Large Scale Synthesis of NiCo Layered Double Hydroxides for Superior Asymmetric Electrochemical Capacitor

A comparison increasing the photodegradation power of a Ag/g-C3N4 /CoNi-LDH nanocomposite: Photocatalytic activity toward water treatment

For environmental applications, it is crucial to rationally design and synthesize photocatalysts with positive exciton splitting and interfacial charge transfer. Here, a novel Ag-bridged dual Z-scheme Ag/g-C3N4/CoNi-LDH plasmonic heterojunction was successfully synthesized using a simple method, with the goal of overcoming the common drawbacks of traditional photocatalysts such as weak photoresponsivity, rapid combination of photo-generated carriers, and unstable structure. These materials were characterized by XRD, FT-IR, SEM, TEM UV-Vis/DRS, and XPS to verify the structure and stability of the heterostructure. The pristine LDH, g-C3N4, and Ag/g-C3N4/CoNi-LDH composite were investigated as photocatalysts for water remediation, an environmentally motivated process. Specifically, the photocatalytic degradation of tetracycline was studied as a model reaction. The performance of the supports and composite catalyst were determined by evaluating both the degradation and adsorption phenomenon. The influence of several experimental parameters such as catalyst loading, pH, and tetracycline concentration were evaluated. The current study provides important data for water treatment and similar environmental protection applications.

Ni- and Co-Based MOF-Derived NixCo3-xO4 Materials: As an Efficient Anode for Direct Methanol Fuel Cell Application

Finding inexpensive and efficient anode materials is crucial for the oxidation of methanol in the direct methanol fuel cell (DMFC), which is the key electrode reaction. Herein, we report metal-organic framework (MOF)-derived Co3O4, NiO, and NixCo3-xO4 (where x = 1.5, 1, and 0.6) materials deposited on nickel foam as efficient anode material for methanol oxidation. Among them, NiCo2O4 exhibited the highest methanol oxidation activity, owing to its lowest charge-transfer resistance (0.097 Ω) and high electrochemically active surface area (1950 cm2), resulting in the lowest onset potential of 0.35 V vs Hg/HgO. The optimized Ni-to-Co ratio and synergistic effect between Ni and Co metals enable NiCo2O4 to achieve the highest mass activity of 151 mA mg-1 and geometric current density of 288 mA cm-2, demonstrating excellent durability over 14 h at 0.6 V. In addition, to optimize methanol concentration, all the electrocatalysts were tested in a range of methanol concentrations, showing 0.5 M methanol as the optimal concentration. This study focuses on optimizing the metal ratio and methanol concentration to achieve the highest catalytic activity. Additionally, this lays the foundation for developing diverse MOF-derived electrocatalysts and advancing DMFCs.

Supercapattery-Diode: Using Layered Double Hydroxide Nanosheets for Unidirectional Energy Storage

The supercapacitor-diode (CAPode) is a device that integrates the functionality of an ionic diode with that of a conventional supercapacitor. The unique combination of energy storage and rectification properties in CAPodes is relevant for iontronics, alternate current rectifiers, logic operations, grid stabilization, and even biomedical applications. Here, we propose a novel aqueous-phase supercapattery-diode with excellent energy storage [total specific capacity (CT) = 162 C g-1, energy density = 34 W h kg-1 at 1.0 A g-1] as well as rectifying properties [rectification ratio I (RRI) of 23, and rectification ratio II (RRII) of 0.98]; the unidirectional energy storage is achieved by the utilization of an ion-selective redox reaction of battery-type layered double hydroxide (LDH) nanosheets serving as the electroactive material as well as asymmetric device configuration of supercapattery-diode in the KOH electrolyte. This work expands the types of CAPodes and importantly exemplifies the significance of integrating battery-type LDH and their redox chemistry, allowing a simultaneous increase in charge storage and rectification properties.

Tailored Engineering of Layered Double Hydroxide Catalysts for Biomass Valorization: A Way Towards Waste to Wealth

Layered double hydroxides (LDH) have significant attention in recent times due to their unique characteristic properties, including layered structure, variable compositions, tunable acidity and basicity, memory effect, and their ability to transform into various kinds of catalysts, which make them desirable for various types of catalytic applications, such as electrocatalysis, photocatalysis, and thermocatalysis. In addition, the upcycling of lignocellulose biomass and its derived compounds has emerged as a promising strategy for the synthesis of valuable products and fine chemicals. The current review focuses on recent advancements in LDH-based catalysts for biomass conversion reactions. Specifically, this review highlights the structural features and advantages of LDH and LDH-derived catalysts for biomass conversion reactions, followed by a detailed summary of the different synthesis methods and different strategies used to tailor their properties. Subsequently, LDH-based catalysts for hydrogenation, oxidation, coupling, and isomerization reactions of biomass-derived molecules are critically summarized in a very detailed manner. The review concludes with a discussion on future research directions in this field which anticipates that further exploration of LDH-based catalysts and integration of cutting-edge technologies into biomass conversion reactions hold promise for addressing future energy challenges, potentially leading to a carbon-neutral or carbon-positive future.

