Layered Double Hydroxides Research Articles

A Short Review of Layered Double Oxide-Based Catalysts for NH3-SCR: Synthesis and NOx Removal

Nitrogen oxides are one of the main atmospheric pollutants and pose a threat to the ecological environment and human health. Selective catalytic reduction (NH3-SCR) is an effective way of removing nitrogen oxides, with the catalyst being the key to this technology. Two-dimensional nanostructured layered double oxide (LDO) has attracted increasing attention due to the controllability of cations in the layers and the exchangeability of anions between layers. As a derivative of layered double hydroxide (LDH), LDO not only inherits the controllability and diversity inherent in the LDH structure but also exhibits excellent performance in the catalytic field. This article contains three main sections. It begins with a brief discussion of the development of LDO catalysts and analyzes the advantages of the LDO structure. The later section introduces the synthesis methods of LDH, clarifies the conversion relationship between LDH and LDO, and summarizes the modification impacts of the properties of LDO catalysts. The application of LDO catalysts used in NH3-SCR under wild temperature conditions is discussed, and the different types, reaction processes, and mechanisms of LDO catalysts are described in the third section. Finally, future research directions and outlooks are also offered to assist the development of LDO catalysts and overcome the difficult points related to NH3-SCR.

Presulfurized Hydrotreating Catalysts Prepared from Tetrathiotungstate- Intercalated NiZnAl Layered Double Hydroxides

Presulfurized Hydrotreating Catalysts Prepared from Tetrathiotungstate- Intercalated NiZnAl Layered Double Hydroxides

Engineering Lattice Oxygen Regeneration of NiFe Layered Double Hydroxide Enhances Oxygen Evolution Catalysis Durability.

The lattice oxygen mechanism (LOM) endows NiFe layered double hydroxide (NiFe-LDH) with superior oxygen evolution reaction (OER) activity, yet the frequent evolution and sluggish regeneration of lattice oxygen intensify the dissolution of active species. Herein, we overcome this challenge by constructing the NiFe hydroxide/Ni4Mo alloy (NiFe-LDH/Ni4Mo) heterojunction electrocatalyst, featuring the Ni4Mo alloy as the oxygen pump to provide oxygenous intermediates and electrons for NiFe-LDH. The released lattice oxygen can be timely offset by the oxygenous species during the LOM process, balancing the regeneration of lattice oxygen and assuring the enhancement of the durability. In consequence, the durability of NiFe-LDH is significantly enhanced after the modification of Ni4Mo with an impressive durability for over 60 h, much longer than that of NiFe-LDH counterpart with only 10 h. In situ spectra and first-principle simulations reveal that the adsorption of OH- is significantly strengthened owing to the introduction of Ni4Mo, ensuring the rapid regeneration of lattice oxygen. Moreover, NiFe-LDH/Ni4Mo-based anion exchange membrane water electrolyzer (AEMWE) presents an impressive durability for over 150 h at 100 mA cm-2. The oxygen pump strategy opens opportunities to balance the evolution and regeneration of lattice oxygen, enhancing the durability of efficient OER catalysts.

Engineering Lattice Oxygen Regeneration of NiFe Layered Double Hydroxide Enhances Oxygen Evolution Catalysis Durability

The lattice oxygen mechanism (LOM) endows NiFe layered double hydroxide (NiFe‐LDH) with superior oxygen evolution reaction (OER) activity, yet the frequent evolution and sluggish regeneration of lattice oxygen intensify the dissolution of active species. Herein, we overcome this challenge by constructing the NiFe hydroxide/Ni4Mo alloy (NiFe‐LDH/Ni4Mo) heterojunction electrocatalyst, featuring the Ni4Mo alloy as the oxygen pump to provide oxygenous intermediates and electrons for NiFe‐LDH. The released lattice oxygen can be timely offset by the oxygenous species during the LOM process, balancing the regeneration of lattice oxygen and assuring the enhancement of the durability. In consequence, the durability of NiFe‐LDH is significantly enhanced after the modification of Ni4Mo with an impressively durability for over 60 h, much longer than that of NiFe‐LDH counterpart with only 10 h. In‐situ spectra and first‐principle simulations reveal that the adsorption of OH− is significantly strengthened owing to the introduction of Ni4Mo, ensuring the rapid regeneration of lattice oxygen. Moreover, NiFe‐LDH/Ni4Mo‐based anion exchange membrane water electrolyzer (AEMWE) presents an impressive durability for over 150 h at 100 mA cm−2. The oxygen pump strategy opens opportunities to balance the evolution and regeneration of lattice oxygen, enhancing the durability of efficient OER catalysts.

