Abrupt Structural Transformation in Hydrotalcite-like Compounds Mg1-xAlx(OH)2(NO3)x·nH2O as a Continuous Function of Nitrate Anions

NiFe Layered Double Hydroxides with Controlled Composition and Morphology for the Efficient Removal of Cr(VI) from Water

A layered double hydroxide (LDH) composed of Ni2+ and Fe3+ with a Fe3+/(Ni2+ + Fe3+) ratio of 0.05, which is not commonly available, was successfully prepared by coprecipitation from an aqueous solution of glycerol containing nickel nitrate and iron nitrate. Precipitation using NaOH as a precipitating agent at room temperature or 120 °C under hydrothermal conditions gave products with micrometer-sized aggregates of nanometer-sized unshaped particles, while that using urea yielded LDHs with a foam-like porous architecture composed of platy particles with a size of 100-300 nm. The products were examined to remove Cr(VI) from an acidic (pH = 3) aqueous solution of K2Cr2O7 by adsorption and photocatalytic reduction. The foam-like porous NiFe-LDH exhibited the highest adsorbed amount (122 mg g-1) and rate (0.017 g mg-1 min-1) in the dark and the highest rate (0.012 min-1) of photocatalytic Cr(VI) reduction among the NiFe-LDHs prepared in the present study, which can be explained as a positive effect of the foam-like porous architecture. These performances were superior to those of other reported LDHs, showing the importance of the composition and the particle morphology to boost the removal of Cr(VI).

Determination of the Catalytic Activity of a Peroxidase-like Nanozyme and Differences among Layered Double Hydroxides with Different Anions and Cations

Nanomaterials with enzyme-like activity, namely, nanozymes, have been widely used as substitutes for natural enzymes, and they show excellent potential for application in many fields, such as biotechnology, environmental chemistry, and medicine. Layered double hydroxides (LDHs) are inorganic nanomaterials with adjustable compositions, simple preparation methods, and low costs and are some of the most promising candidate materials for the preparation of nanozymes. Here, we studied the syntheses and peroxidase-like activities of LDHs with four anions and four cations. First, LDHs prepared by the coprecipitation-hydrothermal method adopted hexagonal lamellar structures with good dispersion and uniform particle sizes. The Lambert-Beer law showed that the prepared LDHs exhibited good enzymatic activity. Later, the Km and Vmax values of the LDHs with different anionic/cationic materials intercalated into their structures were compared. Under the optimum conditions, the Vmax of Mg2Al-NO3-LDH was 7.35 × 10-2, which is 2-4 times higher than that of the LDHs containing other anions; the Vmax values of NiFe-LDH and FeAl-LDH were 0.152 and 0.284, respectively, which are 10 times higher than those of the LDHs with other cations. Importantly, according to kinetic analyses of the enzymatic reactions, the effects of Fe2+ and Fe3+ on the LDH enzyme activity were greater than those of the intercalated anions. This study showed that NiFe-LDH and FeAl-LDH with high catalytic activities are candidate materials for peroxidase simulations, which may provide new strategies for the application of LDHs in biosensors, antioxidants, biotechnology, and other nanozyme applications.

Curcumin in exfoliated layered double hydroxide nanoparticles: Pre-clinical evaluation as lung cancer nanomedicine

Rationally designed ∼ 100 nm sized curcumin (CRC) loaded exfoliated layered double hydroxide nanoparticles (X-LDH/CRC-NPs) have been tested for its suitability as nanomedicine in non-small cell lung cancer (NSCLC) cell lines (A549 and NCI-H460) resulting enhanced apoptosis. Preclinical evaluation on A549 tumor bearing nude mouse model confirmed that such a well-designed X-LDH/CRC NPs would be highly advantageous for treating lung cancers.

O2-Supplying Nanozymes Alleviate Hypoxia and Deplete Lactate to Eliminate Tumors and Activate Antitumor Immunity

