Xue Duan

Preparation of layered double hydroxides and their applications as additives in polymers, as precursors to magnetic materials and in biology and medicine.

In recent years layered double hydroxides (LDHs), also known as hydrotalcite-like materials, have attracted considerable interest from both industry and academia. In this article, we discuss methods of preparing LDHs with an emphasis on the way in which particle size and morphology can be controlled with regard to specific target applications; scale-up of one such preparation procedure is also described. In addition, we review selected applications of LDHs developed by our own and other laboratories.

Preparation of Fe3O4@SiO2@Layered Double Hydroxide Core–Shell Microspheres for Magnetic Separation of Proteins

Three-component microspheres containing an SiO(2)-coated Fe(3)O(4) magnetite core and a layered double hydroxide (LDH) nanoplatelet shell have been synthesized via an in situ growth method. The resulting Fe(3)O(4)@SiO(2)@NiAl-LDH microspheres display three-dimensional core-shell architecture with flowerlike morphology, large surface area (83 m(2)/g), and uniform mesochannels (4.3 nm). The Ni(2+) cations in the NiAl-LDH shell provide docking sites for histidine and the materials exhibit excellent performance in the separation of a histidine (His)-tagged green fluorescent protein, with a binding capacity as high as 239 μg/mg. The microspheres show highly selective adsorption of the His-tagged protein from Escherichia coli lysate, demonstrating their practical applicability. Moreover, the microspheres possess superparamagnetism and high saturation magnetization (36.8 emu/g), which allows them to be easily separated from solution by means of an external magnetic field and subsequently reused. The high stability and selectivity of the Fe(3)O(4)@SiO(2)@NiAl-LDH microspheres for the His-tagged protein were retained over several separation cycles. Therefore, this work provides a promising approach for the design and synthesis of multifunctional LDH microspheres, which can be used for the practical purification of recombinant proteins, as well as having other potential applications in a variety of biomedical fields including drug delivery and biosensors.

A Cocrystal Strategy to Tune the Luminescent Properties of Stilbene-Type Organic Solid-State Materials†

The one- and two-photon luminescence of stilbene-type solid-state materials can be tuned and controlled from blue to yellow color by a supramolecular cocrystal method.

Layered double hydroxide films: synthesis, properties and applications

Layered double hydroxide (LDH) films have been widely investigated in the last few years because of their promising applications in areas such as catalysis, anti-corrosion coatings for metals, and as components in optical, electrical, and magnetic devices. In this Feature Article we review recent work, from our own laboratory and elsewhere, on the synthesis, properties and applications of functional LDH films, and also offer some perspectives for the design of future multifunctional LDH films.

Biotemplated hierarchical nanostructure of layered double hydroxides with improved photocatalysis performance.

We report a biomorphic hierarchical mixed metal oxide (MMO) framework through a biotemplated synthesis method. A uniform Al(2)O(3) coating was deposited on the surface of the biotemplate with an atomic layer deposition (ALD) process, and the film of ZnAl-layered double hydroxide (ZnAl-LDH), which faithfully inherits the surface structure of the biotemplate, was prepared by an in situ growth technique. Subsequently, a polycrystal ZnAl-MMO framework obtained by calcination of the LDH precursor has been demonstrated as an effective and recyclable photocatalyst for the decomposition of dyes in water, owing to its rather high specific surface area and hierarchical distribution of pore size. Therefore, the new strategy reported in this work can be used to fabricate a variety of biomorphic LDHs as well as MMO frameworks through replication of complicated and hierarchical biological structures for the purpose of catalysis, adsorbents, and other potential applications.

Reversibly Thermochromic, Fluorescent Ultrathin Films with a Supramolecular Architecture†

Tunable luminescent materials that respond to different external stimuli have attracted great attention during the last few years, owing to their potential applications in fluorescent switches, sensors, and optical recording devices. Mechanisms responsible for the change in luminescence include chemical reactions and alteration of the molecular packing mode. Since solid-state chemical reactions frequently have low conversion efficiency, recent attention has focused on controlling and tuning the molecular packing mode as a strategy for the design and preparation of intelligent luminescent materials. To date, although several types of responsive luminescent materials have been developed (e.g., piezochromic, deformation-induced chromic, photochromic, thermochromic, and humidity-related colorimetric luminescent systems), challenges remain. For instance, to meet the requirements of luminescent devices or sensors, it is important to be able to assemble ordered thin films with regular molecular orientation and intermolecular packing mode on two-dimensional surfaces. Switching of solid-state luminescence based on such ordered thin films is rather rare, however. Therefore, it is of crucial importance to develop new ways to fabricate ordered film systems with fluorescent properties which respond to environmental stimuli. Furthermore, fast response, facile reversibility, and stable repeatability are all necessary from the viewpoint of practical application of such materials in sensors. Therefore, there is an urgent demand to develop new types of solid-state responsive materials as well as sensors with high efficiency, stability, and reproducibility. Herein we present a supramolecular ultrathin film (UTF) system with thermochromic luminescence (TCL) based on the layer-by-layer (LBL) assembly of anionic bis(2-sulfonatostyryl)biphenyl (BSB, Scheme 1a) and positively charged layered double hydroxide (LDH, Scheme 1b) nanosheets as basic building blocks. BSB is generally used as a fluorescent brightener in the chemical industry; moreover, the phenylenevinylene unit in BSB also has attracted considerable interest because of its excellent optical and electronic properties. LDHs are a class of layered anionic clays which have been widely used in the fields of catalysis, biology, and optical materials. LDHs can be exfoliated into positively charged nanosheets which can be fabricated into functional ultrathin films (UTFs) by LBL deposition of alternate layers of the LDH and polymers or metal complexes. However, LBL assembly of LDH nanosheets with small anions has rarely been reported because of the tendency of the small anions to escape from the nanosheets. Herein we describe fabrication of ordered BSB/LDH UTFs (Scheme 1) with a fast and reversible TCL response at ambient temperature. The TCL behavior of the assembled BSB anions, which is absent for their pristine form, originates from the host–guest interactions within the UTF system. Molecular dynamics (MD) and periodic density functional theoretical (PDFT) studies demonstrate that the TCL process of the BSB/LDH system is related to the changes in the orientation and aggregation of BSB anions between LDH monolayers. Moreover, coassembly of BSB with other luminescent anions into a UTF allows fabrication of responsive TCL film systems, in which the ratio of the luminescence at two different wavelengths can be reversibly transformed by varying the temperature, thus altering the luminescent color of the film. Therefore, this work provides a feasible route for designing and constructing luminescent supramolecular structures with potential applications in sensors and switching. The multilayer assembly process of the BSB/LDH UTFs was monitored by UV/Vis absorption spectra, which showed Scheme 1. Assembly process for the (BSB/LDH)n UTF. a) Chemical structure and schematic representation of BSB. b) Schematic illustrations of one Mg–Al–LDH monolayer. c) Quartz glass substrate.

