Surface Engineering of Graphene Oxide Shells Using Lamellar LDH Nanostructures

Bioinspired construction of ATP/Co-Al-Zn LDH nanozyme with enhanced peroxidase-mimic performance for efficient bactericidal activity through membrane disruption

In recent years, overuse of antibiotics has led to emerging antibiotic-resistant strains of bacteria. Consequently, creating new, highly productive antibacterial agents is crucial. In this work, we synthesized copper-aluminum-zinc layered double hydroxide (Co-Al-Zn LDH) and modified it using adenosine triphosphate. After characterization, the enzyme-like activity of the prepared particles was evaluated. The results indicated peroxidase-mimic performance of ATP/Co-Al-Zn LDH with Km values of 0.38 mM and 1.69 mM for TMB (3,3',5,5'-tetramethylbenzidine) and hydrogen peroxide (H2O2), respectively, which were lower than that of horseradish peroxidase. The highest peroxidase-like activity of ATP/Co-Al-Zn LDH was achieved at 20 °C, pH 4, with a 1.02 mg/mL catalyst, 231 μM TMB, and 1.9 mM H2O2. The bactericidal activity of the developed nanozyme was studied against E. coli and S. aureus. The peroxidase-mimic nanozyme decomposes H2O2 and generates free radicals to kill bacteria in vitro. The minimum inhibitory concentration (MIC) of ATP/Co-Al-Zn LDH was 15 μg/mL and 20 μg/mL for S. aureus and E. coli, respectively. The morphological characteristics of the nanozyme-treated bacterial cells showed dramatic changes in bacterial morphology. Our results revealed higher antibacterial activity of ATP/Co-Al-Zn LDH against S. aureus. Therefore, the developed nanozyme could serve as a substitute for conventional antibiotics.

Application of ANN and RSM for Rhodamine B and Safranine-O Decolorization on Zinc-Carbon Battery Waste Derived Ag/CoFe-LDH/rGO Catalyst

The present work is first aimed at recovering graphite from carbon rods of waste zinc-carbon (Zn-C) batteries for applications such as wastewater treatment, in order to contribute to the development of a sustainable environment. Then, a composite material, cobalt-iron layered double hydroxide combination with reduced graphene oxide, and with subsequent Ag nanoparticles deposition via NaBH4 reduction method (Ag/CoFe-LDH/rGO) was prepared for the catalytic activity of Rhodamine B (RhB) and Safranine-O (SO) as model contaminants from aquatic media. The catalytic activity of RhB and SO by Ag/CoFe-LDH/rGO in the presence of NaBH4 was studied to model and optimize the process parameters (NaBH4 amount, reaction time, initial dye concentration (Co), and catalyst dosage) via central composite design (CCD)-response surface methodology (RSM). Also, an artificial neural network (ANN) model was developed to estimate the catalytic activity of each dye using an RSM data set. The catalytic activities of 99.54% and 99.96% were obtained for RhB and SO dyes, respectively, under the optimal conditions: NaBH4 amount 12.32 mM, reaction time 3.19 min, Co 33.46 mg/L, and catalyst dosage 1.24 mg/mL for RhB dye; NaBH4 amount 16.76 mM, reaction time 3.06 min, Co 15.10 mg/L, and catalyst dosage 1.46 mg/mL for SO dye. The optimum conditions of process parameters by ANN with gray wolf optimizer (GWO) were in good agreement with the points determined the RSM-CCD. These results demonstrate that RSM and ANN approaches can be applied practically and efficiently to maximize the catalytic activity of RhB and SO by Ag/CoFe-LDH/rGO in the existence of NaBH4. On the other hand, from the kinetic and thermodynamic studies, the positive activation enthalpy, ΔH# and the negative activation entropy, ΔS# values for each dye demonstrated that the catalytic performance was endothermic and less random at the solid/liquid interface.

