Comparative Study of Mg/M(III) (M=Al, Ga, In) Layered Double Hydroxides Obtained by Coprecipitation and the Sol-Gel Method

Various layered double hydroxides (LDHs) consisting of magnesium and a trivalent metal (Al, Ga or In) in an Mg/M(III) ratio of 3 were prepared by precipitation from the corresponding nitrates and also from magnesium ethoxide and the acetylacetonates of the trivalent metals using the sol-gel method. The six LDHs thus obtained were calcined at 500°C. All solids were characterized by XRD and IR spectroscopy prior to and after calcination. Their textural properties were determined from nitrogen adsorption measurements and their surface chemical properties by CO₂ chemisorption.     

Insights on the Structural Chemistry of Hydrocalumite and Hydrotalcite-like Materials: Investigation of the Series Ca2M(OH)6Cl·2H2O (M: Al, Ga, Fe, and Sc) by X-Ray Powder Diffraction

Hydrotalcite and hydrocalumite are two close minerals belonging to the layered double hydroxide family. Both structures are based on positive brucite-like layers alternating with layers containing anions and water molecules. Most of synthetic (LDHs) are hydrotalcite-like materials. On the other hand, the hydrocalumite structure type is rare for those less broad in composition, typically Ca²⁺ and Al³⁺ in the hydroxide layers. In order to get further insight into the conditions of stabilization of this structure type, we have undertaken the synthesis and the structural characterization by powder X-ray diffraction of the series Ca₂M³⁺(OH)₆Cl·2H₂O(M³⁺:Al³⁺, Ga³⁺, Fe³⁺ and Sc³⁺). The incorporation of Sc³⁺ ions is quite original. All phases crystallize in the rhombohedral space group R-3 resulting in a three-layers polytype. The main consequence of the replacement of Al³⁺ cations by large M³⁺ cations is a compression of the octahedral layers like it proceeds in hydrotalcite-like materials. The existence of Sc-containing phase allows us to say that it is the size of Ca²⁺ ions and the pronounced anisotropy of coordination spheres around Ca²⁺ and M³⁺ which are responsible for the ordered distribution of cations in hydrocalumite-like materials.     

聚N-异丙基丙烯酰胺/类水滑石复合水凝胶的制备及温敏性

以类水滑石(LDHs)和N-异丙基丙烯酰胺(NIPA)为原材料,采用自由基引发聚合制得了有机无机PNIPA/LDHs温度敏感复合水凝胶。 通过热重分析仪(TGA)、示差扫描量热仪(DSC)和扫描电子显微镜(SEM)等技术手段表征了材料的结构和性能。 结果表明,PNIPA/LDHs复合水凝胶在33 ℃左右可实现溶胶-凝胶的可逆性变化,LDHs质量分数基本不影响复合水凝胶的胶凝化温度和胶凝时间。 LDHs添加可使PNIPA/LDHs复合水凝胶的热稳定性较NIPA有大幅度提升。 随LDHs质量分数及n(Mg):n(Al)的增加,复合凝胶的吸热峰值稍有增加。 所合成PNIPA/LDHs复合水凝胶表面粗糙不平,具有一定的孔洞结构。     

Determination of Cr(III) and Cr(VI) in industrial and environmental liquid samples by EDXRF method

A rapid, sensitive and selective procedure for determination of Cr(III) and Cr(VI) in environmental and industrial liquid samples via preconcentration with ammonium pyrrolidine dithiocarbamate (APDC) and determination by means of the EDXRF was described. The effect of pH in the range of 3-11 on the recovery of Cr(III) and Cr(VI) has been investigated separately and in combination of these two species. The influence of organic matter, carbonate species and elements V, Mn and Fe on the recovery of each chromium specie (separately/in combination) over whole pH range was also tested in order to simulate condition occurring in natural waters that usually contain certain amount of dissolved organic matter and carbonate ions. Cr(VI) and Cr(III) have shown different behaviors in reaction with APDC at different pH ranges and therefore it is possible to separate those two species. It was found that Cr(VI) creates complex with APDC only in the pH range from 3 to 5 with quantitative recovery (app. 98%) at pH 3, but there was no recovery of Cr(III) at that pH. On the contrary, in pH range from 6 to 11, reaction with Cr(III) and APDC reviled that the only reaction product is Cr(OH)₃ instead of the expected Cr(III)-APDC complex. All reaction products were characterized by IR spectroscopy.     

