Metal-organic frameworks template-directed growth of layered double hydroxides: A fantastic conversion of functional materials

Understanding the phase structure evolution and charge storage mechanism of FeCoNi-MOFs as electrodes for asymmetric supercapacitors

Metal-organic frameworks (MOFs) due to abundant apertures, adjustable components, and multi-purpose structures have broad application prospects in supercapacitors. However, its low conductivity, poor stability, and difficulty growing evenly on the conductive substrate limit the electrochemical energy storage performance. Herein, with FeCoNi-OH nanosheets serving as the precursors, the trimetallic FeCoNi-MOF (FCNM) multilayer structure is successfully synthesized on activated carbon cloth (AC), and its optimal growth state (FCNM/AC-12 h) is achieved by regulating the reaction time. The FCNM/AC-12 h with enhanced kinetics and multi-metal synergies achieve an excellent capacitance (13.02 F/cm2 at 1 mA/cm2) and a good cycle stability (the capacity is 83.33 % of the initial value after 10,000 cycles). Its phase structural evolution and charge storage mechanism during the electrode process are investigated through in-depth electrochemical testing and ex-situ characterization. Furthermore, when the power density is 1.6 mW/cm2, the FCNM/AC-12 h//AAC device exhibits a high energy density of 1.134 mWh/cm2, and its capacity retains 97.89 % of the initial value after 10,000 cycles at 50 mA/cm2. This work provides reliable experimental guidance for synthesizing multi-metal MOFs on carbon cloth and revealing its energy storage mechanism.

High-performance disposable electrochemical sensors for creatinine derived from hollow CoNi-LDH@Creatinine-imprinted Poly(methacrylic acid) (i-PMA) composites

BACKGROUND

Layered double hydroxides (LDHs), featuring a 2D layered structure, are an emerging class of inorganic porous materials for electrochemical biosensors. Presently, they are primarily utilized in the electrochemical detection of oxygen-containing biomolecules. However, there are currently no reported LDH sensors, particularly CoNi-LDH ones, designed for the electrochemical detection of creatinine (Cre), a widely studied nitrogen-containing biomolecule. Here, to realize electrochemical detection of creatinine, a unique hollow CoNi-LDH/creatinine imprinted polymethacrylic acid (H-LDH@i-PMA) composite is developed through a pioneering combination of a hollow CoNi-LDH (H-LDH) structure and the molecular imprinting polymer (MIP) coating technique.

RESULTS

The materials are comprehensively characterized using FT-IR, PXRD, XPS, TEM, CV, and EIS. Disposable Au-screen printed electrodes are fabricated with both H-LDH and H-LDH@i-PMA, and the sensing of Cre is subsequently investigated via cyclic voltammetry and differential pulse voltammetry methods. The H-LDH@i-PMA sensor exhibits superior porosity, a larger electroactive area, and enhanced electron-transfer kinetics in comparison to H-LDH sensor. The H-LDH@i-PMA sensor achieves a wide detection range of 0-1000 nM, accompanied by a low detection limit of 236 pM, and five-times more sensitivity for Cre than non-imprinted H-LDH sensor. Futhermore, it demonstrates robust selectivity against interferents such as ascorbic acid, uric acid, guanine, and glutamine. When tested with real salivary samples, it exhibits a recovery rate of 99.0 ± 1.80 %, and maintains excellent reusability over a period of four weeks.

SIGNIFICANCE

These exceptional results are due to superior electroactive area, tailor-made recognition sites, and greater electron-transfer kinetics of H-LDH@i-PMA as compared to the non-imprinted LDH sensor. This is the first reported use of an LDH-based sensor for the detection of Cre, providing valuable insights into developing high-performance electrochemical sensors for various biomolecules.