An enzyme-free sensor based on La-doped CoFe-layered double hydroxide decorated on reduced graphene oxide for sensitive electrochemical detection of urea

The successful synthesis of La-doped CoFe LDH@rGO nanocomposite is reported combining the advantages of LDH and rGO and shows promising performances in electrochemical sensors. The structure of the obtained nanocomposite was investigated using Fourier transform infrared spectroscopy (FTIR), X-ray diffraction pattern (XRD), and field emission scanning electron microscope images (FE-SEM). Then, it was directly utilized to construct a carbon paste electrode (CPE) for urea detection. The electrochemical performance of the sensor was evaluated by various electrochemical methods. The La-CoFe LDH@rGO electrode exhibited excellent electrocatalytic properties, including a wide linear working range of 0.001-23.5 mM, very high sensitivity of 1.07 ± 0.023 µA µM-1 cm-2, a low detection limit of 0.33 ± 0.11 µM, and rapid response time of 5 s towards urea detection at the working potential of 0.4 V. Furthermore, the sensor displayed a high selectivity in different matrices, appropriate reproducibility, and long shelf life without activity loss during 3 months of storage under ambient conditions. Further tests were performed on serum and milk samples to confirm the capability of the proposed sensor for practical applications, demonstrating a reasonable recovery of 94.8 to 102% with an RSD value below 3%. Consequently, the synergistic effect of each component led to the good electrocatalytic activity of the modified electrode towards urea.

A robust and facile label-free method for highly sensitive colorimetric detection of ascorbic acid in fresh fruits based on peroxidase-like activity of modified FeCo-LDH@WO3 nanocomposite

Many compounds such as amino acids and oligonucleotides have been shown to effectively change peroxidase-like activity of nanoparticles. While a few studies have focused on mimicking the active site of natural enzymes on nanozymes and thus increasing their substrate affinity. Therefore, in this work, the surface of FeCo@WO3 nanocomposite was modified using guanosine triphosphate (GTP) to mimic the histidine of peroxidase enzyme's active site and its modification was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Fourier-transform infrared spectroscopy (FT-IR). Then, the peroxidase-mimicking activity of the modified nanocomposite was tested using a colorimetric method, based on the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) in the presence of hydrogen peroxide (H2O2). It was found that GTP improves the activity of FeCo@WO3 as a natural peroxidase active site's distal histidine residue. Ascorbic acid (AA) is a powerful antioxidant that induces the reduction of blue color (oxidized TMB) ox-TMB to colorless TMB. The colorimetric method was applied for the sensitive detection of AA in common fruits. The linear range of AA was 10-100 μM with a limit of detection (LOD) of 0.27 μM, which provides a rapid and sensitive method for testing AA in the field of food analysis.

MXenes - Versatile 2D materials for identification of biomarkers and contaminants in large scale environments - A review

Recent years have seen a lot of interest in transition metal carbides/carbonitrides (MXenes), Which is one of newly proliferating two-dimensional (2D) materials.The advantages and applications of synthesizing MXenes-based biosensing systems are interesting. There is an urgent requirement for synthesis of MXenes. Through foliation, physical adsorption, and interface modification,it has been proposed that many biological disorders are related to genetic mutation. Majority of mutations were discovered to be nucleotide mismatches. Consequently, accurate -nucleotide mismatched discrimination is crucial for both diagnosing and treating diseases. To differentiate between such a sensitivealterations in the DNA duplex, several detection methods, particularly Electrochemical-luminescence (ECL) ones, have really been investigated.M_n+1X_nT_x is common name for MXenes, a novel family of two-dimensional (2D) transition metal carbides, nitrides, and carbonitrides, where T stands for interface termination units (i.e. = O, OH, and/or F). These electronic characteristics of MXenes may be changed between conductive to semiconducting due to abundant organometallic chemistry.Solid-state ECL sensors predicated on MXene would provide the facile nucleotide detection and convenience for usage with minimal training, mobility and possibly minimal cost.This study emphasizes upcoming requirements and possibilities in this area while describing the accomplishments achieved in the usage and employing of MXenes in the research and development of facile biomarkerdetection and their significance in designing electrochemical sensors. Opportunities are addressed for creating 2D MXene materials sensors and devices with incorporated biomolecule sensing. MXenes Carry out this process sensors, address the advantages of using MXenes and their variants as detecting materials for gathering different types of data, and attempt to clarify the design principles and operation of related MXene-based sensors, such as nucleotide detection, Single nucleotide detectors, Cancer theranostics, Biosensing capabilities, Gliotoxin detection, SARS-COV-2 nucleocapsid detection, electrochemical sensors, visual sensors, and humidity sensors. Finally, we examine the major issues and prospects for MXene-based materials used in various sensing applications.

