Adsorption of Chemical Warfare Agents Over C24 Fullerene: Effects of Decoration of Cobalt

Journal of Alloys and Compounds 735 (2018) 2148e2161

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Journal of Alloys and Compounds

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Adsorption of chemical warfare agents over C24 fullerene: Effects of decoration of cobalt

* Alireza Soltani a, , Masoud Bezi Javan b, Mohammad T. Baei c, Zivar Azmoodeh d a Golestan Rheumatology Research Center, Golestan University of Medical Science, Gorgan, Iran b Physics Department, Faculty of Sciences, Golestan University, Gorgan, Iran c Department of Chemistry, Azadshahr Branch, Islamic Azad University, Azadshahr, Golestan, Iran d Young Researchers and Elite Club, Behshahr Branch, Islamic Azad University, Behshahr, Iran article info abstract

Article history: The present theoretical study suggests the adsorption of the chemical warfare agents (Soman, Chlor- Received 16 May 2017 osoman, Sarin, and Chlorosarin) over the pure and cobalt-decorated C24 fullerenes by using PBE func- Received in revised form tional. For all four species, adsorption on the C24 fullerene takes place via a CoeO]P dative covalent 16 October 2017 bond between a cobalt-decorated site. It has been indicated that the interaction between the chemical Accepted 28 November 2017 warfare agents and the cobalt-decorated C fullerene is more stable than that of the pure C fullerene. Available online 1 December 2017 24 24 We found that the cobalt-decorated C24 fullerene is the most favorable site for Sarin and Soman in comparison with Chlorosarin and Chlorosoman. In addition, the interactions of chemical warfare agents Keywords: C fullerene with cobalt-decorated C24 fullerene can be responsible to alter of the structural and electronic properties. 24 © Co adsorption 2017 Elsevier B.V. All rights reserved. Chemical toxic agents Density functional theory Thermodynamic stability

1. Introduction sensor [9e11], hydrogen storage [12,13], and biomedical applications [14,15]. Carbon nano-cages can be utilized to improve and The detection and removing from chemical warfare agents advance toxic gas detection technologies; it is substantial to (CWAs) are a substantial issue for our safety and health. The comprehend how each type of device may be appropriate [16,17]. C4H10FO2P (isopropyl methylphosphonofluoridate) and C7H16FO2P Rather and Wael investigated fullerene-C60 sensor for ultra-high (3, 3-dimethyl-2-buthyl methylphosphonoflouridate) or Sarin and sensitive detection of bisphenol molecule by green technology Soman, respectively, are extremely toxic substances belong to the [18]. For example, Shariatinia and Shahidi performed a DFT study class of organophosphorus compounds which are highly threat- upon the physical adsorption of cyclophosphamide derivatives on ening for the living organisms. The first utilization of Sarin was fullerene C60 surface [19]. Very recently, Sun and co-workers [20] reported when Iraqi army bombarded Iranian citizens in August have shown the interactions of low molecular weight natural 1988. Japanese cult used liquid Sarin to attack a building in Mat- organic acids with C60 in vacuum and water using Molecular dy- sumoto and the Tokyo subway in 1994 and 1995, respectively [1e4]. namics simulations (MD). Mahdy et al. reported that the transition To this time, several investigations into the adsorption of chemical metal doped fullerene C60 systems introduced as a promising warfare agents have been reported computationally [5e7]. candidate for the detection of CO and NO gases compared to the With the discovery of C60 fullerene by Korto et al., in 1985 [8], pure C60 [21]. Xu and co-workers theoretically investigated the search for highly stable cages with broad range of applications have structural and electronic properties of C24-glycine and Gd@C24- been significantly accelerated and reported. Several experimental glycine using the hybrid DFT-B3LYP functional [22]. It was found and theoretical reports have been directed towards the imple- that the adsorption of glycine from the amino nitrogen is ener- mentation of carbon nanostructures in applications like chemical getically favorable to interact with C24 nano-cage. Baei and co- workers reported a theoretical study of nicotine adsorption in different configurations over C24 nano-cage using B3LYP functional * Corresponding author. [23]. They found that the C24 nano-cage can be used as electronic E-mail addresses: [email protected], [email protected] sensor for nicotine detection. Recently, the interaction between (A. Soltani). https://doi.org/10.1016/j.jallcom.2017.11.350 0925-8388/© 2017 Elsevier B.V. All rights reserved. A. Soltani et al. / Journal of Alloys and Compounds 735 (2018) 2148e2161 2149

