Use Of Layered Double Hydroxides Research Articles

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.

Layered Double Hydroxides: Recent Progress and Promising Perspectives Toward Biomedical Applications.

Layered double hydroxides (LDHs) have been widely studied for biomedical applications due to their excellent properties, such as good biocompatibility, degradability, interlayer ion exchangeability, high loading capacity, pH-responsive release, and large specific surface area. Furthermore, the flexibility in the structural composition and ease of surface modification of LDHs makes it possible to develop specifically functionalized LDHs to meet the needs of different applications. In this review, the recent advances of LDHs for biomedical applications, which include LDH-based drug delivery systems, LDHs for cancer diagnosis and therapy, tissue engineering, coatings, functional membranes, and biosensors, are comprehensively discussed. From these various biomedical research fields, it can be seen that there is great potential and possibility for the use of LDHs in biomedical applications. However, at the same time, it must be recognized that the actual clinical translation of LDHs is still very limited. Therefore, the current limitations of related research on LDHs are discussed by combining limited examples of actual clinical translation with requirements for clinical translation of biomaterials. Finally, an outlook on future research related to LDHs is provided.

The adsorption and diffusion behavior of chloride in recycled aggregate concrete incorporated with calcined LDHs

Recycled concrete aggregate (RCA) is an important form for reusing of waste concrete. However, the presence of corrosive ions, specifically chloride ions, which are absorbed on the surface of RCA or infiltrated from the external environment, significantly affects the mechanical performance and durability of recycled aggregate concrete (RAC). This paper aims to suppress the erosion and diffusion of chloride ions in RAC by adding calcined layered double hydroxides (LDOs), utilizing the restructuring and anions exchange properties of LDOs. The dissolution ratio of chloride ions carried by RCA and the adsorption efficiency of LDOs on the leaching ions were analyzed using the silver nitrate titration method. The maximum chloride adsorption capacity of the LDOs is 31.052 mg/g. Additionally, the inhibitory effect and mechanism of LDOs on chloride ion attack were detailed evaluated by the techniques combining mercury intrusion porosimetry (MIP), scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM and EDS), rapid chloride migration coefficient method (RCM), and electrochemical impedance spectrum. The results indicate that LDOs exhibit a good adsorption effect on chloride ions leaching from RCA, and the adsorption efficiency is negative correlation with the pH value. Furthermore, the small size effect of LDOs plays a filling role in the pores of concrete, increasing the compactness and penetration resistance of chloride ions of RAC. This work provides a promising approach to enhance the mechanical and durability properties of RAC by incorporating with LDOs utilizing its chloride ion capture feature and nano-filling effect. And the findings of this research can also be extended to the use of LDOs for treatment of other corrosive anions, such as SO42− and CO32− in RAC, demonstrating its applicability in a broader context.

Hybridize magnesium-iron layered double hydroxide with biopolymers to develop multiple pathways for phosphate sorption and release: A potential slow release phosphorus fertilizer

The intensive use of chemical fertilizers presents a dilemma for sustaining food production or causing soil degradation and posing agricultural contamination. The reduction of phosphorus (P) fertilizer usage is particularly crucial because it is a limited resource. This situation calls for the development of efficient P fertilizers to address the impending P deficiency. Mg-Fe layered double hydroxides (LDH) with 0.5 and 2.5 M metal precursors were hybridized with chitosan (CTS) and carboxymethyl cellulose (CMC) to design alternatives of slow release P fertilizers. While phosphate (PO4) sorption capacities were in the order of Mg-Fe LDH > 2.5LDH-CTS/CMC > 0.5LDH-CTS/CMC, PO4 release from 0.5LDH-CTS exhibited a rate constant ∼2.6–7.6 times lower than that of other samples, which had not reached equilibration even after 2688 h. Fe-EXAFS data implied the greatest degree of isomorphic substitution into LDH interlayer of 0.5LDH-CTS. In addition to intercalated PO4, P-XANES data also suggested the organic-P and Fe(III)-P on 0.5LDH-CTS, causing versatile retention processes. After 2688 h of PO4 release, LDH structure gradually weathered and transformed primarily into a structure dominated by ferric (oxyhydrox)oxides. On 0.5LDH-CTS, however, 14.3% of Fe inventory was contributed by Fe(II) species. The Fe(II) domains in conjunction with the likely remaining Mg-Fe LDH structure and amorphous Mg(OH)2 provided bonding sites for PO4, serving as the key factor for the continuous PO4 release beyond 2688 h. Such extended duration of PO4 release warrants the use of LDHs hybridized with biopolymers as promising substitutes for slow release P fertilizers.