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.

Silicon dioxide nanoparticles decorated on graphene oxide nanosheets and their application in poly(l-lactic acid) scaffold

INTRODUCTION

The aggregation of graphene oxide (GO) is considered as main challenge, although GO possesses excellent mechanical properties which arouses widespread attention as reinforcement for polymers.

OBJECTIVES

In this study, silicon dioxide (SiO₂) nanoparticles were decorated onto surface of GO nanosheets through in situ growth method for promoting dispersion of GO in poly(l-lactic acid) (PLLA) bone scaffold.

METHODS

Hydroxyl and carboxyl functional groups of GO provided sites for SiO₂ nucleation, and SiO₂ grew with hydrolysis and polycondensation of tetraethyl orthosilicate (TEOS) and finally formed nanoparticles onto surface of GO with covalent bonds. Then, the GO@ SiO₂ nanocomposite was blended with PLLA for the fabrication of bone scaffold by selective laser sintering (SLS).

RESULT

The results indicated that the obtained SiO₂ were distributed relatively uniformly on surface of GO under TEOS concentration of 0.10 mol/L (GO@SiO₂-10), and the covering of SiO₂ on GO could increase interlayer distance of GO nanosheets from 0.799 nm to 0.894 nm, thus reducing van der Waals forces between GO nanosheets and facilitating the dispersion. Tensile and compressive strength of scaffold containing GO@SiO₂ hybrids were significantly enhanced, especially for the scaffold containing GO@SiO₂-10 hybrids with enhancement of 30.95 % in tensile strength and 66.33 % in compressive strength compared with the scaffold containing GO. Additionally, cell adhesion and fluorescence experiments demonstrated excellent cytocompatibility of the scaffold.

CONCLUSIONS

The good dispersion of GO@SiO₂ enhances the mechanical properties and cytocompatibility of scaffold, making it a potential candidate for bone tissue engineering applications.

Hierarchical Nanocages Assembled by NiCo-Layered Double Hydroxide Nanosheets for a High-Performance Hybrid Supercapacitor

Layered double hydroxides (LDHs) have attracted broad attention as cathode materials for hybrid supercapacitors (HSCs) because of their ultrahigh theoretical specific capacitance, high compositional flexibility, and adjustable interlayer spacing. However, as reported, specific capacitance of LDHs is still far below the theoretical value, inspiring countless efforts to these ongoing challenges. Herein, a hierarchical nanocage structure assembled by NiCo-LDH nanosheet arrays was rationally designed and fabricated via a facile solvothermal method assisted by the ZIF-67 template. The transformation from the ZIF-67 template to this hollow structure is achieved by a synergistic effect involving the Kirkendall effect and the Ostwald ripening process. The enlarged specific surface area co-occurred with broadened interlayer spacing of LDH nanosheets by finely increasing the Ni concentration, leading to synchronous improvement of electron/ion transfer kinetics. The optimized NiCo-LDH-210 electrode displays a maximum specific capacitance of 2203.6 F g^-1 at 2 A g^-1, excellent rate capability, and satisfactory cycling stability because of the highly exposed active sites and shortened ion transport paths provided by vertically aligned LDH nanosheets together with the cavity. Furthermore, the assembled HSC device achieves a superior energy density of 57.3 Wh kg^-1 with prominent cycling stability. Impressively, the design concept of complex construction derived from metal-organic frameworks (MOF) derivatives shows tremendous potential for use in energy storage systems.