Directed Growth of Metal-Organic Frameworks and Their Derived Carbon-Based Network for Efficient Electrocatalytic Oxygen Reduction

A honeycomb-like carbon-based network is obtained by in situ nucleation and directed growth of metal-organic framework (MOF) arrays on the surface of layered double hydroxide (LDH) nanoplatelets, followed by a subsequent pyrolysis process, which exhibits largely enhanced electrocatalytic ORR performances. A successful paradigm for the directed growth of highly oriented MOF arrays is demonstrated, with potential applications for energy storage and conversion.

Ordered poly(p-phenylene)/layered double hydroxide ultrathin films with blue luminescence by layer-by-layer assembly.

Lavender layers: A poly(p-phenylene) anionic derivate and exfoliated Mg-Al layered double hydroxide monolayers were assembled into ultrathin films with well-defined blue fluorescence (see picture; the numbers indicate the number of bilayers), long-range order, and high photostability. These films work as multiple quantum-well structures for valence electrons.

Layered Double Hydroxide‐based Nanomaterials as Highly Efficient Catalysts and Adsorbents

Layered double hydroxides (LDHs) are a class of anion clays consisting of brucite-like host layers and interlayer anions, which have attracted increasing interest in the fields of catalysis/adsorption. By virtue of the versatility in composition, morphology, and architecture of LDH materials, as well as their unique structural properties (intercalation, topological transformation, and self-assembly with other functional materials), LDHs display great potential in the design and fabrication of nanomaterials applied in photocatalysis, heterogeneous catalysis, and adsorption/separation processes. Taking advantage of the structural merits and various control synthesis strategies of LDHs, the active center structure (e.g., crystal facets, defects, geometric and electronic states, etc.) and macro-nano morphology can be facilely manipulated for specific catalytic/adsorbent processes with largely enhanced performances. In this review, the latest advancements in the design and preparation of LDH-based functional nanomaterials for sustainable development in catalysis and adsorption are summarized.

Layered Host–Guest Materials with Reversible Piezochromic Luminescence

Luminescent materials sensitive to environmental stimuli are of great interest from both scientific and engineering aspects, due to their potential applications in fluorescent switches and optical devices. Pressure is one of the most common natural external stimuli, and thus pressure-induced chromic (known as piezochromic) luminescent (PCL) materials can be used to probe changes in pressure, especially under extreme conditions. To date, the study of PCL materials remains in its infancy compared with those of pH-, lightand temperaturesensitive materials. It has been recognized that one strategy to tune the fluorescence of a compound is to alter its molecular arrangement and packing mode since this can modify the intermolecular interactions. Although great efforts have recently been devoted to the study of pure organic fluorophores with PCL properties, the rational design and preparation of such materials remains a considerable challenge. Materials with a two-dimensional (2D) layered structure, such as clays, 12] are a large family of functional organized systems, characterized by tunable interlayer volume and variable interlayer guest. Recently, interest has focused on 2D clay-chromophore supramolecular hybrid materials, since they show novel functionality (such as enhanced photostabilization) which differ from those of their individual components. Importantly, the orientation and arrangement of the luminescent guest species can be tuned within the interlayer galleries of the 2D matrix, which facilitates the modulation of the luminescence properties of the fluorophore ensemble. Layered double hydroxides (LDHs) are one important type of layered matrix which exhibit a particularly large versatility by virtue of their tunable chemical composition and gallery space. The LDH sheets are sufficiently flexible to deform over intercalated bulky guests, and slipping of LDH sheets can occur on increasing the external pressure. Based on the premise that a minor change in the molecular configuration can dramatically influence the host– guest interactions, we have fabricated a new type of PCL material by the assembly of an organic fluorophore (2,2’-(1,2ethenediyl)bis[5-[[4-(diethylamino)-6-[(2,5disulfophenyl) amino]-1,3,5-triazin-2-yl] amino]benzene sulfonate anion, denoted as BTZB, shown in Figure 1 a) into the interlayer galleries of LDH hosts. BTZB is a flexible long-chain stilbene derivative with four rotatable aromatic amine units, and thus its molecular conformation and intermolecular interactions can be tuned more easily by external perturbations than is the case for rigid molecules. It was found that the BTZBintercalated LDH material exhibited optical responses to variations in external pressure, including changes in lumines-