Nanoflower-like NiCoFe layered hydroxide by in-situ electrochemical corrosion as highly efficient electrocatalyst for water oxidation

Layered double hydroxides have been widely applied for oxygen evolution reaction (OER) in the alkaline water electrolysis. However, the issues of poor connection between the catalyst and nickel foam and the specific mechanisms for active sites has not been fully documented. In this study, the in-situ nickel foam etching in a mixed solution of ferric chloride and cobalt nitrate at low temperatures was adopted for NiCoFe layered ternary hydroxides (NiCoFe LTHs) synthesis with a better tight integration. Physicochemical characterization indicated that the NiCoFe LTHs could grow directly through corroding nickel foam with a nano-flower-like morphology and structures. That is favorable for electron transfer from the catalytic layer to the conductive substrate. With the transition metal ions interaction and the tight integration construction, NiCo1Fe4-LTH-T60/NF presented an enhanced electrolysis performance with the overpotential of 234 mV (1.464 V vs. RHE) at current density of 100 mA cm−2 in 1 M KOH electrolyte. The Tafel slope for NiCo1Fe4-LTH-T60/NF electrode was 36.19 mV dec−1 for an enhanced OER kinetics. Besides, it demonstrated faster interfacial charge transfer process, better intrinsic electrochemical activity and stability in large current stability testing. It was revealed that the synergistic effect of the transition metal ions interaction enhancement and the mechanism of oxygen evolution elementary reaction for NiCo1Fe4-LTH-T60/NF during the water electrolysis by the electrochemical and theoretical calculation. This work provides theoretical basis and experimental support for the design and synthesis of future OER catalyst and substrate, which is significant for hydrogen and oxygen generation from water electrolysis.

Coral-like Composite Based on SnO2@Rice Husk Nanoparticles Modified with Polyaniline Coated on Ni–Co Layered Double Hydroxide as an Innovative Electrode for Superior Supercapacitor Performance

Coral-like Composite Based on SnO₂@Rice Husk Nanoparticles Modified with Polyaniline Coated on Ni–Co Layered Double Hydroxide as an Innovative Electrode for Superior Supercapacitor Performance

Confining Pt Nanoparticles in Layered Double Hydroxide Derived Hollow Mesoporous MgAl‐Oxide Nanospheres for Boosting Selective Transfer Hydrogenation

AbstractCatalytic transfer hydrogenation (CTH) is a safe and effective strategy for producing unsaturated alcohols (UOLs) from biomass‐derived α,β‐unsaturated aldehydes/ketones. Accordingly, the design of CTH catalysts that possess both extreme activity and superior selectivity is highly desirable. Herein, we develop a highly efficient Pt@hMgAl catalyst with Pt nanoparticles (NPs) confined in the layered double hydroxide derived hollow MgAl‐oxide nanospheres (hMgAl), which shows an enhanced catalytic performance in CTH of furfural (FFR) to furfuryl alcohol (FOL) compared to the hMgAl catalyst without Pt NPs inside. It is found that the reaction rate over the Pt@hMgAl (12.8 mmol gcat−1 h−1) is ~26 times higher than that over the hMgAl (0.5 mmol gcat−1 h−1). The excellent catalytic performance of Pt@hMgAl originates from the synergy between Pt‐(Mg−O−Al) interfacial sites, where the acid‐base site of Mg−O−Al activates the C=O bond of FFR, while the nearby Pt site facilitates the dehydrogenation of 2‐propanol. Moreover, the reaction rate over the Pt@hMgAl can further increase to 21.8 mmol gcat−1 h−1 after introducing H2 into the reaction system, where the FOL selectivity is still higher than 99 % due to the synergy of Pt‐(Mg−O−Al) interfacial sites. This work provides a straightforward approach to construct a hollow‐structured catalyst with abundant metal/oxide interfaces, which could significantly enhance the CTH efficiency for α,β‐unsaturated alcohols production.

