LDH Hybrid Research Articles

High-Performance Catalytic Reduction of 4-Nitrophenol to 4-Aminophenol over Pt Nanoparticles Supported on Co-Al LDH Nanosheets

In this study, a Pt@Co-Al LDH hybrid structure was fabricated by assembling the metal precursor PtCl62− with the exfoliated LDH nanosheets followed by in situ reduction by NaBH4. The morphology, composition and microstructure of the hybrid were characterized by FESEM, HRTEM, XRD, XPS and BET techniques. Pt nanoparticles (NPs) with an average particle size of 3.1 nm were successfully and uniformly loaded on the surface of LDH nanosheets. The catalytic activity of the Pt@Co-Al LDH hybrid was tested for the reduction of 4-nitrophenol, which is one of the most frequent pollutants in wastewater effluent from the pharmaceutical and textile industries. The hybrid displays superior catalytic activity and stability in the reduction of 4-NP under environmental conditions with NaBH4 as a reducing agent. The hybrid can be recovered in a simple way and still shows high catalytic activity after five reuses.

CaAl–NO2 LDH hybrid self-healing microcapsules with chloride triggering: Towards synergistic corrosion resistance

The synergistic corrosion resistance microcapsules (SCRMs) were synthesized by utilizing CaAl–NO2 LDH (NO2-LDH) as chloride trigger and high-performance corrosion inhibitor to hybridize self-healing microcapsules. The morphology, chemical structure and self-healing performance of the microcapsules were characterized. The chloride triggering and corrosion resistance property of the SCRMs were evaluated. The interaction of hybrid wall, NO2-LDH and chloride ion was calculated by first-principles. The findings revealed that the microcapsules show regular spherical with obvious core-wall structure. EDS and chemical structure measurements confirmed that NO2-LDH was successfully embedded within the microcapsule wall. The SCRMs showed excellent corrosion resistance property in simulated chloride-contaminated concrete pore solution (SCPS), and the highest inhibition efficiency was 97.85%. The microcapsule wall was hybridized by NO2-LDH species through chemical pathways. The first-principles calculation results confirmed that Ca and Al species are the main factors for chloride ion immobilization of hybrid wall. The ion exchange process of microcapsules destroys the molecular force of NO2-LDH@ethyl cellulose hybrid wall and improves the mechanical triggering efficiency of microcapsules in cement-based composites.

Construction of 3D Hierarchical Co3O4@CoFe-LDH Heterostructures with Effective Interfacial Charge Redistribution for Rechargeable Liquid/Solid Zn-Air Batteries.

Constructing three-dimensional (3D) hierarchical heterostructures is an appealing but challenging strategy to improve the performance of catalysts for electrical energy devices. Here, an efficient and robust flexible self-supporting catalyst, interface coupling of ultrathin CoFe-LDH nanosheets and Co3O4 nanowire arrays on the carbon cloth (CC/Co3O4@CoFe-LDH), was proposed for boosting oxygen evolution reaction (OER) in rechargeable liquid/solid Zn-air batteries (ZABs). The strong interfacial interaction between the CoFe-LDH and Co3O4 heterostructures stimulated the charge redistribution in their coupling regions, which improved the electron conductivity and optimized the adsorption free energy of OER intermediates, ultimately boosting the intrinsic OER performance. Besides, the 3D hierarchical nanoarray structure facilitated the exposure of catalytically active centers and rapid electron/mass transfer during the OER process. As such, the CC/Co3O4@CoFe-LDH catalyst achieved excellent OER catalytic activity in alkaline medium, with a small overpotential of 237 mV at 10 mA cm-2, a low Tafel slope of 35.43 mV dec-1, and long-term durability of up to 48 h, significantly outperforming the commercial RuO2 catalyst. More impressively, the liquid and flexible solid-state ZABs assembled by the CC/Co3O4@CoFe-LDH hybrid catalyst as the OER catalyst presented a stable open circuit voltage, large power density, superb cycling life, and satisfactory flexibility, indicating great potential applications in energy technology. This work provides a good guidance for the development of advanced electrocatalysts with heterostructures and an in-depth understanding of electronic modulation at the heterogeneous interface.

