Structure Of Layered Double Hydroxides Research Articles

Efficient removal of Congo red from aqueous solutions using calcined and uncalcined MgZnFe ternary layered double hydroxide (LDH)

This study investigates the textile industries' dye Congo-red removal from aqueous solution using the calcined and uncalcined [Mg0.52+Zn0.252+Fe0.253+(OH)2].(CO32−)0.125.H2O ternary layered double hydroxide (LDH). XRD confirms the successful formation of the crystalline structure of LDH. FTIR analysis shows that the peak position at 1108 cm−1, which indicates the presence of S = O group. TEM analysis reveals the formation of a hexagonal shape morphology, whereas BET measurements demonstrate an improvement in surface area after calcination. This study analyzed dye adsorption, which is affected by interaction time, solution pH, and adsorbent dosage. The adsorption data is analyzed using the Langmuir isotherm and Freundlich isotherm, while the kinetics data is analyzed using pseudo-first-order, pseudo-second-order, and intraparticle diffusion models. The change in enthalpy (ΔH0) being positive and the change in Gibbs free energy (ΔG0) being negative designates that the adsorption process is endothermic and occurs spontaneously. The Langmuir isotherm model analyzed the adsorption isotherm data and calculated the amount of adsorbate adsorbed by adsorbent. The maximum amount of Congo-red adsorbed by calcined and uncalcined layered double hydroxide are 205.76 and 89.76 mg g-1. These results suggested that calcined layered double hydroxide is a significant adsorbent for removing effluents from wastewater.

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.

Leaching Peculiarity of Uranium-Containing Layered Double Hydroxide Sediment Varied with Environmental Anions.

In this research, we focus our attention on the leaching peculiarity of uranium-containing Mg-Al layered double hydroxide (LDH) which is one kind of waste sediment in uranium tailings, generated by the alkalinization of uranyl raffinate. The effect of inorganic (CO32-, SO42-, PO43-) and organic (C2O42-, C6H6O72-, C6H16O24P62-) anions were investigated. Atomic force microscopy result showed that the thickness of CO32--LDH increased to 8.6 nm compared to original LDH whose thickness was 6.7 nm. Compared with the control sample (5.58 μm), the grain size with C6H16O24P62- anion grew to 7.04 μm. A large amount of CO32- can stay in LDH, up to 1.78 mol percent, while the C6H16O24P62- anion was only 0.41 mol percent. X-ray diffraction results showed that the anions could change the crystal structure of LDH, especially the C6H18O24P6 anion, and theoretical calculation also conformed this result. The leaching tests showed that the introduction of anions improved the leaching efficiency of UO22+ from LDH. The introduction of anions destroyed the super buffer property of LDH. Theoretical calculation results indicated that the anions could grab UO22+ and help the UO22+ escape from the LDH. This research gave guidance for long-term disposal of uranium-containing tailings.

Atomic-level structural engineering of La-doped CoMoP composite for enhanced overall water splitting

A series of La-doped CoMoP composites were fabricated through an in-situ phosphorization strategy with La–CoMo layered double hydroxide (LDH) as precursors. The homogenous dispersion of metal ions within the LDH structure facilitated the creation of a uniformly atomic-level La-doped CoMoP composite. Among these, the 5 % La-doped CoMoP exhibited the best performance, requiring only 41 mV overpotential for hydrogen evolution reaction (HER) and 303 mV for oxygen evolution reaction (OER) to reach a current density of 10 mA cm−2. For overall water splitting, it achieved a current density of 10 mA cm−2 at a cell voltage of just 1.61 V and maintained a stable performance over 24 h. The modulation effect of rare-earth elements, combined with the synergistic interactions among transition metal ions, contributes to its excellent bifunctional electrocatalytic performance.