CWAs and materials was studied mainly upon the adsorptions of our knowledge, few reports have been performed on the adsorp- Soman and Sarin over Amorphous silica [24], gAl2O3 [25], Clay tion of Soman (SOF), Chlorosoman (SOC), Sarin (SAF), and Chlor- mineral fragments [26], and hydroxide brucite [27]. To the best of osarin (SAC) over carbon nanostructures and also Co decorated

Fig. 1. Adsorption conﬁgurations of Sarin (a), Chlorosarin (b), Soman (c), Chlorosoman (d) on the pure C24 fullerene.

Table 1

Optimized structural geometries of Sarin, Chlorosarin, Soman and Chlorosoman chemical agents interacting with the pure and Co-decorated C24 fullerenes using the PBE functional. Lengths are in angstrom (Å).

Property PeF/Ǻ P]O/Ǻ PeCl/Ǻ CeC/Ǻ CoeC/Ǻ CoeO/Ǻ O]PeO/ CeCoeO/

Sarin 1.631 1.489 eeee 117.4 e Chlorosarin e 1.492 2.103 ee e 117.7 e Soman 1.616 1.492 eeee 117.2 e Chlorosoman e 1.493 2.102 ee e 117.9 e

C24 ee e 1.492 eee e Sarin/C24 1.630 1.491 e 1.491 ee117.5 e Chlorosarin/C24 e 1.495 2.101 1.490 ee117.6 e Soman/C24 1.629 1.491 e 1.491 ee117.5 e Chlorosoman/C24 e 1.495 2.099 1.492 ee117.8 e CoeC24 ee e 1.542 1.952 ee e Sarin/CoeC24 1.614 1.510 e 2.156 1.827 1.991 117.4 153.1 Chlorosarin/CoeC24 e 1.520 2.071 1.540 1.940 1.950 116.7 150.3 Soman/CoeC24 e 1.525 2.063 1.542 1.938 1.950 116.8 148.2 Chlorosoman/CoeC24 1.611 1.513 e 2.158 1.828 1.995 117.4 150.4 2150 A. Soltani et al. / Journal of Alloys and Compounds 735 (2018) 2148e2161

Table 2

The structural and electronic parameters and quantum molecular descriptor of chemical warfare agents on the pure C24 fullerene.

Property C24 Sa(Cl) Sa(F) So(Cl) So(F) Sa(Cl)/C24 Sa(F)/ C24 So(Cl)/ C24 So(F)/ C24

EHOMO/eV 5.69 6.61 7.00 6.89 6.60 5.46 5.46 5.45 5.52 ELUMO/eV 4.49 0.77 0.79 1.26 0.73 4.26 4.26 4.24 4.32 Eg/eV 1.20 5.84 6.21 5.63 7.33 1.20 1.20 1.21 1.20 D/Debye 0.0 3.13 3.00 3.30 2.94 3.74 3.68 3.80 3.13

