Layered Double Hydroxide Particles Research Articles

Seeding effects of submicron CaAl-NO3 LDH particles on the hydration and properties of Portland cement and sulfoaluminate cement pastes

Layered double hydroxide (LDH) is reported to improve the durability of concretes, primarily due to its ability to exchange anionic species, including chloride, which is implicated in corrosion-driven durability issues. However, there is no comprehensive study investigating the effect of LDH on the properties of different cement systems at both early and mature ages. In this study, the early age and mature age properties of Portland cement (OPC) and calcium sulfoaluminate (CSA) cement pastes seeded with submicron-sized calcium aluminum-NO3 LDH (CaAl-NO3 LDH) were investigated. The effects of the 1–5%mass dosage of LDH on the hydration of both cement systems were characterized by rheology, isothermal calorimetry, porosimetry, compressive strength tests, thermogravimetric analysis, and x-ray diffraction. Time-dependent rheology results indicate that CaAl-NO3 LDH seeding enhanced the buildability of cement pastes, as evidenced by increased plasticity loss, hardening, and yield stress. While LDH seeding accelerated hydration kinetics for both CSA and OPC pastes, interestingly, the OPC exhibited reduced heat release, suggesting potential applications of LDH as heat sink in various areas, including building in hot climates, reducing heat and crack-propensity in mass concrete placements, and 3D-printed OPC-based concretes. Although LDH slightly decreased compressive strengths at both 1d and 28d, its primary role was to expedite the hydration process without enhancing the microstructure or strength of the final product.

Oleic acid-modified layered double hydroxide for Pickering emulsions: (I) Interfacial properties

Layered double hydroxides (LDHs) are one type of potential emulsifiers for Pickering emulsions. Surface modification can regulate their surface properties, thereby affecting their emulsifying behavior. However, there is still a lack of full understanding of the impact of surface modification on their surface properties. In the current work, one Mg3Al-Cl LDH was modified using oleic acid (OA), obtaining six OA-modified products with different OA loadings. Their contact angles and relative dielectric constants were determined, and their surface properties including the interfacial free energies (γ) and solubility parameters (δ) were then estimated from the data. Their apparent molar volumes were estimated using the γ and δ data. OA molecules are coated on the LDH surface via the bidentate bonding mode to form monolayers. The OA modification has no obvious impact on the structure and morphology of LDH particles, but can significantly affect their surface properties. This work provides a better understanding of the dependence of surface properties of LDHs on the surface modification.

Restricted reaction of layered double hydroxide nanoparticles with phosphate in a confined microsphere space

Over the past decades, considerable efforts have been made to find useful solutions for phosphate pollution control. The state transition of nanomaterials from freely dispersed to encapsulated provides a realizable route for their application in phosphate elimination. The separation convenience offered by encapsulation has been widely recognized, however, the unique binding mode of nanostructures and phosphate in the confined space remains unclear, limiting its further development. Here, carboxymethyl cellulose (CMC) microspheres were used as hosts to deploy layered double hydroxide (LDH) nanoparticles. On this basis, we described an attempt to explore the adsorption behavior of LDH and phosphate in the microsphere space. Compared to their freely dispersed analogues, LDH particles exhibited higher structural stability, wider pH adaptability, and better phosphate selectivity when spatially confined in the CMC microsphere. Nevertheless, the kinetic process was severely inhibited by three orders of magnitude. Besides, the saturated phosphate adsorption capacity was also reduced to 74.6 % of the freely dispersed system. A combinative characterization revealed that the highly electronegative CMC host not only causes electrostatic repulsion to phosphate, but also extracts the electron density of the metal center of LDH, weakening its ability to act as a Lewis acid site for phosphate binding. Meanwhile, the microsphere encapsulation also hinders the ion exchange function of interlayer anions and phosphate. This study offers an objective insight into the reaction of LDH and phosphate in the confined microsphere space, which may contribute to the advanced design of encapsulation strategies for nanoparticles.