Layered rare-earth hydroxides as multi-modal medical imaging probes: particle size optimisation and compositional exploration

Recently, layered rare-earth hydroxides (LRHs) have received growing attention in the field of theranostics. We have previously reported the hydrothermal synthesis of layered terbium hydroxide (LTbH), which exhibited high biocompatibility, reversible uptake of a range of model drugs, and release-sensitive phosphorescence. Despite these favourable properties, LTbH particles produced by the reported method suffered from poor size-uniformity (670 ± 564 nm), and are thus not suitable for therapeutic applications. To ameliorate this issue, we first derive an optimised hydrothermal synthesis method to generate LTbH particles with a high degree of homogeneity and reproducibility, within a size range appropriate for in vivo applications (152 ± 59 nm, n = 6). Subsequently, we apply this optimised method to synthesise a selected range of LRH materials (R = Pr, Nd, Gd, Dy, Er, Yb), four of which produced particles with an average size under 200 nm (Pr, Nd, Gd, and Dy) without the need for further optimisation. Finally, we incorporate Gd and Tb into LRHs in varying molar ratios (1 : 3, 1 : 1, and 3 : 1) and assess the combined magnetic relaxivity and phosphorescence properties of the resultant LRH materials. The lead formulation, LGd1.41Tb0.59H, was demonstrated to significantly shorten the T2 relaxation time of water (r2 = 52.06 mM-1 s-1), in addition to exhibiting a strong phosphorescence signal (over twice that of the other LRH formulations, including previously reported LTbH), therefore holding great promise as a potential multi-modal medical imaging probe.

Cobalt coordinated carbon quantum dots boosting the performance of NiCo-LDH for energy storage

Transition metal layered double hydroxides have extremely high specific capacitances but suffer from poor rate performance and cycling stability due to their low conductivity and structural stability. In this study, cobalt-coordinated carbon quantum dots (CoCQDs) were designed and synthesized to enhance the energy storage performance of nickel-cobalt layered double hydroxides (NiCo-LDH). Nickel and cobalt ions were co-electrodeposited with the CoCQDs to form a NiCo-LDH based composite electrode (denoted as CoC@LDH). Since the CoCQDs participated in the formation of the NiCo-LDH, the carbon quantum dots could be strongly bonded to the NiCo-LDH nanosheets through coordination interactions. Thus, the conductivity as well as the structure stability of the NiCo-LDH was effectively improved, which greatly boosted the cycle stability and rate performance of the NiCo-LDH. Several CoCQDs with different Co contents (nCoCQDs, n = 0.5, 1.0, 2.0) were fabricated and their effects on the performance of the resultant electrodes nCoC@LDH were investigated. The 1.0CoC@LDH electrode exhibited an impressive specific capacitance of 1867 F g-1 at 1 A-g-1, along with a significantly enhanced capacitance retention of 84.6 % after 6000 cycles at 5 A g-1 (benchmark 49.5 %). This ingenious design provides a new avenue for fabricating pseudo-capacitive materials with unprecedented high performance.

Enhancing the electrochemical activity of zinc cobalt sulfide via heterojunction with MoS2 metal phase for overall water splitting

The integration of diverse components into a single heterostructure represents an innovative approach that boosts the quantity and variety of active centers, thereby enhancing the catalytic activity for both hydrogen evolution reactions (HER) and oxygen evolution reactions (OER) in the water splitting process. In this study, a novel, hierarchically porous one-dimensional nanowire array comprising zinc cobalt sulfide and molybdenum disulfide (MoS2@Zn0.76Co0.24S) was successfully synthesized on a Ni foam substrate using an efficient and straightforward hydrothermal synthesis strategy. The incorporation of the metallic phase of molybdenum disulfide elevates the electronic conductivity of MoS2@Zn0.76Co0.24S, resulting in impressively low overpotentials. At 20, 50, and 100 mA cm-2, the overpotentials for oxygen evolution reaction (OER) are merely 90 mV, 170 mV, and 240 mV, respectively. Similarly, for hydrogen evolution reaction (HER), the overpotentials are 169 mV, 237 mV, and 301 mV at the same current densities in 1.0 M potassium hydroxide solution. The utilization of the MoS2@Zn0.76Co0.24S /NF electrolyzer demonstrates its exceptional performance as a catalyst in alkaline electrolyzers. Operating at a mere 1.45 V and 10 mA cm-2, it showcases outstanding efficiency. Achieving a current density of 405 mA cm-2, the system generates hydrogen at a rate of 3.1 mL/min with a purity of 99.997%, achieving an impressive cell efficiency of 68.28% and a voltage of 1.85 V. Furthermore, the MoS2@Zn0.76Co0.24S /NF hybrid exhibits seamless integration with solar cells, establishing a photovoltaic electrochemical system for comprehensive water splitting. This wireless assembly harnesses the excellent performance of the hybrid nanowire, offering a promising solution for efficient, durable, and cost-effective bifunctional electrocatalysts in the realm of renewable energy.