层板Ni2+的引入对CuCr类水滑石晶体结构的影响研究

采用自行创制的成核晶化隔离法将Ni^2 引入层状双金属复合氢氧化物(LDHs)的层板,首次合成得到了层板含Ni^2 的三元金属铜镍铬的碳酸根型LDHs(CuNiCr—LDHs),通过X射线衍射(XRD)、红外光谱(FT-IR)、透射电镜(TEM)、热重及微商热重分析(TODTG)、等离子电感偶合元素分析(ICP)和激光粒度分析等手段对产物的晶体结构特征进行了研究,结果表明：当反应Cu^2 ／Ni^2 ／Cr^3 投料摩尔比介于1：2：1～1：3：1之间,晶化温度为180℃和晶化时间大于4h时,利用成核晶化隔离法可以合成得到晶型规整的CuNiCr—LDHs;研究同时发现,层板引入Ni^2 后可以削弱Cu^2 的Jahn-Tellex效应对层板对称性的影响,提高了LDHs的晶型完整性和结构稳定性。     

溶胶-凝胶法制备双钙钛矿型氧化物SrLaMnBO6(B:Mo,W)及其磁学性能

溶胶-凝胶法制备双钙钛矿型氧化物SrLaMnBO6(B:Mo;W)及其磁学性能;双钙钛矿型;溶胶 凝胶;掺杂;晶胞参数;磁性     

Immobilization of anionic iron(III) porphyrins into ordered macroporous layered double hydroxides and investigation of catalytic activity in oxidation reactions

The first generation anionic iron(III) porphyrin [Fe(TSPP)] and the second generation anionic complexes [Fe(TDFSPP)], [Fe(TCFSPP)], and [Fe(TDCSPP)] were immobilized into three-dimensionally macroporous layered double hydroxide (3DM-LDH), using the direct reconstruction of 3DM-LDH from macroporous mixed oxides MOX or the anionic exchange on DDS intercalated 3DM-LDH. The macroporous layered double hydroxides were obtained at the surface of nanometric polystyrene spheres, which were synthesized by an inverse opal method. Polystyrene was removed after calcination in oxidizing atmosphere, nanostructured mixed oxides (3DM-MOX) were obtained, which after reconstruction give origin to macroporous layered double hydroxide (3DM-LDH). Following metalloporphyrin immobilization, the resulting materials were characterized by powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), UV–vis (glycerin mull) spectroscopy, attenuated total reflectance Fourier transform infrared spectroscopy (ATR/FTIR), and electron paramagnetic resonance (EPR). Results revealed that the complexes are either immobilized at the surface of the macroporous layered double hydroxide or intercalated between the layers, displacing some dodecylsufate anions. The obtained materials were investigated as catalysts for oxidation reactions, to find out whether they function as cytochrome P-450 models.     

Comparison Between Sol-Gel,Coprecipitation and Wet Mixing Synthesis of ZnAl2O4

ZnAl₂O₄ was prepared by hydrolyzing a mixture of aluminum alkoxide with zinc nitrate dissolved in hexylene glycol and calcining at 800°C. The results are compared with those obtained by wet mixing and coprecipitation. The sol-gel method produces solids whose surface areas and pore volumes are 100% larger and with a more homogeneous pore size distribution.     

Preparation and Characterisation of Li-Al-glycine Layered Double Hydroxides (LDHs)-Polymer Nanocomposites

LiAl-Layered Double Hydroxides, containing glycinate anions, have been prepared using LiAlO₂. The glycine containing LDHs were then exfoliated in chloroform. Dispersions of approximately 0.03 g of the LDH in 15 ml of the solvent were possible. Nanocomposites using the exfoliated LiAl-glycine LDH and polyethyleneglycol were prepared by adding appropriate amounts of polymer to the LDH-chloroform dispersion. The clay-polymer nanocomposites were then characterised using powder X-ray diffraction. The thermal and mechanical properties of the composites are reported. The results suggest that composites containing individual (exfoliated) LDH layers were obtained with the mechanical and thermal properties of the composites noticeably superior to those of the parent polymer.     

