Ni-Al layered double hydroxides electrodeposition from a chloride solution

Ni-Al LDHs was electrodeposited from a NiCl₂-AlCl₃ solution. In order to analyze the electrodeposition process, electrolytes with initial Al content range of 0–20% were used. With increasing Al content in the sample, the preferred orientations of (0 0 3) and (0 0 6), increased crystallinity, and decreased interlayer spacing were observed from the XRD results. A dissolution–recrystallization of (0 0 3) plane was detected among the Ni-Al LDHs from the strongly alkaline solution soaking results, which was found to be conducted easily in high Al-containing samples. The pH of the Al-containing electrolyte was much lower than that of pure NiCl₂ solution because lower pH was needed to start a precipitation reaction in the AlCl₃-NiCl₂ solution. The electrodeposition yield and current efficiency were found to decrease obviously in the electrolytes with initial Al content higher than 10%, which was attributed to the increasing Al content in the sample and diffusion of the complex ions. The electrodeposition pattern was in-situ in the electrolyte initially containing 10% Al, then, it developed toward and off in-situ in electrolytes initially containing 0–10% and 10–20% Al.     

Thermal evolution of V(III)-containing layered double hydroxides

A study is reported on the thermal evolution of Mg, V layered double hydroxides with interlayer carbonate anions and different Mg/V molar ratios (from 1 to 4). Decomposition in O₂ occurs at lower temperature than that in N₂; the stability of the layered structure decreases as the V content increases. Oxidation of layer V³⁺ cations occurs in the same temperature range as dehydroxylation and decarbonation. The nature of the crystalline phases formed upon calcination at high temperatures strongly depends on the Mg/V molar ratio in the initial solid.     

金属氢氧化物直接制备对苯二甲酸插层水滑石及其应用

以新制备的Mg(OH)_2和Al(OH)_3滤饼与对苯二甲酸通过水热反应制备了对苯二甲酸插层水滑石(TALDHs).使用X射线衍射(XRD)、热重-差热分析、扫描电镜(SEM)等技术对TA-LDHs与碳酸根型水滑石(CO3-LDHs)进行对比研究,结果显示,对苯二甲酸离子成功插入到LDHs层间,产物结构完整、晶相单一,所制得的TA-LDHs为片状.CO3-LDHs和TA-LDHs分别作为纳米填料,以两种不同的添加方式制备聚对苯二甲酸乙二醇酯(PET)/LDHs纳米复合材料.对复合材料进行XRD和SEM研究,结果表明在酯交换反应前添加2%TA-LDHs所制备的PET/LDHs纳米复合材料的层板被部分剥离,分散性最好.     

Homogeneous precipitation of layered Ni(II)-Cr(III) double hydroxides

An adequate account of the hydrolytic properties of Cr3+ and Ni2+ allows setting the conditions for homogeneous nucleation of layered Ni(II)-Cr(III) double hydroxides; water exchange and hydrolysis rate constants indicate that, at very high rates of base dosing, formation of heteronuclear Cr(III)-Ni(II) hydroxo species should prevail over precipitation of active Cr(OH)3. This is realized by the urea method under microwave-assisted hydrothermal conditions. This approach yields crystalline Ni1-xCrx(OH)2(CO3)x/2nH2O (x approximately 0.32-0.36) in less than 5 min at 453 K; higher degrees of crystallinity are obtained at higher temperatures and/or longer aging times. Formation of Ni(II)-Cr(III) LDHs upon microwave-assisted hydrothermal aging of freshly coprecipitated Ni(OH)2+Cr(OH)3 mixtures takes longer, due to a different operating mechanism. The implications of the advanced rationale for the design of synthesis procedures are stressed. It is proposed that homogeneous nucleation of Ni(II)-Cr(III) LDHs involves the edge-on condensation of planar heteronuclear Cr(III)-Ni(II) hydroxo trimers. Ordered aggregation of primary particles leads to the final platelet crystals, a process that involves the exchange of CO2-(3) ions dangling at the crystallites' edges by bridging OH-.     