Oxygen-doped NiCoP derived from Ni-MOFs for high performance asymmetric supercapacitor

Oxygen doping strategy is one of the most effective methods to improve the electrochemical properties of nickel-cobalt phosphide (NiCoP)-based capacitors by adjusting its inherent electronic structure. In this paper, O-doped NiCoP microspheres derived from porous nanostructured nickel metal-organic frameworks (Ni-MOFs) were constructed through solvothermal method followed by phosphorization treatment. The O-doping concentration has a siginificant influence on the rate performance and cycle stability. The optimized O-doped NiCoP electrode material shows a specific capacitance of 632.4 F-g-1at 1 A-g-1and a high retention rate of 56.9% at 20 A g-1. The corresponding NiCoP-based asymmetric supercapacitor exhibits a high energy density of 30.1 Wh kg-1when the power density is 800.9 W kg-1, and can still maintain 82.1% of the initial capacity after 10 000 cycles at 5 A g-1.

Rational Design of a Copper Cobalt Sulfide/Tungsten Disulfide Heterostructure for Excellent Overall Water Splitting

Integrating different components into a heterostructure is a novel approach that increases the number of active centers to enhance the catalytic activities of a catalyst. This study uses an efficient, facile hydrothermal strategy to synthesize a unique heterostructure of copper cobalt sulfide and tungsten disulfide (CuCo2S4-WS2) nanowires on a Ni foam (NF) substrate. The nanowire arrays (CuCo2S4-WS2/NF) with multiple integrated active sites exhibit small overpotentials of 202 (299) and 240 (320) mV for HER and OER at 20 (50) mA cm-2 and 1.54 V (10 mA cm-2) for an electrolyzer in 1.0 M KOH, surpassing commercial and previously reported catalysts. A solar electrolyzer composed of CuCo2S4-WS2 bifunctional electrodes also produced significant amounts of hydrogen through a water splitting process. The remarkable performance is accredited to the extended electroactive surface area, reasonable density of states near the Fermi level, optimal adsorption free energies, and good charge transfer ability, further validating the excellent dual function of CuCo2S4-WS2/NF in electrochemical water splitting.

Tuning the Surface Electronic Structure of Amorphous NiWO4 by Doping Fe as an Electrocatalyst for OER

Water electrolysis is considered as one of the alternative potential approaches for producing renewable energy. Due to the sluggish kinetic nature of oxygen evolution reaction (OER), it encounters a significant overpotential to achieve water electrolysis. Hence, the advancement of cost-effective transition metal-based catalysts toward water splitting has gained global attention in recent years. In this work, the doping of Fe over amorphous NiWO₄ increased the OER activity effectively and achieved stable oxygen evolution in the alkaline medium, which show better electrocatalytic activity as compared to crystalline tungstate. As NiWO₄ has poor activity toward OER in the alkaline medium, the doping of Fe³⁺ will tune the electronic structure of Ni in NiWO₄ and boost the OER activity. The as-synthesized Fe-doped amorphous NiWO₄ exhibits a low overpotential of 230 mV to achieve a current density of 10 mA cm^-2 and a lower Tafel slope value of 48 mV dec^-1 toward OER in 1.0 M KOH solution. The catalyst also exhibits long-term static stability of 30 h during chronoamperometric study. The doping of Fe improves the electronic conductivity of Ni-3d states in NiWO₄ which play a dominant role for better catalytic activity via synergistic interaction between Fe and active Ni sites. In future, these results offer an alternative route for precious metal-free catalysts in alkaline medium and can be explicitly used in various tungstate-based materials to increase the synergism between the doped atom and metal ions in tungstate-based materials for further improvement in the electrocatalytic performance.

Magnetic biosensors for identification of SARS-CoV-2, Influenza, HIV, and Ebola viruses: a review

Infectious diseases such as novel coronavirus (SARS-CoV-2), Influenza, HIV, Ebola, etc kill many people around the world every year (SARS-CoV-2 in 2019, Ebola in 2013, HIV in 1980, Influenza in 1918). For example, SARS-CoV-2 has plagued higher than 317 000 000 people around the world from December 2019 to January 13, 2022. Some infectious diseases do not yet have not a proper vaccine, drug, therapeutic, and/or detection method, which makes rapid identification and definitive treatments the main challenges. Different device techniques have been used to detect infectious diseases. However, in recent years, magnetic materials have emerged as active sensors/biosensors for detecting viral, bacterial, and plasmids agents. In this review, the recent applications of magnetic materials in biosensors for infectious viruses detection have been discussed. Also, this work addresses the future trends and perspectives of magnetic biosensors.

Optimized Fabrication of Bimetallic ZnCo Metal-Organic Framework at NiCo-Layered Double Hydroxides for Multiple Storage and Capability Synergy All-Solid-State Supercapacitors

