MgAl-layered Double Hydroxide Research Articles

Recyclable and Reusable Catalyst of Chitosan-Modified MgAl-Layered Double Hydroxide for Biodiesel Production

Recyclable and Reusable Catalyst of Chitosan-Modified MgAl-Layered Double Hydroxide for Biodiesel Production

Preparation and Catalytic Properties of Gold Single-Atom and Cluster Catalysts Utilizing Nanoparticulate Mg-Al Layered Double Hydroxides.

Au single atoms and clusters were stabilized on Mg-Al layered double hydroxide nanoparticles (LDH NPs), and the obtained Au@LDH NPs were supported on SiO2 and CeO2. After hydrogen reduction, Au single atoms were found together with Au clusters on LDH/SiO2. In contrast to Au single-atom catalysts which are deposited in metal vacancies of oxide supports, the LDH NPs stabilize very small Au species despite the absence of metal vacancies. The obtained Au(0)@LDH/SiO2 catalyzed aerobic oxidation of alcohols, and Au single atoms maintained after the reaction. Given that only Au NPs were observed on bulk LDH, the abundant surface OH group of LDH NPs would contribute to stabilize Au, resulting in higher activity than Au/LDH-bulk. After calcination to transform LDH to mixed metal oxide (MMO), the obtained Au(0)@MMO/SiO2 also exhibited high catalytic activity. Moreover, Au(0)@LDH/CeO2 exhibited higher activity and excellent selectivity for hydrogenation of 4-nitrostyrene to 4-aminostyrene than conventional Au catalysts such as Au/CeO2 and Au/TiO2. We demonstrated that Au size can be minimized using LDH NPs, exhibiting high catalytic performance. The basic surface OH groups of LDH would be also beneficial for deprotonation of alcohols and heterolytic dissociation of H2 in the catalytic reactions.

MgAl-Layered Double Hydroxide-Coated Bio-Silica as an Adsorbent for Anionic Pollutants Removal: A Case Study of the Implementation of Sustainable Technologies.

The adsorption efficiency of Cr(VI) and anionic textile dyes onto MgAl-layered double hydroxides (LDHs) and MgAl-LDH coated on bio-silica (b-SiO2) nanoparticles (MgAl-LDH@SiO2) derived from waste rice husks was studied in this work. The material was characterized using field-emission scanning electron microscopy (FE-SEM/EDS), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopic (XPS) techniques. The adsorption capacities of MgAl-LDH@SiO2 were increased by 12.2%, 11.7%, 10.6%, and 10.0% in the processes of Cr(VI), Acid Blue 225 (AB-225), Acid Violet 109 (AV-109), and Acid Green 40 (AG-40) dye removal versus MgAl-LDH. The obtained results indicated the contribution of b-SiO2 to the development of active surface functionalities of MgAl-LDH. A kinetic study indicated lower intraparticle diffusional transport resistance. Physisorption is the dominant mechanism for dye removal, while surface complexation dominates in the processes of Cr(VI) removal. The disposal of effluent water after five adsorption/desorption cycles was attained using enzymatic decolorization, photocatalytic degradation of the dyes, and chromate reduction, satisfying the prescribed national legislation. Under optimal conditions and using immobilized horseradish peroxidase (HRP), efficient decolorization of effluent solutions containing AB-225 and AV-109 dyes was achieved. Exhausted MgAl-LDH@SiO2 was processed by dissolution/precipitation of Mg and Al hydroxides, while residual silica was used as a reinforcing filler in polyester composites. The fire-proofing properties of composites with Mg and Al hydroxides were also improved, which provides a closed loop with zero waste generation. The development of wastewater treatment technologies and the production of potentially marketable composites led to the successful achievement of both low environmental impacts and circular economy implementation.

Effects of amino alcohols-intercalated MgAl-LDH nanocomposites on the properties of sulfoaluminate cement-based materials

