The effect of interlayer anion on the reactivity of Mg–Al layered double hydroxides: Improving and extending the customization capacity of anionic clays

Adsorption of polycyclic aromatic hydrocarbons over CuZnFeAl–LDH modified by sodium dodecyl sulfate

Polycyclic aromatic hydrocarbons (PAHs) have received extensive attention due to being highly toxic, mutagenic, and carcinogenic organic pollutants. As a result, a series of adsorbents have been designed and developed to solve the problem. In this paper, CuZnFeAl–S has been explored as a highly efficient adsorbent for PAHs. First, CuZnFeAl–LDH was prepared using a coprecipitation method and then calcined at 500 °C to obtain CuZnFeAlO. Finally, CuZnFeAl–S was prepared by modifying CuZnFeAlO with sodium dodecyl sulfate (SDS). The physical and chemical properties of the adsorbents were characterized by XRD, N₂ adsorption–desorption, SEM, ICP, FT-IR, TG-DSC, and IGC; subsequently their adsorption performance was investigated. The results show that the surface properties of CuZnFeAl–S changed from hydrophilic to hydrophobic after SDS modification, which enhanced the adsorption of PAHs obviously. The removal of naphthalene and phenanthrene on CuZnFeAl–S reached 97.3% and 90.3%, respectively. And the adsorption process of naphthalene and phenanthrene conforms to Langmuir adsorption and Freundlich adsorption, respectively. Besides, the adsorption thermodynamics indicate that the adsorption of PAHs was a spontaneous exothermic reaction. The highly efficient PAH adsorption performance of CuZnFeAl–S is the synergistic result of various molecule interactions, such as hydrogen bonding, π–π interactions, and electrostatic attraction.

CuZnFeAl–S improves the adsorption of polycyclic aromatic hydrocarbons, which has a profound impact on environmental treatment.

Exploring a new free-standing polyelectrolyte (PEM) thin film as a predictive tool for drug-mucin interactions: Insights on drug transport through mucosal surfaces

The main objective of the present work was to design a biomimetic free-standing multilayered PEM film, constructed by the layer-by-layer (LbL) assembly approach, based on natural biopolymers and intended to recreate the complex mucus-mimetic matrices in order to provide mechanistic insights into biophysical interactions between drugs and the physiological gel-forming mucin network of mucus that covers the mucosal epithelia named as(CS/ALG)/(PGM) PEM film. The obtained results indicate that mucin may delay or increase drug precipitation on the mucus layer, depending on specific drug-mucin interactions driving drug supersaturation or drug crystallization phenomena. It was found that the drug lipophilicity characteristics governed the mucin binding degree, which had an influencing role on the drug translocation across this gel-like hydrogel. Moreover, the ionization of these drugs did not have a significant role on the drug binding ability to mucin as much as the lipophilicity properties did. The (CS/ALG)/(PGM) PEM film may be a promising tool to routine testing drug-mucus interactions to evaluate biophysical interactions between this protective barrier of the organism against different drug therapeutic products or external aggressive agents, leading to the optimization of drug delivery products or drugs for particular disease states.

Specific Ion Effects on the Colloidal Stability of Layered Double Hydroxide Single-layer Nanosheets

The surface charge properties and aggregation behavior of positively charged Mg-Al-NO₃ layered double hydroxide (LDH) single-layer nanosheets dispersed in water were investigated in the presence of K⁺ salts with different mono-, di-, and trivalent anions, using electrophoresis and dynamic light scattering techniques. An increase in the salt concentration can significantly decrease the effective surface charge density (σ_eff) of LDHs, leading to the aggregation of nanosheets. The critical coagulation concentration (CCC) or ionic strength (CCIS) of salts for nanosheets significantly decreases with an increase in the valence of anions. Specific ion effects, with a partially reverse Hofmeister series, are observed. On the basis of the Stern model and the DLVO theory, the relationship of CCC with σ_eff and the ionic valences of salts (z_i) is theoretically analyzed, which can accurately describe the dependence of CCC on the σ_eff and z_i but cannot explain the origin of specific ion effects. To explore the origin of specific ion effects, a correlation between CCIS and the specific adsorption energy (E_sc) of anions within the Stern layer is developed. Especially, an empirical relationship of E_sc with the characteristic physical parameters of anions is proposed. Our model can accurately predict the CCISs of at least monovalent anions and divalent anions (CO₃^2- and SO₄^2-), demonstrating that the specific ion effects observed can be attributed to the differences in ionic size, polarizability, and hydration free energy (or the formation capacity of anion-cation pairs) of different anions. This work not only deepens the understanding of specific ion effects on the colloidal stability but also provides useful information for the potential applications of LDH single-layer nanosheets.

