Hybrid materials based on layered double hydroxides (LDHs) exhibit great potential in diverse fields such as health care, polymer composites, environment, catalysis, and energy generation. Indeed, ...the compositional flexibility and the scalability of LDH structures, their low cost, and their ease of synthesis have made hybrid LDHs extremely attractive for constructing smart and high‐performance multifunctional materials. This review provides a comprehensive and critical overview of the current research on multifunctional hybrid LDHs. Organic–inorganic hybrid LDHs, intercalated and surface‐immobilized structures, are both specifically addressed. The new trends and strategies for hybrid LDH synthesis are first described, and then the potential of the latest hybrid LDHs, polymer LDH nanocomposites, and LDH bio‐nanocomposites are presented. Significant achievements published from ≈2010, including authors' results, which employ hybrid LDH assemblies in materials science, medicine, polymer nanocomposites, cement chemistry, and environmental technologies, are specifically addressed. It is concluded with remarks on present challenges and future prospects.
The concept of multifunctionality has exploded in materials science during the last decade, and this trend also applies to hybrid layered double hydroxides (LDHs). In this Feature Article, after a survey of the diverse approaches to hybrid LDH synthesis, significant achievements based on the use of hybrid LDH assemblies in materials science, medicine, polymer nanocomposites, cement chemistry, and environmental technologies are specifically addressed.
An original concept based on carbon replica method and adapted on organic/inorganic (O/I) hybrid layered double hydroxide (LDH) assembly is used to impart resulting carbon composites and replicas ...with interesting electrochemical properties. Thanks to the isomorphous cation substitution possible within the LDH layers, a series of O/I materials are prepared using the emulsifier 2-acrylamido-2-methyl-1-propanesulfonate acid (AMPS) as a source of carbon and Zn2Al, Co2Al0.5Fe0.5 and Ni2Al as the LDH framework container. The process of carbonization and acid leaching is characterized by in situ X-ray diffractometry, Raman spectroscopy, and the pore formation of the resulting carbon replica by nitrogen adsorption. According to the carbonization/acid-leaching procedure, the electrochemical behavior is characterized in various aqueous electrolytes, using four salts, including 1.0 M NaNO3, 0.5 M Na2SO4, 1 M Na2SO3, and 6 M KOH by means of cyclic voltammetry, galvanostatic mode, and complex impedance spectroscopy. Here, the key facet is the combination of the capacitive behavior of carbon, the pseudo-capacitive response coming from its functionalized surface, as well as redox reactions resulting from the inorganic particles present in the carbon composite and acting as a pore former during the acid leaching. From an optimized potential window of 1.2 V in 1 M Na2SO3, an electric energy of 11.0 W h/kg associated with a power density of 87.75 kW/kg is retrieved at a current density of 10 mA/g for carbon replica obtained from Co2Al0.5Fe0.5/AMPS, and this is determined to be stable at moderate regime without significant capacitance fading. Meanwhile, a corresponding carbon composite, i.e., before acid leaching, presents over an optimized potential window of 1.8 V, a capacitance per surface unit of 92.6 μF/cm2 at slow scan rate, largely because of the pseudo-capacitance effect, and a reversible redox reaction of 43 mAh/g is obtained at the C/3 regime in galvanostatic mode. Finally, preliminary tests in an asymmetric capacitor give some hints on the versatility of the new innovative approach using electrochemically active template, which creates the carbon part with suitable (pseudo)-capacitive properties, as well as being electronically conductive embedding inorganic redox centers.
The dissolution of microcrystalline cellulose in 1-butyl-3-methylimidazolium acetate C sub(4)C sub(1)ImOAc was studied using a solid-liquid equilibrium method based on polarized-light optical ...microscopy from 30 to 100 degree C. We found that C sub(4)C sub(1)ImOAc could dissolve as much as 25 wt% of cellulose at temperatures below 100 degree C. The structure of the composite phase obtained after cooling a solution of 16 wt% of cellulose in C sub(4)C sub(1)ImOAc was analyzed by low angle X-ray diffraction showing the absence of microcrystalline cellulose, but depicting an extensive long range isotropic ordering. With the aim of improving the dissolution of cellulose in the ionic liquid, dimethyl sulfoxide, DMSO, was added as a co-solvent. It was observed that it enhances the solvent power of the ionic liquid by decreasing the time needed for dissolution, even at low temperatures. In order to understand what makes DMSO a good co-solvent, two approaches were followed. Firstly, we studied experimentally the mass transport properties (viscosity and ionic conductivity) of C sub(4)C sub(1)ImOAc + DMSO mixtures at different compositions and, secondly, we assessed the molecular structure and interactions around glucose, the structural unit of cellulose, by means of molecular dynamics simulations. As expected, DMSO dramatically decreases the viscosity and increases the conductivity of the mixtures, but without inducing cation-anion dissociation in the ionic liquid. These results were confirmed by molecular simulation as it was found that the presence of a 0.5 mole fraction concentration of DMSO does not significantly affect the hydrogen-bond network in the ionic liquid. Furthermore, molecular dynamics shows that in the C sub(4)C sub(1)ImOAc + DMSO equimolar mixture, DMSO does not interact specifically with glucose. We conclude that DMSO improves the solvation capabilities of the ionic liquid because it facilitates mass transport by decreasing the solvent viscosity without significantly affecting the specific interactions between cations and anions or between the ionic liquid and the polymer. The behavior of DMSO as a co-solvent was compared with that of water and it was found that water molecules are more probably found near glucose than those of DMSO, thus interfering with ionic liquid-glucose interactions, which might explain the unsuitability of water as a co-solvent for cellulose in ionic liquids.