Direct hypoxia alleviation and lactate depletion in the tumor microenvironment (TME) are promising for effective cancer therapy but still very challenging. To address this challenge, the current research directly reshapes the TME for inhibiting tumor growth and activating the antitumor immunity using a drug-free nanozyme. Herein, the acid-sensitive nanozymes were constructed based on peroxidized layered double hydroxide nanoparticles for O₂ self-supply and self-boosted lactate depletion. The coloading of partially cross-linked catalase and lactate oxidase enabled the acid-sensitive nanozymes to promote three reactions, that is, (1) H₂O₂ generation from MgO₂ hydrolysis (30% at pH 7.4 vs 63% at pH 6.0 in 8 h); (2) O₂ generation from H₂O₂ (12% at pH 7.4 vs 21% at pH 6.0 in 2 h); and (3) lactate depletion by in situ generated O₂ (50% under hypoxia vs 75% under normoxia in 24 h in vitro) in parallel or tandem. These promoted reactions together efficiently induced colon cancer cell apoptosis under the hypoxic conditions, significantly inhibited tumor growth (>95%), and suppressed distant tumor growth upon seven administrations in every 3 days and moreover transformed the immunosuppressive tumor into "hot" one in the colon tumor-bearing mouse model. This is the first example for a nanozyme that supplies sufficient O₂ for hypoxia relief and lactate depletion, thus providing a new insight into drug-free nanomaterial-mediated TME-targeted cancer therapy.

Clay nanoparticles efficiently deliver small interfering RNA to intact plant leaf cells

RNA interference is triggered in plants by the exogenous application of double-stranded RNA or small interfering RNA (siRNA) to silence the expression of target genes. This approach can potentially provide insights into metabolic pathways and gene function and afford plant protection against viruses and other plant pathogens. However, the effective delivery of biomolecules such as siRNA into plant cells is difficult because of the unique barrier imposed by the plant cell wall. Here, we demonstrate that 40-nm layered double hydroxide (LDH) nanoparticles are rapidly taken up by intact Nicotiana benthamiana leaf cells and by chloroplasts, following their application via infiltration. We also describe the distribution of infiltrated LDH nanoparticles in leaves and demonstrate their translocation through the apoplast and vasculature system. Furthermore, we show that 40-nm LDH nanoparticles can greatly enhance the internalization of nucleic acids by N. benthamiana leaf cells to facilitate siRNA-mediated downregulation of targeted transgene mRNA by >70% within 1 day of exogenous application. Together, our results show that 40-nm LDH nanoparticle is an effective platform for delivery of siRNA into intact plant leaf cells.

Layered double hydroxides for corrosion-related applications—Main developments from 20 years 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 20 years 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.

Comparative Physicochemical and Catalytic Study of Nanocrystalline Mg-Al Hydrotalcites Precipitated with Inorganic and Organic Bases

Synthetic Mg-Al hydrotalcites (HT) are environmentally friendly solid bases frequently applied as catalysts in base catalyzed reactions. The most common synthesis method, using NaOH as precipitant, is problematized by the possibility of introducing undesired Na contamination. Alkali-free synthesis is usually performed with NH₃aq, a precipitant which is less efficient in incorporation of Mg into HT lattice. In the present work, organic bases, tetrabutylammonium hydroxide and choline hydroxide, were successfully employed as precipitating agents in a new alkali-free route of Mg-Al HT synthesis. HT solids were also obtained with inorganic bases, NH₃aq and NaOH. Characterization with X-ray diffraction, elemental analysis, scanning electron microscopy, Fourier-transform infrared spectroscopy and thermogravimetry/differential scanning calorimetry, confirmed the formation of nanocrystalline HT compounds with all employed bases. HT prepared with NH₃aq exhibited an Mg deficit, which was detrimental to the catalytic activity in base catalyzed reactions. The effect was attributed to the tendency of Mg²⁺ to form ammine complexes, a conclusion supported by quantum mechanical calculations. HT prepared with NaOH showed the highest crystallinity, which was unfavorable for catalytic application. The addition of starch to the synthesis medium provided a means by which to diminish the crystal size of all HT precipitates. Catalytic tests of the Baeyer-Villiger oxidation of cyclohexanone demonstrated that the highest yields of ε-caprolactone were obtained with fine-crystalline HT catalysts prepared with organic bases in the presence of a starch template.

Demand-oriented construction of Mo3S13-LDH: A versatile scavenger for highly selective and efficient removal of toxic Ag(I), Hg(II), As(III), and Cr(VI) from water