Sulfoaluminate cement-based materials (SCBMs) have low mechanical properties in the early stages when they are used in grouting reinforcement engineering. The mechanical properties of cement-based materials can be improved by nanotechnology. Hydrotalcite is a layered anionic clay with adjustable interlayer anions and nanometer spacing. To date, the effect of amino alcohols (ethanolamine (MEA), diethanolamine (DEA), and triethanolamine (TEA))-intercalated MgAl-layered double hydroxides (LDH) nanocomposites (denoted as MgAl-LDH-TEA, MgAl-LDH-DEA, and MgAl-LDH-MEA) on the properties of SCBMs have not been studied. Herein, we demonstrate that intercalated MgAl-LDH exhibit a decrease in crystallinity, an increase in particle size, and improved early mechanical properties compared to unmodified LDHs. MgAl-LDH modified by TEA, DEA, and MEA all have a nucleation effect and provide nucleation sites for ettringite. Simultaneously, the intercalated hydrotalcite can release higher concentrations of magnesium ions into the slurry, forming a magnesium-containing ettringite phase and accelerating the hydration of SCBMs. Modified MgAl-LDH can also release amino alcohols, affecting the hydration process of the paste. The modified LDHs affect the hydration and compressive strength of SCBMs owing to the combined action of the nucleation of LDHs and the release of magnesium ions and amino alcohols compounds.

Synergistic effect of carbon molecular sieve and alkali metal nitrate on promoting intermediate-temperature adsorption of CO2 over MgAl-layered double hydroxide

The development of intermediate-temperature adsorbents with high CO2 adsorption capacity is crucial for the tandem integration with CO2 hydrogenation catalyst, aimed at enhancing economy viability and minimizing energy consumption in Carbon capture, utilization and storage (CCUS). Although certain porous carbon materials (PCM) have been employed to enhance CO2 adsorption capability of layered double hydroxide (LDH), there remains an urgent necessity to identify more cost-effective and efficient PCM alternatives. Herein, alkali metal nitrates ((Li0.3Na0.18K0.52)NO3, hereafter referred to as LiNaK) modified layered double hydroxide (LDH)/carbon molecular sieve (CMS) composite (LiNaK-LDH/CMS) as promising adsorbents for CO2 capture was reported. The effects of CMS addition and nitrate loading, the calcination and adsorption temperature, as well as the cycling stability were investigated systematically. The results revealed that the CO2 capture capacity of the LiNaK-modified layered double oxide (LDO)/CMS composite (30 mol%LiNaK-LDO/CMS15%)-incorporating with 15 wt% CMS addition and 30 mol% nitrate loading-achieved a remarkable CO2 adsorption capacity of 1.32 mmol/g at 300 °C due to the synergetic interactions between CMS and nitrate; this represents nearly a sevenfold enhancement compared to initial LDO performance. Moreover, the 30 mol%LiNaK-LDO/CMS15% adsorbent also demonstrated commendable cyclic stability after ten adsorption/desorption cycles, retaining over 85 % of its initial adsorption capacity within half of adsorption time. Based on both obtained adsorption performance and characterization data from the adsorbents, a pre-adsorption enhancing CO2 intermediate-temperature adsorption mechanism over LiNaK-LDH/CMS composite through air calcination processes is proposed. This study significantly advances LDH-based adsorbent for future research into CO2 intermediate-temperature adsorption.

Physico-chemical Studies of Alkali-Free MgAl Layered Double Hydroxide for Electrolyte Conductivity Studies at Ambient Temperature

Physico-chemical Studies of Alkali-Free MgAl Layered Double Hydroxide for Electrolyte Conductivity Studies at Ambient Temperature

Effects of Mg-based admixtures on chloride diffusion in alkali-activated fly ash-slag mortars

This study evaluated the effects of various Mg-based admixtures, including magnesium oxide (MgO), layered double hydroxides (LDH), and calcined layered double hydroxides (CLDH), on the chloride resistance of alkali-activated fly ash-slag (AAFS) mortars. To this end, chloride diffusion tests were conducted on AAFS mortars containing 5 wt% MgO, Mg-Al-CO3 LDH, and CLDH. The results revealed that all Mg-based admixtures investigated in this study enhanced the chloride resistance of AAFS mortars. The inclusion of MgO led to a finer pore structure and promoted the formation of more Friedel's salt, thereby enhancing the chloride resistance performance. Although the inclusion of Mg-Al-CO3 LDH and CLDH resulted in more lager pores in the matrix, leading to slightly lower compressive strength, the overall content of Mg-Al LDH and Friedel's salt formed in the system increased, which led to an improved chloride binding capacity and enhanced chloride resistance.

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.

