Structural studies of Na-montmorillonite exchanged with Fe2+, Cr3+, and Ti4+ by N2 adsorption and EXAFS

The structures of Fe(2+)-, Cr(3+)-, and Ti(4+)-modified montmorillonite prepared from ion exchange of the Na-clay with Fe(2+), Cr(3+), and Ti(4+) were investigated. Conventional BET surface area and spectroscopic analysis by extended adsorption fine structure (EXAFS) were applied. It was shown that the BET surface area of Na-clay was similar to that of Fe-clay, but somewhat different from those of Cr- and Ti-clay; it decreased in the order Na- > Fe- > Ti- > Cr-montmorillonite. This sequence appeared to be consistent with the ion size Na(+) (0.95 nm)>Fe(2+) (0.65 nm)>Cr(3+) (0.62 nm), except for Ti(4+) (0.69 nm). EXAFS data showed that some Si atoms within montmorillonite were replaced by Ti atoms and that a neostructure of titanium oxide was formed.     

Characterization of Anilinepentacyanoferrate (II) and (III)

The anilinepentacyanoferrate (II) complex has been characterized in aqueous solution. The complex exhibits a predominant ligand field transition at λ_max = 415 nm with ?_max = 494 M^?1 cm^?1. The corresponding Fe(III) complex displays a strong absorption at λ_max = 700nm(?_max = 1.61×10⁴ M^?1 sec^?1) which can be assigned as a ligand to metal charge transfer transition. The rate constants of formation and dissociation for the Fc(II) complex are (3.14±0.18)×10² M^?1W^?1 and 0.985±0.005 sec^?1, respectively, at μ = 0.10 M LiClO₄, pH = 8 and T = 25°C. The cyclic voltammetry of the complex shows that a reversible redox process is observed with E_1/2 value of 0.51±0.01 V vs. NHE at μ = 0.10 M LiClO₄, pH = 8 and T = 25°C. The kinetic study of the oxidation of the Fe(II) complex by ferricyanide ion yielded the rate constant of the reaction k_et = (1.43±0.04)x10 M sec^?1 at μ = 0.10 M LiClO₄, pH = 8 and T = 25°C.     

Stable second‐order NLO semi‐IPN system based on bipyridine‐containing polyimide and alkoxysilane dye

An organosoluble polyimide based on bipyridyl moiety and an alkoxysilane dye have been developed for second‐order non‐linear optics (NLOs). This bipyridine‐containing polyimide exhibits a glass transition temperature of 254°C and a degradation temperature of 400°C. An NLO‐active semi‐interpenetrating network (IPN) system was prepared by blending the polyimide with the alkoxysilane dye via in situ sol‐gel process of alkoxysilane. The selection of this bipyridine‐containing polyimide as the polymeric matrices provides improved solubility and thermal stability, and most importantly enhanced intermolecular interactions. No aggregation of the NLO chromophores in the polyimide matrices was observed through morphology and NLO studies. Under the limitation of chromophore degradation at elevated temperatures, the pristine poled/cured alkoxysilane dye exhibits poorer long‐term stability. By introducing the polyimide upon a silica network by the semi‐IPN system, randomization of the oriented chromophores can be effectively suppressed. Using in situ contact poling, the r₃₃ coefficients of 2.2–17.0 pm/V were obtained for the optically clear semi‐IPN NLO materials. Excellent temporal stability (100°C) was also achieved for these semi‐IPN materials. Copyright © 2005 John Wiley & Sons, Ltd.     

Adsorption of tannic acid, humic acid, and dyes from water using the composite of chitosan and activated clay

Chitosan is a well-known excellent adsorbent for a number of organics and metal ions, but its mechanical properties and specific gravity should be enhanced for practical operation. In this study, activated clay was added in chitosan slurry to prepare composite beads. The adsorption isotherms and kinetics of two organic acids (tannic acid, humic acid) and two dyes (methylene blue, reactive dye RR222) using composite beads, activated clay, and chitosan beads were compared. With composite beads as an adsorbent, all the isotherms were better fitted by the Freundlich equation. The adsorption capacities with composite beads were generally comparable to those with chitosan beads but much larger than those with activated clay. The pseudo-first-order and pseudo-second-order equations were then screened to describe the adsorption processes. It was shown that the adsorption of larger molecules such as tannic acid (MW, 1700 g mol(-1)), humic acid, and RR222 from water onto composite beads was better described by the pseudo-first-order kinetic model. The rate parameters of the intraparticle diffusion model for adsorption onto such adsorbents were also evaluated and compared to identify the adsorption mechanisms.     