Inspired by the classic ion-exchange reaction, a single phase material of Mg_0.66Al_0.34(OH)₂(Mo₃S₁₃)_0.03(NO₃)_0.14(CO₃)_0.07·H₂O (Mo₃S₁₃-LDH) was masterly constructed by intercalating Mo₃S₁₃^2- into the MgAl-LDH gallery. Prepared Mo₃S₁₃-LDH displays excellent binding affinity and high selectivity for Ag(I) and Hg(II) in a mixed solution, in which an apparent selectivity order of Hg(II) > Ag(I) ≫ Pb(II), Cu(II), Ni(II), Co(II), Cd(II), and Mn(II) is observed. Enormous capture capacities (q_m^Ag = 446.4 mg/g, q_m^Hg = 354.6 mg/g) and fast equilibration time (within 60 min) place Mo₃S₁₃-LDH in the upper ranks of materials for such removal. For oxoanions, As(III) (HAsO₃^2-) and Cr(VI) (CrO₄^2-) can be specifically trapped by Mo₃S₁₃-LDH with comparable loading ability (q_m^As = 61.8 mg/g, q_m^Cr = 90.6 mg/g) in the coexistence of multiple interfering anions. Notably, high Hg(II) and Cr(VI) concentrations are finally reduced below the safe limit of drinking water. The excellent capture capacity of Mo₃S₁₃-LDH benefits from the rational design by following two aspects: (i) the multiple sulfur ligands in Mo₃S₁₃^2- groups give place to various capture modes and different affinity orders for target ions, and (ii) large-sized Mo₃S₁₃^2- groups widen the interlayer spacing of LDH, thereby accelerating the mass transfer process. Furthermore, the satisfactory structural stability of Mo₃S₁₃-LDH is also reflected through the unchanged hexagonal prismatic shape after adsorption. All of these highlight the great potential of Mo₃S₁₃-LDH for the application in water remediation.

Precipitation of (Mg/Fe-CTAB) - Layered double hydroxide nanoparticles onto sewage sludge for producing novel sorbent to remove Congo red and methylene blue dyes from aqueous environment

Preparation of new sorbent from precipitation of nano-sized (Mg/Fe-CTAB)- layered double hydroxide (LDH) on the surfaces of sewage sludge byproduct to remove the anionic and cationic dyes was the focal point of this work. The presence of nanoparticles and enlarged of interlayers by CTAB intercalation have increased the sludge surface area from 5.34 to 10.32 m²/g. The CTAB mass 0.03 g/50 mL, sludge dosage 1 g/50 mL and (Mg/Fe) molar ratio 2 were the best preparation conditions required to obtain effective sorbent with efficiencies exceeded 93% for MB and CR dyes. These efficiencies were obtained under operational conditions for batch study of 0.5 g coated sludge per 50 mL colored dye solution, initial pH 3 (for CR) and 12 (for MB), and time 3 h for 10 mg/L dyes at 200 rpm. Models of Langmuir and pseudo second-order have a high capability in the representation of sorption records with maximum capacities of adsorption 163.6 and 132.6 mg/g for CR and MB dye, respectively. The X-ray diffraction analysis proved that the calcite occurred mainly at 2θ = 29.8° while quartz corresponded to the 21, 26.6, 36.4, 36.9, 50.1, 60.01 and 68.4°. Characterization tests showed that nano-sized particles of magnesium/iron were precipitated on the sludge due to the formation of hydrotalcite-like compounds with an increase in the percentages of Mg and Fe from 0.87 and 1.36 to 4.25 and 3.03%, respectively. The results showed that the electrostatic attraction, intra-particle diffusion and hydrogen bonding were predominant mechanisms for removal of CR and MB onto coated sludge.

Recovering metal ions from oxalic acid leaching palygorskite-rich clay wastewater to fabricate layered mixed metal oxide/carbon composites for high-efficient removing Congo red

This study developed a sustainable way to transform metallic residues in wastewater and spent adsorbents that adsorbed organic pollutants into novel high-efficiency adsorbents to treat water pollution again. The metal ions recovered from oxalic acid leaching palygorskite-rich clay wastewater was used to construct the hydrotalcite-like composites, after adsorbing organic pollutants, which was calcined and carbonized to convert into the mixed metal oxide/carbon composites (MMO/Cs). The fabricated MMO/Cs showed outstanding adsorption performance for the anionic azo dye Congo Red (CR). Especially, the MMO/C2 with the M²⁺/M³⁺ molar ratio of 2, which adjusted by supplementing Mg²⁺, had ultra-high adsorption capacity and ultra-clean removal efficiency for CR. The adsorption capacity was as high as 3303 mg/g, and only 0.5 g/L MMO/C2 dosing treatment for 6 h could completely decolor and remove the 2000 mg/L CR aqueous solution. Moreover, MMO/Cs exhibited the ability to simultaneous remove CR and Methylene blue (MB) mixed dye contaminants, and demonstrated the excellent recyclability. This work provides a promising method for the high-value conversion of waste resources and the synthesis of high-efficiency adsorbents.

