Morphologies, Preparations and Applications of Layered Double Hydroxide Micro-/Nanostructures

Layered double hydroxides (LDHs), also well-known as hydrotalcite-like layered clays, have been widely investigated in the fields of catalysts and catalyst support, anion exchanger, electrical and optical functional materials, flame retardants and nanoadditives. This feature article focuses on the progress in micro-/nanostructured LDHs in terms of morphology, and also on the preparations, applications, and perspectives of the LDHs with different morphologies

Preparation of Nickel–Aluminum-Containing Layered Double Hydroxide Films by Secondary (Seeded) Growth Method and Their Electrochemical Properties

Thin films of nickel–aluminum-containing layered double hydroxide (NiAl-LDH) have been prepared on nickel foil and nickel foam substrates by secondary (seeded) growth of NiAl-LDH seed layer. The preparation procedure consists of deposition of LDH seeds from a colloidal suspension on the substrate by dip coating, followed by hydrothermal treatment of the nanocrystals to form the LDH film. The secondary grown film is found to provide a higher crystallinity and more uniform composition of metal cations in the film layer than the in situ grown film on seed-free substrate under identical hydrothermal conditions. A systematic investigation of the film evolution process reveals that the crystallite growth rate is relatively fast for the secondary grown film because of the presence of LDH nanocrystal seeds. Electrochemical performance of the resulting NiAl-LDH films as positive electrode material was further assessed as an example of their practical applications. The secondary grown film electrode delivers improved recharge–discharge capacity and cycling stability compared with that of the in situ grown film, which can be explained by the existence of a unique microstructure of the former. Our findings show an example for the effective fabrication of LDH film with controllable microstructure and enhanced application performance through a secondary (seeded) growth procedure

A Method of High Throughput Monitoring Crop Physiology Using Chlorophyll Fluorescence and Multispectral Imaging

We present a high throughput crop physiology condition monitoring system and corresponding monitoring method. The monitoring system can perform large-area chlorophyll fluorescence imaging and multispectral imaging. The monitoring method can determine the crop current condition continuously and non-destructively. We choose chlorophyll fluorescence parameters and relative reflectance of multispectral as the indicators of crop physiological status. Using tomato as experiment subject, the typical crop physiological stress, such as drought, nutrition deficiency and plant disease can be distinguished by the monitoring method. Furthermore, we have studied the correlation between the physiological indicators and the degree of stress. Besides realizing the continuous monitoring of crop physiology, the monitoring system and method provide the possibility of machine automatic diagnosis of the plant physiology.Highlights: A newly designed high throughput crop physiology monitoring system and the corresponding monitoring method are described in this study. Different types of stress can induce distinct fluorescence and spectral characteristics, which can be used to evaluate the physiological status of plants

Triple-Confined Well-Dispersed Biactive NiCo₂S₄/Ni_0.96S on Graphene Aerogel for High-Efficiency Lithium Storage

Layered double hydroxides (LDHs), also known as hydrotalcite-like anionic clay compounds, have attracted increasing interest in electrochemical energy storage, in the main form of LDH precursor-derived transition metal oxides (TMOs). One typical approach to improve cycling stability of the LDH-derived TMOs is to introduce one- and two-dimensional conductive carbonaceous supports, such as carbon nanotubes and graphene. We herein demonstrate an effective approach to improve the electrochemical performances of well-dispersed biactive NiCo₂S₄/Ni_0.96S as anode nanomaterials for lithium-ion batteries (LIBs), by introducing a three-dimensional graphene aerogel (3DGA) support. The resultant 3DGA supported NiCo₂S₄/Ni_0.96S (3DGA/NCS) composite, obtained by sulfuration of NiCo-layered double hydroxide (NiCo-LDH) precursor in situ grown on the 3DGA support (3DGA/NiCo-LDH). Electrochemical tests show that the 3DGA/NCS composite indeed delivers the greatly enhanced electrochemical performances compared with the NiCo₂S₄/Ni_0.96S counterpart on two-dimensional graphene aerogel, i.e., a high reversible capacity of 965 mA h g^–1 after 200 cycles at 100 mA g^–1 and especially a superlong cycling stability of 620 mA h g^–1 after 800 cycles at 1 A g^–1. The enhancements could be ascribed to the compositional and structural advantages of boosting electrochemical performances: (i) well-dispersed NiCo₂S₄/Ni_0.96S nanoparticles with interfacial nanodomains resulting from both the dual surface confinements of the 3DGA support and the crystallographic confinement of NiCo-well-arranged LDH crystalline layer, (ii) an appropriate specific surface area and a wide pore size distribution of mesopores and macropores, and (iii) highly conductive 3DGA support that is measured experimentally by using electrochemical impedance spectra to underlie the enhancement. Our results demonstrate that the tunable LDH precursor-derived synthesis route may be extended to prepare various transition metal sulfides and even transition metal phosphides for energy storage with the aid of tunable cationic type and molar ratio

Preparation and Regulating Cell Adhesion of Anion-Exchangeable Layered Double Hydroxide Micropatterned Arrays

We describe a reliable preparation of MgAl-layered double hydroxide (MgAl-LDH) micropatterned arrays on gold substrate by combining SO₃^–-terminated self-assembly monolayer and photolithography. The synthesis route is readily extended to prepare LDH arrays on the SO₃^–-terminated polymer-bonded glass substrate amenable for cell imaging. The anion-exchangeable MgAl-LDH micropattern can act both as bioadhesive region for selective cell adhesion and as nanocarrier for drug molecules to regulate cell behaviors. Quantitative analysis of cell adhesion shows that selective HepG2 cell adhesion and spreading are promoted by the micropatterned MgAl-LDH, and also suppressed by methotrexate drug released from the LDH interlayer galleries

Solid-Solution Sulfides Derived from Tunable Layered Double Hydroxide Precursors/Graphene Aerogel for Pseudocapacitors and Sodium-Ion Batteries

Transition-metal sulfides (TMSs) are suggested as promising electrode materials for electrochemical pseudocapacitors and lithium- and sodium-ion batteries; however, they typically involve mixed composites or conventionally stoichiometric TMSs (such as NiCo₂S₄ and Ni₂CoS₄<b>)</b>. Herein we demonstrate a preparation of solid-solution sulfide (Ni_0.7Co_0.3)­S₂ supported on three-dimensional graphene aerogel (3DGA) via a sulfuration of NiCo-layered double hydroxide (NiCo-LDH) precursor/3DGA. The electrochemical tests show that the (Ni_0.7Co_0.3)­S₂/3DGA electrode exhibits a capacitance of 2165 F g^–1 at 1 A g^–1, 2055 F g^–1 at 2 A g^–1, and 1478 F g^–1 at 10 A g^–1; preserves 78.5% capacitance retention upon 1000 cycles for pseudocapacitors; and in particular, possesses a relatively high charge capacity of 388.7 mA h g^–1 after 50 cycles at 100 mA g^–1 as anode nanomaterials for sodium-ion batteries. Furthermore, the electrochemical performances are readily tuned by varying the cationic type of the tunable LDH precursors to prepare different solid-solution sulfides, such as (Ni_0.7Fe_0.3)­S₂/3DGA and (Co_0.7Fe_0.3)­S₂/3DGA. Our results show that engineering LDH precursors can offer an alternative for preparing diverse transition-metal sulfides for energy storage