Rational design and structural regulation of hybrid nanomaterials with superior electrochemical performance are crucial for developing sustainable energy storage platforms. Among these materials, NiCo-layered double hydroxides (NiCo-LDHs) demonstrate an exceptional charge storage capabilities owing to their tunable 2D lamellar structure, large interlayer spacing, and rich redox electrochemically active sites. However, NiCo-LDHs still suffer from sever agglomeration of their particles with limited charge transfer rates, resulting in an inadequate rate capability. In this study, bimetallic ZnCo-metal organic framework (MOF) tripods were grown on the surface of NiCo-LDH nanowires, which significantly reduced the self-agglomeration and stacking of the NiCo-LDH nanowire arrays, offering more accessible active sites for charge transfer and shortening the path for ion diffusion. The fabricated hybrid ZnCo-MOF@NiCo-LDH and its individual counterparts were tested as supercapacitor electrodes. The ZnCo-MOF@NiCo-LDH electrode demonstrated a remarkable specific capacitance of 1611 F g^-1 at 2 A g^-1 with an enhanced rate capability of 66% from 2 to 20 A g^-1. Moreover, an asymmetric all solid-state supercapacitor device was constructed using ZnCo-MOF@NiCo-LDH and palm tree-derived activated carbon (P-AC) as positive and negative poles, respectively. The constructed device can store a high specific energy of 44.5 Wh Kg^-1 and deliver a specific power of 876.7 W Kg^-1 with outstanding Columbic efficiency over 10,000 charging/discharging cycles at 15 A g^-1.

Foldable and wearable supercapacitors for powering healthcare monitoring applications with improved performance based on hierarchically co-assembled CoO/NiCo networks

Small-scale and high-performance energy storage devices have drawn tremendous attention with their portable, lightweight, and multi-functionalized features. Here, we present a foldable supercapacitor with affordable flexibility by adopting a developed design and electrode material system as a way to extend usability. Notably, to resolve the limited energy density of conventional capacitors, we successfully synthesize the CoO/NiCo-layered double hydroxide (LDH) core-shell nanostructure on Ni framework as a cathode material. Further, glucose-based activated carbon (GBAC) is utilized for the anode. The CoO/NiCo-LDH electrodes exhibited a high specific capacitance of ∼284.8 mAh g^-1 at 1 A g^-1, and GBAC delivers a high specific capacitance of ∼166 F g^-1 at 1 A g^-1. In the following, the combinatorial integration of these materials enabled the asymmetric supercapacitor (ASC) to increase the energy density by enhancing the capacitance and the voltage window, in which a hydrogel-based electrolyte was facilitated for the foldable and wearable capability. The energy density of the ASC device was ∼24.9 Wh kg^-1 at a power density of ∼779.5 W kg^-1 with a voltage window of ∼1.6 V. As demonstrated, a self-powered energy source was demonstrated by a serially connected multi-ASC device with a help of a commercial solar cell, which was employed for powering wearable healthcare monitoring devices, including personal alarms for patients and recording the human body's electrical signals. The present work offers a viable approach to preparing potential candidates for high-performance electrodes of supercapacitors with deformable configurations to extend the powering capability of other electronic devices with physical functionalities used in wearable electronics.

Ce3+ ion regulated CoNi-hydroxides for ultrahigh charge rate supercapacitors

α-form Ce3+:CoNi-LDH//AC supercapacitors exhibited an energy density of 30 W h kg−1 at a power density of 10 kW kg−1 thanks the unique crystal and electronic structures of Ce3+:CoNi-LDH.

Pillared-MOF@NiV-LDH Composite as a Remarkable Electrocatalyst for Water Oxidation

Oxygen evolution reaction (OER) represents a highly important electrochemical transformation in energy storage and conversion technologies. Considering the low rate of this four-electron half-reaction, there is a demand for efficient, stable, and noble-metal-free electrocatalysts to improve the kinetic and economical parameters. In this work, a new pillared-MOF@NiV-LDH nanocomposite based on a Co^II metal-organic framework (pillared-MOF) and heterometallic Ni/V-layered double hydroxide (NiV-LDH) was assembled via a simple protocol, characterized, and explored as an electrocatalyst in OER. A remarkable electrocatalytic efficiency of pillared-MOF@NiV-LDH in 1 M KOH is evidenced by a low overpotential (238 mV at 10 mA cm^-2 current density) and a small value of the Tafel slope (62 mV dec^-1). These parameters are very close to those of the reference IrO₂ electrocatalyst and are superior to the majority of the LDH- and MOF-based systems previously applied for OER. Excellent stability of pillared-MOF@NiV-LDH was confirmed by the chronopotentiometry tests for 70 h and linear-sweep voltammetry after 7000 cycles. Features such as rich electroactive sites, porous structure, high surface area, and synergic effect between pillared-MOF and NiV-LDH are likely responsible for the remarkable electrocatalytic efficiency of this electrocatalyst in OER. Despite prior reports on the application of NiV-LDH in OER, the present study describes the first example where this type of LDH is blended with MOF to generate a nanocomposite material. The interface between the two components of the composite can improve the electronic structure and, in turn, the electrocatalytic behavior. The introduction of this composite paves the way toward the synthesis of other multicomponent materials with potential applications in different energy fields.

Efficient and reusable catalysis of benzylic C-H oxidation over layered [Co5(OH)6]4+ derivatives

Aerobic oxidation of benzylic C(sp³)-H bonds in a green and heterogeneous manner is a major target in organic catalysis. Herein, we report the synthesis of 3D coordination polymers containing [Co₅(OH)₆]⁴⁺ layers, affording reusable and efficient oxidation of ethylbenezene and tetralin by using O₂ as the oxidant. Moreover, the cleavage of Co^II-carboxylate bonding renders atomically thin cobaltate nanosheets and enhanced catalytic performance. This is one of the top catalytic performances for Co^II-catalyzed benzylic C(sp³)-H oxidation (∼0.02 mol% Co and 76% conversion for nanosheets), ascribed to the exposed, accessible and coordinatively unsaturated Co^II species.