Layered double hydroxides for corrosion-related applications-Main developments from 20years of research at CICECO.

This work describes the main advances carried out in the field of corrosion protection using layered double hydroxides (LDH), both as additive/pigment-based systems in organic coatings and as conversion films/pre-treatments. In the context of the research topic "Celebrating 20years of CICECO", the main works reported herein are based on SECOP's group (CICECO) main advances over the years. More specifically, this review describes structure and properties of LDH, delving into the corrosion field with description of pioneering works, use of LDH as additives to organic coatings, conversion layers, application in reinforced concrete and corrosion detection, and environmental impact of these materials. Moreover, the use of computational tools for the design of LDH materials and understanding of ion-exchange reactions is also presented. The review ends with a critical analysis of the field and future perspectives on the use of LDH for corrosion protection. From the work carried out LDH seem very tenable, versatile, and advantageous for corrosion protection applications, although several obstacles will have to be overcome before their use become commonplace.

Layered Double Hydroxides (LDH) as nanocarriers for antimicrobial chemotherapy: From formulation to targeted applications

Layered double hydroxides, shortly LDH, are commonly used in medical applications, particularly in human therapies for their abilities to sorb and/or entrap, and then release active drugs. In this work, we synthesized several original LDH nanocarriers that strictly host antibiotics into their interlayer space and can be used for antimicrobial purpose. Combining Infrared and XRD analyses, we evidenced the total antibiotic intercalation within the nanocarriers. Our results also highlighted the high stability of synthesized LDH in solution and particularly in rich nutritive medium used as surrogate for biological media. According to our microbial toxicity assays, we demonstrated that the antibacterial activity of LDH was purely bacteriostatic in absence of hosted biocides molecules. Besides, we observed an additive effect in LDH antibacterial activity when antibiotics were hosted and released from these nanocarriers. The use of LDH as nanocarriers for the delivery of antimicrobial agents should be of major interest in antimicrobial purpose as they offer the possibility to be recycled and reloaded with antimicrobial agents after total release.

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.

Cyano-Anion Intercalated Layered Double Hydroxides for Electrocatalytic Degradation of Acetaldehyde in Gas Phase

Layered double hydroxides (LDHs) are identified as potential material in water splitting or oxygen evolution reaction (OER). Since the water splitting potential is minimized when the use of LDH modified electrode, the application of the LDHs has been still challenged in air pollution control but the water splitting potential should be attempted to extended. Anions or cations intercalation has many applications in electrocatalysis and energy harvesting field. In this approach, the present work aimed to investigate a cyano-anion intercalation on NiCo-LDH and its application to degradation of acetaldehyde in gas phase.The NiCo-LDH was prepared using coprecipitation method under a low temperature. The prepared NiCo-LDH was intercalated with cyano-anion using KCN. After surface characterization to confirm the intercalation of cyano-anion, the NiCo-CN-LDH was coated on a 3D metal foam electrode using a 5% Nafion solution. Redox behavior of the prepared NiCo-CN-LDH electrode was observed in 1M KOH solution by cyclic voltammetry (CV) technique. Once identified the water splitting potential window, the NiCo-CN-LDH electrode was examined on the acetaldehyde (AA) reduction/oxidation in the 1M KOH solution. To evaluate the NiCo-CN-LDH electrode effect on AA, the potential truncated CV at various potential regions. After solution-phase CV analysis, the NiCo-CN-LDH electrode was fitted into Nafion membrane divided electrolytic flow through cell for the gas-phase degradation analysis either by anodic or cathodic half-cell. The NiCo-CN-LDH electrode’s redox behavior was analyzed and compared with solution phase redox behavior. Then the NiCo-CN-LDH electrode was applied on the AA degradation either by oxidation or reduction by continuous flow of AA gas. The degradation efficiency was monitored by ex-situ GC-MS. The promoted effect of cyano-anion on widening the water splitting potential window and its usage on gas phase AA degradation will be discussed in detail at the conference.Acknowledgement: This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (Grant No.: NRF-2021R1I1A1A01049901) and from the Grant No. NRF-2020R1A6A1A03042742.

