Spinel ferrites (MFe2O4): Synthesis, improvement and catalytic application in environment and energy field

Construction of manganese ferrite/zinc ferrite anchored graphene-based hierarchical aerogel photocatalysts following Z-scheme electron transfer for visible-light-driven carbon dioxide reduction

Herein, atomic-level interfacial coupling between spinel-type MnFe2O4 (MFA) and ZnFe2O4 (ZFA) was achieved via a sol-gel method combined with phase separation. These composites were then anchored onto a three-dimensional graphene aerogel (GA) through ethylenediamine-assisted hydrothermal self-assembly, forming a hierarchically porous MFA/ZFA@GA with a high surface area (191.06 m2/g). The optimized MFA/ZFA@GA exhibited a CO production rate of 21.14 μmol·g-1·h-1 (96 % selectivity, 94 % stability) under visible light, a 3.87-fold enhancement over single-component systems. The in-situ MFA/ZFA heterojunction and graphene-enhanced electron transfer synergistically prolonged photogenerated electron lifetime by 10 times. The hierarchical pores also boosted CO2 adsorption (7.66 wt%), the appreciable saturation magnetization intensity (37.49 emu/g) enabled magnetic separation recovery, and *COOH monitoring confirmed rapid desorption kinetics for high CO selectivity. Experiments combined with theoretical calculations revealed a Z-scheme mechanism: MnFe2O4's reductive electrons (-0.79 V vs. NHE) drove CO2 reduction, while ZnFe2O4's oxidative holes (1.50 V vs. NHE) facilitated H2O oxidation. Strategic integration of heterostructures, carbon hybridization, and aerogel architectures offered an efficient pathway for monolithic photocatalyst design.

Achieving CNTs Growth by Inducing Nanoparticle Nucleation via Non-Active Fe2O3 Clusters Anchored on the α-Al2O3 Surface

This research presents a regulation strategy of constructing a heterogeneous bilayer catalyst of Fe and Al2O3, namely, Fe-Al2O3, through interfacial interaction and particle nucleation, in order to modulate the size and catalytic activity of Fe sites and achieve the growth of carbon nanotubes (CNTs). Through temperature control, the noncatalytically active Fe2O3 clusters on the surface of Al2O3 are exposed, inducing multiple nucleation of Fe clusters on its surface. Under the synergistic effect of the confinement at the Fe-Al2O3 interface, the fabrication of small Fe nanoparticles is accomplished. The results indicate that the catalytically active Fe nanoparticles have a diameter of approximately 10 nm, and the grown CNTs have a diameter of approximately 15 nm. Based on the systematic characterization results, the nonactive Fe2O3 clusters confined by strong interfacial interaction induce multiple nucleation of Fe on their surface during multiple loading processes, facilitating the formation of nanoparticles. Additionally, the strong interaction between Al2O3 and Fe induces the formation of FeAl4O8, thereby enhancing the thermal stability of the nanoparticles. In conclusion, the targeted regulation of the interfacial interaction of the catalyst active sites offers guidance for the low-cost and large-scale preparation of small nanoparticle catalyst particles.

Boosting arsenic removal with metastable Fe2+/Mn3+ redox process in MnFe2O4/rGO composites for high capacity and stability

Fe-Mn oxides exhibit significant potential in the application of chemical and electrochemical remediation of groundwater arsenic contamination. However, the mechanism controlling the equilibrium between chemisorption inhibition and capacitive adsorption enhancement at ferromanganese oxide electrodes is unclear, posing significant challenges to achieving both electrochemical arsenic removal efficiency and cycle stability. Here, we introduce for the first time a defect engineering strategy to synthesize defect-rich, reduced graphene oxide-anchored MnFe2O4 composites (MnFe2O4/rGO). The electrochemically efficient arsenic removal capacity (102.6 mg·g-1) and sustained cycling stability (30 cycles with >95 % efficiency) are achieved through the synergistic pseudocapacitive effect of metastable Fe-Mn bimetallic. 80 % of the arsenic removal is due to pseudocapacitive effects driven by reversible redox reactions of metastable Fe2+/Mn3+ in MnFe2O4 tetrahedral coordination revealed by X-ray photoelectron spectrum (XPS). The electronic microenvironment of iron site is modulated by Mn atom reducing the arsenic adsorption energy on MnFe2O4/rGO electrode based on electronic impedance spectrum (EIS) and density function theory (DFT). Continuous flow experiments reveal that this electrochemical system deeply purifies 5 L arsenic-laden groundwater (1 mg·L-1) below World Health Organization's (WHO) drinking water guidelines with lower energy consumption and high selectivity. This study provides valuable insights for tailoring effective, stable electrodes in electrochemical arsenic removal.

Ternary AgFe2O4/SBA-16/SO3H Heterojunction Photocatalyst for the Sustainable Production of 5-Hydroxymethylfurfural under Mild Conditions

The use of solar energy to convert biomass and its derivatives into high-value chemicals has garnered significant interest as a sustainable alternative to fossil fuels. However, designing high-performance photocatalysts that can selectively catalyze biobased molecules remains a significant challenge in this field. In this paper, we describe the application of a ternary AgFe2O4/SBA-16/SO3H photocatalyst in the photocatalytic conversion of biomass-derived sugars to 5-hydroxymethylfurfural (HMF) using deep eutectic solvents (DESs) as green reaction media under visible light illumination. The photocatalyst was prepared by a facile sonication and postmodification method, and its crystal structure, functional groups, surface morphology, and optical features were analyzed through various characterization techniques. The influence of numerous essential variables on the photocatalytic production of HMF from fructose over the prepared photocatalyst was examined. The ideal reaction parameters were found to be 20 mg of photocatalyst quantity and 100 mg of fructose in choline chloride:glycerol under exposure to white LED light (9 W) at 80 °C, to afford 95% HMF yield in 2 h. The recyclability of the photocatalyst was established over five consecutive cycles, demonstrating its stability. This research provides an idea for AgFe2O4-based photocatalysts and a promising catalytic mode for biomass conversion using mild and efficient photocatalytic methodologies.

Production of Cu0.5Zn0.5Fe2O4 Nanostructures as a Hyperthermia Agent for Cancer Healing

Cancer is a pervasive and devastating disease affecting various parts of the body, posing significant challenges to human societies. Recently, the development of novel magnetic and biocompatible nanoparticles has emerged as a promising approach for magnetic hyperthermia in cancer treatment, complementing existing therapeutic methods. In the present work, Cu0.5Zn0.5Fe2O4 mixed spinel nanoparticles were produced via a sol-gel combustion route. The produced magnetic nanopowders were studied via FTIR, SEM, XRD, and VSM techniques. XRD results confirmed the formation of the spinel structure of ferrites. Microstructural investigations showed that the synthesized nanoparticles have a particle size ranging from 20 to 200 nm. The VSM results displayed that the saturation magnetization and coercivity of Cu0.5Zn0.5Fe2O4 nanoparticles were 57 emu/g and 24 Oe, respectively. Saturation magnetization for the Cu0.5Zn0.5Fe2O4 specimens improved with increasing heat treatment temperature. In order to examine the samples' heating effectiveness for magnetic hyperthermia therapy, various magnetic fields were used. The temperature of the Cu0.5Zn0.5Fe2O4 powders increased from 37°C to 47°C in 10 min when exposed to a 400-Oe magnetic field and 200-kHz frequency. Results showed that the fabricated products have the potential to be used as hyperthermia agents for cancer therapy. The novelty of this study focuses on the use of Cu0.5Zn0.5Fe2O4 mixed spinel as a new hyperthermia agent with more biocompatible constituent elements.