Structural features and dynamic behaviour of the interlayer space of layered double hydroxide coatings

Layered double hydroxide (LDH) offer great potentialities to design functional coatings with customizable properties by exploiting their anion exchange properties. We investigated the anion exchange properties and expansion capacity of the interlayer space relating to the starting film morphology. ZnAl LDH coatings of different thicknesses and morphologies were first obtained by an in situ method using Al-based substrates. When the anion to intercalate is relatively bigger than the starting nitrates, the intercalation may be constrained by the initial LDH particle size and density composing the film. After optimising the morphology, the intercalation of three functional anions with potential antimicrobial properties was successfully achieved with an expansion of the interlayer space up to 150 % while holding the coating integrity. The release of the guest anion was studied by immersion in physiological saline solution. Finally, the possibility to regenerate the coating was demonstrated supporting the potential of these hybrid coatings for applications.

Synthesis of organic layered double hydroxide from waste bischofite and its application on ageing resistance of asphalt

For the utilization of waste bischofite from salt lakes, the waste bischofite was utilized to synthesize layered double hydroxide (LDH) by hydrothermal method, and the synthesized LDH was further organically intercalated with 3,5-Di-tert-butyl-4-hydroxyphenylpropionic acid (antioxidant, DPA) by anion exchange methods. Then, the synthesized LDH and DPA intercalated LDH (DPA-LDH) were applied to improve the ageing resistance of asphalt. X-ray diffraction and Fourier transform infrared spectroscopy manifested that LDH and DPA-LDH had been successfully synthesized. After DPA intercalation, the adhesive aggregation among LDH particles was obviously ameliorated, and the contact angle of LDH increased from 31.3° to 77.9°, the hydrophilicity of LDH was significantly decreased. The effect of LDH and DPA-LDH (3 % by weight of asphalt) on rheological properties, chemical constituents and molecular weight of asphalt before and after ageing were comprehensively studied. The high-temperature performance grade of asphalt increased from PG64 to PG70 with the addition of LDH and DPA-LDH, which indicated that LDH and DPA-LDH could enhance the high-temperature performance of asphalt. After ageing, the high and low- temperature performance of asphalt worsened, the colloidal stability index (CI) decreased from 3.548 to 1.844, the gel index (GI) was 48 %, the colloidal structure tended to gel structure, the molecular weight (Mw) enlarged from 3387 to 4101 (the Mw growth rate of 21 %). LDH could restrain the destruction of ageing on rheological properties, the colloidal structure gel of asphalt (the GI of 37.4 %) and molecular weight (the Mw growth rate of 13 %) of asphalt, and strengthen the ageing resistance of asphalt. Furthermore, the enhancement of DPA-LDH (the GI of 16.7 % and the Mw growth rate of 6 %) on the ageing resistance of asphalt was more superior than LDH. The result showed that the synthesized DPA-LDH exhibited outstanding performance in improving the ageing resistance of asphalt, which was beneficial to the long-life pavement and the utilization of abandoned bischofite from salt lakes.

Comprehensive Analysis of the Chemical and Structural Transformations of Mg-Al-CO3 Layered Double Hydroxides with Different Mg/Al Ratios at Elevated Temperatures.

Mg-Al layered double hydroxides (LDHs) with CO32- interlayer anions are promising CO2 adsorbents. Here, we analyzed the quantitative gas evolution behaviors of Mg-Al LDH particles with different Mg/Al ratios during the multistep chemical/structural transformations at elevated temperatures. The Mg/Al molar ratio strongly affects the behavior: the transformation changes from two apparent steps to three steps depending on the Mg/Al ratio. The transformation occurs in essentially the same way as that observed for large Mg-Al LDH crystals: (1) release of the interlayer water, (2) partial dehydroxylation of the hydroxyl layers followed by coordination of carbonate ions to the metals, and (3) collapse of the layered structure. We provide a molecular/atomic level picture of the structure in each step of the transformation by first-principles density functional theory (DFT) calculation. The structurally optimized model and reexamination of experimental data showed that step (1) results in a large decrease in the interlayer distance of the LDH from ∼7.6 to ∼6.7 Å (a decrease of ∼0.9 Å) and the possible explanation is the waving of the metal hydroxide layers. This study provides a comprehensive understanding of the structural changes of LDHs with various Mg/Al ratios to resolve the various interpretations in the literature.

