Geometry Optimization as Molecular Modeling on Activating Carbon with Polypirrole
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Geometry Optimization as Molecular Modeling on Activating Carbon with Polypirrole Y.C. Esquivel Aguilar1, J.H. Pacheco Sánchez1 1
División de Estudios de Posgrado e Investigación, Instituto Tecnológico de Toluca, Metepec 52149, México Abstract Activation of carbon using polypyrrole as activating agent is searched through Molecular Modeling. The Geometry Optimizations carried out helped to observe carbon effect when is attacked by a polymer in order to give an estimation of the pore size diameter of carbon. In this first approximation pore size diameters is about 30 % with respect to BET (Brunauer, P. Emmett y E. Teller) isotherms experimental data. Keywords: activated carbon, pyrrole polymer, density functional. INTRODUCTION Unlike carbon, the activated carbon has a structure formed by spaces or gaps which determine the adsorption property of the material. The parameters characterizing an activated carbon since the viewpoint of adsorbing capacity are: the surface area, pore distribution and pore size [1]. The pores classified by their size have pore sizes diameters (psd) ranging at micropores (psd < 2.0 nm), mesopores (2.0 nm < psd 5.0 nm) [2]. It is known that the storage capacity of some electronic devices increases when porosity of the activated carbon of its electrodes grows since micropore up to mesopore [3], it means there is an increased pore size. The voids of the porous structure of the activated carbon are microscopic in size. Pyrrole is an aromatic organic compound made up five-membered rings [𝐶4 𝐻5 𝑁]𝑛 as its chemical formula, where 𝑛 = 1,2,3,4,5, … .., is the molecules number as shown in Figure 1a. Figure 1b exhibits one polypyrrole polymer chain of three units.
a)
b)
Fig.1 a) Pyrrole, b) Polypyrrole
Molecular interactions occur when the molecules are close enough, due to intermolecular forces of attraction and repulsion, which provide stability to the bond between several molecules. These forces generate an asymmetrical potential well with the location of the minimum potential which corresponds to the equilibrium magnitudes of distance and bonding force. [4].The geometry optimization is an iterative process attempting to find a minimum in the potential energy surface (PES) [4], different lengths and bond angles up to a point where the molecular structures are balanced or stable.
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METHODOLOGY For analysis in the ground state of the electronic structures of simulated systems a functional of the electronic energy minimized with respect to the electron density was used. Such method is known as Density Functional Theory [5]. It was investigated about CA-pyrrole interaction using C1 symmetry group, by means of an electronic structure model proposed by Delley [6]. The density functional proposed by Perdew [8] for an exchange gradient corrected of exchange potential is used in a self
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