Cobalt, nickel and zinc spinel ferrites with high transmittance and UV-blocking for advanced optical applications

This study successfully synthesized and characterized CoFe2O4, NiFe2O4, and ZnFe2O4 ferrite nanoparticles. The results showed that CoFe2O4 and NiFe2O4 exhibited ferrimagnetic behavior, while ZnFe2O4 demonstrated antiferromagnetic properties. These magnetic characteristics influence the material's response to electromagnetic radiation, such as visible and infrared light. Optical studies revealed that CoFe2O4 had the highest radiation absorption, while ZnFe2O4 showed superior reflection and transmission. The ferrites' band gap energies, ranging from 3.3 to 3.6 eV, played a key role in their optical properties, with higher energy absorption and lower energy reflection. The refractive index varied with photon energy, reaching its peak at lower energy levels due to oxygen vacancies. Additionally, the optical conductivity increased with higher photon energy, peaking at 4.3 eV. These findings suggest promising applications in light transmission and sensing, with ferrites offering versatile optical properties that can be tailored for various uses.

Efficient activation of peroxymonosulfate by Mo2TiC2Tx@Co for sustained emerging micropollutant removal: Mo vacancy-mediated activation in Fenton-like reactions

Developing advanced heterogeneous catalysts through structural modifications effectively enhances the catalytic activity of non-homogeneous catalysts for removing emerging micropollutants (EMPs). In this study, Mo2TiC2Tx@Co with Mo vacancies was synthesized using the Lewis molten salt method, which efficiently activates peroxymonosulfate (PMS) and continuously degrades EMPs in water. The abundant Mo vacancy structure in the material acts as an anchoring site for Co nanoparticles and a co-catalytic site for Fenton-like reactions, enabling PMS adsorption and activation. Furthermore, Mo facilitates the redox cycling of Co3+/Co2+ through electron transfer. Mo vacancy-mediated activation in Fenton-like reactions enabled the Mo2TiC2Tx@Co/PMS system to achieve superior degradation efficiency for sulfamethoxazole (SMX) and several other EMPs, with the SMX degradation rate being 52.7 times higher than that of the Mo2TiAlC2/PMS system. The system exhibited robust resistance to various anionic species and maintained high activity over a wide pH range. The Mo2TiC2Tx@Co /PMS system degrades EMPs in water through both free radical (SO4•- and •OH) and non-radical (1O2) mechanisms, enhancing EMPs removal from complex water environments. This study aims to develop an efficient and sustainable heterogeneous catalyst, offering a viable solution for the long-term and effective degradation of EMPs in water.

Improving CO Oxidation Catalysis Over High Entropy Spinels by Increasing Disorder

Enhancing the activity and stability of earth-abundant, heterogeneous catalysts remains a key challenge, requiring new materials design strategies to replace platinum-group metals. Herein, it is demonstrated that increasing the configurational disorder of spinel metal oxides (M3O4, where M is a combination of Cr, Mn, Fe, Co, Ni, Cu, and Zn) leads to significant improvements in carbon monoxide (CO) oxidation performance. A substantial 63% decrease in the T10 value (temperature to reach 10% CO oxidation) is observed by systematically increasing the number of first-row transition metals within the spinel oxide. Long-term stability studies reveal that the most disordered 7-metal spinel oxide exhibited superior resistance to catalyst deactivation compared to the 4-metal variant, showing a decrease in activity of only 4.7% versus 12.2% during 14 h of operation. A solventless thermolysis approach is developed to synthesize a series of medium entropy spinel oxide (MESO) and high entropy spinel oxides (HESOs) from discrete, air-stable molecular precursors. Comprehensive crystal structure determination, elemental distribution analysis, and surface characterization are conducted, establishing a clear structure-function relationship between elemental composition, configurational disorder, and catalytic performance. This work highlights how configurational disorder can serve as an effective design principle for developing both active and stable catalysts.

Magnetic Investigation of Se/In Codoped Co0.5Ni0.5Fe2O4 Spinel Nanoparticles Synthesized via the Sonochemical Route

The magnetic traits of sonochemically synthesized Co0.5Ni0.5InxSe3xFe2-5xO4 nanoparticles [(In/Se → Co0.5Ni0.5Fe2O4) (x ≤ 0.1) NPs] have been investigated in detail. X-ray powder diffraction analysis confirmed the purity and cubic phase crystalline structure of all products. The products' chemical composition has been confirmed by EDX and elemental mapping analyses. The magnetization characteristics of Co0.5Ni0.5In2xSe3xFe2-6xO4 (In/Se → Co0.5Ni0.5Fe2O4) (x ≤ 0.1) NPs revealed superparamagnetic behavior at room temperature and ferrimagnetic behavior at low temperatures (Ts). The blocking temperature (TB) that defines the superparamagnetic-ferrimagnetic state transition was also determined via analysis of the ZFC and FC magnetization curves. TB was found to move to lower Ts as the amount of selenium amount increased. Moreover, the undoped Co0.5Ni0.5Fe2O4 NPs displayed the highest magnetic characteristics (such as Ms, Mr, Hc, Keff, and nB), which are depressed after In/Se codoping. The superparamagnetic feature could be promising for some interesting applications, including biosensing, magnetic hyperthermia, magnetic resonance imaging, and targeted drug delivery, while the ferrimagnetic behavior can make the material interesting for electrical applications.

Synergistic effect of ZnO-ZnFe2O4 heterostructures for enhanced surface catalytic activity in Cr(VI) reduction, green H2 generation and CO sensing: an experimental study supported by DFT

Increasing energy demand is an indication of progress, but it necessitates careful management of environmental pollution for maintaining a healthy life and ensuring a better planet for future generations. Heterostructure material-based catalysts have emerged as a comprehensive solution to combat the diverse challenges related to energy and environment. Herein, an n-n-type ZnO-ZnFe2O4 heterostructure was synthesized via a simple reflux followed by a co-precipitation technique for the same. Detailed photocatalytic and gas sensing studies revealed that a 50% ZnO-50% ZnFe2O4-based sample (ZZF-11) showed the highest Cr(VI) degradation with a rate constant of ∼159 × 10-4 s-1, which was ∼23 times higher than that of pristine ZnO and 6.4 times higher than that of pristine ZnFe2O4. Additionally, the ZZF-11 sample produced ∼550 μmol g-1 of H2 within a 300 minute interval via a photocatalytic water-splitting reaction. The ZZF-11 sensor also showed a significantly high response to 1 ppm CO gas (S = 29.4%) compared to all other pure and composite samples. The formation of the heterostructure and transfer of charges through the interface played an important role here. The most possible mechanism for the enhanced surface catalytic performance of ZZF-11 was critically analysed by corroborating the experimental results with DFT results. This study demonstrates a unified pathway to enhance the various surface catalytic processes by tuning different parameters of the heterostructure material to simultaneously overcome environment- and energy-related issues.