Partially amorphous NiFe layered double hydroxides enabling highly-efficiency oxygen evolution reaction at high current density

Layered double hydroxide (LDH) serves as an innovative catalyst for water electrolysis, showcasing outstanding performance in the oxygen evolution reaction (OER) under alkaline conditions. However, it faces challenges due to its low electrical conductivity and limited accessibility to active sites. In this work, the flexibility advantages of disordered amorphous and ordered crystals in NiFe LDH were combined to improve OER performance and maintain long-term stability. This combination induces a variety of effects, including improving the intrinsic activity, changing the OER mechanism from adsorb evolution mechanism (AEM) to lattice oxygen mechanism (LOM), and promoting the reaction kinetics of the catalyst. Moreover, the porous structure of NiFe LDH can efficiently alleviate the issue of local acidic environment induced by prolonged OER reaction, satisfying the criteria for long-term stability. Therefore, the NiFe-2.0 LDH catalyst only requires an ultralow overpotential of 189 mV at a current density of 10 mA cm−2 with Tafel slope of 43 mV dec−1. More importantly, the catalyst not only displays excellent electrocatalytic activity with an overpotential of 289 mV but also represents an outstanding stability over 80 h at an ultra-high current density of 1 A cm−2. This study provides a promising strategy for optimizing the catalytic activity and stability of catalyst at ampere current density, which is expected to achieve commercial applications.

Doxorubicin-Intercalated Li-Al-Based LDHs as Potential Drug Delivery Nanovehicle with pH-Responsive Therapeutic Cargo for Tumor Treatment.

Clinical oncology is currently experiencing a technology bottleneck due to the expeditious evolution of therapy defiance in tumors. Although drugs used in chemotherapy work for a sort of cell death with potential clinical application, the effectiveness of chemotherapy-inducing drugs is subject to several endogenous conditions when used alone, necessitating the urgent need for controlled mechanisms. A tumor-targeted drug delivery therapy using Li-Al (M+/M3+)-based layered double hydroxide (LDHs) family has been proposed with the general chemical formula [M+1-x M3+x (OH)]2x+[(Am-)2x/m. n(H2O)]2x-, which is fully biodegradable and works in connection with the therapeutic interaction between LDH nanocarriers and anticancerous doxorubicin (DOX). Compositional variation of Li and Al in LDHs has been used as a nanoplatform, which provides a functional balance between circulation lifetime, drug loading capacity, encapsulation efficiency, and tumor-specific uptake to act as self-regulatory therapeutic cargo to be released intracellularly. First-principle analyses based on DFT have been employed to investigate the interaction of bonding and electronic structure of LDH with DOX and assess its capability and potential for a superior drug carrier. Following the internalization into cancer cells, nanoformulations are carried to the nucleus via lysosomes, and the mechanistic pathways have been revealed. Additionally, in vitro along with in vivo therapeutic assessments on melanoma-bearing mice show a dimensional effect of nanoformulation for better biocompatibility and excellent synergetic anticancer activity. Further, the severe toxic consequences associated with traditional chemotherapy have been eradicated by using injectable hydrogel placed just beneath the tumor site, and regulated release of the drug has been confirmed through protein expression applying various markers. However, Li-Al-based LDH nanocarriers open up new design options for multifunctional nanomedicine, which has intriguing potential for use in cancer treatment through sustained drug delivery.

Adsorption of Fluoride Ions Using Si–Al–Mg Layered Double Hydroxides

ABSTRACT Removal of fluoride ions from water environments has become a research topic because high concentrations of fluoride ions in drinking water are harmful to the human body. The adsorption of fluoride ions by a Si – Al – Mg layered double hydroxide (LDH) was investigated in this study. The prepared adsorbent had a hydrotalcite-like LDH structure, which was decomposed by calcination and reconstructed upon contacting water. The adsorption process followed pseudo-second-order kinetics. Granulation of the adsorbent for application to chromatographic operation decreased the adsorption rate constant. Adsorption of fluoride ions was high at 7 < pHeq <10 and decreased at higher pHs. The adsorption mechanism involved ion exchange between the fluoride ions in aqueous solution and chloride ions in the adsorbent as well as physisorption via van der Waals forces. The adsorbent was selective towards fluoride ions over nitrate and sulfate ions, although the adsorption of fluoride ions was suppressed in the presence of chloride, carbonate, and phosphate ions. Chromatographic operation using the granulated adsorbent with an alumina-based binder was characterized by slow kinetics, necessitating a low flow rate for the feed solution. The prepared adsorbent was also used to selectively adsorb fluoride ions from simulated wastewater produced by the semiconductor manufacturing process.