Halogen-free layered double hydroxide-cyclotriphosphazene carboxylate flame retardants: effects of cyclotriphosphazene di, tetra and hexacarboxylate intercalation on layered double hydroxides against the combustible epoxy resin coated on wood substrates

The development of halogen-free flame retardants as environmentally friendly and renewable materials for heat and fire-resistant applications in the field of electronics is important to ensure safety measures. In this regard, we have proposed a simple and halogen-free strategy for the synthesis of flame retardant LDH-PN materials to decrease the fire hazards of epoxy resin (EP), via a co-precipitation reaction between Mg(NO₃)₂ and Al(NO₃)₃ and the subsequent incorporation of different cyclotriphosphazene (PN) carboxylate anions. The cyclotriphosphazene-based di, tetra and hexacarboxylate-intercalated layered double hydroxides are designated as LDH-PN-DC, LDH-PN-TC and LDH-PN-HC, respectively. Furthermore, the intercalation of cyclotriphosphazene carboxylate anions into the LDH layers was confirmed by PXRD, FT-IR, TGA, solid-state ³¹P NMR, nitrogen adsorption and desorption analysis (BET), HR-SEM and XPS. Evaluation of the flame retardant (vertical burning test and limiting oxygen index) properties was demonstrated by formulating the LDH-PN materials with epoxy resin (EP) in different ratios coated on wood substrates to achieve the desired behaviour of the EP/LDH-PN composites. Structure–property analysis reveals that EP/LDH-PN-TC-20 wt% and EP/LDH-PN-HC-20 wt% achieved a V₀ rating in the UL-94 V test and achieved higher LOI values (27.7 vol% for EP/LDH-PN-TC-20 wt% and 29 vol% for EP/LDH-PN-HC-20 wt%) compared to the epoxy-coated wood substrate (23.2 vol%), whereas EP/LDH-PN-DC failed in the vertical burning test for various weight percentages of LDH-PN-DC from 5 wt% to 20 wt% in the composites, with a lower LOI value of 22.1 vol%. Excellent flame retardancy was observed for EP/LDH-PN-TC and EP/LDH-PN-HC due to the presence of more binding sites of carboxylate anions in the LDH layers and less or no spiro groups in cyclotriphosphazene compared to that in EP/LDH-PN-DC. In addition, the synergistic flame retardant effect of the combination of LDH and cyclotriphosphazene on the epoxy resin composites remains very effective in creating a non-volatile protective film on the surface of the wood substrate to shelter it from air, absorb the heat and increase the ignition time, which prevents the supply of oxygen during the combustion process. The results of this study show that the proposed strategy for designing flame-retardant properties represents the state-of-the-art, competent coating of inorganic materials for the protection and functionalization of wood substrates.

The flame retardant properties of the different types of cyclotriphosphazene carboxylate-intercalated LDH materials are emphasized by increasing the number of binding sites and decreasing the number of spiro groups in the cyclotriphosphazene core.

Sheet-like clay nanoparticles deliver RNA into developing pollen to efficiently silence a target gene

Topical application of double-stranded RNA (dsRNA) can induce RNA interference (RNAi) and modify traits in plants without genetic modification. However, delivering dsRNA into plant cells remains challenging. Using developing tomato (Solanum lycopersicum) pollen as a model plant cell system, we demonstrate that layered double hydroxide (LDH) nanoparticles up to 50 nm in diameter are readily internalized, particularly by early bicellular pollen, in both energy-dependent and energy-independent manners and without physical or chemical aids. More importantly, these LDH nanoparticles efficiently deliver dsRNA into tomato pollen within 2-4 h of incubation, resulting in an 89% decrease in transgene reporter mRNA levels in early bicellular pollen 3-d post-treatment, compared with a 37% decrease induced by the same dose of naked dsRNA. The target gene silencing is dependent on the LDH particle size, the dsRNA dose, the LDH-dsRNA complexing ratio, and the treatment time. Our findings indicate that LDH nanoparticles are an effective nonviral vector for the effective delivery of dsRNA and other biomolecules into plant cells.

