Benzoic acid-modified 2D Ni-MOF for high-performance supercapacitors

Facile synthesis of novel Ni-BDC-NH2/Au NPs SERS substrates with synergistic enhancement effects for high-performance detection

Substrate materials with high sensitivity and good reproducibility are highly desirable for the practical applications of surface-enhanced Raman scattering (SERS) techniques. In this study, a novel gold nanoparticle-loaded Ni-based metal-organic framework (Ni-BDC-NH2/Au NPs) SERS substrate was successfully synthesized via an electrostatic self-assembly method. The enhancement of the SERS signal is achieved owing to the synergy between the chemical enhancement (CM) effect of Ni-BDC-NH2 and the electromagnetic enhancement (EM) of Au NPs, and the enriching of the analyte near the SERS "hot spots" through the strong adsorption capacity of Ni-BDC-NH2. The Ni-BDC-NH2/Au NPs exhibited a high enhancement factor (EF) of 1.10 × 107 and a low detection limit of 5 × 10-9 mol L-1. Besides, the substrate material showed exceptional stability for up to 45 days at room temperature. The Ni-BDC-NH2/Au NPs was used to detect methylene blue (MB), displaying a wide linear range (5 × 10-7 to 5 × 10-5 mol L-1) and high recoveries (86.82-104.46%). These results indicate that the Ni-BDC-NH2/Au NPs hybrid substrate has great potential for the detection of environmental pollution in practical applications.

Interface Engineering of Network-Like 1D/2D (NHCNT/Ni─MOF) Hybrid Nanoarchitecture for Electrocatalytic Water Splitting

Here, integrated functional components into a hybrid heterostructure via highly stabilized network-like interconnected electronic nanoarchitecture of 1D N-doped holey-carbon nanotube (NHCNT) with 2D nickel─metal-organic framework (Ni─MOF) nanosheets are developed as high-performance electrocatalyst for overall water splitting. The NHCNT promoting electron transport pathways in electrocatalyst, and formation of holes in nanotubes further enables excellent diffusion of ions for promoting the overall reaction rate. An excellent combination of 1D/2D structure of NHCNT/Ni─MOF-4 electrocatalyst exhibits excellent oxygen evolution reaction (η10 = 207.8 mV, and Tafel = 62.6 mV dec-1) and reasonable hydrogen evolution reaction (η10 = 159.8 mV, and Tafel = 107.69 mV dec-1) activity with consistent and stable performance in a 1 m KOH. The highly interconnected network structure contains Ni2+ and Ni3+ species in the NHCNT/Ni─MOF-4 electrocatalyst, which possesses high specific surface area (SSA) (235.53 m2 g-1), electrochemically active surface area (ECSA) (796.2 cm2), mass activity (4.76 mA mg-1), and turnover frequency (3.99 × 10-2 s-1), which provide remarkable electrocatalytic performance via generating synergy between the NHCNT and Ni─MOF. For overall water splitting, NHCNT/Ni─MOF-4 attains a low cell voltage (1.77 V@10 mA cm-2).

Facile Growing of Ni-MOFs on Ni Foam by Self-Dissociation Strategy for Electrochemical Energy Storage

Metal-organic frameworks (MOFs) with redox metal centers have come into view as potential materials for electrochemical energy storage. However, the poor electrical conductivity largely impedes the potentiality of MOFs to construct high-performance electrodes in supercapacitors. In this work, a self-dissociation strategy has been applied to construct Ni-MOF microbelts on Ni foam (NF), where the NF is used as both a support and a Ni source. The transmission channels between the Ni-MOF and NF are favorable for the charge transport due to the in situ self-assembly of the TPA linkers with the dissociated Ni ions from the Ni foam. The grown Ni-MOF microbelt arrays can offer abundant active sites for redox reactions. The prepared Ni-MOF/NF-s electrode can yield a high capacitance of 1124 F g-1 at 1 A g-1 and retains 590 F g-1 at 10 A g-1. This design may offer a controllable protocol for the construction of MOF microbelt arrays on various metal substrates.

