CoAl Layered Double Hydroxides Research Articles

Chemical and Structural Transformations of M-Al-CO3 Layered Double Hydroxides (M = Mg, Zn, or Co, M/Al = 2) at Elevated Temperatures: Quantitative Descriptions and Effect of Divalent Cations.

Layered double hydroxides (LDHs) exhibit diverse chemical compositions and are being designed for promising applications such as CO2 adsorbents. Although many researchers have analyzed CO2 gas evolution and structural transformation behavior at elevated temperatures, there are still inconsistencies in results on the effect of different metal ions in LDHs. In this study, on the basis of atomic/molecular-level findings from our previous study on multistep structural/chemical transformation of Mg-Al LDHs, we analyzed the quantitative gas evolution behavior and structural transformations of M-Al-CO3 LDHs with different divalent metal ions (M = Mg, Zn, or Co, M/Al = 2) at elevated temperatures. Our quantitative analysis revealed that all three LDH samples undergo the three-step chemical transformations: release of interlayer water, partial dehydroxylation of the hydroxyl layers, and complete dehydroxylation of layers and decomposition of interlayer CO32-. However, the temperature range for each step differs, as do the structural transformations for each sample: the layered structure collapses in the first step for Zn-Al LDH and Co-Al LDH, and the third step for Mg-Al LDH. Our results provide for quantitative and concrete understanding of the effect of divalent metal ions in LDHs on thermal decomposition.

Visible-Light-Driven Photocatalytic H2 Production Using Composites of Co-Al Layered Double Hydroxides and Graphene Derivatives.

The direct conversion of solar energy into chemical energy represents an enormous challenge for current science. One of the commonly proposed photocatalytic systems is composed of a photosensitizer (PS) and a catalyst, together with a sacrificial electron donor (ED) when only the reduction of protons to H2 is addressed. Layered double hydroxides (LDH) have emerged as effective catalysts. Herein, two Co-Al LDH and their composites with graphene oxide (GO) or graphene quantum dots (GQD) have been prepared by coprecipitation and urea hydrolysis, which determined their structure and so their catalytic performance, giving H2 productions between 1409 and 8643 μmol g-1 using a ruthenium complex as PS and triethanolamine as ED at 450 nm. The influence of different factors, including the integration of both components, on their catalytic behavior, has been studied. The proper arrangement between the particles of both components seems to be the determining factor for achieving a synergistic interaction between LDH and GO or GQD. The novel Co-Al LDH composite with intercalated GQD achieved an outstanding catalytic efficiency (8643 μmol H2 g-1) and exhibited excellent reusability after 3 reaction cycles, thus representing an optimal integration between graphene materials and Co-Al LDH for visible light driven H2 photocatalytic production.

Regulation of triazine-COF and CoAl-LDH substrates in composites for high-performance neurofilament-light chains electrochemical immunosensors

Early diagnosis of Alzheimer’s disease (AD) can be achieved through the detection of neurofilament light chain (NfL) biomarker, which can slow down the progress of AD and improve quality of life for patients. In this paper, polyvalent Tb-metal organic frameworks (Tb-MOF) and CoAl-layered double hydroxides (CoAl-LDH) are directly acceded to the synthesis system of triazine-covalent organic frameworks (triazine-COF) using one-pot synthesis to obtain the COF-based composite (COF/MOF-LDH). Similarly, the composite of LDH-based (LDH/MOF-COF) is acquired by integrating Tb-MOF and triazine-COF into the synthesis system of CoAl-LDH via hydrothermal procedure. COF/MOF-LDH and LDH/MOF-COF are used as electrode modification materials to construct label-free electrochemical immunosensors for anchoring and detecting NfL. Under optimal conditions for detecting NfL, both modified sensors exhibit high degree of selectivity, stability and reproducibility. However, the COF/MOF-LDH sensor displays a wider linear concentration range (0.05 pg/mL - 100 ng/mL) with lower limit detection of 0.017 pg/mL (S/N=3), and high sensitivity of 130.8 μA·ng−1·mL·cm−2, attributing to large conjugation system of triazine-COF used for substrate modulation and the immobilisation of the anti-NfL through strong π-π* affect and hydrogen bonding. Likely, the incorporation of polyvalent Tb-MOF and CoAl-LDH in COF/MOF-LDH considerably enhance sensitivity via improving active sites and response signals. Furthermore, the morphology, pore size and specific surface area differences of the composites are a reflection of the results of the substrate material control strategy. Especially, the N2 adsorption/desorption tests indicate the larger mesoporous structure of COF/MOF-LDH which facilitate the electron transfer and anti-NfL immobilization. Taken together, the immunosensor based on COF/MOF-LDH shows excellent detection performance which provides a pathway for early screening of AD.

