Computational study of CO and NO adsorption on magnesium oxide nanotubes Javad Beheshtian a , Mohammad Kamfiroozi b , Zargham Bagheri c , Ali Ahmadi d,n a Department of Chemistry, Shahid Rajaee Teacher Training University, P.O. Box 16875-163, Tehran, Iran b Department of Chemistry, Islamic Azad University, Shiraz Branch, Shiraz, Iran c Physics Group, Science Department, Islamic Azad University, Islamshahr Branch, P.O. Box 33135-369, Islamshahr, Tehran, Iran d Young Researchers Club, Islamic Azad University, Islamshahr Branch, Tehran, Iran article info Article history: Received 8 August 2011 Received in revised form 3 September 2011 Accepted 13 September 2011 Available online 22 September 2011 abstract The adsorption of CO and NO molecules on the MgO nanotubes was investigated using density functional theory calculations. The adsorption energies of CO and NO were estimated to ranging from 0.35 to  0.16 eV and  0.28 to 0.13 eV, respectively. The most stable adsorption configurations are those in which the C or N atoms the adsorbates are close to the Mg atom of the tube surface. It was found that the MgO nanotubes selectively act against the CO and NO gaseous molecules. Their electrical conductivity are sensitive to NO gaseous molecule while is not to CO one, indicating that they may be potential sensors for NO molecule. These findings are characterized by analyzing the features in the electron density of states. Crown Copyright & 2011 Published by Elsevier B.V. All rights reserved. 1. Introduction The importance of environmental gas monitoring and control- ling is now recognized as an important area and much research has been focused on the development of suitable gas-sensitive materials for continuous monitoring and setting off alarms for hazardous chemical vapors present beyond specified levels [1–3]. Nitrogen oxide and carbon monoxide are known to be extremely harmful to the human body and also a main cause of air pollution. Therefore, effective methods have been highly demanded to monitor and suppress the nitrogen oxide for atmospheric envir- onmental measurements and controls [4,5]. Gas sensor devices have traditionally comprised thin films of metal oxides, with tin oxide, zinc oxide and indium oxide being some of the most common materials employed. With the recent discovery of novel metal oxide nanostructures, sensors compris- ing nanoarrays or single nanostructures have shown improved performance over the thin films [6,7]. These sensors have been shown to function at lower temperatures, making them ideal for biological applications as well as offering lower operating costs. One of the most common metal oxides that have been synthesized in a range of nanostructure morphologies is magne- sium oxide (MgO) [8]. The MgO is considered as a model system for solid state and surface studies because of its simple structure and ionic bonding. It also exhibits catalytic activity for a wide variety of reactions [9]. It has been established that the catalytic activity of MgO is due to a small number of defect sites (steps, kinks, corners, etc.) with surface ions, particularly oxygen, having low coordination numbers. MgO is particularly interesting in nanoparticle form. It has been possible to prepare MgO in very high surface area (500 m 2 /g) with average crystallite sizes of about 4 nm [10]. The high surface areas and the intrinsically high surface reactivity allow these materials to be especially effective as adsorbents [11]. Kakkar et al. have studied the electronic and geometrical structures of MgO nanotubes (MgONTs) by density functional theory (DFT) calculations. They have found several modes of adsorption for formaldehyde on the MgO nanosurfaces. Depend- ing upon the coordination site, different adsorption products are formed and all the reactions are highly exothermic [12,13]. Here, we report a theoretical study on the adsorption of CO and NO on the MgONTs. In this work, computations based on DFT calculations were performed to elucidate the relationship between the electronic structures of MgONT and the character- istics of adsorbed molecules. 2. Computational methods Geometry optimizations, molecular electrostatic potential (MEP) and density of states (DOS) analyses were performed on a6  5 MgONT and different NO- or CO -MgONT configurations at the spin-unrestricted B3LYP/6-31G* level of theory as implemen- ted in Gaussian 98 suite of program [14]. The B3LYP/6-31G* is a Contents lists available at SciVerse ScienceDirect journal homepage: www.elsevier.com/locate/physe Physica E 1386-9477/$ - see front matter Crown Copyright & 2011 Published by Elsevier B.V. All rights reserved. doi:10.1016/j.physe.2011.09.016 n Corresponding author. Tel.: þ98 912 5061827. E-mail address: ahmadi.iau@gmail.com (A. Ahmadi). Physica E 44 (2011) 546–549