Remediation of Cd-contaminated soil through different layered double hydroxides: The weakness of delamination and mechanism

The great variability of the reaction of layered double hydroxides (LDHs) with anions and cations, especially the ultra-thin thickness, large specific surface area and fully-exposed active sites of single LDHs, may be crucial factors in the remediation of Cd-contaminated soil. In this study, the environmental behavior of Cd was investigated through sequential extraction method and plant potting tests, so as to verify the immobilization efficiency of LDHs and single LDHs in Cd-polluted soil. The results revealed that S-LDHs differed significantly from the original LDHs, and Ca-LDH were the best material for immobilizing Cd. Through sequential extraction procedures, the exchangeable fraction of Cd decreased and its residual fraction increased by forming CdCO3(s) and Cd5(OH)8(NO3)2.2 H2O. After treating the Cd-contaminated soil, the LDH layers were restacked through the XRD-pattern-confirmed S-Mg-LDH, while S-Ca-LDH were more converted to CaCO3 and Cd5(OH)8(NO3)2.2 H2O. Through investigating the structural changes of stabilizers in soil remediation via a series of characterization, the difference between Mg-LDH and S-Mg-LDH was in the generation of CdCO3(s), while that between Ca-LDH and S-Ca-LDH was in the formation of CdAl-LDH-CO3. Single LDHs and LDHs showed the opposite effect when reacting with different pollutants (Cd and Cr), and single LDHs were not as effective for Cd in soil as was previously reported. These results helped with a better understanding of the use of LDHs as a solidified agent as well as the mechanisms involved.

A review on heavy metal ions adsorption from water by layered double hydroxide and its composites

• We selected to review topics related to the specific application of LDH removal of heavy metals. • Classify and summarize its modification methods, absorption properties, composition, structure, and other aspects. • It is determined that future research needs to reduce environmental impact and economic costs to promote the synthesis and use of LDH. • This system summary will provide helpful guidance for preparing high-efficiency LDHs-based adsorbents and offer critical clues to elucidating the adsorption behavior of heavy metals on LDHs-based materials. Heavy metal pollution is highly toxic and persistent, posing a severe threat to human health, agriculture, and the safe environment. Therefore, there is an urgent need for fast and efficient heavy metal removal technology to deal with emergency response to heavy metal leakage. In recent years, the development of a unique layered double hydroxide material has attracted widespread attention in sewage treatment. Due to these fundamental scientific issues, the general concern about environmental pollution management of LDH-based materials, and the recent significant developments in this field, it is necessary to conduct a thematic review. This article summarizes 474 related articles published since 2005 and outlines functionalized layered double hydroxide (LDH) research status as heavy metal adsorption materials. In addition, there is still a lack of reviews on the adsorption characteristics, interaction mechanism, and application of LDHs-based nanomaterials in heavy metal removal. Here, the primary purpose of this article is to systematically summarize LDHs-based materials and their applications in removing heavy metals from aqueous solutions ( Fig. 1 ). First, we will focus on its preparation and modification methods to understand LDH intuitively. Subsequently, the effects of different environmental conditions on factors such as pH, temperature, and contact time were summarized. Finally, the interaction mechanism between LDHs composites and heavy metals is briefly described, and a quick conclusion is given.

A comparative study of the use of layered double hydroxides (LDHs) and zeolite to reduce nitrate leaching in greenhouse maize farming

The use of Layered Double Hydroxides (LDHs) and zeolite to reduce nitrate leaching in greenhouse maize farming was investigated. A research was conducted using a completely randomized factorial design experiment with 5 different treatments of zeolite and LDH application, 3 treatments of LDH (4, 8 and 16 g LDH per kg of soil), 1 zeolite treatment (16 g zeolite per kg of soil), 2 amounts of nitrate fertilizer with urea source (150 and 300 kg urea per hectare), 2 urea fertilizer installments with the control sample. In this research, the irrigation was repeated four times to collect the effluent. The results showed that the highest concentration of nitrate output in effluent was related to treatments without LDH and zeolite, and the lowest level was obtained with 16 g LDH kg−1 soil treatment. Using 16 g LDH kg−1 soil reduced N-nitrate leaching loss by up to 75% compared to the control sample. Comparison of using 16 g LDH kg−1 soil with 16 g zeolite kg−1 soil showed that LDH has a much higher ability to absorb nitrate from soil and prevent its leaching. Such that the lowest amount of LDH, 4 g LDH kg−1 soil, had more impact on mean reduction of effluent’s nitrate concentration compared to 16 g zeolite kg−1 soil. With increasing the use of LDH and two-installment application of fertilizer increased the number of green leaves and biological yield.

