A review on the recent advances, challenges and future aspect of layered double hydroxides (LDH) – Containing hybrids as promising adsorbents for dyes removal

Mechanism Responsible for Changes in the Luminescence Properties of Terbium (III)-Doped Layered Double Hydroxides During Carbonate/Chloride Exchange

Layered double hydroxides (LDHs) have been actively studied as water purification, battery, capacitor, and catalytic materials because they exhibit anion-exchange capabilities. Furthermore, photoluminescent LDHs are potentially useful as materials capable of detecting toxic anions. These materials can be synthesized using various combinations of divalent and trivalent metal cations. Herein, we investigate the synthesis and photoluminescence (PL) properties of Mg (Al, Tb)-LDHs with different incorporated interlayer anions, specifically carbonate (CO3 2-) and chloride (Cl-). The CO3 2--incorporated Mg (Al, Tb)-LDH was synthesized using a hydrothermal method, whereas Cl- was introduced through anion exchange. Characterization techniques confirmed that Tb3+ has been successfully doped into the LDH structure without impurities. The CO3 2--incorporated Mg (Al, Tb)-LDH was significantly more photoluminescent than its Cl- counterpart. However, further analysis using electron spin resonance and X-ray absorption fine structure techniques revealed that the Tb3+ electronic state is unaffected by the anionic species. Synchrotron radiation X-ray diffractometry and subsequent Rietveld analysis revealed that thermal fluctuations of the anionic species and hydrated water in the interlayer space are the primary factors that influence PL intensity. These findings highlight the crucial role played by the thermal stabilities of the interlayer components in determining the PL properties of Mg (Al, Tb)-LDH.

Advanced nanofibers for water treatment: Unveiling the potential of electrospun polyacrylonitrile membranes

The challenges pertaining to the potable water scarcity and pollution motivates us to envision innovative strategies. Industrial wastewater containing hazardous heavy metals, synthetic dyes, and oil exacerbates the pursuit of clean drinking water. Among the array of available technologies, electrospun nanofiber membranes have garnered attention due to their efficiency, high surface-to-volume ratio, cost-effectiveness, scalability, and multifunctionality. These membranes possess distinct physical and chemical attributes that position them as ideal solutions to water purification challenges. Their versatility enables effective contaminant removal through filtration, adsorption, and chemical interactions. Polyacrylonitrile (PAN) emerges as a frontrunner among electrospun polymers due to its affordability, remarkable physical and chemical characteristics, and the ease of production. Research efforts have been dedicated to the study of electrospun PAN membranes, exploring modifications in terms of the functionalization of PAN molecular chain, incorporation of appropriate nanoparticles, and composition with other functional polymers. Parameters such as functional groups, hydrophilicity, mechanical properties, porosity, pore structure, reusability, sustainability, zeta potential, and operational conditions significantly influence the performance of electrospun PAN membranes in treating the contaminated water. Despite progress, challenges surrounding fouling, toxicity, scalability, selectivity, and production costs ought to be addressed strategically to enhance their practicality and real-world viability. This review comprehensively scrutinizes the current landscape of available electrospun PAN membranes in water treatment encompassing diverse range of synthesized entities and experimental outcomes. Additionally, the review delves into various approaches undertaken to optimize the performance of electrospun PAN membranes while proposing potential strategies to overcome the existing hindrances. By carefully analyzing the parameters that impact the performance of these membranes, this overview offers invaluable guidelines for researchers and engineers, thus empowering them to design tailored electrospun nanofiber membranes for specific water purification applications. As the innovative research continues and strategic efforts address the current challenges, these membranes can play a pivotal role in enhancing water quality, mitigating water scarcity, and contributing to environmental sustainability. The widespread application of electrospun nanofiber membranes in water treatment has the potential to create a lasting positive impact on global water resources and the environment. A dedicated effort towards their implementation will undoubtedly mark a crucial step towards a more sustainable and water-secure future.

Activated carbon cloth with MnCoAl layer double hydroxide nanocomposite for the separation and preconcentration of Pb(II) and Ni(II) from food samples

A novel dispersive solid phase microextraction (dSP-ME) technique using activated carbon cloth (ACC) and layered double hydroxide (LDH) has been developed for enriching and extracting Pb(II) and Ni(II). The ACC@MnCoAl-LDH nanosorbent, has proven with high surface area, superior extraction dynamics and efficiency, compared to traditional sorbents. Structural features of the new ACC@MnCoAl-LDH sorbent were also characterized. Analytical parameters such as pH, adsorbent quantity, sample volume, eluent volume, adsorption/desorption time, and concentration were optimized, using 7.5 mg of adsorbent. Limit of detection (LOD), limit of quantification (LOQ), and preconcentration factor (PF) were determined at 0.71 μgL -1, 2.35 μgL -1 and 25 for Pb(II) and 0.07 μgL -1, 0.22 μgL -1 and 30 for Ni(II). Validation tests also performed using certified reference materials (CRMs). The % RSD was calculated at 2.5-7.8 for Pb(II) and 3.5-8.2 for Ni(II). The method was applied to determine Pb(II) and Ni(II) levels in packet juices, noodles, and water samples.

Clustered flower-like Mg/Al/Fe-LDHs-based material for highly efficient Fenton degradation of crystal violet wastewater

In this study, a ternary hydrotalcite of Mg/Al/Fe/SDBS-LDHs was synthesized via a hydrothermal method, utilizing sodium dodecyl benzene sulfonate (SDBS) as a modifier. The prepared Mg/Al/Fe/SDBS-LDHs were characterized using FT-IR, SEM, XRD, TG, BET, ESR and XPS techniques. The CV removal process was monitored and analyzed using UV-vis spectroscopy, DFT and LC-MS methods. The results demonstrated that the Mg/Al/Fe/SDBS-LDHs exhibited a clustered, flower-like structure with irregular pores, which facilitated CV removal. Under optimal conditions, the degradation rate of Mg/Al/Fe1/SDBS-LDHs (500 °C, 2 h) reached 99.3 % at a molar ratio of Mg:Al:Fe = 1:3:1. Moreover, the maximum CV removal capacity increased to 963 mg/g upon the addition of 0.1 mL H2O2. The influence of various factors on CV removal, including the initial solution pH, reaction temperature, and coexisting ions, was systematically examined. DFT calculations reveal that in the optimized molecular structure of CV, the carbon atoms C1, C2, C5, and C7 are highly susceptible to be attacked by hydroxyl radicals (·OH). LC-MS and UV-vis analyses revealed that CV degradation generated (4-aminophenyl) (p-tolyl) methanone,4-aminobenzoic acid, and 4-aminophenol, which were subsequently mineralized into CO2 and H2O. This work presents a novel approach to the degradation of high-concentration printing and dyeing wastewater using hydrotalcite, highlighting its potential application for actual wastewater treatment.

Fabrication and Modification of Hydrotalcite-Based Photocatalysts and Their Composites for CO2 Reduction: A Critical Review

Layered double hydroxides (LDHs), which resemble hydrotalcite, are a type of materials with cationic layers and exchangeable interlayer anions. They have drawn lots of curiosity as a high-temperature CO2 adsorbent because of its quick desorption/sorption kinetics and renewability. Due to its extensive divalent or trivalent cationic metals, high anion exchange property, memory effect, adjustable behavior, bio-friendliness, easy to prepare and relatively low cost, the LDHs-based materials are becoming increasingly popular for photocatalytic CO2 reduction reaction (CO2RR). Fabrication and modification are good ways to move forward the advancement of LDHs-based catalysts, which will help chemistry and materials science make great progress. In this review we discussed structural characteristics and the methods for preparation and modification of LDHs-based photocatalysts. We also highlighted and discussed the major developments and applications in photocatalytic CO2RR as well as the photocatalytic mechanism. The goal of the present review is to give a broad summary of the various LDHs-based photocatalysts and the corresponding design strategies, which could motivate more excellent research works to explore this kind of CO2RR photocatalysts to further increase CO2 conversion yield and selectivity.

