Water-swellable MgAl-LDH (layered double hydroxide) hybrids: synthesis, characterization, and film preparation

LDH hybrids were synthesized from Cl (-)MgAl-LDHs by anion exchange with short-chain alkyl carboxylate intercalants: C n H 2 n+1 COO (-) ( n = 0-3). Among them, LDH3 (LDH with Mg/Al = 3) hybrids containing acetate ( n = 1) and propionate ( n = 2) exhibited swelling behavior in water. The action of water on acetate-LDH3 (AcO-LDH3) and propionate-LDH3 (PrO-LDH3) led to semitransparent suspensions via a viscous gel state. From the X-ray diffraction profiles of the gels, only a broad feature was observed by the loss of the sharp reflections. The reflections reappeared for the films obtained by drying the gel, indicating the restacking of the LDH nanosheets into the original stacked structure. Observation using atomic force microscopy revealed delaminated nanosheets with a thickness of 1.1-1.5 nm with the same morphological features as the starting LDHs. XRD measurement and AFM observation supported the formation of unilamellar LDH sheets. Semitransparent self-standing LDH films were obtained by peeling off the films formed on a PE (polyethylene) substrate by drying the colloidal suspension thereon. The thickness of the obtained flexible films ranged from 10 to 25 microm, and they could be anion exchanged with inorganic and organic anions in the film state.     

Ordered Ultrathin Films of Perylene Anions and Layered Double Hydroxide Using Exfoliation‐coassembly Method

Recently, the fabrication of ordered luminescent ultrathin film (UTF) materials based on layered double hydroxides (LDHs) has received much attention. However, how to obtain these UTFs assembled by small anions and LDHs nanosheets is still a challenge. Herein, perylene 3,4,9,10‐tetracarboxylate (PTCB) was firstly chosen as the anion with the aim to obtain PTCB/LDH UTFs, which cannot be formed based on typical layer‐by‐layer (LBL) method. Then, the polymer anions (such as poly 4‐styrene sulfonate (PSS) and poly vinyl sulfonate (PVS)) were further chosen as the co‐assembled units with PTCB, which can act as carriers to assemble with LDH nanosheets. The as‐obtained PTCB@PSS/LDH and PTCB@PVS/LDH UTFs present long range ordered structures confirmed by powder X‐ray diffraction (XRD), scanning electron microscopy (SEM) and atomic force microscopy (AFM). Moreover, these two UTF systems show polarized luminescence with the emissive anisotropy of ca. 0.62 and 0.73. Therefore, this work presents an exfoliation‐coassembly way to develop LDH‐based ordered luminescent films, which may benefit their future optical display applications.     

General synthesis and delamination of highly crystalline transition-metal-bearing layered double hydroxides

In this paper, we describe a general process for the synthesis and delamination of a family of highly crystalline Al-based and transition-metal-bearing layered double hydroxides (LDHs). Large-sized and monodispersed hexagonal platelike particles of binary-component M(II)-Al-CO3 and ternary-component M(II)-M'(II)-Al-CO3 LDHs (M(II) and M'(II) = Fe, Co, Ni, or Zn) were prepared at first by the urea method under optimized conditions. These CO32--LDHs were converted into other monovalent-anion-containing LDHs by means of a salt-acid treatment and subsequent anion-exchange processes. Finally, well-defined LDH nanosheets were obtained by delamination of NO3--LDHs in formamide.     

(羟基喜树碱@胆酸钠)-层状双金属氢氧化物纳米杂化物的组装及表征

采用“药物修饰-共组装”法制备了(羟基喜树碱@胆酸钠)-层状双金属氢氧化物纳米杂化物. 先用胆酸钠(SCL)包裹羟基喜树碱(HCPT)形成胶束, 再与微反应器制备的层状双氢氧化物(LDH)纳米片共组装形成纳米杂化物, 其载药量可达12.9%, 杂化物中HCPT以高生物活性的内酯形式存在. 采用聚乙二醇(PEG)和羧甲基纤维素(CMC)分别对所制备的(HCPT@SCL)-LDH纳米杂化物进行了表面修饰, 结果表明, 纳米杂化物的分散性得到明显改善; PEG的修饰效果优于CMC, 所获得的PEG-(HCPT@SCL)-LDH杂化物的平均粒径可小至约70 nm, 具有良好的分散性和药物缓释效果. 其药物释放过程可用准二级动力学方程描述, 颗粒内部扩散是药物释放过程的控制步骤.     

