Regulation of the Fe/Ni ratio on the morphology of FexNiyO4 and the performance of nitrate reduction in ammonia synthesis

The combination of theoretical calculations and experimental synthesis provides valuable insights into the performance of FexNiyO4 as a catalyst for ammonia (NH3) synthesis through the electrocatalytic nitrate reduction reaction (eNO3-RR). Here, an observation of a volcano-shaped trend in the theoretical calculations reveals that the catalytic activity of FexNiyO4 for NH3 synthesis varies with the Fe/Ni ratio. The subsequent experimental syntheses of FexNiyO4 with different Fe/Ni ratios validate this trend and demonstrate the morphological changes associated with the varying Fe/Ni ratios. The evolution of the FexNiyO4 morphology from nanosheets to sea urchin-like structures, nanowires and nanoflowers composed of rotated nanosheets as the Fe/Ni ratio increases further supports the influence of the composition on the resulting morphology. This morphological diversity can be attributed to the specific growth conditions and self-assembly processes involved in the synthesis. The correlation between the Fe/Ni ratio, morphology and NH3 yield reinforces the theoretical calculations. The observed volcanic trend in the NH3 yield, consistent with the theoretical predictions, indicates that there is an optimal Fe/Ni ratio (Fe2NiO4) with the highest NH3 yield of 12.51 mg h-1 cm-2 at -1.1 V. The excellent Faradaic efficiency of 95.97 % in neutral solution further highlights the suitability of Fe2NiO4 as a catalyst for NH3 synthesis through eNO3-RR. Moreover, the remarkable stability of FexNiyO4, regardless of the Fe/Ni ratio, is an important finding. The consistent performance of FexNiyO4 indicates its potential for long-term and practical applications in NH3 synthesis. Furthermore, the observed morphological changes, volcano-shaped trend in the NH3 yield and remarkable stability of FexNiyO4 highlight its potential as a promising catalyst.

Metal-organic framework-derived metal oxides for resistive gas sensing: a review

Gas sensors with exceptional sensitivity and selectivity are vital in the real-time surveillance of noxious and harmful gases. Despite this, traditional gas sensing materials still face a number of challenges, such as poor selectivity, insufficient detection limits, and short lifespan. Metal oxides, which are derived from metal-organic framework materials (MOFs), have been widely used in the field of gas sensors because they have a high surface area and large pore volume. Incorporating metal oxides derived from MOFs into gas sensors can improve their sensitivity and selectivity, thus opening up new possibilities for the development of innovative, high-performance gas sensors. This article examines the gas sensing process of metal oxide semiconductors (MOS), evaluates the advances made in the research of different structures of MOF-derived metal oxides in resistive gas sensors, and provides information on their potential applications and future advancements.

Recent Progress in Spinel Ferrite (MFe2O4) Chemiresistive Based Gas Sensors

Gas-sensing technology has gained significant attention in recent years due to the increasing concern for environmental safety and human health caused by reactive gases. In particular, spinel ferrite (MFe2O4), a metal oxide semiconductor with a spinel structure, has emerged as a promising material for gas-sensing applications. This review article aims to provide an overview of the latest developments in spinel-ferrite-based gas sensors. It begins by discussing the gas-sensing mechanism of spinel ferrite sensors, which involves the interaction between the target gas molecules and the surface of the sensor material. The unique properties of spinel ferrite, such as its high surface area, tunable bandgap, and excellent stability, contribute to its gas-sensing capabilities. The article then delves into recent advancements in gas sensors based on spinel ferrite, focusing on various aspects such as microstructures, element doping, and heterostructure materials. The microstructure of spinel ferrite can be tailored to enhance the gas-sensing performance by controlling factors such as the grain size, porosity, and surface area. Element doping, such as incorporating transition metal ions, can further enhance the gas-sensing properties by modifying the electronic structure and surface chemistry of the sensor material. Additionally, the integration of spinel ferrite with other semiconductors in heterostructure configurations has shown potential for improving the selectivity and overall sensing performance. Furthermore, the article suggests that the combination of spinel ferrite and semiconductors can enhance the selectivity, stability, and sensing performance of gas sensors at room or low temperatures. This is particularly important for practical applications where real-time and accurate gas detection is crucial. In conclusion, this review highlights the potential of spinel-ferrite-based gas sensors and provides insights into the latest advancements in this field. The combination of spinel ferrite with other materials and the optimization of sensor parameters offer opportunities for the development of highly efficient and reliable gas-sensing devices for early detection and warning systems.