One-pot synthesis of the organomodified layered double hydroxides - glibenclamide biocompatible nanoparticles

In this work, synthesis of sodium dodecyl sulfate (SDS) organomodified LDH Zn₂Al carrying glibenclamide (GLIB) was performed in one step and in one-pot to obtain nanoparticles (NP). XRD data showed GLIB adsolubilization (d = 14.03 Å) and NP coating with Eudragit L100®. In addition, thermal and XRD data showed exfoliated/intercalated nanocomposite for NP S5 (LDH associated with SDS and Eudragit L100®). LDH organophilization and GLIB intercalation reduced surface area (SBET 23.58 m²/g) and NP size (469 nm). In addition, the change in zeta potential (-35.5 ζ) relative to pristine LDH (SBET 41.34 m²/g, 688.8 nm and +14 ζ) indicated that LDH functionalization seems an appropriate approach to produce NP with greater colloidal stability and enhanced functionality. The zinc release data from the LDH matrix (2.96 % ±0.002 ppm) showed the effectiveness of the coating in acid medium (pH 1.2) and the release data from GLIB showed the kinetics of release of zero order with release in simulated intestinal medium (pH 7.4) of 88 % and 73 % (24 h) for uncoated and coated NP, respectively. All NP were considered biocompatible in the WST-1 assay on BALB 3T3 fibroblast strains making these NP promising therapeutically.

Technetium immobilization by materials through sorption and redox-driven processes: A literature review

The objective of this review is to evaluate materials for use as a barrier or other deployed technology to treat technetium-99 (Tc) in the subsurface. To achieve this, Tc interactions with different materials are considered within the context of remediation strategies. Several naturally occurring materials are considered for Tc immobilization, including iron oxides and low solubility sulfide phases. Synthetic materials are also considered, and include tin-based materials, sorbents (resins, activated carbon, modified clays), layered double hydroxides, metal organic frameworks, cationic polymeric networks and aerogels. All of the materials were evaluated for their potential in-situ and ex-situ performance with respect to long-term Tc uptake and immobilization, environmental impacts and deployability. Other factors such as the technology maturity, cost and availability were also considered. Given the difficulty of evaluating materials under different experimental conditions (e.g., solution chemistry, redox conditions, solution to solid ratio, Tc concentration etc.), a subset of these materials will be selected, on the basis of this review, for subsequent standardized batch loading tests.

Ciprofloxacin-intercalated layered double hydroxide-in-hybrid films as composite dressings for controlled antimicrobial topical delivery

Films based on biopolymers and loaded with antimicrobial agents are convenient pharmaceutical dosage forms for topical application. Inorganic carriers loaded with these agents lead to composite materials, which combined with polymers produce further functionality. Here, hybrid composite films based on layered double hydroxide (LDH) and hyaluronan (HS) as ciprofloxacin (Cip) delivery systems were studied as an alternative for prophylaxis and treatment of opportunistic infections in wounds. Cip-intercalated Zn-Al LDH (LDH-Cip), with high drug loading and crystallinity, were obtained by a precipitation at variable pH method, and then included in a HS dispersion for obtaining the hybrid composite films by solvent casting. Physicochemical characterization of films showed that a composite material where the HS acted as matrix and LDH-Cip aggregates acted as filler were obtained. LDH-Cip were uniformly dispersed along the (LDH-Cip)/HS films, which exhibited roughness in their surface, increasing their swelling capacity in PBS pH = 5.8. Controlled releases of Cip toward PBS at pH = 5.8 and 7.4 were obtained, and the best fits for the release profiles were found with Higuchi and Korsmeyer-Peppas models, respectively. (LDH-Cip)/HS films exhibited antimicrobial activity against S. aureus. These films would then provide sustained release of Cip after topical administration, maintaining a suitable level of antibacterial activity, combined with the wound healing properties of the HS. The interesting properties shown by the (LDH-Cip)/HS films make them a promising alternative for application in skin wounds.