Construction of ZnAl LDH-Derived Sulfides with Etching Modification to Trigger Photocatalytic H2 Production and Degradation Oxidation.

Constructing novel functional photocatalysts represents a promising approach to optimize the energy band structure and facilitate the separation of photogenerated carriers. Layered double hydroxides (LDHs) exhibit notable advantages in photocatalysis due to the exceptional photoelectrochemical properties and elevated number of active surface atoms. However, an unsuitable band gap and limited carrier migration have inhibited their development in photocatalysis. Herein, we propose a novel in situ topological vulcanization strategy for optimizing the photocatalytic activity of ZnAl LDH-derived sulfides (ZnAlSx). The subsequent etching process via a 1 M NaOH solution was introduced to construct the ZnSx photocatalysts. Then, the crystallinity of the crystals was enhanced by etching to further improve the catalytic activity and stability of ZnSx. The as-synthesized ZnSx shows an excellent photocatalytic hydrogen production rate (11.89 mmol/g/h) and tetracycline degradation efficiency (91.94%) under light illumination, and its hydrogen evolution efficiency is approximately 176 and 2 times greater than that of ZnAl LDH and ZnAlSx, respectively. The characterization and density functional theory (DFT) analysis confirmed that the surface electronic properties and energy band structure of ZnAl LDH were significantly optimized after experimental treatment, resulting in enhanced carrier separation and photooxidative reduction capacity. Combining in situ topological vulcanization and etching to realize the functional conversion of ZnAl LDH provides promising insights into the construction of high-performance, low-cost photocatalysts.

Dual-function CoNi-LDH hollow porous spheres for morphology-driven adsorptive removal and photo-oxidative degradation of anionic dyes

The layered double hydroxides (LDHs) emerged as a class of low-cost potential adsorbents for organic pollutant separation, whereas the deep study of organic dye separation regulated by LDH hollow morphology under ambient conditions is still lacking. To address this gap, ZIF-67, Bulk-CoNi-LDH, and HPS-CoNi-LDH materials of different morphology and porosity were synthesized and investigated in the dye separation process. Methyl orange (MO), congo-red (CR), methylene blue (MB), and rhodamine B (Rhb) dyes were selected as model dye pollutants. The spectroscopic and structural analysis reveals the HPS-CoNi-LDH exhibits less-aggregated 2D nanosheets, high BET surface area of 163.2 m2/g, large pore size of 12.29 nm, greater positive surface charges (27.5 mV), superior optical (2.18 eV), and charge-separation capabilities as compared to Bulk-CoNi-LDH, Which provides potential sites for adsorptive and photo-degradation for anionic dyes under natural sunlight. Therefore, it achieves a remarkable removal efficiency of 92.6% for methyl orange (15 ppm) with a superior kinetic rate of 3.0×10−2 min−1 within 90 min, outperforming Bulk-CoNi-LDH and ZIF-67 having removal efficiency of 71.7% and 40.8%, and kinetic rate of 1.35×10−2 and 0.5×10−2 min−1, respectively. Poor removal efficiency and kinetic by ZIF-67 was mainly due to its smaller pore size (1.16 nm) and surface-confined charges (6.13 mV). Additionally, HPS-CoNi-LDH exhibits superb selectivity (at a ppm level) and excellent recyclability under ambient conditions. The mechanism of photo-catalytic reaction is discussed. These results delineate the hollow morphological LDH structure could be a worthy candidate for selective wastewater treatment and useful for sustainable conditions, which points the way to other crucial anionic micropollutant remediation.