Corrosion-controlled surface engineering improves the adhesion of materials for stable free-standing electrodes

Directly anchoring active materials on porous conductive substrates is considered an effective strategy to obtain a high-activity electrode since the direct contact between active materials and substrates benefits charge transfer, and the presence of porous structures provides more active sites. However, due to the presence of strong stress and weak adhesion, active materials loaded on the substrate are very easy to peel off during assembly and use, which can greatly shorten the lifetime of use. Herein, an ultrasonic corrosion strategy is proposed to regulate the surface of a metal substrate. We find that ultrasonic oxygen corrosion and interfacial water control play key roles in fabricating the complex electrode, which can help the surface of Cu foam to form special lamellar cross-linked CuO nanoarchitectures with strong adhesion and then overcome the defect of the deposited NiCo layered double hydroxides (NC LDH) on the stress and adhesion. The expected electrode shows more than 70% improvement in cycling stability at an ultra-high current density of 20 A g^-1, relative to the active material layer of the electrode with strong stress and weak adhesion. Meanwhile, benefiting from its lamellar cross-linked nanoarchitectures having large specific surface area and many nano-pores, it presents a high specific capacitance of 3010.8F g^-1 at 1 A g^-1 and a good rate capability of 59.3% at 50 A g^-1. It is foreseen that this finding provides a novel, universal strategy for managing the surface and interface of the metal substrate, thereby obtaining a reliable, stable electrode.

Alkali-Free Hydrothermally Reconstructed NiAl Layered Double Hydroxides for Catalytic Transesterification

NiAl layered double hydroxides (LDHs) are promising bifunctional catalysts comprising tunable redox and Lewis acidic sites. However, most studies of NiAl LDH employ alkali hydroxide carbonate precipitants which may contaminate the final LDH catalyst and leach into reaction media. Here, we report an alkali-free route to prepare NixAl LDHs with a composition range x = 1.7 to 4.1 using (NH4)2CO3 and NH4OH as precipitants. Activation of LDHs by calcination–rehydration protocols reveal NixAl LDHs can be reconstructed under mild hydrothermal treatment (110 °C for 12 h), with the degree of reconstruction increasing with Ni content. Catalyst activity for tributyrin transesterification with methanol was found to increase with Ni content and corresponding base site loadings; TOFs also increased, suggesting that base sites in the reconstructed LDH are more effective for transesterification. Hydrothermally reconstructed Ni4.1Al LDH was active for the transesterification of C4–C12 triglycerides with methanol and was stable towards leaching during transesterification.

Designing of two dimensional lanthanum cobalt hydroxide engineered high performance supercapacitor for longer stability under redox active electrolyte

Redox active electrolyte supercapacitors differ significantly from the conventional electrolytes based storage devices but face a long term stability issue which requires a different approach while designing the systems. Here, we show the change in layered double hydroxides (LDHs) systems with rare earth elements (lanthanum) can drastically influence the stability of two dimensional LDH systems in redox electrolyte. We find that the choice of rare earth element (lanthanum) having magnetic properties and higher thermal and chemical stability has a profound effect on the stability of La-Co LDHs electrode in redox electrolyte. The fabricated hybrid device with rare earth based positive electrode and carbon as negative electrode having redox electrolyte leads to long stable high volumetric/gravimetric capacity at high discharge rate, demonstrates the importance of considering the rare earth elements while designing the LDH systems for redox active supercapacitor development.

Fe doped NiS nanosheet arrays grown on carbon fiber paper for a highly efficient electrocatalytic oxygen evolution reaction

Developing efficient and low-cost non-noble metal catalysts for the oxygen evolution reaction (OER) is important for hydrogen production through water electrolysis. Herein, Fe doped NiS nanosheets directly grown on conductive carbon fiber paper (Fe-NiS@CFP) were fabricated through a two-step hydrothermal process. The microstructure, interface and electronic states of the prepared sample were modulated by Fe doping, exhibiting small internal and interface charge-transfer resistance. Benefiting from these factors, Fe-NiS@CFP shows superior electrocatalytic performance with an overpotential of 275 mV at 100 mA cm^-2 and maintains the activity for at least 50 h as a working electrode for the OER. This work may provide insights into the design and fabrication of non-noble metal sulfide electrocatalysts.

Investigating the Impact of the Washing Steps of Layered Double Hydroxides (LDH) on the Electrochemical Performance

The washing of layered double hydroxides (LDH) material is mostly purposed to discard the unreacted products after the reaction has been completed. However, this study demonstrated that the washing stage can also be targeted to optimise the electrochemical performance of LDH by using an appropriate solvent. Solvents, namely, ethanol, acetone, and an ethanol-acetone solution (2:1) were used for the washing of LDH and the impacts thereof on the structural, physical, chemical, morphological, and electrochemical properties were investigated. Using Williamson-Hall analysis, we observed modifications on the crystalline domain. The specific surface area and pore parameters for all the samples were also differently affected. The Fourier transform infrared (FTIR) measurements displayed evident changes in the basic sites. The electrochemical performances of samples were analysed. The sample washed with the ethanol-acetone solution exhibited a specific capacitance of 1807.26 Fg-1 at 10 mVs-1, which is higher than that of other samples as well as low internal resistance compared to its counterpart. This demonstrates that the use of an appropriate solvent during the washing stage of LDH affects the electrochemical properties.