Effect of reagent addition and aging by microwave on the structure of layered double hydroxides

A series of MgAl-layered double hydroxides (MgAl-LDHs) were prepared by variable pH precipitation. The addition of the metal (M) containing solution to the base (B=NaOH) solution, either rapidly (r) or dropwise (d), led to the obtention of the MBr and MBd samples, respectively. In the other hand, by inverting the order of the added solution (pH increase methodology), BMr and BMd were obtained. The BMd sample was microwave aged at 80 °C, 150 °C and 220 °C for 45 min. The results of powder X-ray diffraction showed that rapid precipitation produces more crystalline LDHs than those obtained by dripping. The crystallinity of BMd was improved by microwave aging. All precipitation conditions produced nanoparticles with an average size of around 27.5 nm, which increased almost 5-fold with the microwave treatment. Precipitation by increasing pH gave LDHs with low pore volume, which increased during the heat treatment. Nevertheless, the specific surface area decreased significantly with aging temperature due to the increase in particle size.

Removal of Hg(II) with MgAl-layered double hydroxide functionalized by schiff base ligands: Application and condition optimization

To effectively remove heavy metal Hg(II) from water bodies, a novel adsorbent of MgAl-layered double hydroxide (LDH) was designed and functionalized with Schiff base. The characterization results of the adsorbent (MgAl-LDH@SiO2-AG) show that the Schiff base polymer was successfully coated onto the outside surface of MgAl-LDH with hexagonal structure. The theoretical maximum adsorption capacity to Hg(II) is 228.46 mg/g at pH 7 and 298 K. The different pH solutions were investigated from pH 2 to 8, and the optimal capacity of MgAl-LDH@SiO2-AG toward Hg(II) achieves 268.7 mg/g at pH = 7.2, T = 36.8 °C, C0 = 32.1 mg/L and dosage = 0.083 g/L. In reality, the adsorbent not only exhibits efficient removal of Hg(II) in various water bodies, including lake water, river water, effluent from sewage treatment plant, but also has an excellent selectivity in electroplating wastewater containing different heavy metal ions. Low contents of TN and TP in real wastewater have less effect on the removal of Hg(II). Moreover, the prepared adsorbent had a good reusability and stability. The reaction mechanism mainly involves chelation with nitrogen/oxygen-containing groups and the predominant participation of nitrogen atoms in the Schiff base functional group. The removal of Hg(II) relies on the pseudo-second-order kinetics and Langmuir model, and is an endothermic and spontaneous chemical reaction. The present work offers a practical method for preparing highly effective adsorptive materials with the LDH composites and for the treatment of heavy metal Hg(II) from water bodies.

Highly efficient removal of Pb2+ and Cd2+ on MgAl-LDH modified with carbon dots, citric acid and amino silane: Kinetic, isothermal and mechanistic studies

To increase active sites for Pb2+ and Cd2+ removal, MgAl-layered double hydroxide (MgAl-LDH) was modified with carbon dots (CDs), citric acid (CA) and 3-triethoxysilylpropylamine (APTES) via a step-by-step hydrothermal method. The resultant composite (LCC-NH2) exhibited excellent removal capacity of 511.5 mg/g and 166.0 mg/g for Pb2+ and Cd2+ at 298 K, which were 6-fold and 12-fold that of MgAl-LDH. Pb2+ and Cd2+ removal fits best to the pseudo-second-order kinetic and Langmuir isotherm models. And thermodynamic studies indicated the adsorption of Pb2+ and Cd2+ on LCC-NH2 was spontaneous. In a multifaceted metal system, LCC-NH2 still demonstrated superior removal capacity for Pb2+ and Cd2+. However, it showed greater selectivity for Pb2+ than Cd2+. The mechanism studies indicated the efficient removal of Pb2+ and Cd2+ was mainly attributed to the synergistic effect encompassing isomeric substitution, chelation, and precipitation. Therefore, LCC-NH2 offers considerable potential for practical applications in environmental remediation efforts.

Photo-assisted arsenic removal by MgFeAl-layered double hydroxide: Understanding the activation of Al3+ by Fe3+ incorporation