Preparation of MgGa Layered Double Hydroxides and Possible Compositional Variation

Layered double hydroxides (LDHs), shown as the general formula of [M2+1-xM3+x(OH)2]x+(An-)x/n∙yH2O, are useful for various applications such as anion exchangers/adsorbents, catalysts and catalysts' supports, and drug/gene carriers due to their structural, compositional and morphological characteristics and their variation. The x value (M3+/(M2+ + M3+) ratio) in layered double hydroxides (LDHs), corresponding to the layer charge density, is one of the important parameters for controlling the properties of LDHs. The x values in commonly available LDHs are limited (0.2 < x < 0.3). In order to obtain LDHs with x < 0.2, Mg2+ Ga3+-LDHs with interlayer iodide were examined. The linear correlation between lattice parameter a and x value in the products with x of 0.06-0.24 was seen, suggesting the successful substitution of Mg2+ in the brucite-like sheet with Ga3+. Carbonate and dodecyl sulfate types MgGa-LDH were prepared by ion exchange with carbonate anion and reconstruction in aqueous solution of sodium dodecyl sulfate. The products with x of 0.06 were dispersed in water and hexanol better than those with x of 0.24 for MgGa-LDHs containing carbonate and dodecyl sulfate, respectively, suggesting effects of the lower layer charge density on the dispersion.

Intercalation of a manganese(ii)-thiacalixarene luminescent complex in layered double hydroxides: synthesis and photophysical characterization

The luminescent complex [(ThiaSO₂)₂(Mn^II)₄F]⁻ (ThiaSO₂ = p-tert-butylsulfonylcalixarene) was introduced between layered double hydroxides. The material displays a very high sensitivity to its luminescence emission with oxygen.

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.

A Low-Cost Layered Double Hydroxide (LDH) Based Amperometric Sensor for the Detection of Isoproturon in Water Using Carbon Paste Modified Electrode

In this work, a Layered Double Hydroxide (NiAl-LDH) was obtained by coprecipitation method and used to elaborate an electrochemical sensor for the determination of isoproturon, which is a hazardous pollutant, widely used in agriculture, and its residue is distributed into aqueous environment through run-off and leaching from the soil. Various physicochemical techniques such as FT-IR spectroscopy, X-ray diffraction, and thermal analysis were used to characterize this material. The anionic exchange capacity of NiAl-LDH on carbon paste modified electrode was investigated toward [Fe(CN)₆]^3- using cyclic voltammetry. Used as electrode modifier of carbon paste electrode for isoproturon detection, a remarkable increase in isoproturon signal on modified carbon paste electrode by LDH was observed. The peak current obtained after 3 min of preconcentration in 25 μM ISO on NiAl-LDH/CPE was 2.6 times higher than that exhibited by the same analyte on the unmodified CPE, thereby opening the way to the development of a sensitive method for the detection of ISO. Other parameters that can affect the stripping response (preconcentration time, pH of detection medium, and LDH loading within the paste) were investigated to optimize the proposed sensor. After optimization, a linear calibration curve was obtained in the concentration range from 2 × 10^-8 to 1.8 × 10^-7 M, leading to a detection limit of 1 × 10^-9 M (S/N = 3). The relative standard deviation for 5 identical measurements was 2.7%. The interfering effect of some compounds and ions was examined on the stripping response of ISO. The applicability of the method was verified by the determination of ISO in spiked water sample.

Favorable Intercalation of Nitrate Ions with Fluorine-Substituted Layered Double Hydroxides

Understanding and controlling confined nanospace to accommodate substrates and promote high ion conduction are essential to various fields. Layered double hydroxides (LDHs) have emerged as promising candidates for anion exchangers using the interlayer nanospace in their crystal structures. Miyata reported in 1983 that the affinity of anions for intercalation with most major Mg-Al LDHs increased in the following order: NO₃^- < Br^- < F^- < SO₄^2- < HPO₃^2-. Attempts to alter the affinity with different metal cations (M²⁺ and M³⁺) have been unsuccessful. Analyses of the crystalline structures of LDHs, positively charged host layers, interlayer anions, and interlayer water molecules indicate that they inevitably interact through hydrogen bonding. In other words, the affinity of LDHs for anions is controlled by tuning the hydrogen bonding. In this study, we prepared fluorine-substituted LDHs (F-LDHs) with different Mg/Al ratios by partially replacing the OH structural groups, which originated from the host layer, with fluorine atoms; the resulting change in affinity was investigated. The distribution coefficient, which is a useful indicator of the affinity of an LDH for a particular anion, was examined. The results showed that only F-LDHs with Mg/Al ratios of 3.5 exhibited high affinity, especially for NO₃^- ions, and the affinity increased in the following order: HPO₄^2- < SO₄^2- < F^- < Br^- < NO₃^-. The separation factors of these specific F-LDHs with respect to both NO₃^-/F^- and NO₃^-/SO₄^2- were higher than that of LDHs with other compositions by 1 order of magnitude. Raman spectroscopy above 3000 cm^-1 revealed that the fluorine substitution of LDHs significantly changed the hydrogen bonding nature in the interlayer space. Highly electronegative fluorine atoms significantly decrease the extent of hydrogen bonding interactions between OH structural groups and both interlayer water molecules and anions, wherein steric effects are induced by the shrunken interlayer space, and van der Waals forces are revealed to be the predominant interaction with anions. Therefore, the highest affinity was observed for NO₃^- ions in F-LDHs.