Spindle-Shaped Ni-Fe-Layered Double Hydroxide: Effect of Etching Time on Flexible Energy Storage

The rising demand for efficient energy storage in flexible electronics is driving the search for materials that are well-suited for the fabrication of these devices. Layered Double Hydroxides (LDHs) stand out as a remarkable material with a layered structure that embodies exceptional electrochemical properties. In this study, both double-shelled and single-shelled NiFe-Layered Double Hydroxide (LDH) particles are prepared using spindle-shaped MIL-101(Fe) as the template. These NiFe-LDH particles are then utilized to develop a flexible energy storage device. Transmission electron microscopy(TEM) analysis revealed that the as-synthesized NiFe-LDH particles transformed into hollow single-shells from a double-shelled structure as the aging time increased, which significantly influenced the electrochemical performances. Despite the decreasing specific capacitance and energy density with longer etching times, the sample etched for 2 h (NiFe-LDH 2h) demonstrated the highest capacitance of 9.24 mF·cm⁻2 and an energy density of 0.46 µW·h·cm⁻2, highlighting its promising performance for energy storage applications. X-ray photoelectron spectroscopy (XPS) analysis revealed the highest Ni2+: Ni3+ ratio, and Fe: Ni ratio for NiFe- LDH 2h samples, which further influences the energy storage properties. The ability to maintain the high performance of these materials across different bending angles further emphasizes its versatility and relevance in emerging flexible electronics markets.

Integration of metal-organic frameworks and clay toward functional composite materials

Metal-organic frameworks (MOFs) have become increasingly important as a class of porous crystalline materials because of their diverse applications. At the same time, significant progress has been achieved in the field of MOF-based composite materials toward novel applications based on the synergistic effect of two or more different components. Clay materials have been explored recently in MOF chemistry for the synthesis of MOF-clay composites, which are a new class of functional materials synthesized by a cooperative combination of MOFs with clay. Such composites have evolved only in the recent past with important functions and applications, such as enhanced gas storage and separation, CO2 capture and conversion, catalysis, drug delivery, and water harvesting. Notably, the typical shortcomings of MOFs, such as moisture sensitivity, poor water dispersibility, poor thermal and chemical stability, and poor processability, could be overcome by developing novel MOF-clay composites. This article provides a concise overview of MOF-clay composites and their applications in various fields that will drive the interest of researchers to explore the emerging field of MOF-clay chemistry. In the initial sections, we classify the clays that have been used in MOF chemistry and briefly discuss their structures and chemistry. We also present the advantages of MOF-clay composites and discuss their synthetic methodologies. In the later sections, we classify different MOF-clay composites based on the clay and present some representative examples of such composites that show unique properties and applications. Finally, the development in this field is summarized, and the future scope of such composites is discussed.

Co-In Bimetallic Hydroxide Nanosheet Arrays With Coexisting Hydroxyl and Metal Vacancies Anchored on Rod-Like MOF Template for Enhanced Photocatalytic CO2 Reduction

Layered double hydroxides (LDHs) can serves as catalysts for CO2 photocatalytic reduction (CO2PR). However, the conventionally synthesized LDHs undergo undesired aggregation, which results in an insufficient number of active sites and limits the desirable electron transfer required for CO2PR. The metal-organic framework (MOF) template-grown LDHs demonstrate excellent promise for exploiting the strengths of both MOFs and LDHs. Herein, the in situ growth of MIL-68(In)-NH2 MOF-templated Co-In bimetallic catalyst (CoIn-LDH/MOF) having an ultrathin nanosheet morphology on the preserved rod-like MOF template is demonstrated. Compared to the conventionally grown bimetallic LDH (CoIn-LDH), CoIn-LDH/MOF not only exposes more active sites but also possesses hydroxyl vacancies (VOH) and Co vacancies (VCo). Thus, CoIn-LDH/MOF performs a higher CO generation rate of 2320 µmol g-1 h-1 during CO2PR, demonstrating improved activity and selectivity than those in CoIn-LDH. Experiments coupled with calculations reveal that the CoIn-LDH/MOF-driven CO2PR follows the *COOH pathway. The lower energy barriers for the formation of *COOH and CO(g) can be attributed to the coexistence of VOH and VCo in CoIn-LDH/MOF, effectively promoting charge transfer and enhancing CO2PR performance. This study provides a new strategy to obtain high-performant LDH-based catalysts with improved morphology.

