Water Molecules in Hydrotalcite‐like Layered Double Hydroxides: Interplay between the Hydration of the Anions and the Metal Hydroxide Layer

Layered double hydroxides comprise positively charged metal hydroxide layers and intercalated anions. These materials are obtained from aqueous medium both in nature and in the laboratory. Consequently the layered double hydroxides include a considerable amount of water. The presented study was designed to determine the proportion of water associated with the hydration sphere of the anion as opposed to that of the metal hydroxide slab. Among the two differently bound water species observed in all layered double hydroxides, the weakly bound water is associated with the metal hydroxide layer and is lost at 100 °C, whereas the strongly bound water is in the hydration sphere of the anion and is lost at higher temperatures (100 °C ≤ T ≤ 250 °C). This is in contrast to the better known cationic clays, wherein all the intercalated water is generally found to be in the hydration sphere of the cations. Further the water molecules in layered double hydroxides also bond to each other, leading to the incorporation of water in excess of what is predicted by the Miyata formula (Miyata, 1975) based on crystal chemical considerations. The excess water is one of the reasons for the poor crystallinity of layered hydroxides.     

Amine‐Assisted Syntheses of Carbonate‐Free and Highly Crystalline Nitrate‐Containing Zn‐Al Layered Double Hydroxides

Zn‐Al layered double hydroxides (LDHs), with nitrate as the charge balancing anion in the interlayer space, were synthesized by precipitation from homogeneous solution containing different amines [e.g., hexamethylenetetraamine (HMTA), diethylenediamine (DEDA), trimethylamine (TMA) and dimethylamine (DMA)]. The applied method does not require nitrogen atmosphere. The solution pH and concentration of different amines were varied in order to identify the controlling parameters and whether nitrate or carbonate are the interlayer anion. Particularly, the addition of amines turns out to be an effective tool for the synthesis of nitrate containing Zn‐Al LDHs independent from the nitrogen atmosphere. The structure, textural, composition, and morphological properties were investigated using the powder X‐ray diffraction (PXRD), thermogravimetric analysis (TGA), FT‐IR spectroscopy, and scanning electron microscopy (SEM). The analyses showed that the samples had high crystallinity and purity. The NO₃‐ZnAl LDHs samples show that LDH sheets are predominantly smooth textured and the thickness of LDH sheets are found to be around 23 nm. The results also indicate that this method successfully produces a NO₃^– form Zn‐Al LDH that is almost identical to the one synthesized by conventional methods.     

Synthesis of Nordstrandite and Nordstrandite-Derived Layered Double Hydroxides of Li and Al: A Comparative Study with the Bayerite Counterpart

The layered double hydroxides (LDHs) of Li and Al can be synthesized from the four polymorphs of Al(OH)₃, namely gibbsite, bayerite, nordstrandite, and doyleite. The crystal structure of this class of compounds depends on the type of the precursor used due to their topotactic reaction mechanism. While the LDHs derived from gibbsite and bayerite yield different crystal structures, the incorporation of Li into nordstrandite was expected to yield new LDH structures different from those derived from gibbsite and bayerite. The structure of nordstrandite derived LDHs were however identical to that derived from the bayerite counterpart. The absence of symmetry in the interlayer of nordstrandite (C₁) makes it unsuitable to accommodate the intercalating anions with different molecular symmetries. To make the interlayer gallery suitable for the anions, the metal hydroxide layers of the nordstrandite translate, transforming nordstrandite to bayerite. The bayerite with site symmetries O_h and C₂ stabilizes the anions in the interlayer by hydrogen bonding. The transformation of nordstrandite to bayerite, when soaked in lithium salt solution is, therefore, a manifestation of the intercalating anions.     