Syntheses of Ni-Based Layered-Double Hydroxide Materials Via Liquid Phase Deposition Method for Alkaline Water Electrolysis

For the sustainable society, hydrogen production has received much attention during decades. The alkaline water electrolysis process has been recognized as one of the important processes for hydrogen products. For the achievements of an effective water electrolysis system, the decrease of the overpotential on the oxygen evolution reaction (OER), which is the four-electron and proton transfer process. These complex 4-electron sluggish processes lead to the large energy losses in the whole water electrolysis. Although the noble catalysts such as IrO2 or RuO2 exhibit high OER activity, their large-scale applications are limited due to cost problem. From this point of view, the low-cost transition metal materials, especially Ni-based catalysts, have been extensively studied. And also, it has been reported that the well-defined layered double hydroxide (LDH) structures can promote water oxidation through the interlayer anion effects. Despite this fact, the specific procedures for the preparation of Ni-based LDH structures have not been well established. Therefore, in this study, we have investigated the preparation of Ni-based LDH structures in the aqueous solution at room temperature, the so-called liquid phased deposition (LPD) method.Through the LPD method, we have synthesized various types of Ni-based LDH structures. As an example, the Ni-Al LDH structures were synthesized on the conductive substrate. It was found that our synthesized Ni-Al LDH exhibited relatively high OER activity and durability against electrochemical potential cycling [1]. In addition, the dependencies of the OER activity on the interlayer anion species were clearly demonstrated. In addition, the other types of Ni alloy LDHs were also prepared and their OER activity was investigated. Through the electrochemical measurements, we have confirmed the advantages of our materials prepared by LPD methods as an anode for alkaline water electrolysis.

Architecting layered double hydroxides: Exploring their structural mastery and transformative influence on wood staining

Traditional wood staining processes involve the extensive use of inorganic salts and fixing agents. The exploration of a low-concentration yet highly efficient wood staining method is crucial for the low-carbon, environmentally friendly, and high-quality development of wooden products. In this study, we employed metal-organic framework (MOF) as precursors for layered double hydroxides (LDHs), achieving control over the coloration of poplar wood towards a blue-green hue through the hydrolysis-induced exchange between MOF and hydroxide ions, using an ultra-low concentration (0.016 mol/L) Cu2+ solution. Exploiting the unique micro-nano structure of LDHs and their anion exchange properties, we successfully engineered a superhydrophobic surface (WCA=151.8°) for wood by introducing hydrophobic long chains. The resulting stained wood exhibited superior water resistance, self-cleaning ability, wear resistance, resistance to UV aging, and mold prevention. A key highlight of our preparation process lies in the utilization of extremely low concentrations of metal ion solutions, emphasizing its environmentally friendly, efficient, and multifunctional characteristics. This research provides a novel and efficient green staining approach for wood, opening up new avenues for the high-quality and sustainable development of wood materials.

Styrene-butadiene-styrene block copolymer modified bitumen with ultraviolet absorbent intercalated layered double hydroxide: Compatibility and anti-ageing properties

2-hydroxy-4-methoxybenzophenone-5-sulfonic acid (ultraviolet absorbent, BP) intercalated layered double hydroxide (LDH) was synthesized to enhance the anti-ageing properties of styrene–butadiene–styrene block copolymer (SBS) modified bitumen (SMB). X-ray diffraction and UV–vis spectroscopy indicated that BP has been successfully substituted into LDH interlamination, and BP intercalated LDH (BP-LDH) exhibited better UV absorptive capacity than LDH. Then, the physical and rheological properties, chemical structure of BP-LDH and LDH modified SMB before and after ageing were comprehensively studied. Compared with LDH, BP-LDH possessed the smaller difference in solubility parameters (δ) and the stronger interaction energy (Einter) with SMB, resulting in the better compatibility of BP-LDH modified SMB. The high-temperature stability of SMB was promoted with the addition of BP-LDH or LDH, especially BP-LDH. After ageing, the temperature susceptibility, low-temperature anti-cracking and anti-fatigue cracking of SMB were deteriorated, the oxygen-containing groups (C = O and S = O) in SMB noticeably increased and carbon–carbon double bond (C = C) concurrently decreased. LDH could mitigate the ruin of ageing on the performance and chemical structures of SMB, and strengthen the anti-ageing performance. Furthermore, BP intercalated modification could further significantly heighten the performance of LDH.

