Interaction of functionalized benzene molecules with carbon nanopores Douglas L. Irving a , Susan B. Sinnott a, * , Angela S. Lindner b a Department of Materials Science and Engineering, University of Florida, 154 Rhines Hall, Gainesville, FL 32611-6400, USA b Department of Environmental Engineering Sciences, University of Florida, Gainesville, FL 32611, USA Received 9 February 2004; in final form 16 March 2004 Published online: Abstract Benzene and its substituted analogs are considered hazardous because of their high risk to public health and the environment. Porous carbon materials are widely studied for their potential ability to act as a filter of carcinogenic materials. This study uses first- principles calculations to explore the selective adsorption of benzene and benzenes with substituents varying in electronegativity and size in a graphitic slit and (9,9) carbon nanotubes. The results show that the molecular adhesion energies are dependent on the bulkiness of substituent but are much less dependent on their electronegatives. Ó 2004 Elsevier B.V. All rights reserved. 1. Introduction Porous carbon materials are used to absorb, separate and purify molecular mixtures in a variety of applica- tions [1]. Organic molecules have been shown to have a particularly high affinity for the interiors of carbon pores [2,3]. Carbon nanotubes are a relatively new class of porous carbon material that have been under inves- tigation for some time for gas storage [4,5] and the separation of molecular mixtures [6]. Membranes com- posed of carbon nanotubes have recently been synthe- sized and found to function well in molecular separations [7]. Benzene and many of its substituted analogues be- long to a class of 188 compounds designated by the US Environmental Protection Agency [8] as ‘hazardous air pollutants,’ or ‘air toxics’ [9]. Exposure to these chemi- cals from sources such as chemical plants, oil refineries, and gas stations results after contact with contaminated air, foods, or water. Forty-five air toxics standards ap- plying to 82 categories of major industrial sources have been issued thus far by the US EPA [9]. Given the in- creasing stringency of these standards, new technologies for effective removal of these compounds are in demand. In this Letter, we report the results of first-principles calculations that are used to study the effect of adding substituents to benzene on the adhesion energy to ideal graphitic silts and carbon nanotube (CNT) systems. This work presents a first basis for study of the effec- tiveness of carbon-based systems for removal of substi- tuted benzene compounds in traditional and new nanoporous carbon materials. 2. Computational details The approach followed in this study is density func- tional theory (DFT) [10–12] in the CASTEP ASTEP program [13,14], where plane-waves and the ultrasoft pseudopo- tentials of Vanderbilt [15] are used to treat the electronic wave functions. The plane-waves in the calculation are expanded to a kinetic energy cutoff of 380 eV for all calculations unless otherwise specified. The exchange- correlation contribution to the total energy is calculated using the gradient corrected local density approximation of Perdew and Wang (GGA-PW91) [16–18]. One k-point at the gamma point of the unit cell is used in the majority of the calculations. The convergence criteria * Corresponding author. Fax: +352-846-3355. E-mail address: sinnott@mse.ufl.edu (S.B. Sinnott). 0009-2614/$ - see front matter Ó 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.cplett.2004.03.073 Chemical Physics Letters 389 (2004) 96–100 www.elsevier.com/locate/cplett