Electrospinning Derived NiO/NiFe2O4 Fiber-in-Tube Composite for Fast Triethylamine Detection under Different Humidity

Designing high-performance triethylamine gas sensors with the stable gas response and low resistance variation in air under a wide relative humidity range is expected for human health and environmental surveillance. Here, a novel porous NiO/NiFe₂O₄ fiber-in-tube nanostructure is prepared by the electrospinning process. The characterizations related to microstructure and surface morphology are carried out. Meanwhile, the gas sensing performance of the porous fiber-in-tube NiO/NiFe₂O₄ materials is evaluated and compared systematically. The results indicate that the introduction of NiO as the second component can not only reduce the baseline resistance of NiFe₂O₄ gas sensors dramatically but also optimize the gas sensing performance to a significant extent. Especially, the fabricated sensor based on the NiO/NiFe₂O₄ fiber-in-tube with a Ni/Fe molar ratio of 1.5 exhibits the best performance. The gas response while detecting 50 ppm triethylamine at 300 °C is about 3.6 times higher than that with Ni/Fe molar ratio of 0.5. Moreover, the response values become more stable, and the baseline resistance has a lower variation under a wide relative humidity range, demonstrating the excellent humidity resistance. These phenomena might be ascribed to the distinctive fiber-in-tube nanostructure as well as the heterojunction between NiFe₂O₄ and NiO.

A novel monoclinic metal oxide catalyst for oxygen evolution reaction in alkaline media

The main bottleneck of electrolytic water for hydrogen production in alkaline media is the oxygen evolution reaction (OER) involving four-electron transfer. Designing highly efficient OER catalysts is attractive to accelerate...

High-performance electrochemical nitrate reduction to ammonia under ambient conditions using NiFe2O4 nanosheet arrays

NiFe2O4/CC is a highly active electrocatalyst for the conversion of nitrate to ammonia under ambient conditions, achieving a remarkably high faradaic efficiency of 96.6% and a large yield of 10.3 mg h−1 cm−2 in 0.1 M PBS with 0.1 M NaNO3.

Efficient Photocatalytic Reduction of CO2 to CO Using NiFe2O4@N/C/SnO2 Derived from FeNi Metal-Organic Framework

Use of light is considered an effective approach to convert CO₂ into usable chemical energy. In the present study, an iron- and nickel-containing bimetallic metal-organic framework (MOF) was synthesized via a simple solvothermal route. SnO₂ was then composited with the said MOF, and the obtained material was calcined and annealed to fabricate a series of nanophotocatalysts. The annealed sample displayed superior photocatalytic activity to the calcined sample, possibly due to the carbon-nitrogen layer formed after annealing mediating the charge-transfer process. The results of photocatalytic experiments indicated that using [Ru(bpy)₃]Cl₂·6H₂O as a photosensitizer and triethanolamine (TEOA) and acetonitrile (MeCN) as sacrificial agents, the catalyst sample was annealed at 450 °C (NiFe₂O₄@N/C/SnO₂-450) to afford the highest CO yield from CO₂ (2057.41 μmol g^-1 h^-1). The increase in the photocatalytic ability of the nanocomposites is basically attributed to multiple synergistic effects between NiFe₂O₄ and SnO₂, which reduce the recombination probability of the photo-induced electrons and holes. Ultimately, a photocatalytic reaction mechanism is proposed for NiFe₂O₄@N/C/SnO₂ in the reduction of CO₂.

