One-step facile synthesis of nickel-chromium layered double hydroxide nanoflakes for high-performance supercapacitors

Advances in anion-intercalated layered double hydroxides for supercapacitors: study of chemical modifications and classifications

Hybrid material-based electrochemical supercapacitors (SCs) possessing improved energy density (ED), enhanced stability, high porosity, and a large accessible surface area have attracted attention as promising energy storage devices. SCs also demonstrate excellent specific capacitance (Cs) across various current densities, increased capacitance, and high cell voltages, all contributing to improved ED. Layered double hydroxides (LDHs), with their anionic exchange capabilities and laminar structures, offer significant potential for boosting charge transfer in SCs. This review provides a comprehensive overview of the recent advances in anion-based LDHs, discussing their storage mechanisms, chemical modifications, and classification based on interlayer anions. The roles of different anions, including monovalent, divalent, and polyoxometalates, in enhancing storage properties are examined. In addition, the challenges, future research directions, and practical perspectives of anion-storing LDHs are presented. Hence, this review provides a concise overview of anion-based LDHs for SCs, highlighting their potential significance in energy storage applications.

NiCr-LDH/V4C3 MXene nanocomposites as an efficient electrocatalyst for urea oxidation

The quest for highly efficient electrocatalysts for direct urea fuel cells (DUFCs) is vital in addressing the energy deficits and environmental crisis. Ni-based LDHs are widely known for their substantial capability in urea oxidation reactions (UOR). This study involved the synthesis of NiCr-LDH/V4C3 MXene nanocomposites (NCVs) and the evaluation of their electrochemical efficiency towards UOR. The hybridization of V4C3 with NiCr-LDH improved the redox kinetics of the nanocomposite. NCV-21 achieved a notable efficiency of 10 mA cm-2 at a lower onset potential of 1.36 V versus the reversible hydrogen electrode in a 1.0 M KOH solution containing 0.33 M urea. Furthermore, it demonstrated an enhanced current density of 112.64 mA cm-2 and long-term durability. The robust interaction and electronic coupling between NiCr-LDH and V4C3 MXene, marked by superior current density and significant charge transfer, confers the nanocomposite with remarkable catalytic activity and stability towards substantial urea oxidation performance. Based on the results obtained, the NiCr-LDH/V4C3 MXene nanocomposite is an efficient anodic catalyst for urea oxidation. This study will open a new avenue for the development of various LDH/MXene nanocomposites for energy conservation applications.

V-Doping Strategy Induces the Construction of the CoFe-LDHs/NF Electrodes with Higher Conductivity to Achieve Higher Energy Density for Advanced Energy Storage Devices

Doping of metal ions shows promising potential in optimizing and modulating the electrical conductivity of layered double hydroxides (LDHs). However, there is still much room for improvement in common metal ions and conventional doping methods. In contrast to previous methodologies, a hollow triangular nanoflower structure of CoFeV-LDHs is devised, which is enriched with a greater number of oxygen vacancies. This resulted in a significant enhancement in the conductivity of the LDHs, leading to an increase in energy density following the appropriate doping of V. To investigate the impact of V-doping on the energy density of the LDHs, in situ XPS and in situ X-ray spectroscopy is employed. Regarding electrochemical performance, the CoFeV-LDHs/NF electrode with optimal doping ratio exhibited a specific capacitance of 881 F g-1 at a current density of 1 A g-1. The capacitance remained at 90.53% after 3000 cycles. In addition, the constructed battery-type supercapacitor CoFeV-LDHs/NF-2//AC exhibited an impressive energy density of 124.7 Wh kg-1 at a power density of 850 W kg-1 and capacitance remained almost unchanged at 95.2% after 3000 cycles. All the above demonstrates the great potential of V-doped LDHs and brings a new way for the subsequent research of LDHs.

