Exfoliation Of Layered Double Hydroxide Research Articles

Exfoliation of carboxymethylcellulose-intercalated layered double hydroxide in water

• Exfoliation of Layered Double Hydroxides (LDH) in water using low power sonicator. • Intercalation of carboxymethylcellulose (CMC) polymer into the LDH interlayer space . • The d-value of CMC-intercalated LDH is sensitive to the relative humidity. • AFM technique confirmed the presence of single and double layers of LDH after sonication. • Stable LDH-polymer dispersions in water with concentration of 10 g L −1 were obtained.

Efficient Exfoliation of Layered Double Hydroxides; Effect of Cationic Ratio, Hydration State, Anions and Their Orientations.

The exfoliation ability of nitrate based Mg1−xAlx(OH)2(NO3)x·mH2O layered double hydroxides (Mg-Al LDH) in formamide into single or multilayer nanosheets depends strongly on nitrate anion orientation and layer charge. Our systematic studies used materials that were likely to disclose differences with respect to anion type and their concentrations in the interlayer gallery. We assured to avoid any carbonate incorporation into the galleries for nitrate, chloride, iodide, and sulfate based Mg-Al LDHs. Furthermore, the comparative exfoliation experiments were conducted for fully hydrated samples with as similar particle morphology as possible. The exfoliation of nitrate Mg-Al LDH is far superior to similar clays with carbonate, sulfate, chloride, or iodide as charge balancing anions. Quantitative analysis of exfoliation yield for pre-treated, fully hydrated samples, shows an optimum composition for exfoliation into single nanosheets of around x ≈ 0.25, while double or triple layered sheets are encountered for other x-values. We observe a clear correlation between the expansion of the interlayer gallery due to progressing tilts of nitrate anions and water molecules out of the horizontal interlayer plane, suspension turbidity, and degree of exfoliation. The established correlations extends to nitrate Ni-Al LDH materials. We finally claim that morphology is a dominating parameter, with house-of-card morphology particles exfoliation far less than platelet-like particles. Hence, hydrothermal treatment may be favorable to enhance exfoliation yields.

Advanced Exfoliation Strategies for Layered Double Hydroxides and Applications in Energy Conversion and Storage

AbstractAlong with the increasing aggravation of energy and environmental problems, the demand and utilization of renewable energy have increased. The rational design of advanced functional materials serves as a critical point for the improvement of performance and the practical application in renewable energy devices. Layered double hydroxides (LDHs) with 2D layered structures are promising energy materials for their unique physical and chemical properties. Nevertheless, the applications are limited by the structure of stacking with irrational electronic structure, sluggish mass transfer, and low activity. The exfoliation of LDHs into single‐ or few‐layered nanosheets appears to be a promising approach to overcome the above disadvantages. Herein, the recent progress on the development of exfoliation strategies for LDHs including liquid phase exfoliation, plasma‐induced exfoliation, and other advanced exfoliation strategies is highlighted and the applications in energy conversion and storage are systematically introduced.

Recent advance in ultrathin/ultrasmall layered double hydroxides

Layered double hydroxides (LDHs), as a class of anionic intercalation materials, have been widely used in various fields such as photo/electro-catalysis, biology, medicine, etc. With the dramatic development of nanotechnology, LDHs-based multifunctional materials have drawn great attention due to their unique properties. This review particularly focuses on the fine control of the particle size and thickness of LDHs from three different perspectives including synthetic strategy, characteristic method, LDHs application, which may pave a new pathway for the rational design of LDHs-based functional materials. In this review, there are five individual synthetic methods summarized of ultrathin/ultrasmall LDH. The first one is involving separate nucleation and aging steps. LDHs have been prepared by the rapid mixing of the precursor solutions at the nucleation step and followed by a separate aging step. Moreover, the size distribution of LDH is narrow. The second method is exfoliation of LDHs through chemical agents such as formamide, acetone, alcohol or plasma. LDHs can be exfoliation into a thin layer or even a single layer. This method provides a new type of nanosheet with ultimate two-dimensional anisotropy and positive charge. The third method is the reverse microemulsions, which can be used to control the nucleation and growth of LDHs. The size can be precisely controlled between 30−200 nm by this method. The fourth is one step method. By introducing a layer growth inhibitor, the interactions between neighboring layers have been wakened and thus we can directly synthesize LDHs single-layer nanosheets. This facile one-step method offers significant savings in both cost and time; The fifth method is synthesis of LDHs with base materials (graphene oxide, nitrogen-doped graphene) by the surface confinement effect, and the size of LDHs synthesis by this method is 5−6 nm. To date, many advanced characterization methods have been used to give a better understanding of the LDHs structure and reaction mechanism. X-ray absorption fine structure spectroscopy (XAFS) is widely used to obtain structural information of LDHs that include the bond length, valence state, defect structure and structural disorder. In addition, X-ray photoelectron spectroscopy (XPS) has been used to probe information of LDHs about structural evolution and valence state through changing binding energy. Besides, positron annihilation spectrometry (PAS) is a well-established technique to convey information on the local electronic environment in LDHs and can give insight into the defect characteristics even at atomic scales. Mossbauer spectroscopy has been used to probe the iron-based LDHs cause it can provide a unique means by which to probe the Fe sites in these LDHs. What count is, DFT calculations have been applied to elucidate the reaction mechanism and exploration of the structure-property relationships of LDHs. With the advancement of technology, DFT calculation may provide more useful information and thereby guide the experiments. Through changing the particle size and thickness of LDHs, we can control the microstructure and electronic structure of LDH which plays an important role to influence the chemical and physical properties. A variety of ultrathin/ultrasmall LDHs functional materials have been used in whthin many fields such as catalytic property, adsorption property, optical property and biological application, etc. It is believed that in the future, the foundation and application fields of hydrotalcite-based functional materials will be more extensive. LDHs with different grain sizes, layer thicknesses, defect types, and electronic structures will receive more extensive attention and research.