Surface Structure Engineering of Nanosheet-Assembled NiFe2O4 Fluffy Flowers for Gas Sensing

In this work, we present a strategy to improve the gas-sensing performance of NiFe₂O₄ via a controllable annealing Ni/Fe precursor to fluffy NiFe₂O₄ nanosheet flowers. X-ray diffraction (XRD), a scanning electron microscope (SEM), nitrogen adsorption–desorption measurements and X-ray photoelectron spectroscopy (XPS) were used to characterize the crystal structure, morphology, specific surface area and surface structure. The gas-sensing performance was tested and the results demonstrate that the response was strongly influenced by the specific surface area and surface structure. The resultant NiFe₂O₄ nanosheet flowers with a heating rate of 8 °C min⁻¹, which have a fluffier morphology and more oxygen vacancies in the surface, exhibited enhanced response and shortened response time toward ethanol. The easy approach facilitates the mass production of gas sensors based on bimetallic ferrites with high sensing performance via controlling the morphology and surface structure.

Four dual-functional luminescent Zn(ii)-MOFs based on 1,2,4,5-benzenetetracarboxylic acid with pyridylbenzimidazole ligands for detection of iron(iii) ions and acetylacetone

Four Zn-MOFs with different topological types were synthesized and characterized, MOFs 1–4 have excellent sensitivity, selectivity, recyclability and structural stabilities for detecting acac/Fe³⁺ in the naked eye range.

A novel dual-tasking hollow cube NiFe2O4-NiCo-LDH@rGO hierarchical material for high preformance supercapacitor and glucose sensor

Binary transition metal oxides as electroactive materials have continuously aroused grumous attention due to their high theoretical specific capacitance, high valtage window, and multiple oxidation states. However, the tiny specific surface area, poor conductivity and unsatisfactory cycle stability limit their practical application. Hence, a synthetic strategy is designed to fabricate a dual-tasking hollow cube nickel ferrite (NiFe₂O₄) - based composite (NiFe₂O₄-NiCo-LDH@rGO) with hierarchical structure. The composite is constructed by firstly preparing hollow NiFe₂O₄ from cube-like Ni - Fe bimetallic organic framework (NiFe-MOF), and then integrating nickel cobalt layered double hydroxide (NiCo-LDH) nanowires, together with reduced graphene oxide (rGO) via pyrolysis in conjuction with hydrothermal method. The NiFe₂O₄ possessing cubic hollow structure contributes to a huge accessible surface area, meanwhile alleviates large volume expansion/contraction effect, which facilitates suffcient permeation of the electrolyte and rapid ion/charge transport, and results in high cycling stability. The introduction of layered NiCo-LDH results in hierarchical structure and thus offers maximum contact areas with electrolyte, which heightens the specific capacitance of obtained composite and enhances the electro-catlytic activity towards oxidation of glucose. Furthermore, rGO layer greatly improves the electrical conductivity and ion diffusion/transport capability of composite. Benefiting from the unique structure and individual components of NiFe₂O₄-NiCo-LDH@rGO composite, the electrode delivers a high specific capacitance (750 C g^-1) and superb durability. Simultaneously, the asymmetrical device based on NiFe₂O₄-NiCo-LDH@rGO as positive electrode delivers remarkable energy density (50 Wh kg^-1). Moreover, NiFe₂O₄-NiCo-LDH@rGO exhibits good sensing performance with a sensitivity of 111.86 µA/µM cm^-2, the wide linear range of 3.500 × 10^-5 - 4.525 × 10^-3 M, and the detection limit of 12.94 × 10^-6 M with a signal to noise ratio of 3. Consequently, the NiFe₂O₄-NiCo-LDH@rGO could provide a prospective notion constructing bifunctional materials with hollow-cube hierarchical structure in the field of supercapacitors and electrochemical sensors.

Enhanced triethylamine sensing performance of metal–organic framework derived nest-type Fe-doped NiO nanostructure

The response of our Fe-doped NiO TEA sensor was about 21 times higher than that of the pure sensor. The quick response time and recovery time, good selectivity and stability, and enhanced gas sensing properties could be attributed to Fe-doping.