Integrating carbon quantum dots with oxygen vacancy modified nickel-based metal organic frameworks for photocatalytic CO2 reduction to CH4 with approximately 100 % selectivity

Solar-light-driven reduction of CO2 into renewable fuels has great potential in the production of sustainable energy, addressing the energy crisis and environmental problems simultaneously. However, it is a significant challenge to achieve high selectivity for the conversion of CO2 into CH4, which is a type of fuel with a high calorific value. Herein, carbon quantum dots (CQDs) were integrated with an oxygen vacancy modified nickel-based metal organic frameworks (NiMOFs) to form the CQDs-X/NiMOFV series, which exhibited superior performance for CO2 photoreduction into CH4 compared with pure NiMOFs in the presence of hole scavengers under visible light irradiation. The highest yielding rate of CH4 (1 mmol g-1 h-1) and selectivity (97.58 %) were obtained using a CQDs-25/NiMOFV catalyst. Most importantly, in diluted CO2 atmosphere, the yield of CH4 was almost unchanged and the selectivity of CH4 over CQDs-25/NiMOFV was higher than that in pure CO2. The superior performance of CQDs-25/NiMOFV may be attributed to the following two factors: (i) both CQDs and oxygen vacancies facilitate the transmission of electrons to promote the eight-electron reaction producing CH4, and (ii) oxygen vacancies can act as the electron trap to capture the photogenerated electrons to react with adsorbed CO2 on Ni2+. This study offers a valuable strategy for designing efficient photocatalysts to convert CO2 into CH4 with superior selectivity.

High-Density Atomic Level Defect Engineering of 2D Fe-Based Metal-Organic Frameworks Boosts Oxygen and Hydrogen Evolution Reactions

Electrocatalysts based on metal-organic frameworks (MOFs) attracted significant attention for water splitting, while the transition between MOFs and metal oxyhydroxide poses a great challenge in identifying authentic active sites and long-term stability. Herein, we employ on-purpose defect engineering to create high-density atomic level defects on two-dimensional Fe-MOFs. The coordination number of Fe changes from 6 to 4.46, and over 28% of unsaturated Fe sites are formed in the optimized Fe-MOF. In situ characterizations of the most optimized Fe-MOF0.3 electrocatalyst during the oxygen evolution reaction (OER) process using Fourier transform infrared and Raman spectroscopy have revealed that some Fe unsaturated sites become oxidized with a concomitant dissociation of water molecules, causing generation of the crucial *OH intermediates and Fe oxyhydroxide. Moreover, the presence of Fe oxyhydroxide is compatible with the Volmer and Heyrovsky steps during the hydrogen evolution reaction (HER) process, which lower its energy barrier and accelerate the kinetics. As a result, the optimized Fe-MOF electrodes delivered remarkable OER (259 mV at 10 mA cm-2) and HER (36 mV at 10 mA cm-2) performance. Our study offers comprehensive understanding of the effect of phase transformation on the electrocatalytic process of MOF-based materials.

A 0D Ge(II)-Halide-Based Perovskite with Enhanced Semiconducting Behavior for Electronic Capacitors

Perovskite materials have surged to the forefront of materials science, captivating researchers worldwide with their distinctive crystal lattice arrangement and remarkable optical, electric and dielectric attributes. The current study focuses on the development of a novel zero-dimensional (0D) Ge(II)-based hybrid perovskite, formulated as NH3(CH2)2NH3GeF6, and synthesized through a gradual evaporation process conducted at room temperature. The crystal structure is characterized by an arrangement of organic cations and isolated octahedral [GeF6]2- groups. This configuration is stabilized by relatively weak intermolecular bonds. A comprehensive analysis of the material's thermal properties using differential scanning calorimetry (DSC) revealed a distinct phase transition occurring at approximately 323 K, which was further confirmed through electrical measurements. The studied compound provided a broad absorption range across the visible spectrum and an optical band gap of 3.30 eV, indicating its potential for semiconducting applications in optoelectronic devices. Photoluminescence PL analysis displays a blueish broad-band emission with a high color rendering index CRI value of 91, when excited at 325 nm. This emission primarily originates from the self-trapped excitons (STEs) recombination in the inorganic [GeF6]2-. Herein, the temperature-dependent behavior of grain conductivity exhibited an Arrhenius-type pattern, with an activation energy (E a) of 0.46 eV, confirming the semiconductor nature of the investigated compound. In addition, a deep investigation of the alternating current conductivity, analyzed using Jonscher's law, demonstrates that the conduction mechanism is effectively described by the correlated barrier hopping (CBH) model. The dielectric performances show a significant dielectric constant (ε' ∼ 103). Thus, all these interesting physical properties of this hybrid perovskite have paved the way for advancements in various technological applications, particularly in the field of electronic capacitors.