Toward High Corrosion Resistivity and High Efficiency in Seawater Oxygen Evolution: The Synergy of Fe and Ni Dopants in Co Layered Double Hydroxide Ultrathin Nanosheets

Toward High Corrosion Resistivity and High Efficiency in Seawater Oxygen Evolution: The Synergy of Fe and Ni Dopants in Co Layered Double Hydroxide Ultrathin Nanosheets

Sweat‐Permeable, Microbiota‐Preserving, Mechanically Antibacterial Patch for Long‐Term Interfacing with Perspiring Skin

AbstractThe prolonged health monitoring using wearable technology faces challenges stemming from perspiration, including bacterial proliferation, compromised adhesion, signal quality deterioration, and user discomfort. Notably, excessive sweat fosters bacterial colonization, escalating infection risks, and compromising biomarker analysis. Existing antibacterial approaches, unfortunately, risk disrupting the delicate balance of skin microbiota. To address this, a Janus patch featuring Zn‐Al layered double hydroxide (LDH) modification is developed, which exhibits sustained antibacterial properties while preserving the epidermal microecology. It integrates a hydrophobic LDH fabric that mechanically eradicates bacteria via a nanoknife effect, and a laser‐engraved medical adhesive with microholes for unidirectional sweat transport. This innovative design not only enhances adhesion stability but also safeguards the skin microbiome by preventing direct contact with Zn‐Al LDH. Moreover, the patch seamlessly interfaces with sweat‐monitoring technologies like microfluidic paper‐based analytical devices (uPADs) sensors, ensuring 100% antibacterial efficacy and efficient sweat redirection for reliable detection while prioritizing user comfort. It can serve as a durable bridge between perspiring skin and epidermal sensors, revolutionizing the realm of long‐term health monitoring.

Tailoring Interlayer Microenvironment of 2D Layered Double Hydroxides for CO2 Reduction with Enhanced C2+ Production.

Both the physicochemical properties of catalytic material and the structure of loaded catalyst layer (CL) on gas diffusion electrode (GDE) are of crucial importance in determining the conversion efficiency and product selectivity of carbon dioxide reduction reaction (CO2RR). However, the highly reducing reaction condition of CO2RR will lead to the uncontrollable structural and compositional changes of catalysts, making it difficult to tailor surface properties and microstructure of the real active species for favored products. Herein, the interlayer microenvironment of copper-based layered double hydroxides (LDHs) is rationally tuned by a facile ink solvent engineering, which affects both the surface characters and microstructure of CL on GDE, leading to distinct catalytic activity and product selectivity. According to series of in situ and ex situ techniques, the appropriate surface wettability and thickness of porous CL are found to play critical roles in controlling the local CO2 concentration and water dissociation steps that are key for hydrogenation during CO2RR, leading to a high Faradaic efficiency of 75.3% for C2+ products and a partial current density of 275mAcm-2 at -0.8V versus RHE. This work provides insights into rational design of efficient electrocatalysts toward CO2RR for multi-carbon generation.

Transforming Prussian Blue Analogues: The Future-Centric Pathway to Rise of Thin Layered Double Hydroxides for Superior Water Oxidation: An Overview

Prussian blue analogues (PBAs)[1–5] have exhibited great performance towards electrochemical water oxidation because of their high activity and stability. However, there were some challenges because of their limited surface area and less accessible active sites. Herein this work, we have explored the synthesis of a Prussian blue analogue-based thin layered double hydroxide (PBA-TLDH)[6–9] through a reconstruction method. The (PBA-TLDH) possessed high surface area and a large number of active sites for enhanced electrochemical water oxidation. These PBA-LDH materials were well characterized by X-ray diffraction, Fourier transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM), and electrochemical techniques[1,7,10–12]. The PBA-TLDH materials had a well-defined thin layered structure with the PBAs uniformly distributed in the interlayer spaces of the LDHs. The PBA-LDH catalyst showed enhanced electrocatalytic activity towards water oxidation, with a very low overpotentials up to 240 mV and current density of 10 mA cm-2,[9,13–16] have been achieved which is significantly lower than that of the pristine PBAs. Moreover, these thin layered double hydroxides material showed excellent stability over large electrochemical cycle. This work provides a new strategy for the design and synthesis of highly active and stable electrocatalysts for water oxidation.

