Adsorptive removal of heavy metal anions from water by layered double hydroxide: A review

High-valence heavy metals with high ecotoxicity are generally found in water in the form of anions, and this increases heavy metal pollution intensity and treatment difficulty. Recent studies have pointed to the potential efficiency of layered double hydroxides (LDHs) to meet this challenge. In this review, we retrospectively research the development of LDHs using a Java application called CiteSpace. We describe the unique layer structure, highly adjustable chemical properties, and diverse synthesis methods of LDHs, all of which decide the effective adsorption of heavy metal anions by LDHs. Subsequently, we focus on discussing the adsorption mechanism of LDHs on heavy metal anions, as well as the current state of research and future directions for microscopic interaction mechanisms. For practical applications, it is critical to improve the adsorption selectivity and stability. We then recommend solutions to improve the adsorption selectivity and stability after identifying the influencing mechanism. Finally, we provide our perspectives on the future development of LDHs adsorption of heavy metal anions.

Topology dependent modification of layered double hydroxide for therapeutic and diagnostic platform

Layered double hydroxide is a family of two-dimensional materials with wide range of compositions. Recently, its ability to accommodate various chemical species and biocompatibility have been attracted in the biomedical applications to develop drug delivery system and nanodiagnostics. In this review, we categorized biomedical approaches of layered double hydroxide with respect to the three topologies of, namely, interlayer space, outer surface with particle edge, and the lattice points. There have been extensive researches on the intercalation of drug or tracing to make use of interlayer space of layered double hydroxide for drug stabilization, sustained release, cellular delivery and etc. Outer surface or edge has been utilized to immobilization of large therapeutic moieties and to attach tracing moiety. Lattice points consisting of various metal species could be utilized for the specific metal species like paramagnetic elements or radioisotopes. Based on these topologies in layered double hydroxide, both the synthetic routes and the achieved functionalities in terms of biomedical application will be discussed.

Recent progress in layered double hydroxides as a cancer theranostic nanoplatform

Layered double hydroxide (LDH) has been a big challenge in exploring new hybrid materials by intercalating inorganic, organic, or bio molecules into their lamellar lattice, those which often showed dual functions from each other or new mutative properties. Recently, nano-bio convergence technology becomes one of the most extensively studied research fields in the view point of developing advanced drugs and diagnostic agents to fight against disease and eventually to improve the lives of human beings. Therefore, LDH as one of the nanomaterials have been intensively investigated not only as biocompatible drug delivery vehicle for cancer chemotherapy but also as diagnostic and imaging agents. In the present review, we have attempted to summarize theranostic functions of drug-LDH hybrid nanoparticles including their synthetic methods, physico-chemical and biological properties, and their unique mechanism overcoming drug resistance, and targeting properties based on in vitro and finally in vivo results. This article is categorized under: Diagnostic Tools > Diagnostic Nanodevices Diagnostic Tools > in vivo Nanodiagnostics and Imaging.

Facile Mechanochemical Approach To Synthesizing Edible Food Preservation Coatings Based On Alginate/Ascorbic Acid-Layered Double Hydroxide Bio-Nanohybrids

A bionanohybrid based on ascorbic acid-intercalated layered double hydroxides (LDHs) was synthesized using a facile and novel mechanochemical grinding technique, and its efficacy as an edible food coating is reported. Ascorbic acid-intercalated Mg-Al-LDHs (AA-LDHs) are synthesized using a green water-assisted grinding approach. The successful synthesis of the mechanochemically ground AA-LDHs was confirmed by the shifts observed in the basal peaks of the LDHs based on a powder X-ray diffraction, changes in the positions of vibrational frequencies of ascorbic acid based on Fourier Transform Infrared Spectroscopy, and significant changes in the intensity and peak positions of the core-shell bands based on X-ray photoelectron spectroscopy. The resulting nanohybrid further demonstrates thermal stability in thermogravimetric and derivative thermogravimetric analysis. Transmission electron microscopy images of the mechanochemically synthesized AA-LDHs reveal a plate-like morphology, which is a characteristic of the hydrotalcite-like structure. In a novel application, an edible coating was prepared by blending the AA-LDHs into a biocompatible alginate matrix, and the coating was developed on freshly plucked strawberries using the dip-coating method. In order to evaluate the efficacy of the coating, the total phenolic content, pH, microbial growth, weight loss, titratable acidity, and ascorbic acid content were monitored in the coated and uncoated fruits for a period of 18 days. The results reveal that the shelf life of strawberries increases from 9 days to 15 days for the nanohybrid coated fruits, suggesting the potential food preservation applications of the nanohybrid.