Controllable Synthesis of Cobalt-Containing Nanosheet Array-Like Ternary CuCoAl-LDH/rGO Hybrids To Boost the Catalytic Efficiency for 4-Nitrophenol Reduction

A series of Co-doped ternary Cu_xCo_3-xAl-layered double hydroxide (LDH)/rGO nanosheet array hybrids (x = 0.5, 1.0, 1.5, and 2.0) were successfully prepared using the preconditioned pH value aqueous-phase coprecipitation strategy. The Cu_xCo_3-xAl-LDH/rGO hybrids are featured as hexagonal CuCoAl-LDH nanosheets in situ anchoring onto both sides of the rGO surface in an ab-plane vertically interlaced growth pattern. The Cu_xCo_3-xAl-LDH/rGO hybrids show excellent activity for the complete conversion of 4-nitrophenol to 4-aminophenol, especially Cu_1.5Co_1.5Al-LDH/rGO with the highest k_app value of 49.2 × 10^-3 s^-1 and TOF of 232.8 h^-1, clearly higher than most copper-containing samples in the literature and even some precious ones. Thermodynamic analysis was carried out, and the values of Ea, ΔH^#, ΔS^#, and ΔG^# were estimated. The best activity of Cu_1.5Co_1.5Al-LDH/rGO can be mainly ascribed to the in situ-formed ultrafine Cu₂O NPs (∼4.3 nm) along with a small amount of Cu⁰ species, the electron transfer effect induced by atomically dispersed Co²⁺ species leading to the formation of electron-rich Cu species along with the Co²⁺/Co³⁺ redox couple, the strong Cu₂O-CuCoAl-LDH-rGO synergy upon the nanosheet array morphology with a high surface area and pore volume, and enhanced adsorption of reactants upon π-π stacking via an rGO layer. Meanwhile, the Cu_1.5Co_1.5Al-LDH/rGO exhibits an excellent universality and good cycling stability for 10 continuous runs. The Cu_1.5Co_1.5Al-LDH/rGO also shows superior efficiency in the catalytic reduction of 4-NP solution with a high concentration (20 mM) and displays excellent reduction performance in the fixed-bed test, implying the potential applications of the current Co-doped hierarchical ternary Cu-based LDH/rGO hybrids in the continuous treatment of practical wastewater.

Graphene Quantum Dots Pinned on Nanosheets-Assembled NiCo-LDH Hollow Micro-Tunnels: Toward High-Performance Pouch-Type Supercapacitor via the Regulated Electron Localization

A combined delicate micro-/nano-architecture and corresponding surface modification at the nanometer level can co-tailor the physicochemical properties to realize an advanced supercapacitor electrode material. Herein, nanosheets-assembled nickel-cobalt-layered double hydroxide (NiCo-LDH) hollow micro-tunnels strongly coupled with higher-Fermi-level graphene quantum dots (GQDs) are reported. The unique hollow structure endows the electrolyte accessible to more electroactive sites, while 2D nanosheets have excellent surface chemistry, which favors rapid ion/electron transfer, synergistically resulting in more super-capacitive activities. The experimental and density functional theory calculations recognize that such a precise decoration generally tunes the charge density distribution at the near-surface due to the Fermi-level difference of two components, thus regulating the electron localization, while decorating with conductive GQDs co-improves the charge mobility, affording superior capacitive response and electrode integrity. The as-acquired GQDs@LDH-2 electrode yields excellent capacitance reaching ≈1628 F g^-1 at 1 A g^-1 and durable cycling longevity (86.2% capacitive retention after 8000 cycles). When coupled with reduced graphene oxide-based negative electrode, the hybrid device unveils an impressive energy/power density (46 Wh kg^-1 / 7440 W kg^-1 ); moreover, a flexible pouch-type supercapacitor can be constructed based on this hybrid system, which holds high mechanical properties and stable energy and power output at various situations, showcasing superb application prospects.

