CoAl-layered Double Hydroxide Research Articles

Layered Double Hydroxide Derivatives for Polyolefin Upcycling.

While Ru-catalyzed hydrogenolysis holds significant promise in converting waste polyolefins into value-added alkane fuels, a major constraint is the high cost of noble metal catalysts. In this work, we propose, for the first time, that Co-based catalysts derived from CoAl-layered double hydroxide (LDH) are alternatives for efficient polyolefin hydrogenolysis. Leveraging the chemical flexibility of the LDH platform, we reveal that metallic Co species serve as highly efficient active sites for polyolefin hydrogenolysis. Furthermore, we introduced Ni into the Co framework to tackle the issue of restricted hydrogenation ability associated with contiguous Co-Co sites. In-situ analysis indicates that the integration of Ni induces electron transfer and facilitates hydrogen spillover. This dual effect synergistically enhances the hydrogenation/desorption of olefin intermediates, resulting in a significant reduction in the yield of low-value CH4 from 27.1 to 12.6%. Through leveraging the unique properties of LDH, we have developed efficient and cost-effective catalysts for the sustainable recycling and valorization of waste polyolefin materials.

Construction of skyloft-like polyamide membrane on tubular ceramic support for high-flux nanofiltration

Polyamide (PA) thin-film composite membrane has been widely used in water/wastewater treatment, but construction of such membrane on a three-dimensional inorganic macroporous support remains a challenge, thus limiting the further application under harsh conditions. Herein, we propose a skyloft-like PA membrane on a commercial tubular ceramic macrofiltration support. This membrane built on stilts comprises an ultrathin PA canopy of ∼ 33 nm and pillars (∼1 μm-thick) of vertically aligned CoAl-layered double hydroxide (LDH) nanosheets and covalent organic framework (COF) nanospheres. The prepared PA/OH-COF/F-COF/LDH membrane shows a high water permeance of up to 736.6 L m-2h−1 MPa−1 together with a satisfactory rejection rate of > 90 % for various small molecules including dyes and antibiotics (> ∼1 nm). The resultant membrane also demonstrates a good dye desalination performance (with a selectivity of up to 197), illustrating an outstanding permselectivty. A long-term and continuous cross-flow nanofiltration indicates a robust stability of the membrane.

Switchable superlyophobic CoAl-layered double hydroxide (LDH)-based mesh membranes for separation of various oil/water systems and removal of soluble organic pollutants

Switchable surface wettability has attracted tremendous attention owing to its potential applications, but it is still thorny to construct under-liquid dual superlyophobic surfaces for reversible separation of emulsified oil/water mixtures and treatment of complex oily wastewater. In this work, a CoAl-LDH-based mesh membrane was prepared for switchable separation of emulsified oily wastewater. The interpenetrating CoAl-LDH nanosheets were grown on the stainless steel mesh (SSM) forming a micro-/nano hierarchical structure via a hydrothermal method, which endows the membrane with under-liquid dual superlyophobicity. The obtained CoAl-LDH membrane exhibited switchable separation capability for both oil/water mixtures and oil/water emulsions with high fluxes and efficiencies (99.7%). In addition, the CoAl-LDH membrane could not only separate but also photodegrade the oil-in-water (O/W) emulsions containing soluble organic pollutants. Interestingly, after introducing a ZnO nanorod layer, the LDH/ZnO membrane exhibited progressive removal efficiency (99%) and photodegradation efficiency (＞99%) for methylene blue (MB). The cycled and harsh condition tests also confirmed the stability and robustness of the prepared membranes. The excellent separation performance and photocatalytic property endow the membranes appealing to practical oil/water separation and oily wastewater treatment.

Vitamin C-regulated CoAl- layered double hydroxide with oxygen vacancies to efficiently activate peroxydisulfate for sulfamethoxazole removal triggered via reactive oxygen and high-valent cobalt species