Efficient microplastics adsorption in aqueous environments via bidirectional ordered graphene oxide/nanocellulose aerogels

Microplastics not only accumulate various harmful substances but also are ingested by marine organisms and humans, causing immeasurable impacts. Therefore, the removal of microplastics has become a crucial proposition for addressing the issue of microplastic pollution. This study investigated a bidirectional ordered graphene oxide (GO)/nanocellulose aerogels (D-DPGG) to remove microplastics from water bodies. The concentration of microplastics before and after adsorption was measured using a fluorescence spectrophotometer. D-DPGG aerogel exhibited excellent adsorption performance for microplastics (241.56 mg/g) and maintained high adsorption efficiency (>80 %) over 20 cycles of adsorption testing. Additionally, the link between GO and dual-directional treatment significantly improved the aerogel microstructure. It had an apparent layered structure in the transverse direction and improves the mechanical properties. D-DPGG aerogel not only served as an effective solution in adsorption but also held promise as a novel material in directional structural design.

Layered double hydroxide-based electrode materials derived from metal-organic frameworks: synthesis and applications in supercapacitors

Metal-organic frameworks (MOFs) have emerged as promising electrode materials for supercapacitors (SCs) due to their highly porous structures, tunable chemical compositions, and diverse morphologies. However, their applications are hindered by low conductivity and poor cycling performance. A novel approach for resolving this issue involves the growth of layered double hydroxides (LDHs) using MOFs as efficient templates or precursors for electrode material preparation. This method effectively enhances the stability, electrical conductivity, and mass transport ability of MOFs. The MOF-derived LDH exhibits a well-defined porous micro-/nano-structure, facilitating the dispersion of active sites and preventing the aggregation of LDHs. Firstly, this paper introduces synthesis strategies for converting MOFs into LDHs. Subsequently, recent research progress in MOF-derived LDHs encompassing pristine LDH powders, LDH composites, and LDH-based arrays, along with their applications in SCs, is overviewed. Finally, the challenges associated with MOF-derived LDH electrode materials and potential solutions are discussed.

Microplastics/nanoplastics in porous media: Key factors controlling their transport and retention behaviors

Till now, microplastics/nano-plastics(M/NPs) have received a lot of attention as emerging contaminant. As a typical but complex porous medium, soil is not only a large reservoir of M/NPs but also a gateway for M/NPs to enter groundwater. Therefore, the review of the factors controlling the transport behavior of M/NPs in porous media can provide important guidance for the risk assessment of M/NPs in soil and groundwater. In this study, the key factors controlling the transport behavior of M/NPs in porous media are systematically divided into three groups: (1) nature of M/NPs affecting M/NPs transport in porous media, (2) nature of flow affecting M/NPs transport in porous media, (3) nature of porous media affecting M/NPs transport. In each group, the specific control factors for M/NPs transport in porous media are discussed in detail. In addition to the above factors, some substances (colloids or pollutants) present in natural porous media (such as soil or sediments) will co-transport with M/NPs and affect its mobility. According to the different properties of co-transported substances, the mechanism of promoting or inhibiting the migration behavior of M/NPs in porous media was discussed. Finally, the limitations and future research directions of M/NPs transport in porous media are pointed out. This review can provide a useful reference for predicting the transport of M/NPs in natural porous media.

Metal Selenide-Based Superstructure Nanoarrays with Ultrahigh Capacity for Alkaline Zn Batteries

Transition metal selenides (TMSs) have great potential as cathode materials for alkaline Zn batteries (AZBs) owing to their high theoretical capacity and metallic conductivity. However, achieving a high specific capacity remains a formidable challenge due to the low structural stability and sluggish reaction kinetics of single-phase TMS. Herein, a facile method for fabricating a robust CoSe2@Ni3Se4@Ni(OH)2 superstructure nanoarray (CNSNA) as an AZB cathode is presented. The sophisticated design enables structural stability and abundant active surface sites for efficient charge storage. Furthermore, the redox mediator K3[Fe(CN)6] is employed to expedite the reaction kinetics and introduce supplementary redox reactions, further enhancing the charge storage capability. Consequently, the CNSNA electrode delivers an exceptional specific capacitance (609.08 mAh g-1 at 1 A g-1), surpassing all previously reported selenide-based materials. High-rate capability (239.37 mAh g-1 at 20 A g-1) and long cycling stability have also been achieved. The comprehensive charge storage mechanism studies confirmed the structural integrity, kinetic improvement, and high reactivity of the CNSNA superstructure. Moreover, the corresponding AZB based on CNSNA demonstrates an extraordinarily high energy density of 516.58 Wh kg-1. The work offers guidance in the construction of superstructure-based TMS electrode materials, paving the way for the development of high-performance AZBs.