Layered Double Hydroxides as Systems for Capturing Small-Molecule Air Pollutants: A Density Functional Theory Study.

Air pollutants are usually formed by easily spreading small molecules, representing a severe problem for human health, especially in urban centers. Despite the efforts to stem their diffusion, many diseases are still associated with exposure to these molecules. The present study focuses on modeling and designing two-dimensional systems called Layered Double Hydroxides (LDHs), which can potentially trap these molecules. For this purpose, a Density Functional Theory (DFT) approach has been used to study the role of the elemental composition of LDHs, the type of counterion, and the ability of these systems to intercalate NO2 and SO2 between the LDH layers. The results demonstrated how the counterion determines the different possible spacing between the layers, modulating the internalization capacity of pollutants and determining the stability degree of the system for a long-lasting effect. The variations in structural properties, the density of states (DOS), and the description of the charge transfer have been reported, thus allowing the investigation of aspects that are difficult to observe from an experimental point of view and, at the same time, providing essential details for the effective development of systems that can counteract the spread of air pollutants.

Synthesis of eco-friendly CaCO3@Zn-Al MMO core-shell nanoflowers photocatalyst using bio–eggshell waste for improved photocatalytic degradation of RhB under visible light irradiation

In this study, a type-I heterojunction was synthesized based on eggshell waste doped mixed metal oxide (ES@ZnAl MMO) for the degradation of RhB dye under visible light irradiation. The ES@ZnAl MMO core-shell was synthesized using waste eggshell and layered double hydroxide (LDH) as primary precursors. After their mechanochemical assembly and thermal treatment, CaCO3 was formed in both calcite and vaterite forms, alongside mixed metal oxides derived from the LDH (ZnO and Al2O3). The formation of a heterojunction between the semiconductors results in an improved activation of sites, a decrease in bandgap energy from 5.72 to 3.44 eV, and an increase in degradation capacity. The elemental composition, morphology, structural, and optical properties of the ES@ZnAl MMO nanocomposite were analyzed using various techniques. The optimal ES@ZnAl MMO photocatalyst demonstrated superior performance, reaching over 98% of RhB dye degradation under optimal conditions, outperforming pure ZnAl LDH, ZnAl MMO, and ES. After five run cycles, the ES@ZnAl MMO heterojunction still maintained a high photocatalytic performance for RhB dye (99%). Furthermore, it displayed high performance in degrading various other pollutants, including OG, IC, MB, and 2.4-DP, with degradation efficiencies of 97%, 99%, 99%, and 87%, respectively. This economically advantageous heterojunction showed its importance in environmental remediation, presenting a promising solution for addressing diverse pollution challenges.

Interface-engineered Ni(Fe/Al)-LDHs/g-C3N4 nanosheets with metallic Fe/Al[sbnd]N bonds for efficient photocatalytic degradation of tetracycline hydrochloride

To improve the photogenerated electron–hole separation efficiency and the number of reactive oxygen species of g-C3N4 in visible light. Herein, an interface-engineered Ni(Fe/Al)-LDHs/g-C3N4 nanosheets with Fe/AlN bonds were prepared, which shows highly enhanced photocatalytic degradation performance with excellent structural stability. The interfacial structure of g-C3N4 was precisely regulated by metal Fe/Al on the surface of layered double hydroxides (LDHs), which could form Fe/AlN bonds as the interfacial charge transfer channels. In addition, the metal Ni and Fe/Al on the surface of LDHs nanosheets can furnish more photocatalytic active sites and interface synergy. The obtained 7 %NiFe-LDHs/g-C3N4 owns the degradation rate of 99.23 % for tetracycline hydrochloride (TCH) in visible light. This work highlights a rational interface engineering strategy for the formation of a composite structure with interface interaction for efficient photocatalysts.