Nanohybrid Layered Double Hydroxides Used to Remove Several Dyes from Water

For the preparation and characterization of several layer double hydroxides (LDH) with inorganic interlayer anions (carbonate and nitrate) and nanohybrids, two organo-LDHs were studied in detail. The dodecylbenzene sulfonate (DBS) was used as an organic interlayer anion to modify the hydrophilic nature of the interlayer. The aim of the modification of the layered double hydroxides (LDH) was to change the hydrophilic character of the interlayer to hydrophobic with the purpose of improving its ability to adsorb several (anionic and cationic) dyes from water. These compounds have been used as adsorbents of amaranth (Am), diamine green B (DGB) and brilliant green (BG) dyes. Adsorption tests were conducted using variable pH values, contact times and initial dye concentrations (adsorption isotherms) to identify the optimum conditions for the intended purpose. Adsorbents and adsorption products were characterized by several physicochemical techniques. The results of the adsorption tests showed that the organo-LDH nanohybrids could be efficient adsorbents in the removal of studied dyes from water. Thus, it can be concluded that nanohybrids studied in this work might act as suitable supports in the design of adsorbents for the removal of a wide spectrum of dyes with the aim of reducing the adverse effects on water resources.

Predicting Points of Zero Net Charge of Layered Double Hydroxides

Many models such as electrostatic and crystallographic models have been developed to predict the point of zero net charge (PZNC) of (hydr)oxides without structural charges. Nevertheless, there is still a lack of feasible models for the prediction of the PZNC of structurally charged (hydr)oxides such as layered double hydroxides (LDHs), a large class of lamellar inorganic materials possessing positive structural charges. Herein, a modified electrostatic model is proposed by taking the structural charge (σ_st) and the Pauling's electrostatic valence principle into account, to correlate the PZNC with the characteristic physical constants of (hydr)oxides. The new model suggests that the PZNC of structurally charged (hydr)oxides is proportional to their σ_st, which was confirmed by the PZNC data of 28 LDH samples. The model can be used to describe or predict the PZNC of LDHs and also may provide guidance for the designed synthesis and application of LDH materials.

Sodium dodecylsulfate-layered double hydroxide and its use in the adsorption of 17β-estradiol in wastewater

Modified Mg₃Al layered double hydroxide (LDH) intercalated with dodecylsulfate anion composites, which were designated as SDS-LDH composites, were synthesized by coprecipitation. The samples were characterized using SEM, EDX, FT-IR, zeta potential analysis, and XRD. The results showed that the SDS-LDH composites contain a thicker and larger porous interconnected network than inorganic LDH due to the enlarged inter-layer distance. The outstanding adsorption performance of SDS-LDH composites toward 17β-estradiol (E2) was investigated under different conditions, including solution pH, adsorbent dosage, ion strength, reaction time, and temperature. When the solution pH was 7 and the adsorbent dosage was 2 g L⁻¹, the removal rate of E2 reached the maximum at 94%, whereas inorganic LDH displayed a poor E2 removal rate of 10%. The presence of various ions (Na⁺, SO₄²⁻, CI⁻, and H₂PO₄⁻) in aqueous solution exerted no significant adverse effects on the adsorption process. The adsorption equilibrium was reached within 20 min, and the adsorption fitted well with the pseudo-second-order model and the Freundlich isotherm. The thermodynamic test revealed that the adsorption process was spontaneous and endothermic. Phosphorus was selected as the index for evaluating the adsorption capacity of SDS-LDH composites for inorganic ions. The removal rates of total phosphorus and PO₄³⁻ were 43.71% and 55.93% for SDS-LDH composites at 2 g L⁻¹. The removal rate of PO₄³⁻ reached up to 85% when the contact time was 120 min and the dosage was 3 g L⁻¹ for SDS-LDH composites, which were approximately close to those of inorganic LDH of 30 min and 2 g L⁻¹, respectively. This finding indicates that the removal capacity of SDS-LDH composites for PO₄³⁻ decreased after the dodecylsulfate anions intercalated into the interlayer. The composites retained their high efficiency and stability after desorption and regeneration with alkali treatment. This study demonstrated that SDS-LDH composites are a promising adsorbent for the recovery and abatement of trace-level E2 in secondary effluents of wastewater treatment plants.