A new method for the preparation of MgAl layered double hydroxide-copper metal-organic frameworks structures: application to electrocatalytic oxidation of formaldehyde

In this research, we present a novel design protocol for the in-situ synthesis of MgAl layered double hydroxide-copper metal-organic frameworks (LDH-MOFs) nanocomposite based on the electrocoagulation process and chemical method. The overall goal in this project is the primary synthesis of para-phthalic acid (PTA) intercalated MgAl-LDH with Cu (II) ions to produce the paddle-wheel like Cu-(PTA) MOFs nanocrystals on/in the MgAl-LDH structure. The physicochemical properties of final product; Cu-(PTA) MOFs/MgAl-LDH, were characterized by the surface analysis and chemical identification methods (SEM, EDX, TEM, XRD, BET, FTIR, CHN, DLS, etc.). The Cu-(PTA) MOFs/MgAl-LDH nanocomposite was used to modification of the carbon paste electrode (CPE); Cu-(PTA) MOFs/MgAl-LDH/CPE. The electrochemical performance of Cu-(PTA) MOFs/MgAl-LDH/CPE was demonstrated through the utilization of electrochemical methods. The results show a stable redox behavior of the Cu (III)/Cu (II) at the surface of Cu-(PTA) MOFs/MgAl-LDH/CPE in alkaline medium (aqueous 0.1 M NaOH electrolyte). Then, the Cu-(PTA) MOFs/MgAl-LDH/CPE was used as a new electrocatalyst toward the oxidation of formaldehyde (FA). Electrochemical data show that the Cu-(PTA) MOFs/MgAl-LDH/CPE exhibits superior electrocatalytic performance on the oxidation of FA. Also the diffusion coefficient, exchange current density (J°) and mean value of catalytic rate constant (Kcat) were found to be 1.18 × 10-6 cm2 s-1, 23 mA cm-2 and 0.4537 × 104 cm3 mol-1 s-1, respectively. In general, it can be said the Cu-(PTA) MOFs/MgAl-LDHs is promising candidate for applications in direct formaldehyde fuel cells.

Rational synthesis of FeNiCo-LDH nanozyme for colorimetric detection of deferoxamine mesylate

The accurate surveillance and sensitive detection of deferoxamine mesylate (DFO) is of great significance to ensure the safety of thalassemia major patients. Herein, we report a new nanozyme-based colorimetric sensor platform for DFO detection. First, a metal-organic framework (ZIF-67) was used as a precursor for the synthesis of FeNiCo-LDH (Layered Double Hydroxide, LDH) via an ion exchange reaction stirring at room temperature. The results of electron microscopy and nitrogen adsorption-desorption showed that FeNiCo-LDH exhibited a 3D hollow and mesopores structure, which supplied more exposed active sites and faster transfer of mass. The as-prepared FeNiCo-LDH showed superior peroxidase-like activity with a low Km and high υmax. It can catalyze the decomposition of H2O2 to generate reactive oxygen species (ROS) and further react with 3,3',5,5'-tetramethylbenzidine (TMB) to form blue oxidized TMB (oxTMB), which has a characteristic absorption at 652 nm. Once DFO was introduced, it can complex with FeNiCo-LDH and inhibit the peroxidase-like activity of FeNiCo-LDH, making the color of oxTMB lighter. The quantitative range of DFO was 0.8-28 μM with a detection limit of 0.71 μM. This established method was applied to the detection of DFO content in urine samples of thalassemia patients, and the spiked recoveries were falling between 97.7% and 109.6%, with a relative standard deviation was less than 5%, providing a promising tool for the clinical medication of thalassemia patients.