In this study, a vitamin C-regulated CoAl-layered double hydroxide with abundant oxygen vacancies was synthesized via a simple hydrothermal process. The resulting CoAl-layered double hydroxide was employed to activate peroxydisulfate for removal of sulfamethoxazole. The effect of the experimental parameters such as pH, catalyst dose and peroxydisulfate concentration on sulfamethoxazole removal was investigated. The current system exhibited excellent catalytic performance for sulfamethoxazole removal in a broad pH range (i.e., pH 3.0–11.0). Under the optimized condition, 94.2% of sulfamethoxazole was degraded within 15 min, accompanied by a 67.6% reduction in chemical oxygen demand. The effective sulfamethoxazole degradation could be attributed to four pathways. Firstly, the ≡ Co2+ in catalyst reacted with peroxydisulfate to generate reactive species, including SO4•−, •OH, O2•− and 1O2, which could degrade sulfamethoxazole. Secondly, the oxygen vacancies could modulate intrinsic electrons, resulted in the surface activation of catalyst and accelerated charge transfer, which was favorable for the degradation of sulfamethoxazole. Thirdly, the presence of vitamin C not only promoted the formation of oxygen vacancies but also expanded the interlayer spacing of layered double hydroxide. A large interlayer spacing facilitated the diffusion of peroxydisulfate and pollutants in the interlayer and improved the utilization efficiency of the active site. Lastly, the high-valent cobalt species exhibited excellent oxidation ability and enhanced the catalyst performance through continuously being employed as an electron acceptor. This study provided a valuable insight for the design and application of Co-based catalysts in peroxydisulfate-based advanced oxidation processes.

A hierarchical 3D hybrid CoAl-layered double hydroxide/TiO2/Ti3C2 MXene S-scheme photocatalyst with 2D/0D/2D contact interfaces for sustainable pollutant degradation

Environmental pollution, particularly that derived from waterborne antibiotics, is a rising concern because of its detrimental effects on aquatic ecosystems and human health. Hence, in this study, we present a hierarchical 3D-structured hybrid photocatalyst comprising a CoAl-layered double hydroxide (LDH), TiO2, and Ti3C2 MXene synthesized using an in situ hydrothermal method. Various characterization techniques revealed that the hybrid CoAl-LDH/TiO2/Ti3C2 photocatalyst exhibited improved optical absorption, and the tailored 2D/0D/2D contact interfaces among the constituents enhanced charge migration and minimized electron-hole recombination. The results of electron paramagnetic resonance and in situ-irradiated X-ray photoelectron spectroscopy analyses confirmed that the hybrid photocatalyst follows an S-scheme mechanism that not only promotes the separation of photoinduced electron-hole pairs but also preserves their robust redox capability. The amalgamation of the three components resulted in synergistic advantages. Consequently, the optimized CoAl-LDH/TiO2/Ti3C2 photocatalyst exhibited remarkable performance in degrading and mineralizing the antibiotic diclofenac sodium (DFS) and the dyes rhodamine B and indigo carmine, surpassing its constituents and previously reported photocatalysts. Furthermore, the hybrid retained high efficiency across multiple cycles, underscoring its potential reusability. Therefore, this study demonstrates the potential of the developed hybrid photocatalyst for sustainable water treatment, thereby fostering cleaner aqueous environments.

3D-printed solid phase microextraction fiber based on Co-Al layered double hydroxide nanosheets; application in determination of phenolic acids in fruit juice samples

3D printing technology has attracted great attention in various fields of science and technology. Application of this technology in manufacturing analytical tools is developing fast. High precision in manufacturing designed objects, fast production and low cost also green production approach by using biodegradable materials like polylactic acid is promising bright future in scientific researches. The development of new approaches in improving the functional groups of the surface of 3D printed objects in order to make 3D printed parts more functional with conventional 3D printed materials, causes the entry of many advanced materials in this field. In this study, a novel solid phase microextraction fiber was prepared based on Co-Al layered double hydroxide (LDH) nanosheets in-situ growth on 3D-printed aluminum-polylactic acid (PLA) composite and its application for determination of phenolic acids (PAs) including vanillic acid (VA), ferulic acid (FA), p-coumaric acid (p-CA), p-hydroxybenzoic acid (HBA), protocatechuic acid (PCA) and caffeic acid (CA) in fruit juice samples was investigated. The proposed fiber was prepared via a robust one-step hydrothermal synthesis of Co-Al LDH on an anodized 3D-printed Al-PLA fiber. Factors crucial for the extraction, including pH, extraction and desorption time and ionic strength were explored in detail. Under the optimal experimental conditions, for all PAs except PCA, LOD, LOQ and LDR were obtained as 0.03, 0.1 and 0.1–100.0 µgL−1, respectively. For PCA, LOD, LOQ and LDR were obtained as 0.15, 0.50 and 0.5–100.0 µgL−1, respectively.