Fabrication of MgAl LDH@graphene oxide nanohybrids and their effect on the thermal stability and crystallization behavior of polypropylene

The co-precipitation method is used to fabricate layered double hydroxide (LDH) nanohybrids with surface engineering of graphene oxide (GO) by radially grafting borate-LDH (BLDH) to BLDH@GO nanosheets, aiming at improving the surface characteristics and compatibility of LDH with the polymer matrix. The results prove the successful fabrication of BLDH@GO and LDH@GO nanosheets. The nanosheets are mixed into polypropylene (PP) by melt blending to study the structure and properties of the composites. The PP composites with BLDH@GO and BLDH have both exfoliation structures and aggregation structures, and the two nanosheets show enhanced interfacial interactions with the PP matrix compared with LDH and LDH@GO. The initial decomposition temperatures of the PP composites are lower than those of the neat PP, but the thermal degradation temperatures of the PP composites are higher. Compared with the other samples, BLDH@GO provides a higher nucleation density, reflected in a smaller spherulite size and a higher crystallization temperature confirmed by the differential scanning calorimetry (DSC) results. BLDH@GO shifts the crystallization temperature of PP to higher values (compared to the neat PP) due to the nucleation effect, which is in line with the increase in the nucleation density detected by polarized optical microscopy (POM).

Oriented Nanosheet-Assembled CoNi-LDH Cages with Efficient Ion Diffusion for Quasi-Solid-State Hybrid Supercapacitors

Fast-charged energy-storage technologies have become important nowadays as they are required by many applications, including automobiles. This inspires the exploitation of hybrid supercapacitors (HSCs) with the advantages of fast charge offered by the capacitor characters and high energy density from the property of battery technology. The challenges lay in the construction of advanced materials with high pseudocapacitive activity. Herein, a metal-organic framework derivative is utilized to address the problems. Specifically, polyhedral CoNi layered double hydroxide (CoNi-LDH_x) cages assembled in the form of nanosheet arrays are prepared from ZIF-67 using a facile ion-exchange approach. Based on the control over the mass ratio of ZIF-67 to Ni salt, the optimal CoNi-LDH₂ is attained. It exhibits ultrahigh capacities ranging from 1031.4 to 667.3 C g^-1 under 1-25 A g^-1, thanks to rich Faradaic active spots and the accelerated kinetics provided by the synergy between nanosheet arrays and the hollow structure. The CoNi-LDH₂-based HSC with the gel electrolyte shares remarkable energy output of 49 Wh kg^-1 and approving cyclability with almost no capacity decay after 12 000 cycles. This is an advancement vs many related studies and can arouse tremendous interests of researchers in solving the main problems of energy storage.

Selective dispersion of neutral nanoplates and the interfacial structure of copolymers based on coarse-grained molecular dynamics simulations

The selective dispersion of neutral nanoplates (NNP) and the control of the interfacial structure of copolymers are challenging. In this work, we employ coarse-grained molecular dynamics (CGMD) to investigate the dispersion of NNP and the interfacial structure. The introduction of NNP significantly changes the interfacial structure and formation mechanism of diblock copolymers (DBCP), which is related to the matrix phase, distribution, composition, and length of two different chain segments (A and B) in A_mB_n-DBCP. The phase-weak groups that have a poor interaction with NNP will stack easily, whereas the stacking degree for the phase-rich groups that have a strong interaction with NNP decreases due to the addition of NNP. The interaction between two phases will be enhanced, which is favorable for the formation of a random network structure. Due to the strong interaction of the phase-rich groups with NNP, the NNP change the accumulation types of phase-weak groups and enhances the combination of two chain segments in favor of the formation of a cylindrical micelle-like structure. The transmission electron microscopy (TEM) images show that layered double hydroxide (LDH) orientationally distributes in the acrylic acid chain segments in ethylene acrylic acid (EAA) random copolymers, which is in agreement with the theoretical simulation results. This proves that the selective dispersion of LDH in copolymers affects their interfacial structure.