Novel, eco-friendly α-tocopherol/layered double hydroxides/poly(3-hydroxyoctanoate)-based active packaging materials with enhanced antimicrobial, barrier and antioxidant activities

Among various climate actions taken as a response to environmental concerns, important and highly influential are ones related to the packaging industry being still one of the largest plastic sectors responsible for the majority of post-consumer wastes. Therefore, in this manuscript, for the first time assessment of the potential application of biodegradable bacterially derived poly(3-hydroxyoctanoate) (P(3HO)) doped with functional 2D nanoparticles as a more sustainable active packaging material has been investigated. In particular, P(3HO) combined with two types of layered double hydroxide (LDHs) modified with α-tocopherol (type of vitamin E) was applied for the fabrication of polymeric nanocomposite films and a comprehensive investigation of their structure and relevant properties (mechanical, barrier, bactericidal, and antioxidative) was performed. Permeation study revealed that P(3HO)-based films with 4 wt% tocopherol-modified nanoparticles meet the barrier requirements for storing fruits and vegetables, whereas antibacterial assay indicated inhibited growth of Gram-positive bacteria (particularly S. Aureus). Monitoring of polyphenols (PPH) content in strawberries after 6 days of storage at room conditions showed a slightly higher level of PPH with reference to fresh fruits, which indicates the preserved freshness of strawberries kept in P(3HO) containing 4 wt% Zn-based LDHs modified with tocopherol contrary to fruits kept in commercial polypropylene packaging which led to significant drop in PPH content. Thus, the application-focused experiments indicated that investigated P(3HO)-based nanocomposites are promising candidates for more sustainable active packaging that may extend the shelf-life of fruits and protect consumers from food-borne pathogenic bacteria.

Layered double hydroxide nanozyme (LDHzyme)-assisted high-performance electrochemical analysis of organ transplant therapeutic drug concentration

The variability in mycophenolic acid (MPA) exposure levels among organ transplant patients is substantial and directly influences the drug’s therapeutic efficacy. Therefore, precise monitoring of MPA blood concentrations is imperative to devise personalized diagnostic and treatment plans tailored to individual patient profiles. In this study, we developed a screen-printed carbon electrode (SPCE) incorporating Layered Double Hydroxide-based nanozymes (LDHzymes) and multi-walled carbon nanotubes (MWCNT) to achieve high-sensitivity and stable determination of MPA in blood samples. We synthesized three distinct LDHzymes via a straightforward co-precipitation method, selecting CuMn-LDHzyme for its superior electrochemical properties and laccase activity in the context of MPA detection. The sensor’s performance was enhanced by the amalgamation of CuMn-LDHzyme with MWCNT, leveraging the laccase-like activity of CuMn-LDHzyme and the exceptional conductivity of MWCNT to amplify the oxidation current response to MPA. This integration significantly bolstered the sensor’s detection capabilities. The developed electrochemical sensor exhibited remarkable characteristics, including high selectivity, stability, repeatability, and reproducibility. It demonstrated a notable sensitivity with a detection range of 0.5 µM to 200 µM for MPA, and a detection limit of 0.1 µM, effectively detecting MPA in mouse blood samples. These attributes underscore the sensors as promising tool for clinical drug detection, ensuring fast and precise monitoring of MPA levels in organ transplant patients. This innovative approach holds significant promise for advancing personalized medical care and improving therapeutic outcomes.

Dual Cocatalytic Sites Synergize NiFe Layered Double Hydroxide to Boost Oxygen Evolution Reaction in Anion Exchange Membrane Water Electrolyzer

AbstractNickel‐iron layered double hydroxide (LDH) is a promising cost‐efficient catalyst to replace noble metals for alkaline oxygen evolution reaction (OER), yet its intrinsic activity under high current density conditions is not satisfactory, which greatly constrains the industrial application of NiFe LDH catalysts. Herein, a new class of integrated Co and W co‐doped NiFe LDH catalysts is reported with dual cocatalytic sites for alkaline OER catalysis. The optimized Co2.8, W3.8‐NiFe LDH integrated catalyst has superior alkaline OER activity (255 mV@1000 mA cm−2) and excellent catalytic stability (200 h@500 mA cm−2). The turnover frequency value of Co2.8, W3.8‐NiFe LDH can reach 4.02 s−1 at 1.49 V versus RHE, which is 9.6 times higher than that of NiFe LDH and superior to the noble metal catalysts. Moreover, it can achieve 1.0 A cm−2 at 1.86 V and maintain 300‐h stable operation in anion exchange membrane water electrolyzer. Theoretical and experimental studies indicate that W sites promote the *OH adsorption and Co sites favor protons desorption of OH*. These dual cocatalytic sites jointly promote *O coverage, effectively accelerating alkaline OER kinetic.