Exfoliation of layered double hydroxides by an electrostatic repulsion in aqueous solution

Ni/Fe layered double hydroxides (Ni/Fe LDHs) with 11-aminoundecanoic acid (AUA) as pillared species (Ni/Fe LDHs-AUA with Ni/Fe = 4) was prepared by a co-precipitation method. The prepared Ni/Fe LDHs-AUA material was successfully delaminated in an aqueous system by a novel host–guest repulsive interaction process. The delaminated LDHs nanosheets were confirmed by XRD, TG-DSC, TEM, AFM, and IR analyses. XRD measurement on the slurry centrifuged from the solution showed an amorphous halo and the crystalline phase of Ni/Fe LDHs-AUA lost its sharp reflections at pH value of 2.0. After freeze-drying the slurry, the broad pattern was converted into a basal diffraction pattern, indicating the restacking of delaminated nanosheets to restore the original stacked form. AFM images showed that a large part of Ni/Fe LDHs-AUA was delaminated into one elementary layer at least, and the delaminated nanosheets had disk-like shapes with a diameter of ca. 100 nm. IR results confirmed the AUA molecules released from the interlayer accompanied with the delamination process and they could not be restacked into the interlayer during freeze-drying the delaminated nanosheets.     

水滑石衍生的复合氧化物催化氧化挥发性有机气体的研究进展（英文）

挥发性有机化合物(VOCs)是大气颗粒污染物(PM_2.5)和臭氧污染的主要前体物,来源于工业活动(如溶剂使用过程)、汽车尾气以及植物排放等,具有毒性,对人类和自然生命产生危害.催化氧化技术是在催化剂表面,在较低的操作温度(200-450℃)下,将VOCs非均相催化氧化成CO₂和H₂O,是一种最为有效的分解VOCs的方法,具有副产物少,能耗低的优点.VOCs分解用催化剂主要分为贵金属和金属氧化物两大类.贵金属催化剂活性高,但价格昂贵.因此科研工作者一直在诸多方面调控过渡金属氧化物,例如制备方法、组分协同、结构缺陷等,期望获得高活性、低成本的催化剂.水滑石(LDHs)是一种层状双金属氢氧化物,由带正电荷的金属氢氧化物层板和层间阴离子组成,可以表示为[M_1-x²⁺M_x³⁺(OH)₂](A^n-)_x/n·mH₂O.鉴于LDHs特有的结构特点,层板元素可调、比...     

Photoactive oriented films of layered double hydroxides

The treatment of nano-ordered oriented films of layered double hydroxide (LDH) with dodecyl sulfate increased the interlayer distance from 0.4 to 1.96 nm, which allowed the intercalation of 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin (TPPS). The re-stacking of separated layers and the rebuilding of crystals oriented parallel to the surface of quartz slides was confirmed by X-ray diffraction and atomic force microscopy. The hybrid films contained homogeneously distributed porphyrin molecules with preserved photophysical properties such as fluorescence, triplet state formation, and energy transfer, thus forming singlet oxygen.     

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.     

Mesoporous mixed metal oxides derived from P123-templated Mg-Al layered double hydroxides

We report the preparation of mesoporous mixed metal oxides (MMOs) through a soft template method. Different amounts of P123 were used as structure directing agent to synthesize P123-templated Mg-Al layered double hydroxides (LDHs). After calcination of as-synthesized LDHs at 500 °C, the ordered mesopores were obtained by removal of P123. The mesoporous Mg-Al MMOs fabricated by using 2 wt% P123 exhibited a high specific surface area of 108.1 m²/g, and wide distribution of pore size (2-18 nm). An investigation of the “memory effect” of the mesoporous MMOs revealed that they were successfully reconstructed to ibuprofen intercalated LDHs having different gallery heights, which indicated different intercalation capacities. Due to their mesoporosity these unique MMOs have particular potential as drug or catalyst carriers.     

