A first principles study of CO 2 adsorption is presented for a group of metal-organic frameworks (MOFs) known as CPO-27-M, where M ¼ Mg, Mn, Fe, Co, Ni, Cu, and Zn. These materials consist of onedimensional channels with a high concentration of open metal sites and have been identified as among the most promising MOFs for CO 2 capture. In addition, extensive, high-pressure, experimental adsorption results are reported for CO 2 , CH 4 , and N 2 at temperatures ranging from 278 K to 473 K. Isosteric heats of adsorption were calculated from the variable-temperature isotherms. The binding energies of CO 2 calculated using an MP2-based QM/MM method are in good agreement with those obtained from experiments. The relative CO 2 binding strengths for the different transition metals can be explained by the relative strength of electrostatic interactions caused by the effective charge of the metal atom in the direction of the open metal site induced by incomplete screening of 3d electrons. The Mn, Fe, Co, Ni, and Cu versions of CPO-27 are predicted to be anti-ferromagnetic in their ground states. Selectivities for CO 2 over CH 4 or N 2 were calculated from the experimental isotherms using ideal adsorbed solution theory.
Silver‐loading asymmetric cellulose acetate (CA) hollow fiber membrane was spun via the dry jet‐wet spinning technique. The spinning solution was prepared by dissolving AgNO3 and CA in N,N‐dimethylformamide (DMF). The silver ions were reduced in the spinning dope into silver nano‐particles. The morphology of the resulting hollow fibers was examined using a scanning electron microscope and the silver content in the fiber was measured using an inductively coupled plasma atomic emission spectrometer. The antibacterial activities were evaluated. These hollow fibers had a sponge‐like structure and dense inner and outer surfaces. At a 50 k magnification, the pore on the skin layer was not observable, while the nodule size was smaller than 10 nm. The residual silver content of as‐spun hollow fiber was about 60% of the original silver added in the polymer solution. After immersing in water bath for 180 days, the silver content in the bulk of the hollow fibers decreased to 60% and the silver content on the surface reduced to 10%, yet still showed antibacterial activity against Escherichia coli and Staphylococcus aureus. After permeating with water for 5 days, the silver content in the hollow fibers decreased, and did not show antibacterial activity against E. coli and S. aureus. Thus, silver content must be periodically replenished after permeation. The proper range of AgNO3 in the spinning solution for CA hollow fiber should be about 100–1000 ppm. Copyright © 2005 John Wiley & Sons, Ltd.
We demonstrate a new method (U.S. Patent Appl., serial no. 60/908039) for synthesizing carbon nanotubes (CNTs), using first-principles and classical molecular dynamics simulations. The single-walled nanotubes (SWNTs) are formed by folding graphene nanoribbons patterned on graphite films through adsorption of atoms of varying coverage, which introduces an external stress to drive the folding process. The diameter and chirality of SWNTs can be a priori controlled by patterning graphene nanoribbons with predefined width and direction so that the postsynthesis sorting process is eliminated. Our method allows potentially mass production of identical tubes and easy integration into device structures on a substrate.
We predict a new class of 2-D crystalline "bulk" magnets-the graphene nanohole (GNH) superlattices with each GNH acting like a "super" magnetic atom, using first principles calculations. We show that such superlattices can exhibit long-range magnetic order above room temperature, with a collective magnetic behavior governed by inter-NH spin spin interactions in additional to intra-NH spin ordering. Furthermore, magnetic semiconductors can be made by doping magnetic NHs into semiconducting NH superlattices. The possibility of engineering magnetic GNHs for storage media and spintronics applications is discussed. KEYWORDSGraphene, magnetism, spin, magnetic semiconductor, superlattice Nanostructured magnetic materials have a wide range of applications, such as being used for storage media. Magnetism is commonly associated with elements containing localized d or f electrons, i.e., the itinerant ferromagnetism [1,2]. In contrast, the elements containing diffuse sp electrons are intrinsically nonmagnetic, but magnetism can be induced in sp-element materials extrinsically by defects and impurities. There have been continuing efforts in searching for new magnetic nanomaterials, and much recent interest has been devoted to magnetism of carbon-based [3 7] , especially graphene-based structures [8 18] such as graphene nanoribbons [8,9,11,18] and nanoflakes [16,17]. Graphene nanoribbons [8,9,11,18] and nanoflakes [16,17] with zigzag edges have been shown to exhibit magnetism, originated from the localized edge states that give rise to a high density of states at the Fermi level rendering a spin-polarization instability [1]. However, these structures exhibit only local magnetization, lacking the long-range magnetic order with a well-defined transition temperature. Also, it is practically diffi cult to control the magnetic properties of individual nanoribbons and nanofl akes and integrate them into devices.Here we predict a new class of graphene-based magnetic nanostructures, the superlattices of graphene nanoholes (GNHs), which exhibit long-range magnetic order and collective "bulk" magnetism. This allows us to go beyond the current scope limited to the spins within a single nanoribbon or nanoflake. In fact, the superlattices consisting of a periodic array of NH spins form a unique family of magnetic 2-D crystals with the NH acting like a "super" magnetic atom. Their collective magnetic behavior depends on not only the local intra-NH spin property but also the long-range inter-NH spin spin interactions. The type of magnetic order, i.e., ferromagnetic (FM) vs antiferromagnetic (AF), can be controlled by using different NH shapes and superlattice symmetries, and the ordering Nano Research 57 Nano Res (2008) 1: 56 62 temperature can be tuned by NH size and density well above room temperature. It is also possible to combine magnetic NHs with nonmagnetic semiconducting NHs to form magnetic semiconductors. Our fi ndings represent a unique organic material exhibiting collective "bulk" magnetism, with significant implications in study...
The present study evaluates the morphological changes in root canal walls and temperature changes at root surfaces as a result of intracanal irradiation by erbium,chromium:YSGG laser under various conditions in vitro. Sixty single-rooted human teeth were examined. Root canals were prepared, and laser irradiation was performed using an optic fiber at output powers ranging from 1 to 6 W with or without water spray cooling. Specimens were evaluated by stereoscopy, scanning electron microscopy, and thermography. Carbonization and cracks were observed in all samples irradiated without cooling, whereas little or no carbonization and no smear layer or debris were observed in samples irradiated with cooling. Maximum temperature rise at irradiation without cooling was above 37 degrees C, whereas that at irradiation with cooling was 8 degrees C. Results of the present study indicate that erbium,chromium:YSGG laser irradiation with water spray cooling is a useful method for removal of smear layer and debris from root canals.
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