Intercalation of Ionic Liquids into LDH Structures for Microwave-Accelerated Polymerizations.

Microwave-accelerated ring-opening polymerization (ROP) of cyclic esters catalyzed by ionic liquid (IL) anions, intercalated into layered double hydroxides (LDHs), has been recently described as a fast and environmentally friendly synthetic way to prepare biodegradable polyester/LDH nanocomposites. However, to observe this synergistic catalytic effect between microwaves and IL anions and to achieve a homogeneous structure of the final polymer nanocomposite, the IL anions must be efficiently intercalated inside the LDH structure. Herein, we investigate the effects of various metal compositions of M2+/Al3+ LDHs (M = Mg, Co, and Ca) and different LDH synthetic routes (one-step direct coprecipitation, two-step coprecipitation/anion exchange, and two-step urea/anion exchange) on the intercalation efficiency of trihexyltetradecylphosphonium bis(2,4,4-trimethylpentyl)phosphinate IL. The most effective IL anion intercalation was observed for Ca2+/Al3+ LDH prepared using the two-step method consisting of coprecipitation and subsequent anion exchange. After optimization, this synthetic pathway led to the production of LDHs with intercalated IL anions and a reduced amount of intercalated water (<0.6 wt %). The catalytic ability of thus optimized LDH particles was demonstrated on the microwave-assisted ROP of ε-caprolactone, showing rapid progress of polymerization. Within minutes, the polycaprolactones with an average molecular mass in the range of 20 000-50 000 g/mol containing fully delaminated and exfoliated LDH nanoparticles were obtained.

Composite with natural ingredients and layered double hydroxide nanoparticles as antioxidant and sunscreen powder material

Layered double hydroxides (LDH) are versatile matrices for designing advanced materials. The need to explore green or sustainable methodologies is scarcely reported. In this project, we evaluated the antioxidant properties and sun protection factor (SPF) of LDH composites with natural components from tomato. The results indicated that the 11 % of organic matter content in the composites is sufficient to increase their antioxidant properties, such as higher antioxidant activity towards ABTS·+ than towards DPPH·. The composite also improves degradation in oxygen atmosphere detected in the Rapidoxy assay, while the SPF indicated that the LDH particles play a crucial role as sunscreen rather than the organic content. This study found that the composite formed by lycopene and LDH particles enhances the hydro-dispersibility and improved the antioxidant stability of lycopene which are key properties to develop cosmetics or food ingredients.

Assessing the Adjuvant Effect of Layered Double Hydroxides (LDH) on BALB/c Mice.

The discovery and validation of new adjuvants are critical areas for vaccinology. Mineral materials (e.g., alum microparticles) have been used for a long time as adjuvants in human vaccine formulations. Nonetheless, the use of nanosized materials is a promising approach to diversify the properties of adjuvants. Nanoclays are potential adjuvants proposed by some research groups. However, their adjuvant mechanisms and safety have not been fully elucidated. Herein, we aimed at expanding the knowledge on the potential adjuvanticity of layered double hydroxide (LDH) nanoparticles by reporting a detailed method for the synthesis and characterization of LDHs and the adsorption of a model antigen (bovine serum albumin, BSA). LDHs varying in diameter (from 56 to 88 nm) were obtained, and an in vitro evaluation revealed that the LDHs are not inherently toxic. BSA was passively adsorbed onto the LDHs, and the immunogenicity in mice of the conjugates obtained was compared to that of free BSA and BSA co-administered with alum (Alum-BSA). The LDH-BSA conjugates induced a higher humoral response that lasted for a longer period compared with that of free BSA and Alum-BSA, confirming that LDH exerts adjuvant effects. The 56 nm LDH particles were deemed as the more efficient carrier since they induced a higher and more balanced Th1/Th2 response than the 88 nm particles. This study is a contribution toward expanding the characterization and use of nanoclays in vaccinology and justifies further studies with pathogen-specific antigens.