Construction of a Z-scheme heterojunction photocatalyst with oxygen vacancies using cobalt–alumina-layered double hydroxide dispersed between bismuth oxybromide layers for efficient photocatalytic reduction of carbon dioxide

Under the context of energy shortages and global warming, the photocatalytic reduction of carbon dioxide (CO2) to carbon monoxide (CO) using simulated sunlight has attracted considerable research attention. Herein, three-dimensional (3D) Z-scheme cobalt–alumina-layered double hydroxide/bismuth oxybromide (CoAl-layered double hydroxide (LDH)/BiOBr) heterojunction photocatalysts with oxygen vacancies were constructed by intercalating two-dimensional CoAl-LDH between BiOBr layers in the mechanical mixing. The conversion of CO2 in the water phase was greatly improved compared to CoAl-LDH/BiOBr under 300-W xenon light. The transformation efficiency of 23.62 μmol⋅g−1⋅h−1 for CoAl-LDH/BiOBr-10 (CBO-10) is 2.96 and 8.34 times that of pure BiOBr and CoAl-LDH, respectively, with CO selectivity in the obtained products reaching as high as 95 %. Furthermore, CBO-10 catalysts exhibited outstanding stability in terms of structure and catalytic performance. The construction of Z-scheme heterojunctions and oxygen vacancies enlarges the photoresponse range of the BiOBr catalyst while reducing the photoelectron–hole recombination efficiency. The unique 3D structure offers more Z-scheme heterojunction interfaces for the separation and transfer of electrons between CoAl-LDH and BiOBr during photoreaction. This study is expected to guide the development of new high-performance photocatalysts and the selective regulation of reduction products.

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.

Fluorescent Co/Al-layered double hydroxide intercalated Schiff base-chitosan composite for sensing multiple e-waste metals

An organic-inorganic composite was fabricated by the intercalation of chitosan Schiff base (Chitosan@SB) in the layers of Co/Al layered double hydroxide (Co/Al-LDH) to get the amalgamated properties of parent materials like fluorescent nature and porosity. The structural properties of Chitosan Schiff base intercalated layered double hydroxide (Chitosan@SB-Co/Al-LDH) were explored through FT-IR, PXRD, TGA, BET, HRTEM, and SEM analysis. The composite Chitosan@SB-Co/Al-LDH showed a fluorescence peak pointed at 501 nm (λexc = 370 nm) and a porous surface with heterogeneous texture. It showed an outstanding turn-off signal in the presence of selective metallic species i.e., Cu2+, Fe3+, Al3+, Cr3+, Hg2+, and Pb2+ ions thus acting as a sensing probe for the e-waste metals. Moreover, the Density-Functional Theory supports the procedure of interaction between Chitosan@SB-Co/Al-LDH and metal ions. Furthermore, the composite has been investigated for real life uses in sewage waste water samples.

Thiocyanate Removal from Aqueous Solution by a Synthetic CoAl-Layered Double Hydroxide with Nitrate Intercalation

Thiocyanate Removal from Aqueous Solution by a Synthetic CoAl-Layered Double Hydroxide with Nitrate Intercalation

Nitrogen self-doped chitosan carbon aerogel integrating with CoAl-LDH for ultra-efficient sulfamethoxazole degradation based on PS-AOPs: From batch to continuous process

Nitrogen self-doped chitosan carbon aerogel (NCCA) integrating with CoAl layered double hydroxide (CoAl-LDH) was successfully fabricated and utilized for the ultra-efficient activation of peroxymonosulfate (PMS) toward sulfamethoxazole (SMX) degradation. And the NCCA/CoAl-LDH-2 catalyst possessed the highest catalytic activity with 97.5% of SMX degradation efficiency in 5 min and 74.8% of total organic carbon (TOC) removal efficiency in 30 min, may being on account of the synergistic interaction between NCCA and CoAl-LDH. Additionally, the NCCA/CoAl-LDH-2 catalyst not only had good reusability and stability, but also could realize continuous degradation of SMX solutions via a fixed-bed reactor. Furthermore, the results of quenching tests, electrochemical measurements as well as electron paramagnetic resonance (EPR) analysis demonstrated that both non-radical and radical processes participated in the SMX degradation, in which the latter played a predominant role. X-ray photoelectron spectroscopy (XPS) corroborated that the main active sites were the CO groups and graphitic N of NCCA, and the Co3+/Co2+ redox cycle of CoAl-LDH. High-performance liquid chromatography-mass spectrometry (HPLC-MS) analysis and density functional theory (DFT) calculation containing the laplacian bond order (LBO) and Fukui index were carried out to deeply explore the reasonable SMX degradation pathways. This current study provided a theoretical basis to design an efficient PMS activation system toward continuous antibiotics degradation.