Acetate anions intercalated Fe/Mg-layered double hydroxides modified biochar for efficient adsorption of anionic and cationic heavy metal ions from polluted water

The simultaneous removal of anionic and cationic heavy metals presents a challenge for adsorbents. In this study, acetate (Ac-) was utilized as the intercalating anion for layered double hydroxide (LDH) to prepare a novel biochar composite adsorbent (Ac-LB) designed for the adsorption of Pb(II), Cu(II), and As(V). By utilizing Ac- as the intercalating anion, the interlayer space of the LDH was enlarged from 0.803 nm to 0.869 nm, exposing more adsorption sites for the LDH and enhancing the affinity for heavy metals. The results of the adsorption experiments showed that the adsorption effect of Ac-LB on heavy metals was significantly improved compared to the original FeMg-LDH modified biochar composites (LB), and the maximum adsorption capacity of Pb(II), Cu(II), and As(V) were 402.70, 68.50, and 21.68 mg/g, respectively. Wastewater simulation tests further confirmed the promising application of Ac-LB for heavy metal adsorption. The analysis of the adsorption mechanism revealed that surface complexation, electrostatic adsorption, and chemical deposition were the main mechanisms of action between heavy metals (Pb(II) and Cu(II)) and Ac-LB. Additionally, Cu(II) ions underwent a homogeneous substitution reaction with Ac-LB. The adsorption process of As(V) by Ac-LB mainly relied on complexation and ion-exchange reactions. Lastly, the modification of the LDH structure by Ac− as an intercalating anion, thereby increasing the affinity for heavy metals, was further illustrated using density-functional theory (DFT) calculations.

A 2D self-cascade catalytic system based on CoCuFe-LDH nanosheets for accelerated healing of infected wounds

The emergence of drug-resistant bacteria has rendered traditional antibiotics ineffective, posing a serious threat to human health. There is an urgent need to find alternative antimicrobial agents. Inspired by enzyme immobilization and multi-enzyme biocatalysis, we have designed a tri-metal layered double hydroxide (LDHs)-based cascade catalytic system (CoCuFe-LDH@Gox nanosheets) for treating drug-resistant bacterial infections and promoting wound healing. The synergistic effects of the Co, Cu, and Fe in the tri-metal LDHs structure endow CoCuFe-LDH nanosheets with excellent peroxidase (POD)-like activity. The large specific surface area of CoCuFe-LDH nanosheets render them ideal carriers for glucose oxidase (Gox). CoCuFe-LDH@Gox nanosheets can catalyze glucose to produce gluconic acid and H2O2. The generated gluconic acid decreases the local pH, further enhancing the POD-like activity of CoCuFe-LDH@Gox nanosheets at wound site. CoCuFe-LDH@Gox nanosheets can then catalyze H2O2 generating hydroxyl radicals (•OH) to effectively kill drug-resistant bacteria. This synergistic integration of the catalytic LDHs and the Gox components enables the cascade catalytic system to be highly effective against drug-resistant bacteria. In addition to its remarkable antibacterial properties, this LDHs-based system also exhibits excellent biocompatibility and considerable immunomodulatory capabilities. It can accelerate the healing of drug-resistant bacteria-infected wounds by inhibiting the inflammatory response and regulating macrophage polarization. These multifunctional attributes make the CoCuFe-LDH@Gox nanosheets a highly promising candidate for the treatment of drug-resistant bacterial infections in future clinical applications.