Synthesis of FeNiCo Ternary Hydroxides through Green Grinding Method with Metal-Organic Frameworks as Precursors for Oxygen Evolution Reaction

Metal-organic framework (MOF)-derived materials have been widely applied to diversified fields until now due to their flexible processibility. Different kinds of suitable materials can be synthesized by varying MOF templates/precursors and synthesis methods. An appropriate method can skillfully fabricate the materials with excellent performance while meeting the environmentally friendly concept. In this work, a green and flexible grinding method was introduced to synthesize MOF-derived FeNiCo trimetallic materials without solvent-assistance, in which Co-ZIF-L was selected as a sacrificial precursor and Fe³⁺ and Ni²⁺ as etchants and dopants. Surprisingly, the as-prepared FeNiCo ternary hydroxides supported on Ni foam (G-FeNi-Co-ZIF-L/NF) showed superior electrocatalytic performance for the oxygen evolution reaction (OER) with a low overpotential of 248 mV at 10 mA cm^-2 . This work provides a prospective approach to synthesize various MOF-derived multi-metallic materials, which also opens the door for syntheses of OER electrocatalysts.

Self-Therapeutic Cobalt Hydroxide Nanosheets (Co(OH)2 NS) for Ovarian Cancer Therapy

High-grade serous ovarian cancer (HGSOC) is one of the major life-threatening cancers in women, with a survival rate of less than 50%. So far, chemotherapy is the main therapeutic tool to cure this lethal disease; however, in many cases, it fails to cure HGSOC even with severe side effects. Self-therapeutic nanomaterials could be an effective alternative to chemotherapy, facilitated by their diverse physicochemical properties and the ability to generate reactive species for killing cancer cells. Herein, inorganic cobalt hydroxide nanosheets (Co(OH)₂ NS) were synthesized by a simple solution process at room temperature, and morphological, spectroscopic, and crystallographic analyses revealed the formation of Co(OH)₂ NS with good crystallinity and purity. The as-prepared Co(OH)₂ NS showed excellent potency, comparable to the FDA-approved cisplatin drug to kill ovarian cancer cells. Flow cytometric analysis (nnexin V) revealed increased cellular apoptosis for Co(OH)₂ NS than cobalt acetate (the precursor). Tracking experiments demonstrated that Co(OH)₂ NS are internalized through the lysosome pathway, although relocalization in the cytoplasm has been observed. Hence, Co(OH)₂ NS could be an effective self-therapeutic drug and open up an area for the optimization of self-therapeutic properties of cobalt nanomaterials for cancer treatment.

Controllable Morphology of Sea-Urchin-like Nickel-Cobalt Carbonate Hydroxide as a Supercapacitor Electrode with Battery-like Behavior

Nickel-cobalt carbonate hydroxide with a three-dimensional (3D) sea-urchin-like structure was successfully developed by the hydrothermal process. The obtained structure enables the enhancement of charge/ion diffusion for the high-performance supercapacitor electrodes. The mole ratio of nickel to cobalt plays a vital role in the densely packed sea-urchin-like structure formation and electrochemical properties. At optimized nickel/cobalt mole ratio (1:2), the highest specific capacitance of 950.2 F g^-1 at 1 A g^-1 and the excellent cycling stability of 178.3% after 3000 charging/discharging cycles at 40 mV s^-1 are achieved. This nickel-cobalt carbonate hydroxide electrode yields an energy density in the range of 42.9-15.8 Wh kg^-1, with power density in the range of 285.0-2849.9 W kg^-1. The charge/discharge mechanism at the atomic level as monitored by time-resolved X-ray absorption spectroscopy (TR-XAS) indicates that the high capacitance behavior in a nickel-cobalt carbonate hydroxide is mainly dominated by cobalt carbonate hydroxide.

A novel and facile green synthesis method to prepare LDH/MOF nanocomposite for removal of Cd(II) and Pb(II)

To date, many nanoadsorbents have been developed and used to eliminate heavy metal contamination, however, one of the challenges ahead is the preparation of adsorbents from processes in which toxic organic solvents are used in the least possible amount. Herein, we have developed a new carboxylic acid-functionalized layered double hydroxide/metal-organic framework nanocomposite (LDH/MOF NC) using a simple, effective, and green in situ method. UiO-66-(Zr)-(COOH)₂ MOF nanocrystals were grown uniformly over the whole surface of COOH-functionalized Ni₅₀Co₅₀-LDH ultrathin nanosheets in a green water system under a normal solvothermal condition at 100 °C. The synthesized LDH/MOF NC was used as a potential adsorbent for removal of toxic Cd(II) and Pb(II) from water and the influence of important factors on the adsorption process was monitored. Various non-linear isotherm and kinetic models were used to find plausible mechanisms involved in the adsorption, and it was found that the Langmuir and pseudo-first-order models show the best agreement with isotherm and kinetic data, respectively. The calculated maximum adsorption capacities of Cd(II) and Pb(II) by the LDH/MOF NC were found to be 415.3 and 301.4 mg g^-1, respectively, based on the Langmuir model (pH = 5.0, adsorbent dose = 0.02 g, solution volume = 20 mL, contact time = 120 min, temperature = 25 ℃, shaking speed 200 rpm).

