Theoretical Study of Sarin Adsorption On
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Chemical Physics Letters 738 (2020) 136816 Contents lists available at ScienceDirect Chemical Physics Letters journal homepage: www.elsevier.com/locate/cplett Research paper Theoretical study of sarin adsorption on (12,0) boron nitride nanotube doped with silicon atoms T ⁎ ⁎ Jeziel Rodrigues dos Santosa, , Elson Longo da Silvab, Osmair Vital de Oliveirac, , José Divino dos Santosa a Universidade Estadual de Goiás, Campus Anápolis, CEP: 75.132-903 GO, Brazil b INCTMN, LIEC, Departamento de Química da Universidade Federal de São Carlos, CEP: 13.565-905 São Carlos, SP, Brazil c Instituto Federal de Educação, Ciência e Tecnologia de São Paulo, Campus Catanduva, CEP: 15.808-305 Catanduva, SP, Brazil HIGHLIGHTS • DFT method was used to study the adsorption of nerve agent sarin by BNNT. • Electronic properties of pristine BNNT are improved by Si impurity atoms. • The adsorption of sarin by Si-doped BNNT is highest favorable than the pure BNNT. • Si-doped BNNT can be a new gas sensor for sarin gas detection and its derivatives. ARTICLE INFO ABSTRACT Keywords: Sarin gas is one of the most lethal nerve agent used in chemical warfare, which its detection is import to prevent Nerve agent sarin a chemical attack and to identify a contamination area. Herein, density functional theory was used to investigate Gas sensor the (12,0) boron nitride nanotube (BNNT) and Si–doped BNNT as possible candidates to sarin detection. The Si- Boron nitride nanotube atoms doped improve the electronic properties of nanotubes by altering the electrostatic potential, HOMO and DFT LUMO energies. Based in the adsorption energies and the conductivity increased to ~33 and 350%, respectively, for Si- and 2Si-BNNT imply that they can be used for sarin detection. 1. Introduction War II, Iraq/Iran War (1981–1989), in the Tokyo subway attack (1995), in the Syrian Civil War (2012), and recently in the Syrian attack in Neurotoxic chemical agents are a class of substances which direct 2017. Therefore, the detection of sarin can be useful for military and and indirectly perturb the Human and animal nervous system by acting civil defense to prevent chemical attack using this neurotoxic agent and in the neural cell or in the metabolic process of this system [1]. These others. In this way, different methodologies have been used to detect substances are chemically classified into the organophosphorus group chemical agents like infrared spectroscopy [3], mobility spectroscopy and they are organic compounds degradable. Moreover, these com- [4], calorimetric [5], surface acoustic waver sensors [6], electro- pounds are very harmful and/or lethal for Human, consequently they chemical detectors [7], carbon nanotube (CNT) chemical sensor [8]. has been used as high-impact military artifice in called chemical war- Among them, chemical sensors based in CNT have an advantage to fare. These agents inhibit the acetylcholinesterase irreversibly leading produce portable sensing method and they can be coupled with elec- the loss of the control of central nervous system. Among the neurotoxic trical devices as conductometric, electrochemical, and others [8]. agents, the most used in the chemical warfare are belong the G-series as However, CNTs offer non-specific sensing responses for nerve agent and tabun, sarin and soman gases, which these two last were developed their mimics. Another disadvantage, the electronic properties of CNTs during the World War II [2]. In this series, they are absorbed through are high dependent of their chirality [9]. So, the boron nitride nanotube the lungs causing seizures, loss of body control, paralyses muscles in- (BNNT) appears as an excellent candidate to substitute the CNT because cluding heart and diaphragm. Sarin gas is the most neurotoxic agent their electronic properties are independent of their diameter and chir- known and largely used in chemical attack. It was used in the World ality [10–12]. For instance, the band gap of the BNNT is 5–6eV[13,14] ⁎ Corresponding authors. E-mail addresses: [email protected] (J.R. dos Santos), [email protected] (O.V. de Oliveira). https://doi.org/10.1016/j.cplett.2019.136816 Received 14 August 2019; Received in revised form 13 September 2019; Accepted 1 October 2019 Available online 09 October 2019 0009-2614/ © 2019 Elsevier B.V. All rights reserved. J.R. dos Santos, et al. Chemical Physics Letters 738 (2020) 136816 independently of these properties. Therefore, the BNNT is an excellent optimized structures with minimum energy obtained at DFT method. insulator, contrary to CNTs which are semimetallic and semiconductor Overall, as can see in the Fig. 1, it was not observed significant material [15]. Moreover, BNNTs are stable in oxidation resistance and structural change in the BNNT doped with Si atoms. The main differ- it has high thermal resistance above 900 °C. Experimentally, BNNT was ence noted is attributed to the Si