Layered Double Hydroxides with Hydrotalcite—type Structure Containing Fe^3＋,Al^3＋ and Mg^2＋

IntroductionLayered double hydroxides( LDHs) with hy-drotalcite ( HT ) - type structure are composed oftrivalent and divalent metal ions and have the gen-eral formula[1] ,[M2 + 1-x M3 + x ( OH) 2 ]x+ An-x/ n· m H2 O,where M3 + is a trivalentmental ion,such as Al3 + ,Fe3 + ,La3 + ,Ni3 + ,Mn3 + etc.,M2 + is a divalentmetal ion,such as Mg2 + ,Zn2 + ,Ca2 + ,Cu2 + ,Co2 +etc.,An-is a charge compensating anion,such asOH-,Cl-,NO-3 ,CO2 -3 etc.,m is the number ofthe moles of co- intercalat…     

Intercalation of Sulfanilic Acid‐Phenol‐Formaldehyde Polycondensate into Hydrocalumite Type Layered Double ­Hydroxide

Polycondensates containing sulfonate groups, referred to as concrete superplasticizers, are widely used in the construction industry. A sulfanilic acid–phenol–formaldehyde polycondensate (SPF) with M_w ≈ 100.000 g · mol^–1 was synthesized from sulfanilic acid, phenol and formaldehyde by polycondensation reaction, and its intercalation into hydrocalumite type Layered Double Hydroxide (LDH) was investigated. Preparation was done by rehydration of tricalcium aluminate, a cement constituent, in the presence of the polymer. According to the XRD pattern, SPF was successfully intercalated. A d value of approx. 2.6 nm was found. Elemental composition of the new organo‐mineral phase reveals charge balancing of the cationic LDH main layers by the polycondensate. Thermogravimetry indicates that thermal degradation of intercalated SPF occurs at higher temperature, compared to non‐intercalated SPF. According to SEM imaging, the novel Ca‐Al‐LDH phase exhibits the morphology of intergrown platelets. Ultra‐thin nanosheets (foils) with approx. 50 nm thickness were obtained. The layered structure and d value obtained from diffraction analysis were confirmed by TEM imaging. The new hydride can be used as cement and concrete additive.     

Hydrothermal Synthesis of Nanorods and Nanowires of Mg/Al Layered Double Hydroxides

Layered double hydroxides (LDHs) are a class of synthetic anion clays, characterized by the formula[MⅡ1-xMⅢx (OH)2]x (An- )x/n·yH2O (where M =metal and A = anion, usually carbonate)[1-3]. A large number of LDHs with a wide variety of M Ⅱ-M Ⅲ cation pairs including M Ⅰ-M Ⅲ ( e. g. , Li-Al ) and M Ⅱ-MⅣ( e. g. , Co-Ti) have been reported. Thus the identities of the cations(MⅠ , MⅡ , MⅢ and MⅣ) and the interlayer anion (An-) together with the value of the stoichiometric coefficient (x) may vary widely, giving rise to a large class of isostructural materials.     

Synthesis and Characterization of Layered Double Hydroxides Containing Optically Active Transition Metal Ion

The acetate intercalated layered double hydroxides of Zn and Mn, have been synthesized by chimie douce method. The materials were characterized by XRD, TGA, CHN, IR, XPS, SEM-EDX and UV-visible spectroscopy. The photoluminescence properties was also studied. The optical properties of layered hydroxides are active transition metal ion dependent, particularly d¹⁻¹⁰ system plays an important role. Simultaneously the role of host – guest orientation has been considered the basis of photoluminescence. Acetate ion can be exchanged with iodide and sulphate ions. The decomposed product resulted the pure phase Mn doped zinc oxide are also reported.     

