Effect of the layer charge on the interaction of porphyrin dyes in layered silicates dispersions

Interaction between tetracationic porphyrin, 5,10,15,20-tetrakis(N-methylpyridinium-4-yl)porphyrin (TMPyP), and layered silicates in aqueous dispersions was studied using absorption, steady-state and time-resolved fluorescence spectroscopies. The charge density of silicates increases in order synthetic laponite (LAP)<Kunipia F montmorillonite (KF)<synthetic fluorohectorite (FHT). Interpretations of the spectra of layered silicate-porphyrin (LSP) systems considered models of dye adsorption on clay mineral colloid particles, analyzing phenomena occurring in similar systems such as structural changes of TMPyP and the formation of dye molecular assemblies. Structural changes of TMPyP, including flattening of the porphyrin molecule, do not fully explain all the spectral observations. One should mention variations of the Q-bands and fluorescence spectra in dependence on the layer charge. The molecular association of the TMPyP molecules is expected to occur to a certain extent in dependence on the layer charge of a clay mineral template. H-aggregates were not observed in any system. Only FHT colloids induced the formation of at least two components with significantly different spectral properties.     

Model for evolution of periodic layered structure in the SiO2/Mg system

A mathematical model for the growth of MgO/Mg₂Si periodic layered structure (PLS) is presented based on Fick's diffusion law and conservation of matter. The model explains the temporal evolution of the width of periodic layers at different temperatures, for layers distant enough from the Mg source. It is demonstrated that the difference in thickness of a pair of any two adjacent layers decreases with increasing temperature.     

Controlled synthesis and characterization of layered manganese oxide nanostructures with different morphologies

Layered manganese oxide nanostructures with different morphologies, such as nanowire bundles, cotton agglomerates, and platelikes were successfully fabricated by a simple and template-free hydrothermal method based on a reaction of KMnO₄ and KOH solutions with different concentrations. The obtained nanowire bundles were assembled by nanowires with diameters of 10 to 200 nm and lengths up to 5–10 μm. The cotton agglomerates were composed of manganese oxide layers with a thickness of about 10 nm. Both the concentration of KOH solutions and the reaction temperature played an important role in the formation of layered manganese oxide nanostructures with different morphologies. XRD, SEM, TEM, HRTEM, SAED, TG-DTA, and chemical analysis were employed to characterize these materials. On the basis of the experimental results, a possible formation mechanism of layered manganese oxide nanostructures with different morphologies was presented. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Raman study of high temperature insulator-insulator transition in Ba2Co9O14

The insulator-insulator transition, at T_t = 570 K, in layered cobalt oxide Ba₂Co₉O₁₄ was investigated using Raman scattering technique. High temperature (300–800 K) measurements have evidenced no structural transition occurring at T_t. The obtained results are rather consistent with low to high spin-state transition of Co³⁺ ions in the Co₃O₁₂ octahedral trimer. More precisely, only one cobalt ion located in the central octahedron of the trimer undergoes this transition.     

高透明高韧性黏土/聚乙烯醇人造贝壳

天然贝壳由碳酸钙片和少量生物聚合物组成,同时具有高的强度和韧性.这些优异的力学性能主要归因于高的碳酸钙片含量、精心设计的层状结构、强的界面粘结和碳酸钙片适当的长径比,使得贝壳以片拔出的形式断裂,导致优异的强度和韧性.受天然贝壳结构和力学性能之间关系的启发,采用蒸发诱导自组装方法制备了黏土/聚乙烯醇人造贝壳,其中黏土的含量为52 wt%.扫描电镜、透射电镜和X射线衍射证实了其层状结构.红外光谱证实黏土和聚乙烯醇之间形成氢键.拉伸测试测得人造贝壳强度为(90.2±8.0)MPa,与天然贝壳(80~135 MPa)相当;人造贝壳断裂应变高达(14.7±2.3)%,远高于天然贝壳(约2%);人造贝壳拉伸韧性高达(10.6±3.0)MJ/m3.此外,所制备的人造贝壳透明,透明度高达90%以上.     

A thermo-elastoplastic model for soft rocks considering structure

In the fields of nuclear waste geological deposit, geothermy and deep mining, the effects of temperature on the mechanical behaviors of soft rocks cannot be neglected. Experimental data in the literature also showed that the structure of soft rocks cannot be ignored. Based on the superloading yield surface and the concept of temperature-deduced equivalent stress, a thermo-elastoplastic model for soft rocks is proposed considering the structure. Compared to the superloading yield surface, only one parameter is added, i.e. the linear thermal expansion coefficient. The predicted results and the comparisons with experimental data in the literature show that the proposed model is capable of simultaneously describing heat increase and heat decrease of soft rocks. A stronger initial structure leads to a greater strength of the soft rocks. Heat increase and heat decrease can be converted between each other due to the change of the initial structure of soft rocks. Furthermore, regardless of the heat increase or heat decrease, a larger linear thermal expansion coefficient or a greater temperature always leads to a much rapider degradation of the structure. The degradation trend will be more obvious for the coupled greater values of linear thermal expansion coefficient and temperature. Lastly, compared to heat decrease, the structure will degrade more easily in the case of heat increase.     