Trimetallic ferrite functionalized by guaninium tartrate ionic liquid (Co0.2Zn0.6Cu0.2Fe2O4-SiO2@[GuaH]+[Tar]2‒[GuaH]+) as a novel inorganic-bioorganic nanostructure to promote aqua-mediated synthesis of polyhydroxy-substituted pyridine-dipyrimidine fused heterocycles

In this work, a Cobalt-Zinc-Copper ferrite (Co0.2Zn0.6Cu0.2Fe2O4, CZCF) was synthesized and functionalized with silica and guaninium tartrate ionic liquid (Co0.2Zn0.6Cu0.2Fe2O4-SiO2@[GuaH]+[Tar]2‒[GuaH]+). The novel bio-nanostructure was characterized by various techniques such as fourier transform infrared spectroscopy (FT-IR), energy dispersive X-ray analysis (EDAX), EDAX mapping, field emission scanning electron microscopy (FESEM), X-ray fluorescence (XRF), X-ray diffraction (XRD), thermogravimetric/differential thermal gravimetric analysis (TGA/DTG), vibrating sample magnetometry (VSM), high resolution transmission electron microscopy (HRTEM), and zeta potential analysis. The synthesized bio-nanocomposite exhibited high catalytic activity for the aqua-mediated synthesis of polyhydroxy-substituted pyridine-dipyrimidine fused heterocycles through the one-pot pseudo four-component reaction of carbohydrates (sugars), barbituric acid, and amines under refluxing conditions. The recyclability and reusability of the bio-nanocatalyst were successfully investigated for up to three runs. Moreover, the features of the recovered Co0.2Zn0.6Cu0.2Fe2O4-SiO2@[GuaH]+[Tar]2‒[GuaH]+ were examined via the EDAX analysis and FESEM images. In the theoretical section, the interaction sites between L-tartaric acid and guanine in an aqueous medium were investigated at the B3LYP/6-311++G(d,p) computational level. Additionally, the formation of more stable configurations of dimers and trimers in IL was studied from a thermodynamic point of view.

Effect of multivalent ion doping on magnetic, electrical, and dielectric properties of nickel ferrite nanoparticles

The nanoscale spinel structured ferrites co-doped with multi-valence ions are of great interest and proving to be promising for numerous applications. In light of this, herein we report tetravalent titanium ions (Ti4+) and divalent zinc ions (Zn2+) co-doped nickel ferrites with generic formula of NiFe2 - 2xTixZnxO4 (x = 0.00 ≤ x ≤ 0.20 in step of 0.05). The sol gel self combustion method in assistance with citric acid as fuel was employed to prepare the samples. The X-ray diffraction (XRD) analysis with Rietveld refinement was performed to confirm the single-phase cubic spinel structure. The sphere type grain morphology of the samples was revealed by SEM images. The compositional studies carried out by EDAX showed desired formation of the composition with absence of impurities in the samples. The characteristics bands belonging to the spinel ferrites were appeared in IR spectra confirming the successive sample forming. The different surface parameters including surface area and pore volume was estimated using Brunauer-Emmett-Teller (BET) analysis. The low coercive nature with soft magnetism was observed with the co-doping as revealed by M-H plots. The electric and dielectric parameters showed decrementing behaviour with increment in Ti4+-Zn2+ co-doping. This study outcome signifies that the Ti4+-Zn2+ co-doping in nickel ferrites could be a prominent for many nanoelectronics applications.

Studying the Defects in Spinel Compounds: Discovery, Formation Mechanisms, Classification, and Influence on Catalytic Properties

Spinel ferrites demonstrate extensive applications in different areas, like electrodes for electrochemical devices, gas sensors, catalysts, and magnetic adsorbents for environmentally important processes. However, defects in the real spinel structure can change the many physical and chemical properties of spinel ferrites. Although the number of defects in a crystal spinel lattice is small, their influence on the vast majority of physical properties could be really decisive. This review provides an overview of the structural characteristics of spinel compounds (e.g., CoFe2O4, NiFe2O4, ZnFe2O4, Fe3O4, γ-Fe2O3, Co3O4, Mn3O4, NiCo2O4, ZnCo2O4, Co2MnO4, etc.) and examines the influence of defects on their properties. Attention was paid to the classification (0D, 1D, 2D, and 3D defects), nomenclature, and the formation of point and surface defects in ferrites. An in-depth description of the defects responsible for the physicochemical properties and the methodologies employed for their determination are presented. DFT as the most common simulation approach is described in relation to modeling the point defects in spinel compounds. The significant influence of defect distribution on the magnetic interactions between cations, enhancing magnetic properties, is highlighted. The main defect-engineering strategies (direct synthesis and post-treatment) are described. An antistructural notation of active centers in spinel cobalt ferrite is presented. It is shown that the introduction of cations with different charges (e.g., Cu(I), Mn(II), Ce(III), or Ce(IV)) into the cobalt ferrite spinel matrix results in the formation of various point defects. The ability to predict the type of defects and their impact on material properties is the basis of defect engineering, which is currently an extremely promising direction in modern materials science.

A Critical Review of the Synthesis and Applications of Spinel-Derived Catalysts to Bio-Oil Upgrading

The transformation of renewable bio-oil into value-added chemicals and bio-oil through catalytic processes embodies an efficient approach within the realm of advancing sustainable energy. Spinel-based catalysts have garnered significant attention owing to their ability to precisely tune metals within the framework, thereby facilitating adjustments to structural, physical, and electronic properties, coupled with their remarkable thermal stability. This review aims to provide a comprehensive overview of recent advancements in spinel-based catalysts tailored specifically for upgrading bio-oil. Its objective is to shed light on their potential to address the limitations of conventional catalysts, thereby advancing sustainable biofuel production. Initially, a comprehensive analysis is conducted on different metal oxide composites in terms of their similarity and dissimilarity on properties. Subsequently, the synthesis methodologies of spinels are scrutinised and potential avenues for their modification are explored. Following this, an in-depth discussion ensues regarding the utilisation of spinels as catalysts or catalyst precursors for catalytic cracking, ketonisation, catalytic hydrodeoxygenation, steam and aqueous-phase reforming, as well as electrocatalytic upgrading of bio-oil, with a specific emphasis on elucidating their catalytic reactivity, and underlying structure-activity correlation and catalysis mechanisms. Finally, the challenges and potential prospects in utilising spinels for the catalytic valorisation of renewable biofuel are addressed, with a specific focus on the use of machine learning - based approaches to optimise the structure and activity of spinel catalysts. This review aims to provide specific directions for further exploration and maximisation of the spinel catalysts in the bio-oil upgrading field.

Self-sensing magnetic actuator based on sustainable collagen hybrid nanocomposites

Taking into account that natural polymers are renewable and biodegradable, hybrid materials based on natural polymers are required for advanced technological applications with reduced environmental footprint. In this work, sustainable composites have been developed based on collagen as a polymeric matrix and different magnetic fillers, in order to tailor magnetic response. The composites were prepared by solution casting with 30 wt% of magnetite nanoparticles (Fe3O4 NPs), magnetite nanorods (Fe3O4 NRs) or cobalt ferrite nanoparticles (CoFe2O4 NPs). It is shown that the magnetic filler type has no bearing on the morphology, physical-chemical, or thermal characteristics of the composites, whereas the mechanical properties are determined by the magnetic filler, leading to a reduction in tensile strength, with values of 4.95 MPa for Fe3O4 NPs, 9.20 MPa for Fe3O4 NRs and 5.21 MPa for CoFe2O4 NPs containing samples. However, the highest magnetization saturation is obtained for Fe3O4 NPs (44 emu.g-1) and the higher coercive field for CoFe2O4 NPs (2062 Oe). In order to prove functionality of the developed composites, a self-sensing magnetic actuator device has been developed with the composite film with CoFe2O4 NPs, showing high stability over cycling.