EF/eV 5.09 3.69 3.89 4.07 2.94 4.86 3.69 4.85 4.92 Ead/eV eeeee0.03 0.02 0.04 0.03 D/Ǻ eeeee0.03 0.02 0.04 0.03 I/eV 5.69 6.61 7.00 6.89 6.60 5.46 5.46 5.45 5.52 A/eV 4.49 0.77 0.79 1.26 0.73 4.26 4.26 4.24 4.32 h/eV 0.60 2.92 3.11 2.82 2.94 2.92 2.92 0.47 0.19 m/eV 5.09 3.69 3.90 4.08 3.67 3.69 3.69 4.18 4.05 S/eV-1 0.83 0.17 0.16 0.18 0.17 0.117 0.117 1.063 2.63 u/eV 21.59 2.33 2.44 2.95 2.29 1.593 1.593 18.573 43.13

DNmax 0.84 1.26 1.25 1.45 1.25 1.26 1.26 8.89 21.32

carbon nanostructure so in this research we are studying the adsorbents or sensor materials for the removal or detection of possibility of application of C24 and its Co decorated as an these toxic agents.

Fig. 2. Adsorption conﬁgurations of Sarin (e), Chlorosarin (f), Soman (g), Chlorosoman (h) on the Co-doped C24 nano-cage. A. Soltani et al. / Journal of Alloys and Compounds 735 (2018) 2148e2161 2151