Zingiber officinale Extract (ZOE) Incorporated with Layered Double Hydroxide Hybrid through Reconstruction to Preserve Antioxidant Activity of ZOE against Ultrasound and Microwave Irradiation

We prepared Zingiber officinale extract (ZOE) incorporated in a layered double hydroxide (LDH) hybrid through a reconstruction method in order to preserve the antioxidant activity of ZOE from ultrasound and microwave irradiation. X-ray patterns, infrared spectroscopy, and scanning electron microscopy suggested that ZOE moieties were encapsulated in the interparticle space of reconstructed LDH, thus preserving its intact structure. Dynamic light scattering and zeta-potential measurement also supported the hypothesis that ZOE moieties were located in the interparticle pore of LDH rather than at the surface of LDH particles. Thermogravimetry analysis revealed that thermal stability of encapsulated ZOE could be enhanced by LDH encapsulation. Radical scavenging assay showed that antioxidant activity of ZOE-LDH hybrid was increased after ultrasound and microwave irradiation, while ZOE itself dramatically lost its antioxidant activity upon ultrasound and microwave treatment.

Hydrotalcite-Derived Mixed Oxides for the Synthesis of a Key Vitamin A Intermediate Reducing Waste

The synthesis of hydroxenin monoacetate, a key intermediate in the manufacture of vitamin A, relies on the undesirable use of stoichiometric amounts of organic bases such as pyridine. Although the final product (vitamin A acetate) can be produced from hydroxenin diacetate, using the monoacetylated intermediate improves the overall process yield. Aiming to identify more efficient, environmentally benign alternatives, this work first studies the homogeneous acetylation reaction using pyridine. The addition of the base is found to enhance the rate of hydroxenin monoacetate formation, confirming its catalytic role, but also yields non-negligible amounts of hydroxenin diacetate. On the basis of these insights, Mg- and Al-containing hydrotalcites are explored because of their broad scope as base catalysts and the ability to finely tune their properties. The reaction kinetics are greatly enhanced via controlled thermal activation, forming high surface area mixed metal oxides displaying Lewis basic sites. In contrast, a Brønsted basic material synthesized by the reconstruction of a mixed oxide performs similarly to the as-synthesized hydrotalcite. Variation of the Mg/Al ratio from 1 to 3 has no significant impact, but activity losses are observed at higher values because of a reduced number of basic sites. After optimizing the reaction conditions, hydroxenin monoacetate yields >60% are obtained in five consecutive cycles without the need for any intermediate treatment. The findings confirm the potential of hydrotalcite-derived materials as highly selective catalysts for the production of vitamins with reduced levels of organic waste.

