Fabrication of MgFe2O4/MoS2 Heterostructure Nanowires for Photoelectrochemical Catalysis

Enhancing photocatalytic wastewater treatment: investigating the promising applications of nickel ferrite and its novel nanocomposites

Water contamination ranks highest among the challenges posed by the rapidly increasing environmental contamination, which is thought to be the most pressing issue globally. The development of innovative techniques for the successful removal of diverse types of undesirable pollutants from wastewater would therefore yield a huge return on investment. Nowadays, the removal of many organic and synthetic pollutants from the environmental matrix is anticipated to be possible by photocatalytic degradation, owing to its low energy consumption, high catalytic activity, and low overall cost. In this context, magnetic nanoparticles received greater attention as photocatalytic materials from the scientific community in wastewater treatment for the removal of different kinds of pollutants due to their specific properties. The present study provides an overview of the recent advances in water treatment using nickel ferrite nanoparticles and their nanocomposites as photocatalysts. Furthermore, a proposed mechanism for these photocatalysts to generate active free radicals under visible and ultraviolet light has been described. The review concludes that photocatalysts based on NiFe2O4 have potential applications in water purification technologies. However, more research is still needed to determine their practical application in water treatment facilities.

Engineering Rich Active Sites and Efficient Water Dissociation for Ni-Doped MoS2/CoS2 Hierarchical Structures toward Excellent Alkaline Hydrogen Evolution

Besides improving charge transfer, there are two key factors, such as increasing active sites and promoting water dissociation, to be deeply investigated to realize high-performance MoS₂-based electrocatalysts in alkaline hydrogen evolution reaction (HER). Herein, we have demonstrated the synergistic engineering to realize rich unsaturated sulfur atoms and activated O-H bonds toward the water for Ni-doped MoS₂/CoS₂ hierarchical structures by an approach to Ni doping coupled with in situ sulfurizing for excellent alkaline HER. In this work, the Ni-doped atoms are evolved into Ni(OH)₂ during alkaline HER. Interestingly, the extra unsaturated sulfur atoms will be modulated into MoS₂ nanosheets by breaking Ni-S bonds during the formation of Ni(OH)₂. On the other hand, the higher the mass of the Ni precursor (m_Ni) for the fabrication of our samples, the more Ni(OH)₂ is evolved, indicating a stronger ability for water dissociation of our samples during alkaline HER. Our results further reveal that regulating m_Ni is crucial to the HER activity of the as-synthesized samples. By regulating m_Ni to 0.300 g, a balance between increasing active sites and promoting water dissociation is achieved for the Ni-doped MoS₂/CoS₂ samples to boost alkaline HER. Consequently, the optimal samples present the highest HER activity among all counterparts, accompanied by reliable long-term stability. This work will promise important applications in the field of electrocatalytic hydrogen evolution in alkaline environments.

Hollow CuFe2O4/MgFe2O4 Heterojunction Boost Photocatalytic Oxidation Activity for Organic Pollutants

P-n heterojunction-structured CuFe2O4/MgFe2O4 hollow spheres with a diameter of 250 nm were synthesized using a template-free solvothermal method, and time-dependent morphological studies were carried out to investigate the hollow formation mechanism. The CuFe2O4/MgFe2O4 with a molar ratio of 1:2 (Cu:Mg) had the highest degradation efficiency with the model organic dye Acid Orange 7, with a degradation rate of 91.96% over 60 min. The synthesized CuFe2O4/MgFe2O4 nanocomposites were characterized by XRD, TEM, HRTEM, UV-vis spectroscopy, Mott–Schottky, and EIS. Due to the synthesis of the p-n heterojunction, CuFe2O4/MgFe2O4 has efficient photogenerated carriers, and the hollow structure has a higher specific surface area and stronger adsorption capacity, which is significantly better than that of CuFe2O4 and MgFe2O4 in terms of photocatalytic performance. The outstanding performance shows that the p-n heterostructure of CuFe2O4/MgFe2O4 has potential for application in wastewater degradation.