Recent trends in magnetic spinel ferrites and their composites as heterogeneous Fenton-like catalysts: A review

In recent years, there has been a growing interest in utilizing spinel ferrite and their nanocomposites as Fenton-like catalysts. The use of these materials offers numerous advantages, including ability to efficiently degrade pollutants and potential for long-term and repeated use facilitated by their magnetic properties that make them easily recoverable. The remarkable catalytic properties, stability, and reusability of these materials make them highly attractive for researchers. This paper encompasses a comprehensive review of various aspects related to the Fenton process and the utilization of spinel ferrite and their composites in catalytic applications. Firstly, it provides an overview of the background, principles, mechanisms, and key parameters governing the Fenton reaction, along with the role of physical field assistance in enhancing the process. Secondly, it delves into the advantages and mechanisms of H2O2 activation induced by different spinel ferrite and their composites for the removal of organic pollutants, shedding light on their efficacy in environmental remediation. Thirdly, the paper explores the application of these materials in various Fenton-like processes, including Fenon-like, photo-Fenton-like, sono-Fenton-like, and electro-Fenton-like, for the effective removal of different types of contaminants. Furthermore, it addresses important considerations such as the toxicity, recovery, and reuse of these materials. Finally, the paper presents the challenges associated with H2O2 activation by these materials, along with proposed directions for future improvements.

Elucidating the effects of nitrogen and phosphorus co-doped carbon on complex spinel NiFe2O4 towards oxygen reduction reaction in alkaline media

The study presents for the first time complex spinel NiFe2O4 nanoparticles supported on nitrogen and phosphorus co-doped carbon nanosheets (NPCNS) prepared using sol gel and the carbonization of graphitic carbon nitride with lecithin as a highly active and durable electrocatalyst for oxygen reduction reaction. The physicochemical properties of complex spinel NiFe2O4 on NPCNS and subsequent nanomaterials were investigated using techniques such as X-ray diffraction, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and transmission electron microscopy. The electrochemical activity of the electrocatalysts was evaluated using hydrodynamic linear sweep voltammetry, cyclic voltammetry, electrochemical impedance spectroscopy, and chronoamperometry. The electrocatalytic performance of the NiFe2O4/NPCNS nanohybrid electrocatalyst is dominated by the 4e- transfer mechanism, with an onset potential of 0.92 V vs. RHE, which is closer to that of the Pt/C, and a current density of 7.81 mA/cm2 that far exceeds that of the Pt/C. The nanohybrid demonstrated the best stability after 14 400 s, outstanding durability after 521 cycles, and the best ability to oxidize methanol and remove CO from its active sites during CO tolerance studies. This improved catalytic activity can be attributed to small nanoparticle sizes of the unique complex spinel nickel ferrite structure, N-Fe/Ni coordination of nanocomposite, high dispersion, substantial ECSA of 47.03 mF/cm2, and synergy caused by strong metal-support and electronic coupling interactions.

A critical review of approaches to enhance the performance of bio-electro-Fenton and photo-bio-electro-Fenton systems

The development of sustainable advanced energy conversion technologies and efficient pollutant treatment processes is a viable solution to the two global crises of the lack of non-renewable energy resources and environmental harm. In recent years, the interaction of biological and chemical oxidation units to utilize biomass has been extensively studied. Among these systems, bio-electro-Fenton (BEF) and photo-bio-electro-Fenton (PBEF) systems have shown prospects for application due to making rational and practical conversion and use of energy. This review compared and analyzed the electron transfer mechanisms in BEF and PBEF systems, and systematically summarized the techniques for enhancing system performance based on the generation, transfer, and utilization of electrons, including increasing the anode electron recovery efficiency, enhancing the generation of reactive oxygen species, and optimizing operational modes. This review compared the effects of different methods on the electron flow process and fully evaluated the benefits and drawbacks. This review may provide straightforward suggestions and methods to enhance the performance of BEF and PBEF systems and inspire the reader to explore the generation and utilization of sustainable energy more deeply.

Peroxydisulfate-based Non-radical Oxidation of Rhodamine B by Fe-Mn Doped Granular Activated Carbon: Kinetics and Mechanism Study

While numerous persulfate-based advanced oxidation processes (AOPs) have been studied based on fancy catalysts, the practical combination of Fe or Mn modified granular activated carbon (GAC) has seldom been investigated. The present study focused on a green and readily synthesized Fe-Mn bimetallic oxide doped GAC (Fe-Mn@GAC), to uncover its catalytic kinetics and mechanism when used in the peroxydisulfate (PDS)-based oxidation process for degrading Rhodamine B (RhB), a representative xenobiotic dye. The synthesized Fe-Mn@GAC was characterized by SEM-EDS, XRD, ICP-OES and XPS analyses to confirm its physicochemical properties. The catalytic kinetics of Fe-Mn@GAC+PDS system were evaluated under varying conditions, including PDS and catalyst dosages, solution pH, and the presence of anions. It was found Fe-Mn@GAC exhibited robust catalytic performance, being insensitive to a wide pH range from 3 to 11, and the presence of anions such as Cl-, SO4 2-, NO3 - and CO3 2-. The catalytic mechanism was investigated by EPR and quenching experiments. The results indicated the catalytic system processed a non-radical oxidation pathway, dominated by direct electron transfer between RhB and Fe-Mn@GAC, with singlet oxygen (1O2) playing a secondary role. The catalytic system also managed to maintain a RhB removal above 81 % in successive 10 cycles, and recover to 89.5 % after simple DI water rinse, showing great reusability. The catalytic system was further challenged by real dye-containing wastewater, achieving a decolorization rate of 84.5 %. This work not only provides fresh insight into the kinetics and mechanism of the Fe-Mn@GAC+PDS catalytic system, but also demonstrates its potential in the practical application in real dye-containing wastewater treatment.

FeNi2S4-A Potent Bifunctional Efficient Electrocatalyst for the Overall Electrochemical Water Splitting in Alkaline Electrolyte

For a carbon-neutral society, the production of hydrogen as a clean fuel through water electrolysis is currently of great interest. Since water electrolysis is a laborious energetic reaction, it requires high energy to maintain efficient and sustainable production of hydrogen. Catalytic electrodes can reduce the required energy and minimize production costs. In this context, herein, a bifunctional electrocatalyst made from iron nickel sulfide (FeNi2S4 [FNS]) for the overall electrochemical water splitting is introduced. Compared to Fe2NiO4 (FNO), FNS shows a significantly improved performance toward both OER and HER in alkaline electrolytes. At the same time, the FNS electrode exhibits high activity toward the overall electrochemical water splitting, achieving a current density of 10 mA cm-2 at 1.63 V, which is favourable compared to previously published nonprecious electrocatalysts for overall water splitting. The long-term chronopotentiometry test reveals an activation followed by a subsequent stable overall cell potential at around 2.12 V for 20 h at 100 mA cm-2.

Abukhadra M, El-Sherbeeny AM. Electrical transport and dielectric relaxation mechanism in Zn0.5Cd0.5Fe2O4 spinel ferrite: A temperature- and frequency-dependent complex impedance study

In the present study, the frequency-dependent dielectric relaxation and electrical conduction mechanisms in sol-gel-derived Zn0.5Cd0.5Fe2O4 (ZCFO) spinel ferrite were studied in the temperature range of 343-438 K. The formation of the ZCFO spinel ferrite phase with space group Fd3m was confirmed by X-ray diffraction analysis. The dielectric relaxation and electrical conduction mechanisms were studied using complex impedance spectroscopy (CIS). In the Nyquist plots, depressed semicircles were fitted with an equivalent circuit model with configuration (RGBQGB) (RGQG), signifying the contributions from grain boundaries and grains to the charge transport mechanism in the sample. The frequency-dependent AC conductivity was found to follow Jonscher's power law, and the frequency exponent term depicted the overlapping large polaron hopping (OLPH) model as the dominant transport mechanism. The activation energies for conductivity, electric modulus and impedance were calculated to identify the nature of the charge carriers governing the relaxation and conduction mechanisms in the prepared sample. Complex modulus studies confirmed the non-Debye type of dielectric relaxation, whereas tangent loss and dielectric constant analyses confirmed the thermally activated hopping mechanism of charge carriers in Zn0.5Cd0.5Fe2O4 spinel ferrite.