Exfoliation of layered double hydroxides by use of zwitterionic surfactants in aqueous solution

A new strategy to exfoliate inorganic layered double hydroxide (LDH) solids to micrometer-sized and positively-charged nanosheets in aqueous solution is presented. The procedure involves intercalation of zwitterionic surfactant into the decarbonated LDH by ion exchange, followed by simply stirring the surfactant-intercalated LDH in an aqueous solution of pH = 2. Since the charge of zwitterionic surfactant can be varied from anionic to cationic by adjusting the pH, the zwitterionic ions present in the interlayer were converted to cationic at pH = 2, resulting in the exfoliation of LDH by electrostatic repulsion. The delaminated LDHs nanosheets were confirmed by XRD, TEM, and AFM analyses. This simple method did not need reflux at high temperature, overcame the drawback of using organic solvents, and even resulted in a stably colloidal dispersion of nanosheets.

A convenient green preparation of layered double hydroxide/polyacrylamide nanocomposite hydrogels with ultrahigh deformability.

A convenient green preparation method has been developed to achieve layered double hydroxide (LDH)/polymer nanocomposite (NC) hydrogels. In contrast to previous publications using toxic organic solvent of formamide or methanol in LDH exfoliation or anion exchange, the interlayer anion exchange and exfoliation of LDH are completed in one step with the help of an amino acid (L-serine). The LDH/polyacrylamide (PAM) NC hydrogels are achieved by a convenient exfoliation-adsorption in situ polymerization method. The exfoliation of LDH is characterized by dynamic light scattering and transmission electron microscopy. Interestingly, the developed NC hydrogels reveal ultrahigh deformability and extraordinary stretchability, confirmed by qualitative images and qualitative tensile and compression tests. The molecular mechanism for the ultrahigh deformability and extraordinary stretchability is discussed by crosslinking density, inter-crosslinking molecular weight and swelling tests. We believe that the findings reported herein will deepen our understanding towards the chemistry of network soft materials including gels, and further widen the applications of polymer hydrogels in mechanical devices such as artificial muscles, biomedical devices and drug delivery systems.

Fabrication and characterization of positively charged hybrid ultrafiltration and nanofiltration membranes via the in-situ exfoliation of Mg/Al hydrotalcite

Layered double hydroxides (LDHs) recently have attracted intense research for their electric property. In particular, the exfoliation of LDHs provides a new type ultimate two-dimensional nanosheet with higher positive charge density. In this work, Mg/Al hydrotalcite was prepared and exfoliated in dimethylacetamide (DMAc) and then the resulting colloidal solution was used to fabricate antisymmetric membranes using polyethersulfone as membrane material via phase inversion method. Both ultrafiltration and nanofiltration membranes were prepared to investigate the effect of exfoliated Mg/Al hydrotalcite content on the membrane properties. The morphology of membranes was investigated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Hydrophilicity, water flux, and rejections of all prepared membranes were tested and the results indicated that both ultrafiltration and nanofiltration membranes showed good separation property. Ultrafiltration membranes exhibited higher rejection (above 85%) for PEG 20000 and lower protein adsorption amount for positively charged proteins, which may be used in some separation fields of proteins. Nanofiltration membranes showed higher rejection for PEG 400 but a much lower value for MgSO4, and therefore such membrane may have a potential application in desalination for organic matter.