External Micro-PIXE Measurements: Preliminary Results on Volcanic Rocks from Nyiragongo Volcano

The external microbeam facility at the 3 MV Tandetron accelerator of the LABEC Laboratory of INFN in Florence has been used to determine, by PIXE, major, minor and trace element abundances of minerals and groundmass in the lavas from the active Nyiragongo Volcano (Democratic Republic of Congo), which is well known for its lava lake intra-crateric activity [e.g. 1, 2]. During the last eruption of this volcano (January, 2002), two main flows entered the Goma town producing major devastation, forcing the rapid exodus of about 300,000 people and causing the death of 150 persons [3]. After this eruption, the interest of the scientific community on this volcanic area suddenly increased. In this respect, determination of major and trace element abundances in mineral phases and groundmass of lavas may allow to constrain the evolution of magma within the volcanic system from a quantitative view point, thus helping to better understand the way this volcano works. PIXE measurements have been performed in a two-detector setup that makes it possible to simultaneously detect and quantify all elements from Na to the heaviest ones; possible compositional zoning effects in the crystals can also be reliably measured thanks to the good space resolution of the microbeam facility (better than 10 μm) and to the possibility of performing one- and bi-dimensional scans over the areas of interest. Concentration maps of all elements can be obtained, both on-line and a posteriori: the data are collected with a list-mode acquisition system, which allows the distribution of any detected element to be reconstructed after completing the scan.     

Line broadening in the PXRD patterns of layered hydroxides: The relative effects of crystallite size and structural disorder

Layered hydroxides crystallize in a hexagonal structure and incorporate a number of different types of structural disorders as an exigency of anisotropic bonding. Structural disorder contributes to the non-uniform broadening of lines in the powder X-ray diffraction pattern. Common among the disorders are stacking faults, which broaden theh0ℓ/0kℓ reflections. Interstratification selectively broadens the 00l reflections and turbostratic disorder broadens the 0kℓ reflections. The line broadening caused by structural disorder has to be discounted before estimates of particle size are made by applying the Scherrer formula. Dedicated to Prof J Gopalakrishnan on his 62nd birthday.     

Determination of Iron in Layered Crystal Sodium Disilicate and Sodium Silicate by Flame Atomic Absorption Spectrometry with Boric Acid as a Matrix Modifier

As a novel type builder for phosphate-free detergent1,2, layered crystal sodium disilicate has many advantages over other builders for phosphate detergents. The raw material of layered crystal sodium disilicate is sodium silicate. Because of the effects o…     

Nanostructured layered copper hydroxy dodecyl sulfate: A potential fire retardant for poly(vinyl ester) (PVE)

Composites of poly(vinyl ester) (PVE) with copper hydroxy dodecyl sulfate (CHDS) were prepared by thermal curing. The efficiency of the additive, CHDS, in reducing flammability is demonstrated via cone calorimetry and thermogravimetric analysis (TGA). The addition of 1-10% by mass of the CHDS additive resulted in significant increments in char formation (∼4-11%) from thermogravimetric analysis (TGA). Incorporation of the CHDS into the polymer matrix at these low concentrations leads to substantial reductions in the total heat release (∼20-30%) but no significant change in the peak heat release rate. The composite materials generally ignite more quickly, however, the flame extinguishes faster for the composites relative to the virgin polymer. X-ray diffraction (XRD) and infrared spectroscopic analyses of the residues collected at various stages during thermal decomposition of the composites, suggest the participation of copper-containing species in promoting enhanced thermal stability of PVE.     

Solvent-free synthesis of three layered manganese sulfate-oxalates with different pore apertures

Three manganese sulfate-oxalates, namely, H₂pip·Mn₂(SO₄)₂(ox)(H₂O)₂·2H₂O (1), H₃ipa⋅Mn₂(SO₄)(ox)_2.5·H₂O (2), and H₃dpta⋅Mn₂(SO₄)₂(ox)_1.5(H₂O)₃ (3), were prepared under solvent-free conditions, where pip = piperazine, ox = oxalate, ipa = 3,3′-iminobis(N,N-dimethylpropylamine), and dpta = dipropylenetriamine. These compounds have different layered structures intercalated with organic cations. Their pore apertures range from small 8-membered ring (8 MR) to large 12 MR and extra-large 20 MR. The temperature dependence of the magnetic susceptibility of these compounds were also investigated.     

Stabilization of antioxidant gallate in layered double hydroxide by exfoliation and reassembling reaction