Exploring the impact of washing media on the adsorption properties of Mg-Al Layered Double Hydroxide Nanoparticles

Environmental remediation has emerged as a critical concern, with dye removal via adsorption being a particularly effective approach. This study demonstrates that appropriately synthesized Mg-Al-Layered Double Hydroxides (LDHs) exhibit exceptional adsorption capacities for anionic dyes. We investigate the impact of different washing media on the material's morphology, surface area, and adsorption capabilities. Notably, washing LDH with ethanol (LDHE) instead of water (LDHW) results in a significant reduction in particle size (70 and 200 nm), a nearly fourfold increase in surface area (197 and 52 m2/g), and a doubling of the maximum adsorption capacity for Congo red (CR) dye. The adsorption studies reveal that LDHE maintains its high CR adsorption efficiency across a variety of pH levels, in the presence of co-existing ions, and in simulated industrial effluent. The ion exchange interaction between the R-SO3- bonds in CR and the cationic layers of LDH (with the loss of carbonate anions) may be responsible for the adsorption. The rapid dye removal at lower concentrations and the impressive maximum adsorption capacity of 2452 mg/g (one of the highest ever reported for pure/single LDH systems) at higher concentrations highlight the potential of LDHE as a valuable adsorbent for large-scale applications.

Melanin-intercalated layered double hydroxide LDH/MNP as a stable photothermal agent

Melanin nanoparticles (MNPs) are a type of electronegative compound that can be used as photothermal agent for cancer treatment. Nevertheless, the agglomeration of MNP, which is one of the limitations in practice, contributes to the instability of MNP. Pristine layered double hydroxide (LDH), as a kind of positive inorganic material when there exist no other cargo between its layers, can accommodate electronegative molecules between its layers to endow them with stable properties. Hence, in this study, electronegative MNP was intercalated into LDH lamellas via ion-exchange method to obtain the stable original photothermal agent LDH/MNP, solving the tough problem of MNP's agglomeration. The surface morphology, X-ray diffraction and fourier transform infrared spectra affirmed the successful intercalation of MNP between LDH lamellas. The Z-average particle sizes of LDH/MNP on day 0, 7 and 14 were measured as 221.8 nm, 227.6 nm and 230.5 nm without obvious fluctuation, while the particle sizes of MNP went through dramatic enlargement from 105.8 nm (day 0) to 856.1 nm (day 7), indicating the better stability of LDH/MNP than MNP. The typical polymer dispersity index (PDI) values on day 0, 7 and 14 verified the better stability of LDH/MNP, too. Photothermal properties of LDH/MNP were assessed and the results ensured the representative photothermal properties of LDH/MNP. The fine cytocompatibility of LDH/MNP was verified via cytotoxicity test. Results confirmed that the agglomeration of MNP disappeared after its intercalation into LDH and LDH/MNP possessed fine stability as well as typical photothermal property. The intercalation of MNP into LDH gave the photothermal agent MNP a promising way for its better stability and long-term availability in photothermal treatment.

Characterization and application of LDH with chitosan composites investigated by positron annihilation lifetime spectroscopy and surface texture for the adsorption of methyl orange

With a rapid increase in industrial growth around the world, the demand for an entirely novel category of nanoparticles and technologies for wastewater treatment has become a key concern for environmental protection. Recently, hybrids of layered double hydroxides (LDH), particularly those containing LDH, have gained attention as potential nanoscale adsorbents for water treatment. Recent research has shown that LDH-containing composites are interesting versatile materials with the ability to be used in energy storage, photocatalysis, nanocomposites, and water treatment. In the current work, LDH-containing composites were utilized as adsorbents for the purpose of purifying water. The adsorbents investigated are Zn-Co-Fe/LDH/Chitosan-in situ sample preparation (LDH/CS1) and Zn-Co-Fe/LDH/Chitosan-ex situ sample preparation (LDH/CS2). Furthermore, LDH/CS1 and LDH/CS2 were investigated for wastewater treatment from methyl orange dye (MO) with various adsorption conditions. When the initial MO concentration was 20 mg/L and the amount of adsorbent was 0.1 g, the removal efficiency reached 72.8 and 91.7% for LDH/CS1 and LDH/CS2, respectively. The MO's maximum adsorption capabilities are 160.78 and 165.89 mg/g for LDH/CS1 and LDH/CS2, respectively, which is much greater than that of comparable commercial adsorbents. MO adsorption onto LDH/CS1 and LDH/CS2 was best characterized by the pseudo-second-order kinetic model. The equilibrium adsorption data was followed by the Freundlich and Langmuir models. The adsorption is favorable as evidenced by the equilibrium parameter RL values for MO adsorption onto LDH/CS1 and LDH/CS2, which were 0.227 and 0.144, respectively. Using the free volume distribution method and the positron annihilation lifetime technique, the nanostructure of the materials was examined.

Adsorptive removal of heavy metals from aqueous solutions: Progress of adsorbents development and their effectiveness

Increased levels of heavy metals (HMs) in aquatic environments poses serious health and ecological concerns. Hence, several approaches have been proposed to eliminate/reduce the levels of HMs before the discharge/reuse of HMs-contaminated waters. Adsorption is one of the most attractive processes for water decontamination; however, the efficiency of this process greatly depends on the choice of adsorbent. Therefore, the key aim of this article is to review the progress in the development and application of different classes of conventional and emerging adsorbents for the abatement of HMs from contaminated waters. Adsorbents that are based on activated carbon, natural materials, microbial, clay minerals, layered double hydroxides (LDHs), nano-zerovalent iron (nZVI), graphene, carbon nanotubes (CNTs), metal organic frameworks (MOFs), and zeolitic imidazolate frameworks (ZIFs) are critically reviewed, with more emphasis on the last four adsorbents and their nanocomposites since they have the potential to significantly boost the HMs removal efficiency from contaminated waters. Furthermore, the optimal process conditions to achieve efficient performance are discussed. Additionally, adsorption isotherm, kinetics, thermodynamics, mechanisms, and effects of varying adsorption process parameters have been introduced. Moreover, heavy metal removal driven by other processes such as oxidation, reduction, and precipitation that might concurrently occur in parallel with adsorption have been reviewed. The application of adsorption for the treatment of real wastewater has been also reviewed. Finally, challenges, limitations and potential areas for improvements in the adsorptive removal of HMs from contaminated waters are identified and discussed. Thus, this article serves as a comprehensive reference for the recent developments in the field of adsorptive removal of heavy metals from wastewater. The proposed future research work at the end of this review could help in addressing some of the key limitations facing this technology, and create a platform for boosting the efficiency of the adsorptive removal of heavy metals.

Adsorptive removal of organic pollutants from aqueous solutions using novel GO/bentonite/MgFeAl-LTH nanocomposite

The contamination of water with organic pollutants such as dyes and phenols is a serious environmental problem, requiring effective treatment methods. In the present study, a novel nanocomposite was synthesized by intercalating graphene oxide and bentonite clay into MgFeAl-layered triple hydroxide (GO/BENT/LTH), which was characterized using different techniques. The adsorption efficacy of the GO/BENT/LTH nanocomposite was assessed via the removal of two harmful organic water pollutants, namely methyl orange (MO) and 2-nitrophenol (2NP). The obtained results revealed that the maximum adsorption capacities (qmax) of MO and 2NP reached 3106.3 and 2063.5 mg/g, respectively, demonstrating the excellent adsorption performance of the nanocomposite. Furthermore, this study examined the effects of contact time, initial MO and 2NP concentrations, pH, and temperature of the wastewater samples on the adsorptive removal of MO and 2NP by the GO/BENT/LTH nanocomposite. The pH, zeta potential, and FTIR investigations suggested the presence of more than one adsorption mechanism. Thermodynamic investigations elucidated the exothermic nature of the adsorption of MO and 2NP onto the GO/BENT/LTH nanocomposite, with MO adsorption being more sensitive to temperature change. Additionally, regeneration studies revealed a marginal loss in the MO and 2NP removal with the repetitive use of the GO/BENT/LTH nanocomposite, demonstrating its reusability. Overall, the findings of this study reveal the promise of the GO/BENT/LTH nanocomposite for effective water decontamination.