Synthesis and Characterization of α‐Titanium Phosphate/Propylamine Intercalation Compounds Containing Transition‐Metal Ions

Polycrystalline intercalated TiM_xH_2−nx(PO₄)₂· yC₃H₇NH₂·wH₂O compounds with transition metal (TM) ions (Mⁿ⁺ = Co²⁺, Ni²⁺, Fe³⁺ or Cr³⁺) have been prepared by means of an indirect route and characterised using X-ray diffraction, scanning electron microscopy, chemical and thermal analysis, X-ray absorption and magnetic measurements. These novel pillared layered materials, which were obtained from the monoclinic (P2₁/c space group) α-Ti(HPO₄)₂·H₂O phase, lose its crystallinity after intercalation. However all the TM ions are octahedrally surrounded by 6 oxygen atoms, although the X-ray absorption spectra evidence a clear dependence on the temperature. Surprisingly, all the materials behave as paramagnetic down to 1.5 K, but they exhibit different colours, what means that they are optically active (Co²⁺: violet; Ni²⁺: pale green; Fe³⁺: yellow; Cr³⁺: dark green).     

Studies on Synthesis and Properties of Mg-Al-nitrate Layered Double Hydroxides

Layered double hydroxides (LDHs), or the so-called hydrotalcite-like compounds, are important clay materials owing to their intercalation ability of anionic species and other physicochemical properties for application as anion adsorbents, medicine stabilizers, ion-exchangers, ionic conductors, catalysts and catalyst supports 1-2. The general formula is, [MⅡ1-x MⅢx(OH)2]x+ [Xm-x/m·nH2O]x-, abbreviated by: [MⅡ-MⅢ-X]. The net positive charge, due to substitution of trivalent by divale…     

Synthesis and Characterization of [Zn‐Al] Layered Double Hydroxides: Effect of the Operating Parameters

In this study, [Zn‐Al] layered double hydroxides (LDHs ) were prepared using the coprecipitation method at constant pH . The synthesis parameters (including the aging time, synthesis pH , nature of the alkali, concentration of metallic salts, and the cationic molar ratio R = Zn/Al) were varied in order to elucidate their effect on the properties of the obtained materials. Different characterization techniques, namely X‐ray diffraction, Fourier transform infrared, thermogravimetric analysis‐differential thermogravimetry, transmission electron microscopy, energy‐dispersive X‐ray, inductively coupled plasma, and photoluminescence, were used in this study. It was found that obtaining well‐crystallized LDHs requires (i) an aging time of 24 h and (ii) a synthesis pH value in the range 8–12. Our results also show that the concentration of the cationic metallic salts has no influence on the structural properties of the LDHs . The use of NH₄OH as alkali for adjusting the pH value during the synthesis favors the formation of nitrated LDH phases while NaOH gives rise to carbonated ones. Moreover, it was found that irrespective of the molar cationic ratio used (between 1 and 5), [Zn‐Al] LDHs could be obtained. The sample synthesized at R = 2 exhibited the best crystallinity.     

Synthesis and Characterization of Poly(ethylene terephthalate)/Modified Lithium‐Aluminum‐Layered Double Hydroxide Nanocomposites Prepared Using In‐situ Polymerization

Layered double hydroxides are a type of layered stacked compound, which can be intercalated with organic‐molecule modifiers. An ion‐exchange process for layered double hydroxide (LDH) was used to intercalate water‐soluble sulfanilic acid salt (SAS) and dimethyl 5‐sulfoisopthalate (DMSI) into lithium aluminum layered double hydroxides (LiAl LDHs). In this work, a hydrothermal process was used to modify LiAl LDHs, and the modified LiAl LDHs were treated with either SAS or DMSI through an ion‐exchange process and were then intercalated using bis‐hydroxyethylene terephthalate (BHET). The results indicate that the modified LiAl LDHs improved the interlayer compatibility between the PET and LiAl LDH layers; thus, enabling the oligomer molecules to more easily enter the gallery of the LiAl LDH layers so that polymer chains could be included between the LDH layers during polymerization of the matrix. The better barrier, mechanical properties, and thermal stability of these new types of PET nanocomposites are discussed.     