A. R, Fouad OA. Polyvinylpyrrolidone and freeze drying-assisted growth of an α-Ni(OH)2/reduced graphene oxide hybrid structure as a superior electrode material for supercapacitors

The electrode of 30 wt% α-Ni(OH)₂/rGO hybrid structure displayed a promising material for supercapacitors. It showed a specific capacitance (capacity) of 1050 F g⁻¹ (580 C g⁻¹), and its hybrid device exhibited a high energy density of 60 W h kg⁻¹.

In situ growth of an Fe-doped NiCo-MOF electrocatalyst from layered double hydroxide effectively enhances electrocatalytic oxygen evolution performance

The hierarchical book-like Fe-NiCo-MOF exhibits superior OER performance coupled with outstanding stability at a high current density.

Effect of Binding Affinity of Crystal Water on the Electrochemical Performance of Layered Double Hydroxides

The ever-increasing demand for safe batteries has driven research efforts to develop aqueous rechargeable batteries. In this regard, Ni-based layered double hydroxides (LDHs) have received marked attention owing to their adequate operating potential, high specific capacity, and decent cycling performance. Nevertheless, the effect of immobile intercalants (e. g., crystal water and anions) that are inherently present in the interlayer galleries is barely understood. In this paper, we report that the electrochemical performance of LDH largely depends on the extent to which the crystallinity is affected by the binding strength of crystal water to the transition metal slabs. A series of infrared spectroscopy and in-situ X-ray absorption analyses reveal that the lattice disordering in LDHs is beneficial for accommodating the stress during the (de)intercalation of carrier ions, which serves as the origin of their superior specific capacities and cycle life. This study presents a useful structure-property relationship of the way in which the binding affinity of crystal water affects the key electrochemical properties of the host electrode materials.

Zn-Al Layered Double Hydroxide Film Functionalized by a Luminescent Octahedral Molybdenum Cluster: Ultraviolet-Visible Photoconductivity Response

A novel UV-Vis photodetector consisting of an octahedral molybdenum cluster-functionalized Zn₂Al layered double hydroxide (LDH) has been successfully synthesized by co-precipitation and delamination methods under ambient conditions. The electrophoretic deposition process has been used as a low-cost, fast, and effective method to fabricate thin and transparent nanocomposite films containing a dense and regular layered structure. The study provided evidence that the presence of the Mo₆ cluster units between the LDH does not affect the ionic conduction mechanism of the LDH, which linearly depends on the relative humidity and temperature. Moreover, the photocurrent response is remarkably extended to the visible domain. The reproducibility and stabilization of the photocurrent response caused by the Mo₆ cluster-functionalized LDH have been verified upon light excitation at 540 nm. Additionally, it was demonstrated that the films show advantageously strong adherence properties for application requirements.

High performance flexible hybrid supercapacitors based on nickel hydroxide deposited on copper oxide supported by copper foam for a sunlight-powered rechargeable energy storage system

Herein, an integrated system combining solar cells with a hybrid supercapacitor for operating a homemade windmill device was assembled, achieving energy conversion, storage and utilization. As a candidate for positive electrode of hybrid supercapacitor devices, battery-like Ni(OH)₂@CuO@Cu binder-free electrode was fabricated by a two-step process at ambient temperature. CuO@Cu was prepared by chemical oxidation method to act as the supporting electrode for electrochemical deposition of Ni(OH)₂. Various deposition times (30, 50, 90, 150 and 200 s) were investigated to optimize the energy storage characteristics of the resulting Ni(OH)₂@CuO@Cu electrode materials. Among all the samples, Ni(OH)₂@CuO@Cu-150 exhibited the largest areal capacity of 7063 mC cm^-2 at 20 mA cm^-2, and was therefore chosen as the positive electrode in a hybrid supercapacitor device. Using N-doped reduced graphene oxide on nickel foam (N-rGO/NF) as the negative electrode, a hybrid supercapacitor was assembled. It displayed good flexibility, cycling stability and high areal energy density of 130.4 μWh cm^-2 at a power density of 1.6 mW cm^-2. Two hybrid supercapacitor devices were connected in series to successfully lighten up a red LED for 12 min 39 s, while three devices assembled in series were able to successfully power a three-digit digital display for 1 min 28 s. Interestingly, the hybrid supercapacitor device, charged by solar cells, further operated a homemade windmill device for 59 s, achieving sunlight-powered integration system. All of the findings suggested the practical application potential of the hybrid supercapacitor based on Ni(OH)₂@CuO@Cu composite as energy storage device.