The Cation Distributions of Zn-doped Normal Spinel MgFe2O4 Ferrite and Its Magnetic Properties

Determining the exact occupation sites of the doping ions in spinel ferrites is vital for tailoring and improving their magnetic properties. In this study, the distribution and occupation sites of cations in MgFe₂O₄ and Zn-doped MgFe₂O₄ ferrite are imaged by Cs-STEM. The experimental STEM images along [001], [011] and [111] orientations suggest that the divalent Mg²⁺ cations occupy all A sites, and the trivalent Fe³⁺ cations occupy all B sites in MgFe₂O₄ ferrite prepared by electrospinning, which is consistent with the normal spinel structure. We further clarify that the preferred sites of dopant Zn²⁺ ions are Fe³⁺ crystallographic sites in the Zn-doped MgFe₂O₄ ferrite nanofibers. Magnetic measurements show that Zn doping affects the spin states of the Fe³⁺, and the Fe³⁺-O²⁻-Fe³⁺ super-exchange interaction leads to enhancements in the magnetization and reduction in the Curie temperature. Our work should contribute a significant step toward eventually realizing the practical application of doped spinel ferrites.

Adsorptive removal of pollutants from water using magnesium ferrite nanoadsorbent: a promising future material for water purification

Nanoadsorbents having large specific surface area, high pore volume with tunable pore size, affordability and easy magnetic separation gained much popularity in recent time. Iron-based nanoadsorbents showed higher adsorption capacity for different pollutant removal from water among other periodic elements. Spinel ferrite nanomaterials among iron-bearing adsorbent class performed better than single iron oxide and hydroxides due to their large surface area, mesoporous pore, high pore volume and stability. This work aimed at focusing on water treatment using magnesium ferrite (MgFe₂O₄) nanomaterials. Synthesis routes, properties and pollutant adsorption were critically investigated to explore the performance of magnesium ferrite in water treatment. Structural and surface properties were greatly affected by the factors involved in different synthesis routes and iron and magnesium ratio. Complete removal of pollutants through adsorption was achieved using magnesium ferrite. Pollutant adsorption capacity of MgFe₂O₄ and its modified forms was found several folds higher than Fe₂O₃ and Fe₃O₄ nanomaterials. In addition, MgFe₂O₄ showed strong stability in water than other pure iron oxide and hydroxide. Modification with graphene oxide, activated carbon, biochar and silica was demonstrated to be beneficial for enhanced adsorption capacity. Complex formation was suggested as a dominant mechanism for pollutant adsorption. These nanomaterials could be a viable and competitive adsorbent for diverse pollutant removal from water.

Elevating the charge separation of MgFe2O4 nanostructures by Zn ions for enhanced photocatalytic and photoelectrochemical water splitting

Magnesium ferrites (MgFe₂O₄) are important class of ferrites that have been receiving greater attention as promising excellent photocatalyst due to its low cost, wide light spectrum response and environment-friendly nature. However, its poor electronic conductivity and fast charge carrier recombination hinders its electrocatalytical applications. Hence, accelerating charge carriers separation efficiency is important to modify the photoelectrochemical performance of MgFe₂O₄. Herein, novel Zn ions doped MgFe₂O₄ nanospheres are fabricated for the first time. Zn ions are doped into MgFe₂O₄ nanostructures from surface to enhance their charge separation efficiency. The doped MgFe₂O₄ nanostructures show significant photocatalytic activity and enhanced photocurrent density than that of pristine MgFe₂O₄.The improved photoelectrocatalytic performance is attributed to doping effect, were Zn ions actually enhance the conductivity. Zn ions enhance the activity of MgFe₂O₄ and accelerate the charge transfer properties in MgFe₂O₄. The results highlight that Zn doped MgFe₂O₄ nanospheres could be a potential candidate for photocatalytic and photoelectrochemical applications.