Melanin-intercalated layered double hydroxide LDH/MNP as a stable photothermal agent

Melanin nanoparticles (MNPs) are a type of electronegative compound that can be used as photothermal agent for cancer treatment. Nevertheless, the agglomeration of MNP, which is one of the limitations in practice, contributes to the instability of MNP. Pristine layered double hydroxide (LDH), as a kind of positive inorganic material when there exist no other cargo between its layers, can accommodate electronegative molecules between its layers to endow them with stable properties. Hence, in this study, electronegative MNP was intercalated into LDH lamellas via ion-exchange method to obtain the stable original photothermal agent LDH/MNP, solving the tough problem of MNP's agglomeration. The surface morphology, X-ray diffraction and fourier transform infrared spectra affirmed the successful intercalation of MNP between LDH lamellas. The Z-average particle sizes of LDH/MNP on day 0, 7 and 14 were measured as 221.8 nm, 227.6 nm and 230.5 nm without obvious fluctuation, while the particle sizes of MNP went through dramatic enlargement from 105.8 nm (day 0) to 856.1 nm (day 7), indicating the better stability of LDH/MNP than MNP. The typical polymer dispersity index (PDI) values on day 0, 7 and 14 verified the better stability of LDH/MNP, too. Photothermal properties of LDH/MNP were assessed and the results ensured the representative photothermal properties of LDH/MNP. The fine cytocompatibility of LDH/MNP was verified via cytotoxicity test. Results confirmed that the agglomeration of MNP disappeared after its intercalation into LDH and LDH/MNP possessed fine stability as well as typical photothermal property. The intercalation of MNP into LDH gave the photothermal agent MNP a promising way for its better stability and long-term availability in photothermal treatment.

Hydrothermally Synthesized ZnCr- and NiCr-Layered Double Hydroxides as Hydrogen Evolution Photocatalysts

The layered double hydroxides (LDHs) of transition metals are of great interest as building blocks for the creation of composite photocatalytic materials for hydrogen production, environmental remediation and other applications. However, the synthesis of most LDHs is reported only by the conventional coprecipitation method, which makes it difficult to control the catalyst's crystallinity. In the present study, ZnCr- and NiCr-LDHs have been successfully prepared using a facile hydrothermal approach. Varying the hydrothermal synthesis conditions allowed us to obtain target products with a controllable crystallite size in the range of 2-26 nm and a specific surface area of 45-83 m2∙g-1. The LDHs synthesized were investigated as photocatalysts of hydrogen generation from aqueous methanol. It was revealed that the photocatalytic activity of ZnCr-LDH samples grows monotonically with the increase in their average crystallite size, while that of NiCr-LDH ones reaches a maximum with intermediate-sized crystallites and then decreases due to the specific surface area reduction. The concentration dependence of the hydrogen evolution activity is generally consistent with the standard Langmuir-Hinshelwood model for heterogeneous catalysis. At a methanol content of 50 mol. %, the rate of hydrogen generation over ZnCr- and NiCr-LDHs reaches 88 and 41 μmol∙h-1∙g-1, respectively. The hydrothermally synthesized LDHs with enhanced crystallinity may be of interest for further fabrication of their nanosheets being promising components of new composite photocatalysts.

Tailoring NiCoCu layered double hydroxide with Ag-citrate/polyaniline/functionalized SWCNTs nanocomposites for supercapacitor applications

Supercapacitors have substantially altered the landscape of sophisticated energy storage devices with their exceptional power density along with prolonged cyclic stability. On the contrary, their energy density remains low, requiring research to compete with conventional battery storage devices. This study addresses the disparities between energy and power densities in energy storage technologies by exploring the integration of layered double hydroxides (LDH) and highly conductive materials to develop an innovative energy storage system. Four electrodes were fabricated via a hydrothermal process using NiCoCu LDH, Ag-citrate, PANI, and f-SWCNTs. The optimal electrode demonstrated exceptional electrochemical properties; at 0.5 A g-1, it possessed specific capacitances of 807 F g-1, twice as high as those of the pure sample. The constructed asymmetric supercapacitor device attained energy densities of 62.15 W h kg-1 and 22.44 W h kg-1, corresponding to power densities of 1275 W kg-1 and 11 900 W kg-1, respectively. Furthermore, it maintained 100% cyclic stability and a coulombic efficiency of 95% for 4000 charge-discharge cycles. The concept of a supercapacitor of the hybrid grade was reinforced by power law investigations, which unveiled b-values in the interval of 0.5 to 1. This research emphasizes the considerable potential of supercapacitor-grade NiCoCu LDH/Ag-citrate-PANI-f-SWCNTs nanocomposites for superior rate performance, robust cycle stability, and enhanced energy storage capacity.