As for the stabilization of chemically sensitive bioactive molecule in this study, gallic acid (GA) with antioxidant property was intercalated into interlayer space of layered double hydroxide (LDH), which was realized by exfoliation and reassembling reaction. At first, the pristine nitrate-type Zn₂Al-LDH in solid state was synthesized via co-precipitation followed by the hydrothermal treatment at 80 °C for 6 h, and then exfoliated in formamide to form a colloidal solution of exfoliated LDH nanosheets, and finally reassembled in the presence of GA to prepare GA intercalated LDH (GA-LDH) desired, where the pH was adjusted to 8.0 in order to deprotonate GA to form gallate anion. According to the XRD analysis, GA-LDH showed well-developed (00l) diffraction peaks with a basal spacing of 1.15 nm, which was estimated to be larger than that of the pristine LDH (0.88 nm), indicating that gallate molecules were incorporated into LDH layers with perpendicular orientation. From the FT-IR spectra it was found that gallic acid was completely deprotonated into gallate, and stabilized in between LDH lattices via electrostatic interaction. The content of GA in GA-LDH was determined to be around 23 wt% by UV–vis spectroscopic study, which was also confirmed by HPLC analysis. According to the in-vitro release of GA out of GA-LDH in PBS solution (pH 7.4) at 4 °C, GA was sustainably released from GA-LDH nanohybrid up to 86% within 72 h. The antioxidant property of GA-LDH was almost the same with that of intact GA which was examined by DPPH. The photostability of GA-LDH under UV light irradiation was immensely enhanced compared to intact GA. It is, therefore, concluded that the present GA-LDH nanohybrid can be considered as an excellent antioxidant material with high chemical- and photo-stabilities, and controlled release property.     

Layered double hydroxide films on nanoporous anodic aluminum oxide/aluminum wire: a new fiber for rapid analysis of Origanum vulgare essential oils

Zn/Al layered double hydroxide (LDH) films were fabricated in situ with anodic aluminium oxide aluminium as both the substrate and the sole aluminium source by means of urea hydrolysis. Headspace solid phase microextraction using LDH fibre in combination with capillary GC–MS was utilised as a monitoring technique for the collection and detection of the volatile compounds of Origanum vulgare. Experimental parameters, including the sample weight, microwave power, extraction time and humidity effect, were examined and optimised.     

Intercalation of poly(methyl methacrylate) into tyramine-modified layered silicates through hydrogen-bonding interaction

Layered silicates modified with tyramine hydrochloride () were prepared and subsequently used in the preparation of polymer–layered silicate nanocomposites. Accordingly, surfaces of tyramine-modified silicate layers are partially covered with the phenol groups, which are able to form hydrogen bonds with the carbonyl groups of PMMA. In this study the solution-mediated process was applied to prepare two PMMA-based nanocomposites from tyramine-modified montmorillonite and Laponite (TAMMT and TALAP). Through hydrogen bonding, PMMA molecules are absorbed onto the silicate surfaces, and hence silicate layers can be dispersed in the polymer matrix. In the case of using TAMMT whose size is 300–500 nm, the intercalated nanocomposite is obtained. While using TALAP which has the much smaller diameter (25–50 nm) compared to TAMMT, the corresponding nanocomposite exhibits a mixed intercalated/exfoliated morphology. The nano-morphology of the nanocomposites was characterized by means of X-ray diffraction and TEM. FTIR was used to verify the presence of hydrogen bonds between PMMA and the surface phenol groups, and in addition, the interaction between PMMA and the surface oxygens of silicates.     

Phosphate-intercalated Ca-Fe-layered double hydroxides: Crystal structure, bonding character, and release kinetics of phosphate

The nitrate-form of Ca-Fe-layered double hydroxide (Ca-Fe-LDH) was synthesized via co-precipitation method, and its phosphate-intercalates were prepared by ion-exchange reaction. According to X-ray diffraction analysis, the Ca-Fe-LDH-NO₃⁻ compound and its H₂PO₄⁻-intercalate showed hexagonal layered structures, whereas the ion-exchange reaction with HPO₄²⁻ caused a frustration of the layer ordering of LDH. Fe K-edge X-ray absorption spectroscopy clearly demonstrated that the Ca-Fe-LDH lattice with trivalent iron ions was well-maintained after the ion-exchange with HPO₄²⁻ and H₂PO₄⁻. Under acidic conditions, phosphate ions were slowly released from the Ca-Fe-LDH lattice and the simultaneous release of hydroxide caused the neutralization of acidic media. Fitting analysis based on kinetic models indicated a heterogeneous diffusion process of phosphates and a distinct dependence of release rate on the charge of phosphates. This study strongly suggested that Ca-Fe-LDH is applicable as bifunctional vector for slow release of phosphate fertilizer and for the neutralization of acid soil.     

诺氟沙星插层镁铝水滑石新型药物-无机复合材料的超分子结构、热稳定性和缓释性能

采用共沉淀和离子交换方法将抗生素类药物诺氟沙星(Nor)插入到Mg-Al-LDHs层间, 制备了一种新型的药物-无机复合材料. 借助XRD, FTIR, UV-Vis, TG-DTA和ICP等手段对样品进行了表征. 结果表明, Nor-阴离子可取代层间的NO3-, 组装得到晶体结构良好的Nor-LDHs. XRD表征得到Nor-LDHs的层间距为1.29~1.33 nm, 并与根据PM3半经验分子轨道法优化计算得到的Nor-三维尺寸进行比较, 推测客体Nor-是沿短轴方向以单层垂直交替的方式排布于层间, 与主体层板通过氢键与静电作用形成超分子结构; 该超分子结构诺氟沙星-水滑石复合材料与诺氟沙星相比, 其热稳定性、耐酸性及缓释性能均有大幅度提高, 缓释实验数据符合Bhaskar方程和一级动力学方程模型.