Due to weak affinity of the adsorbents for As(III), the arsenic removal, especially in the form of H3AsO3, remains to be highly challenging. Herein, the MgAl-layered double hydroxide (MgAl-LDH) and the MgFeAl-LDH are prepared successfully by coprecipitation method. Under full spectrum illumination, the MgAl-LDH shows As(III) removal from 20 mg/L to 2.19 mg/L, while the MgFeAl-LDH is able to reduce As(III) from 20 mg/L to 0.025 mg/L, which is two orders of magnitude lower than that by MgAl-LDH and significantly below the groundwater limit of 0.05 mg·L−1 of As(III). Moreover, the removal capacity of MgFeAl-LDH is 2.2 times (101.6 mg g−1) that of MgAl-LDH (45.7 mg g−1). Note that the MgFeAl-LDH can reach equilibrium in 1 h and the kinetic curve is in good agreement with the pseudo-second-order model. XPS and DFT reveal that the presence of Fe3+ in MgFeAl-LDH increases the electron density of Al3+ via electron transfer from Fe3+ to Al3+, reducing the adsorption energy of As on Al3+ sites and efficiently activating Al3+, while the adsorption sites expand from single Mg2+ sites in MgAl-LDH to Mg2+, Al3+ and Fe3+ sites in MgFeAl-LDH. Furthermore, EXAFS indicates that the incorporation of Fe3+ in MgFeAl-LDH results in enhanced photo-oxidation of H3AsO3 to HAsO42− and extends the light absorption by generating intermediate energy levels, thereby improving the As removal capacity.

Layered double hydroxides for simultaneous and long-term immobilization of metal(loid)s in soil under simulated aging

Soil contamination by toxic metals and metalloids poses a grave threat to food security and human well-being. Immobilization serves as an effective method for the remediation of soils contaminated by metal(loid)s. Nevertheless, the ability of soil amendments for simultaneous immobilization of cations and oxyanions, and the long-term effectiveness of immobilization need substantial improvements. In this study, we used a series of layered double hydroxides (LDHs), including Mg-Al LDH and Ca-Al LDH fabricated from pure chemicals, and one waste-derived LDH synthesized using granulated ground blast furnace slag (GGBS), for the immobilization of Cu, Zn, As, and Sb in a historically contaminated soil obscured from a mining-affected region. The LDHs were first subjected to iron (Fe) modification to enhance their short-term immobilization performances toward metal(loid)s. Furthermore, the long-term effectiveness of Fe-modified LDHs was examined via two sets of experiments, including column experiments simulating 2-year water leaching, and accelerated aging experiments simulating 100-year proton attack. It was observed that Fe-modified LDHs, either made from pure chemicals or GGBS, demonstrated promising long-term immobilization performances toward metal(loid)s. Results from this study are encouraging for the future use of LDHs for simultaneous and long-term immobilization of metal(loid)s in soil.

Effect of V2O7 4− anion intercalation on the microstructure and corrosion resistance of MgAl Layered Double Hydroxides films on LA43M Mg-Li alloy

ABSTRACT To improve the corrosion resistance of LA43M alloy, MgAl-NO3 −-Layered Double Hydroxides (LDH) was prepared on the surface of the alloy by an in situ hydrothermal method, and uniform and dense MgAl-V2O7 4−-LDH films were successfully obtained by ion-exchange over different times. SEM, XRD, EDS, electrochemical polarisation, EIS and hydrogen evolution experiments were conducted to analyse microstructure and corrosion resistance of these films. The results verified that with increase of the ion-exchange reaction time, the nanosheets of the MgAl-V2O7 4−-LDH film are larger in size, uniformly distributed, and slightly increased in thickness. The surface of the modified MgAl-V2O7 4−-LDH film grown for 4 h on the surface had a staggered and tilted manner, and the gaps between the nanosheets were small, making it more effective in blocking the corrosive medium. The MgAl-NO3 −-LDH film modified by V2O7 4− anion intercalation can further improve the corrosion resistance of the LA43M alloy.

Effectiveness of gellan gum scaffolds loaded with Boswellia serrata extract for in-situ modulation of pro-inflammatory pathways affecting cartilage healing

In this study, we developed a composite hydrogel based on Gellan gum containing Boswellia serrata extract (BSE). BSE was either incorporated directly or loaded into an MgAl-layered double hydroxide (LDH) clay to create a multifunctional cartilage substitute. This composite was designed to provide anti-inflammatory properties while enhancing chondrogenesis. Additionally, LDH was exploited to facilitate the loading of hydrophobic BSE components and to improve the hydrogel's mechanical properties. A calcination process was also adopted on LDH to increase BSE loading. Physicochemical and mechanical characterizations were performed by spectroscopic (XPS and FTIR), thermogravimetric, rheological, compression test, weight loss and morphological (SEM) investigations. RPLC-ESI-FTMS was employed to investigate the boswellic acids release in simulated synovial fluid. The composites were cytocompatible and capable of supporting the mesenchymal stem cells (hMSC) growth in a 3D-conformation. Loading BSE resulted in the modulation of the pro-inflammatory cascade by down-regulating COX2, PGE2 and IL1β. Chondrogenesis studies demonstrated an enhanced differentiation, leading to the up-regulation of COL 2 and ACAN. This effect was attributed to the efficacy of BSE in reducing the inflammation through PGE2 down-regulation and IL10 up-regulation. Proteomics studies confirmed gene expression findings by revealing an anti-inflammatory protein signature during chondrogenesis of the cells cultivated onto loaded specimens. Concluding, BSE-loaded composites hold promise as a tool for the in-situ modulation of the inflammatory cascade while preserving cartilage healing.