Ultra-fast degradation of ciprofloxacin by the peroxymonosulfate activation using a Co/Al-LDH decorated magnetic hydrochar: Structural design, catalytic performance and synergistic effects

CoFe2O4/BHC-LDH3 catalyst was constructed by decoration of Co/Al layered double hydroxides (Co/Al-LDH) on bamboo hydrochar (BHC) loaded with magnetic CoFe2O4 to activate peroxymonosulfate (PMS) for ciprofloxacin (CIP) degradation. Taking advantage of structural modulation and synergistic effects between the multi-components, CoFe2O4/BHC-LDH3 demonstrated high efficient PMS activation and ultra-fast CIP removal (91.50 % within 10 min), compared with BHC (6.26 %), CoFe2O4 (26.32 %), and Co/Al-LDH (40.10 %). Both free radical (SO4–) and non-radical (1O2) were crucial during the degradation process, and a substantial decrease in aquatic toxicity of the intermediates was observed. Additionally, the stability of CoFe2O4/BHC-LDH3 in actual water environment was tested using a fixed-bed reactor, illustrating the CoFe2O4/BHC-LDH3 has good stability and anti-interference ability in long-term operation. Possible degradation pathways of CIP in the CoFe2O4/BHC-LDH3 + PMS system were proposed based on liquid chromatography-mass spectrometer analysis and density functional theory calculation. This work provides new strategies for hydrochar-supported catalyst synthesis for organic pollutants decomposition.

Competitive Adsorption of Anionic Dyes from Aqueous Single and Binary Solutions with CoAl Layered Double Hydroxide

Layered double hydroxides (LDH) have previously been extensively studied as high capacity adsorbents for the removal of dyes from water. However, a comprehensive understanding of why one dye is adsorbed more than another still remains unknown. In addition, a very little is known about how adsorption mechanisms scale when more than one dye is present in the solution. The adsorption capacity of cobalt-aluminum (CoAl) LDH was investigated for methyl orange (MO), remazol brilliant blue (RBBR) and allura red (AR), at different dye concentrations. The maximum mass of dye adsorbed was obtained for MO (2.267 mmol/g), followed by RBBR (0.258 mmol/g) and AR (0.195 mmol/g). X-Ray Diffraction and Fourier transform infrared analysis results demonstrated that surface adsorption and electrostatic interactions contributed to the adsorption while intercalation did not. In a binary solution of MO and RBBR, the highest mass of MO adsorbed was reduced to 1.521 mmol/g while the maximum RBBR mass adsorbed increased to 0.268 mmol/g. CoAl LDH had a preferential adsorption for RBBR within concentrations up to 0.026 mmol/L while MO was preferred at higher concentrations. Overall, the findings suggest that the adsorption capacity of an LDH is highly dependent on the number, characteristics and the equilibrium concentrations of dyes present in a solution.