Thermomechanical properties and crystallization behavior of layered double hydroxide/poly(ethylene terephthalate) nanocomposites prepared by in‐situ polymerization

Thermomechanical properties and crystallization behavior of poly(ethylene terephthalate) (PET) nanocomposites containing layered double hydroxide (LDH) were investigated. To enhance the compatibility between PET matrix and LDH, dimethyl 5‐sulfoisophthalate (DMSI) anion intercalated LDH (LDH‐DMSI) was synthesized by coprecipitation method, and its structure was confirmed by Fourier transform infrared (FTIR) spectrometer and X‐ray diffraction (XRD) measurements. Then, PET nanocomposites with LDH‐DMSI content of 0, 0.5, 1.0, and 2.0 wt% were prepared by in‐situ polymerization. The dispersion morphologies were observed by transmission electron microscopy (TEM) and XRD, showing that LDH‐DMSI was exfoliated in PET matrix. Thermal and mechanical properties, such as thermal stability, tensile modulus, and tensile yield strength of nanocomposites, were enhanced by exfoliated LDH‐DMSI nanolayers. However, elongation at break was drastically decreased with LDH loading owing to the increased stiffness and microvoids. The effect of exfoliated nanolayers, which acted as a nucleating agent confirmed by differential scanning calorimeter (DSC), on the microstructural parameters during isothermal crystallization, was analyzed by synchrotron small‐angle X‐ray scattering (SAXS). It is believed that nanocomposites could be crystallized more easily owing to the increased nucleation sites, which lead to the decrease of average amorphous region size and the long period with the increase of LDH‐DMSI content. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 28–40, 2007     

Synthesis of Inorganic Compounds (Metal, Oxide and Hydroxide) in Polyol Medium: A Versatile Route Related to the Sol-Gel Process

A new route for the preparation of powdery metal, oxide and hydroxide materials is presented as a chimie douce alternative to the sol-gel method. It consists in the reduction or the hydrolysis of a metal salt dissolved and heated in a polyol medium. It appears through zinc and cobalt examples that the use of acetate precursors contrarily to chloride or sulfate ones leads to the precipitation of a solid (metal, oxide, hydroxide) whose nature depends on two main factors: the hydrolysis ratio, defined by the water to metal molar ratio, and the reaction temperature. As in the sol-gel method, acetate leads to the formation of intermediate alkoxyacetate complex. The absence of water favors metal formation while its presence favors oxide or hydroxyacetate formation.     

In Situ Synthesis of MnMgFe-LDH on Biochar for Electrochemical Detection and Removal of Cd2+ in Aqueous Solution

Herein, MnMgFe-layered double hydroxides/biochar (MnMgFe-LDHs/BC) composite was fabricated by immobilizing MnMgFe-LDHs on BC via the coprecipitation method, which was employed as an effective material for the detection and removal of Cd²⁺ from aqueous media. A lamellar structure of MnMgFe-LDHs with abundant surface-hydroxyl groups and various interlayer anions inside present a greater chance of trapping Cd²⁺. Meanwhile, the conductive BC with a porous structure provides numerous channels for the adsorption of Cd²⁺. Using the MnMgFe-LDHs/BC-based sensor, Cd²⁺ can be detected with a low limit of detection down to 0.03 ng/L. The feasibility of detecting Cd²⁺ in paddy water was also carried out, with satisfactory recoveries ranging from 97.3 to 102.3%. In addition, the MnMgFe-LDHs/BC material as an adsorbent was applied to remove Cd²⁺ from water with adsorption capacity of 118 mg/g, and the removal efficiency can reach 91%. These results suggest that the as-prepared MnMgFe-LDHs/BC can serve as a favorable platform for efficient determination and removal of Cd²⁺ in water.     