Hybridization of layered double hydroxides with functional particles

Layered double hydroxides (LDHs) are a class of materials with useful properties associated with their anion exchange abilities as well as redox and adsorptive properties for a wide range of applications including adsorbents, catalysts and their supports, electrodes, pigments, ceramic precursors, and drug carriers. In order to satisfy the requirements for each application as well as to find alternative applications, the preparation of LDHs with the desired composition and particle morphology and post-synthetic modification by the host-guest interactions have been examined. In addition, the hybridization of LDHs with various functional particles has been reported to design materials of modified, improved, and multiple functions. In the present article, the preparation, the heterostructure and the application of hybrids containing LDHs as the main component are overviewed.

Activation of peroxydisulfate via BiCoFe-layered double hydroxide for effective degradation of aniline

The sulfate radical-based advanced oxidation processes (SR-AOPs) is a promising method for the degradation of pollutants, with the development of highly efficient catalysts for persulfate activation has been widely concerned. The novel BiCoFe-LDH (BCF-x) was synthesized successfully by coprecipitation method, which can activate peroxydisulfate (PDS) efficiently to degrade aniline. Comparative analysis with pure CoFe-LDH revealed a remarkable increase in reaction rate constant by approximately 14.66 times; the degradation rate of aniline (10 mg/L) was 100% in 60 min with the condition of 0.5 g/L BCF-1.5 and 0.5 g/L PDS, due to BCF-1.5 which was characterized as a complex of CoFe-LDH and Bi2O2CO3, promoting electron transport to improve the efficiency of activated PDS. In the reaction system, SO4•-, ·OH, and 1O2 were responsible for the aniline degradation and ·OH was the primary one. Furthermore, this work proposes a reaction electron transfer catalytic mechanism, which provided a new insight and good application prospect for efficient activation of PDS for pollutant degradation.

Advances of Layered Double Hydroxide-Based Materials for Tumor Imaging and Therapy

Layered double hydroxides (LDH) are a class of functional anionic clays that typically consist of orthorhombic arrays of metal hydroxides with anions sandwiched between the layers. Due to their unique properties, including high chemical stability, good biocompatibility, controlled drug loading, and enhanced drug bioavailability, LDHs have many potential applications in the medical field. Especially in the fields of bioimaging and tumor therapy. This paper reviews the research progress of LDHs and their nanocomposites in the field of tumor imaging and therapy. First, the structure and advantages of LDH are discussed. Then, several commonly used methods for the preparation of LDH are presented, including co-precipitation, hydrothermal and ion exchange methods. Subsequently, recent advances in layered hydroxides and their nanocomposites for cancer imaging and therapy are highlighted. Finally, based on current research, we summaries the prospects and challenges of layered hydroxides and nanocomposites for cancer diagnosis and therapy.

Efficient phosphate removal by Mg-La binary layered double hydroxides: synthesis optimization, adsorption performance, and inner mechanism

Layered double hydroxides (LDH) hold great promise as phosphate adsorbents; however, the conventional binary LDH exhibits low adsorption rate and adsorption capacity. In this study, Mg and La were chosen as binary metals in the synthesis of Mg-La LDH to enhance phosphate efficient adsorption. Different molar ratios of Mg to La (2:1, 3:1, and 4:1) were investigated to further enhance P adsorption. The best performing Mg-La LDH, with Mg to La ratio is 4:1 (LDH-4), presented a larger adsorption capacity and faster adsorption rate than other Mg-La LDH. The maximum adsorption capacity (87.23 mg/g) and the rapid adsorption rate in the initial 25 min of LDH-4 (70 mg/(g·h)) were at least 1.6 times and 1.8 times higher than the others. The kinetics, isotherms, the effect of initial pH and co-existing anions, and the adsorption-desorption cycle experiment were studied. The batch experiment results proved that the chemisorption progress occurred on the single-layered LDH surface and the optimized LDH exhibited strong anti-interference capability. Furthermore, the structural characteristics and adsorption mechanism were further investigated by SEM, BET, FTIR, XRD, and XPS. The characterization results showed that the different metal ratios could lead to changes in the metal hydroxide layer and the main ions inside. At lower Mg/La ratios, distortion occurred in the hydroxide layer, resulting in lower crystallinity and lower performance. The characterization results also proved that the main mechanisms of phosphate adsorption are electrostatic adsorption, ion exchange, and inner-sphere complexation. The results emphasized that the Mg-La LDH was efficient in phosphate removal and could be successfully used for this purpose.

The effect of the number of SO3- groups on the adsorption of anionic dyes by the synthesized hydroxyapatite/Mg-Al LDH nanocomposite

In this study, a new nanocomposite of hydroxyapatite (HA)/Mg-Al layered double hydroxide (LDH) was successfully formed via a facile co-precipitation method and applied to adsorb three anionic dyes of alizarin red S (ARS), Congo red (CR), and reactive red 120 (RR120) differing in the number of SO3- groups from aqueous solution. Based on a combination of characterization analysis and adsorption experiments, HA/Mg-Al LDH nanocomposite showed better adsorption performance than HA and Mg-Al LDH. Using XRD and TEM analyses, the crystallinity and the presence of nanoparticles were confirmed. According to the SEM investigation, the Mg-Al LDH layers in the nanocomposite structure were delaminated, while HA nanorods were formed at the surface of Mg-Al LDH nanoparticles. The higher BET surface area of the novel HA/Mg-Al LDH nanocomposite compared to HA and Mg-Al LDH provided its superior adsorption performance. Considering an effective amount of adsorbent dosage, pH 5 was selected as the optimum pH for each of the three dye solutions. According to the results from the study of contact time and initial concentration, the pseudo-second-order kinetic (R2 = 0.9987, 0.9951, and 0.9922) and Langmuir isotherm (R2 = 0.9873, 0.9956, and 0.9727) best fitted the data for ARS, CR, and RR120, respectively. Anionic dyes with different numbers of SO3- groups demonstrated distinct adsorption mechanisms for HA and Mg-Al LDH nanoparticles, indicating that the adsorption capacity is influenced by the number of SO3- groups, with HA/Mg-Al LDH nanocomposite offering superior performance toward dyes with higher numbers of SO3- groups. Furthermore, ΔH° less than 40 kJ/mol, positive ΔS°, and negative ΔG° accompanied by the mechanism clarifying show physical spontaneous adsorption without an external source of energy and increase the randomness of the process during the adsorption, respectively. Finally, the regeneration study demonstrated that the nanocomposite could be utilized for multiple adsorption-desorption cycles, proposing the HA/Mg-Al LDH as an economically and environmentally friendly adsorbent in the adsorption of anionic dyes in water treatment processes.

Photocatalytic activity of the biogenic mediated green synthesized CuO nanoparticles confined into MgAl LDH matrix

The global concern over water pollution caused by organic pollutants such as methylene blue (MB) and other dyes has reached a critical level. Herein, the Allium cepa L. peel extract was utilized to fabricate copper oxide (CuO) nanoparticles. The CuO was combined with MgAl-layered double hydroxides (MgAl-LDHs) via a co-precipitation method with varying weight ratios of the CuO/LDHs. The composite catalysts were characterized and tested for the degradation of MB dye. The CuO/MgAl-LDH (1:2) showed the highest photocatalytic performance and achieved 99.20% MB degradation. However, only 90.03, 85.30, 71.87, and 35.53% MB dye was degraded with CuO/MgAl-LDHs (1:1), CuO/MgAl-LDHs (2:1), CuO, and MgAl-LDHs catalysts, respectively. Furthermore, a pseudo-first-order rate constant of the CuO/MgAl-LDHs (1:2) was 0.03141 min-1 while the rate constants for CuO and MgAl-LDHs were 0.0156 and 0.0052 min-1, respectively. The results demonstrated that the composite catalysts exhibited an improved catalytic performance than the pristine CuO and MgAl-LDHs. The higher photocatalytic performances of composite catalysts may be due to the uniform distribution of CuO nanoparticles into the LDH matrix, the higher surface area, and the lower electron and hole recombination rates. Therefore, the CuO/MgAl-LDHs composite catalyst can be one of the candidates used in environmental remediation.