Theranostic Bioabsorbable Bone Fixation Plate with Drug-Layered Double Hydroxide Nanohybrids

A bioabsorbable polymeric bone plate enabled with both diagnostic and therapeutic functionalities (radiopacity and sustained drug release, respectively) is proposed. To this end, a drug-inorganic nanohybrid (RS-LDH) is examined as a theranostic agent by intercalating an anti-resorptive bone remodeling drug, risedronate (RS) into a layered double hydroxide (LDH) via an ion-exchange reaction. The RS-LDH is prepared as a sheet with a biodegradable polymer, poly(lactic-co-glycolic acid), and is then attached onto the clinically approved bioabsorbable bone plate to produce the theranostic plate. Because of the presence of the metals in the LDH, the theranostic plate results in discernible in vivo X-ray images for up to four weeks after implantation. Concurrently, bone regeneration is also significantly improved compared with the other control groups, likely because of this material's sustained drug-release property. The theranostic plate is also largely biocompatible, similar to the plate already approved for clinical use. It is concluded that the combination of a biodegradable bone plate with RS-LDH nanohybrids can constitute a promising system with theranostic ability in both X-ray diagnosis and expedited bone repair.

Acetyl salicylic acid–ZnAl layered double hydroxide functional nanohybrid for skin care application

In this study, a pharmaceutically active ingredient, acetyl salicylic acid (ASA), was intercalated into ZnAl layered double hydroxide (LDH). The ASA–LDH-based cream showed its high prospects in curing skin disorders like razor bumps in a short span of time.

Effect of biotechnologically modified alginates on LDH structures

Four alginates possessing different guluronic/mannuronic acid ratios and one acetylated alginate were investigated with respect to their behaviour during intercalation into layered double hydroxides (LDHs). Two alginates were commercial products while the others were synthesised by way of bacterial fermentation and in one sample followed by enzymatic treatment. Intercalation was performed by way of co-precipitation of aluminium nitrate and zinc nitrate in alginate solution at a pH of 8·5–9. The products were characterised by powder X-ray diffraction, elemental analysis, wide-angle X-ray scattering, scanning electron microscopy and magic angle spinning (MAS) NMR spectroscopy. All alginates intercalate well into the Zn2Al-LDH host structure. With an increase in the content of guluronic acid in the alginate, the d-spacing (interlayer distance) in the alginate-LDH compound increases from 1·28 to 1·85 nm. Similarly, acetylation of the carboxylic groups leads to an increased steric volume of such alginate and therefore to a higher d-spacing (1·72 nm). The results indicate that different guluronic/mannuronic acid ratios can be used to trigger the steric size of the alginates and consequently the d-spacing of the alginate-LDHs. 13C CP MAS NMR spectroscopy confirmed an interaction between the carboxylic groups present in the alginate with the inorganic main layer.

In vitro controlled release of vitamin C from Ca/Al layered double hydroxide drug delivery system

A new drug delivery system for vitamin C (VC), Ca/Al layered double hydroxide (LDH), is demonstrated in this work. VC anions were intercalated successfully in the Ca/Al LDH gallery by a coprecipitation method. The interlayer space of 9.8Å suggests that VC anions are vertical to the LDH layers in the form of interdigitated bilayer. The loading of VC in LDH is 36.4wt.%. The thermal stability of VC is significantly enhanced after intercalation. In vitro VC release results show that the release time of VC in a phosphate buffer at pH7.4 was significantly extended, and the maximal percentage of VC released is 80% of the total. The Avrami-Erofe'ev equation most satisfactorily explains the release kinetics of VC, which is that the release of VC is mainly dominated by the ion-exchange reaction.

Drug-inorganic-polymer nanohybrid for transdermal delivery

For transdermal drug delivery, we prepared a drug-inorganic nanohybrid (FB-LDH) by intercalating a transdermal model drug, flurbiprofen (FB), into the layered double hydroxides (LDHs) via coprecipitation reaction. The X-ray diffraction patterns and FT-IR spectra of the FB-LDH indicated that the FB molecules were successfully intercalated via electrostatic interaction within the LDH lattices. The in vitro drug release revealed that the Eudragit(®) S-100 in release media could facilitate the drug out-diffusion by effectively replacing the intercalated drug and also enlarging the lattice spacing of the FB-LDH. In this work, a hydrophobic gel suspension of the FB-LDH was suggested as a transdermal controlled delivery formulation, where the suspensions were mixed with varying amounts of Eudragit(®) S-100 aqueous solution. The Frantz diffusion cell experiments using mouse full-skins showed that a lag time and steady-state flux of the drug could be controlled from 12.8h and 3.28μgcm(-2)h(-1) to less than 1h and 14.57μgcm(-2)h(-1), respectively, by increasing the mass fraction of Eudragit(®) S-100 solution in gel suspensions from 0% to 20% (w/w), respectively. Therefore, we conclude gel formulation of the FB-LDH have a potential for transdermal controlled drug delivery.