Layered double hydroxide/polyethylene terephthalate nanocomposites. Influence of the intercalated LDH anion and the type of polymerization heating method

Conventional and microwave heating routes have been used to prepare PET–LDH (polyethylene terephthalate–layered double hydroxide) composites with 1–10 wt% LDH by in situ polymerization. To enhance the compatibility between PET and the LDH, terephthalate or dodecyl sulphate had been previously intercalated in the LDH. PXRD and TEM were used to detect the degree of dispersion of the filler and the type of the polymeric composites obtained, and FTIR spectroscopy confirmed that the polymerization process had taken place. The thermal stability of these composites, as studied by thermogravimetric analysis, was enhanced when the microwave heating method was applied. Dodecyl sulphate was more effective than terephthalate to exfoliate the samples, which only occurred for the terephthalate ones under microwave irradiation.     

Unveiling the Occurrence of Co(III) in NiCo Layered Electroactive Hydroxides: The Role of Distorted Environments

Co- and Ni-based layered hydroxides constitute a unique class of two-dimensional inorganic materials with exceptional chemical diversity, physicochemical properties and outstanding performance as supercapacitors and overall water splitting catalysts. Recently, the occurrence of Co(III) in these phases has been proposed as a key factor that enhance their electrochemical performance. However, the origin of this centers and control over its contents remains as an open question. We employed the Epoxide Route to synthesize a whole set of α-NiCo layered hydroxides. The PXRD and XAS characterization alert about the occurrence of Co(III) as a consequence of the increment in the Ni content. DFT+U simulation suggest that the shortening of the Co−O distance promotes a structural distortion in the Co environments, resulting in a double degeneration in the octahedral Co 3d orbitals. Hence, a strong modification of the electronic properties leaves the system prone to oxidation, by the appearance of Co localized electronic states on the Fermi level. This work combines a microscopic interpretation supported by a multiscale crystallochemical analysis, regarding the so-called synergistic redox behavior of Co and Ni, offering fundamental tools for the controllable design of highly efficient electroactive materials. To the best of our knowledge, this is the first computational–experimental investigation of the electronic and structural details of α-NiCo hydroxides, laying the foundation for the fine tuning of electronic properties in layered hydroxides.     

Synthesis of heptamolybdate‐intercalated MgAl LDHs and its application in polyurethane elastomer

Heptamolybdate (Mo₇O₂₄^6?) was intercalated in the interlayer space between MgAl‐layered double hydroxides (Mo‐MgAl LDHs) by the hydrothermal and ion exchange method, and then polyurethane elastomer (PUE) based composites were prepared by the prepolymerization method with different amounts of Mo‐MgAl LDHs. X‐ray diffraction (XRD), Fourier transform infrared (FTIR) spectra, laser Raman spectroscopy (LRS), and scanning electron microscopy (SEM) were employed to characterize the obtained LDHs. The performance of the PUE/LDHs were evaluated by measuring their thermal gravimetric, heat release rate (HRR), and smoke density (Ds). The results show that PUE/LDH composites exhibit a lower peak heat release rate (pk‐HRR), Ds, and a prolonged combustion time, in comparison with neat PUE. Comparison between NO₃‐MgAl LDHs and Mo‐MgAl LDHs containing composites show that the introduction of Mo⁶⁺ is able to facilitate flame retardance and smoke suppression efficiency, which results mainly from the presence of MoO₃ derived from the decomposition of Mo₇O₂₄^6? intercalated LDHs. Mo‐MgAl LDHs reduce the pk‐HRR of composites by 39% with only 1 wt.% content, and the maximum Ds of composites is reduced to a minimal value of 274 with 10 wt.% Mo‐MgAl LDHs. More importantly, LDHs would improve the mechanical properties at a low content. The experimental results reveal the potential of Mo₇O₂₄^6? intercalated LDHs to improve both the flame retardancy and smoke suppression of PUE. Copyright © 2015 John Wiley & Sons, Ltd.     