Conservation of order, disorder, and "crystallinity" during anion-exchange reactions among layered double hydroxides (LDHs) of Zn with Al

Carbonate and chloride ions mediate an ordered stacking of metal hydroxide slabs to yield ordered layered double hydroxides (LDHs) of Zn with Al, by virtue of their ability to occupy crystallographically well-defined interlayer sites. Other anions such as ClO(4)- (T(d)), BrO(3)- (C(3v)), and NO(3)- (coordination symmetry C(2v)) whose symmetry does not match the symmetry of the interlayer sites (D(3h) or O(h)) introduce a significant number of stacking faults, leading to turbostratic disorder. SO(4)(2-) ions (coordination symmetry C(3v)) alter the long-range stacking of the metal hydroxide slabs to nucleate a different polytype. The degree of disorder is also affected by the method of synthesis. Anion-exchange reactions yield a solid with a greater degree of order if the incoming ion is a CO3(2-) or Cl-. Incoming NO(3)- ions yield an interstratified phase, whereas incoming SO(4)(2-) ions generate turbostratic disorder. Conservation or its converse, elimination, of stacking disorders during anion exchange is the net result of several competing factors such as (i) the orientation of the hydroxyl groups in the interlayer region, (ii) the symmetry of the interlayer sites, (iii) the symmetry of the incoming ion, and (iv) the configuration of the anion. These short-range interactions ultimately affect the long-range stacking order or "crystallinity" of the LDH.     

Ion-exchange properties of colloidal particle consisting of polyaniline and poly(vinyl alcohol) fixed on silica-gel powder.

A colloidal powder was prepared by fixing polyaniline (PANI, conducting polymer), poly(vinyl alcohol) (PVA, surfactant stabilizer) and a suitable dopant anion to silica-gel powder. This hydrophilic composite colloidal particle incorporates anions with the protonation of PANI in an acidic solution. The anion can be exchanged with other anions when the colloid is immersed in an acidic solution. Thus, the PANI colloid works as an ion exchanger. The ion-exchange properties on the composite colloidal powder were investigated. Anions were successfully and easily exchanged in the order Br- < Cl- < NO3- < ClO4- < SCN-. This ion-exchange selectivity corresponds largely to the ion-exchange equilibrium constants, which are based on a hydrophobic interaction between the anion and colloid. However, this ion-exchange selectivity does not agree simply with the lipophilic order, but is instead explainable by a gap in the effective ion-exchange capacity due to a size effect between the micropore on the colloidal particle formed by the dopant anion in polymerization and anion sizes in the hydrophobic environment.     

Ordered blue luminescent ultrathin films by the effective coassembly of tris(8-hydroxyquinolate-5-sulfonate)aluminum and polyanions with layered double hydroxides

This article reports a novel method to assemble a small anion with exfoliated Mg-Al-layered double hydroxide (LDH) nanosheets into ordered ultrathin films (UTFs) by employing the layer-by-layer assembly technique. The premixing solution of tris(8-hydroxyquinolate-5-sulfonate)aluminum(III) (AQS(3-)) with three kinds of polyanions-poly(acrylic acid), ((C(3)H(4)O(2))(n), PAA), poly(styrene 4-sulfonate) ([CH(2)CH(C(6)H(4))SO(3)](m), PSS), and poly[5-methoxy-2-(3-sulfopropoxy)-1,4-phenylene vinylene] (C(12)H(13)O(5)S)(n), PPV)-has been used as building blocks to assemble alternatively with LDH nanosheets. The UV-vis absorption and fluorescence spectroscopy of (AQS-polyanion/LDH)(n) UTFs presents stepwise growth upon increasing deposited cycles in comparison with the (AQS/LDH)(n) film under the same experimental process. (AQS-PPV/LDH)(n) UTF displays complex fluorescence originating from AQS and PPV. The (AQS/LDH)(n) and (AQS-polyanion/LDH)(n) UTFs exhibit higher blue-polarized photoemission character with a luminescence anisotropy (r) of ca. 0.12-0.20 and a longer fluorescence lifetime than that of the Na(3)AQS film with r = 0.04. X-ray diffraction, scanning electron microscopy, and atomic force microscopy demonstrated that the UTFs were orderly periodically layered structures with a thickness of ca. 3.0 nm per bilayer. Therefore, this work gives a feasible method for immobilizing small anions into the gallery of LDHs.     