Valproate intercalated in layered double hydroxides: Synthesis, characterization, release kinetics and biocompatibility studies

Layered double hydroxides (LDHs) are biocompatible materials with excellent anion exchange properties, making them suitable for use as drug carriers by incorporating the drug in its anionic form within their layered structure. In this study, an LDH was synthetized through ion exchange with valproate (VAL), an anticonvulsant drug, using an LDH with nitrate as the parent material. The resulting LDH-VAL sample underwent a comprehensive multi-technique characterization using XRD, TG-DSC, TEM, SEM, EDS, FTIR, XPS and zeta potential measurements. Dissolution kinetics and VAL release kinetics in an ample range of pH (3–9), along with biological assays to test biocompatibility, were also performed. All techniques confirmed the successful intercalation of the drug into the LDH structure, displacing all the nitrate ions of the parent material and increasing the basal spacing d003 from 8.8 Å to 18.3 Å. VAL release in NaCl and physiological buffer solutions was incongruent with LDH dissolution, clearly indicating that VAL release was controlled by an ion exchange process. In 0.9 % NaCl solutions, 90–100 % of VAL was released with only 15–20 % of LDH dissolution, and in buffer solutions 100 % of VAL was released with, at the most, 30 % of LDH dissolution. Biological assays, including lactate dehydrogenase activity, serum calcium concentration and histological analysis of blood samples, confirmed that the prepared LDH-VAL is a biocompatible material with a potential use as a nanodrug carrier.

Conversion of secondary aluminum dross into hierarchical carbonate-intercalated Mg-Al layered double hydroxide for efficient CO2 capture

This paper explores the preparation of hierarchical Mg-Al layered double hydroxide (LDH) from secondary aluminum dross waste for the first time. The aluminum content of the waste was initially extracted in the form of a sodium aluminate solution using a multistep wet chemical process. CO3-intercalated Mg-Al LDH was then prepared at pH values of 9 and 11 by adding magnesium chloride to a mixed solution of sodium aluminate and sodium carbonate. The X-ray diffraction (XRD) analysis revealed that a pure LDH structure could be formed at pH 11. The quantification of the XRD data revealed that the synthesized LDH had an interlayer spacing of 3.1 Å. The microstructural porosity was 0.76 cm3/g, and the specific surface area was 134 m2/g. The field emission scanning electron microscopy (FESEM) analysis revealed a hierarchical layered structure composed of flake-like particles in the microstructure. The elemental mapping of the synthesized LDH showed a proper distribution of Mg, Al, C, and O. The synthesized Mg-Al-CO3 LDH was then used for a study on CO2 capture. The CO2 capture experiments demonstrated that the amount of CO2 adsorption is influenced by temperature, gas pressure, adsorbent mass, and exposure duration. Investigating the effects of time and temperature revealed that a CO2 adsorption of 0.94 mmol/g can be achieved at a temperature of 25 °C during a 90-minute exposure period. Varying the gas pressure from 1 to 2.5 bar, while maintaining a constant temperature of 25 °C and an adsorbent mass of 1.5 g, resulted in an increase in CO2 adsorption from 1.7 to 2.3 mmol/g. Reusability tests showed that the LDH could maintain a satisfactory adsorption value of 0.84 mmol/g after 5 cycles, indicating its potential for repeated use.

Binder free cobalt Manganese layered double hydroxide anode conjugated with bioderived rGO cathode for sustainable, high-performance asymmetric supercapacitors

Metal-organic frameworks (MOFs) possessmultifunctional characteristicssuch as tuneable pore structure and high specific surface area and are being designed with great interest to enhance the electrochemical properties of current energy storage devices. In this aspect, MOFs-derived layered double hydroxides (LDHs) are important candidates for advanced supercapacitors due to their high electrochemical activity and electric conductivity. Herein, we report synthesis of Cobalt Manganese layered double hydroxides (CoMn LDH) utilising Co MOF as a precursor via ion exchange method, while optimising the dosage of Mn to achieve the best possible structural outcome. The unique structure of CoMn LDH expressed high electrochemical parameters possessing specific capacitance of 1305F/g at 1 A/g. Afterwards, an asymmetric supercapacitor device was fabricated employing CoMn LDH as cathode and coffee grounds derived rGO (reduced graphene oxide) as anode. The as-prepared asymmetric supercapacitor device demonstrated a maximum working potential window of 1.2 V with energy and power density of 23.8 Wh/kg and 0.30 kW/Kg respectively. The device also exhibits superiorcoulombic efficiency and capacitance retention of 71.11 % and 82.7 % respectively over 3010 charge–discharge cycles that represents an effectiveapproach towards sustainable and effectiveenergy storage devices. In a nutshell, our study centred on adjusting composition, engineering structures, and assembling devices.