Constructing CoAl-LDO/MoO3−x S-scheme heterojunctions for enhanced photocatalytic CO2 reduction

Converting CO2 into chemicals and fuels by solar energy can alleviate global warming and solve the energy crisis. In this work, CoAl-LDO/MoO3−x (LDO/MO) composites were successfully prepared and achieved efficient CO2 reduction under visible light. The CoAl-layered double oxides (CoAl-LDO) evolved from CoAl-layered double hydroxide (CoAl-LDH) exhibited a more robust structure, broader light absorption, and improved CO2 adsorption ability. The local surface plasmon resonance (LSPR) effect excited by nonstoichiometric MoO3−x broadened the photo-response range of CoAl-LDO/MoO3−x. In addition, constructing step-scheme (S-scheme) heterojunctions could simultaneously optimize the migration mechanism of photogenerated electrons and holes, and retain carriers with strong redox ability. Therefore, the production rates of CO and CH4 on the optimal LDO/MO composite were 7 and 9 times higher than the pristine CoAl-LDH, respectively. This work hybridizes oxidation photocatalysts and LDO-based materials to optimize the charge separation and migration mechanisms, which guides the modification of LDO-based materials.

Synthesis and catalytic performance of nanoflower-like Ru@CoAl-LDH composite catalyst for NaBH4 hydrolysis

Sodium borohydride (NaBH4) has been widely regarded as the one of most promising future hydrogen (H2)-generated materials. Therefore, it is necessary to find a catalyst with higher catalytic performance to promote the on-demand H2 release of NaBH4 hydrolysis. In this study, a [email protected] catalyst was developed by immobilizing Ru nanoparticles (Ru NPs) on the surface of Co Al Layered Double Hydroxide (CoAl-LDH) nanocurds. The Ru NPs were prepared by H2 reduction, and nanoflower-like CoAl-LDH was synthesized through a one-step solvothermal method. The microstructure and composition of the catalysts were investigated through scanning electron microscopy, high-resolution transmission electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. The results showed that [email protected] exhibited good catalytic performance toward the NaBH4 hydrolysis. At 30 °C, the hydrogen generation rate of the hydrolysis reaction was 44.34 L·min−1·gRu−1, and the reaction activation energy was 38.83 kJ·mol−1, and superior to many catalysts of the same type. Because of its high activity, low activation energy and excellent economic performance, this catalyst has high potential for applications in NaBH4 hydrolysis.

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.

Superhigh and Robust Ion Selectivity in Membranes Assembled with Monolayer Clay Nanosheets.

It is crucial to control the ion transport in membranes for various technological applications such as energy storage and conversion. The emerging functional two-dimensional (2D) nanosheets such as graphene oxide and MXenes show great potential for constructing ordered nanochannels, but the assembled membranes suffer from low ion selectivity and stability. Here a class of robust charge-selective membranes with superhigh cation/anion selectivity, which are assembled with monolayer nanosheets of cationic/anionic clays that inherently have permanent and uniform charges on each layer is reported. The transport number of cations/anions of cationic vermiculite nanosheet membranes (VNMs)/anionic Co-Al layered double hydroxide (CoAl-LDH) nanosheet membranes is over 0.90 in different NaCl concentration gradients, outperforming all the reported ion-selective membranes. Importantly, this excellent ion selectivity can persist at high-concentration salt solutions, under acidic and alkaline conditions, and for a wide range of ions of different sizes and charges. By coupling a pair of cation-selective vermiculite membrane and anion-selective CoAl-LDH membrane, a reverse electrodialysis device which shows an output power density of 0.7W m-2 and energy conversion efficiency of 45.5% is constructed. This work provides a new strategy to rationally design high-performance ion-selective membranes by using 2D nanosheets with inherent surface charges for controllable ion-transport applications.

Metal Vacancies in CoAl-Layered Double Hydroxide Nanosheets Enabling Boosted Visible Light Driven CO2 Photoreduction

Metal Vacancies in CoAl-Layered Double Hydroxide Nanosheets Enabling Boosted Visible Light Driven CO₂ Photoreduction

Growth Mechanism and Corrosion Resistance of a Co-Al Layered Double Hydroxide Film Grown In Situ on a Steel Substrate

The growth mechanism of layered double hydroxide (LDH) films grown in situ on steel via hydrothermal treatment is still unclear. In this study, the mechanism of Co-Al-CO3-LDH film grown in situ on a steel substrate was investigated in detail. During the hydrothermal reaction, the in situ growth process of Co-Al LDH on steel involved three steps: (1) hydrolysis of Al3+ and etching of the steel surface, (2) hydrolysis of urea and promotion of LDH nuclei, and (3) crystallization of LDH. More importantly, the generation of Al(OH)3 determined the integrity of the LDH film grown on the steel surface, and a suitable heating rate was also the key factor that affected the growth of the ordered and regular LDH nanoflakes. Therefore, this work provides a comprehensive understanding of the in situ LDH growth mechanism on steel and may facilitate optimal LDH film preparation.