In the field of biodegradable polymers such as poly(Lactic Acid) (PLA), it is quite well known that their kinetics of hydrolysis strongly depend on the pH of the hydrolyzing medium. The idea explored ...during this study focused on PLA, is the addition of additives that are able to control the pH of water when it diffuses inside the polymer. For instance, acids (i.e. succinic acid, also used as food additive) are bio- and eco- friendly additives that are able to play this role. In order to control the release of these molecules and their dispersion inside the polymer, their intercalation in biocompatible nanofillers like layered double hydroxides (LDH) is here considered. The additives have been dispersed in the polymer by melt compounding, commonly used in the plastic industry. Several composites of PLA (4032D) and LDH intercalated with organic acids (succinic, fumaric, and ascorbic acid) have been obtained by an extrusion process. From all extruded materials, PLA films obtained by compression molding were then subjected to hydrolysis tests. The results showed that the mentioned molecules, dispersed in the polymer, are able to control the rate of hydrolysis, and experimental results show an increase of degradation time for samples containing LDH-organic acid (in particular with LDH-succinic acid), making such hybrid additives an appropriate and efficient solution for PLA.
By selecting two electroactive species immobilized in a layered double hydroxide backbone (LDH) host, one able to act as a positive electrode material and the other as a negative one, it was possible ...to match their capacity to design an innovative energy storage device. Each electrode material is based on electroactive species, riboflavin phosphate (RF) on one side and ferrocene carboxylate (FCm) on the other, both interleaved into a layered double hydroxide (LDH) host structure to avoid any possible molecule migration and instability. The intercalation of the electroactive guest molecules is demonstrated by X-ray diffraction with the observation of an interlayer LDH spacing of about 2 nm in each case. When successfully hosted into LDH interlayer space, the electrochemical behavior of each hybrid assembly was scrutinized separately in aqueous electrolyte to characterize the redox reaction occurring upon cycling and found to be a rapid faradic type. Both electrode materials were placed face to face to achieve a new aqueous battery (16C rate) that provides a first cycle-capacity of about 7 mAh per gram of working electrode material LDH/FCm at 10 mV/s over a voltage window of 2.2 V in 1M sodium acetate, thus validating the hybrid LDH host approach on both electrode materials even if the cyclability of the assembly has not yet been met.
Hybridization of layered double hydroxide (LDH) platelets of Zn2Al cation intra-sheet composition was performed with L-tyrosine (TYR), L-tryptophan (TRP) and 3-(4-hydroxyphenyl) propionic (HPP) acid, ...and the hybrid LDH materials were characterized by the means of conventional techniques as X-ray diffraction and thermal analysis to address their sandwich structures and their mass formulae, respectively. Subsequently they have been considered as "green" filler and dispersed into poly(butylene succinate) (PBS) through a melt extrusion process. In regard of the rheological properties, it was possible to extend the PBS chain thus leading to a better processability. Another aspect was the ability to stand photo-degradation under UV radiation for applicative purposes. Owing to the organic chromophores acting as potential UV stabilizers, it was found a higher chain extension effect for PBS in the case of LDH/TRP that was also performing in time of irradiation tests. This opens new routes for designing filler of "white and green" relevances to endow bio-source polymer with properties for practical applications and in respect of environment and global sustainability.
Display omitted
•The organo-modified Zn-Al layered double hydroxides were synthesized.•3-(4-hydroxyphenyl)propionic acid, L-tyrosine and L-tryptophan were intercalated.•PBS composites with Zn-Al LDHs were prepared by melt extrusion.•The effect of Zn-Al LDHs on chain extension and photostability of PBS was observed.