Challenges and Strategies for Synthesizing High Performance Micro and Nanoscale High Entropy Oxide Materials

High-entropy oxide micro/nano materials (HEO MNMs) have shown broad application prospects and have become hot materials in recent years. This review comprehensively provides an overview of the latest developments and covers key aspects of HEO MNMs, by discussing design principles, computer-aided structural design, synthesis challenges and strategies, as well as application areas. The analysis of the synthesis process includes the role of high-throughput process in large-scale synthesis of HEOs MNMs, along with the effects of temperature elevation and undercooling on the formation of HEO MNMs. Additionally, the article summarizes the application of high-precision and in situ characterization devices in the field of HEO MNMs, offering robust support for related research. Finally, a brief introduction to the main applications of HEO MNMs is provided, emphasizing their key performances. This review offers valuable guidance for future research on HEO MNMs, outlining critical issues and challenges in the current field.

Green synthesis and characterization of polyphenol-coated magnesium-substituted manganese ferrite nanoparticles: Antibacterial and antioxidant properties

Magnesium-substituted manganese ferrite (Mn0.9Mg0.1Fe2O4) nanoparticles were obtained through a wet chemical method and coated with green-extracted polyphenol from Punica granatum peel. The obtained spinel nanocomposite was fully characterized. The X-ray diffraction pattern revealed a single phase with an average crystalline size of 3.33-8.74 nm, confirming the cubic-spinel structure. The FESEM micrograph showed a quasi-spherical shape with nearly uniform particles, indicating mild agglomeration. The mean size of the Mn0.9Mg0.1Fe2O4 was 13.66 nm with a standard deviation of 2.05. The BET isotherms indicated a surface area of 85.45 m2/g. The basic groups attached to the external surface of Mg-doped spinel ferrite were discovered. The resulted superparamagnetic modified doped-nanoferrite particles showed antibacterial activity as well as antioxidant efficiency through studying Catalase (CAT), Glutathione (GSH), and Glutathione Peroxidase (GSH-Px) parameters. The outcomes highlight the promising potential of polyphenol-functionalized Mn0.9Mg0.1Fe2O4 magnetite nanosized particles for the development of novel anti-biofilm agents.

Sludge dewaterability improvement with microbial fuel cell powered electro-Fenton system (MFCⓅEFs): Performance and mechanisms

Throughout the entire process of sludge treatment and disposal, it is crucial to explore stable and efficient techniques to improve sludge dewaterability, which can facilitate subsequent resource utilization and space and cost savings. Traditional Fenton oxidation has been widely researched to enhance the performance of sludge dewaterability, which was limited by the additional energy input and the instabilities of Fe2+ and H2O2. To reduce the consumption of energy and chemicals and further break the rate-limiting step of the iron cycle, a novel and feasible method that constructed microbial fuel cell powered electro-Fenton systems (MFCⓅEFs) with ferrite and biochar electrode (MgFe2O4@BC/CF) was successfully demonstrated. The MFCⓅEFs with MgFe2O4@BC/CF electrode achieved specific resistance filtration and sludge cake water content of 2.52 × 1012 m/kg and 66.54 %. Cellular structure and extracellular polymeric substances (EPS) were disrupted, releasing partially bound water and destroying hydrophilic structures to facilitate sludge flocs aggregation, which was attributed to the oxidation of hydroxyl radicals. The consistent electron supply supplied by MFCⓅEFs and catalytically active sites on the surface of the multifunctional functional group electrode was responsible for producing more hydroxyl radicals and possessing a better oxidizing ability. The study provided an innovative process for sludge dewaterability improvement with high efficiency and low energy consumption, which presented new insights into the green treatment of sludge.

Synthesis and characterization of magnesium ferrite-activated carbon composites derived from orange peels for enhanced supercapacitor performance

Supercapacitors have emerged as highly efficient energy storage devices, relying on electrochemical processes. The performance of these devices can be influenced by several factors, with key considerations including the selection of electrode materials and the type of electrolyte utilized. Transition metal oxide electrodes are commonly used in supercapacitors, as they greatly influence the electrochemical performance of these devices. Nonetheless, ferrites' low energy density poses a limitation. Hence, it is crucial to create electrode materials featuring unique and distinct structures, while also exploring the ideal electrolyte types, to enhance the electrochemical performance of supercapacitors incorporating magnesium ferrites (MF). In this study, we effectively prepared magnesium ferrites (MgFe2O4) supported on activated carbon (AC) derived from orange peels (OP) using a simple hydrothermal method. The resulting blends underwent comprehensive characterization employing various methods, including FTIR, XRD, TEM, SEM, EDX, and mapping analysis. Moreover, the electrochemical performance of MgFe2O4@AC composites was evaluated using GCD and CV techniques. Remarkably, the MF45-AC electrode material showed exceptional electrochemical behavior, demonstrating a specific capacitance of 870 F·g-1 within current density of 1.0 A g-1 and potential windows spanning from 0 to 0.5 V. Additionally, the prepared electrodes displayed exceptional cycling stability, with AC, MF, and MF45-AC retaining 89.6%, 94.2%, and 95.1% of their initial specific capacitance, respectively, even after 5000 cycles. These findings underscore the potential of MF-AC composites as superior electrode materials for supercapacitors. The development of such composites, combined with tailored electrolyte concentrations, holds significant promise for advancing the electrochemical performance and energy density of supercapacitor devices.

Lanthanide-Assisted Nanozyme Performs Optical and Magnetic Resonance Dual-Modality Logical Signal for In Vitro Diagnosis

The iron nanozyme-based colorimetric method, which is widely applied for biosubstrate detection in in vitro diagnosis (IVD), faces some limitations. The optimal catalytic conditions of iron nanozymes necessitate a strong acidic environment, high temperature, and other restrictive factors; additionally, the colorimetric results are highly influenced by optical interferences. To address these challenges, iron nanozymes doped with various transition elements were efficiently prepared in this study, and notably, the manganese-modified one displayed a high catalytic activity owing to its electron transfer property. Furthermore, the introduction of lanthanide ions into the catalytic reactions, specifically the neodymium ion, significantly boosted the generation efficiency of hydroxyl radicals; importantly, this enhancement extended to a wide range of pH levels and temperatures, amplifying the detection signal. Moreover, the nanozyme's superparamagnetic characteristic was also employed to perform a logical optical and magnetic resonance dual-modality detection for substrates, effectively eliminating background optical interference and ensuring a reliable verification of the signal's authenticity. Based on this magnetic signal, the integration of natural glucose oxidase with the nanozyme resulted in a notable 61.5% increase in detection sensitivity, surpassing the capabilities of the traditional colorimetric approach. Consequently, the incorporation of lanthanide ions into the magnetic nanozyme enables the effective identification of physiological biomarkers through the dual-modality signal. This not only guarantees enhanced sensitivity but also demonstrates significant potential for future applications.

MgFe2O4@Tris magnetic nanoparticles: an effective and powerful catalyst for one-pot synthesis of pyrazolopyranopyrimidine and tetrahydrodipyrazolopyridine derivatives

Magnesium (Mg) as a metal has wide applications, but its use in chemical reactions is rarely reported. Currently, magnesium catalytic processes are being developed to synthesize basic chemical compounds. Therefore, an effective and recyclable nano-catalyst was synthesized using MgFe2O4@Tris in this study. The structure of MgFe2O4@Tris was characterized by various techniques including Fourier-transform infrared (FT-IR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray (EDX), thermogravimetric analysis (TGA), X-ray diffraction (XRD), and vibrating sample magnetometer (VSM) techniques. Finally, the catalytic activity of this nano-catalyst was evaluated for the synthesis of pyrazolopyranopyrimidine and tetrahydrodipyrazolopyridine derivatives. Among the advantages of this catalyst are its high catalytic activity, high yields, use of environmentally friendly solvents, easy magnetic separation, and the possibility of reusing the catalyst.