atoms that are outside of 0.09 nm from synthesized by first time in 1995 thought arc discharge [16], and ac- the B95N96SiH24 and B94N96Si2H24 surface. This is due the Van der tually others methods like chemical vapor deposition [17], laser abla- Waals radius (0.210 nm) of the Si atom to be slight high than the boron tion [18] and thermal plasma jet [19] are used to their synthesis. atom (0.192 nm). Wang [43] obtained this same geometrical distortion BNNTs have been applied for polymer composite reinforcement [20], in Si-doped BNNT using periodic DFT calculations. Regarding the for piezo actuators [21], drug carrier [22],infield emission technology structural change of nanotubes, the same pattern was observed for the [23,24], sensing [25,26], etc. Recently, the possible use of BNNTs as gas complexes, implying that the sarin adsorbed preserve the BNNT, sensor has attracted the attention of many researchers. In the manner B95N96SiH24 and B94N96Si2H24 structures. These observations are in that, theoretical methods were used to study the adsorption of oxazole concordance with the lowest root mean square deviation (RMSD) va- and isoxazole [27], hydrogen halides [28], hydrogen cyanide [29], lues (< 0.01 nm) calculated from the superposition between Si–doped carbon monoxide [30], cyanogen chloride [31] and ammonia [32] in BNNT and pristine BNNT structure. For sarin–BNNT, it was observed a BNNTs. Regarding the chemical agents, the adsorption of soman and shortest distance between the boron and oxygen atom (sarin) with chlorosoman by (8,0) BNNT [33], and a sarin derivative by (6,0) BNNT distance of 0.294 nm. Whereas, for the sarin–B95N96SiH24 and sar- [34] were studied at theoretical level. In both studies, the authors find in–B94N96Si2H24, this distance was, respectively, 0.165 and 0.178 nm. that these nerve agents interact weakly with pristine BNNT. Therefore, From the NBO analysis, it was confirmed that the oxygen bound to improve the BNNT electronic sensitivity, herein a large zigzag (12,0) covalently with Si atom of the B95N96SiH24 and partially with BNNT and it doped with silicon atoms were studied at density func- B94N96Si2H24 compounds with bond order of 1.11 and 0.63, respec- tional theory (DFT) with intention to enhance the sarin-BNNT inter- tively. Contrary, there is not formation of covalent bond between BNNT actions. For instance, Si-doped BNNT was forecast by Guerini [35] from and sarin, keeping bond order of 0.04. Therefore, the OeSi bond ob- theoretical methods, and posterior it was synthesized in 2009 by Cho tained in our calculations is in good agreement with experimental data [36] using thermal chemical vapor deposition. In both studies, it was (0.161 nm). For all nanotubes, the boron-nitrogen bond is confirmed the improvement of BNNT reactivity up replacing B by the Si 0.144–0.145 nm in excellent agreement with the hexagonal crystal atom. structure of the boron nitride (0.145 nm). In the next section, the electronic structures for pure compounds and for complexes are pre- 2. Methodology sented and discussed to understand the energetic process involved. The initial structure of the zigzag (12,0) BNNT formed by 96 boron 3.2. Electronic structure and 69 nitrogen atoms was built using a script written in-house. The end atoms were saturated by 24 hydrogen atoms to avoid the boundary The electronic properties were used to clarify the chemisorption – effects, forming the B96N96H24 compound. This nanotube model has 9.4 process of the sarin by BNNT and Si atoms doped BNNT. Initially, it is and 15.4 Å of diameter and length, respectively. For the complexes, the important evaluate the Si–doped BNNT stability, which this can be fi initial con gurations were built by positioning sarin (C4H10FO2P) mo- addressed by the formation energy (ΔEformation) using the equation, lecule in different regions around the BNNT and Si atoms–doped BNNT ΔE(EE)(EEformation=+−+ doped - BNNTnn B BNNT Si) (2) surfaces. The sarin, the pristine BNNT and it doped with Si atom (B95N96SiH24 in doublet state and B94N96Si2H24 in singlet state), and the where Edoped-BNNT is the total energy of one or two silicon doped with – – – complexes (sarin BNNT, sarin B95N96SiH24 and sarin B94N96Si2H24) BNNT, n is the number of Si or B atoms substituted, nEB is the total were optimized initially with the semiempirical Hamiltonian PM7 [37] energy B atom, EBNNT is the total energy of the pristine BNNT and nESi is using MOPAC2016 program [38]. Posteriorly, the structures with the total energy of Si atom. The ΔEformation values for B95N96SiH24 and minimum energies were re-optimized with DFT calculations con- B94N96Si2H24 are 3.46 and 8.30 eV, respectively. For 1Si–doped BNNT, sidering the B3LYP hybrid functional [39] with 6-31G(d) basis set. This the ΔEformation has low value compared to the reported in the literature procedure was chosen to balance the computational cost and quality of (4.06 eV) using DFT//B3LYP/ECP method [44], but these values are in the results.