Layered double hydroxide nanoparticles as target-specific delivery carriers: uptake mechanism and toxicity

Layered double hydroxides (LDHs), also known as anionic nanoclays or hydrotalcite-like compounds, have attracted a great deal of interest for their potential as delivery carriers. In this article, we describe the cellular uptake behaviors and uptake pathway of LDHs in vitro and in vivo, which can not only explain the mechanism by which high efficacy of biomolecules delivered through LDH nanocarriers could be obtained, but also provide novel strategies to enhance their delivery efficiency. Toxicological effects of LDHs in cell lines and in animal models are also present, aiming at providing critical information about their toxicity potential, which should be carefully considered for their biomedical application. Understanding the uptake behaviors, uptake mechanism and toxicity of LDHs in terms of dose-response relationship, diverse physicochemical properties and interaction with different biological systems is important to optimize delivery efficiency as well as biocompatibility.

Applications of advanced hybrid organic-inorganic nanomaterials: from laboratory to market

Today cross-cutting approaches, where molecular engineering and clever processing are synergistically coupled, allow the chemist to tailor complex hybrid systems of various shapes with perfect mastery at different size scales, composition, functionality, and morphology. Hybrid materials with organic-inorganic or bio-inorganic character represent not only a new field of basic research but also, via their remarkable new properties and multifunctional nature, hybrids offer prospects for many new applications in extremely diverse fields. The description and discussion of the major applications of hybrid inorganic-organic (or biologic) materials are the major topic of this critical review. Indeed, today the very large set of accessible hybrid materials span a wide spectrum of properties which yield the emergence of innovative industrial applications in various domains such as optics, micro-electronics, transportation, health, energy, housing, and the environment among others (526 references).

Immobilization of Ibuprofen and Copper-Ibuprofen Drugs on Layered Double Hydroxides

The immobilization of the NSAID ibuprofen (Hibp) and the Cu(II)-ibp compound on magnesium-aluminum layered double hydroxides (Mg3Al-LDH) is described. Ibuprofen was intercalated on LDHs by three routes (ion exchange, co-precipitation, and reconstruction). The organic drug and the Cu(II)-ibp were also immobilized by adsorption on LDH external surfaces. Materials were characterized by elemental analysis, UV/VIS, FTIR, and Raman spectroscopies, powder X-ray diffractometry (XRD), thermogravimetry, and electronic paramagnetic resonance (EPR). Mg3Al-(ibp)(cop) (30% w/w of drug/material) and Mg3Al-(ibp)(ie) (33%) materials exhibit bilayer arrangements of ibp anions intercalated between the host layers. Mg3Al-(ibp)(rec) and Mg3Al-(ibp)(ads) contain 13% and 6.2% of ibuprofenate, respectively. Mg3Al-(Cu-ibp)(ads) exhibits two Cu centers in different environments interacting with host layers. Pharmacological potential of materials are compared considering the amounts of immobilized drugs and their buffering properties. Mg3Al-(ibp)(ie) and Mg3Al-(ibp)(cop) exhibit poor buffering property, but contain high ibp amounts. Mg3Al-(ibp)(ads) despite having buffering property, contains low amount of ibuprofen. Mg3Al-(ibp)(rec) combines significant amount of immobilized ibp with good buffering property. Mg3Al-(Cu-ibp)(ads), due to the buffering property, may be an interesting new formulation aiming to decrease gastric irritation.