Rapid and effective removal of copper, nitrate and trichloromethane from aqueous media by aluminium alloys

Zero-valent iron (ZVI) has been extensively studied for its efficacy in removing heavy metals, nitrate, and chlorinated organic compounds from contaminated water. However, its limited effectiveness due to rapid passivation and poor selectivity is prompting for alternative solutions, such as the use of aluminium alloys. In this study, the efficacy of five distinct aluminium alloys, namely Al-Mg, Al-Fe, Al-Cu, and Al-Ni, each comprising 50 % Al by mass at a concentration of 10 g/L, was assessed using copper, nitrate and trichloromethane (TCM) as model contaminants. Results show that chemical pollutants reacted immediately with Al-Mg. On the contrary, the remaining three alloys exhibited a delay of 24 h before demonstrating significant reactivity. Remarkably, Al-Mg alloy reduced nitrate exclusively to ammonium, indicating minimal preference for nitrate reduction to N2. In contrast, the Al-Cu, Al-Ni, and Al-Fe alloys exhibited N2 selectivity of 3 %, 5 %, and 19 %, respectively. The removal efficiency of copper, nitrate and TCM reached 99 % within 24 h, 95 % within 48h and 48 % within 48h, respectively. Noteworthy findings included the correlation between Fe concentration within the Al-Fe alloy and an increased N2 selectivity from 9.3 % to 24.1 %. This resulted in an increase of Fe concentration from 10 % to 58 % albeit with a concurrent reduction in reactivity. Cu2+ removal by Al-Fe alloy occurred via direct electron transfer, while the removal of nitrate and TCM was facilitated by atomic hydrogen generated by the alloy's hydrolysis. Intriguingly, nitrate and TCM suppressed Cu2+ reduction, whereas Cu2+ improved nitrate reduction and TCM degradation. These findings demonstrate the great potential of Al-Mg and Al-Fe alloys as highly efficient agents for water remediation.

Combined Steam and CO2 Reforming of Methane over the Hierarchical Ni-ZrO2 Nanosheets/Al2O3 Catalysts at Ultralow Temperature and under Low Steam

This research developed hierarchical 10 wt % Ni-1 wt % ZrO2/Al2O3 catalysts for combined steam and CO2 reforming of methane (CSCRM) reaction to produce syngas for gas-to-liquid (GTL) application under the ultralow temperature and low steam condition. The hierarchical nanosheet catalysts were prepared via a novel impregnation technique assisted by ammonia vapor diffusion with various times (1, 6, and 12 h) to develop the different magnitude of hierarchical nanosheets on the surface. Then, CSCRM at 600 °C was performed on the catalysts for 6 h. The results evidenced the improvement of H2 selectivity, reaching an appropriate H2/CO ratio (1.9-2.0) in FT subunits in the GTL process when nanosheets existed on the surface due to the increase in H2O adsorption-dissociation sites. The good dispersion of hierarchical nanosheets accompanied by the ZrO2 promoter successfully enhanced the CH4 conversion and the coke prevention through the spread nanosheets because of the increase in the number of active sites and the surface interaction. The interaction of hierarchical nanosheets created the H2O activation-dissociation sites that allowed CO2 to be selective on the oxygen vacancy sites, producing more OH* and OH* on the catalyst surface to resist the carbon deposition during CSCRM operation.

High-performance biochar-loaded MgAl-layered double oxide adsorbents derived from sewage sludge towards nanoplastics removal: Mechanism elucidation and QSAR modeling

Utilization of sewage sludge for the fabrication of environmental functional materials is highly desirable to achieve pollution mitigation and resource recovery. In the present work, we introduced a novel MgAl-layered double oxide (LDO)@biochar composite adsorbent in-situ fabricated from Al-rich sewage sludge, and its excellent application in nanoplastics adsorption. Initially, fifteen model contaminants with varied conjugate structures, hydrogen bonding and ionic properties were selected for an investigation of adsorption behavior and adsorption selectivity on LDO@biochar. Structural variation of LDO@biochar suggested reconstruction of the layered double hydroxide (LDH) during the adsorption process due to the "memory effect". Under the synergy of LDH and biochar, the contaminants were adsorbed via multiple adsorbent-adsorbate interactions, including anion exchange, electrostatic interaction, hydrogen bonding and π-π conjugation. Then, a quantitative structure-activity relationship (QSAR) model was constructed by integrating the number of hydrogen bond acceptors, polarity surface area, number of aromatic rings, and Fukui index f(-)x together to reflect the affinity of each contaminant to the adsorbent. Guided by the QSAR model, the negatively charged polystyrene nanoplastics with continuously conjugated aromatic rings were predicted to be effectively adsorbed on LDO@biochar. Experimental tests confirmed a great capacity of LDO@biochar towards the polystyrene nanoplastics, given the equilibrium adsorption capacity as high as 360 mg g-1 at 30-50 °C. This work not only opened up a new avenue for sustainable utilization of sewage sludge towards high-performance environmental functional materials, but also demonstrated the potential of the QSAR analysis as a rapid and accurate approach for guiding the application of an adsorbent to new emerging containments.

Eu3+ doped ZnAl layered double hydroxides as calibrationless, fluorescent sensors for carbonate

The photoluminescence properties (PL) of Eu3+ hosted in the hydroxide layers of layered double hydroxides (LDHs) enables calibrationless quantification of anions in the interlayers. The concept is demonstrated during the nitrate-to-carbonate ion exchange in Zn2+/Al3+/Eu3+ LDHs and can be implemented as a remote optical sensor to detect intrusion of anions such as Cl- or CO32-.

Development of Novel PET-PAN Electrospun Nanocomposite Membrane Embedded with Layered Double Hydroxides Hybrid for Efficient Wastewater Treatment

Layered double hydroxides (LDHs) with their unique structural chemistry create opportunities to be modified with polymers, making different nanocomposites. In the current research, a novel PET-PAN embedded with Mg-AI-LDH-PVA nanocomposite membrane was fabricated through electrospinning. SEM, EDX, FTIR, XRD, and AFM were carried out to investigate the structure and morphology of the nanocomposite membrane. The characterization of the optimized nanocomposite membrane showed a beadless, smooth structure with a nanofiber diameter of 695 nm. The water contact angle and tensile strength were 16° and 1.4 Mpa, respectively, showing an increase in the hydrophilicity and stability of the nanocomposite membrane by the addition of Mg-Al-LDH-PVA. To evaluate the adsorption performance of the nanocomposite membrane, operating parameters were achieved for Cr(VI) and methyl orange at pH 2.0 and pH 4.0, respectively, including contact time, adsorbate dose, and pollutant concentration. The adsorption data of the nanocomposite membrane showed the removal of 68% and 80% for Cr(VI) and methyl orange, respectively. The process of adsorption followed a Langmuir isotherm model that fit well and pseudo-2nd order kinetics with R2 values of 0.97 and 0.99, respectively. The recycling results showed the membrane's stability for up to five cycles. The developed membrane can be used for efficient removal of pollutants from wastewater.