2. Methodologies functional are 0.21 and 0.14 eV, respectively [41]. The NBO analysis shows a charge about 0.016 and 0.010 electrons are In the present work, all the calculations for the toxic agents transferred from C24 fullerene to SOC and SOF and the charges (Soman, Chlorosoman, Sarin, and Chlorosarin) adsorption over pure about 0.015 and 0.010 electrons are transferred from C24 fullerene and Co-doped C24 fullerenes have been carried out using GAUSSIAN to SAC and SAF, respectively, indicating that the chemical toxic 03 program package [28]. Subsequently, all the structures have agents do not interact strongly (physical adsorption) with the been optimized using density functional theory (DFT) with the exterior surface of C24 fullerene. Perdew-Burke-Ernzerhof (PBE) exchange-correlation functional [29] and 6-311þþG** standard basis set. For the Co atom, the 3.2. Adsorption of Sarin and Chlorosarin on Co-doped C standard LANL2DZ basis set was used throughout the calculations 24 [30]. The PBE density functional has been previously reported to The adsorptions of Sarin (SAF) and Chlorosarin (SAC) on the study carbon nanostructures [31e33]. Natural bond orbital (NBO) outer surface of Co-decorated C fullerene were studied at the GGA analysis was calculated by using PBE functional. Molecular elec- 24 level (PBE) as described in Fig. 2. Geometrical parameters and trostatic potential (MEP), HOMO and LUMO orbitals, and spin adsorption energies are calculated and reported in Tables 1 and 3. density plots of molecular configurations was generated with the Addition of cobalt impurity to nano-cluster leads to symmetry GaussView [34] program (Gaussian, Inc. Pittsburgh, PA). The cor- change from C4h (in the case of C24)toC4v (in the case of Co- responding binding energies (Eb) of the mentioned systems were decorated C24) splits the 3d shell into a doublet of eg (dxz,dyz) determined through the following equation: 2 2 2 symmetry and three singlets of a1g (dz ), b2g(dxy) and b1g(dx-y) symmetry. The calculated value of binding energy of cobalt adsor- Eb ¼ Eadsorbent-C24 e (Eadsorbent þ EC24) þ BSSE (1) bed on the surface of C24 fullerene is negative (0.53 eV), showing the interaction between two specious is exothermic in nature. Baei E ¼ E e (E þ E ) þ BSSE (2) b adsorbent-decorated-C24 adsorbent Decorated-C24 and co-workers [42] reported the doping of Co atom at the center of C fullerene is endothermic with an energy value of þ2.81 eV. where E and E are the total energies of 20 adsorbent-C24 adsorbent-doped-C24 Manna and co-workers [43] have shown the encapsulation of a soman, chlorosoman, sarin and chlorosarin as adsorbates over the plutonium atom within C leads to highly stable Pu@C fullerene. pure and Co-decorated C fullerenes as adsorbents. E is the 24 24 24 adsorbate After structural optimization, we found the chemisorption energy total energies of the soman, chlorosoman, sarin and chlorosarin of one SAC by using O atom upon the Co-decorated C molecules and E and E is the total energies of the 24 C24 Decorated-C24 about 1.29 eV and 0.11 electrons charges were transferred from pure and Co-decorated C fullerenes. The basis set superposition 24 the adsorbate to the fullerene as Co atom act as Lewis acid, error (BSSE) for the binding energy was computed by implement- accepting electron pair from Lewis base (O atom of SAC). Therefore, ing the counterpoise method. HOMO-LUMO gap energies, Natural the interactions between Co 3d electrons and O 2p lone pair elec- bond orbital (NBO), molecular electrostatic potential (MEP), partial trons both raise the energy of the 3d sublevel and lift the de- density of states (PDOS) analyses, and quantum molecular de- generacy of the 3d orbitals. The natural electron configuration of scriptors were calculated accordingly at the same level of theory cobalt atom in Co-decorated C fullerene is altered from [Ar] 4s0.07 according to previous literature reports [35e40]. 24 3d3.41 to [Ar] 4s0.30 3d7.93 and [Ar] 4s0.303d8.00 after the interaction with SAF and SAC chemical agents, respectively, while the natural 3. Results and discussion electron configurations of oxygen and phosphorous atoms are found to be [He] 2s0.89 2p2.64 and [He] 3s0.42 3p0.87 on the adsorp- 3.1. Adsorption of the chemical toxic agents on C24 fullerene 0.89 2.64 tion of SAF with Co-decorated C24 fullerene and He] 2s 2p and [He] 3s0.47 3p0.98 on the adsorption of SAC with Co-decorated We have considered here several adsorption configurations for per one of the toxic agents including Sarin (SAF), Chlorosarin (SAC), Soman (SOF), Chlorosoman (SOC) which participate in the inter- Table 3 action with the pure C24 nano-cage. After full structural optimiza- The thermodynamic and electronic parameters and quantum molecular descriptor tion without any constraints, the most stable structures are of chemical warfare agents on the Co-decorated C24 fullerene. obtained upon the relaxation processes which are shown in Fig. 1 Property CoC24 Sa(Cl)/CoC24 Sa(F)/CoC24 So(Cl)/CoC24 So(F)/CoC24 (See Fig. 1). We performed full structural relaxation in the C24 aEHOMO/eV 5.12 4.61 4.50 4.60 4.48 fullerene with each of the toxic agents to examine the equilibrium aELUMO/eV 4.41 3.70 3.58 3.69 3.56 geometries, energetic and electronic properties in Tables 1 and 2. aEg/eV 0.71 0.91 0.92 0.91 0.92 e After full optimization, we found the binding energies of Sarin and DEg/% 28.17 29.58 28.17 29.58 Chlorosarin on the surface of C fullerene is equal to 0.02 EF/eV 4.77 4.16 4.04 4.15 4.02 24 bEHOMO/eV 4.79 4.26 4.40 4.25 4.39 and 0.03 eV, respectively. In contrast, Soman and Chlorosoman bE /eV 4.44 3.94 3.90 3.94 3.92 LUMO adsorptions on the surface of C24 fullerene predict values of 0.03 bEg/eV 0.35 0.32 0.50 0.31 0.47 e and 0.04 eV, respectively. For all complexes, there is a little DEg/% 8.57 42.86 11.43 34.28 different from binding energy and the equilibrium height. As can be EF/eV 4.62 4.10 4.15 4.10 4.16 D/Debye 5.76 12.57 12.63 12.54 12.84 seen in Table 2, the equilibrium height of toxic agents with the C24 Ead/eV e 1.29 1.60 1.31 1.65 fullerene is 3.122 Å (SAC), 3.307 Å (SAF), 3.217 Å (SOC), and 3.318 Å D/Ǻ 1.950 1.939 1.830 1.938 1.828 (SOF) which predicts weak physisorption owing to van der Waals DG/eV e 1.60 2.06 1.51 2.15 forces between participating specious in the interaction process. DH/eV e 2.10 2.61 2.06 2.68 Our calculations present a small change in isometric structure of I/eV 5.12 4.61 4.50 4.60 4.48 A/eV 4.41 3.70 3.58 3.69 3.56 C24 fullerene. Vaise and co-workers [27] calculated the phys- h/eV 0.36 0.46 0.46 0.46 0.46 isorption of Sarin on brucite with an amount of 0.26 eV. Javan m/eV 4.77 4.16 4.04 4.15 4.02 et al. studied the physisorption of Soman and Chlorosoman over the S/eV-1 1.41 1.10 1.09 1.10 1.09 outer surface BN nanotube with the energy values of 0.052 u/eV 31.98 18.97 17.74 18.88 17.56 DN 13.25 9.04 8.78 9.02 8.74 and 0.098 eV at B3LYP functional, while these values at M06-2X max 2152 A. Soltani et al. / Journal of Alloys and Compounds 735 (2018) 2148e2161