DNA programmed Mg-Al layered double hydroxide-based bi-adjuvant nanovaccines

Implementation of adjuvants is a requirement for inducing antigen-specific immune responses against infectious diseases. The conventional aluminum adjuvants used in clinical trials suffer from insufficient cellular immune response. Herein, we develop a bi-adjuvant nanovaccine containing receptor-binding domain (RBD) as antigen and DNA programmed Mg/Al layered double hydroxide (Mg/Al-LDH) as adjuvants, and thus achieve co-activation of potent humoral and cellular immune responses. The Mg/Al-LDH consisting of positively charged layers is firstly employed as scaffold to adsorb antigen via electrostatic interaction, and then CpG and dendritic cell (DC)-targeting aptamers co-encoded ultra-long DNA chains are easily decorated on the Mg/Al-LDH via interfacial assembly. The nanoscale formulations and interfacial targeting aptamers of nanovaccine facilitate their endocytosis by DC cells; the Mg/Al-LDH structure is acid-responsive and ensures the Al ions-inducing antigen cross-presentation for durable generation of antibody (Th2 immune response); and the agonist CpG in DNA chains can bind to the Toll-like receptor 9 (TLR 9) to activate cellular immunity (Th1 immune response). The bi-adjuvant nanovaccine fully combines the advantages of nanosheet alum-like adjuvant and precisely customization of DNA, and thus balances the Th1/Th2 immune response for compensating the deficiency of traditional alum adjuvant, providing a design guidance for creating next-generation of safe and efficient adjuvants in immunology.

Development of Mg-Al LDH and LDO as novel protective materials for deacidification of paper-based relics

Acidification of paper-based relics is a common problem, leading to their degradation and eventual loss. Paper deacidification is highly dependent on a limited variety of alkaline materials, and the development of new materials that are safe, efficient and easy-to-prepare is highly demanded to ensure a high level of safety and effective protection of paper-based relic. This study proposes the introduction of layered double hydroxide (LDH) and its calcined product, mixed metal oxide (layered double oxide (LDO)), as innovative protective materials for the deacidification of paper with varying levels of acidity. The results demonstrate that treatment with Mg-Al LDH/LDO can effectively modify the pH of acidic paper (e.g., pH ∼ 4.0–6.4) to a neutral or weakly basic state, maintaining this desirable pH range even under long-term accelerated aging condition. Remarkably, LDH proves to be well-suited for the protection of slightly acidified paper (e.g., pH > 5.5), while LDO serves as an especially option for the deacidification of severely acidified paper (e.g., pH ≤ 5.5). During aqueous deacidification, due to the memory effect of the LDH-based materials, LDO is converted to rehydrated LDH, which creates a mild and appropriate alkaline retention in the paper, avoiding damage caused by strong alkalinity such as cellulose degradation and pigment fading during subsequent long-term natural preservation of the paper. Furthermore, Mg-Al LDH/LDO materials also exhibit flame-retardant and bacteriostatic properties. This opens up opportunities for the safe, efficient and multifunctional protection of acidified paper-based relics.

Molybdenum-Oxysulfide-Functionalized MgAl-Layered Double Hydroxides─A Sorbent for Selenium Oxoanions.