Self-assembled ZnO microspheres coated with carbon dot-doped CoNi LDH wrinkled films as electrochemical sensors for highly sensitive detection of hydrazine.

In this study, a 3D surface-folded composite was prepared in situ as a hydrazine sensor by loading a hybrid film of CoNi-layered double hydroxides (LDHs) with nitrogen-doped carbon dots on self-assembled ZnO microspheres. The nanocomposite was characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR), and the electrochemical behavior of the sensors was investigated by cyclic voltammetry (CV), amperometry and electrochemical impedance spectroscopy (EIS). The results showed that ZnO microspheres with nitrogen-doped carbon dots strongly coupled with LDHs can significantly reduce the charge transfer resistance, accelerate the oxidation kinetics of hydrazine, and effectively increase the electrochemically active surface area (ECSA). The sensor achieved ultra-sensitive (13 040 μA mM-1 cm-2 (S/N = 3)) detection of hydrazine in the concentration range of 0.7 μM to 4 mM, exhibited excellent selectivity, reproducibility and high stability, and was successfully applied to the determination of hydrazine in actual environmental water samples and landfill leachate samples.

Ca-Al LDH hybrid self-healing microcapsules for corrosion protection

Ca-Al LDH hybrid self-healing microcapsules were fabricated with tung oil as core and ethyl cellulose (EC) as wall via solvent evaporation method. The self-healing and chlorine adsorption properties of hybrid microcapsules in cement-based materials were investigated. The corrosion resistance performance of microcapsules in simulated chlorine-contaminated concrete pore solution (SCPS) was characterized by electrochemical probe technique. First-principles based on density functional theory was applied to study the hybrid mechanism of Ca-Al LDH on self-healing microcapsules. The results demonstrate that the nano-layered Ca-Al LDH within the hybrid wall provided additional nucleation sites for cement hydration. The chlorine adsorption capacity of cement paste doped with 3 wt% and 6 wt% microcapsules was 14.7% and 26.7% higher than that of pure cement paste in SCPS, respectively. Hybrid microcapsules improved the anticorrosion of steel bars in SCPS by coupling effect of self-healing and chlorine resistance. The formation of Ca-Al LDH@EC hybrid materials is an exothermic process with perfect binding stability. The chlorine adsorption property of microcapsules was improved by the interface charge redistribution of Ca-Al LDH@EC hybrid materials.

Construction of new recoverable Ag-Fe3O4@Ca–Al LDH nanohybrids for visible light degradation of piroxicam

Herein, for the first time, a hybrid material is used as an efficient photocatalyst to degrade piroxicam under visible light. By the use of Ag-Fe3O4@Ca–Al LDH hybrid (AFL hybrid), piroxicam (PX) solution was 95% degraded to CO2 and H2O in 150 min. The kinetic study showed that the degradation reaction of PX over photocatalyst adjusts well to a pseudo-first-order reaction kinetic. Optimizing the effective factors on reaction rates such as %Ag, PX solution concentrations, Na2SO4 amount, and catalyst dosage increased the rate constant to 0.03 min−1. The optical and electrical characteristics of AFL hybrid were studied through solid-state UV–vis diffuse absorption, photoluminescence emission (PL) spectroscopy, and photocurrent response, which predicted the high catalytic performance of the hybrid. The active radical capturing tests exhibited that O2– playing a major role in PX photodegradation by the assistant of Na2SO4. Also, the hybrid recovered easily by an external magnetic field.