Enhancing Water Oxidation Catalysis by Controlling Metal Cation Distribution in Layered Double Hydroxides

AbstractThe sluggish kinetics of the oxygen evolution reaction (OER), the limiting step of the electrochemical water splitting process, hinders the eventual commercialization of this important renewable energy strategy. Hence, the development of efficient electrocatalysts for this reaction is crucial. Multi‐metal‐based (hydr)oxides are promising OER electrocatalysts because the electronic interactions between multiple constituent metal cations can potentially enhance electrochemical performances. However, complex compositions may not always lead to positive synergistic effects. The appropriate distribution of the cations is also critical. However, the high dispersibility of cations in these hydroxides renders the control of their distribution challenging. Herein, an approach is reported to control the metal cation distribution in layered double hydroxides (LDHs) to improve their OER performances. Restacking of exfoliated NiFe and CoAl LDH nanosheets leads to electrochemical synergistic effects between different nanosheets. As far as it is known, the restacked LDH described herein exhibits the lowest overpotential (224 mV) and Tafel slope (34.26 mV dec−1) among reported powder‐type (hydr)oxide and alloy OER electrocatalysts with more than three different metal cations. Thus, a new design approach is suggested to enhance the electrochemical performances of LDHs.

Integration of CoAl-Layered Double Hydroxides on Commensal Bacteria to Enable Targeted Tumor Inhibition and Immunotherapy.

Combining targeted therapy and immunotherapy brings hope for a complete cancer cure. Due to their selective colonization and immune activation capacity, some bacteria have the potential to realize targeted immunotherapy. Herein, a biohybrid system was designed and synthesized by cladding NO3--intercalated cobalt aluminum layered double hydroxides (LDH) on anaerobic Propionibacterium acnes (PA) (PA@LDH). In this system, the covering of LDH reduces the pathogenicity of PA to normal tissues and alters its surface charge for prolonged in vivo circulation. Once the tumor site is reached, the acid-responsive degradation of LDH enables PA exposure. PA can colonize and convert nitrate ions to nitric oxide (NO) through denitrification. Then, NO reacts with intracellular O2·- to produce toxic reactive nitrogen species ONOO- and induce tumor cell apoptosis. In addition, cobalt ions released from LDH can inhibit the activity of superoxide dismutase (SOD), thus increasing the level of O2·- and further enhancing the antitumor effect. Moreover, PA exposure activates M2-to-M1 macrophage polarization and a range of immune responses, thereby achieving a sustained antitumor activity. In vitro and in vivo results reveal that the biohybrid system eliminates solid tumors and inhibits tumor metastasis effectively. Overall, the biohybrid strategy provides a new avenue for realizing simultaneous immunotherapy and targeted therapy.

Assembly Engineering of Rh Atoms on CoAl-Layered Double Hydroxide Nanosheets for Boosting Alkaline Water Splitting

Layered double hydroxides (LDHs), especially Co-based LDHs, are regarded as a class of promising electrocatalysts toward overall water splitting, due to their good performance in oxygen evolution reaction (OER). However, inferior activity toward hydrogen evolution reaction (HER) hinders their scale-up applications. Here, a one-step hydrothermal strategy is proposed to fabricate 3D self-supported Rh-incorporated CoAl LDH (Rh/CoAl LDH) nanosheet arrays as bifunctional catalysts for overall water splitting. The thickness and lateral size of CoAl LDHs depend strongly on the introduced content of Rh atoms. Importantly, Rh incorporation distorts the local atomic arrangement owing to different atom sizes on the CoAl laminate. The strong interaction between Rh atoms and CoAl LDHs dramatically boosts the HER activity by facilitating HER kinetics and improves the OER performance simultaneously. The Rh/CoAl-300 LDH electrode with optimized composition only requires an overpotential of 71 mV to reach 10 mA/cm2 for HER and 390 mV to achieve 100 mA/cm2 for OER. The alkaline electrolyzer assembled by bifunctional Rh/CoAl-300 LDH electrodes only needs a cell voltage of 1.54 V at an overall water splitting of 10 mA/cm2.

Unique three-dimensional heterostructure of MoS2@Co-MOF decorated with Co-Al layered double hydroxide: An effective synergistic alkaline hydrogen evolution electrocatalyst

Development of non-platinum based electrocatalysts with optimized structure is significantly important to realize the blueprint of "hydrogen economy". Herein, a three-dimensional (3D) nanoflower heterostructure composite electrocatalyst for alkaline hydrogen evolution reaction (HER) is constructed (MoS2@Co-MOF@CoAl-LDHs/NF), which is composed of CoAl layered double hydroxides (CoAl-LDHs), in-situ Co-MOF and activated molybdenum disulfide (MoS2). Benefiting from the coordination effect between the components, act outs outstanding electrocatalytic activity for HER process, requiring only an overpotential of 96 mV to achieve 10 mA cm−2, a Tafel plot of 73.53 mV dec−1 in 1.0 M potassium hydroxide (KOH) solution, of which the overpotential and the Tafel plot compare favorably to the majority of reported non-noble-metal HER electrocatalyst material. Given the above description, this work breaks new prospects for the development of high-performance electrocatalysts in media that are not conducive to traditional catalyst design.

