Layered Double Hydroxide Nanosheets: Synthesis Strategies and Applications in the Field of Energy Conversion

In recent years, layered double hydroxides (LDH) nanosheets have garnered substantial attention as intriguing inorganic anionic layered clay materials. These nanosheets have captured the attention of researchers due to their unique physicochemical properties. This review aims to showcase the latest advancements in laboratory research concerning LDH nanosheets, with a specific emphasis on their methods of preparation. This review provides detailed insights into the factors influencing the anionic conductivity of LDH, along with delineating the applications of LDH nanosheets in the realm of energy conversion. Notably, the review highlights the crucial role of LDH nanosheets in the oxygen evolution reaction (OER), a vital process in water splitting and diverse electrochemical applications. The review emphasizes the significant potential of LDH nanosheets in enhancing supercapacitor technology, owing to their high surface area and exceptional charge storage capacity. Additionally, it elucidates the prospective application of LDH nanosheets as anion exchange membranes in anion exchange membrane fuel cells, potentially revolutionizing fuel cell performance through improved efficiency and stability facilitated by enhanced ion transport properties.

Rosmarinic and Glycyrrhetinic Acid-Modified Layered Double Hydroxides as Functional Additives for Poly(Lactic Acid)/Poly(Butylene Succinate) Blends

Immobilizing natural antioxidant and biologically active molecules in layered double hydroxides (LDHs) is an excellent method to retain and release these substances in a controlled manner, as well as protect them from thermal and photochemical degradation. Herein, we describe the preparation of host-guest systems based on LDHs and rosmarinic and glycyrrhetinic acids, two molecules obtained from the extraction of herbs and licorice root, respectively, with antioxidant, antimicrobial, and anti-inflammatory properties. Intercalation between the lamellae of the mono-deprotonated anions of rosmarinic and glycyrrhetinic acid (RA and GA), alone or in the presence of an alkyl surfactant, allows for readily dispersible systems in biobased polymer matrices such as poly(lactic acid) (PLA), poly(butylene succinate) (PBS), and a 60/40 wt./wt. PLA/PBS blend. The composites based on the PLA/PBS blend showed better interphase compatibility than the neat blend, correlated with increased adhesion at the interface and a decreased dispersed phase size. In addition, we proved that the active species migrate slowly from thin films of the composite materials in a hydroalcoholic solvent, confirming the optimization of the release process. Finally, both host-guest systems and polymeric composites showed antioxidant capacity and, in the case of the PLA composite containing LDH-RA, excellent inhibitory capacity against E. coli and S. aureus.

Preparation of two dimensional layered double hydroxide nanosheets and their applications

Layered double hydroxides (LDHs) with their highly flexible and tunable chemical composition and physical properties have attracted tremendous attention in recent years. LDHs have found widespread application as catalysts, anion exchange materials, fire retardants, and nano-fillers in polymer nanocomposites. The ability to exfoliate LDHs into ultrathin nanosheets enables a range of new opportunities for multifunctional materials. In this review we summarize the current available LDH exfoliation methods. In particular, we highlight recent developments for the direct synthesis of single-layer LDH nanosheets, as well as the emerging applications of LDH nanosheets in catalyzing oxygen evolution reactions and preparing light emitting devices, supercapacitors, and flame retardant nanocomposites.

Synthesis of CoAl-layered double hydroxide/graphene oxide nanohybrid and its reinforcing effect in phenolic foams

A graphene oxide (GO) immobilized with layered double hydroxide (CoAl-LDH/GO) nanohybrid was prepared via a hydrothermal method and characterized by transmission electron microscopy, field emission scan electronic microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy and thermogravimetric analysis (TGA). The TGA results show that the immobilization of CoAl-LDH nanoparticles on GO surface greatly promotes the thermal stability of GO. More importantly, the incorporation of the CoAl-LDH/GO nanohybrid into PF foams leads to not only a great improvement in their mechanical strengths but also a reduction in their brittleness and friability. Specifically, compared to neat phenolic (PF) foam, at only 0.9 phr (parts per hundred of resin by mass) of CoAl-LDH/GO, the compressive and flexural strengths of the modified PF foam increase by 54.8% and 35.2%, respectively, and pulverization ratio decreases by 55.2%. The addition of the CoAl-LDH/GO nanohybrid also results in an increase in the limiting oxygen index and a decrease in the peak heat release of the modified PF foam in cone calorimeter test. Moreover, the thermal stability of the PF foam is enhanced by the addition of the nanohybrid.

