Fe species.     

Innovative impregnation process for production of γ-Fe2O3–activated carbon nanocomposite

An immobilized superparamagnetic nanocomposite comprising γ-Fe₂O₃ and activated carbon was synthesized via a facile thermal decomposition route. To prepare the magnetically functionalized nanocomposite, treated activated carbon (TAC) loaded with lepidocrocite (γ-FeOOH) nanoparticles (MAC-1) was first produced via a wet chemical method. Then magnetic activated carbon (AC/γ-Fe₂O₃, MAC-2) was fabricated by thermal decomposition of MAC-1 at 250 °C under argon gas for 1 h. Characterization analyses confirmed that superparamagnetic spherical maghemite nanoparticles of 21±2 nm in size were homogeneously dispersed on the TAC. The specific surface area was 643.8 m² g⁻¹ for TAC, 289 m² g⁻¹ for MAC-1, and 303.5 m² g⁻¹ for MAC-2. The industrially friendly nanocomposite was applied as an adsorbent for pollutant removal from aqueous solution.     

Phase-Modulation of Iron/Nickel Phosphides Nanocrystals “Armored” with Porous P-Doped Carbon and Anchored on P-Doped Graphene Nanohybrids for Enhanced Overall Water Splitting

Transition metal phosphides (TMPs) nanostructures have emerged as important electroactive materials for energy storage and conversion. Nonetheless, the phase modulation of iron/nickel phosphides nanocrystals or related nanohybrids remains challenging, and their electrocatalytic overall water splitting (OWS) performances are not fully investigated. Here, the phase-controlled synthesis of iron/nickel phosphides nanocrystals “armored” with porous P-doped carbon (PC) and anchored on P-doped graphene (PG) nanohybrids, including FeP–Fe₂P@PC/PG, FeP–(Ni_xFe_1-x)₂P@PC/PG, (Ni_xFe_1-x)₂P@PC/PG, and Ni₂P@PC/PG, are realized by thermal conversion of predesigned supramolecular gels under Ar/H₂ atmosphere and tuning Fe/Ni ratio in gel precursors. Thanks to phase-modulation-induced increase of available catalytic active sites and optimization of surface/interface electronic structures, the resultant pure-phase (Ni_xFe_1-x)₂P@PC/PG exhibits the highest electrocatalytic activity for both hydrogen and oxygen evolution in alkaline media. Remarkably, using it as a bifunctional catalyst, the fabricated (Ni_xFe_1-x)₂P@PC/PG || (Ni_xFe_1-x)₂P@PC/PG electrolyzer needs exceptional low cell voltage (1.45 V) to reach 10 mA cm⁻² water-splitting current, outperforming its mixed phase and monometallic phosphides counterparts and recently reported bifunctional catalysts based devices, and Pt/C || IrO₂ electrolyzer. Also, such (Ni_xFe_1-x)₂P@PC/PG || (Ni_xFe_1-x)₂P@PC/PG device manifests outstanding durability for OWS. This work may shed light on optimizing TMPs nanostructures by combining phase-modulation and heteroatoms-doped carbon double-confinement strategies, and accelerate their applications in OWS or other renewable energy options.     

Direct thermal decomposition synthesis and characterization of hematite (α-Fe2O3) nanoparticles

Hematite (α-Fe₂O₃₎ nanoparticles were prepared via direct thermal decomposition method using γ-Fe₂O₃ as a wet chemically synthesized precursor. The precursor was calcinated in air at 500 °C. Samples were characterized by Thermogravimetric analysis (TGA), X-ray diffraction, Infrared, Scanning electron microscopy, Transmission electron microscopy (TEM) and Photon correlation spectroscopy (PCS). TEM and PCS analyses revealed that the average particle size of the α-Fe₂O₃ nanoparticles synthesized at 500 °C are about 18±2 nm and 50±3 nm for 1 h and 24±2 nm and 82±3 nm for 2 h, respectively. The difference in average particle size determined by PCS and TEM analysis is due to the electrostatic forces between particles, and their agglomeration in PCS analysis. Magnetic properties have been detected by a Vibrating sample magnetometry at room temperature. The α-Fe₂O₃ nanoparticles exhibited a weak ferromagnetic behavior at room temperature.     

Effect of Ultraviolet Radiation and Electric Field on the Conductivity of Structures Based on α- and ε-Ga2O3

Semiconductors - The effect of ultraviolet radiation and a strong electric field on the conductivity of structures based on two types of polymorphic gallium-oxide films is studied. Both types of...     

Effect of the Phase Composition and Local Crystal Structure on the Transport Properties of the ZrO2–Y2O3 and ZrO2–Gd2O3 Solid Solutions

Russian Microelectronics - The results of investigating the crystal structure, ionic conductivity, and local structure of the (ZrO2)1 –x(Gd2O3)x and (ZrO2)1 –x(Y2O3)x (x = 0.04, 0.08,...     

Atomic-Precision Tailoring of Au–Ag Core–Shell Composite Nanoparticles for Direct Electrochemical-Plasmonic Hydrogen Evolution in Water Splitting

Traditionally, bandgap materials are a prerequisite to photocatalysis since they can harness a reasonable range of the solar spectrum. However, the high impedance across the bandgap and the low concentration of intrinsic charge carriers have limited their energy conversion. By contrast, metallic nanoparticles possess a sea of free electrons that can effectively promote the transition to the excited state for reactions. Here, an atomic layer of a bimetallic concoction of silver–gold shells is precisely fabricated onto an Au core via a sonochemical dispersion approach to form a core–shell of Au–Ag that exploits the wide availability of excited states of Ag while maintaining an efficient localized surface plasmon resonance (LSPR) of Au. Catalytic results demonstrate that this mix of Ag and Au can convert solar energy to hydrogen at high efficiency with an increase of 112.5% at an optimized potential of −0.5 V when compared to light-off conditions under the electrochemical LSPR. This outperforms the commercial Pt catalysts by 62.1% with a hydrogen production rate of 1870 µmol g⁻¹ h⁻¹ at room temperature. This study opens a new route for tuning the range of light capture of hydrogen evolution reaction catalysts using fabricated core–shell material through the combination of LSPR with electrochemical means.