Intercalation chemistry and thermal characteristics of layered double hydroxides possessing organic phosphonates and sulfonates

The distinct roles of organic sulfonates that enable delamination in water and formation of microporous structures via thermal activation are elucidated.

A novel composite of layered double hydroxide/geopolymer for co-immobilization of Cs+ and SeO42- from aqueous solution

Geopolymers are always considered as promising materials for the treatment of radioactive wastes. In order to extend the application of geopolymer to the immobilization of anionic species, a novel composite of layered double hydroxide/geopolymer (LDH/GEO) was synthesized and applied for cosorption of Cs⁺ and SeO₄^2-. The ability of LDH/GEO to sorb Cs⁺ was maintained as that of pure GEO, even though the surface of geopolymer was homogeneously covered by the LDH platelets. The sorption of Cs⁺ onto LDH/GEO composite occurred via ion exchange, which was controlled by particle diffusion. It is different with Cs⁺ sorption onto pure GEO governed by film diffusion. Therefore, "Pocket diffusion" was proposed for the particle diffusion as the case of LDH/GEO because this kind of diffusion would be restricted in a certain distance around the ring entrance gate due to the amorphous essence of GEO. For SeO₄^2- sorption by LDH/GEO, ion-exchange with the interlayer NO₃^- and surface sorption could be the main mechanisms. Importantly, the sorption speed of SeO₄^2- achieved by LDH/GEO composite was much faster than that by pure LDH. In the binary system (Cs⁺+ SeO₄^2-), the sorption of Cs⁺ was slightly suppressed compared to the single system, which might be due to the formation of ion-pair complex of [CsSeO₄]^-. However, it did not have negative effect on the SeO₄^2- sorption. In the presence of other cations or anions, the cosorption performances of Cs⁺ and SeO₄^2- were satisfactorily obtained. Furthermore, the Cs⁺ and SeO₄^2- sorption densities were superior to the previously reported values. The combined MgAl-LDH/geopolymer composite could be a promising material for the immobilization of Cs⁺ and SeO₄^2-, and this work would provide guidance for the development of geopolymer-based materials for environmental applications.

High-Power Ultrasonic Synthesis and Magnetic-Field-Assisted Arrangement of Nanosized Crystallites of Cobalt-Containing Layered Double Hydroxides

High-quality stoichiometric Co2Al–NO3 and Co2Al–CO3 layered double hydroxides (LDHs) have been obtained by precipitation followed by anion exchange, both high-power-sonication assisted. Application of high-power ultrasound has been demonstrated to result in a considerable acceleration of the crystallization process and the anion-exchange reaction. Two independent approaches were used to form bulk and 2-D samples of Co2Al–NO3 with the oriented crystallites, namely uniaxial pressing of deposits from sonicated LDH slurries and magnetic field-assisted arrangement of LDH crystallites precipitating on glass substrates. A convenient way of preparation of semi-transparent compacts with relatively big blocks of oriented crystallites have been demonstrated. Thin dense transparent films of highly-ordered crystallites of Co2Al–NO3 LDH have been produced and characterized.

One-step synthesis and growth mechanism of nitrate intercalated ZnAl LDH conversion coatings on zinc

An approach for the synthesis of ZnAl-NO3 LDH conversion coatings on zinc in an aqueous acidic Al(NO3)3/NaNO3 solution is demonstrated for the first time. The growth mechanism has been investigated using time resolved structural, microstructural and analytical methods. A LDH growth model involving both electrochemical and chemical processes is suggested.

Hierarchical spheres of Mg–Al LDH for the removal of phosphate ions: effect of alumina polymorph as precursor

In order to tailor the morphology of the layered double hydroxide (LDHs) particles, we focused on a synthesis method involving the use of Al₂O₃ as a precursor, employing Al₂O₃ with different crystal structures (e.g., α-Al₂O₃, θ-Al₂O₃, and γ-Al₂O₃) as well as amorphous Al₂O₃.