Control of particle growth and enhancement of photoluminescence, adsorption efficiency, and photocatalytic activity for zinc sulfide and cadmium sulfide using CoAl-layered double hydroxide system

The fabrication of zinc sulfide (ZnS) and cadmium sulfide (CdS) hybrids was carried out by the sulfidization of Zn(II) or Cd(II) adsorbed in dodecylsulfate modified CoAl-layered double hydroxide through solid-liquid reaction. The TEM images showed the nanocrystals of ZnS (2.61 nm) or CdS (3.29 nm) orderly distributed on the nanosheets. The BET surface area of ZnS (1.13 m2/g) and CdS (0.78 m2/g) was largely improved by intercalating in the interlayer space of CoAl-layered double hydroxide system (15-20 m2/g). The spectroscopic observations further confirmed the formation of ZnS or CdS nanoparticles in the hybrid as the evidence of the blue-shifted absorption onset (39-44 nm), and the increase of the photoluminescence intensity (3-4 times) relative to those of bare ZnS and CdS. The nanohybrids could be applicable as the adsorbent and photocatalyst on purifying wastewater contaminated with Congo red dye. By the adsorptive removal, the hybrids exhibited the maximum adsorption capacity of 216-234 mg/g, resulting from the effect of CoAl-layered double hydroxide. In addition, the photocatalytic degradation was completely conducted by using CdS hybrid with the rate constant of 0.0115 min-1, because the host-guest and/or guest-guest interactions promoted the greater optical performance, and adsorption and photocatalytic efficiencies.

Comparison of Kinetics of Adsorption of Permanganate on Co-Al-Layered Double Hydroxide and MoS2 Nanocompounds.

Permanganate ions were adsorbed on carbonate intercalated Co-Al-layered double hydroxide (Co-Al-LDH) and MoS2 and after a while the adsorbed ions were reduced to MnO2. Reduction of adsorbed ion was catalyzed on the surface of carbonate intercalated Co-Al-LDH but ions reacted with MoS2 surface. Adsorption kinetic tests were carried out at different temperatures, ionic strengths, pH, initial adsorbate concentrations and shaking rates. The adsorption kinetics was studied by the kinetics of adsorption study in the regions with constant adsorption acceleration (KASRA) model and KASRA, ideal-second-order (ISO), intraparticle diffusion, Elovich and (non-ideal process of adsorption kinetics (NIPPON) equations.In this work, a new equation called NIPPON equation was introduced. In this equation, it was assumed that during a non-ideal process, adsorbate species molecules were adsorbed simultaneously on the same type adsorption sites with different activities. Indeed, the average values of adsorption kinetic parameters were calculated by the NIPPON equation. Also, the character of boundaries of regions obtained from the KASRA model can be determined by this equation.

Surface properties and de-polluting performance of a photocatalytic coating incorporating novel core@shell nanospheres for cementitious substrate

The surface of long-term exposed building materials usually shows serious deterioration under continuous environmental erosion, which can greatly shorten the service life of building structures. The application prospect of multifunctional photocatalytic materials in civil engineering is promising but the engineering application is still limited due to the inherent defects of traditional photocatalytic materials. In this paper, the ordinary Portland cement (OPC) and alkali activated slag (AAS) mortar samples were prepared with a photocatalytic coating incorporating novel core@shell nanospheres which feature with TiO2 core and CoAl-layered double hydroxide shell (TiO2@CoAl-LDH). The surface roughness, microhardness, contact angle and capillary water absorption of coated and uncoated mortars were analyzed and characterized to explore the effect of photocatalytic coating on surface properties. The photocatalytic activity and photo-induced hydrophilicity of the coated mortar were investigated by degrading methylene blue and contact angle tests. A simulated rainwater washing test was designed to evaluate the long-term stability of photocatalytic coatings on mortar substrate. The results show that compared with unwashed coated mortar, the coated mortar after rainwater washing can still maintain a higher photocatalytic activity, whereby the surface hydrophilicity was increased with the decrease of the surface roughness and capillary water absorption. As a newly developed protective coating material, TiO2@CoAl-LDH is expected to confer multifunctional properties to the cementitious materials.