ZnAl LDH-based Derivative Materials as Photocatalysts: Synthesis, Characterization, and Catalytic Performance in Tetracycline Degradation

Layered Double Hydroxide (LDH)-derived materials exhibited different characteristics from LDH precursors. The conversion of ZnAl LDH into its derivative material has been carried out to find the best catalyst for TC degradation. ZnAl (LDH)-based catalysts in this study have been effectively synthesized using coprecipitation, calcination, and restacking procedures. ZnAl Layered Double Oxide (LDO) is derived from the calcination of ZnAl LDH at 500°C. ZnAl LDH was also modified by adding Garcinia mangostana pericarp extract (GME). XRD, FT-IR, UV-DRS, and SEM-EDX were used to investigate the synthesized catalyst. ZnAl LDH exhibited the typical LDH FT-IR spectra, whereas ZnAl LDO showed metal oxide-like spectra, and the ZnAl-GME composite displayed the combination spectra of precursor material. The ZnAl LDH XRD diffraction pattern exhibited the attributes of a layered material, whereas the other three catalysts did not. Calcination destroyed the layered structure of ZnAl LDH, whereas the addition of GME to LDH and LDO generated a single-layered composite. The modified ZnAl-GME composite showed a decrease in both particle size and bandgap energy. At an ideal pH of 5, the synthesized catalyst was used in a batch system photodegradation of 5 mg/L Tetracycline (TC), employing solar light irradiation. ZnAl LDO holds the most significant catalytic activity and structural stability through the fifth regeneration cycle, degraded TC up to 100% in 90 minutes.

Graphene Materials from Coke-like Wastes as Proactive Support of Nickel-Iron Electro-Catalysts for Water Splitting.

Graphene materials, used as electrocatalyst support in green hydrogen production, contribute to increasing the efficiency and robustness of various systems. However, the preparation of a hybrid catalyst containing graphene materials from industrial wastes is still a challenge due to the heterogeneity of the waste. We report the synthesis of 3D electrodes using graphene oxides (GOs) from industrial waste (IW) prepared by immersion onto Toray carbon paper as a 3D support onto GO suspensions and electrodepositing NiFe layered double hydroxides (LDHs). Standard graphite was also used as the reference. The morphology of the two hybrid electrodes was determined by SEM, HRTEM, XPS. Although very similar in both, the sample containing graphene from IW (higher Csp3 hybridization in the graphene layer) has a NiFe phase with less crystallinity and larger presence of Fe2+ ions. These electrodes exhibited similar activity and stability as electrocatalysts of the oxygen evolution reaction (OER), demonstrating the proactive effect of the graphene into the 3D electrode even when this is prepared from heterogeneous industrial waste. Moreover, the defective graphenic structure of the waste GO enhances the reaction kinetics and improves the electron transfer rate, possibly due to the small differences in the electrodeposited NiFe LDH structure.

Ni,Fe,Co-LDH Coated Porous Transport Layers for Zero-Gap Alkaline Water Electrolyzers.

Next-generation alkaline water electrolyzers will be based on zero-gap configuration to further reduce costs related to technology and to improve performance. Here, anodic porous transport layers (PTLs) for zero-gap alkaline electrolysis are prepared through a facile one-step electrodeposition of Ni,Fe,Co-based layered double hydroxides (LDH) on 304 stainless steel (SS) meshes. Electrodeposited LDH structures are characterized using Scanning Electron Microscopy (SEM) confirming the formation of high surface area catalytic layers. Finally, bi and trimetallic LDH-based PTLs are tested as electrodes for oxygen evolution reaction (OER) in 1 M KOH solution. The best electrodes are based on FeCo LDH, reaching 10 mA cm-2 with an overpotential value of 300 mV. These PTLs are also tested with a chronopotentiometric measurement carried out for 100 h at 50 mA cm-2, showing outstanding durability without signs of electrocatalytic activity degradation.