Obtaining high efficiency room temperature phosphorescence (RTP) by employing non-noble metals poses two challenges: (1) strengthening spin–orbit coupling of excitons to improve the rate of intersystem crossing (ISC) by using non-noble metals with small-atomic-number; (2) employing structural confinement to enhance radiation relaxation because harsh conditions, including carefully selected matrices, rigid solid-state crystalline structure and low temperature, are commonly needed. Here, layered double hydroxides (LDHs) with orderly non-noble metal arrangements were used as an inorganic matrix to activate RTP of carbon dots (CDs). The Zn orderly arranged on the LDH layer contributes to the enhancement in spin–orbit coupling of excitons and the decrease in the energy gap for the singlet–triplet state. The structural confinements of the LDH layer and nano-interlayer testify that the phosphorescence of CDs-LDHs originates from the suppressed radiationless relaxation processes. Using the high tunability of metal species and ratios on the LDH layer, this method can be widely applied to optimize ISC and phosphorescence properties.

Graphene quantum dots (GQDs) should be expected to become an alternative material for removal of several pollutants from water due to their lager specific surface areas, abundant functional groups, and excellent biocompatibility. However, very little effort focused on adsorption behavior as higher water solubility of GQDs. Here we not only showed highly efficient adsorption of GQDs confined in two-dimensional (2D) hydrophobic space for nonionic organic adsorbates but also systematically explored the interaction between adsorbents and adsorbates. The cointercalation of citrate and dodecyl sulfate (SDS) into interlayer of layered double hydroxides (LDHs) was prepared by hydrothermal method to obtain GQDs confined in 2D hydrophobic space. The adsorption efficiency of (GQDs+SDS)-LDHs for 2,4,6-trichlorophenol is 80%, which is higher than that of GQDs-LDHs (15%) and SDS-LDHs (40%). Adsorption mechanism showed the synergistic effects of hydrophobic, hydrogen bond, and π–π interaction were responsible for adsorption of nonionic organic adsorbates by (GQDs+SDS)-LDHs. As a result, this work not only solved the problems of high water solubility and aggregation of GQDs by immobilizing and dispersing GQDs in 2D confined and hydrophobic interlayer of LDHs but realized highly efficient adsorption of GQDs-based complex for nonionic organic adsorbates. Therefore, this strategy might be expanded to adsorb a wide variety of adsorbates by employing the structure designable ability of GQDs-LDHs-based composites.

•Fabrication of optical chemosensors based on the self-assembly of Azobenzene (2-(3,6-disulfo-8-hydroxynaphthylazo)-1,8-dihydroxynaphthalene-3,6-disulfonate) and layered double hydroxides (LDHs) nanosheet has been reported.•The film shows a stepwise and regular growth and a periodical layered structure perpendiculars to the substrates.•The film demonstrates sensory property for Be2+ and reversible response to UV and visible light.•Study on the mechanism shows the light-controlled reversible behavior leads to reversible change of elements, structure and morphology of the ultrathin film.This paper reports the fabrication of optical chemosensors based on the self-assembly of Azobenzene (2-(3,6-disulfo-8-hydroxynaphthylazo)-1,8-dihydroxynaphthalene-3,6-disulfonate) and layered double hydroxides (LDHs) nanosheet, which demonstrates sensory property for Be2+ and reversible response to UV and visible light. The fluorescence intensity of the UTF is linear proportional to Be2+ concentration in the range 0.1–1.2 μM. The absolute detection limit is 3 nM (S/N = 3). Moreover, the UTF shows reversibly optical behavior through alternate irradiating by UV and visible light. Combining sensory and light response property, the light-controlled reversible sensor for detection of Be2+ was realized. The chemosensor displays a good repeatability (RSD less than 1.1% in 5 consecutive measurements). Study on the mechanism shows the light-controlled reversible behavior leads to reversible change of elements, structure and morphology of the UTF confirmed by XPS, Raman, XRD, and AFM. Therefore, we provided a high efficient, clean and environmental-friendly method to achieve reversibility of optical chemosensor by employing light as controlled condition, which open a new avenue to design the advanced optical sensors and switches.This paper reports the fabrication of optical chemosensors based on the self-assembly of Azobenzene (2-(3,6-disulfo-8-hydroxynaphthylazo)-1,8-dihydroxynaphthalene-3,6-disulfonate) and layered double hydroxides (LDHs) nanosheet, which demonstrates sensory property for Be2+ and reversible response to UV and visible light. Combining sensory and light response property, the light-controlled reversible sensor for detection of Be2+ was realized. Therefore, we provided a high efficient, clean and environmental-friendly method to achieve reversibility of optical chemosensor by employing light as controlled condition, which open a new avenue to design the advanced optical sensors and switches.