A Combination of Adsorption and Photocatalysis Processes for the Removal of Direct Blue 71 (DB71) Dye on Fe-Doped Layered Double Hydroxides

Pollution in ecosystems has increased, especially in water, due to the pollutant agents that alter their chemical, physical and biological characteristics. This requires actions to resolve or at least reduce the harmful effects generated on the environment and people’s health. Many of the contaminants present in water come from the industrial sector, with the textile industry being one of the most impactful as it uses mostly synthetic dyes, which are characterized as being recalcitrant and toxic, so they cannot be degraded by conventional water treatment methods. Advanced oxidation processes have a great potential for application, especially those that use heterogeneous photocatalysis. The present research evaluates the efficiency in the adsorption and degradation of the triazoic Direct Blue 71 dye in aqueous mediums at concentrations of 600 ppm by the heterogeneous photocatalysis method. The photocatalysts used are layered double hydroxides (LDHs) with a Mg/Al = 3 ratio and are thermally activated and doped with Fe at 1, 3 and 5% w/w. The most efficient materials achieved removal percentages greater than 80% by means of a second-order kinetic model with a DB71 half-life decolorization of less than one hour; as shown by an HPLC study, the absence of intermediate products would confirm the mineralization of the dye.

Enhanced phosphorus adsorption performance of ZnAl-LDO by fluorine‑chlorine co-doping and synergistic mechanism exploration

Layered double hydroxides (LDHs) and their calcined products layered double oxides (LDOs) are widely used as adsorbents for pollutant removal. Their adsorption performance are significantly influenced by intercalated ions, while previous studies primarily focusing on the impact of individual ions. For the first time, this paper reports the mechanism of the synergistic enhancement of phosphate adsorption properties of LDO by bicomponent interlayer ions. The ZnAl-LDO by fluorine‑chlorine co-doping (F, Cl-ZnAl-LDO) exhibits excellent adsorption capacity of 158.9 mgP/g, surpassing that of single-component intercalation Cl-ZnAl-LDO and F-ZnAl-LDO, as well as most LDH-based adsorbents. Further research and density functional theory calculations indicate the differential adsorption enhancement mechanism of the interlayer ions. Chlorine functions as the exchanged anion, whereas fluorine facilitates the complete replacement of chloride ions and hydroxyl groups by phosphate. This finding highlights the potential of utilizing the synergistic effects between different interlayer ions to design and synthesize advanced phosphate adsorbent materials.

Interactions between antibiotic removal, water matrix characteristics and layered double hydroxide sorbent material

Sorption by layered double hydroxides (LDH) is gaining substantial interest for remediating emerging contaminants, including pharmaceuticals from wastewaters. Findings from a sorbent material performing successfully in lab-based studies using non-environmental (laboratory-sourced) water cannot be assumed to translate to equal performance under environmental downstream applications. However, studies evaluating sorbent material performance for removal of pollutants and understanding material interactions with environmental waters are limited. This study evaluates the removal of the antibiotic amoxicillin (AMX) using a Mg2Al–NO3-LDH sorbent material from laboratory-grade water and wastewater effluent (WWE). AMX is successfully removed (94.53 ± 4.30 % within 24 h) in laboratory-grade water (under batch sorption conditions: 100 μg/L AMX, 0.2 g/L LDH, 20 °C). The comparison of LDH removal performance in laboratory grade and WWE shows a decreased maximum removal of AMX in WWE (13.39 ± 5.53 %). A lower final AMX concentration is observed in the WWE without the presence of LDH, compared to the ‘removal’ experiments in WWE with the presence of LDH, indicating a contribution of non-sorption removal pathways of AMX. This is proposed to be due to the difference in metal concentrations in the WWE with and without LDH present. The presence of LDH is found to decrease concentrations of metal pollutants in WWE, such as Zn concentration decreasing by 85 % over 24 h, changing water characteristics. Overall, this paper reports that an LDH performs differently in laboratory-sourced water and a wastewater effluent. This provides evidence that sorbent material performance needs to be evaluated in complex water matrices to ensure that it is representative of how a sorbent material will perform in an environmental application, which is the end goal of developing such technologies. Finally, good practice recommendations are provided for future lab-scale sorption experiments evaluating the performance of any new sorbent materials for water treatment applications.