ZnCuAl-LDH/Bi2MoO6纳米复合材料的构建及其可见光催化降解性能

In this study, pure Bi₂MoO₆ was synthesized via a solvothermal method. A ZnCuAl-layered double hydroxide (LDH)/Bi₂MoO₆ (denoted as LDH/Bi₂MoO₆) nanocomposite was synthesized via a steady-state co-precipitation route using Bi₂MoO₆ as the matric material. LDH was deposited on the surface of Bi₂MoO₆ with a close contact interface. The specific surface area of the resulting LDH/Bi₂MoO₆ composite increased up to 19.1 m²∙g⁻¹ owing to the stacking arrangement between LDH and the Bi₂MoO₆ nanosheets, resulting in the generation of a large number of reactive sites. In addition, the light absorption region of the LDH/Bi₂MoO₆ composite was larger than those of pure LDH and Bi₂MoO₆ because of the formation of a heterojunction structure and the possible quantum size effect. The photocatalytic performance of the as-prepared samples was evaluated by carrying out the degradation of rhodamine B (RhB) using them under visible light irradiation. Compared to pure LDH and Bi₂MoO₆, the LDH/Bi₂MoO₆ nanocomposite exhibited enhanced photocatalytic activity for the degradation of RhB. With an increase in the LDH content, the photocatalytic activity of the LDH/Bi₂MoO₆ composite first increased and then decreased. Although the addition of an optimum amount of LDH was beneficial for the generation of electron-hole pairs, excessive LDH on the surface of Bi₂MoO₆ decreased the visible light absorption ability of both the components, thus reducing photocatalytic activity of the composite. This indicates that an appropriate LDH:Bi₂MoO₆ molar ratio is necessary for obtaining LDH/Bi₂MoO₆ composites with excellent photocatalytic activity. Furthermore, the LDH/Bi₂MoO₆ composite showed high photocatalytic stability and reusability. The structure of the LDH/Bi₂MoO₆ composite remained almost unchanged even after four photodegradation cycles. The enhanced photocatalytic performance of the composite can be attributed to the combined effect of its heterojunction structure and high specific surface area, which are beneficial for effective separation of photogenerated charge carriers and the availability of a large number of active sites for photocatalysis. It was found that •OH and O₂^•− were the main reactive species, while e⁻ and h⁺ contributed little to the photodegradation process. The generation, transfer, and separation of photoinduced electrons and holes in the composites were investigated by transient photocurrent responses, electrochemical impedance spectroscopy Nyquist plots, and photoluminescence measurements. The results showed that the heterojunction structure of the composites played a key role in enhancing their photocatalytic activity. A possible photodegradation mechanism was proposed for the composite. This study will provide a facile approach for the preparation of LDH- and/or Bi₂MoO₆-based nanocomposites. The LDH/Bi₂MoO₆ nanocomposite prepared in this study showed huge potential to be used as a visible-light photocatalyst for degrading environmental pollutants.     

类水滑石材料主客体插层结构的构筑及特性的理论研究

因主体层板和层间客体具有丰富的可调性, 类水滑石材料(LDHs)在催化、 吸附、 生物医药及光、 电、 磁等方面展现出了广阔的应用前景. 近年来理论研究已成为揭示LDHs微观结构和性质的重要手段, 本文系统综述了LDHs材料主体结构、 客体结构以及主客体相互作用3个方面的理论研究工作进展, 及其在作为光驱动催化剂方面应用的理论研究. 从主体元素构成、 元素比例、 电荷分布、 拓扑结构转变、 能带结构、 态密度、 层间阴离子组成、 离子交换性能、 主客体作用力、 能量性质及光催化性能等方面, 在原子、 电子尺度上揭示了LDHs材料结构-性能之间的构效关系, 为以其为材料平台构筑一系列基于超分子插层结构主客体间相互作用的新型功能材料、 扩展材料的功能性提供了丰富的理论信息和有益指导.     

Embedding Alkyldiamine into Layered α-Titanium Phosphate via Direct-Ion Exchange and its Application in EuIII Removal from Water

Diamine-pillared α-titanium phosphate (α-TiP) was prepared via direct ion exchange method. Moreover, 1,3-propanediamine, as the pillaring agent, was used to investigate the effect of pH, content and temperature on the interlayer distance of α-TiP. The structure and properties of the samples were characterized by X-ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FT-IR), Field Emission Scanning Electron Microscopy (SEM), and Differential Thermal Analysis (TG). The results show that the interlayer distance of α-TiP was enlarged from 7.6 Å to 16.18 Å as the carbon chain of the intercalating diamine increased from (NH₂(CH₂)_nNH₂) (n = 2 to 7). The layer space structure consists of monomolecular alkyl chains with an average tilt angle of 75.6°. The uptake values for these five alkyldiamine cations were 3.780, 3.261, 2.443, 2.175, and 1.954 mmol, per gram of TiP, respectively. Also, we found that the direct ion exchange method is more effective in a weak acidic environment. The variation of interlayer distance was a consecutive process, and unaffected by temperature. The 1,3-propanediamine intercalation product (α-TiPPda) showed excellent performance towards Eu^III adsorption in water with removal efficiencies ≥ 99 %.