The Influence of the Electrodeposition Parameters on the Properties of Mn-Co-Based Nanofilms as Anode Materials for Alkaline Electrolysers

In this work, the influence of the synthesis conditions on the structure, morphology, and electrocatalytic performance for the oxygen evolution reaction (OER) of Mn-Co-based films is studied. For this purpose, Mn-Co nanofilm is electrochemically synthesised in a one-step process on nickel foam in the presence of metal nitrates without any additives. The possible mechanism of the synthesis is proposed. The morphology and structure of the catalysts are studied by various techniques including scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and transmission electron microscopy. The analyses show that the as-deposited catalysts consist mainly of oxides/hydroxides and/or (oxy)hydroxides based on Mn²⁺, Co²⁺, and Co³⁺. The alkaline post-treatment of the film results in the formation of Mn-Co (oxy)hydroxides and crystalline Co(OH)₂ with a β-phase hexagonal platelet-like shape structure, indicating a layered double hydroxide structure, desirable for the OER. Electrochemical studies show that the catalytic performance of Mn-Co was dependent on the concentration of Mn versus Co in the synthesis solution and on the deposition charge. The optimised Mn-Co/Ni foam is characterised by a specific surface area of 10.5 m²·g⁻¹, a pore volume of 0.0042 cm³·g⁻¹, and high electrochemical stability with an overpotential deviation around 330–340 mV at 10 mA·cm⁻²_geo for 70 h.

n-Butanol/Water Interface-Aided Physicochemical Tuning of Two-Dimensional Transition-Metal Oxides

Herein, we report a facile regulation of the interface of two immiscible solvents, n-butanol and water, to achieve the physicochemical tuning of the transition-metal oxide nickel cobaltite. The crystal nucleation and the growth of nickel cobaltite into distinct morphology are highly dependent on the orientation and the mass transfer of the reactive species through the reactive interface layer. A distinct two-dimensional flakelike (1 nm thickness) nickel cobaltite is formed at the interface of n-butanol/water in a 1:1 solvent ratio. Rather, one-dimensional needles and irregular interconnected networks are achieved, as aqueous and organic counterparts are, respectively, increased. The impact of the solvent ratio on doping metal ions (Co²⁺ and Ni²⁺) at the interstitial sites of fcc spinel structure is evident from the X-ray and electronic absorption investigations. It is presumed that the interface-assisted synthesis may provide a simple and novel way to develop and adopt various transition-metal oxides for wide applications.

Wire-Shaped 3D-Hybrid Supercapacitors as Substitutes for Batteries

We report a wire-shaped three-dimensional (3D)-hybrid supercapacitor with high volumetric capacitance and high energy density due to an interconnected 3D-configuration of the electrode allowing for large number of electrochemical active sites, easy access of electrolyte ions, and facile charge transport for flexible wearable applications. The interconnected and compact electrode delivers a high volumetric capacitance (gravimetric capacitance) of 73 F cm^-3 (2446 F g^-1), excellent rate capability, and cycle stability. The 3D-nickel cobalt-layered double hydroxide onto 3D-nickel wire (NiCo LDH/3D-Ni)//the 3D-manganese oxide onto 3D-nickel wire (Mn₃O₄/3D-Ni) hybrid supercapacitor exhibits energy density of 153.3 Wh kg^-1 and power density of 8810 W kg^-1. The red light-emitting diode powered by the as-prepared hybrid supercapacitor can operate for 80 min after being charged for tens of seconds and exhibit excellent electrochemical stability under various deformation conditions. The results verify that such wire-shaped 3D-hybrid supercapacitors are promising alternatives for batteries with long charge-discharge times, for smart wearable and implantable devices.

A hierarchical LDH/MOF nanocomposite: single, simultaneous and consecutive adsorption of a reactive dye and Cr(vi)

The design and development of an environmentally benign porous adsorbent for effective simultaneous adsorption of organic dyes and heavy metals from water are important but remain a big challenge. Herein, we have designed a layered double hydroxide/metal-organic framework-based hierarchical nanocomposite (LDH/MOF HNC) by a facile, room-temperature in situ approach. This paper for the first time reports a hierarchical trimodal micro-meso-macroporous LDH/MOF composite with a high surface area (surface area 1282 m2 g-1 and pore volume 0.93 cm3 g-1), synthesised by uniformly growing MOF nanocrystals on the surface of LDH nanosheet ultrathin films. An attempt is made to quantitatively demonstrate the adsorption data via suitable nonlinear kinetic and isotherm equations for single, simultaneous, and consecutive adsorption of the orange II reactive dye and Cr(vi). Experiments were performed at various values of pH (6.0-11.0), adsorbent dosages (1.0-8.0 mg), adsorbate concentrations (5-500 mg L-1), and temperatures (293-323 K). The Langmuir model revealed a satisfactory fit to the equilibrium data of the LDH/MOF HNC (correlation coefficients R2 > 0.98) with a calculated maximum adsorption capacity of 1173 and 733 mg g-1 for orange II and Cr(vi), respectively, in a simultaneous adsorption system. The results of the study demonstrated that LDH/MOF HNCs could potentially be applied as a promising nanoadsorbent for the simultaneous removal and extraction of toxic dyes and metals from water.

Cobalt-based layered double hydroxides revisited: evidence for oxidizing radical generation

Layered double hydroxides (LDHs) containing transition metal elements such as cobalt show interesting reactivity related to the complexity of cobalt chemistry.