纳米Fe3O4/PVDF磁性复合膜的原位制备及表征

通过膜相渗透原位化学沉积法制备了聚合物基Fe3O4/聚偏氟乙烯（PVDF）磁性纳米复合膜，研究了复合膜制备的适宜条件，采用红外光谱（FT-IR）、差热分析（DSC）、X射线衍射、扫描电镜（SEM）等手段对复合膜的组成、结构进行了表征和分析，通过气体渗透法测定了复合膜的孔径随制备条件的变化情况. FT-IR和XRD图谱结果表明，在基膜中原位生成Fe3O4后不影响基膜PVDF的分子结构；复合膜中的Fe3O4粒子尺寸为68 nm左右，复合膜的磁化率达0.044 cm3•g－1；复合膜的磁化率、平均孔径、最大孔径及孔径分布范围随反应条件的改变而有明显变化.     

荧光磁性双功能Fe_3O_4/Alendronate@CdSe/CdS纳米复合物的制备与表征

采用化学共沉淀法制备了磁性Fe3O4纳米颗粒,并用四甲基氢氧化铵(TMAOH)、阿伦磷酸钠、丙烯酸丁酯和无水乙二胺对Fe3O4纳米颗粒表面进行修饰,制备出3代表面胺基化的Fe3O4树状分子.采用油相合成的方法制备CdSe/CdS量子点,再用巯基乙酸进行修饰,使其具有良好的水溶性和较好的稳定性.将制备的Fe3O4树状分子与修饰后的量子点进行连接,制备出双功能树状Fe3O4/Alendronate@CdSe/CdS微球.通过这种方法得到的材料的荧光性能明显增强,但材料的荧光性能并不随代数成线性变化的.     

Adsorption of Metanil Yellow Azoic Dye from Aqueous Solution onto Mg‐Fe‐NO3 Layered Double Hydroxide

We report the preparation and characterization of a layered double hydroxide (LDH) adsorbent for azoic dye, metanil yellow (yellow GX; YGX) removal. The nanoparticles of Mg‐Fe‐LDH‐NO₃ adsorbent were prepared with Mg/Fe molar ratio of 3:1 by a hydrothermal process and coprecipitation method at pH 9.5 and were characterized by X‐ray powder diffraction (XRPD), thermal gravimetric analysis (TGA), elemental analysis, and Fourier transform infrared spectroscopy (FT‐IR). The size and morphology of nanoparticles were examined by scanning electron microscopy (SEM). The XRD patterns indicate that the intercalation of YGX between the LDH layers has not occurred and surface adsorption has happened. In the adsorption experiments, the Gibbs free energy ΔG⁰ values, the enthalpy ΔH⁰, and entropy ΔS⁰ was determined. The isotherms showed that the adsorption of YGX by Mg‐Fe‐LDH‐NO₃ was both consistent with Langmuir and Freundlich equations.     

Peroxidase‐Like Layered Double Hydroxide Nanoflakes for Electrocatalytic Reduction of H2O2

Peroxidase‐like layered double hydroxide (LDH) nanoflakes were synthesized directly and facilely by a one‐pot chemical method, hydrothermal treatment. The as‐prepared LDHs were characterized by transmission electron microscopy, scanning electron microscopy, X‐ray diffraction, Fourier transform IR, and cyclic voltammetry. The functionalized LDHs immobilized on the glassy carbon electrode exhibited a well‐defined pair of redox peaks, excellent electrocatalytic activity toward the reduction of hydrogen peroxide without inhibition of dissolved oxygen and a higher affinity for H₂O₂, just like the peroxidase. The low apparent Michaelis–Menten constant was only 242 μM. The electrochemical response to H₂O₂ shows a linear range of 12–254 μM with the calculated detection limit of 2.3 μM at a signal‐to‐noise ratio of 3. Furthermore, compared with most metal hexacyanoferrates, the peroxidase‐like LDHs are very stable in neutral and alkaline solution. The electrochemical and electrocatalytic behavior of the functionalized LDHs indicate that they may be useful to explore man‐made mimics of enzyme in electrochemical biosensors.     