The determination of synthesis conditions and color properties of pigments based on layered double hydroxides with Co as a guest cation

Nail polish, in particular gel polish, is the most commonly used cosmetic product. A component of the gel polish, which determines the consumer color characteristics of the gel polish. Layered double hydroxides (LDH) are promising pigments. To expand the range of colors and shades of pigments, the use of LDH with colored host and guest cations is promising. The parameters of synthesis and color characteristics of samples of Zn-Co and Cu-Co hydroxide pigments were studied. To obtain LDH with Co as a guest cation in the synthesis, the conversion of cobalt to the trivalent state was carried out at a temperature of 80 °C using oxidation with atmospheric oxygen or sodium hypochlorite. The oxidation efficiency was evaluated by X-ray phase analysis by the presence or absence of cobalt-containing phases. The color characteristics of the synthesized pigment samples were studied by spectroscopic measurement and calculation in RGB, CIELab, and LCH color models. The low efficiency of cobalt oxidation at the moment of Zn-Co LDH synthesis with atmospheric oxygen at an elevated synthesis temperature of 80 °C was shown, while cobalt was released as a separate Co3O4 phase. A higher efficiency of cobalt oxidation at the moment of synthesis using sodium hypochlorite with the formation of Zn-Co LDH was revealed. It is recommended to use the hypochlorite oxidation of Co2+ to Co3+ in the LDH synthesis with Co in the form of a guest cation. The formation of a separate phase of zinc oxide was found in both types of oxidation due to the thermal decomposition of zinc hydroxide. Comparative analysis of color characteristics showed that all samples have a brown color of different saturation. It was revealed that during the formation of Co-containing LDH, the lightness of the color decreases. Color saturation increases in the case of a colored host cation, such as Cu.

Development of a Mesoporous Silica-Supported Layered Double Hydroxide Catalyst for the Reduction of Oxygenated Compounds in E. grandis Fast Pyrolysis Oils

Biomass fast pyrolysis oil is a potential renewable alternative to fossil fuels, but its viability is constrained by its corrosiveness, low higher heating value and instability, caused by high oxygenate concentrations. A few studies have outlined layered double hydroxides (LDHs) as possible catalysts for the improvement of biomass pyrolysis oil characteristics. In this study, the goal was to reduce the concentration of oxygen-rich compounds in E. grandis fast pyrolysis oils using CaAl- and MgAl- LDHs. The LDHs were supported by mesoporous silica, synthesised at different pHs to obtain different pore sizes (3.3 to 4.8 nm) and surface areas (up to 600 m2/g). The effects of the support pore sizes and use of LDHs were investigated. GC/MS results revealed that MgAl-LDH significantly reduced the concentrations of ketones and oxygenated aromatics in the electrostatic precipitator oils and increased the concentration of aliphatics. CaAl-LDH had the opposite effect. There was little effect on the oxygenate concentrations of the heat exchanger oils, suggesting that there was a greater extent of conversion of the lighter oil compounds. Bomb calorimetry also showed a marked increase in higher heating values (16.2 to 22.5 MJ/kg) in the electrostatic precipitator oils when using MgAl-LDH. It was also found that the mesoporous silica support synthesised at a pH of 7 was the most effective, likely due to the intermediate average pore width (4 nm).

The Curing Kinetics of Multiscale [Ni(EDTA)]-2 Intercalated Zn-Al Layered Double Hydroxides: Glass Fiber–Epoxy Composite Prepreg