Nickel-cobalt metal-organic frameworks based flexible hydrogel as a wearable contact lens for electrochemical sensing of urea in tear samples

A flexible, wearable, non-invasive contact lens sensor utilizing nickel-cobalt metal-organic framework (Ni-Co-MOF) based hydrogel is introduced for urea monitoring in tear samples. The synthesized Ni-Co-MOF hydrogel exhibits a porous structure with interconnected voids, as visualized by Scanning Electron Microscopy (SEM). Detailed structural and vibrational properties of the material were characterized using X-ray Diffraction (XRD), Fourier Transform Infrared (FTIR) spectroscopy, and Raman spectroscopy. The developed Ni-Co-MOF hydrogel sensor showcases a detection limit of 0.445 mM for urea within a linear range of 0.5-70 mM. Notably, it demonstrates exceptional selectivity, effectively distinguishing against interfering species like UA, AA, glucose, dopamine, Cl-, K+, Na+, Ca2+, and IgG. The enhanced electrocatalytic performance of the Ni-Co-MOF hydrogel electrode is attributed to the presence of Ni and Co, fostering Ni2+ oxidation on the surface and forming a Co2+ complex that acts as a catalyst for urea oxidation. The fabricated sensor exhibits successful detection and retrieval of urea in simulated tear samples, showcasing promising potential for bioanalytical applications. The binder-free, non-toxic nature of the Ni-Co-MOF hydrogel sensor presents exciting avenues for future utilization in non-enzymatic electrochemical sensing, including applications in wearable devices, point-of-care diagnostics, and personalized healthcare monitoring.

Flower-like Ni/Mn/MC microspheres derived from metal-organic frameworks for electrocatalytic degradation of ceftriaxone sodium

This study demonstrated the design and fabrication of flower-like Ni/Mn-MOFs materials, and three-dimensional ultrathin flower-like Ni/Mn/MC microspheres were fabricated by embedding metal or metal oxide nanoparticles into a porous carbon skeleton via high-temperature pyrolysis at 600 °C and used for the electrocatalytic degradation of ceftriaxone sodium. This unique ultrathin porous flower-like structure can expose more active sites, provide rapid ion/electron transfer, and improve electrocatalytic activity. Meanwhile, the excellent electrical conductivity of the carbon skeleton, as well as the rational composition and synergistic effect of the two components, can promote the generation of active radicals (•OH and •O2-) in the reaction system, which accelerates the electrochemical degradation process and improves the electrocatalytic degradation performance. The results showed that the Ni/Mn/MC-5:1 composite prepared when the molar ratio of Ni: Mn was 5:1 exhibited the best electrocatalytic degradation performance for the degradation of sodium ceftriaxone. The composites showed 98.2% degradation of ceftriaxone sodium in 120 min and maintained sound degradation after 20 cycles. Therefore, we concluded that this novel multicomponent composite has good electrocatalytic activity and stability for the degradation of antibiotic wastewater.

Target-regulated photoactivities of CdS/Ni-MOF heterojunction with [Ru(bpy)2dppz]2+ intercalator: a bisphenol A photoelectrochemical aptasensor

Bisphenol A (BPA), an important endocrine disrupting compound, has infiltrated human daily lives through electronic devices, food containers, and children's toys. Developing of novel BPA assay methods with high sensitivity holds tremendous importance in valuing the pollution state. Here, we constructed an ultrasensitive photoelectrochemical (PEC) aptasensor for BPA determination by regulating photoactivities of CdS/Ni-based metal-organic framework (CdS/Ni-MOF) with [Ru(bpy)2dppz]2+ sensitizer. CdS/Ni-MOF spheres exhibited excellent photocatalytic performance, serving as a potential sensing platform for the construction of target recognition process. [Ru(bpy)2dppz]2+ were embedded into DNA double-stranded structure, functioning as sensitizer for modulating the signal response of the developed PEC aptasensor. The proposed PEC sensor exhibited outstanding analytical performances, including a wide linear range (0.1 to 1000.0 nM), low detection limit (0.026 nM, at 3σ/m), excellent selectivity, and high stability. This work provides a perspective for the design of ideal photosensitive materials and signal amplification strategies and extends their application in environment analysis.