四硼酸根阴离子对氯型水滑石前体插层组装的动力学研究

根据四硼酸根对氯型水滑石(LDH—Cl)前体插层组装时溶液浓度的变化和不同反应进程产物的EDS,IR,XRD,TEM和TG—DTA表征研究了四硼酸根插层组装的动力学．结果表明,氯离子的交换溶出符合Stumm模型,四硼酸根的插入受控于扩散过程模型,插层产物保留了前驱体的层状结构及微孔结构,但插入大体积复杂离子B4O5(OH)4^2-引起晶胞c轴向体积和粒子尺寸的变化较大,晶胞参数c由2．399nm增大到2．558nm,通道高度h由0．3228nm增大到0．3756nm,粒子面向直径Da由15．16nm减小到8．92nm,径向尺寸Dc由10．93nm减小到4．55nrn;比表面积由92．63m^2／g增大到111．20m^2／g,LDH热分解特征亦有较大变化．     

导电聚苯胺与Fe3O4磁性纳米颗粒复合物的合成与表征

对十二烷基苯磺酸(DBSA)掺杂的导电聚苯胺(PAn-DBSA)的氯仿溶液,在pH为中性的条件下,采用“修饰-再掺杂(Modification-re-doped)法”合成了含有Fe₃O₄磁性纳米颗粒的导电聚苯胺复合物的有机溶液.用FTIR,XRD,TEM,UV-Vis和SQUID等对所得复合物进行了表征,结果表明,该复合物呈现超顺磁性和半导体的导电性,并具有较好的透明性.     

Synthesis and Characterization of Polymer Brushes Containing β-Cyclodextrin Grafted to Magnetic Nanoparticles for Determination of Naproxen in Urine

β-Cyclodextrin containing polymer brushes were grafted to magnetic nanoparticles following free radical copolymerization of N,N-dimethylacrylamide and allyl glycidyl ether on the surface. The products were characterized by Fourier transform infrared spectroscopy, thermogravimetric analysis, elemental analysis, and transmission electron microscopy and employed for solid phase extraction of naproxen in human urine. The profile of the naproxen adsorbed by the nanoparticles demonstrated high accessibility of the β-cyclodextrin. Scatchard analysis indicated that the capacity of the nanoparticles was 112 µmol g^?1 at 25°C and a pH of 5. The adsorption data of naproxen were considered by Langmuir, Freundlich, Redlich–Peterson, and Temkin isotherms. Approximately 55% of naproxen was released in simulated gastric fluid in 30 min and 94% in simulated intestinal fluid in 30 h. These data have indicated the utility of the naproxen loaded- β-cyclodextrin containing polymer brushes grafted to magnetic nanoparticles for enteric drug delivery.     

Effect of Electrolytes and Polymers on the Thixotropy of Mg‐Al‐Layered Double Hydroxides/Kaolinite Dispersions

The effect of electrolytes (NaCl and CaCl₂) and polymers (CPAM and HPAM) on the thixotropy of Mg‐Al‐layered double hydroxide (LDHs)/kaolinite dispersions has been investigated. It was observed that the type of thixotropy in LDH/kaolinite dispersions may be affected by NaCl, but not by CaCl₂ in range of concentration of interest. The type of thixotropy in LDH/kaolinite dispersion with R=0 transformed from positive thixotropy to complex thixotropy and at last positive thixotropy again with the concentration of NaCl in range of 0.00–0.10 mol·L⁻¹; the type of thixotropy in LDHs/kaolinite dispersions with R=0.25 transformed from complex thixotropy to positive thixotropy and then complex thixotropy again with the concentration of NaCl in range of 0.00–0.10 mol·L⁻¹. The type of thixotropy in LDH/kaolinite dispersion with R=0 may be not affected by cationic polyacrylamide (CPAM) and hydrolyzed polyacrylamide (HPAM); but the LDHs/kaolinite dispersions with R=0.25 transformed from complex thixotropy to positive thixotropy with the both polymers concentration in range of interest, which indicated that the microstructure of the dispersion changed from weak folc sediments structure to steric network structure.