Selective adsorption of nitrate in water by organosilicon quaternary ammonium salt modified derived nickel-iron layered double hydroxide: Adsorption characteristics and mechanism

Nitrate (NO3-) is a widespread pollutant in the water environment. Due to its physicochemical properties, such as negative monovalent charge, traditional adsorption treatment processes have low selectivity for NO3- removal, resulting in low removal efficiency of NO3- by adsorbents in the presence of interfering ions. Therefore, to improve the adsorption selectivity and efficiency of NO3-. In this study, we used organosilicon quaternary modified derived nickel-iron layered double hydroxide (NiFe-MLDH/OQAS) for selective removal of NO3-. NiFe-MLDH/OQAS has a flowery globular structure, with interconnected nanosheets on the surface providing more adsorption sites for NO3-, which improves the adsorption rate and adsorption amount. What's more, the nitrate removal rate of NiFe-MLDH/OQAS only decreased by about 14.36% in the presence of the same concentration of interfering ions, and the maximum adsorption amount reached 61.05 mg/g, showing good selectivity and adsorption amount. Various characterization analyses indicate that the nitrate selectivity of NiFe-MLDH/OQAS is attributed to its unique layer spacing, as well as the abundant functional groups on the material surface. Finally, we demonstrated through experiments that NiFe-MLDH/OQAS has good cyclic regeneration ability and environmental safety. These findings demonstrate the great potential of NiFe-MLDH/OQAS for selective adsorption of NO3-.

Metal-organic framework (MOF)-derived flower-like Ni-MOF@NiV-layered double hydroxides as peroxidase mimetics for colorimetric detection of hydroquinone

BACKGROUND

Nanozymes are one of the ideal substitutes for natural enzymes because of their excellent chemical stability and simple preparation methods. However, due to the limited catalytic ability of most reported nanozymes, constructing nanomaterials with low cost and high activity is gradually becoming an exploration focus in the field of nanozymes. Heteroatom doping of metal-organic frameworks is one of potential approaches to design nanozymes with high catalytic performance. Due to their multiple valence states properties, V-doped metal-organic framework (MOF)-derived LDH is expected to be a good enzyme-like catalyst. To our knowledge, the V-doped MOF-derived LDH as nanozyme is not explored before.

RESULTS

We report the in-situ synthesis of NiV-layered double hydroxides (LDHs) on nickel-based MOF, i.e. Ni-MOF@NiV-LDHs. The MOF surface is covered by 2D nanosheets. This unique structural design increases the specific surface area of the material, enables more exposure of catalytic active sites to participate in reactions and accelerates the electron transfer rate. The Ni-MOF@NiV-LDHs have high peroxidase-like activity able to catalyze TMB oxidation by H2O2 via the generation of •OH and O2•-. Relative to Ni-MOF, the Ni-MOF@NiV-LDHs shows 47-fold peroxidase-like activity rise. It had good affinity to TMB and H2O2, with the Michaelis-Menten constants of 0.12 mM and 0.007 mM, respectively. The hydroquinone (HQ) consumed the reactive oxygen species generated in the TMB + H2O2+Ni-MOF@NiV-LDHs system to inhibit the TMB oxidation. On this basis, a sensitive and rapid assay for determining HQ was developed, with a linear range of 0.50-70 μM and a LOD of 0.37 μM.

SIGNIFICANCE

This work provided some clues for the further development of novel nanozymes with high catalytic performance via a strategy of heteroatom doping. And the constructed colorimetric analysis method was successfully utilized for the determination of HQ in actual waters, which has the potential for practical application in the analysis of environmental pollutants.

Under-Coordinated CoFe Layered Double Hydroxide Nanocages Derived from Nanoconfined Hydrolysis of Bimetal Organic Compounds for Efficient Electrocatalytic Water Oxidation

Hierarchically structured bimetal hydroxides are promising for electrocatalytic oxygen evolution reaction (OER), yet synthetically challenging. Here, the nanoconfined hydrolysis of a hitherto unknown CoFe-bimetal-organic compound (b-MOC) is reported for the controllable synthesis of highly OER active nanostructures of CoFe layered double hydroxide (LDH). The nanoporous structures trigger the nanoconfined hydrolysis in the sacrificial b-MOC template, producing CoFe LDH core-shell octahedrons, nanoporous octahedrons, and hollow nanocages with abundant under-coordinated metal sites. The hollow nanocages of CoFe LDH demonstrate a remarkable turnover frequency (TOF) of 0.0505 s-1 for OER catalysis at an overpotential of 300 mV. It is durable in up to 50 h of electrolysis at step current densities of 10-100 mA cm-2 . Ex situ and in situ X-ray absorption spectroscopic analysis combined with theoretical calculations suggests that under-coordinated Co cations can bind with deprotonated Fe-OH motifs to form OER active Fe-O-Co dimmers in the electrochemical oxidation process, thereby contributing to the good catalytic activity. This work presents an efficient strategy for the synthesis of highly under-coordinated bimetal hydroxide nanostructures. The mechanistic understanding underscores the power of maximizing the amount of bimetal-dimer sites for efficient OER catalysis.