Comprehensive Insights into the Family of Atomically Thin 2D-Materials for Diverse Photocatalytic Applications

2D materials with their fascinating physiochemical, structural, and electronic properties have attracted researchers and have been used for a variety of applications such as electrocatalysis, photocatalysis, energy storage, magnetoresistance, and sensing. In recent times, 2D materials have gained great momentum in the spectrum of photocatalytic applications such as pollutant degradation, water splitting, CO2 reduction, NH3 production, microbial disinfection, and heavy metal reduction, thanks to their superior properties including visible light responsive band gap, improved charge separation and electron mobility, suppressed charge recombination and high surface reactive sites, and thus enhance the photocatalytic properties rationally as compared to 3D and other low-dimensional materials. In this context, this review spot-lights the family of various 2D materials, their properties and their 2D structure-induced photocatalytic mechanisms while giving an overview on their synthesis methods along with a detailed discussion on their diverse photocatalytic applications. Furthermore, the challenges and the future opportunities are also presented related to the future developments and advancements of 2D materials for the large-scale real-time photocatalytic applications.

Preparation and characterization of a novel nanocomposite based on MnCr-layered double oxide and CoFe2O4 spinel ferrite for methyl orange adsorption

Herein, the adsorption of methyl orange (MO), a dangerous anionic dye, from an aqueous solution was investigated using a novel magnetic nanocomposite adsorbent. A nanocomposite entitled manganese chromium-layered double oxide/cobalt spinel ferrite, (MnCr)-LDO5wt.%/CoFe2O4, which links the interlayer structural characteristics of layered double oxides (LDOs) with the magnetic properties of spinel ferrites (SFs) was synthesized using the eco-friendly co-precipitation technique. Determination of structural parameters, crystallite size, and micro-strain was done using X-ray diffraction (XRD) analysis. Transmission electron microscopy (TEM) was used to determine grain shape and size. Surface analysis was performed using X-ray photoelectron spectroscopy (XPS) to identify elements and oxidation states present in the prepared nanocomposite. Vibrating sample magnetometer (VSM) was utilized to examine the magnetic characteristic. A comprehensive comparative study about the effectiveness and durability of CoFe2O4 and (MnCr)5wt.%/CoFe2O4 as nanoadsorbents for MO was conducted. Numerous variables, including contact time, MO concentration, adsorbent dosage, and pH were tested for their effects on the adsorption removal percentages. The findings showed that the maximum removal percentage was 86.1% for 25 ppm of MO was for 0.1 g/100 mL of (MnCr)-LDO5wt.%/CoFe2O4 at pH = 3. Investigations of isotherms and kinetics were conducted under batch conditions. The Langmuir isotherm matched the experimental data, for both nanoadsorbents, quite well due to the homogeneous distribution of active sites. Adsorption kinetics data were found to be compatible with intra-particle diffusion and pseudo-second order models for CoFe2O4 and (MnCr)5wt.%/CoFe2O4, respectively. A total of five adsorption-desorption cycles were performed to determine the prepared adsorbents' recyclable nature.

Simultaneous adsorption of methylene blue and amoxicillin by starch-impregnated MgAl layered double hydroxide: Parametric optimization, isothermal studies and thermo-kinetic analysis

Textile and pharmaceutical effluents contain significant amounts of dyes and antibiotics, which pose a serious threat to the ecosystem when discharged directly. Therefore, they should be treated by facile treatment techniques using low-cost materials. Layered double hydroxide (LDH) and its hybrids have emerged as robust and economic adsorbents for water treatment. Herein, magnesium/aluminum LDH and its starch-based composite were synthesized by a co-precipitation technique. The physicochemical features of the developed adsorbents were thoroughly characterized using various analytical tools. The developed materials were tested for the eradication of methylene blue (MB) and amoxicillin (AMX) in batch mode adsorption by varying operating conditions. Adsorption performance depends on the solution's pH. Under optimum adsorption conditions of pH 11, adsorbent dosage of 50 mg/L, and treatment time of 120 min, starch-impregnated MgAl-LDH exhibited maximum MB and AMX adsorption capacities of 114.94 and 48.08 mg/g, respectively. The adsorption mechanism states that hydrogen bonds and weak van der Waals forces are responsible for the removal of pollutants by the developed materials. Moreover, equilibrium and kinetic studies revealed that the removal of dye and antibiotic followed the Freundlich and Langmuir models with the pseudo-second-order reaction kinetics, respectively. The spent adsorbents were regenerated using 0.1 M HCl (for MB) and methanol (for AMX) eluent, and reusability studies ensured that the developed adsorbents retained their performance for up to four consecutive adsorption/desorption cycles. MgAl-LDH and its starch-based hybrid could thus be used to effectively remove organic contaminants from wastewater streams on a commercial scale.

FeCa-based layered double hydroxide, a high-performance phosphorus adsorbent in constructed wetlands and ecological dams - A pilot scale study

Research studies have modified traditional substances to seek fast-acting removal of phosphorus in constructed wetlands (CWs) and ecological dams, rather than develop a brand-new nano-adsorbent. This work synthesized FeCa-based layered double hydroxide (FeCa-LDH) with a chemical co-precipitation method, and the performance, mechanism and factors of phosphorus removal were investigated. FeCa-LDH showed a marked ability to adsorb phosphorus from waste water, with a removal efficiency of 94.4% and 98.2% in CWs and ecological dams, respectively. Both FTIR and XPS spectrum evidenced that FeCa-LDH removed phosphorus via electrostatic and hydrogen-bonding adsorption, as well as a coordination reaction and interlayer anion exchange. FeCa-LDH showed a higher capacity to remove phosphorus in alkaline and neutral waste water than in acid conditions. Co-occurrence anions, which influenced the efficiency of the phosphorus removal capacity are considered in the sequence below: CO32- ≈ HCO3- > SO42- > NO3-. Innovatively, FeCa-LDH was not affected by the low-temperature limitation for CWs, and phosphorus removal efficiency at 5 °C was almost equal to that at 25 °C. These results cast a new idea on the construction, application and phosphorus removal performance of CWs and ecological dams.

Layered by layered construction of three novel ZnCo-LDHs/g-C3N4 for the removal of sunset yellow by adsorption-photocatalytic process

The removal of organic dyes has attracted attention by adsorption-photocatalytic synergetic process in water treatment technology. Three novel ZnCo-LDHs/g-C3N4 were successfully prepared for the first time by layered construction technique through the hydrolysis of triethanolamine in this paper. They exhibited high specific surface area which facilitates the adsorption of sunset yellow (SY) from solution to catalyst surface. All the target pollutant dyes are very effectively removed by the three ZnCo-LDHs/g-C3N4 composites through synergetic effect of adsorption and photocatalysis process under UV irradiation (λ = 365 nm). The order of synergistic degradation effect for SY is as follows: ZnCo-LDHs/g-C3N4-3 (99.6%) > ZnCo-LDHs/g-C3N4-2 (99.5%) > ZnCo-LDHs/g-C3N4-1 (99.3%) > pure g-C3N4 (77.4%) > pure ZnCo-LDHs (44.2.6%) at the initial concentration of 75 mg L-1. ZnCo-LDHs/g-C3N4-3 has the largest k value (0.0284 min-1) in SY degradation, which is 2.8 times that of g-C3N4. ZnCo-LDHs/g-C3N4-3 is a very promising adsorption-photocatalyst for the removal of SY from wastewater. The electron spin resonance experiments demonstrate that OH·, 1O2, and O2- are the dominant active species and oxides SY together. This result demonstrates that the three ZnCo-LDHs/g-C3N4 have practical applications as efficient adsorption-photocatalytic materials and also provides a synergetic strategy for the removal of SY wastewater.

The mechanism of fluorescence quenching of naphthalimide A/C leak detector by copper (II)

BACKGROUND

Fluorescence quenching is an interesting phenomenon with the potential to be applied across various fields. The mechanism is commonly used across analytical applications for monitoring the concentration of trace substances. Naphthalimide and its family of compounds are commonly used as fluorescent detectors. This work investigated an analytical technique through which naphthalimide-based dyes could be quantified. A commercial A/C leak detector was used as the dye and Cu²⁺ ions as the quencher. Experiments were also conducted to investigate the effect of temperature on quenching. To study the mechanism of quenching further, density functional theory (DFT) was used.