Low-Temperature Synthesis of Mesoporous Half-Metallic High-Entropy Spinel Oxide Nanofibers for Photocatalytic CO2 Reduction

High-entropy oxides (HEOs) exhibit great prospects owing to their varied composition, chemical adaptability, adjustable light-absorption ability, and strong stability. In this study, we report a strategy to synthesize a series of porous high-entropy spinel oxide (HESO) nanofibers (NFs) at a low temperature of 400 °C by a sol-gel electrospinning technique. The key lies in selecting six acetylacetonate salt precursors with similar coordination abilities, maintaining a high-entropy disordered state during the transformation from stable sols to gel NFs. The as-synthesized HESO NFs of (NiCuMnCoZnFe)3O4 show a high specific surface area of 66.48 m2/g, a diverse elemental composition, a dual bandgap, half-metallicity property, and abundant defects. The diverse elements provide various synergistic catalytic sites, and oxygen vacancies act as active sites for electron-hole separation, while the half-metallicity and dual-bandgap structure offer excellent light absorption ability, thus expanding its applicability to a wide range of photocatalytic processes. As a result, the HESO NFs can efficiently convert CO2 into CH4 and CO with high yields of 8.03 and 15.89 μmol g-1 h-1, respectively, without using photosensitizers or sacrificial agents.

Bifunctional green nanoferrites as catalysts for simultaneous organic pollutants reduction and hydrogen generation: Upcycling strategy

The upcycling strategy is an approach that includes the conversion of waste into new higher value-added products. This study reports on a new methodology for the environmentally friendly synthesis of MFe2O4 spinel nanoferrites (M = Co, Cu, Fe and Mn) to be used as catalysts applied in the upcycling method. Thus, the reduction of 4-nitrophenol (4-NP), methyl orange, and methyl red to commercially valuable compounds was evaluated, as well as the simultaneous generation of hydrogen in a short time. Therefore, an eco-friendly synthesis was proposed, according to the 12 principles of green chemistry and sustainability. Product were obtained with satisfactory properties in terms of crystallinity, magnetic particle size, and magnetization. The materials exhibited excellent performance in catalytic reduction of 4-NP, whose reduction time decreased in the order MnFe2O4 > Fe3O4 > CoFe2O4 > CuFe2O4. This behavior highlighted the CuFe2O4 nanoferrite, which achieved 4-NP reduction in just 10 s. It proved that it could also be reused for 10 consecutive cycles while maintaining its crystalline structure. The catalyst was also effective in the reduction of azo dyes and subsequent production of substituted aromatic compounds suitable for use in chemical processes. Under the optimized conditions, the green CuFe2O4 catalyst was effective in producing hydrogen by hydrolysis. HGR and activation energy (Ea) values were of the order of 19,600 mL g-1 min-1 and 25.5 kJ mol-1, respectively. The results demonstrated the potential of this simple strategy for the environmental pollutant elimination and power generation.

Synthesis of ZnFe2O4 Nanospheres with Tunable Morphology for Lithium Storage

ZnFe2O4 (ZFO) nanospheres with complex structures have been synthesized by a one-step simple solvothermal method using two different types of precursors-metal chlorides and nitrates -and were fully characterized by XRD, SEM, XPS, and EDS. The ZFO nanospheres synthesized from chloride salts (ZFO_C) were loose with a size range of 100-200 nm, while the ZFO nanospheres synthesized from nitrate salts (ZFO_N) were dense with a size range of 300-500 nm but consisted of smaller nanoplates. The different morphologies may be caused by the different hydrolysis rates and different stabilizing effects of chloride and nitrate ions interacting with the facets of forming nanoparticles. Electrochemical tests of nitrate-based ZFO nanospheres as anode materials for lithium-ion batteries demonstrated their higher cyclic stability. The ZFO_C and ZFO_N samples have initial specific discharge/charge capacities of 1354/1020 and 1357/954 mAh∙g-1, respectively, with coulombic efficiencies of 75% and 71%. By the 100th cycle, ZFO_N has a capacity of 276 mAh∙g-1, and for ZFO_C, only 210 mAh∙g-1 remains after 100 cycles.

Co-Mn-Fe spinel-carbon composite catalysts enhanced persulfate activation for degradation of neonicotinoid insecticides: (Non) radical path identification, degradation pathway and toxicity analysis

The extensive utilization of neonicotinoid insecticides (NNIs) in agricultural practices ultimately poses a significant threat to both the environment and human health. This work focuses on the efficient degradation and detoxification of the representative NNI, thiamethoxam (THX), and explores the underlying mechanism using a Co-Fe-Mn mixed spinel doped carbon composite catalyst activated persulfate. The findings demonstrate that the composite effectively degrades THX, achieving a degradation rate of 95% in 30 mins, while requiring only a fraction (one-sixteenth) of the oxidant dosage compared to pure carbon. The study aimed to examine the negative impact of reactive halogens on reactive oxygen species within a saline environment. The degradation byproducts were linked to the presence of two common electron-withdrawing groups, namely halogens and nitro in the THX molecule. It was hypothesized that the degradation process was primarily influenced by C-N bond breaking and hydroxylation occurring between the diazine oxide and 2-chlorothiazole rings. Consequently, dehalogenation and carbonylation processes facilitated the elimination of halogenated components and pharmacophores from the THX, leading to detoxification. In addition to the identified free radical pathway including SO4•-, •OH and O2•- contributed to THX degradation, the participation of non-radical pathways (1O2 and electron transfer) were also confirmed. The efficacy of detoxification was further validated through toxicity assessment, employing quantitative conformation relationship prediction and microbial culture utilizing Bacillus subtilis.

Simplified synthesis of direct Z-scheme Bi2WO6/PhC2Cu heterojunction that shows enhanced photocatalytic degradation of 2,4,6-TCP: Kinetic study and mechanistic insights

For this work, we employed n-type Bi2WO6 and p-type PhC2Cu to formulate a direct Z-scheme Bi2WO6/PhC2Cu (PCBW) photocatalyst via simplified ultrasonic stirring technique. An optimal 0.6PCBW composite exhibited the capacity to rapidly photodegrade 2,4,6-TCP (98.6% in 120 min) under low-power blue LED light, which was 8.53 times and 12.53 times faster than for pristine PhC2Cu and Bi2WO6, respectively. Moreover, electron spin resonance (ESR), time-resolved PL spectra, and quantitative ROS tests indicated that the PCBW enhanced the separation capacity of photocarriers. It also more readily associated with dissolved oxygen in water to generate reactive oxygen species (ROS). Among them, the ability of PCBW to produce ·O2- in one hour was 12.07 times faster than for pure PhC2Cu. In addition, the H2O2 formation rate and apparent quantum efficiency of PCBW are 10.73 times that of PhC2Cu, which indicates that PCBW not only has excellent photocatalytic performance, but also has outstanding ROS production ability. Furthermore, Ag photodeposition, in situ X-ray photoelectron spectroscopy (XPS) and density functional theory (DFT) calculations were utilized to determine the photogenerated electron migration paths in the PCBW, which systematically confirmed that Z-scheme heterojunction were successfully formed. Finally, based on the intermediate products, three potential 2,4,6-TCP degradation pathways were proposed.