CoAl-Layered double hydroxides coupled with BiOCl as Z-Scheme heterostructure for enhanced photocatalytic removal of antibiotic pollutants under visible light

CoAl-Layered double hydroxides coupled with BiOCl as Z-Scheme heterostructure for enhanced photocatalytic removal of antibiotic pollutants under visible light

Synergy of Various Defects in CoAl-Layered Double Hydroxides Photocatalyzed CO2 Reduction: A First-Principles Study

Synergy of Various Defects in CoAl-Layered Double Hydroxides Photocatalyzed CO2 Reduction: A First-Principles Study

Carbonate-free CoAl layered double hydroxides supercapacitors: Controlled precipitation via acid mediated decomplexation

Layered double hydroxides (LDH) belong to a class of highly versatile compounds used in a myriad of applications such as energy storage, catalysis, heavy metal adsorption, etc. Given the high tunability of its structure, ranging from different metal cations to different types of intercalations, LDH can be readily customised to suit the intended applications. One of the inherent problem of LDH lies in their carbonate contamination. The presence of CO32− anions in the intercalation greatly affects the versatility and tunability of LDH. Carbonate intercalation also poses as an interfering species for reactions involving carbonate as intermediates or final products. Unfortunately, existing synthesis procedures of LDH produce either carbonates during the precipitating process or poorly crystallised LDH that absorbs atmospheric carbon dioxide to form carbonates during the drying process; either way results in carbonate contaminated LDH. In this work, we address the problem with the use of ethylenediamine (EDA) complexation followed by controlled decomplexation to prepare CoAl LDH (LDH-EDA). It is shown that the obtained LDH-EDA is carbonate-free and outperforms the CoAl LDH obtained using conventional urea method (LDH-Urea) in terms of crystallinity, surface area and pseudocapacitive properties. Through a detailed experimental and computational study of the preparation mechanism, we propose that ammonium nitrate acts as an acid that mediates the decomplexation of the cobalt (II) trisethylenediamine complex, freeing Co2+ ion in a control manner for the second precipitation process. The multistep process has allowed a controlled rate of formation of LDH, resulting in the highly crystalline LDH-EDA microstructures with pure nitrate intercalation and a flower-like morphology.

Construction of Bi2WO6/CoAl-LDHs S-scheme heterojunction with efficient photo-Fenton-like catalytic performance: Experimental and theoretical studies

The photo-Fenton-like catalytic process has shown great application potential in environmental remediation. Herein, a novel photo-Fenton-like catalyst of Bi2WO6 nanosheets decorated hortensia-like CoAl-layered double hydroxides (Bi2WO6/CoAl-LDHs) was synthesized via hydrothermal process. The optimized Bi2WO6/CoAl-LDHs composite performed the high-efficiency photo-Fenton-like catalytic performance for oxytetracycline (OTC) removal (98.47%) in the mediation of visible-light and H2O2. The comparative experiment, technical characterization and density functional theory calculation results indicated that the efficient photo-Fenton-like catalytic performance of Bi2WO6/CoAl-LDHs was attributed to the synergistic action of the Fenton-like process of cobalt ions in CoAl-LDHs, an internal electric field and the S-scheme heterojunction form between Bi2WO6 and CoAl-LDHs, which could significantly promote the active substance formation and the photocatalytic process in the catalytic system. This study will stimulate the new inspiration of designing the efficient catalytic system for environmental remediation and other fields.