The effect of Zn, Al layered double hydroxide on thermal decomposition of poly(vinyl chloride)

Poly(vinyl chloride)/layered double hydroxide (LDH) composite was prepared by mixing 4 wt% Zn₂Al-CO₃-LDH with PVC and fluxing at 180 °C. The thermal decomposition behaviour of the LDH + PVC composite in air and nitrogen environments was systematically investigated. We found that mixing Zn₂Al-CO₃-LDH into PVC facilitates dehydrochlorination from ca. 300 to 270 °C but reduces the reaction extent to leave more chlorine on the polyene backbones both in air and N₂. We have also found that at 400-550 °C, both in air and N₂, LDH assists the formation of char-like materials and decreases the release of volatile hydrocarbons. From 550 to 800 °C, the char-like materials are mostly retained in N₂ while they are almost completely thermo-oxidized (burned) in air. Thus, addition of Zn₂Al-CO₃-LDH to PVC does not increase the thermal stability, but does promote charring to retard the generation of flame. The influence of LDH on PVC thermal properties has been also addressed mechanically.     

单一阴离子交换柱同时分离有机酸和无机阴阳离子

研究了用乙二胺四乙酸（ＥＤＴＡ）作淋洗液时，性质迥异的有机酸、无机阴离子和碱土金属离子（Ｃａ＾２＋、Ｍｇ＾２＋）在同一阴离子交换柱上的同时分离以及保留机理，结果表明，在离子交换机理之外，非离子交换机理对有机酸及钙镁的ＥＤＴＡ络阴郭的保留行为起一定的辅助作用，９种有机酸和无机阴阳离子在１０ｍｉｎ内得到了较好的分离。各离子的电导检测灵敏度在１０＾－９至１０＾－１１ｍｏｌ，能满足环境和食吕分析的要求。     

Intercalation of Norfloxacin into Layered Double Hydroxides by Delamination/Restacking Process and its Controlled-Release Property

Norfloxacin (NFX)-layered double hydroxide (LDH) intercalated nanocomposite was synthesized by delamination/restacking process. In this method, LDH particles were first delaminated to well-dispersed two-dimensional nanosheets in formamide, and then the LDH nanosheets and NFX anions co-assembled into NFX-LDH nanocomposite. Characterization by powder x-ray diffraction, Fourier transform infrared spectroscopy, elemental analysis, and thermogravimetry revealed that the product had an expanded LDH structure. This finding indicated that NFX was successfully intercalated into LDH layers, and NFX had both horizontal and vertical orientation in the interlayers of NFX-LDH nanocomposite. Additionally, the delamination/restacking method displayed various remarkable advantages such as simple procedure, short reaction time, and mild conditions compared with the conventional methods of ion exchange, co-precipitation, and reconstruction. Results further showed that the thermal stability of NFX greatly improved after intercalation into LDH layers and that NFX release of the NFX-LDH nanocomposite was gradual, suggesting potential use as an effective drug delivery system.     

不纯流动相对离子法分析无机阴离子的影响(英文)

 采用离子模拟研究了流动相不纯对样品中无机阴离子测定造成的干扰。结果表明 ,在流动相中加入Cl-,使得其他 6种阴离子响应值增加。这主要是由于Cl-加入的同时也带来了相应的阳离子 ,在通过抑制器时可带来等量的H+ ,H+ 伴随着各个阴离子样品一起通过检测器 ,使总的样品离子响应值增加。在 6种阴离子中 ,F-和NO-2 对AS14柱的亲和力和Cl-相近 ,其响应值随Cl-加入量的变化趋势相似 ;Br-,NO-3 ,PO3 -4及SO2 -4因其对柱的亲和力大于Cl-,它们的响应值随Cl-加入量的变化趋势也相同。     

Layer-by-layer assembly and spontaneous flocculation of oppositely charged oxide and hydroxide nanosheets into inorganic sandwich layered materials