Heterogeneous assembly of Ni-Co layered double hydroxide/sulfonated graphene nanosheet composites as battery-type materials for hybrid supercapacitors

Graphene-based hybrid composites as positive electrodes have aroused great interest in the field of hybrid supercapacitors. However, the charge storage capability of hybrid composites suffers from the scarce interaction between their end members to some extent. Herein, a hybrid composite with electrostatic interaction was obtained by employing a heterogeneous assembly strategy of Ni-Co layered double hydroxide (LDH) and sulfonated graphene nanosheets (SGN). Depending on the substitution of the negatively charged SGN for the interlayer nitrate anions compensating for the positively charged LDH host slabs, the abundance of Ni³⁺ on the surface of the hybrid composite could be increased to intensify the electrostatic interaction within hybrid composites. As expected, the effective coupling of LDH with SGN ensured the uniform incorporation of heterogeneous components. The unique structure of the hybrid composite accelerated electron transfer and ion diffusion processes during electrochemical reactions, which is beneficial to improve the electrochemical performance of battery-type electrodes. Further evaluation showed that the specific capacity of the LDH/SGN hybrid composite is 1177 C g^-1 (2354 F g^-1) at 1 A g^-1. Additionally, the LDH/SGN//AC hybrid supercapacitor achieved an energy density of 43 W h kg^-1 at 800 W kg^-1 and still retained 94% of its initial specific capacitance over 10 000 cycles. The boosting effect of the electrostatic interaction within the hybrid composite on electrochemical properties offers a novel pathway for the development of supercapacitors.

Oriented Assembly of Anisotropic Nanosheets into Ultrathin Flowerlike Superstructures for Energy Storage

The hierarchical ultrathin nanostructures are excellent electrode materials for supercapacitors because of their large surface area and their ability to promote ion and electron transport. Herein, we investigated nine l-amino acids (LAs) as inductive agents to synthesize a series of CoNi-OH/LAs materials for energy storage. With the different amino acids, the assembled CoNi-OH/LAs form a lamellar, flower-shaped, and bulk structure. Among all materials, the ultrathin flowerlike CoNi₂-OH/l-asparagine (CoNi₂-OH/l-Asn) exhibits an excellent specific capacity of 405.4 mAh g^-1 (2608 F g^-1) and a 100% retention rate after 3000 cycles. We also assembled asymmetrical supercapacitor CoNi₂-OH/l-Asn//N-rGO devices, which demonstrated an energy density of 64.9 Wh kg^-1 at 799.9 W kg^-1 and superlong cycling stability (82.4% at 10 A g^-1) over 5000 cycles.

Rationally engineered 3D-dendritic cell-like morphologies of LDH nanostructures using graphene-based core-shell structures

Functionalization of graphene-based materials using chemical moieties not only modify the electronic structure of the underlying graphene but also enable in limited enhancement of targeted properties. Surface modification of graphene-based materials using other nanostructures enhances the effective properties by minimally modifying the properties of pristine graphene backbone. In this pursuit, we have synthesized bio-inspired hierarchical nanostructures based on Ni-Co layered double hydroxide on reduced graphene oxide core-shells using template based wet chemical approach. The material synthesized have been characterized structurally and electrochemically. The fabricated dendritic morphology of the composite delivers a high specific capacity of 1056 Cg^-1. A cost effective solid state hybrid supercapacitor device was also fabricated using the synthesized electrode material which shows excellent performance with high energy density and fast charging capability.