Transition metal sulfides meet electrospinning: versatile synthesis, distinct properties and prospective applications

One-dimensional (1D) electrospun nanomaterials have attracted significant attention due to their unique structures and outstanding chemical and physical properties such as large specific surface area, distinct electronic and mass transport, and mechanical flexibility. Over the past years, the integration of metal sulfides with electrospun nanomaterials has emerged as an exciting research topic owing to the synergistic effects between the two components, leading to novel and interesting properties in energy, optics and catalysis research fields for example. In this review, we focus on the recent development of the preparation of electrospun nanomaterials integrated with functional metal sulfides with distinct nanostructures. These functional materials have been prepared via two efficient strategies, namely direct electrospinning and post-synthesis modification of electrospun nanomaterials. In this review, we systematically present the chemical and physical properties of the electrospun nanomaterials integrated with metal sulfides and their application in electronic and optoelectronic devices, sensing, catalysis, energy conversion and storage, thermal shielding, adsorption and separation, and biomedical technology. Additionally, challenges and further research opportunities in the preparation and application of these novel functional materials are also discussed.

Recent advances in photodegradation of antibiotic residues in water

Antibiotics are widely present in the environment due to their extensive and long-term use in modern medicine. The presence and dispersal of these compounds in the environment lead to the dissemination of antibiotic residues, thereby seriously threatening human and ecosystem health. Thus, the effective management of antibiotic residues in water and the practical applications of the management methods are long-term matters of contention among academics. Particularly, photocatalysis has attracted extensive interest as it enables the treatment of antibiotic residues in an eco-friendly manner. Considerable progress has been achieved in the implementation of photocatalytic treatment of antibiotic residues in the past few years. Therefore, this review provides a comprehensive overview of the recent developments on this important topic. This review primarily focuses on the application of photocatalysis as a promising solution for the efficient decomposition of antibiotic residues in water. Particular emphasis was laid on improvement and modification strategies, such as augmented light harvesting, improved charge separation, and strengthened interface interaction, all of which enable the design of powerful photocatalysts to enhance the photocatalytic removal of antibiotics.

Dual-Mode Aptasensor Assembled by a WO3/Fe2O3 Heterojunction for Paper-Based Colorimetric Prediction/Photoelectrochemical Multicomponent Analysis

The programed bimodal photoelectrochemical (PEC)-sensing platform based on DNA structural switching induced by targets binding to aptamers was innovatively designed for the simultaneous detection of mucin 1 (MUC1) and microRNA 21 (miRNA-21). To promote excellent current intensity as well as enhance the sensitivity of aptasensors, the evenly distributed WO₃/Fe₂O₃ heterojunction was prepared as a transducer material, notably reducing the background signal response and extending the absorption of light. The multifunctional paper-based biocathode was assembled to provide a visual colorimetric assay. When introducing the integrated signal probe (ISP) composed of signal probe 1 (sP1) and signal probe 2 (sP2) on paper-based working units modified with gold nanoparticles (AuNPs), recognition sites of two targets were formed. In the presence of MUC1 protein, both sP1 and the target on the working unit were released into the corresponding colorimetric unit because of the DNA specific recognition. The horseradish peroxidase-streptavidin (HRP-SA) carried by free sP1 could oxidize 3,3',5,5'-tetramethylbenzidine (TMB) to turn a blue-colored oxidized TMB (oxTMB) in the presence of hydrogen peroxide (H₂O₂), which ultimately gained a higher photocurrent signal. Furthermore, miRNA-21 was modified on another working unit by binding with sP2, leading to changes in the current signal and thus enabling real-time detection of analytes with the assistance of a digital multimeter. The PEC aptasensor offered a wide dynamic range of 10 fg·mL^-1-100 ng mL^-1 for MUC1 and 0.1 pM-10 nM for miRNA-21, with a low detection limit of 3.4 fg·mL^-1 and 36 fM, respectively. It laid the foundation for synchronous detection of multiple analytes and initiated a new way for the enhancement in modern next-generation disease diagnosis.