A NiMOF integrated with conductive materials for efficient bifunctional electrocatalysis of urea oxidation and oxygen evolution reactions

The development of urea oxidation reaction (UOR) and oxygen evolution reaction (OER) bifunctional electrocatalysts has dual significance in promoting hydrogen energy production and urea-rich wastewater treatment. Herein, a carboxylated multi-walled carbon nanotube (MWCNT-COOH)-ferrocene carboxylic acid (Fc-COOH) modulated NiMOF hybrid material (MWCNT-NiMOF(Fc)) has been synthesized for dual electrocatalysis of the UOR and OER. The material characterization results indicated that MWCNT-COOH and Fc-COOH were integrated into the framework structure of the NiMOF. The direct interaction between the NiMOF and MWCNT/Fc facilitated electron transfer in the hybrid material and led to lattice strain, which improved the charge transfer kinetics, promoted the exposure of more unsaturated Ni sites, and increased the electrochemically active surface area. These factors together enhanced the electrocatalytic activity of MWCNT-NiMOF(Fc) towards the UOR and OER. Using a glassy carbon electrode as the substrate, MWCNT-NiMOF(Fc) exhibited low potential requirements, low Tafel slopes, and high stability. In overall urea and water splitting electrolysis cells, the excellent UOR and OER dual functional catalytic ability and enormous practical application potential of the MWCNT-NiMOF(Fc) modified foam nickel electrode were further demonstrated. On the basis of the above research, the influence of a KOH environment on urea electrolysis was further studied, and the urea electrolysis products were analyzed, promoting a more comprehensive understanding of the catalytic performance of MWCNT-NiMOF(Fc) for urea oxidation. This study provides a new approach for developing high-performance NiMOF-based electrocatalysts for challenging bifunctional UOR/OER applications, and has potential application value in hydrogen production from urea-containing wastewater electrolysis.

Functionalization strategies of metal-organic frameworks for biomedical applications and treatment of emerging pollutants: A review

One of the representative coordination polymers, metal-organic frameworks (MOFs) material, is of hotspot interest in the multi field thanks to their unique structural characteristics and properties. As a novel hierarchical structural class, MOFs show diverse topologies, intrinsic behaviors, flexibility, etc. However, bare MOFs have less desirable biofunction, high humid sensitivity and instability in water, restraining their efficiencies in biomedical and environmental applications. Thus, a structural modification is required to address such drawbacks. Herein, we pinpoint new strategies in the synthesis and functionalization of MOFs to meet demanding requirements in in vitro tests, i.e., antibacterial face masks against corona virus infection and in wound healing and nanocarriers for drug delivery in anticancer. Regarding the treatment of wastewater containing emerging pollutants such as POPs, PFAS, and PPCPs, functionalized MOFs showed excellent performance with high efficiency and selectivity. Challenges in toxicity, vast database of clinical trials for biomedical tests and production cost can be still presented. MOFs-based composites can be, however, a bright candidate for reasonable replacement of traditional nanomaterials in biomedical and wastewater treatment applications.

Advantages of Bimetallic Organic Frameworks in the Adsorption, Catalysis and Detection for Water Contaminants

The binary metal organic framework (MOF) is composed of two heterometallic ions bonded to an organic ligand. Compared with monometallic MOFs, bimetallic MOFs have greatly improved in terms of structure, porosity, active site, adsorption, selectivity, and stability, which has attracted wide attention. At present, many effective strategies have been designed for the synthesis of bimetallic MOF-based nanomaterials with specific morphology, structure, and function. The results show that bimetallic MOF-based nanocomposites could achieve multiple synergistic effects, which will greatly improve their research in the fields of adsorption, catalysis, energy storage, sensing, and so on. In this review, the main preparation methods of bimetallic MOFs-based materials are summarized, with emphasis on their applications in adsorption, catalysis, and detection of target pollutants in water environments, and perspectives on the future development of bimetallic MOFs-based nanomaterials in the field of water are presented.