Removal of iodine (I− and IO3−) from aqueous solutions using CoAl and NiAl layered double hydroxides

The treatment of radioactive iodine released from nuclear power plants and radiological waste disposal sites is of great concern due to its high mobility and toxicity. In particular, iodide (I−) and iodate (IO3−) are the major iodine species of concern under various pHs and groundwater conditions. Herein, CoAl and NiAl layered double hydroxides (LDHs) were synthesized and investigated to identify the iodine removal mechanism and efficiency. Both CoAl and NiAl LDHs exhibited rapid iodine removal processes within 20 min, following the pseudo-second-order model via ion-exchange with parent NO3− anion in the LDHs. The CoAl LDH’s maximum sorption capacities for I− and IO3− were about 1.67 and 2.16 mmol g−1, respectively, whereas for the NiAl LDH, these were about 2.10 and 2.26 mmol g−1, and they followed the Langmuir isotherm model. Interestingly, both the CoAl and NiAl LDHs showed a preferential ion-exchange affinity for IO3− over I−, which was attributed to the structural similarity of the IO3− and NO3− as well as new formation of secondary Co(IO3)2·2H2O or Ni(IO3)2·2H2O phases. In addition, a desorption study indicated that the selectivity order was SO42− ≥ IO3− ≥ OH− > HCO3− > Cl− > NO3− ≥ I− and demonstrated the higher retention of the IO3− than I− anion. This study provides insights into promising iodine sorbents and the different removal mechanisms of I− and IO3− using CoAl and NiAl LDHs.

4-Aminoacetophenone Intercalated CoAl Layered Double Hydroxides: Synthesis, Characterization and Adsorptive Removal of Cd(II) ions from Water Samples

In the present study, CoAl-NO3 Layered Double Hydroxides (CoAl-NO3-LDH) was synthesized and an enolate anion of 4-Aminoacetophenone (AAP) was intercalated into LDH following the reconstruction approach. The CoAl-NO3-LDH and CoAl-AAP-LDH were characterized by Fourier-Transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD), scanning electron microscope (SEM) and energy dispersive X-ray (EDX) analyses. CoAl-AAP-LDH worked well for adsorption of Cd(II) ions from aqueous samples at optimum pH 7, adsorbent dosage 25 mg, concentration of Cd(II) ions 25 mg L-1 and shaking time 20 min at 25 °C. Different isotherms such as Langmuir, Freundlich and Dubinin-Radushkevich (D-R) isotherms fitted well to adsorption data with correlation coefficient (R2) of 0.998, 0.982 and 0.992, respectively. Monolayered (Qm) and multi-layered (KF) capacities of CoAl-AAP-LDH for adsorption of Cd(II) ions were calculated and found to be 34.40 and 19.44 mg g-1, respectively. Sorption energy was calculated and found to be 9.13 kJ mol-1, indicating chemisorption or ion exchange sorption mechanism. The method worked well for the adsorption of Cd(II) ions from wastewater samples.

A co-activation strategy for enhancing the performance of hematite in photoelectrochemical water oxidation

Hematite (α-Fe2O3) is a promising photoanode for photoelectrochemical (PEC) water splitting. However, the severe charge recombination and sluggish water oxidation kinetics extremely limit its use in photo-hydrogen conversion. Herein, a co-activation strategy is proposed, namely through phosphorus (P) doping and the loading of CoAl-layered double hydroxides (CoAl-LDHs) cocatalysts. Unexpectedly, the integrated system, CoAl-LDHs/P-Fe2O3 photoanode, exhibits an outstanding photocurrent density of 1.56 mA/cm2 at 1.23 V (vs. reversible hydrogen electrode, RHE), under AM 1.5 G, which is 2.6 times of pure α-Fe2O3. Systematic studies reveal that the remarkable PEC performance is attributed to accelerated surface OER kinetics and enhanced carrier separation efficiency. This work provides a feasible strategy to enhance the PEC performance of hematite photoanodes.