Synergistic Sustained Drug-Release System Based on Immobilized Rhamnus frangula L. Phytoextract into Layered Double Hydroxide Covered by Biocompatible Hydrogel.

This work focuses on the synergetic effect obtained by immobilization of Rhamnus frangula L. (RfL) phytoextract in layered double hydroxides (LDHs) matrixes and their subsequent encapsulation into biocompatible hydrogels (HG). In this respect, the LDHs were used as hosts for the immobilization of the phytoextract by a reconstruction method, after which the LDHsRfL were embedded into biocompatible hydrogel (HG) matrixes, based on polyethylene glycol diacrylate (PEGDA), by a radical polymerization reaction. The resulted biocompatible hydrogel composites were characterized by modern methods, while the swelling and rheology measurements revealed that the HG composites steadily improved as the content of RfL phytoextract immobilized on LDHs (LDHsRfL) increased. The following in vitro sustained release of the RfL phytoextract was highlighted by measurements at pH 6.8, in which case the composite HGs with LDHsRfL presented an improved release behavior over the LDHsRfL, thus, underlining the synergistic effect of PEGDA network and LDH particles on the slow-release behavior. The kinetic models used in the RfL release from composite HGs clearly indicate that the release is diffusion controlled in all the cases. The final composite HGs described here may find applications in the pharmaceutical field as devices for the controlled release of drugs.

Biocompatible MgFeCO3 Layered Double Hydroxide (LDH) for Bone Regeneration-Low-Temperature Processing through Cold Sintering and Freeze-Casting.

Layered Double Hydroxides (LDHs) are inorganic compounds of relevance to various domains, where their surface reactivity and/or intercalation capacities can be advantageously exploited for the retention/release of ionic and molecular species. In this study, we have explored specifically the applicability in the field of bone regeneration of one LDH composition, denoted "MgFeCO3", of which components are already present in vivo, so as to convey a biocompatibility character. The propensity to be used as a bone substitute depends, however, on their ability to allow the fabrication of 3D constructs able to be implanted in bone sites. In this work, we display two appealing approaches for the processing of MgFeCO3 LDH particles to prepare (i) porous 3D scaffolds by freeze-casting, involving an alginate biopolymeric matrix, and (ii) pure MgFeCO3 LDH monoliths by Spark Plasma Sintering (SPS) at low temperature. We then explored the capacity of such LDH particles or monoliths to interact quantitatively with molecular moieties/drugs in view of their local release. The experimental data were complemented by computational chemistry calculations (Monte Carlo) to examine in more detail the mineral-organic interactions at play. Finally, preliminary in vitro tests on osteoblastic MG63 cells confirmed the high biocompatible character of this LDH composition. It was confirmed that (i) thermodynamically metastable LDH could be successfully consolidated into a monolith through SPS, (ii) the LDH particles could be incorporated into a polymer matrix through freeze casting, and (iii) the LDH in the consolidated monolith could incorporate and release drug molecules in a controlled manner. In other words, our results indicate that the MgFeCO3 LDH (pyroaurite structure) may be seen as a new promising compound for the setup of bone substitute biomaterials with tailorable drug delivery capacity, including for personalized medicine.