Exfoliated oxide nanosheets such as Ti0.91O2 and Ca2Nb3O10 and layered double hydroxide (LDH) nanosheets of Mg2/3Al1/3(OH)2 were restacked into inorganic sandwich layered materials. Sequential adsorption of these oppositely charged nanosheets from their colloidal suspensions yielded multilayer ultrathin films while their simple mixing produced lamellar flocculates. Eliminating carbonate ions from the reaction system was found to be essential for successfully achieving the sandwich structures. The flocculated materials as well as the films were characterized by atomic force microscopy (AFM), UV-visible absorption spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction (XRD), transmission electron microscopy (TEM), and chemical analysis, which all supported the formation of the ordered sandwich structures. AFM observations revealed alternate dense tiling of LDH nanosheets and oxide nanosheets onto a substrate surface. UV-visible absorption spectra exhibited progressive enhancement of optical density due to oxide nanosheets as a function of deposition cycles, providing strong evidence for regular growth of multilayer films. The combinations of Mg2/3Al1/3(OH)2/Ti0.91O2 and Mg2/3Al1/3(OH)2/Ca2Nb3O10 produced XRD Bragg peaks having multilayer spacings of 1.2 and 2.0 nm, respectively. These basal spacing values are compatible with the sum of thickness of LDH nanosheets and corresponding oxide nanosheets. TEM images of flocculated samples displayed lamellar features with two different constituent layers appearing alternately.     

杯[4]吡咯与含氧阴离子及其离子对弱相互作用的理论研究

在M06-2X/6-31+G(d,p)计算水平上,对杯[4]吡咯(CP)与3种不同构型的含氧阴离子OH-(C(v)、NO3-(D3h)、ClO4-(Td)形成的组装体系进行了理论研究。比较了各体系的构型、结合能、自然键轨道(NBO),利用多功能波函数软件Multiwfn对相互作用力等进行可视化分析。结果发现,无论主-客体的组装计量比是1∶1还是2∶1,阴离子的构型直接影响组装体系的构型。阴离子空间构型越大、整体电负性越强,越倾向于2∶1复合体系。考虑到杯[4]吡咯是典型的离子对受体,本文还研究了主体与NH4+-阴离子的离子对体系的相互作用。在离子对的组装过程中,由于阴、阳离子间的作用占据了主导,从而减弱了阴离子与主体间氢键作用,无论阴离子构型如何,主体与离子对的组装都倾向于1∶1的作用体系。本文结果对深入理解杯吡咯类受体的离子识别作用本质,拓展该类超分子主体的应用范围具有重要的理论意义。     

Phosphate adsorption on synthetic goethite and akaganeite

Low crystalline iron hydroxides such as goethite (alpha-FeOOH) and akaganeite (beta-FeOOH) were synthesized, and the selective adsorption of phosphate ions from phosphate-enriched seawater was examined. The results of the distribution coefficients (K(d)) of oxoanions in mixed anion solutions at pH 8 follow the selectivity order Cl-, NO3-, SO4(2-) < CO3(2-), HPO4(2-) for goethite, and Cl-, CO3(2-) < NO3- < SO4(2) < HPO4(2-) for akaganeite. In seawater, both adsorbents show high selectivity for phosphate ions despite the presence of large amounts of major cations and anions in seawater. The adsorption isotherms fitted better with the Freundlich equation and the maximum uptake of phosphate from phosphate-enriched seawater was 10 mg P/g at an equilibrium phosphate concentration of 0.3 mg P/L on both adsorbents. The phosphate adsorption/desorption cycles show that akaganeite is an excellent adsorbent even after 10 cycles and its chemical stability is good.     

Compositional and structural control on anion sorption capability of layered double hydroxides (LDHs)

Layered double hydroxides (LDHs) have shown great promise as anion getters. In this paper, we demonstrate that the sorption capability of a LDH for a specific oxyanion can be greatly increased by appropriately manipulating material composition and structure. We have synthesized a large set of LDH materials with various combinations of metal cations, interlayer anions, and molar ratios of divalent cation M(II) to trivalent cation M(III). The synthesized materials have then been tested systematically for their sorption capabilities for pertechnetate (TcO(-)(4)). It is discovered that for a given interlayer anion (either CO(2-)(3) or NO(-)(3)) the Ni-Al LDH with a Ni/Al ratio of 3:1 exhibits the highest sorption capability among all the materials tested. The sorption of TcO(-)(4) on M(II)-M(III)-CO(3) LDHs may be dominated by the edge sites of LDH layers and correlated with the basal spacing d(003) of the materials, which increases with the decreasing radii of both divalent and trivalent cations. The sorption reaches its maximum when the layer spacing is just large enough for a pertechnetate anion to fit into a cage space among three adjacent octahedra of metal hydroxides at the edge. Furthermore, the sorption is found to increase with the crystallinity of the materials. For a given combination of metal cations and an interlayer anion, the best crystalline LDH material is obtained generally with a M(II)/M(III) ratio of 3:1. Synthesis with readily exchangeable nitrate as an interlayer anion greatly increases the sorption capability of a LDH material for pertechnetate. The work reported here will help to establish a general structure-property relationship for the related layered materials.     