Co/Co9S8/nitrogen-doping hollow carbon spheres nanocomposite as an efficient and durable electrocatalyst for oxygen reduction reaction

The design of efficient, low-cost, and durable catalysts for oxygen reduction reaction (ORR) is pivotal to fuel cells. Herein, we developed a facile strategy to fabricate a Co/Co9S8/nitrogen-doped hollow carbon spheres (NHCS) nanocomposite via calcining 3-Aminobenzenesulfonic anions within the interlamination of CoAl-layered double hydroxides (CoAl-LDH) at 900 °C in N2 atmosphere. The Co/Co9S8/NHCS nanocomposite with numerous carbon nanosheets possesses large specific surface area and pore volume, and Co/Co9S8 nanoparticles were embedded within the carbon nanosheets. The Co/Co9S8/NHCS nanocomposite exhibits superexcellent ORR activities with an E onset of 0.95 V, an E 1/2 of 0.87 V and a J 1600 rpm of −5.82 mA cm−2 at 0.70 V vs. RHE. Moreover, the Co/Co9S8/NHCS nanocomposite displays prominent methanol tolerance and excellent stability in 0.1 M KOH. This work provides an efficient approach for developing non-precious metal ORR catalysts.

CoAl LDH@Ni-MOF-74 S-Scheme Heterojunction for Efficient Hydrogen Evolution

Metal–organic frameworks (MOFs) and layered double hydroxides (LDHs) have been considered to be one of the most promising and worthy hot spot materials to develop advanced catalysts for efficient hydrogen evolution due to their prominent characteristics, including unique structures, environmentally friendly nature, high redox activities, and homogeneously effective utilization of transition metal atoms. In this work, the delicate S-scheme heterojunction photocatalyst, CoAl LDH@Ni-MOF-74, was rationally designed and successfully constructed by coupling Ni-MOF-74 with CoAl LDH based on their peculiar structure, excellent electronic properties, and opposite surface potential for enhancing hydrogen generation activity under visible light irradiation. The CoAl LDH nanolayers evenly and dispersedly load on the surface of Ni-MOF-74. The CoAl LDH@Ni-MOF-74 exhibited higher photocatalytic hydrogen evolution activity compared with Ni-MOF-74 and CoAl LDH alone, mainly because the formation of the CoAl LDH@Ni-MOF-74 S-scheme heterojunction accelerated the recombination of several electrons (from conduction band (CB) of Ni-MOF-74) and holes (from valence band (VB) of CoAl LDH) and prevented the recombination of other electrons (from CB of CoAl LDH) and holes (from VB of Ni-MOF-74).

Ag nanoparticles-decorated CoAl-layered double hydroxide flower-like hollow microspheres for enhanced energy storage performance

Layered double hydroxides (LDHs) have been considered as one class of promising active electrode materials for supercapacitors due to their tunable composition and chemical versatility. Nonetheless, the poor electrical conductivity hinders their further practical applications in supercapacitors. Herein, CoAl LDH flower-like hollow microspheres are decorated with Ag nanoparticles by a facile one-step solvothermal reaction, followed by chemical bath deposition reaction. Experimental results and theoretical calculations indicate that decorating Ag nanoparticles onto CoAl LDH not only reduces the energy band gap and enhances their electrical conductivity, but also promotes fast diffusion kinetics of electrolyte ions and electrochemical reaction activity. Consequently, the prepared Ag/CoAl LDH electrode demonstrates improved specific capacities of 1214 (825) C g−1 at 3 (30) A g−1 and 91% capacity retention over 10,000 cycles at 10 A g−1 compared to the pristine CoAl LDH electrode. Moreover, using Ag/CoAl LDH and N-doped carbon nanotubes as the positive and negative electrodes, respectively, the assembled hybrid capacitor device delivers an energy density of 61.2 Wh kg−1 at a power density of 800 W kg−1. This work may showcase a great promise of engineering conductive nanoparticles-decorated LDHs-based active materials towards high-performance supercapacitors.

Cover Feature: Boosting the Supercapacitive Behavior of CoAl Layered Double Hydroxides via Tuning the Metal Composition and Interlayer Space (Batteries & Supercaps 6/2020)

Cover Feature: Boosting the Supercapacitive Behavior of CoAl Layered Double Hydroxides via Tuning the Metal Composition and Interlayer Space (Batteries & Supercaps 6/2020)