RESULTS

The method detection limit obtained in this work is 1.7 × 10^-6 mol/L. The results from the quenching experiments demonstrated a pattern which fit a modified Stern-Volmer (SV) model, with an R² value of 0.9886. From the experiments on the effect of temperature, a dynamic quenching behavior was observed given the emission spectra demonstrated an inverse relationship with temperature.

CONCLUSIONS

The quenching of the commercial A/C dye by Cu²⁺ ions can be used to develop a rapid and sensitive detection method for metal ions such as Cu²⁺, and for future fabrication of chemosensors for Cu²⁺.

Hybrid ternary NiCoCu layered double hydroxide electrocatalyst for alkaline hydrogen and oxygen evolution reaction

This study focuses on the electrochemical properties of layered double hydroxide (LDH), which is a specific structure of NiCoCu LDH, and the active species therein, rather than the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) of ternary NiCoCu LDH materials. Six types of catalysts were synthesized using the reflux condenser method and coated onto a nickel foam support electrode. Compared to bare, binary, and ternary electrocatalysts, the NiCoCu LDH electrocatalyst exhibited higher stability. The double layer capacitance (Cdl) of the NiCoCu LDH (12.3 mF cm^-2) is greater than that of the bare and binary electrocatalysts, indicating that the NiCoCu LDH electrocatalyst has a larger electrochemical active surface area. In addition, the NiCoCu LDH electrocatalyst has a lower overpotential of 87 mV and 224 mV for the HER and OER, respectively, indicating its excellent activity with the bare and binary electrocatalysts. Finally, it is demonstrated that the structural characteristics of the NiCoCu LDH contribute to its excellent stability in long-term HER and OER tests.

Starch modified NiFe layered double hydroxide composites for better adsorption and photocatalytic removal of reactive dye and piroxicam-20 drug

One of the most omnipresent problems to the environment is the efficient removal of textile dyes and non-steroidal drugs from wastewater. For this purpose, renewable, sustainable, and biodegradable biopolymers are used. In this study, starch (S) modified NiFe-layered double hydroxide (LDH) composites were successfully synthesized by the co-precipitation method and have been examined as a catalyst for the effective adsorption of reactive blue 19 dye, reactive orange 16 dye, and piroxicam-20 NSAID from wastewater and photocatalytic degradation of reactive red 120 dye. The physicochemical properties of the prepared catalyst were assessed by XRD, FTIR, HRTEM, FE-SEM, DLS, ZETA, and BET. The coarser and more porous micrographs are shown in FESEM, indicating the homogeneous dispersion of layered double hydroxide on starch polymer chains. The S/NiFe-LDH composites have a slightly greater S_BET (6.736 m²/g) than NiFe LDH (4.78 m²/g). The S/NiFe-LDH composite shows remarkable ability in the removal of reactive dyes. The band gap value of NiFe LDH, S/NiFe LDH (0.5:1), and S/NiFe LDH (1:1) composites was calculated as 2.28 eV, 1.80 eV, and 1.74 eV, respectively. The q_max assessed from Langmuir isotherm for removal of piroxicam-20 drug, reactive blue 19 dye, and reactive orange 16 was 2840 mg/g, 149.47 mg/g, and 182.4 mg/g, respectively. The activated chemical adsorption without product desorption is predicted by the Elovich kinetic model. With reactive red 120 dye, S/NiFe-LDH shows photocatalytic degradation within 3 h of irradiation of visible light with 90% removal efficiency and follows a pseudo-first-order kinetic model. The scavenging experiment confirms the involvement of electrons and holes in photocatalytic degradation. With a little decline in adsorption capacity up to five cycles, starch/NiFe LDH was easily regenerated. So, the suitable adsorbent required for wastewater treatment is nanocomposites of LDHs and starch as they enhance the chemical and physical attributes of the composite structure with greater absorption capabilities.

In situ preparation of TiO2/f-MWCNT catalyst using Pluronic F127 assisted sol-gel process for sonocatalytic degradation of methylene blue

In this study, titanium dioxide- Pluronics @F127/functionalized -multi walled carbon nanotubes (TiO₂-F127f-/MWCNT) nanocatalysts were prepared, characterized, and used in methylene blue (MB) degradation under ultrasonic conditions. The characterization studies were performed using TEM, SEM, and XRD analyses to reveal the morphological and chemical properties of TiO₂-F127/MWCNT nanocatalysts. To detect the optimum parameters for MB degradation using TiO₂-F127/f-MWCNT nanocatalysts, several experimental parameters were conducted at various conditions such as different temperatures, pH, catalyst amount, hydrogen peroxide (H₂O₂) concentration, and various reaction contents. Transmission electron microscopy (TEM) analyses showed that TiO₂-F127/f-MWCNT nanocatalysts consisted of a homogenous structure and have a 12.23 nm particle size. The crystalline particle size of TiO₂-F127/MWCNT nanocatalysts was found to be 13.31 nm. Scanning electron microscope (SEM) analyses revealed the surface structure of TiO₂-F127/f-MWCNT nanocatalysts turned to be modified after TiO₂ loaded on MWCNT. Under the optimum conditions; pH: 4, MB concentration: 25 mg/L, H₂O₂ concentration: 30 mol/L, reaction time: and catalyst dose: 24 mg/L, chemical oxygen demand (COD) removal efficiency reached a maximum of 92%. To detect the radical effectiveness, three scavenger solvents were tested. Reuse experiments revealed that TiO₂-F127/f-MWCNT nanocatalysts retained 84.2% catalytical activity after 5 cycles. Gas chromatography-mass spectrometry (GC-MS) was successfully used to identify the generated intermediates. In addition, the GC-MS was successfully used to identify produced intermediates. Based on the experimental results, it has been suggested that •OH radicals are the main active species responsible for the degradation reaction in the presence of the TiO₂-F127/f-MWCNT nanocatalysts.

Defective multi-element hydroxides nanosheets for rapid removal of anionic organic dyes from water and oxygen evolution reaction

Water pollution by dyes is one of the biggest environmental problems. Adsorption technology has been widely used in wastewater treatment. In this work, high-entropy concept is used to design surface defective hydroxides realizing the rapid removal of dyes from water. Multi-element hydroxides (MEHs) containing three (CoMnNi, MEH-Ternary), four (CoMnNiZn, MEH-Quaternary), and five (CoMnNiZnFe, MEH-Quinary) metal elements are successfully synthesized through a polyol process. These as-synthesized MEHs are composed of nanosheets with a brucite-like structure. Along with the increase in compositional complexity (i.e., configurational entropy), the thickness of the nanosheets in these MEHs decreases, while the degree of surface defects increase. These surface defects are probably the active sites for anionic dyes adsorption, suggesting rapid adsorption kinetics with shortened diffusion path length. For MEH-Quinary in 0.2 mM Congo red (CR) and MEH-Ternary in 0.4 mM methyl orange (MO) aqueous solutions, respectively, high removal efficiency > 99.0% is achieved in the first 30 s. Their pseudo-second-order rate constants are two orders of magnitude higher than that of activated carbon and hydrotalcite. MEH-Quinary has maximum CR and MO adsorption quantity of 546.4 and 404.9 mg g^-1, respectively, by Langmuir model. The MEH-Quinary is also a potential electrocatalyst for oxygen evolution reaction.

Layered Double Hydroxide Materials: A Review on Their Preparation, Characterization, and Applications

Layered double hydroxides (LDHs), a type of synthetic clay with assorted potential applications, are deliberated upon in view of their specific properties, such as adsorbent-specific behavior, biocompatibility, fire-retardant capacity, and catalytic and anion exchange properties, among others. LDHs are materials with two-dimensional morphology, high porosity, and exceptionally tunable and exchangeable anionic particles with sensible interlayer spaces. The remarkable feature of LDHs is their flexibility in maintaining the interlayer spaces endowing them with the capacity to accommodate a variety of ionic species, suitable for many applications. Herein, some synthetic methodologies, general characterizations, and applications of LDHs are summarized, encompassing their broader appliances as a remarkable material to serve society and address several problems viz. removal of pollutants and fabrication of sensors and materials with multifaceted useful applications in the medical, electrochemical, catalytic, and agricultural fields, among others.