Review on magnetic spinel ferrite (MFe2O4) nanoparticles: From synthesis to application

Magnetic spinel ferrite materials offer various applications in biomedical, water treatment, and industrial electronic devices, which has sparked a lot of attention. This review focuses on the synthesis, characterization, and applications of spinel ferrites in a variety of fields, particularly spinel ferrites with doping. Spinel ferrites nanoparticles doped with the elements have remarkable electrical and magnetic properties, allowing them to be used in a wide range of applications such as magnetic fields, microwave absorbers, and biomedicine. Furthermore, the physical properties of spinel ferrites can be modified by substituting metallic atoms, resulting in improved performance. The most recent and noteworthy applications of magnetic ferrite nanoparticles are reviewed and discussed in this review. This review goes over the synthesis, doping and applications of different types of metal ferrite nanoparticles, as well as views on how to choose the appropriate magnetic ferrites based on the intended application.

Correlation between Magnetic and Dielectric Response of CoFe2O4:Li1+/Zn2+ Nanopowders Having Improved Structural and Morphological Properties

The vast applicability of spinel cobalt ferrite due to its unique characteristics implies the need for further exploration of its properties. In this regard, structural modification at the O-site of spinel with Li¹⁺/Zn²⁺ was studied in detail for exploration of the correlation between structural, magnetic, and dielectric properties of the doped derivatives. The CTAB-assisted coprecipitation method was adopted for the synthesis of the desired compositions owing to its cost effectiveness and size controlling ability. Redistribution of cations at T- and O-sites resulted in the expansion of the crystal lattice, but no distortion of the cubic structure was observed, which further supports the flexible crystal structure of spinel for accommodating larger Li¹⁺/Zn²⁺ cations. Moreover, an XPS analysis confirmed the co-existence of the most stable oxidation states of Zn²⁺, Li¹⁺, Co²⁺, and Fe³⁺ ions with unstable Co³⁺ and Fe²⁺ ions as well, which induces the probability of hopping mechanisms to a certain extent and is a well-established behavior of cobalt ferrite nanoparticles. The experimental results showed that Li¹⁺/Zn²⁺ co-doped samples exhibit the best magnetic properties at dopant concentration x = 0.3. However, increasing the dopant content causes disturbance at both sites, resulting in decreasing magnetic parameters. It is quite evident from the results that dielectric parameters are closely associated with each other. Therefore, dopant content at x = 0.1 is considered the threshold value exhibiting the highest dielectric parameters, whereas any further increase would result in decreasing the dielectric parameters. The reduced dielectric properties and enhanced magnetic properties make the investigated samples a potential candidate for magnetic recording devices.

Design and Development of Novel Composites Containing Nickel Ferrites Supported on Activated Carbon Derived from Agricultural Wastes and Its Application in Water Remediation

Recently, efficient decontamination of water and wastewater have attracted global attention due to the deficiency in the world's water sources. Herein, activated carbon (AC) derived from willow catkins (WCs) was successfully synthesized using chemical modification techniques and then loaded with different weight percentages of nickel ferrite nanocomposites (10, 25, 45, and 65 wt.%) via a one-step hydrothermal method. The morphology, chemical structure, and surface composition of the nickel ferrite supported on AC (NFAC) were analyzed by XRD, TEM, SEM, EDX, and FTIR spectroscopy. Textural properties (surface area) of the nanocomposites (NC) were investigated by using Brunauer-Emmett-Teller (BET) analysis. The prepared nanocomposites were tested on different dyes to form a system for water remediation and make this photocatalyst convenient to recycle. The photodegradation of rhodamine B dye was investigated by adjusting a variety of factors such as the amount of nickel in nanocomposites, the weight of photocatalyst, reaction time, and photocatalyst reusability. The 45NFAC photocatalyst exhibits excellent degradation efficiency toward rhodamine B dye, reaching 99.7% in 90 min under a simulated source of sunlight. To summarize, NFAC nanocomposites are potential photocatalysts for water environmental remediation because they are effective, reliable, and reusable.

Recent advances in spinel ferrite-based magnetic photocatalysts for efficient degradation of organic pollutants

Although spinel ferrite (MFe₂O₄, M = Zn, Ni, Mn, etc.) has been reported as a promising catalyst, its low photocatalytic activity under visible light greatly restricts its practical application. Spinel ferrite-based photocatalytic composites have exhibited improved efficiency for pollutant degradation, due to interface charge carrier mobility and structural modification. Meanwhile, due to its magnetism and stability, spinel ferrite composite can be easily recycled for long-term utilization, showing its high application potential. In this review, the recent advances in the construction and photocatalytic degradation of spinel ferrite composites are discussed, with an emphasis on the relationship between structural property and photocatalytic activity. In addition, to improve their photocatalytic application, the challenges, gaps and future research prospects are proposed.

Direct Visualization of Magnetic Correlations in Frustrated Spinel ZnFe2 O4

Magnetic materials with the spinel structure (A²⁺ B³⁺ ₂ O₄ ) form the core of numerous magnetic devices, and ZnFe₂ O₄ constitutes a peculiar example where the nature of the magnetism is still unresolved. Susceptibility measurements revealed a cusp around T_c  = 13 K resembling an antiferromagnetic transition, despite the positive Curie-Weiss temperature determined to be Θ_CW  = 102.8(1) K. Bifurcation of field-cooled and zero-field-cooled data below T_c in conjunction with a frequency dependence of the peak position and a non-zero imaginary component below T_c shows it is in fact associated with a spin-glass transition. Highly structured magnetic diffuse neutron scattering from single crystals develops between 50 K and 25 K revealing the presence of magnetic disorder which is correlated in nature. Here, the 3D-mΔPDF method is used to visualize the local magnetic ordering preferences, and ferromagnetic nearest-neighbor and antiferromagnetic third nearest-neighbor correlations are shown to be dominant. Their temperature dependence is extraordinary with some flipping in sign and a strongly varying correlation length. The correlations can be explained by orbital interaction mechanisms for the magnetic pathways and a preferred spin cluster. This study demonstrates the power of the 3D-mΔPDF method in visualizing complex quantum phenomena thereby providing a way to obtain an atomic-scale understanding of magnetic frustration.

Modulating CoFeOX Nanosheets Towards Enhanced CO2 Photoreduction to Syngas: Effect of Calcination Temperature and Mixed-Valence Multi-Metals

CoFeO_X nanosheets were synthesized by a facile coprecipitation and calcination method. The effect of calcination temperature on the crystal texture, morphology and surface areas of CoFeO_X were fully explored. CoFeO_X sample calcined at 600 °C (CoFeO_X -600) showed superior catalytic performance for the reduction of CO₂ under visible light. Compared with the pure Ru(bpy)₃ ²⁺ -sensitized CO₂ reduction system, the CoFeO_X -added system achieved 19-fold enhancement of CO production (45.7 μmol/h). The mixed valence state and nanosheet-like structure of CoFeO_X cocatalyst support its ultra-high charge transfer and abundant CO₂ active adsorption sites exposure, which promote the separation of photogenerated charges, and thus improve the photocatalytic CO₂ reduction activity. Carbon source of CO from CO₂ was verified by ¹³ CO₂ isotopic labelling experiment. Repeated activity experiments confirmed the good stability of CoFeO_X in the CO₂ photoreduction system. This work would provide prospective insights into developing novel cost-effective, efficient, and durable non-precious metal cocatalysts to improve the efficiency of photocatalytic reduction of CO₂ .