Spinel ferrite (AFe2O4)-based heterostructured designs for lithium-ion battery, environmental monitoring, and biomedical applications

The development of spinel ferrite nanomaterial (SFN)-based hybrid architectures has become more popular owing to the fascinating physicochemical properties of SFNs, such as their good electro-optical and catalytic properties, high chemothermal stability, ease of functionalization, and superparamagnetic behaviour. Furthermore, achieving the perfect combination of SFNs and different nanomaterials has promised to open up many unique synergistic effects and advantages. Inspired by the above-mentioned noteworthy properties, numerous and varied applications have been recently developed, such as energy storage in lithium-ion batteries, environmental pollutant monitoring, and, especially, biomedical applications. In this review, recent development efforts relating to SFN-based hybrid designs are described in detail and logically, classified according to 4 major hybrid structures: SFNs/carbonaceous nanomaterials; SFNs/metal–metal oxides; SFNs/MS₂; and SFNs/other materials. The underlying advantages of the additional interactions and combinations of effects, compared to the standalone components, and the potential uses have been analyzed and assessed for each hybrid structure in relation to lithium-ion battery, environmental, and biomedical applications.

We have summarized recent developments in SFN-based hybrid designs. The additional interactions, combination effects, and important changes have been analyzed and assessed for LIB, environmental monitoring, and biomedical applications.

Study on the degradation of accumulated bisphenol S and regeneration of magnetic sludge-derived biochar upon microwave irritation in the presence of hydrogen peroxide for application in integrated process

Based on the multi-functional magnetic sludge-derived biochar (MSBC), an innovative integrated process-coupling accumulation by adsorbing, degradation by microwave (MW)-induced catalytic oxidation in the presence of H₂O₂ and the regeneration of adsorbent simultaneously, was proposed. In this study, bisphenol S (4,4'-sulfonyldiphenol) was chosen as the pollutant model, its behaviors and related mechanism of BPS and MSBC in MW + H₂O₂ system were investigated. The BPS effective degradation on MSBC was proved by decoupling the adsorption and degradation with solvent extraction. OH and h⁺ play vital roles based on the scavenger tests. The synergistic effects of hot-spot of microwave irradiation, activation of H₂O₂, and charge transfer-induced doping effects of MSBC were attributed to the reactions. This work proves the feasibility in economics and energy-save treatment approach for low concentration organic pollutants in water.

Magnetically retrievable ferrite nanoparticles in the catalysis application

In the present review, we summarized the applications of magnetic spinel ferrite nanoparticles as catalysts in organic reactions and transformations. Catalytic applications are comprised of using mostly cobalt, nickel, copper, and zinc ferrites, along with their mixed-metal combinations based on nano ferrites. The spinel ferrites (SFs) are gained principally by wet-chemical, sol-gel or co-precipitation methods, more infrequently by the mechanical high-energy ball milling, spark plasma sintering, sonochemical technique, microwave heating or hydrothermal route. Catalytic processes with the application of ferrite nanoparticles are included decomposition (in particular photocatalytic), reactions of dehydrogenation, oxidation, alkylation, CC coupling, removing organic/inorganic contaminants from aqueous solutions. As significant and remarkable advantages, ferrite nanocatalysts not only are environmentally benign and compatible with green chemistry aspects but also can be simply recovered from reaction systems and recycled up to several times almost without significant loss of their catalytic activity.

Chemical Vapor Deposition Growth and Applications of Two-Dimensional Materials and Their Heterostructures

Two-dimensional (2D) materials have attracted increasing research interest because of the abundant choice of materials with diverse and tunable electronic, optical, and chemical properties. Moreover, 2D material based heterostructures combining several individual 2D materials provide unique platforms to create an almost infinite number of materials and show exotic physical phenomena as well as new properties and applications. To achieve these high expectations, methods for the scalable preparation of 2D materials and 2D heterostructures of high quality and low cost must be developed. Chemical vapor deposition (CVD) is a powerful method which may meet the above requirements, and has been extensively used to grow 2D materials and their heterostructures in recent years, despite several challenges remaining. In this review of the challenges in the CVD growth of 2D materials, we highlight recent advances in the controlled growth of single crystal 2D materials, with an emphasis on semiconducting transition metal dichalcogenides. We provide insight into the growth mechanisms of single crystal 2D domains and the key technologies used to realize wafer-scale growth of continuous and homogeneous 2D films which are important for practical applications. Meanwhile, strategies to design and grow various kinds of 2D material based heterostructures are thoroughly discussed. The applications of CVD-grown 2D materials and their heterostructures in electronics, optoelectronics, sensors, flexible devices, and electrocatalysis are also discussed. Finally, we suggest solutions to these challenges and ideas concerning future developments in this emerging field.