In the present research, the effect of Zn2Al layered double hydroxides (LDH) and nickel (II)-EDTA complex intercalated LDH (LDH-[Ni(EDTA)]-2) on the cure kinetics of glass fiber/epoxy prepreg (GEP) was explored using nonisothermal differential scanning calorimetry (DSC). The results showed that LDH caused a shift in the cure temperature toward lower temperatures while accelerating the curing of epoxy prepregs. The use of LDH-[Ni(EDTA)]-2 more profoundly influenced the acceleration of the curing process. The curing kinetics of prepregs was assessed through the differential isoconversional Friedman (FR) technique and the integration method of Flynn–Wall–Ozawa (FWO) and Kissinger–Akahira–Sunose (KAS). A decrease was detected in the E α value of glass fiber/LDH-[Ni(EDTA)]-2/epoxy (GELP) and glass fiber/LDH-[Ni(EDTA)]-2/epoxy (GELNiP) prepregs at small cure degrees relative to GEP, suggesting the catalytic effect of LDH or LDH-[Ni(EDTA)]-2 on the initial epoxy/amine reaction. Furthermore, LDH-[Ni(EDTA)]-2 performed better due to the catalyst role of nickel (II). Moreover, the activation energy exhibited lower reliance on the degree of conversion in the cases of GELP and GELNiP rather than pure epoxy prepregs. An autocatalytic model was used to evaluate the curing behavior of the system. Based on the results, the curing reaction of the epoxy prepreg can be described by the autocatalytic Šesták-Berggren model even after the incorporation of LDH or LDH-[Ni(EDTA)]-2. The kinetic parameters of the autocatalytic model (such as E α , A , m , n ) and the equations explaining the curing behavior of prepregs were introduced as well whose predictions were in line with the experimental findings.

Effects of layered double hydroxides on the thermal and flame retardant properties of intumescent flame retardant high density polyethylene composites

SummaryIn this study, two layered double hydroxides (LDHs), ZnAl‐LDH, and MgAl‐LDH, were combined with intumescent flame retardant (IFR) consisting of ammonium polyphosphate and tris (2‐hydroxyethyl) isocyanurate to prepare flame retardant high density polyethylene composites. The thermal and flame retardant properties of these composites were investigated by thermogravimetric analysis, limiting oxygen index measurement, and cone calorimetry, while the morphology and chemical structure of the char residue were analyzed by scanning electron microscopy, Fourier transfer infrared spectroscopy, and laser Raman spectroscopy. The results showed that the peak heat release rate (PHRR) of both HD/IFR/Zn‐LDH and HD/IFR/Mg‐LDH composites was 52.0% and 12.0% lower than that of HD and HD/IFR, respectively, suggesting that there was no difference in the reduction of PHRR between the two LDHs. The use of LDHs resulted in the formation of compact char residue with a high graphitic degree, but no significant increase in tensile strength.

Fumonisin B1 Interaction with Mg-Al and Mg-Fe Layered Double Hydroxides: Removal Efficiency and Mechanisms.

Mycotoxins in feed and food are highly toxic and pose a serious danger even at very low concentrations. The use of bentonites in animal diet can reduce toxin bioavailability. However, some mycotoxins like fumonisin B1 (FB1) form anionic species which excludes the use of negatively charged clays. Layered double hydroxides (LDH) with anion-exchange properties, in theory, can be perfect candidates to adsorb FB1. However, fundamental research on the use of LDH for mycotoxins removal is scarce and incomplete. Thus, the presented study was designed to explore such a possibility. The LDH materials with differing chemistry and layer charge were synthesized by co-precipitation both from metal nitrates and chlorides and were then tested for FB1 removal. XRD, FTIR, XPS, and chemical analysis were used for the LDH characterization and to obtain insight into the removal mechanisms. A higher adsorption capacity was observed for the Mg/Al LDH samples (~0.08–0.15 mol/kg) in comparison to the Mg/Fe LDH samples (~0.05–0.09 mol/kg) with no difference in removal efficiency between Cl and NO3 intercalated LDH. The adsorption capacity increased along with lower layer charge of Mg/Al and was attributed to the lower content of bonded carbonates and the increase of non-polar sites which led to matching between the adsorption domains of LDH with FB1. The FTIR analysis confirmed the negative effect of carbonates which hampered the adsorption at pH 7 and led to the highest adsorption at pH 5 (FB1 content ~15.8 ± 0.75 wt.%). The fast surface adsorption (1–2 min) was dominant and XRD analysis of the basal spacing indicated that no FB1 intercalation occurred in the LDH. The XPS confirmed a strong interaction of FB1 with Mg sites of LDH at pH 5 where the interaction with FB1 carboxylate moieties COO− was confirmed. The research confirmed a high affinity and selectivity of LDH structures towards anionic forms of FB1 mycotoxin.