Theoretical Study on the Swelling Mechanism and Structural Stability of Ni3Al-LDH Based on Molecular Dynamics

layered double hydroxide (LDH) as a kind of 2D layer material has a swelling phenomenon. Because swelling significantly affects the adsorption, catalysis, energy storage, and other application properties of LDHs, it is essential to study the interlayer spacing, structural stability, and ion diffusion after swelling. In this paper, a periodic computational model of Ni₃Al-LDH is constructed, and the supramolecular structure, swelling law, stability, and anion diffusion properties of Ni₃Al-LDH are investigated by molecular dynamics theory calculations. The results show that the interlayer water molecules of Ni₃Al-LDH present a regular layered arrangement, combining with the interlayer anions by hydrogen bonds. As the number of water molecules increases, the hydrogen bond between the anion and the basal layer gradually weakens and disappears when the number of water molecules exceeds 32. The hydrogen bond between the anion and the water molecule gradually increases, reaching an extreme value when the number of water molecules is 16. The interlayer spacing of Ni₃Al-LDH is not linear with the number of water molecules. The interlayer spacing increases slowly when the number of water molecules is more than 24. The maximum layer spacing is stable at around 19 Å. The interlayer spacing, binding energy, and hydration energy show an upper limit for swelling: the number of water molecules is 32. When the number of interlayer water molecules is 16, the water molecules' layer structure and LDH interlayer spacing are suitable for anions to obtain the maximum diffusion rate, 10.97 × 10^-8 cm²·s^-1.

Highly effective removal of nickel ions from wastewater by calcium-iron layered double hydroxide

Water pollution due to heavy metals has become a universal environmental problem. Ni(II) is a common heavy metal ion in polluted wastewater, which has high toxicity and carcinogenicity. In this study, the structure of a calcium-iron layered double hydroxide (Ca-Fe-LDHs) was synthesized and characterized by FTIR, XRD, SEM and XPS. Then, Ni(II) ion was effectively removed by Ca-Fe-LDHs and its mechanism for this materials was described. The maximum adsorption capacity of Ni(II) for Ca-Fe-LDHs was 418.9 mg‧g^-1 when the initial concentration of Ni(II) was 1 g/L. The adsorption and removal of Ni(II) by Ca-Fe-LDHs was attributed to the action of hydroxyl groups on the hydrotalcite, generating surface capture. Ni(OH)₂)0.75(H₂O)0.16(NiCO₃)0.09, Ni(OH)₂, NiO, NiSO₄ and other precipitates were generated on its surface. And a small amount of Ni-Fe-LDHs was generated through isomorphic transition before hydrolysis. Therefore, surface capture and isomorphic transition enhanced the removal efficiency of Ni(II) with Ca-Fe-LDHs, making Ca-Fe-LDHs as a potential material for effective removal of Ni(II).

Rational construction and understanding the effect of metal cation substitution of three novel ternary Zn-Co-Ni-LDHs from 2D to 3D and its enhanced adsorption properties for MO

The layered double hydroxides (LDHs) have attracted attention in the water treatment field. In this paper, three novel ternary Zn-Co-Ni-LDH adsorbents were prepared successfully through rational construction from 2D to 3D using triethanolamine (TEA) as an alkali source and a structural controlling reagent by hydrothermal technique. Samples were characterized by the SEM, XRD, XPS, FTIR, BET, solid-state UV/vis spectra, and TG. Three Zn-Co-Ni-LDHs exhibited higher crystallinity and surface area which were beneficial to the adsorption for methyl orange (MO). The maximum adsorption capacity of three Zn-Co-Ni-LDH adsorbents can even reach as high as 1871.65 mg·g^-1, 1799.56 mg·g^-1, and 1646.44 mg·g^-1 for MO, respectively, which surpass those of most previously reported LDH-based adsorbents. The pseudo-second-order kinetic equation fitted the kinetic data of adsorption, while the equilibrium adsorption isotherm data followed the Langmuir model. The adsorption mechanism, electrochemical, and the antibacterial properties of three Zn-Co-Ni-LDHs were also discussed. This results not only demonstrates that three Zn-Co-Ni-LDHs are practical interest as an efficient adsorbent for the removal of MO from dye waste water, but also provides a strategy for the rational design through three ternary Zn-Co-Ni-LDHs from 2D to 3D.

Synthesis of Novel Hierarchical Rod-like Mg-Al bimetallic oxides for enhanced removal of uranium (VI) from wastewater

As one of the most frequently used nuclides for nuclear fuel and toxic heavy metal in polluted solutions, the removal and recovery of U(VI) from wastewater is significant both for nuclear energy and human health. Herein, the novel hierarchical Mg-Al bimetallic oxides (Mg/Al-BOs) were successfully synthesized by a facile hydrothermal-lyophilization-calcination method for enhanced removal of uranium (U(VI)) from wastewater. The as-synthesized Mg/Al-BOs adsorbents were characterized by a variety of techniques including SEM-EDS, XRD, high temperature in-situ XRD, TG-DSC, N₂ adsorption-desorption isotherm and XPS. Batch experiments including the effects of pH, hydration species, interfering ions on U(VI) removal, adsorption kinetics, isotherms and recyclability were systematically studied. Results showed that calcined Mg/Al-BO-24 inherited the hierarchical structure from its hydrotalcite-like precursor and grew the bimetallic oxides of Al₂O₃/MgO into a 3D rod-like and mesoporous network with the large BET surface area (472.4 m²∙g-¹), which presented abundant binding sites on the surface and contributed to preventing the aggregation of Al₂O₃/MgO nanoparticles, allowing the fast uptake of U(VI) for equilibrium within 180 min and the significant increase of maximum adsorption capacity to 411.5 mg∙g-¹. The uptake kinetics and isotherms of U(VI) removal could be well represented by the pseudo-second-order and Langmuir models, respectively. Further, it was demonstrated that U(VI) removal by Mg/Al-BO-24 was less influenced by coexisting cations and the regeneration cycles, indicating the excellent selectivity and reusability for U(VI) by the as-prepared composites. Based on the XPS analysis results, the mechanisms for U(VI) sorption onto the Mg/Al-BO-24 were mainly ascribed to the synergistic surface complexation and electrostatic interaction. These results suggested that Mg/Al-BO-24 prepared by the method reported here was available for developing other multiple metal oxides and would be a promising material for the effective treatment of wastewater with U(VI)-contamination.

Fabrication and Characterization of Cu Nanoparticles Dispersed on ZnAl-Layered Double Hydroxide Nanocatalysts for the Oxidation of Cyclohexane

In the chemical industry, designing high-performance catalysts for the oxidation of cyclohexane into value-added products such as cyclohexanol and cyclohexanone (the combination is known as KA oil) is critical. The catalytic activity of copper nanoparticles supported on layered double hydroxide (LDH) for the liquid phase oxidation of cyclohexane was examined in this study. In this work, we have developed Cu nanoparticles supported on layered double hydroxide nanocatalysts, abbreviated as CuNPs@LDH, by the chemical reduction approach. Various physical methods were used to characterize the resulting material, including ICP-AES, XRD, FTIR, SEM, EDX, HRTEM, and BET surface area. The catalytic activity of copper nanoparticles supported on LDH was examined for the liquid phase oxidation of cyclohexane with tert-butyl hydroperoxide. CuNPs@LDH nanocatalysts with an excellent 52.3% conversion of cyclohexane with 97.2% selectivity of KA oil was obtained after 6 h at 353 K. The hot filtration test further indicated that CuNPs@LDH was a heterogeneous catalyst that could be recycled at least six times without suffering a substantial reduction in its catalytic activity.