Spinel ferrites materials for sulfate radical-based advanced oxidation process: A review

In the past decade, the sulfate radical-based advanced oxidation processes (SR-AOPs) have been increasingly investigated because of their excellent performance and ubiquity in the degradation of emerging contaminants. Generally, sulfate radicals can be generated by activating peroxodisulfate (PDS) or peroxymonosulfate (PMS). To date, spinel ferrites (SF) materials have been greatly favored by researchers in activating PMS/PDS for their capability and unique superiorities. This article reviewed the recent advances in various pure SF, modified SF, and SF composites for PDS/PMS activation. In addition, synthesis methods, mechanisms, and potential applications of SF-based SR-AOPs were also examined and discussed in detail. Finally, we present future research directions and challenges for the application of SF materials in SR-AOPs.

Mg-Fe-Al-O spinel: Preparation and application as a heterogeneous photo-Fenton catalyst for degrading Rhodamine B

It is an urgent need to develop new environmentally friendly spinel ferrites with high catalytic efficiency. In this work, a series of Mg-Fe-Al-O spinels with different ratios of Mg/Al were successfully synthesized by the reaction sintering method and were used as a heterogeneous photo-Fenton catalyst for degradation of Rhodamine B (RhB). The effect of different ratios of Mg/Al on the properties of Mg-Fe-Al-O spinel was characterized and analyzed through a range of advanced characterization techniques and DFT calculations. The influence factors on the photo-Fenton reaction catalyzed by Mg-Fe-Al-O spinels were systematically investigated. The results showed that the prepared Mg-Fe-Al-O spinels had larger lattice parameters, wider bandgap, and stronger magnetism, with the Mg content increased. Among them, Mg-9 (Mg_0.88Fe_1.88Al_0.23O₄) had the best catalytic performance in the photo-Fenton reaction. The degradation efficiency of RhB reached 98.45%, and the TOC removal efficiency was 83.47%. The elemental valence and PDOS of Mg-9 (Mg_0.88Fe_1.88Al_0.23O₄) spinels were closer to MgFe₂O₄. The photo-generated holes could directly oxidize water and hydroxyl to generate reactive oxygen species ·OH, improving the catalytic activity.

Tuning the Structural and Magnetic Properties of the Stuffed Framework Structures MeFe2O4 (Me = Ni, Ca, and Sr)

Spinel ferrite nanoparticles (NPs), have received a lot of attention in medical applications. Therefore, facile synthesis of ferrite NPs of numerous shapes and sizes using the citrate autocombustion technique was utilized in this article. A series of ferrite with the general formula MeFe2O4 [Me = nickle (Ni), calcium (Ca), and strontium (Sr)] are synthesized with varying average ionic radii and cation disorder on the A-site. The structural and morphological characterization of the prepared samples was performed using XRD, HRTEM, FESEM, EDAX, XPS, and Raman analyses. The phase transformation from cubic (Ni) to orthorhombic (Ca) to monoclinic (Sr) was also revealed by XRD. Accordingly, HRTEM images demonstrated nanoparticles in orthorhombic and monoclinic shapes, which are inconsistent with XRD analyses. The coercive field HC for monoclinic SrFe2O4 is ≈ 42 times larger than the Hc for NiFe2O4 with a cubic structure. This deviation in HC compared to the cubic shape particles can be coupled to the shape anisotropy present in SrFe2O4 and refers to the presence of a preferred magnetization direction within the material. The use of monoclinic SrFe2O4 NPs as antifungal activity agents is noteworthy due to their advantages in terms of surface area, efficacy, and biodegradability.

Progress in the Preparation and Modification of Zinc Ferrites Used for the Photocatalytic Degradation of Organic Pollutants

Zinc ferrite is a type of photocatalytic material with high physicochemical stability, narrow band gap, high carrier separation efficiency, high porosity, and paramagnetism, which makes it easy to recover. Thus, zinc ferrite is widely used as a photocatalyst in water treatment. In this paper, the preparation principles as well as the advantages and disadvantages of typical methods used to prepare zinc ferrite including hydrothermal, co-precipitation, sol-gel, and other novel methods such as biosynthesis have been summarized. Modification methods such as elemental doping, composite formation, and morphological modification have been highlighted. Using these modification methods, the catalytic activity of zinc ferrite toward the photocatalytic degradation of organic pollutants in water has been enhanced. Biosynthesis is regarded as a promising preparation method that uses biological materials instead of chemical materials to achieve the large-scale preparation of zinc ferrite using low cost, energy efficient, and environmentally friendly processes. Meanwhile, the combination of multiple modification techniques to enhance the photocatalytic performance of zinc ferrite will be an important research trend in the future.

Controlling Cation Distribution and Morphology in Colloidal Zinc Ferrite Nanocrystals

This paper describes the first synthetic method to achieve independent control over both the cation distribution (quantified by the inversion parameter x) and size of colloidal ZnFe₂O₄ nanocrystals. Use of a heterobimetallic triangular complex of formula ZnFe₂(μ₃-O)(μ₂-O₂CCF₃)₆(H₂O)₃ as a single-source precursor, solvothermal reaction conditions, absence of hydroxyl groups from the reaction solvent, and the presence of oleylamine are required to achieve well-defined, crystalline, and monodisperse ZnFe₂O₄ nanoparticles. The size of the ZnFe₂O₄ nanocrystals increases as the ratio of oleic acid and oleylamine ligands to precursor increases. The inversion parameter increases with increasing solubility of the precursor in the reaction solvent, with the presence of oleic acid in the reaction mixture, and with decreasing reaction temperature. These results are consistent with a mechanism in which ligand exchange between oleic acid and carboxylate ligands bound to the precursor complex influences the degree to which the reaction produces a kinetically trapped or thermodynamically stable cation distribution. Importantly, these results indicate that preservation of the triangular Zn-O-Fe₂ core structure of the precursor in the reactive monomer species is crucial to the production of a phase-pure ZnFe₂O₄ product and to the ability to tune the cation distribution. Overall, these results demonstrate the advantages of using a single-source precursor and solvothermal reaction conditions to achieve synthetic control over the structure of ternary spinel ferrite nanocrystals.

Impact of Ga3+ Ions on the Structure, Magnetic, and Optical Features of Co-Ni Nanostructured Spinel Ferrite Microspheres

Co-Ni ferrite is one of the crucial materials for the electronic industry. A partial substitution with a rare-earth metal brings about modification in crystal lattice and broadens knowledge in the discovery of new magnetic material. Current work reports a Ga³⁺ substitution in the Co-Ni ferrite with composition Co_0.5Ni_0.5Fe_2-xGa_xO₄ (where x = 0.0, 0.2, 0.4, 0.6, 0.8, and 1.0), herein referred to as spinel ferrite microspheres (CoNiGa-SFMCs). The samples were crystallized hydrothermally showing a hollow sphere morphology. The crystal phase, magnetic, morphology, and optical behaviour were examined using various microscopy and spectroscopic tools. While the XRD confirmed the phase of SFMCs, the crystallite size varied between 9 and 12 nm. The Tauc plot obtained from DRS (diffuse reflectance spectroscopy) shows the direct optical energy bandgap (E_g) of the products, with the pristine reading having the value of 1.41 eV E_g; the band gap increased almost linearly up to 1.62 eV along with rising the Ga³⁺ amount. The magnetic features, on the other hand, indicated the decrease in coercivity (H_c) as more Ga³⁺ is introduced. Moreover, there was a gradual increase in both saturation magnetization (M_s) and magnetic moment (nB) with increasing amount of Ga³⁺ till x = 0.6 and then a progressive decline with increases in the x content; this was ascribed to the spin-glass-like behavior at low temperatures. It was detected that magnetic properties correlate well with crystallite/particle size, cation distribution, and anisotropy.