Thermal decomposition of silylated layered double hydroxides

Anionic surfactant and silane modified layered double hydroxides (LDHs) were synthesized through an in situ coprecipitation method. The structure and morphology were characterized by XRD and TEM techniques, and their thermal decomposition processes were investigated using infrared emission spectroscopy (IES) combined with thermogravimetry (TG). The surfactant modified LDHs (H-DS) shows three diffractions located at 1–7° (2θ), while there is only one broad reflection for silane grafted LDHs (H–Si) in this region. The morphologies of the H-DS and H–Si show fibrous exfoliated layers and curved sheets, respectively. The IES spectra and TG curves indicate that alkyl chain combustion and dehydroxylation are overlapped with each other during heating from 373 to 723 K in H-DS and to 873 K in H–Si. Sulfate anion transformation process occurs at 473 K in H-DS and 523 K in H–Si. The derivant of sulfate can exist even above 1073 K. After further decomposition, the metal oxides and the new type of Si–O compounds are formed beginning at around 923 K in silane modified sample.     

Mechano-hydrothermal preparation of Li-Al-OH layered double hydroxides

A mechano-hydrothermal (MHT) method was used to synthesize Li-Al-OH layered double hydroxides (LDHs) from LiOH·H₂O, Al(OH)₃ and H₂O as starting materials. A two-step synthesis was conducted, that is, Al(OH)₃ was milled for 1 h, followed by hydrothermal treatment with LiOH·H₂O solution. Effects of the LiOH/Al(OH)₃ molar ratio (R_Li/Al) and hydrothermal temperature (T_ht) on the crystallinity, morphology, and composition of the product were examined. The resulting LDHs were characterized by X-ray diffraction, transmission electron microscopy, scanning electron microscopy, Fourier transform infrared, and elemental analyses. The results showed that pre-milling plays a key role in the LDH formation during subsequent hydrothermal treatment. The Li/Al molar ratio of the obtained LDHs keeps constant at 0.5, independent from theR_Li/Al (0.5–5.0) in the starting materials. An increase in the T_ht (20–80 °C) can enhance the crystallinity and morphology regularity of the products. The so-obtained Li-Al-OH LDHs exhibit high crystallinity and well-dispersity, which may have wider applications than the aggregate ones obtained using conventional mechanochemical and Li⁺-imbibition methods.     

Stabilization of Co in layered double hydroxides (LDHs) by microwave-assisted ageing

Co-containing layered double hydroxides at different pH have been prepared, and aged following different routes. The solids prepared have been characterized by element chemical analysis, powder X-ray diffraction, thermogravimetric and differential thermal analyses (both in nitrogen and in oxygen), FT-IR and Vis-UV spectroscopies, temperature-programmed reduction and surface area assessment by nitrogen adsorption at −196 °C. The best conditions found to preserve the cobalt species in the divalent oxidation state are preparing the samples at controlled pH, and then submit them to ageing under microwave irradiation.     

Synthesis and characterization of new Mg(2)Al-paratungstate layered double hydroxides

Layered double hydroxides (LDHs, or hydrotalcites) with Mg(2+) and Al(3+) cations in the mixed metal hydroxide layer and paratungstate anions in the interlayer have been prepared. Different methods have been followed: anion exchange with Mg,Al LDHs originally containing nitrate or adipate, reconstruction of the LDH structure from a mildly calcined Mg(2)Al-CO(3) LDH, and coprecipitation. In all cases, the tungsten precursor salt was (NH(4))(10)H(2)W(12)O(42). The prepared solids have been characterized by elemental chemical analysis, powder X-ray diffraction (PXRD), FT-IR spectroscopy, thermogravimetric (TG) and differential thermal (DTA) analyses, scanning electron microscopy (SEM) with EDX (energy-dispersive X-ray analysis), and nitrogen adsorption at -196 degrees C for surface area and surface texture. Most of the synthesis methods used, especially anion exchange starting from a Mg(2)Al-NO(3) precursor at low temperature and short reaction times, lead to formation of a hydrotalcite with a gallery height of 9.8 A; increasing the reaction temperature to 70-100 degrees C and maintaining short contact times leads to a solid with a gallery height of 7.8 A. Both phases have been identified as a result of the intercalation of W(7)O(24)(6)(-) species in different orientations in the interlayer space. If the time of synthesis or the temperature is increased, a more stable phase, with a gallery height of 5.2 A corresponding to a solid with intercalated W(7)O(24)(6)(-), is formed, probably with grafting of the interlayer anion on the brucite-like layers. All systems are microporous. Calcination at 300 degrees C leads to amorphous species, and crystallized MgWO(4) is observed at 700 degrees C.     