A novel top-down strategy for in situ construction of vertically oriented hexagonal NiCr LDHs nanosheet arrays with intercalated sulfate ions on Nichrome fiber for selective solid-phase microextraction of phenolic compounds in water samples

BACKGROUND

Phenolic compounds (PCs) are a class of polar aromatic pollutants with high toxicity in environmental water. Generally the efficient sample preparation is essential for the quantification of ultra-trace target PCs in real water sample before appropriative instrumental analysis. SPME is a convenient, solvent-free and time-saving miniaturized technique and has been recognized as a green alternative to conventional extraction techniques. In SPME, however, commercial fused-silica fibers are limited to the fragility, operation temperature, extraction capacity and selectivity as well as lifetime. Therefore, the development of new SPME fibers is always needed to overcome such limitations.

RESULTS

We presented a novel top-down strategy for in situ construction of vertically oriented hexagonal sulfate intercalated NiCr layered double hydroxide nanosheet arrays (NiCr LDHs-SO4 NSAs) on the Nichrome (NiCr) substrate by hydrothermal treatment in NaOH solution containing (NH4)2S2O8. The results showed that much shorter hydrothermal time was needed for the construction of NiCr@NiCr LDHs-SO4 NSAs fiber in the presence of (NH4)2S2O8. Moreover, the unique NiCr LDHs-SO4 NSAs coating offered open access structure, and thereby more available surface area for adsorption. The resulting fiber exhibited better extraction efficiency for phenolic compounds (PCs), faster mass transfer rate, higher mechanical stability, and longer service life than original NiCr@NiCr LDHs NSs fiber and typical commercially fused-silica fibers. After optimizing conditions, the SPME-HPLC-UV method demonstrated a linear range from 0.05 μg L-1 to 200 μg L-1 with LODs of 0.015-0.156 μg L-1 (S/N = 3) and LOQs of 0.048-0.498 μg L-1 (S/N = 10), as well as good repeatability (3.06%-5.22%) and fiber-to-fiber reproducibility (4.32%-6.49%).

SIGNIFICANCE

The developed SPME-HPLC-UV method with the constructed fiber was applied to the preconcentration and detection of different types of PCs in real water samples, showing satisfactory recoveries ranging from 86.20% to 107.8% with RSDs of 3.18%-6.69%. This study provides a new strategy for in situ construction of bimetallic hydroxides and their derived nanocomposite coatings on the NiCr fiber substrate in practical SPME application.

Growth mechanisms of monolayer hexagonal boron nitride (h-BN) on metal surfaces: theoretical perspectives

Two-dimensional hexagonal boron nitride (h-BN) has appeared as a promising material in diverse areas of applications, including as an excellent substrate for graphene devices, deep-ultraviolet emitters, and tunneling barriers, thanks to its outstanding stability, flat surface, and wide-bandgap. However, for achieving such exciting applications, controllable mass synthesis of high-quality and large-scale h-BN is a precondition. The synthesis of h-BN on metal surfaces using chemical vapor deposition (CVD) has been extensively studied, aiming to obtain large-scale and high-quality materials. The atomic-scale growth process, which is a prerequisite for rationally optimizing growth circumstances, is a key topic in these investigations. Although theoretical investigations on h-BN growth mechanisms are expected to reveal numerous new insights and understandings, different growth methods have completely dissimilar mechanisms, making theoretical research extremely challenging. In this article, we have summarized the recent cutting-edge theoretical research on the growth mechanisms of h-BN on different metal substrates. On the frequently utilized Cu substrate, h-BN development was shown to be more challenging than a simple adsorption-dehydrogenation-growth scenario. Controlling the number of surface layers is also an important challenge. Growth on the Ni surface is controlled by precipitation. An unusual reaction-limited aggregation growth behavior has been seen on interfaces having a significant lattice mismatch to h-BN. With intensive theoretical investigations employing advanced simulation approaches, further progress in understanding h-BN growth processes is predicted, paving the way for guided growth protocol design.