Influences of Cation Ratio, Anion Type, and Water Content on Polytypism of Layered Double Hydroxides

Layered double hydroxides (LDHs) are a significant sink of anions (CO₃^2-, SO₄^2-, NO₃^-, Cl^-, etc.) and divalent transition-metal cations in soil. The anion exchange capacity gives rise to functional materials. The stability of LDHs is determined by the interaction between cation-bearing layers and intercalated water and anions, which is correlated with polytypism and coordination structure. A systematic investigation is performed to show the influence of cation ratio, anion type, and water content on polytypism, swelling behavior, and interlayer structure of Mg-Al-LDHs using molecular dynamics simulations. LDHs intercalated with NO₃^- ions exhibit a polytype transition from 3 R₁ (three-layer rhombohedral polytype) to 1 T (one-layer trigonal polytype) with increasing water content. NO₃^- ions exhibit a D_{3 h} point group symmetry at low water contents. The polytype transition coincides with the complete transformation into tilted NO₃^- ion with a C_{2 v} point group symmetry. The transition appears at a lower water content when the Mg/Al ratio is lower. LDHs with SO₄^2- ions exhibit a three-stage polytypism. The first and last stages are 3 R₁. The intermediate stage could be 1 T or a mixture of different O(octahedra)-type interlayers, which depends on the cation ratio. The relative popularity of SO₄^2- ions with a C _s point group symmetry is characteristic for the intermediate stage, while mostly SO₄^2- ions exhibit a C_{3 v} symmetry. There is no clear relevance between cation ratio and water content at which a polytype transition happens. The configurational adjustments of NO₃^- and SO₄^2- ions facilitate the swelling behavior of LDHs. LDHs with CO₃^2- or Cl^- ions always maintain a 3 R₁ polytype irrespective of water content and hardly swell. The configurations of anions and water reflect local coordination structure due to hydrogen bonds. The layer-stacking way influences long-ranged Coulombic interactions. Hydrogen-bonding structure and long-ranged Coulombic interactions collectively determine polytypism and stability of LDHs.

Studies on drug release kinetics and antibacterial activity against drug-resistant bacteria of cefotaxime sodium loaded layered double hydroxide–fenugreek nanohybrid

Antibacterial activity of a CLF nanohybrid against E. coli 949 ESBL cefotaxime-resistant bacteria via the interaction of penicillin binding protein.

Hierarchical flower-like Ni–Co layered double hydroxide nanostructures: synthesis and super performance

Three-dimensional hierarchical flower-like Ni–Co LDHs have been prepared with a large specific surface area and expanded interlayer spacing as an adsorbent for removing anionic dyes and as an electrode for supercapacitors.

Chemical reactive features of novel amino acids intercalated layered double hydroxides in As(III) and As(V) adsorption

Layered double hydroxides (LDHs) intercalated with amino acids such as methionine (Met) were synthesized as new adsorbents to remediate arsenic-polluted water. This Zn₂Al-Met-LDHs, identified with the formula of Zn_0.7Al_0.3(OH)₂(Met)_0.3·0.32H₂O, has good thermal stability. Adsorption experiments with Zn₂Al-Met-LDHs showed that the residual arsenic in solution could be reduced below the regulation limit, and this adsorption process fitted Langmuir isotherm and the pseudo-second-order kinetics well. A remarkably high removal efficiency and the maximum adsorption capacity for As(III) were achieved, 96.7% and 94.1 mg/g, respectively, at 298 K. The desorption efficiency of As(III) from the arsenic-saturated Zn₂Al-Met-LDHs (<8.7%), far less than that of As(V), promises a specific and reliable uptake of As(III) in sorts of solutions. More importantly, a complete and in-depth spectra analysis through FTIR, XPS and NMR was conducted to explain the excellent performance of Zn₂Al-Met-LDHs in arsenic removal. Herein, two special chemical reactions were proposed as the dominant mechanisms, i.e., hydrogen bonding between the carboxyl group of the host Met and the hydroxyl group of As(III) or As(V), and the formation of a chelate ring between the guest As(III) and the S, N bidentate ligands of the intercalated Met in the LDHs.