Fabrication of Ag3PO4/GO/NiFe2O4 composites with highly efficient and stable visible-light-driven photocatalytic degradation of rhodamine B

Effective visible-light-driven Ag₃PO₄/GO/NiFe₂O₄Z-scheme magnetic composites were successfully fabricated by a simple ion-exchange deposition method. The Ag₃PO₄/GO/NiFe₂O₄ (8%) composite exhibited excellent photocatalytic activity (degradation efficiency was ∼96% within 15 min and kinetic constant reached 0.1956 min⁻¹) and stability when compared to Ag₃PO₄, NiFe₂O₄, and Ag₃PO₄/NiFe₂O₄ for rhodamine B (RhB) degradation. Furthermore, by electrochemical and fluorescence measurements, the Ag₃PO₄/GO/NiFe₂O₄ (8%) material also showed larger transient photocurrent, lower impedance, and longer fluorescence lifetime (7.82 ns). Comparing the activity result dependence with characterization results, it was indicated that photocatalytic activity depended on fast charge transfer from Ag₃PO₄ to NiFe₂O₄ through GO sheet. The h⁺ and ·O₂⁻ species played important roles in RhB degradation under visible-light. A possible Z-scheme mechanism is proposed over the Ag₃PO₄/GO/NiFe₂O₄ (8%) composite. This study might provide a promising visible light responsive photocatalyst for the photocatalytic degradation of organic dyes in wastewater.

Effective visible-light-driven Ag₃PO₄/GO/NiFe₂O₄Z-scheme magnetic composites were successfully fabricated by a simple ion-exchange deposition method. The composites exhibited excellent photocatalytic activity and stability for RhB degradation.

Highly efficient visible-light-driven photocatalytic degradation of rhodamine B by a novel Z-scheme Ag3PO4/MIL-101/NiFe2O4 composite

An Ag₃PO₄/MIL-101/NiFe₂O₄ composite was fabricated by an in situ precipitation method. The results implied that introduction of the MOF enhanced the rapid transfer of electrons from Ag₃PO₄ to NiFe₂O₄.

In situ construction of a heterojunction over the surface of a sandwich structure semiconductor for highly efficient photocatalytic H2 evolution under visible light irradiation

Developing a heterostructure on the surface of a "sandwich" structure semiconductor is essential for full utilization of its heterojunction function and hence for designing efficient solar energy conversion systems. Here, we show that 2D-2D MoS₂/MnSb₂S₄ heterostructure composites are designed for the first time and successfully synthesized by a simple in situ calcination pathway. Under visible light irradiation, the ca. 3.3 wt% MoS₂/MnSb₂S₄ samples exhibited the highest activity for H₂ evolution, which was 7.7 times higher than that of the pristine MnSb₂S₄ monolayer. The outstanding photocatalytic performance was attributed to the MoS₂ nanosheets intimately growing on the surface [SbS]⁺ layers of monolayer MnSb₂S₄ nanosheets with the [SbS]⁺-[MnS₂]^2--[SbS]⁺ sandwich substructure to form the 2D-2D MoS₂/MnSb₂S₄ heterojunction structure. More importantly, we prove that this specific heterojunction structure can lead to more weakening of the constraint of the valence electrons in the composited photocatalysts, which can promote the transfer of photogenerated electrons from MnSb₂S₄ to MoS₂. The present study provides a new design strategy for the construction of a heterostructure to improve the photocatalytic H₂ production activity highly efficiently.

Controllable TiO2 heterostructure with carbon hybrid materials for enhanced photoelectrochemical performance

A TiO₂/RGO/C₃N₄ heterostructure has been successfully designed and fabricated, and the narrow bandgap and conductivity of RGO and C₃N₄ could be beneficial for the generation and separation of photocharges.

One-step syntheses of MoS2/graphitic carbon composites with enhanced photocatalytic activity under visible light irradiation

MoS₂/GC composites were synthesized with sodium alginate as carbon source, and the reason for enhanced photocatalytic activity has been revealed.