Cyclodextrin-intercalated layered double hydroxides for fragrance release

In order to attain the controlled release of fragrance, the intercalation of cyclodextrins (CDs) and fragrance in layered double hydroxides (LDHs) was examined. Carboxymethyl-β-CDs (CMCDs) of various degrees of substitution as well as Mg–Al support were synthesized. CMCDs were intercalated into LDH by the reconstruction method. Powder X-ray diffraction, thermal gravimetric analyses and Fourier transform infrared indicated a successful intercalation of CMCDs into the LDH gallery. The retention capacities of the hybrid materials were investigated in aqueous phase and in gaseous solution by static headspace gas chromatography and multiple headspace extraction. The functionalization of the LDH with CMCD allowed the encapsulation of various organic guests and could prolong the fragrance release time in comparison to that from LDH without CMCD, which can be attributed to the inclusion of the fragrance compound in the CMCD cavity.     

甲氨蝶呤/锌铝层状双氢氧化物的合成以及生物效应研究

在乙醇-水混合体系中,采用改进的共沉淀法将甲氨蝶呤(MTX)插层组装到锌铝类水滑石(LDHs)层间形成了MTX/Zn-Al-LDHs纳米复合物,考察了不同Zn2+/Al3+/MTX摩尔比(R值)对合成MTX/LDHs复合物性质的影响.利用X-射线衍射(XRD)、傅里叶变换红外(FT-IR)、透射电子显微镜(TEM)、扫描电子显微镜(SEM)、原子力显微镜(AFM)和紫外-可见光谱(UV-Vis)等表征了复合物的结构和形貌.结果表明,粒子的尺寸随MTX加入量的增大而减小;粒子沿a-b轴方向的生长速率比沿c轴方向的生长速率快.在磷酸缓冲液中考察了插层药物的控释性能并进行了动力学拟合,结果表明,采用modified Freundlich模型和parabolic diffusion模型分段拟合可较好地描述样品的释药过程.最后,采用MTT法探究了插层药物对肺癌细胞A549增殖的抑制作用,研究表明,复合物粒径越小,MTX/LDHs对癌细胞增殖的抑制作用越大.     

Hydrophobic layered double hydroxides (LDHs): Selective adsorbents for liquid mixtures

 The external and internal surface area of the calcium aluminum double hydroxide [Ca₂Al(OH)₆] NO₃ ⋅ 2H₂O were hydrophobized by the anionic surfactants sodium dodecylsulfate and sodium dodecyl-benzene sulfonate. The adsorption behavior towards liquid mixtures (benzene/n-heptane and n-propanol/ toluene) was studied by determining the surface excess adsorption isotherms, the heats of immersion in these liquids, and the basal spacing, i.e. the expansion of the interlayer space. Both hydrophobic layered double hydroxides (LDHs) adsorbed n-hep-tane, benzene, toluene, and n-pro-panol between the layers with considerable increase of the basal spacing. Interlamellar swelling of the hydrophobizised LDHs in n-heptane was fundamentally different to the behavior of hydrophobized 2 : 1 clay minerals (smectites, vermiculites). The surface excess isotherms for benzene/ heptane mixtures were U-shaped and indicate preferential adsorption of benzene. Dodecylbenzene sulfonate double hydroxide preferentially adsorbed propanol from n-propanol/ toluene mixtures but the dodecyl-sulfate derivative adsorbed both compounds. Received: 23 January 1997 Accepted: 10 February 1997     