Facile synthesis of FeCo layered double oxide/raspberry-like carbon microspheres with hierarchical structure for electromagnetic wave absorption

Transition metal compositions (Fe, Co and Ni) have always been promising candidates for electromagnetic wave (EMW) absorbers. In this study, the FeCo layered double hydroxide (LDH) supported on raspberry-like carbon spheres (RCs) was synthesized by a simple hydrothermal method and the spontaneous electrostatic self-assembly process. The surface FeCo-LDH is then transformed into FeCo layered double oxide (LDO) with different compositions after calcination treatment (650 °C and 700 °C), forming a typical hierarchical structure. The sample calcined at 700 °C exhibited an ultra-wide effective absorption bandwidth (fe) (RL < −10 dB) of 7.4 GHz (from 10.6 to 18.0 GHz) at the matched thickness of 2.2 mm. The remarkable EM wave absorption properties are attributed to the strong interface polarization due to the various phase boundaries in LDO shell as well as sufficient heterointerfaces between LDO shell and RCs. It should be emphasized that LDH is rarely used for EMW absorption, and the use of LDH positively charged characteristics to fabricate hierarchical materials is a meaningful attempt and confirms the potential of LDH in EMW absorbing materials.

Enhanced properties of poly(lactic acid) by concurrent addition of organo-modified Mg-Al layered double hydroxide (LDH) and triethyl citrate

Synergistic effects of organo-modified Mg-Al layered double hydroxide (LDH) and triethyl citrate (TEC) on the properties of poly(lactic acid) (PLA) were demonstrated. PLA/LDH nanocomposites in the absence and presence of TEC were fabricated via solution casting technique. Morphological analysis revealed that as the LDH concentration increases, the number of aggregations is also increased; however, introduction of TEC considerably enhanced the dispersion quality of LDHs. Differential scanning calorimetry results showed that the addition of LDH and TEC had no significant influence on the crystallinity of nanocomposites obtained from solution casting. In contrast, once the samples were cooled from melt, the concurrent use of LDH and TEC led to a dramatic enhancement in the crystallinity of PLA ( X c = 55.5%). Moreover, the LDH nanoparticles counterbalanced the adverse effects of plasticization by TEC leading to enhanced toughness of the final nanocomposites. LDH had also a positive influence on thermal stability of PLA, indicating the heat-insulating role of LDH particles. In conclusion, the concurrent use of LDH and TEC could extend the applicability of PLA especially in food packaging applications.

Mg/Al LDH Enhances Sulfate removal and Clarification of AMD Wastewater in Precipitation Processes.

The sulfate removal from acid mine drainage (AMD) water (initial concentration: 5301 mg/L) was investigated by precipitation and/or adsorption using calcium hydroxide (Ca(OH)2) and synthetic layered double hydroxide (LDH) of the Mg/Al type. The exclusive use of LDH efficiently removed sulfates (64.2% reduction); however, alteration of its structure was observed due to low pH. The use of Ca(OH)2 in different doses calculated in relation to gypsum stoichiometry allowed to achieve an 86% removal of sulfates. Depending on the equilibrium pH, gypsum or ettringite were the main identified phases. The two-step removal, involving the use of Ca(OH)2 followed by LDH, was less efficient than the use of the Ca(OH)2/LDH mixture when the stoichiometric amount of Ca(OH)2 in relation to gypsum was applied. The application of mixture resulted in a fast pH increase, which prevented destruction of the LDH structure. Most importantly, the use of mixture significantly reduced the sludge volume and enhanced its settling velocity.

Rapid Removal and Efficient Recovery of Tetracycline Antibiotics in Aqueous Solution Using Layered Double Hydroxide Components in an In Situ-Adsorption Process

This work demonstrates a simple approach for the efficient removal of tetracycline (TC) antibiotic from an aqueous solution. The in situ-adsorption removal method involved instant precipitation formation of mixed metal hydroxides (MMHs), which could immediately act as a sorbent for capturing TC from an aqueous solution, by employing layered double hydroxide (LDH) components including magnesium and aluminum ions in alkaline conditions. By using this approach, 100% removal of TC can be accomplished within 4 min under optimized conditions. The fast removal possibly resulted from an instantaneous adsorption of TC molecules onto the charged surface of MMHs via hydrogen bonding and electrostatically induced attraction. The results revealed that our removal technique was superior to the use of LDH as a sorbent in terms of both removal kinetics and efficiency. Moreover, the recovery of captured TC was tested under the influence of various common anions. It was found that 98% recovery could be simply achieved by using phosphate, possibly due to its highly charged density. Furthermore, this method was successful for efficient removal of TC in real environmental water samples.