A dedicated small‐angle X‐ray scattering beamline with a superconducting wiggler source at the NSRRC

At the National Synchrotron Radiation Research Center (NSRRC), which operates a 1.5 GeV storage ring, a dedicated small‐angle X‐ray scattering (SAXS) beamline has been installed with an in‐achromat superconducting wiggler insertion device of peak magnetic field 3.1 T. The vertical beam divergence from the X‐ray source is reduced significantly by a collimating mirror. Subsequently the beam is selectively monochromated by a double Si(111) crystal monochromator with high energy resolution (ΔE/E? 2 × 10^?4) in the energy range 5–23 keV, or by a double Mo/B₄C multilayer monochromator for 10–30 times higher flux (～10¹¹ photons s^?1) in the 6–15 keV range. These two monochromators are incorporated into one rotating cradle for fast exchange. The monochromated beam is focused by a toroidal mirror with 1:1 focusing for a small beam divergence and a beam size of ～0.9 mm × 0.3 mm (horizontal × vertical) at the focus point located 26.5 m from the radiation source. A plane mirror installed after the toroidal mirror is selectively used to deflect the beam downwards for grazing‐incidence SAXS (GISAXS) from liquid surfaces. Two online beam‐position monitors separated by 8 m provide an efficient feedback control for an overall beam‐position stability in the 10 µm range. The beam features measured, including the flux density, energy resolution, size and divergence, are consistent with those calculated using the ray‐tracing program SHADOW. With the deflectable beam of relatively high energy resolution and high flux, the new beamline meets the requirements for a wide range of SAXS applications, including anomalous SAXS for multiphase nanoparticles (e.g. semiconductor core‐shell quantum dots) and GISAXS from liquid surfaces.     

The wavelet transform method applied to a coupled chaotic system with asymmetric coupling schemes

The wavelet transform method originated by Wei et al. (2002) [19] is an effective tool for enhancing the transverse stability of the synchronous manifold of a coupled chaotic system. Much of the theoretical study on this matter is centered on networks that are symmetrically coupled. However, in real applications, the coupling topology of a network is often asymmetric; see Belykh et al. (2006)  [23], [24], Chavez et al. (2005)  [25], Hwang et al. (2005)  [26], Juang et al. (2007)  [17], and Wu (2003)  [13]. In this work, a certain type of asymmetric sparse connection topology for networks of coupled chaotic systems is presented. Moreover, our work here represents the first step in understanding how to actually control the stability of global synchronization from dynamical chaos for asymmetrically connected networks of coupled chaotic systems via the wavelet transform method. In particular, we obtain the following results. First, it is shown that the lower bound for achieving synchrony of the coupled chaotic system with the wavelet transform method is independent of the number of nodes. Second, we demonstrate that the wavelet transform method as applied to networks of coupled chaotic systems is even more effective and controllable for asymmetric coupling schemes as compared to the symmetric cases.     

Power Generation Capabilities of Microbial Fuel Cells with Different Oxygen Supplies in the Cathodic Chamber

Two microbial fuel cells (MFCs) inoculated with activated sludge of a wastewater treatment plant were constructed. Oxygen was provided by mechanical aeration in the cathodic chamber of one MFC, whereas it was obtained by the photosynthesis of algae in the other. Electrogenic capabilities of both MFCs were compared under the same operational conditions. Results showed that the MFC with mechanical aeration in the cathodic chamber displayed higher power output than the one with photosynthesis of algae. Good linear relationship between power density and chemical oxygen demand (COD) loading rate was obtained only on the MFC with mechanical aeration. Furthermore, the relationships between power density and effluent COD and between Coulombic efficiency and COD loading rate can only be expressed as binary quadratic equations for the MFC with mechanical aeration and not for the one with photosynthesis of algae.     

Proteomic analysis of chondrocytes exposed to pressure

Chondrocytes are the only cell type present in mature articular cartilage (2-5% of total tissue). The biological activities of the chondrocyte population are regulated by genetic, biologic and biochemical factors, as well as environmental factors (stress, flow and electric field). Although compressive forces within joint articular cartilage are required for maintenance of the normal composition of articular cartilage, there is a lack of knowledge about the number of pressure-related proteins expressed in articular cartilage. Two-dimensional gel electrophoresis (2-DE) and high-performance liquid chromatography-electrospray/tandem mass spectrometry (HPLC/ESI-MS/MS) were used to identify the levels of pressure-related proteins expressed by chondrocytes grown in the presence or absence of hydrostatic pressure. A total of 266 spots were excised from the gels and analyzed by HPLC/ESI-MS/MS. Functional classification of up-regulated proteins indicated that energy and protein fate were the main biological processes occurring in pressurized chondrocytes. Furthermore, membrane-bound transferrin-like protein p97, a marker of chondrocyte differentiation, was only expressed in chondrocytes under hydrostatic pressure. These data suggest that hydrostatic pressure can induce cell differentiation by increasing the expression level of energy metabolism- and protein fate-related proteins, indicating that hydrostatic pressure may be needed for normal biosynthesis and differentiation of articular chondrocytes.