This paper reports the fabrication of a three-dimensional (3D) nanowall structure based on the intercalation of calcein into a layered double hydroxide (LDH) by a modified solvothermal direct growth process, and explores its electrogenerated chemiluminescence (ECL) property for detection of dopamine (DA). X-ray diffraction (XRD) and scanning electron microscopy (SEM) confirmed the calcein/LDH nanowall film possess a preferential orientation with their ab plane perpendicular to the substrate. The nanowall film shows tunable luminescence properties by simple changing the amount of calcein in the LDH interlayer, and the optimum fluorescence intensity occurs in the sample with x = 1.25%. The stable and strong ECL signals suggested that this film possesses excellent operational and storage stability, which is essential for a sensor. The ECL intensity increased linearly with increasing DA concentration from 5.00 × 10−7 to 1.01 × 10−4 M. The detection limit was 3.52 × 10−7 M. The mechanism of the ECL sensor indicates that the 3D micro-morphology of the calcein/LDH nanowall film has a positive influence on the electrochemical property due to its high surface area and reduced interface resistance. Therefore, this work not only provides a preparation method for a chromophore/LDH complex with a 3D micro/nanostructure, but also systematically probed the structure–property relationship of the calcein/LDH nanowall film. According to this strategy, advanced sensors and devices with outstanding optical and electrochemical properties can be achieved.

Highly anisotropic magnetic films are possible to fabricate by control of the coupling between individual magnetic particles. Selective control over coupling in the horizontal and vertical directions are of both fundamental and practical interest. Here we show such control in the multiple layer-by-layer (LBL) self-assembly of layered double hydroxide (LDH) nanosheets (x = 1, 2, 3 and 4) with thicknesses of 5–15 nm, co-assembled with 3-aminopropyl-trimethoxysilane (APTS) modified spherical Fe3O4 nanoparticles (APTS-Fe3O4 NPs) on quartz substrates. The electrostatic charge density on the LDH sheets, controlled by the Mg/Al composition ratio, affects the NP packing in a single horizontal layer, while the thickness of the LDH sheets controls magnetic coupling between layers. The tunable magnetic properties (coercivity Hc, saturation magnetization Ms, anisotropy, and blocking temperatures) are measured as a function of these parameters. The maximum saturation magnetizations Ms, 36.3 and 25.1 emu·g–1 in the perpendicular and parallel direction, respectively, are found for the sample of x = 3 = Mg/Al ratio in the LDH layer, and 15 nm LDH layer thickness. This work provides a general method to adjust the anisotropy of magnetic films based on directional control of coupling of magnetic nanoparticles between and across, LDH nanosheets. We outline how higher anisotropy and even finer control could be achieved by pH and composition control over the electrostatic charge of the assembly components.

The fabrication of the ordered colorimetric molecule/layered double hydroxide (LDH) ultrathin films (UTFs) by the LBL deposition technique was reported, and demonstrates their application as a colorimetric chemosensor for F−. The structural and surface morphology studies show that the UTF is continuous and uniform with stacking order in the normal direction of the substrate. The LDH nanoparticles isolate Alizarin complexone (AC) molecules from each other. The AC/LDH UTFs display a stepwise and regular growth of upon increasing deposition cycles proved by UV–vis absorption and a periodical layered structure perpendicular to the substrates with a thickness of 5.96–6.28 nm per bilayer observed by X-ray diffraction and scanning electron microscopy. Moreover, the (AC/LDH)20 UTF displays an excellent behavior as colorimetric chemosensor for F− with a low detection limit (12.9 μM), good regeneration and reversibility, high stability (light and storage stability) as well as selectivity. In addition, the mechanism of measurement–regeneration cycle for the colorimetric chemosensor indicates F− enters/departs from the AC/LDH UTF giving rise to reversible change in chemical composition and surface morphology of the UTF. Therefore, this work provides new opportunities for fabrication and application of chromophore/LDH UTFs as colorimetric chemosensors.