Modified nano zero-valent iron reduce toxicity of polystyrene microplastics to ryegrass (Lolium Perenne L.)

Microplastics pollution in environments has become a major concern and it has been proven to have adverse impacts on plants, so there is an urgent to find approaches to alleviate the detrimental effects of microplastics. In our study, we investigated the influence of polystyrene microplastics (PSMPs) on the growth, photosynthesis, and oxidative defense system changes of ryegrass, as well as the behavior of MPs at roots. Then three types of nanomaterials were applied to alleviate the adverse impact of PSMPs on ryegrass, which were nano zero-valent iron (nZVI), carboxymethylcellulose-modified-nZVI (C-nZVI) and sulfidated nZVI (S-nZVI), respectively. Our results suggested that PSMPs had significant toxicity to ryegrass, leading to decrease of shoot weight, shoot length and root length. Three nanomaterials regained the weight of ryegrass to a varying extent and made more PSMPs aggregate near roots. In addition, C-nZVI and S-nZVI facilitated the entrance of PSMPs into the root and promoted the chlorophyll a and chlorophyll b contents in leaves. Analysis of antioxidant enzymes and malondialdehyde content indicated that ryegrass coped well with the internalization of PSMPs, and all three types of nZVI could alleviate PSMPs-stress in ryegrass. This study elaborates the toxicity of MPs on plants and provides a novel insight into the fixing of MPs by plants and nanomaterials in environments, which needs to be further explored in future research.

A multiple Kirkendall strategy for converting nanosized zero-valent iron to highly active Fenton-like catalyst for organics degradation

Nanosized zero-valent iron (nZVI) is a promising persulfate (PS) activator, however, its structurally dense oxide shell seriously inhibited electrons transfer for O-O bond cleavage of PS. Herein, we introduced sulfidation and phosphorus-doped biochar for breaking the pristine oxide shell with formation of FeS and FePO4-containing mixed shell. In this case, the faster diffusion rate of iron atoms compared to shell components triggered multiple Kirkendall effects, causing inward fluxion of vacancies with further coalescing into radial nanocracks. Exemplified by trichloroethylene (TCE) removal, such a unique "lemon-slice-like" nanocrack structure favored fast outward transfer of electrons and ferrous ions across the mixed shell to PS activation for high-efficient generation and utilization of reactive species, as evidenced by effective dechlorination (90.6%) and mineralization (85.4%) of TCE. [Formula: see text] contributed most to TCE decomposition, moreover, the SnZVI@PBC gradually became electron-deficient and thus extracted electrons from TCE with achieving nonradical-based degradation. Compared to nZVI/PS process, the SnZVI@PBC/PS system could significantly reduce catalyst dosage (87.5%) and PS amount (68.8%) to achieve nearly complete TCE degradation, and was anti-interference, stable, and pH-universal. This study advanced mechanistic understandings of multiple Kirkendall effects-triggered nanocrack formation on nZVI with corresponding rational design of Fenton-like catalysts for organics degradation.

Functional MOF-Based Materials for Environmental and Biomedical Applications: A Critical Review

Over the last ten years, there has been a growing interest in metal-organic frameworks (MOFs), which are a unique category of porous materials that combine organic and inorganic components. MOFs have garnered significant attention due to their highly favorable characteristics, such as environmentally friendly nature, enhanced surface area and pore volume, hierarchical arrangements, and adjustable properties, as well as their versatile applications in fields such as chemical engineering, materials science, and the environmental and biomedical sectors. This article centers on examining the advancements in using MOFs for environmental remediation purposes. Additionally, it discusses the latest developments in employing MOFs as potential tools for disease diagnosis and drug delivery across various ailments, including cancer, diabetes, neurological disorders, and ocular diseases. Firstly, a concise overview of MOF evolution and the synthetic techniques employed for creating MOFs are provided, presenting their advantages and limitations. Subsequently, the challenges, potential avenues, and perspectives for future advancements in the utilization of MOFs in the respective application domains are addressed. Lastly, a comprehensive comparison of the materials presently employed in these applications is conducted.