Fabrication of Ni−MOF−74@PA−PEI for Radon Removal under Ambient Conditions

Radon is one of the 19 carcinogenic substances identified by the World Health Organization, posing a significant threat to human health and the environment. Properly removing radon under ambient conditions remains challenging. Compared with traditional radon−adsorbent materials such as activated carbon and zeolite, metal–organic framework (MOF) materials provide a high specific surface area, rich structure, and designability. However, MOF material powders demonstrate complications regarding practical use, such as easy accumulation, deactivation, and difficult recovery. Ni−MOF−74 was in situ grown on a porous polyacrylic acid (PA) spherical substrate via stepwise negative pressure impregnation. Ni−MOF−74 was structured as one−dimensional rod−shaped crystals (200–300 nm) in large−pore PA microspheres, whose porous structure increased the diffusion of radon gas. The radon adsorption coefficient of a Ni−MOF−74@PA−polyethyleneimine composite material was 0.49 L/g (293 K, relative humidity of 20%, air carrier). In comparison with pristine Ni−MOF−74 powder, our composite material exhibited enhanced adsorption and longer penetration time. The radon adsorption coefficient of the composite material was found to be from one to two orders of magnitude higher than that of zeolite and silica gel. The proposed material can be used for radon adsorption while overcoming the formation problem of MOF powders. Our preparation approach can provide a reference for the composite process of MOFs and polymers.

Advances of Electroactive Metal-Organic Frameworks

The preparation of electroactive metal-organic frameworks (MOFs) for applications of supercapacitors and batteries has received much attention and remarkable progress during the past few years. MOF-based materials including pristine MOFs, hybrid MOFs or MOF composites, and MOF derivatives are well designed by a combination of organic linkers (e.g., carboxylic acids, conjugated aromatic phenols/thiols, conjugated aromatic amines, and N-heterocyclic donors) and metal salts to construct predictable structures with appropriate properties. This review will focus on construction strategies of pristine MOFs and hybrid MOFs as anodes, cathodes, separators, and electrolytes in supercapacitors and batteries. Descriptions and discussions follow categories of electrochemical double-layer capacitors (EDLCs), pseudocapacitors (PSCs), and hybrid supercapacitors (HSCs) for supercapacitors. In contrast, Li-ion batteries (LIBs), Lithium-sulfur batteries (LSBs), Lithium-oxygen batteries (LOBs), Sodium-ion batteries (SIBs), Sodium-sulfur batteries (SSBs), Zinc-ion batteries (ZIBs), Zinc-air batteries (ZABs), Aluminum-sulfur batteries (ASBs), and others (e.g., LiSe, NiZn, H⁺ , alkaline, organic, and redox flow batteries) are categorized for batteries.

Effect of Solvothermal Temperature on Morphology and Supercapacitor Performance of Ni-MOF

A series of Ni-MOF materials were synthesized via a simple hydrothermal method and can be employed as electrodes for supercapacitors (SCs). Different temperatures were selected to unveil the effect of temperature on the formation, structure, and electrochemical performance of Ni-MOF-x (x = 60, 80, 100, and 120). Ni-MOF-80 possessed a larger specific surface area with a cross-network structure formed on its surface. The synthesized Ni-MOF electrode delivered a specific capacity of 30.89 mA h g^-1 when the current density reached 1 A g^-1 in a three-electrode system. The as-fabricated Ni-MOF materials could be further designed and are expected to deliver satisfactory performance in practice.

CNTs support 2D NiMOF nanosheets for asymmetric supercapacitors with high energy density

The NiMOF/CNTs composite with NiMOF nanosheets grows along the CNTs is synthesized with a one-step solvothermal method, and the NiMOF/CNTs//AC asymmetric supercapacitors provide a high energy density of 113.8 Wh kg−1 at 800.0 W kg−1.