Clay nanosheets for topical delivery of RNAi for sustained protection against plant viruses

Topical application of pathogen-specific double-stranded RNA (dsRNA) for virus resistance in plants represents an attractive alternative to transgenic RNA interference (RNAi). However, the instability of naked dsRNA sprayed on plants has been a major challenge towards its practical application. We demonstrate that dsRNA can be loaded on designer, non-toxic, degradable, layered double hydroxide (LDH) clay nanosheets. Once loaded on LDH, the dsRNA does not wash off, shows sustained release and can be detected on sprayed leaves even 30 days after application. We provide evidence for the degradation of LDH, dsRNA uptake in plant cells and silencing of homologous RNA on topical application. Significantly, a single spray of dsRNA loaded on LDH (BioClay) afforded virus protection for at least 20 days when challenged on sprayed and newly emerged unsprayed leaves. This innovation translates nanotechnology developed for delivery of RNAi for human therapeutics to use in crop protection as an environmentally sustainable and easy to adopt topical spray.

Two-Dimensional Materials Beyond Graphene: Emerging Opportunities for Biomedicine

With the rise of graphene, there is growing attention on two-dimensional (2D) materials in the physical science community during the last decade. Most studies to date focus on the rich set of their superior electrical, optical, catalytic and electrochemical properties and highlight the encouraging opportunities for developing next generation electronics, optoelectronics, catalysis, and energy storage technologies. On the contrary, the biomedicine community has barely recognized the potential of these materials other than graphene. There are very limited published studies on these materials’ biological effects and biomedical applications. Here, we present a brief overview of 2D materials and discuss their potential for biomedical applications in hope of raising biomedical researchers’ awareness of the great opportunities associated with these materials. We first discuss the emergence of 2D materials and review two most important prerequisites for 2D materials’ biomedical applications, synthesis and biocompatibility. We then categorize the existing studies on 2D materials’ biomedical applications into biosensing, drug/gene delivery, antimicrobial, bioimaging and multimode therapeutic applications. We would put special emphasis on the great flexibility of various rational combinations of 2D material superior properties for the design and construction of assorted forms of reagents or devices with highly effective simultaneous diagnostic and therapeutic functions (or theranostics functions). At last, the newly emerging 2D black phosphorous with very rare and interesting properties is introduced as the next promising and important 2D materials to study in the upcoming years.

Porous Ru/RuOx/LDH as highly active heterogeneous catalysts for the aerobic oxidation of alcohols

Porous LDH supported Ru/RuO_x nanocatalysts exhibited much better catalytic activity and stability than conventional Ru-based catalysts for alcohol oxidation.

Encapsulation of palladium porphyrin photosensitizer in layered metal oxide nanoparticles for photodynamic therapy against skin melanoma

We designed a biodegradable nanocarrier of layered double hydroxide (LDH) for photodynamic therapy (PDT) based on the intercalation of a palladium porphyrin photosensitizer (PdTCPP) in the gallery of LDH for melanoma theragnosis. Physical and chemical characterizations have demonstrated the photosensitizer was stable in the layered structures. In addition, the synthesized nanocomposites rendered extremely efficacious therapy in the B16F10 melanoma cell line by improving the solubility of the hydrophobic PdTCPP photosensitizer. The detection of singlet oxygen generation under irradiation at the excitation wavelength of a 532 nm laser was indeed impressive. Furthermore, the in vivo results using a tumour xenograft model in mice indicated the apparent absence of body weight loss and relative organ weight variation to the liver and kidney demonstrated that the nanocomposites were biosafe with a significant reduction in tumour volume for the anti-cancer efficacy of PDT. This drug delivery system using the nanoparticle-photosensitizer hybrid has great potential in melanoma theragnosis.

Methotrexate intercalated layered double hydroxides with the mediation of surfactants: Mechanism exploration and bioassay study

Methotrexatum intercalated layered double hydroxides (MTX/LDHs) hybrids were synthesized by the co-precipitation method and three kinds of nonionic surfactants with different hydrocarbon chain lengths were used. The resulting hybrids were then characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy and transmission electron microscopy (TEM). XRD and FTIR investigations manifest the successful intercalation of MTX anions into the interlayer of LDHs. TEM graphs indicate that the morphology of the hybrids changes with the variation of the chain length of the surfactants, i.e., the particles synthesized using polyethylene glycol (PEG-7) present regular disc morphology with good monodispersity, while samples with the mediation of alkyl polyglycoside (APG-14) are heavily aggregated and samples with the addition of polyvinylpyrrolidone (PVP-10) exhibit irregular branches. Furthermore, the release and bioassay experiments show that monodisperse MTX/LDHs present good controlled-release and are more efficient in the suppression of the tumor cells.