Zn/Al Layered double hydroxides nanostructure as effective controlled release vehicle of nicotinic acid for topical applications

The delivery of active ingredients through the human skin is an arduous exercise because of its structural intricacy and outstanding barrier characteristics. Nanotechnological developments have produced advanced delivery systems based on nanomaterials to reinforce the skin's ability to absorb hydrophobic, hydrophilic active ingredients and macromolecules. In this study, inorganic crystalline layered double hydroxides nanostructures (LDH) were used as an advanced release system for nicotinic acid, with skin lightening properties. Nicotinic acid was incorporated into the interlayer space of Zn/Al LDH, by co-precipitation method to develop LDH hybrids. The LDH hybrids were characterized using FTIR, XRD, TGA, and SEM. Intercalation of nicotinic acid in the interlayer space of Zn/Al LDH was ascertained by the shifting of the basal spacing d (003) reflection in the XRD pattern, to lower angles (2θ). FTIR spectra of the Zn/Al LDH hybrids displayed the absorption frequencies of nicotinic acid that indicated the presence of nicotinic acid within the LDH matrix. TGA showed that nicotinic acid intercalated in the interlayer of LDH exhibited better thermal stability than the free form of nicotinic acid. In vitro release experiments revealed controlled and pH-responsive release of nicotinic acid from Zn/Al LDH. Transdermal permeation studies employing Franz- diffusion cells demonstrated that the formulation containing nicotinic acid-intercalated Zn/Al LDH considerably enhanced the penetration of nicotinic acid compared to the formulation containing the free form of nicotinic acid. Thus, Zn/Al LDH has great potential for use as a sustained and controlled release reservoir of nicotinic acid in skin care and other topical applications.

Statement of Retraction

This article refers to:RETRACTED ARTICLE: LDH hybrid thermosensitive hydrogel for intravaginal delivery of anti-HIV drugs

(Invited) Nanoarray Cathode Design for Durable Zn Batteries

Rechargeable aqueous zinc battery, as a novel promising candidate for grid-scale energy storage, has drawn tremendous attention recently. Our group has been actively working in design nanostructured electrode materials for metal-ion batteries (Na, K, Zn) and electrocatalysts for metal-air batteries. In this talk, I will present our latest results on cathode materials for both Zn-ion battery and Zn-air battery. Specifically, we developed layered ZnOV nanosheets that are directly grown on a 3D graphite current collector. Meanwhile, the anode is also 3D Zn nanosheet array obtained by electro-deposition. As for the Zn-air battery cathode, we employed 3D conductive MOF and Ni-based LDH hybrid materials on conductive carbon support as the electrode both for aqueous alkaline and all-solid-state Zn-battery. The whole material system has a high conductivity, sufficient active sites and low transition energy that render highly reversible redox reaction and inhibition of dendrite formation, as well as extremely soft feature so that it can be appropriate for the application of flexible devices. The all-solid-state Zn-based batteries using CMNC@CC and Zn@CC as the electrodes displays outstanding performance when compared with most of the aqueous oxy/hydroxy or pristine MOFs based energy storage devices.We appreciate the financial support from Agency for Science, Technology, and Research (A*STAR) by AME Individual Research Grant (A1983c0026) and from Singapore MOE AcRF Tier 2 Grant (MOE2017-T2-1-073).

“Ship in a Bottle” design of ZIF-9@CoAl LDH hybrid compound as a high performance asymmetric supercapacitor

The ZIF-9@CoAl LDH compound was successfully synthesized by a “Ship in a Bottle” method. The conductivity of CoAl LDHs was improved by the introduction of 2D ZIF-9 micro-slices.