Morphology-dependent performance of Mg3Al–CO3layered double hydroxide as a nanofiller for polypropylene nanocomposites

In this contribution, the morphology-dependent performance of Mg₃Al–CO₃layered double hydroxide (LDH) as a nanofiller for polypropylene (PP) was evaluated for the first time.

Comparative study of the synergistic effect of binary and ternary LDH with intumescent flame retardant on the properties of polypropylene composites

Functional LDH lead to different fire behaviors of flame retardant polypropylene composites.

Preparation and thermal properties of poly(3-hydroxybutyrate-co-4-hydroxybutyrate)/aluminum-containing layered double hydroxides nanocomposites

In this study, the nanocomposites based on poly(3-hydroxybutyrate- co-4-hydroxybutyrate) (P(3,4)HB) and three kinds of aluminum-containing layered double hydroxides (LDHs) were prepared via melting intercalation. The thermal stability, thermal combustion and thermomechanical properties for these systems were systematically investigated. Both x-ray diffractometry and transmission electron microscopy analyses for P(3,4)HB/LDH system confirm that P(3,4)HB/magnesium–aluminum (MgAl) system has a main exfoliated microstructure and P(3,4)HB/ZnAl system has an intercalated or partially exfoliated microstructure, while P(3,4)HB/NiAl system has an intercalated or phase separated microstructure. The microscale combustion calorimetry results show that the peak of heat release rate for P(3,4)HB/LDH systems, as an important parameter for the assessment of fire hazard of materials, is significantly reduced with the addition of LDHs. The storage modulus of three systems with small amount of LDHs measured by dynamic mechanical analysis is remarkably enhanced. The increment in the storage modulus of P(3,4)HB/LDH nanocomposites will increase with the increase in the atomic number of M2+ of LDHs.

Synthesis of organo cobalt-aluminum layered double hydroxide via a novel single-step self-assembling method and its use as flame retardant nanofiller in PP

Synthesis of polypropylene/organo-layered double hydroxide (PP/OLDH) has been carried out based on self-assembled organocobalt-aluminum LDH (O-CoAl-LDH). The novel method of synthesizing self-assembled CoAl-LDH and its characterization have also been reported in details. This method is proven to be very efficient way of producing OLDH in a single step with homogeneous composition and structure. As flame-retardant nanofiller, O-CoAl-LDH shows significant decrease in heat release rate (HRR), the total heat release (THR) and the heat release capacity (HRC) of the PP composites, though the thermal stability of the compounds decreases slightly compared to the base polymer. Morphological analyses show that the LDH particles are dispersed in PP matrix in a partially exfoliated form. The activation energy calculation based on the Kissinger method reveals that O-CoAl-LDH has a positive effect on the activation energy of thermal decomposition of PP. However, in the presence of this filler, decomposition of the composites starts at an earlier stage than that of pure PP.

Nanocomposites Derived from Polymers and Inorganic Nanoparticles

Polymers are considered to be good hosting matrices for composite materials because they can easily be tailored to yield a variety of bulk physical properties. Moreover, organic polymers generally have long-term stability and good processability. Inorganic nanoparticles possess outstanding optical, catalytic, electronic and magnetic properties, which are significantly different their bulk states. By combining the attractive functionalities of both components, nanocomposites derived from organic polymers and inorganic nanoparticles are expected to display synergistically improved properties. The potential applications of the resultant nanocomposites are various, e.g. automotive, aerospace, opto-electronics, etc. Here, we review recent progress in polymer-based inorganic nanoparticle composites.

Heterogeneous ultrathin films of poly(vinyl alcohol)/layered double hydroxide and montmorillonite nanosheets via layer-by-layer assembly

In this paper, Co-Al layered double hydroxide (LDH) and montmorillonite (MMT) have been exfoliated into charged single layers in the solvent of formamide and water, respectively. The structures of individual layers of LDH and MMT were characterized by X-ray diffraction (XRD) and atomic force microscopy (AFM). The delamination mechanisms of LDH and MMT were also discussed. Furthermore, heterogeneous ultrathin films of poly(vinyl alcohol) (PVA)/charged inorganic nanosheets, (PVA/MMT/PVA/LDH)(n), were fabricated by layer-by-layer (LBL) assembly via hydrogen bonding. The LBL assembly process was monitored by UV-vis spectroscopy, and the structures of the heterogeneous ultrathin films were analyzed by XRD.