Showing papers in "The Journal of Physical Chemistry in 2008"

A microporous metal-organic framework for separation of CO2/N-2 and CO2/CH4 by fixed-bed adsorption

Abstract: A microporous MOF Zn(BDC)(4,4‘-Bipy)0.5 (MOF-508b, BDC = 1,4-benzenedicarboxylate, 4,4‘-Bipy = 4,4‘-bipyridine) was examined for the separation and removal of CO2 from its binary CO2/N2 and CO2/CH4 and ternary CO2/CH4/N2 mixtures by fixed-bed adsorption. With one-dimensional pores of about 4.0 × 4.0 A to induce their differential interactions with the three components, MOF-508b exhibits highly selective adsorption to CO2 with the adsorption capacity of 26.0 wt % at 303 K and 4.5 bar. This is the first example of microporous MOFs for the separation and removal of CO2 from its binary and ternary mixtures by fixed-bed adsorption, establishing the feasibility of the emerging microporous MOFs for their potential applications in this very important industrial and environmental process.

Molecular Dynamics of Ionic Transport and Electrokinetic Effects in Realistic Silica Channels

Abstract: Silica is one of the most widely used inorganic materials in experiments and applications involving aqueous solutions of biomolecules, nanoparticles, etc. In this paper, we construct a detailed atomistic model of a silica interface that captures the essential experimentally known properties of a silica interface. We then perform all-atom molecular dynamics simulations of a silica nanochannel subjected to either an external pressure or an electric field and provide an atomistic description of ionic transport and both electro-osmotic flow and streaming currents for a solution of monovalent (0.4 M NaCl) as well as divalent (0.2 and 1.0 M CaCl{sub 2}) salts. Our results allow a detailed investigation of {zeta}-potentials, Stern layer conductance, charge inversion, ionic mobilities, as well as continuum theories and Onsager relations. We conclude with a discussion on the implications of our results for silica nanopore experiments and micro- and nanofluidic devices.

pH-Dependent Adsorption and Conformational Change of Ferritin Studied on Metal Oxide Surfaces by a Combination of QCM-D and AFM

Abstract: In this work, we have identified key parameters for controlling the surface density of ferritin on metal oxides and observed a conformational change of the protein shell of ferritin occurring exclusively at pH 4. The quartz crystal microbalance with dissipation (QCM-D) monitoring technique was used to examine protein adsorption on gold and Ti-, Si-, Ta-, Al-, and Nb-oxide surfaces. A comparative study of the adsorption to Ti-oxide was made using atomic force microscopy (AFM). The surface density of ferritin was controlled by a variation in the solution pH (from 2 to 8) and the isoelectric point (Ip) of the surface. On the basis of these findings, clear trends in the effect of electrostatic interactions between the ferritin proteins and between ferritin and the surface were found, making it possible to tune the surface density of ferritin through the choice of solution pH and the Ip of the surface. Furthermore, the influence of the pH on the viscoelastic properties of the adsorbed ferritin layer was examin...

Charging of Aerosol Products during Ferrocene Vapor Decomposition in N2 and CO Atmospheres

Abstract: Decomposition of ferrocene vapor in CO and N2 atmospheres in the temperature range from 800 to 1150 °C leading to the formation of single-walled carbon nanotubes (CNTs) and maghemite (γ-Fe2O3) part...

Electronic structure of transition metal-cysteine complexes from X-ray absorption spectroscopy

Abstract: The electronic structures of HgII, NiII, CrIII, and MoV complexes with cysteine were investigated by sulfur K-edge X-ray absorption near-edge structure (XANES) spectroscopy and density functional theory. The covalency in the metal-sulfur bond was determined by analyzing the intensities of the electric-dipole allowed pre-edge features appearing in the XANES spectra below the ionization threshold. Because of the well-defined structures of the selected cysteine complexes, the current work provides a reference set for further sulfur K-edge XAS studies of bioinorganic active sites with transition metal-sulfur bonds from cysteine residues as well as more complex coordination compounds with thiolate ligands.

Carbon-13 NMR Relaxation Study of 1,8-Bis(dimethylamino)naphthalene in Isotropic Solution

Abstract: Nuclear spin relaxation in dimethylformamide-d7 solution of1,8-bis(dimethylamino)naphthalene (DMAN) was investigated. Detailed analysisof 13C longitudinal relaxation in this molecule yielded its rotationaldiffusion tensor. Comparison to protonated form of DMAN, DMANH+, leads toconclusions concerning interaction of the latter with its counterion.