3D Hierarchical NiCo Layered Double Hydroxide Nanosheet Arrays Decorated with Noble Metal Nanoparticles for Enhanced Urea Electrocatalysis

AbstractThe electrocatalysis of urea represents an important potential as an efficient technology for sustainable energy development. This anodic reaction generates hydrogen or electrical power through direct electrooxidation of urea molecules, but is greatly inhibited by its slow kinetics. Therefore, tailoring highly efficient, earth‐abundant, and durable electrocatalysts for urea oxidation reaction (UOR) is a fundamental for the enhancement of green energy conversion technologies. Herein, we report a scalable synthetic strategy to construct three‐dimensional (3D) nickel‐cobalt layered double hydroxide nanosheet arrays (NiCo−LDH NSAs) with silver (Ag0) or gold (Au0) and palladium (Pd0) intercalants as high performance catalysts for UOR. Experimental results suggest that the interlayer spacing of multi‐anions LDH NSAs can effectively afford synergetic effects of increased electrochemical surface area, better exposure of catalytically active sites, and favorable adsorption energy of urea molecules. As expected, the deposition of noble metal nanoparticles (NPs) could successfully modulate the electronic structure, delivering a rise to significantly improved UOR activity. Specifically, the Au/NiCo−LDH hybrid exhibits a superior electro‐catalytic performance toward urea electrooxidation with a highest current. These findings offer an effective pathway to prepare potential earth‐abundant electrocatalysts for direct urea fuel cells (DUFCs).

Constructing Cu2O@Ni-Al LDH core-shell structure for high performance supercapacitor electrode material

To accommodate large volume change of Cu2O for improving its supercapacitor performances, Cu2O@Ni-Al LDH core-shell structure was designed and prepared through nickel-aluminum double hydroxide grown on cubic Cu2O via a simple solvent process. The Cu2O core was wrapped by Ni-Al LDH shell, which provides a high specific area for electrochemical reaction. The results show that the specific capacitance and cycle stability of Cu2O@Ni-Al LDH are superior to those of Cu2O cubic particles. The specific capacitance of Cu2O@Ni-Al LDH hybrid electrode was up to 389 F g−1 at 1 A g−1. Furthermore, a reversible capacitance of 457 F g−1 was obtained after 12,000 cycles at a much higher current density of 10 A g−1. The enhanced performances were ascribed to the unique core-shell structure and the synergistic effects of Cu2O and Ni-Al LDH, which alleviated volume expansion and provided abundant electrochemical active sites.

Synthesis of a novel dual layered double hydroxide hybrid nanomaterial and its application in epoxy nanocomposites

Ease of undesirable agglomeration and low efficiency are two problems that highly restrict the application of MgAl-layered double hydroxides (MgAl-LDH) as suitable flame retardants for epoxy resins. Herein, a new strategy that chose MOFs as the precursor to connect two different LDHs into a hybrid nanomaterial is reported. Nanosheets of NiCo-layered double hydroxides (NiCo-LDH) with multidimensional nanostructures were uniformly anchored on the surface of MgAl-LDH slabs. This led to a better dispersion and stronger interaction within the epoxy matrix, resulting in enhanced strength of the char layers, and also enabled synergistic flame retardant effect to the epoxy nanocomposite, when compared to the case of the unmodified epoxy. The sample passed V-0 rating in UL-94 test and its peak of heat release rate was reduced by 66.7% in cone calorimeter test with the addition of only 2.5 wt% of as-prepared flame retardant. Besides, due to the unique structure of the nanofiller, the mechanical properties of the nanocomposite were only slightly impacted. This is the first report on the synthesis of a dual LDH hybrid nanomaterial, which moreover, improved the flame retardancy of epoxy nanocomposite even when added in relatively low amounts.

Hierarchical CoGa layered double hydroxides grown on nickel foam as high energy density hybrid supercapacitor

Hierarchical cobalt gallium layered double hydroxide microns flower and sheet was in situ gown on Ni foam via a facile and one-step hydrothermal method. The capacity of preparing Co-Ga-layered double hydroxides (Co-Ga-LDH), as supercapacitor electrode, was evaluated via three electrode system. And different feeding ration of cobalt and gallium was attempted to optimize the better capacity performance. The as-obtained Co-Ga (1:1)-LDH hybrid shows the enhanced the specific capacity 1431.5 C/g at current density of 1 A/g and approximately 74% initial capacity at current density of 20 A/g. A hybrid supercapacitor was assembled consisting of Co-Ga-LDH and reduced graphene (rGO), which show the high energy density 68.07 Wh/kg at power density 825 W/kg. To our best knowledge, it is the first time that cobalt gallium layered double hydroxides was prepared and studied in energy storage field.