Thermal, solution and reductive decomposition of Cu-Al layered double hydroxides into oxide products

Cu-Al layered double hydroxides (LDHs) with [Cu]/[Al] ratio 2 adopt a structure with monoclinic symmetry while that with the ratio 0.25 adopt a structure with orthorhombic symmetry. The poor thermodynamic stability of the Cu-Al LDHs is due in part to the low enthalpies of formation of Cu(OH)₂ and CuCO₃ and in part to the higher solubility of the LDH. Consequently, the Cu-Al LDH can be decomposed thermally (150 °C), hydrothermally (150 °C) and reductively (ascorbic acid, ambient temperature) to yield a variety of oxide products. Thermal decomposition at low (400 °C) temperature yields an X-ray amorphous residue, which reconstructs back to the LDH on soaking in water or standing in the ambient. Solution decomposition under hydrothermal conditions yields tenorite at 150 °C itself. Reductive decomposition yields a composite of Cu₂O and Al(OH)₃, which on alkali-leaching of the latter, leads to the formation of fine particles of Cu₂O (<1 μm).     

Incorporation of phosphorus oxyacids into layered double hydroxides

Four phosphonate anions (methyl-, ethyl-, phenyl- and benzylphosphonate) were successfully incorporated into [Cu₂Cr(OH)₆]Cl·yH₂O. It was found that two phases exist for the phenylphosphonate intercalate; one in which the anions are arranged perpendicular to the layers, and one with a tilted orientation. Systematic variation of the reaction conditions allowed the former to be isolated with phase purity, but not the latter. The solid-state ³¹P NMR data suggest that proton transfer may occur between host and guest. Some neutral guest is incorporated in the case of phenylphosphonate and benzylphosphonate, presumably owing to relatively poor solvation of these guests. Heat treatments only resulted in the formation of a covalent bond between host and guest in the case of the methylphosphonate intercalate. The intercalation of the related and redox-active phenylphosphinate into a range of LDHs is also reported. Time-resolved in situ diffraction techniques were used to both monitor and quantify the intercalation of phenylphosphonate into [Cu₂Cr(OH)₆]Cl·yH₂O and phenylphosphinate into the hexagonal form of [LiAl₂(OH)₆]Cl·yH₂O. Kinetic and mechanistic parameters have been determined from the diffraction data.     

Single-step synthesis of layered double hydroxides ultrathin nanosheets

A novel single-step approach was developed to prepare large-scale MgAl-LDHs ultrathin nanosheets. The key point of the successful realization was that we employed a high concentration of H(2)O(2). Oxygen molecules, derived from in situ decomposition of H(2)O(2), were speculated to be the decisive factor leading to complete separation of LDHs layers. The ultrathin nanosheets were characterized by XRD, TEM, AFM, FT-IR, and TG-DSC. The results indicated that the thickness of these nanosheets was about 1.44 nm, which was almost in perfect agreement with the theoretical thickness of two LDHs layers. From the TG-DSC curves, the weight loss of these exfoliated MgAl-LDHs ultrathin nanosheets at 500°C was 18.5%, which was much smaller compared to the 32.3% weight loss of unexfoliated MgAl-LDHs.     

类水滑石催化合成聚(碳酸1,4-丁二醇)酯二醇

采用共沉淀法制备了镁铝类水滑石(Mg-Al-CO3LDH)、镁锌铝类水滑石(Mg-Zn-Al-CO3LDH)和锌铝类水滑石(Zn-Al-CO3LDH),并研究了它们在碳酸二苯酯(DPC)与1,4-丁二醇(1,4-BD)酯交换合成聚碳酸酯二醇(PCDL)反应中的催化活性。在常压反应阶段,以苯酚的产率表征催化剂的活性;在减压缩聚阶段,以产品的数均分子量Mn和羟基值来表征催化剂的活性。结果发现,Zn-Al LDH具有良好的催化活性。在优化反应条件下,获得了Mn和羟基值分别为1600和70.8mg KOH/g的PCDL。