Preparation of ZnMgAl-Layered Double Hydroxide and Rice Husk Biochar Composites for Cu(II) and Pb(II) Ions Removal from Synthetic Wastewater

The efficiency of a new composite material of the layered double hydroxide (LDH) of ZnMgAl and rice husk biochar (RHB) for the removal of Cu(II) and Pb(II) ions from synthetic wastewater was investigated in this study. The images of the scanning electron microscope showed extremely fine crystalline LDH particles decorated on the rough surface of the RHB, while the successful formation of the composite adsorbent (LDH/RHB) was confirmed by the corresponding energy dispersive X-ray and the Fourier-transform infrared spectroscopy. An equilibrium contact time of 30 and 15 min for Cu2+ and Pb2+, respectively, was proposed for the optimum performance of the batch adsorption process. The dose of the LDH/RHB adsorbent was optimized at 0.4 g L−1 yielding maximum adsorption capacities of 117 and 124 mg g−1 for Cu2+ and Pb2+, respectively, with corresponding maximum removal efficiencies of nearly 94% and 99%. A solution pH of 6.0 yielded optimum results with an increasing trend in adsorption capacities and percentage removal by changing the solution pH from 2.0 to 7.0. Based on the best fit of the pseudo-second-order kinetic model to the experimental data, chemisorption was suggested to be the controlling mechanism of adsorption. The fitting of the Langmuir model suggested a monolayer sorption of Cu2+ and Pb2+, and the application of the Dubinin–Radushkevich isotherm proposed physical adsorption.

Formation of Composite Coatings of Layered Double Hydroxide Particles and Hydroxide Gel by Electrophoretic Deposition on Mg Alloy and Corrosion Resistance

To improve the corrosion resistance of Mg alloys, composite coatings of layered double hydroxide intercalated with carbonate (LDH-CO3, hydrotalcite) particles and magnesium and aluminum hydroxide gel were formed on AZ31 Mg alloy by electrophoretic deposition (EPD) using the LDH-CO3 suspension with Mg(NO3)2 and Al(NO3)3 in total of 1.25–125 mmol/L. Wet-dry cyclic corrosion tests were performed for the coated specimens after ultrasonication. LDH-CO3 particle-rich layer and magnesium and aluminum hydroxide gel-rich layer almost alternately piled up to form a composite layer. The hydroxide gel adhered the particles together and to the substrate. At the bottom of the composite layer, flake-shape LDH-structured substance densely covered the substrate surface. The coverage and thickness of the composite layer increased from sub-micrometers to 30 µm with an increase of Mg and Al ion concentrations of the suspension. By ultrasonication, parts of the composite layer delaminated to expose the LDH-structured substance layer, while the coverage by the remaining composite layer increased with an increase of Mg and Al ion concentrations. The LDH-CO3 particles and hydroxide gel composite coatings prevented corrosion initiation even in the areas where the LDH-structured substance layer was exposed.

Oil-in-oil Pickering emulsions stabilized by shigaite-like layered double hydroxide particles

In this work, we report the preparation of simple oil-in-oil emulsions using layered nanoparticles as stabilizers at the interface between silicone and castor oil. Layered double hydroxides with a shigaite-like structure presenting an ideal composition of [Mn6Al3(OH)18][(SO4)2Na].12H2O (S-Na/SO4) were prepared by co-precipitation with increasing pH, followed by particle surface grafting with octhadecyltrimethoxysilane (S-OTMS) in an apolar medium. The powder XRD, SEM, TEM, and specific surface area (BET) techniques showed that the structure and morphology of silane-grafted S-Na/SO4 remained practically unchanged. FTIR, EDS and ICP-OES analyses indicated that the silanes were successfully grafted onto the S-Na/SO4 surface. In addition, to maintaining their structure and morphology, these functionalized materials showed good performance in controlling the hydrophobicity of the surface for application in oil-in-oil emulsions, improving their compatibility for the dispersion in non-polar liquids.