Structural characterization, thermal and mechanical properties of polyurethane–MgAl–layered double hydroxide nanocomposites prepared via physical dispersion

Polymer–clay nanocomposites were prepared via physical dispersion of dodecyl sulfate (DS)-intercalated MgAl–layered double hydroxides (MgAl–LDHs) in polyurethane (PU). The structure, mechanical behavior, thermal stability as well as ultraviolet transmittance of the PU–LDH hybrids were studied systematically. The obtained hybrid materials were characterized with XRD, FTIR, TGA, DSC, UV–Vis spectroscopy, SEM and mechanical testing. The optimal content of MgAl/DS–LDHs in PU was determined. The testing of mechanical properties of PU–MgAl/DS–LDHs nanocomposites showed significant improvements in tensile strength and elongation at break, especially for the DS/LDHs content of 5 wt%. The observed improvement in mechanical properties is attributed to the relatively better reinforcing effect of partially exfoliated DS–LDH layers in PU matrix. DTA and DSC analysis confirmed the increased thermal stability of PU–MgAl/DS–LDH materials. The obtained results suggested potential application of physical dispersion of inorganic additives in the polymer matrix as a promising method for obtaining of PU nanocomposites.

RETRACTED ARTICLE: LDH hybrid thermosensitive hydrogel for intravaginal delivery of anti-HIV drugs

We, the Editors and Publisher of the journal Artificial Cells, Nanomedicine, and Biotechnology, have retracted the following article: Wenxue Tian, Shangcong Han, Xia Huang, Mei Han, Jie Cao, Yan Liang & Yong Sun (2019) LDH hybrid thermosensitive hydrogel for intravaginal delivery of anti-HIV drugs. Artificial Cells, Nanomedicine, and Biotechnology, 47:1, 1234–1240, DOI: 10.1080/21691401.2019.1596935 Since publication, concerns were raised about Figure 3. When approached for an explanation, the authors have been unable to provide a satisfactory response. We are therefore retracting this article and the corresponding author listed in this publication has been informed. We have been informed in our decision-making by our policy on publishing ethics and integrity and the COPE guidelines on retractions. The retracted article will remain online to maintain the scholarly record, but it will be digitally watermarked on each page as ‘Retracted’.

A new valorization route for Olive Mill wastewater: Improvement of durability of PP and PBS composites through multifunctional hybrid systems

Olive Mill wastewater (OMW) is a food waste stream resulting from the production of virgin olive oil, rich in valuable natural biocompounds, such as vanillic acid, ferulic acid, protocatechuic acid, etc. In order to decrease its environmental impact and to exploit the antioxidant properties of its phenol-type molecules, OMW was intercalated into ZnAl-LDH, as well as some biomolecules composing OMW, for a general concept purpose. Such organo-modified LDHs were then employed for the preparation of poly(butylene succinate) (PBS) and polypropylene (PP) composites through melt blending, to obtain materials with improved antioxidant properties and, subsequently, a better durability. A full characterization of LDHs in terms of thermal stability (TGA), morphology (XRD) and chemical modification (FT-IR) has been carried out. The composites were exposed to UV irradiation through accelerated photo-ageing and the molecular modifications were scrutinized by IR spectroscopy, revealing a strong protective role of LDH hybrid filler against oxidative process.

Outstanding chain-extension effect and high UV resistance of polybutylene succinate containing amino-acid-modified layered double hydroxides.