Synthesis and Characterization of Two Novel Complexes of Cr(III) with Benzilmonoxime

The reaction of benzilmonoxime (BMOH) with CrCl₃.6H₂O in methanol gives the mono nuclear Cr(III) complex, [Cr(BMO)3₃ ( 1 ). Reaction of complex 1 with a methanolic solution of KOH at room temperature leads to a di‐nuclear Cr(III)‐Cr(III) complex, [Cr(BMO)₂(OH)]₂ ( 2 ). The complexes were characterized on the basis of their elemental analysis, Mass, IR, ¹H and ¹³C‐NMR and electronic spectra. The IR studies were useful in assigning the coordination mode of the benzilmonoxime ligand to the chromium(III) ion. In addition, the presence of a hydroxo bridge in the dimeric complex 2 is inferred from the IR spectral studies. The electronic spectra of the complexes revealed two bands due to d–d transitions, and one band assignable to an oxygen (p_π)→Cr(eg*) LMCT transition observed in both complexes. An additional charge transfer transition, assignable to μ‐OH(p_π)→Cr(eg*), was only observed for the dimeric complex 2 . The splitting energy and Racah parameter were calculated to be 18484 cm^‐1 and 560 cm^‐1 for [Cr(BMO)₃] ( 1 ), 17986 cm^‐1 and 545 cm^‐1 for [Cr(BMO)₂(OH)]₂ ( 2 ) respectively.     

12-磷钨酸插层MgAl水滑石的合成、表征及催化酯化原油脱酸性能

采用离子交换法合成了不同Mg/Al物质的量比的12-磷钨酸(H_3PW_(12)O_(40),HPW)插层水滑石(LDHs),采用XRD、FT-IR、Raman、ICP-AES、TG-DSC等分析手段表征其物化性质,Hammett指示剂-正丁胺滴定法测定其酸强度和酸量分布。进一步将其用于原油催化酯化脱酸反应,并与NO_3型LDHs对比,探讨酯化活性与催化剂性质之间的关系。结果表明,催化剂的活性主要受酸性和比表面积的影响。HPW插层LDHs的酯化活性明显优于NO3型LDHs,归因于增强的酸性和增大的比表面积。对于弱酸性的NO_3型LDHs,酯化活性与比表面积呈正向关系,Mg/Al物质的量比为4时,具有最大的比表面积和脱酸活性。而对于较强酸性的HPW插层LDHs,酯化活性主要受到酸量的影响,Mg/Al物质的量比为2的催化剂具有最高的酸量和脱酸活性。     

Sol-Gel Synthesis Route for the Preparation of Y(Ba1−x Sr x )2Cu4O8 Superconducting Oxides

Superconducting oxide ceramics of composition Y(Ba_1–x Sr _x )₂Cu₄O₈ (x = 0.00, 0.10, and 0.20) have been prepared by a simple sol-gel method based on the complexation of metal ions in aqueous medium, by chelating acetate and tartarate ligands. Homogeneous sols were obtained by complexing copper ions with tartaric acid, which prevented the flocculation of copper acetate during the gelation process. Single-phase bulk samples were obtained after firing the mixed-metal polymeric acetate-tartarate precursor to 835°C for 70 h in flowing oxygen atmosphere. Thermal decomposition of the gels was studied by thermogravimetry. Effect of strontium substitution on the properties of the compounds was studied by X-ray powder diffraction, electron microscopy, X-ray photoemission spectroscopy and resistivity measurements. These data indicate that nearly monophasic Y(Ba_1–x Sr _x )₂Cu₄O₈ superconducting samples were obtained for x < 0.30. The Sr-doping in the YBa₂Cu₄O₈ (Y-124) phase shows a pronounced effect on the superconducting properties enhancing the critical temperature from 78 K (for the non-substituted sample) to 88 K (for Y(Ba_1–x Sr _x )₂Cu₄O₈).     

Synthesis and Properties of Phenothiazine Derivatives. 2. Spectral (ESR and IR) Characteristics of the Radical-cations of the Phenothiazine N-Derivatives

The temperature dependence of the ESR spectra of the radical-cations of the N-derivatives of phenothiazine were studied in the range of 200-393 K (o-xylene). It was established that at temperatures of 323-333 K the nature of the HFS varies from doublet to quartet with approximate intensity ratios of 1:2:2:1, and this transformation is irreversible. A hypothesis explaining the results is proposed. IR spectroscopy was used to confirm the proposed mechanism of localization of the unpaired electron.