Effective removal of chemically toxic selenium oxoanions at high-capacity and trace levels from contaminated water remains a challenge in current scientific pursuits. Here, we report the functionalization of the MgAl layered double hydroxide with molybdenum-oxysulfide (MoO2S2) anion, referred to as LDH-MoO2S2, and its potential to sequester SeVIO42- and SeIVO32- from aqueous solution. LDH-MoO2S2 nanosheets were synthesized by an ion exchange method in solution. Synchrotron X-ray pair distribution function (PDF) and extended X-ray absorption fine structure (EXAFS) revealed an unexpected transformation of the MoO2S22- to Mo2O2S62- like species during the intercalation process. LDH-MoO2S2 is remarkably efficient in removing SeO42- and SeO32- ions from the ppm to trace level (≤10 ppb), with distribution constant (Kd) ranging from 104 to 105 mL/g. This material showed exceptionally high sorption capacities of 237 and 358 mg/g for SeO42- and SeO32-, respectively. Furthermore, LDH-MoO2S2 demonstrates substantial affinity and efficiency to remove SeO32-/SeO42- even in the presence of competitive ions from contaminated water. Hence, the removal of selenium (VI/IV) oxoanions collectively occurs through reductive precipitation and ion exchange mechanisms. This work provides significant insights into the chemical structure of the MoO2S2 anion into LDH and emphasizes its exceptional potential for high-capacity selenium removal and positioning it as a premier sorbent for selenium oxoanions.

Adsorption behavior of Mg–Al layered double hydroxide on Pb(Ⅱ), Zn(Ⅱ), Cd(Ⅱ), and As(V) coexisting in aqueous solution

MgAl-layered double hydroxide（MgAl-LDH）was synthesized via hydrothermal method, and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), N2 adsorption-desorption, energy dispersive spectrum (EDS). The results proved that the prepared MgAl-LDH exhibited a well-defined layered structure and mesoporous morphology with a large specific surface area, which endowed them with abundant adsorption sites and diffusion mass transfer channels for heavy metal ions. Subsequently, the MgAl-LDH was used to evaluate the adsorption efficiency for Pb(Ⅱ), Zn (Ⅱ), Cd (Ⅱ), and As(V) coexisting in aqueous solutions by batch equilibrium experiments. The results showed favorable adsorption performance of MgAl-LDH toward four coexisting ionic species, with competitive adsorption among the heavy metal ions. Under the experimental conditions, the removal rates of Pb(Ⅱ), Zn (Ⅱ), Cd (Ⅱ), and As(V) ions were 96.7%, 97.1%, 65.2%, and 98.7%, respectively, and the selective order for cation adsorption followed Pb(Ⅱ) > Zn (Ⅱ) > Cd (Ⅱ). Furthermore, the adsorption mechanisms of Pb(Ⅱ), Zn (Ⅱ), Cd (Ⅱ) and As(V) by MgAl-LDH were detailed conducted by XRD, Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) analysis, and could be ascribed to the surface complexation, precipitation and isomorphic replacement for Pb(Ⅱ), Zn (Ⅱ), Cd (Ⅱ) while surface complexation, ion exchange and electrostatic adsorption for As(V).

Biodegradable chelator GLDA intercalated magnesium/aluminum layered double hydroxides for efficient phosphate capture and removal from wastewater

Phosphate removal and recovery from wastewater play a vital role in controlling water eutrophication and facilitating resource recycling. Adsorbents of layered double hydroxides (LDHs) exhibit promising potential in the removal of phosphate; however, the removal efficiency often suffers insufficient as easy aggregation and inevitable loss of LDHs. Herein, a novel N, N–bis (carboxymethyl)–L–glutamic acid intercalated magnesium–aluminum LDH (GLDA@MgAl–LDH) were successfully synthesized. Intercalating with GLDA spawned dual functionality, i.e., the layer spacing expansion elevated the loading of phosphate, while GLDA also acted as additional binding sites toward phosphate. A higher phosphate capture (＞90%) was obtained in pH 5.0–8.0. Phosphate uptake was predominantly observed within the first1h, reaching equilibrium in approximately 4 h. The maximum adsorption capacity of 44.17 mg g–1 was attained for GLDA@MgAl–LDH at pH 6.70, which are far higher than that of pristine MgAl–LDH. GLDA@MgAl–LDH also had the excellent stability and reusability in five adsorption/desorption experiments. The GLDA@MgAl–LDH demonstrated significant efficacy in treating actual phosphate-containing wastewater in the fixed–bed adsorption column. Spectroscopic analysis, in conjunction with density functional theory, elucidated that GLDA intercalation enhanced the adsorption efficiency of MgAl–LDH. The key mechanisms facilitating phosphate removal included electrostatic attraction, anion and ligand exchange, and surface complexation. The above results highlight that GLDA@MgAl–LDH could serve as a promising and environmentally friendly candidate for phosphate treatment from the real wastewater.