Polybutylene succinate (PBS) nanocomposite materials were prepared using a melt compounding process. The Mg2Al-based PBS nanocomposites, dispersed with inorganic–organic hybrid materials (layered double hydroxides, LDHs), were functionalized with the amino acids L-histidine (HIS) and L-phenylalanine (PHE). The rheological and anti-ultraviolet (anti-UV) properties were investigated and compared to filler-free PBS as well as LDH Mg2Al/nitrate as references. Both organo-modified LDHs exhibited a remarkable chain-extension effect for PBS with an outstanding increase in the zero-shear viscosity η0 for PBS–Mg2Al/PHE (two order of magnitude increase as compared to filler-free PBS). These results were compared to data found in the literature. Moreover, HIS and PHE anions embedded into the LDH structure can successfully prevent the chain scission reactions that usually occur during photo-ageing of PBS under UV radiation exposure. This highlights the outstanding performance of the LDH hybrid materials, and in particular, their application as a polymer chain extender and UV stabilizer for PBS, which can likely be extended to other biodegradable polymers.

Deciphering Z-scheme Charge Transfer Dynamics in Heterostructure NiFe-LDH/N-rGO/g-C3N4 Nanocomposite for Photocatalytic Pollutant Removal and Water Splitting Reactions

A series of heterostructure NiFe LDH/N-rGO/g-C3N4 nanocomposite were fabricated by combining calcinations-electrostatic self-assembly and hydrothermal steps. In this method, negatively charged N-rGO was electrostaticaly bonded to the self-assembled interface of n-n type g-C3N4/NiFe LDH hybrid. XRD and AFM results revealed successful formation of heterostructure nanocomposite due to the coupling effect of exfoliated NiFe LDH nanosheets with N-rGO and g-C3N4. Among the as synthesized heterostructure, CNNG3LDH performed superior photocatalytic activities towards 95 and 72% mineralization of RhB and phenol. Furthermore, CNNG3LDH could achieve the highest photocatalytic H2 evolution rate of 2508 μmolg−12h−1 and O2 evolution rate of 1280 μmolg−12h−1 under visible light irradiation. The CNNG3LDH possess lowest PL intensity, reduced arc of the Nyquist plot (43.8 Ώ) and highest photocurrent density (−0.97 mA cm−2) which revealed effective charge separation for superior photocatalytic activities. TRPL spectral results reveal the synergistic effect of layered component in CNNG3LDH for achievable higher life time of excitons of ~16.52 ns. In addition, N-rGO mediator based Z-scheme charge transfer mechanisms in CNNG3LDH were verified by the ESR and TA-PL studies. Enriched oxygen vacancy type defects in NiFe LDH and N-rGO mediated Z-scheme charge transfer mechanistic path strongly manifest the superior photocatalytic activities of the heterostructure materials.

Electric and dielectric behavior of copper-chromium layered double hydroxide intercalated with dodecyl sulfate anions using impedance spectroscopy

The Cu2Cr-DS-LDH hybrid was successfully prepared by the anion exchange method at room temperature. The structure, the chemical composition and the physico-chemical properties of the sample were determined using powder X-ray diffraction (PXRD), Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA) and inductively coupled plasma (ICP). In this work, the electrical and dielectric properties investigated are determined using impedance spectroscopy (IS) in a frequency range of 1 Hz to 1 MHz. Indeed, the Nyquist diagram modelized by an electrical equivalent circuit showed three contributions attributed respectively to the polarization of grains, grains boundaries and interface electrode-sample. This modelization allowed us to determine the intrinsic electrical parameters of the hybrid (resistance, pseudo-capacitance and relaxation time). The presence of the non-Debye relaxation phenomena was confirmed by the frequency analysis of impedance. Moreover, the evolution of the alternating current conductivity (σac) studied obeys the double power law of Jonscher. The ionic conduction of this material was generated through a jump movement by translation of the charge carriers. As for the dielectric behavior of the material, the evolution of dielectric constant as a function of frequency shows relatively high values in a frequency range between 10 Hz and 1 KHz. The low values of the loss tangent obtained in this frequency zone can valorize this LDH hybrid.