SDS-LDH composites were synthesized by coprecipitation. The composites are promising adsorbents for the recovery and abatement of trace-level E2 in secondary effluents of wastewater treatment plants.

Effect of the protein corona on the colloidal stability and reactivity of LDH-based nanocarriers

The physicochemical properties of drug nanocarriers such as layered double hydroxides nanoparticles (LDH-NPs) determine their circulation times in biological media and their interaction with the targeted cells.

Size-tunable LDH–protein hybrids toward the optimization of drug nanocarriers

Stabilization of LDH nanoparticles containing chloride and dodecylsulfate with BSA points to optimization of drug nanocarriers based on these solids.

Organo/LDH nanocomposite as an adsorbent of polycyclic aromatic hydrocarbons in water and soil-water systems

Polycyclic aromatic hydrocarbons (PAHs) are considered as priority pollutants because of their high risk to human health. In this paper, we addressed the issue of using hydrotalcite-based nanocomposites as adsorbents of six low molecular weight PAHs (acenaphthene, fluorene, phenanthrene, anthracene, fluoranthene and pyrene) to reduce their negative effects on the environment. A nanocomposite (HT-DDS) was prepared by intercalating the organic anion dodecylsulfate (DDS) in a Mg-Al hydrotalcite (HT), and then characterized using several analytical techniques. A Mediterranean soil was selected for being a high-risk scenario of groundwater contamination by leaching of pollutants. The nanocomposite displayed enhanced affinity for the PAHs in water as compared to carbonate-hydrotalcite (HTCO(3)) and its calcined product (HT500), and showed a high irreversibility of the adsorption process (hysteresis coefficient, H<0.15). The results revealed an increase of the pollutants retention in the soil by the addition of the nanocomposite that depended on the nanocomposite application rate and also on the hydrophobicity of each PAH. Accordingly, the use of HT-DDS as an amendment or barrier in contaminated soil is proposed for reducing the mobility of PAHs and, consequently, the adverse effect derived from rapid transport losses of the pollutants to the adjoining environmental compartments.

Organo/layered double hydroxide nanohybrids used to remove non ionic pesticides

The preparation and characterization of organo/layered double hydroxide nanohybrids with dodecylsulfate and sebacate as interlayer anion were studied in detail. The aim of the modification of the layered double hydroxides (LDHs) was to change the hydrophilic character of the interlayer to hydrophobic to improve the ability of the nanohybrids to adsorb non-ionic pesticides such as alachlor and metolachlor from water. Adsorption tests were conducted on organo/LDHs using variable pH values, contact times and initial pesticide concentrations (adsorption isotherms) in order to identify the optimum conditions for the intended purpose. Adsorbents and adsorption products were characterized several physicochemical techniques. The adsorption test showed that a noticeable increase of the adsorption of the non-ionic herbicides was produced. Based on the results, the organo/LDHs could be good adsorbents to remove alachlor and metolachlor from water. Different organo/LDHs complexes were prepared by a mechanical mixture and by adsorption. The results show that HTSEB-based complex displays controlled release properties that reduce metolachlor leaching in soil columns compared to a technical product and the other formulations. The release was dependent on the nature of the adsorbent used to prepare the complexes. Thus, it can be concluded that organo/LDHs might act as suitable supports for the design of pesticide slow release formulations with the aim of reducing the adverse effects derived from rapid transport losses of the chemical once applied to soils.