Multifaceted potential applicability of hydrotalcite-type anionic clays from green chemistry to environmental sustainability

Hydrotalcite-like anionic clays (HTs) also known as Layered double hydroxides (LDHs) have been developed as multifunctional materials in numerous applications related to catalysis, adsorption, and ion-exchange processes. These materials constitute an important class of ionic lamellar solid clays of Brucite-like structure which comprise of consecutive layers of divalent and trivalent metal cations with charge balancing anions and water molecules in interlayer space. These materials have received increasing attention in research due to their interesting properties namely layered structure, ease of preparation, flexible tunability, ability to intercalate different types of anions, electronic properties, high thermal stability, high biocompatibility, and easy biodegradation. Moreover, HTs/LDHs have unique tailorable and tuneable characteristics such as both acidic and basic sites, anion exchange capability, surface area, basal spacing, memory effect, and also exhibit high exchange capacities, which makes them versatile materials for a wide range of applications and extended their horizons to diverse areas of science and technology. This study enlightens the various rational researches related to the synthetic methods and features focusing on synthesis and/or fabrication with other hybrids and their applications. The diverse applications (namely catalyst, adsorbent to toxic chemicals, agrochemicals management, non-toxic flame retardants, and recycling of plastics) of these multifunctional materials related to a clean and sustainable environment were also summarized.

Efficient Removal of Eriochrome Black T (EBT) Dye and Chromium (Cr) by Hydrotalcite-Derived Mg-Ca-Al Mixed Metal Oxide Composite

Eriochrome Black T (EBT) and chromium (Cr) are considered to be potential pollutants due to their toxicity and severe impact on the environment. In the current study, hydrotalcite-derived Mg-Ca-Al-LDO mixed metal oxide composite was prepared using a conventional co-precipitation method and explored in terms of the removal of Cr and EBT dye from aqueous solution in a batch mode adsorption process. The prepared Mg-Ca-Al-LDH, Mg-Ca-Al-LDO and spent Mg-Ca-Al-LDO adsorbents were characterized to propose the adsorption mechanism. Different adsorption parameters were examined, such as adsorbent dosage, initial concentration, pH, reaction temperature and contact time. The EBT adsorption kinetic results matched strongly with the pseudo-second-order model for both Cr (R2 = 0.991) and EBT (R2 = 0.999). The Langmuir isotherm model exhibited a maximum adsorption capacity of 65.5 mg/g and 150.3 mg/g for Cr and EBT, respectively. The structure and morphology results obtained after Cr and EBT dye adsorption reveal that the adsorption mechanism is associated with electrostatic interactions and surface complexation of Cr and EBT dye with Mg-Ca-Al-LDO surface functional groups. Moreover, more than 84% of the initial adsorption capacity of EBT and Cr can be achieved on the Mg-Ca-Al-LDO surface after five adsorption/desorption cycles. Finally, the Mg-Ca-Al-LDO mixed metal oxide composite can be potentially used as a cost-effective adsorbent for wastewater treatment processes.

Recent trends in layered double hydroxides based electrochemical and optical (bio)sensors for screening of emerging pharmaceutical compounds

The rapid expansion of the human population has given rise to new environmental and biomedical concerns, contributing to different advancements in the pharmaceutical industry. In the field of analytical chemistry over the last few years, layered double hydroxides (LDHs) have drawn significant attention, owing to their extraordinary properties. Furthermore, the novel advancement of LDH-based optical and electrochemical platforms to detect different pharmaceutical materials has acquired substantial attention because of their outstanding specificity, actual-time controlling, and user-friendliness. This review aims to recapitulate advanced LDHs-based optical and electrochemical sensors and biosensors to identify and measure important pharmaceutical compounds, such as anti-depressant, anti-inflammatory, anti-viral, anti-bacterial, anti-cancer, and anti-fungal drugs. Additionally, fundamental parameters, namely interactions between sensor and analyte, design rationale, classification, selectivity, and specificity are considered. Finally, the development of high-efficiency techniques for optical and electrochemical sensors and biosensors is featured to deliver scientists and readers a complete toolbox to identify a broad scope of pharmaceutical substances. Our goals are: (i) to elucidate the characteristics and capabilities of available LDHs for the identification of pharmaceutical compounds; and (ii) to deliver instances of the feasible opportunities that the existing devices have for the developed sensing of pharmaceuticals regarding the protection of ecosystems and human health at the global level.

Layered Double Hydroxides as Rising-Star Adsorbents for Water Purification: A Brief Discussion

Within the frame of this article, briefly but comprehensively, we present the existing knowledge, perspectives, and challenges for the utilization of Layered Double Hydroxides (LDHs) as adsorbents against a plethora of pollutants in aquatic matrixes. The use of LDHs as adsorbents was established by considering their significant physicochemical features, including their textural, structural, morphological, and chemical composition, as well as their method of synthesis, followed by their advantages and disadvantages as remediation media. The utilization of LDHs towards the adsorptive removal of dyes, metals, oxyanions, and emerging pollutants is critically reviewed, while all the reported kinds of interactions that gather the removal are collectively presented. Finally, future perspectives on the topic are discussed. It is expected that this discussion will encourage researchers in the area to seek new ideas for the design, development, and applications of novel LDHs-based nanomaterials as selective adsorbents, and hence to further explore the potential of their utilization also for analytic approaches to detect and monitor various pollutants.

Recent Breakthrough in Layered Double Hydroxides and Their Applications in Petroleum, Green Energy, and Environmental Remediation

The fast development of the world civilization is continuously based on huge energy consumption. The extra-consumption of fossil fuel (petroleum, coal, and gas) in past decades has caused several political and environmental crises. Accordingly, the world, and especially the scientific community, should discover alternative energy sources to safe-guard our future from severe climate changes. Hydrogen is the ideal energy carrier, where nanomaterials, like layered double hydroxides (LDHs), play a great role in hydrogen production from clean/renewable sources. Here, we review the applications of LDHs in petroleum for the first time, as well as the recent breakthrough in the synthesis of 1D-LDHs and their applications in water splitting to H2. By 1D-LDHs, it is possible to overcome the drawbacks of commercial TiO2, such as its wide bandgap energy (3.2 eV) and working only in the UV-region. Now, we can use TiO2-modified structures for infrared (IR)-induced water splitting to hydrogen. Extending the performance of TiO2 into the IR-region, which includes 53% of sunlight by 1D-LDHs, guarantees high hydrogen evolution rates during the day and night and in cloudy conditions. This is a breakthrough for global hydrogen production and environmental remediation.

Catalytic Membrane with Copper Single-Atom Catalysts for Effective Hydrogen Peroxide Activation and Pollutant Destruction

The superior catalytic property of single-atom catalysts (SACs) renders them highly desirable in the energy and environmental fields. However, using SACs for water decontamination is hindered by their limited spatial distribution and density on engineered surfaces and low stability in complex aqueous environments. Herein, we present copper SACs (Cu₁) anchored on a thiol-doped reactive membrane for water purification. We demonstrate that the fabricated Cu₁ features a Cu-S₂ coordination─one copper atom is bridged by two thiolate sulfur atoms, resulting in high-density Cu-SACs on the membrane (2.1 ± 0.3 Cu atoms per nm²). The Cu-SACs activate peroxide to generate hydroxyl radicals, exhibiting fast kinetics, which are 40-fold higher than those of nanoparticulate Cu catalysts. The Cu₁-functionalized membrane oxidatively removes organic pollutants from feedwater in the presence of peroxide, achieving efficient water purification. We provide evidence that a dual-site cascade mechanism is responsible for in situ regeneration of Cu₁. Specifically, one of the two linked sulfur atoms detaches the oxidized Cu₁ while donating one electron, and an adjacent free thiol rebinds the reduced Cu(I)-S pair, retrieving the Cu-S₂ coordination on the reactive membrane. This work presents a universal, facile approach for engineering robust SACs on water-treatment membranes and broadens the application of SACs to real-world environmental problems.