Recent Advances on Transition-Metal-Based Layered Double Hydroxides Nanosheets for Electrocatalytic Energy Conversion

Transition-metal-based layered double hydroxides (TM-LDHs) nanosheets are promising electrocatalysts in the renewable electrochemical energy conversion system, which are regarded as alternatives to noble metal-based materials. In this review, recent advances on effective and facile strategies to rationally design TM-LDHs nanosheets as electrocatalysts, such as increasing the number of active sties, improving the utilization of active sites (atomic-scale catalysts), modulating the electron configurations, and controlling the lattice facets, are summarized and compared. Then, the utilization of these fabricated TM-LDHs nanosheets for oxygen evolution reaction, hydrogen evolution reaction, urea oxidation reaction, nitrogen reduction reaction, small molecule oxidations, and biomass derivatives upgrading is articulated through systematically discussing the corresponding fundamental design principles and reaction mechanism. Finally, the existing challenges in increasing the density of catalytically active sites and future prospects of TM-LDHs nanosheets-based electrocatalysts in each application are also commented.

Self-assembled monolayer-assisted label-free electrochemical genosensor for specific point-of-care determination of Haemophilus influenzae

For sensitive detection of the L-fuculokinase genome related to the Haemophilus influenzae (H. influenzae), this research work demonstrates the label-free electrochemical-based oligonucleotide genosensing assay relying on the performing hybridization process. To enhance the electrochemical responses, multiple electrochemical modifier-tagged agents were effectively utilized. For attaining this goal, NiCr-layered double hydroxide (NiCr LDH) has been synthesized and combined with biochar (BC) to create an efficient electrochemical signal amplifier that has been immobilized on the surface of the bare Au electrode. Low detection and quantification limits (LOD and LOQ) associated with the designed genosensing bio-platform to detect L-fuculokinase have been achieved to 6.14 fM and 11 fM, respectively. Moreover, the wide linear range of 0.1 to 1000 pM demonstrates the capability of the designed platform. Investigated were the 1-, 2-, and 3-base mismatched sequences, and the negative control samples clarified the high selectivity and better performance of the engineered assay. The values of 96.6-104% and 2.3-3.4% have been obtained for the recoveries and RSDs, respectively. Furthermore, the repeatability and reproducibility of the associated bio-assay have been studied. Consequently, the novel method is appropriate for rapidly and quantitatively detecting H. influenzae, and is considered a better candidate for advanced tests on biological samples such as urine samples.

Nanoarchitecture of graphene nanosheets decorated with NiCr layered double hydroxide for sonophotocatalytic degradation of refractory antibiotics

Highly efficient and durable catalysts for wastewater treatment are urgently required to tackle critical environmental issues. In this regard, NiCr LDH (NC), NiCr LDH-GO (NC-GO), and NiCr LDH-rGO (NC-rGO) nanocomposites were synthesized. The results of XRD, EDX, and FTIR analyses not only explored the crystallographic and chemical structures of catalysts but also confirmed the successful synthesis. Further morphological, physical, chemical, and optical characteristics of the catalysts were evaluated more by SEM, HRTEM, BET, DRS, and XPS techniques. The as-synthesized catalysts were used for the efficient mineralization of rifadin under 50 W LED visible light irradiation and the ultrasonic power of 150 W. Amongst, 0.75 g L^-1 of NC-rGO demonstrated high sonophotocatalytic efficiency (88%) in natural pH (pH = 8) of 15 mg L^-1 of rifadin. The introduced system is also powerful for the decontamination of pharmaceutical-containing wastewater as well as other refractory antibiotics. Moreover, the radical trapping experiments demonstrated that the main reactive species involved in the degradation of rifadin are ^•OH, h⁺, and O₂^•-. The possible intermediates were thoroughly investigated using GCMS analysis. Also, NC-rGO demonstrated superior antibacterial activity in comparison with NC, NC-GO samples.