Boron separation by adsorption and flotation with Mg–Al-LDHs and SDBS from aqueous solution

Layered double hydroxides (LDHs) have been shown to be effective adsorbents for boron. However, solid–liquid separation is still a problem when separating boron from industrial radioactive waste liquid. In this research, three types of Mg–Al-LDHs including Mg–Al-LDH(NO3–), Mg–Al-LDH(Cl–) and Mg–Al-LDH(SO42–) were applied to adsorb boron, and moreover sodium dodecylbenzenesulfonate (SDBS) was used to float the LDH particles from aqueous solution after boron adsorption. The results showed that 60 min was sufficient for the equilibrium adsorption of the three LDHs. The boron adsorption capacity of three LDHs was determined as follows: Mg–Al-LDH(NO3–) > Mg–Al-LDH(Cl–) > Mg–Al-LDH(SO42–), and was 2.0, 0.98 and 0.2 mmol·g−1, each ranging from 0 to 80 mmol·L–1 with the initial boron concentration. The efficiency of boron removal by Mg–Al-LDH(NO3–) and SDBS can reach up to 89.7%. Furthermore, the boron flotation mechanism of SDBS and LDHs has been studied, since SDBS as a flotation agent can react with LDHs and penetrate into the interlayer of LDHs in addition to electrostatic attraction. Therefore, LDHs in solution can be floated onto the foam layer to be separated from the solution, and the clarified solution was obtained. The method is simple and promising for boron removal from aqueous solution.

Alternatingly stacked 2D/2D hybrid via preferential intercalation of nitrate ions between layered double hydroxide and graphene oxide

In this study, zinc-aluminum layered double hydroxide (LDH) with nitrate ion intercalation was developed to form a 2D/2D nanostructured hybrid composite on graphene oxide (GO) thin layers. Differing from ordinary LDH/GO composites where carbonate ion intercalation took place in LDH, the hybrid was achieved with exchangeable nitrate anion, hence allowing the subsequent GO and LDH interaction at the nanoscale level. Highly exfoliated GO product was introduced to the co-precipitation of zinc and aluminum ions at 10–30 %wt. compositions. Properties of the prepared hybrid were characterized by several techniques. This hybrid setup offered a synergistic effect of the two materials and benefitted the physicochemical properties including size-control of LDH particles on GO sheet, higher surface area with mesoporosity, and increased carbon combustion temperature making it heat resistant. The efficient adsorption property was then proven by the removal of both cationic and anionic dyes, i.e., methylene blue and methyl orange, up to 81 and 83 mg/g, respectively, and still recoverable due to its improved stability. The fast-forming mechanism of LDH, with and without GO participation, was revealed by the wide-angle x-ray diffraction, suggesting the initial formation of LDH intermediate that later re-structured to a more uniform nanohybrid. The findings of the study suggest that the 2D/2D hybrid system can be formed under facile precipitation. It is promising for water decontamination, controlled release, and delivery system.

Molecular Dynamics Model to Explore the Initial Stages of Anion Exchange involving Layered Double Hydroxide Particles.

A classical molecular dynamics (MD) model of fully unconstrained layered double hydroxide (LDH) particles in aqueous NaCl solution was developed to explore the initial stages of the anion exchange process, a key feature of LDHs for their application in different fields. In particular, this study focuses on the active corrosion protection mechanism, where LDHs are able to entrap aggressive species from the solution while releasing fewer corrosive species or even corrosion inhibitors. With this purpose in mind, it was explored the release kinetics of the delivery of nitrate and 2-mercaptobenzothiazole (MBT, a typical corrosion inhibitor) from layered double hydroxide particles triggered by the presence of aggressive chloride anions in solution. It was shown that the delamination of the cationic layers occurs during the anion exchange process, which is especially evident in the case of MBT-.