Review: Synthesis of metal organic framework-based composites for application as immunosensors in food safety

Ensuring food safety continues to be one of the major global challenges. For effective food safety monitoring, fast, sensitive, portable, and efficient food safety detection strategies must be devised. Metal organic frameworks (MOFs) are porous crystalline materials that have attracted attention for use in high-performance sensors for food safety detection owing to their advantages such as high porosity, large specific surface area, adjustable structure, and easy surface functional modification. Immunoassay strategies based on antigen-antibody specific binding are one of the important means for accurate and rapid detection of trace contaminants in food. Emerging MOFs and their composites with excellent properties are being synthesized, providing new ideas for immunoassays. This article summarizes the synthesis strategies of MOFs and MOF-based composites and their applications in the immunoassays of food contaminants. The challenges and prospects of the preparation and immunoassay applications of MOF-based composites are also presented. The findings of this study will contribute to the development and application of novel MOF-based composites with excellent properties and provide insights into advanced and efficient strategies for developing immunoassays.

The Collision between g-C3 N4 and QDs in the Fields of Energy and Environment: Synergistic Effects for Efficient Photocatalysis

Recently, graphitic carbon nitride (g-C₃ N₄ ) has attracted increasing interest due to its visible light absorption, suitable energy band structure, and excellent stability. However, low specific surface area, finite visible light response range (<460 nm), and rapid photogenerated electron-hole (e^- -h⁺ ) pairs recombination of the pristine g-C₃ N₄ limit its practical applications. The small size of quantum dots (QDs) endows the properties of abundant active sites, wide absorption spectrum, and adjustable bandgap, but inevitable aggregation. Studies have confirmed that the integration of g-C₃ N₄ and QDs not only overcomes these limitations of individual component, but also successfully inherits each advantage. Encouraged by these advantages, the synthetic strategies and the fundamental of QDs/g-C₃ N₄ composites are briefly elaborated in this review. Particularly, the synergistic effects of QDs/g-C₃ N₄ composites are analyzed comprehensively, including the enhancement of the photocatalytic performance and the avoidance of aggregation. Then, the photocatalytic applications of QDs/g-C₃ N₄ composites in the fields of environment and energy are described and further combined with DFT calculation to further reveal the reaction mechanisms. Moreover, the stability and reusability of QDs/g-C₃ N₄ composites are analyzed. Finally, the future development of these composites and the solution of existing problems are prospected.

Glutaraldehyde fixation promotes palladium and gold nanoparticles formation in yeast and enhances their catalytic activity in 4-nitrophenol reduction

When observing biosynthesized metal nanoparticles in microorganisms, glutaraldehyde is commonly used as a fixative to prepare TEM ultra-thin sections. However, as a chemical reagent with aldehyde groups, its reduction potential on metal ions has yet to be studied elaborately. Herein, we explored the influences of glutaraldehyde on yeast-synthesized gold nanoparticles (AuNPs), palladium nanoparticles (PdNPs) and their catalytic performance. A modified method for ultra-thin section preparation without glutaraldehyde fixation was developed to exclude its influence on AuNPs/PdNPs observation. It was confirmed that glutaraldehyde could promote the biosynthesis of AuNPs and PdNPs extra- and intracellularly, without altering their crystal structure and chemical state. The adsorption and reduction of Au(III)/Pd(II) were attributed to the different components of the yeast cell. Specifically, the amines and carboxyl groups in proteins and polysaccharides were involved in adsorption, while the reducing sugars hydrolyzed from polysaccharides were responsible for Au(III)/Pd(II) reduction. After glutaraldehyde fixation, the catalytic activities of Au/Pd-loaded yeast in 4-nitrophenol reduction were enhanced as well. Therefore, the influence of chemical fixatives in biosynthesized metal nanoparticles should be taken into consideration in regard to SEM, TEM observation and catalytic performance.