MOFs-Derived Porous NiFe2O4 Nano-Octahedrons with Hollow Interiors for an Excellent Toluene Gas Sensor

Toluene is extensively used in many industrial products, which needs to be effectively detected by sensitive gas sensors even at low-ppm-level concentrations. Here, NiFe2O4 nano-octahedrons were calcinated from NiFe-bimetallic metal-organic framework (MOFs) octahedrons synthesized by a facile refluxing method. The co-existence of p-Phthalic acid (PTA) and 3,3-diaminobenzidine (DAB) promotes the formation of smooth NiFe-bimetallic MOFs octahedrons. After subsequent thermal treatment, a big weight loss (about 85%) transformed NiFe2O4 nanoparticles (30 nm) into NiFe2O4 porous nano-octahedrons with hollow interiors. The NiFe2O4 nano-octahedron based sensor exhibited excellent gas sensing properties for toluene with a nice stability, fast response, and recovery time (25 s/40 s to 100 ppm toluene), and a lower detection limitation (1 ppm) at 260 °C. The excellent toluene-sensing properties can not only be derived from the hollow interiors combined with porous nano-octahedrons to favor the diffusion of gas molecules, but also from the efficient catalytic activity of NiFe2O4 nanoparticles.

Porous reduced graphene oxide (rGO)/WO3 nanocomposites for the enhanced detection of NH3 at room temperature

Incorporation of reduced graphene oxide (rGO) modifies the properties of semiconducting metal oxide nanoparticles and makes it possible to tune the surface area and pore size to optimum values, which in turn improves their gas sensing properties. In this work, to improve the ammonia (NH₃) gas sensing characteristics, reduced graphene oxide (rGO) was incorporated into tungsten oxide (WO₃) nanospheres using a simple ultrasonication method. The rGO-WO₃ nanocomposites exhibited porous nanosheets with nanospherical WO₃ as observed with field-emission scanning electron microscopy (FE-SEM). The oxidation state of the rGO-WO₃ nanocomposite was determined using X-ray photoelectron spectroscopy (XPS). Three ratios of (1, 5 and 10% rGO/WO₃) nanocomposites and pure WO₃ showed good selectivity towards NH₃ at 10-100 ppm, and more remarkably at room temperature in the range of about 32-35 °C and at a relative humidity (RH) of 55%. The limit of detection (LOD) of the synthesized rGO-WO₃ nanocomposites was 1.14 ppm, which will highly favour low detection ranges of NH₃. The sensor response was 1.5 times higher than that of the bare WO₃ nanospheres. The sensors showed excellent selectivity, ultrafast response/recovery times (18/24 s), reproducibility and stability even after one month of their preparation. We believe that metal oxides using the rGO modifier can improve the sensitivity and reduce the LOD towards NH₃ and can be used effectively in real-time environmental monitoring.

Morphology Controllable Synthesis of NiO/NiFe2O4 Hetero-Structures for Ultrafast Lithium-Ion Battery

Rational design of high performance anode material with outstanding rate capability and cycling stability is of great importance for lithium ion batteries (LIBs). Herein, a series of NiO/NiFe₂O₄ hetero-structures with adjustable porosity, particle size, and shell/internal structure have been synthesized via a controllable annealing process. The optimized NiO/NiFe₂O₄ (S-NFO) is hierarchical hollow nanocube that is composed of ~5 nm subunits and high porosity. When being applied as anode for LIBs, the S-NFO exhibits high rate capability and excellent cycle stability, which remains high capacity of 1,052 mAh g^-1 after 300 cycles at 5.0 A g^-1 and even 344 mAh g^-1 after 2,000 cycles at 20 A g^-1. Such impressive electrochemical performance of S-NFO is mainly due to three reasons. One is high porosity of its hierarchical hollow shell, which not only promotes the penetration of electrolyte, but also accommodates the volume change during cycling. Another is the small particle size of its subunits, which can effectively shorten the electron/ion diffusion distance and provide more active sites for Li⁺ storage. Besides, the hetero-interfaces between NiO and NiFe₂O₄ also contribute toitsfast charge transport.

ZnxCo3−xO4 bimetallic oxides derived from metal–organic frameworks for enhanced acetone sensing performances

Gas sensors based on Zn_xCo_3−xO₄ bimetallic oxides derived from metal–organic frameworks exhibit a very high response of 35.6 to acetone and the limit of detection is as low as 0.5 ppm.

Improved gas sensing properties of silver-functionalized ZnSnO3 hollow nanocubes

Porous silver-functionalized ZnSnO₃ hollow nanocubes as a gas sensor with an ultra-fast response and recovery speed for acetone detection.