Synthesis, characterization and metal adsorption properties of the new ion exchanger polymer 3-n-propyl(4-methylpyridinium) silsesquioxane chloride

The preparation and anion exchange properties of 3-n-propyl(4-methylpyridinium) silsesquioxane chloride polymer are described. This new polymer was prepared by the sol-gel processing method and is designated as SiPic+Cl-. It is insoluble in water and showed an anion exchange capacity of 1.46x10(-3) mol g-1. The adsorption isotherms of ZnCl2, CdCl2 and HgCl2 were determined from aqueous solutions and the adsorption equilibria simulations fit the model of fixed bidentate centers with the absence of lateral interactions and energetic heterogeneity between them. The metal ions diffuse into the solid solution interface and are dominantly present as MCl2-(4) species for Zn(II), MCl(2-)4 and MCl-3 species for Cd(II) and MCl-3 species for Hg(II).     

Energies and selectivities for anion binding as a function of host conformational preorganisation

The anion binding of tripodal hosts 2-4 has been studied. Increasing levels of conformational preorganisation of the side arms of the hosts led to increased (Cl-) unaltered (Br-) or decreased (NO3-) binding; it was thus possible to change guest selectivities by about an order of magnitude through conformational preorganisation of the flexible host.     

Preparation of 5-benzotriazolyl-4-hydroxy-3-sec-butylbenzenesulfonate anion-intercalated layered double hydroxide and its photostabilizing effect on polypropylene

An organic UV absorber has been intercalated into a layered double hydroxide (LDH) host by ion-exchange method using ZnAl-NO₃-LDH as a precursor with an aqueous solution of the sodium salt of 5-benzotriazolyl-4-hydroxy-3-sec-butylbenzenesulfonic acid (BZO). After intercalation of the UV absorber, the interlayer distance in the LDHs increases from 0.89 to 2.32 nm. Infrared spectra and thermogravimetry and differential thermal analysis (TG-DTA) curves reveal the presence of a complex system of supramolecular host-guest interactions. The thermostability of BZO is markedly enhanced by intercalation in the LDH host. ZnAl-BZO-LDHs/polypropylene composite materials exhibit excellent UV photostability.     

Photoelectrochemical properties of alternating multilayer films composed of titania nanosheets and Zn porphyrin

Alternating multilayer films composed of titania nanosheets and Zn porphyrins were prepared by use of a previously reported Langmuir-Blodgett film-transfer method in order to fabricate photoelectrochemical devices. Closely packed titania nanosheet monolayers on indium tin oxide (ITO), mica, and quartz surfaces strongly adsorbed cationic [5,10,15,20-tetrakis(1-methylpyridinium-4-yl)porphyrinatozinc]4+ (ZnTMPyP4+) by electrostatic interactions. The alternating deposition process afforded nanometer-scale multilayer films with the following structure: solid surface/(titania nanosheet/ZnTMPyP4+)n (n is the number of layers). The multilayer films were characterized by various physical measurements, including AFM, XRD, and UV-visible spectra. The visible-light irradiation of this multilayer film on an ITO electrode in the presence of triethanolamine as an electron donor yielded an anodic photocurrent. The action spectrum was consistent with the absorption spectrum of ZnTMPyP4+, which indicates that the photoexcitation of ZnTMPyP4+ is responsible for the photocurrent generation. However, the photocurrent density decreased with an increasing number of layers, which indicates that the harvesting of photoexcited electrons vertically through the titania nanosheets in the ITO/(titania nanosheet/ZnTMPyP4+)n structure was not efficient. To overcome this problem, the use of a lateral interlayer connection to all of the titania nanosheets with Ag paste was examined. As a result, a dramatic improvement in the photocurrent density was obtained. Thus, for efficient photocurrent generation with the titania nanosheet-ZnTMPyP4+ composite material, the lateral connection to all of the titania nanosheet layers is effective.     

Interaction between biphenols and anions: selective receptor for dihydrogenphosphate

Biphenol was shown to bind dihydrogenphosphate (H2PO4-) selectively over various other anions (MeCO2-, Cl-, Br-, I-, NO3-, HSO4-). The highly selectivity of biphenol toward dihydrogenphosphate is explained in terms of the basicity and shape of the guest anion.