Biodegradable agricultural films made of poly(butylene adipate- co -terephthalate) (PBAT) are interesting alternatives to the most commonly used low-density polyethylene (LDPE) films. ...Photodegradation of both types of polymers can be prevented by the addition of UV stabilizers. To prevent leaching of the additives from the films, the stabilizers can be intercalated in layered double hydroxides (LDH). When LDHs are exfoliated in the polymer a nanocomposite is formed with improved material properties. An ex-ante cradle-to-grave life cycle assessment (LCA) is conducted on the application of nanoclays in agricultural mulching films. The PBAT/LDH nanocomposite is compared with PBAT and LDPE, both of which had been UV-stabilized with the conventionally used compound Irganox 1010. Being key ingredients of the nanocomposites we prepare an ex-ante cradle-to-factory gate LCA for different nanoclay compositions containing surfactants and the non-toxic UV stabilizer p -hydroxycinnamic acid intercalated in LDH sheets. Among the nanoclays, the lowest environmental impact is achieved by LDHs based on magnesium oxide/hydroxide and aluminum oxide/hydroxide, with the surfactant stearate as the intercalated anion. Our comparative analysis of mulching films shows that the lowest non-renewable energy use and greenhouse gas emissions are obtained by LDPE films, which are recycled and incinerated with energy recovery after the second life cycle. However, recycling and energy recovery are not always applied, which makes the biodegradable PBAT an interesting alternative. Further study on the UV stability, tensile strength and bio-based feedstock for PBAT indicates that PBAT containing LDH and p -hydroxycinnamic acid can be an environmentally friendly alternative to LDPE agricultural films containing the UV stabilizer Irganox 1010.
Cinnamic derivatives intercalated into ZnAl layered double hydroxides by coprecipitation are subsequently dispersed into a biodegradable polymer, polybutylene succinate (PBS). The structure and ...composition of the associated organic-inorganic hybrid assemblies are first characterized by X-ray diffraction (XRD) and UV spectroscopy, and then PBS extruded nanocomposite derivatives are evaluated against UV exposure. Using a combination of the PBS nanocomposite structures and the UV and rheological properties relationship, the effect of radiation time on the macromolecular changes undergone by the polymer chains, i.e. chain scissions and cross-linking, as well as on the UV-barrier evolution, is also scrutinized by means of transmission and emission spectroscopies. The combination of organically modified hydrotalcites with PBS could be used as an innovative route for sustainable development of UV protected materials and reduce the environmental impact of UV absorbing chemicals.
Developing green thermal stabilizer for poly(vinyl chloride) (PVC) today is a great challenge for materials as polymer filler. Here, the “salt-oxide/hydroxide” route in mild conditions is used to ...fabricate a series of Mg2Al-CO3-LDH samples from Mg(OH)2 precursors with different average particle sizes from 202 ± 10 nm to 334 ± 13 nm. A linear correlation is observed for the lateral size of the platelets between Mg2Al-CO3-LDH samples and their associated Mg(OH)2 precursors. After surface-organo-modification (SOM), organophilic Mg2Al-CO3-LDH samples are found to be highly dispersed into PVC and investigated as environment-friendly thermal stabilizers. From the static/dynamic tests, the performances are strongly enhanced and related to the particle size of the LDH stabilizer, with the yellowish color aspect appearing later than for the commercial HT-3/PVC. Among the LDH series, the platelets with an average particle lateral size of about 220 ± 10 nm perform the best for the thermal stability for PVC polymer. Among the series, the corresponding PVC composite film presents comparatively the minimum color value in static/dynamic discoloration test, exhibiting the longer ignition time for proton initial release as well as the longer stability time in dehydrochlorination test. It underlines that the salt-oxide/hydroxide route is an efficient and environmentally friendly process in producing high-performance green LDH stabilizer for PVC.
Display omitted
Since these origins, the field of hybrid materials has developed into a broad scientific and technological subject including important fields such as sol–gel chemistry 4–5, polymer nanocomposites ...6–7, and hybrid nanomaterials 8–9. The main issue in this approach is to monitor and control interactions between different bricks and to understand the physico-chemical mechanisms involved at the interfaces between the individual building blocks as well as between different materials. ...the implementation of hybrid systems in devices implies miniaturization. ...nanostructuration or nanoarchitectonics is the core of current research in hybrid materials, and the analysis of advanced hybrid materials needs specialized experimental and theoretical techniques. Polyion complex micelles formed by complexation between poly(ethylene oxide)-b-poly(acrylic acid) (PEO-b-PAA) and an oligo-chitosan-type polyamine was used as a structure-directing agent to prepare ordered mesoporous silica materials in the work “pH-mediated control over the mesostructure of ordered mesoporous materials templated by polyion complex micelles” 22.
PDF