Crystalline phase transformation of Co-MOF derivatives on ordered mesoporous carbons for high-performance supercapacitor applications

Preparation and phase transformation of Co-based metal–organic frameworks derivatives.

Regulation of Structure and Anion-Exchange Performance of Layered Double Hydroxide: Function of the Metal Cation Composition of a Brucite-like Layer

As anion-exchange materials, layered double hydroxides (LDHs) have attracted increasing attention in the fields of selective adsorption and separation, controlled drug release, and environmental remediation. The metal cation composition of the laminate is the essential factor that determines the anion-exchange performance of LDHs. Herein, we review the regulating effects of the metal cation composition on the anion-exchange properties and LDH structure. Specifically, the internal factors affecting the anion-exchange performance of LDHs were analyzed and summarized. These include the intercalation driving force, interlayer domain environment, and LDH morphology, which significantly affect the anion selectivity, anion-exchange capacity, and anion arrangement. By changing the species, valence state, size, and mole ratio of the metal cations, the structural characteristics, charge density, and interlayer spacing of LDHs can be adjusted, which affect the anion-exchange performance of LDHs. The present challenges and future prospects of LDHs are also discussed. To the best of our knowledge, this is the first review to summarize the essential relationship between the metal ion composition and anion-exchange performance of laminates, providing important insights for regulating the anion-exchange performance of LDHs.

A novel, Z-scheme ZnO@AC@FeO photocatalyst, suitable for the intensification of photo-mediated peroxymonosulfate activation: Performance, reactivity and bisphenol A degradation pathways

In this study, the intensification of a UVC-based PMS activation treatment is performed by a novel photocatalyst. Using ZnO nanoparticles coupled with activated carbon (AC), impregnated by ferroferric oxides (FO, magnetite), as an effective Z-scheme photocatalyst (ZACFO), the effective Bisphenol A (BP-A) removal was attained. Several techniques were applied for the characterization of the as-prepared catalyst and proved the successful preparation of ZACFO. The photocatalytic activity of pristine ZnO was significantly improved after its combination with ACFO. It was found that the fabrication of ZACFO heterostructures could inhibit the charge carriers recombination and also accelerate the charge separation of photo-induced e^-/h⁺ pairs. Under this UVC-based photocatalysis-mediated PMS activation system, ZACFO showed an excellent potential as compared to the single constituent catalysts. The complete degradation of 20 mg/L concentration of BP-A was attained in just 20 min with excellent reaction rate constant of 27.3 × 10^-2 min^-1. Besides, over 60% of TOC was eliminated by the integrated ZACFO/PMS/UV system within 60 min of reaction. The minor inhibition by most matrix components, the high recycling capability with minor metals' leaching and the effectiveness in complex matrices, constitute this composite method an efficient and promising process for treating real wastewater samples. Finally, based on the photo-produced reactive intermediates and by-products identified, the Z-scheme photocatalytic mechanism and the plausible pathway of BP-A degradation were proposed comprehensively. The presence and role of radical and non-radical pathways in the decontamination process of BP-A over ZACFO/PMS/UV system was confirmed.

Transformation of metal-organic frameworks with retained networks

Metal-organic frameworks (MOFs) are a class of crystalline porous coordination materials with systematically designable network structures and tunable properties, demonstrating great potential for applications in diverse fields. However, the generally poor stability of dynamic coordination bonds in MOFs hinders their practical applications in harsh environments. Although MOFs have been used as precursors and templates for the production of various derivatives with enhanced stability via thermal treatment, the extreme thermolytic conditions often destroy the network structures, consequently resulting in obvious decreases in porosity and surface areas with undesired characteristics. This feature article discusses the generally used pathways for the transformation of MOFs and the advanced fabrication methods for the production of various MOF-derived materials. We particularly emphasize the recent progress in the designed strategies for customization and derivation tailoring of MOFs, which could produce MOF-derived functional materials with remaining framework skeletons and inherited characteristics (surface area, porosity and properties) of the parent MOFs, exhibiting great promise for practical applications.

Highly active CoNi nanoparticles confined in N-doped carbon microtubes for efficient catalytic performance

CoNi@NCMT magnetic composites with a tubular structure and high coverage of tiny CoNi bimetallic nanoparticles are fabricated as efficient catalysts for the reduction of 4-nitrophenol (4-NP).