Antimicrobial Pickering emulsions stabilized with layered double hydroxides intercalated with SO[formula omitted]/Na[formula omitted]/Ag[formula omitted] and decorated with Ag[formula omitted]/Ag2O nanoparticles

This study aimed to develop Pickering emulsions with high antimicrobial activity. Initially, layered double hydroxides (LDHs) of Zn2Al intercalated with SO42−/Na+ were prepared and exchanged with an excess of Ag2SO4, where some of the Na+ cations were replaced with Ag+ cations and the layered particles were decorated with Ag0/Ag2O nanoparticles. Next, oil-in-water emulsions containing paraffinic oil droplets stabilized with LDH were prepared by ultrasound treatment. Phase separation was established quickly after the sonication process and the particles were organized around the oil droplets. The size of the droplets and the storage stability of the emulsions were determined after 14 days. Emulsions formulated using 0.3 oil fraction and 0.25 wt% of LDH particles were investigated against four microbial strains: Escherichia coli, Staphylococcus aureus, Aspergillus niger and Candida albicans. The assays indicated that the emulsions stabilized with LDH particles exhibited greater activity compared to the dispersed powdered material, suggesting that the emulsion favors the interactions of the nanoparticles with the microorganisms.

Biosurfactant assisted in situ green and clean preparation route for layered double hydroxides and their green metrics-based sustainability assessment

Hybrid advanced multifunctional materials based on layered double hydroxides (LDH) and intercalated guest biomolecule(s) are of high industrial and academic importance and have found promising applications in diverse fields such as biomedical, energy, environment, agriculture, etc. This report strategically develops a new innovative green sonochemical route to incorporate rhamnolipid (RL) and surfactin (SR) into 3D hierarchical flower-like Mg-Al-LDH micro-nano-structures. When compared to traditional mechanochemical co-precipitation and ion-exchange methods, the designed one-pot and scalable method was sustainable and green chemistry compliant, with improved time, energy, and solvent efficiency. RL/SR anions act as an interlayer anion and a template for the fabrication of LDH sheets leads to the increase in the basal spacing and impair LDH sheet interaction. Consequently the vesicle-type phase can be fabricated using biosurfactant in aqueous media under the influence of metal cations induced the curved growth of RL/SR-intercalated LDH nuclei and the flower-like assemblage of LDH particles. The structure, morphology, surface properties, and thermal stability were evaluated. The release profile and kinetics of RL/SR of the intercalated LDHs was studied. Slow and controlled release of SR from the Mg/Al-LDH micro-nano-structures was observed for a prolonged time up to 10 h and followed zeroth-order kinetics, whereas RL release was well described in Higuchi model, indicating the release of the biomolecule via a diffusion mechanism. Cytotoxicity (in L929 and 3T3 fibroblast cells) and haemolytic tests suggested that cytotoxic effect in the range of 25–400 mg/ml and the haemolytic ratio was <4 % at 25–600 mg/ml, showing good biocompatibility of the biosurfactant-intercalated LDHs. Taken together, these micro-nano-structures can be used as potential sustained- or extended-release candidate for agricultural, biomedical or water treatment applications.

First-Principle Colloidal Gate for Controlling Liquid and Molecule Flow Using 2D Claylike Nanoparticles.

Herein, we exploit the natural tendency of two-dimensional (2D) clay nanoparticles to self-assemble and restrict water permeability in soils to fabricate a first of its kind synthetic, pH-activated, reversible, and tunable colloidal flow gate. To realize this, we studied the effect of the pH level of a suspension of claylike layered double hydroxide (LDH) nanoparticles on the LDH coagulation process. We then packed the LDH into a fixed-bed column and examined the effect of pH on mass transport through the column. We found that the 2D platelike LDH particles coagulate in an edge-to-edge configuration, which renders highly nonisotropic aggregates, pivotal for obstructing the transport of liquid and molecules therein. We showed that the coagulation and flow through the column may be regulated by imposing various pH levels as an external stimulus to affect LDH zeta potential. Hence, this work shows that the flow through a column comprising a 2D particle bed can be regulated in a reversible manner by simply alternating the pH of the wash solution, equilibration time, or gate dimensions. Furthermore, we show that, subject to pH treatment, we may open and close the colloidal gate for the transport of large molecules and provide selective transport thereof.