C24 fullerene. The DG and DH values for SAC adsorbed from its 0.702 and 0.154 e, respectively. When SAC adsorbed on the Co- phosphonyl oxygen atom (P]O) are calculated to be 1.60 decorated C24 fullerene, the point charges of C and Co atoms of and 2.10 eV, respectively. The values of DG and DH are negative. As the nano-cage altered to 0.681 and 0.151 electrons compared to results exhibited the value of DG is slightly reduced in comparison the basic values of 0.759 and 0.150 electrons in the SAF adsorbed with DH value that is owing to entropic effect. The interaction on the fullerene, respectively. Sharma and Kakkar found the distance of SAC with the C24 fullerene decorated with Co atom is chemisorption energy of approximately 2.27 eV for SAF on Ti- 1.949 Ả. In contrast, when a single SAF adsorbed on Co-decorated doped MgO nanotube [44]. The infrared (IR) spectrum (Fig. 3)of 1 C24, the binding energy and interaction distance were the SAC indicates the peaks at 502 and 1137 cm which are in about 1.60 eV and 1.991 Ả, respectively. The DG and DH values for related to PeCl and P]O bond stretching, which is in agreement SAF adsorbed on Co-decorated C24 fullerene are calculated to with the results mentioned by Vaiss and co-workers [27]. The P]O be 2.06 and 2.61 eV, respectively, showing that the adsorption of vibrational frequency of a single SAF varies from 1249 cm 1 to 1 SAF is much stronger than that of the SAC. NBO analysis demon- 1185 cm after adsorption process of Co-decorated C24 nano-cage, strated the charges about 0.10 electrons transferred from the SAF to and result was in good agreement with the experimental data (P] 1 1 the Co-decorated C24 fullerene. With respect to the Co-decorated O: 1277 cm at liquid and 1280 or 1240 cm at dilute aqueous C24 fullerene, the point charges upon the Co and C atoms were solutions) as previously mentioned by Kuiper, Elkine, and Braue

Fig. 3. IR spectra of all the complexes. A. Soltani et al. / Journal of Alloys and Compounds 735 (2018) 2148e2161 2153

1 et al. [45e47]. We observed the medium peak at around 906 cm cobalt atom in Co-decorated C24 fullerene interacting with SOF and that is related to antisymmetric CeC stretching vibration between SOC are found to be [Ar] 4s0.19 3d4.540 and [Ar] 4s0.143d4.68, the 6-numbered ring and 12-numbered ring of the Co-decorated respectively, while the natural electron configurations of oxygen 0.89 2.63 C24 fullerene, which is close to the mentioned previous result by and phosphorous atoms are found to be [He] 2s 2p and [He] 0.42 0.87 Xu et al. [22]. The CeH band of SAF adsorbed on Co-decorated C24 3s 3p on the adsorption of Soman with Co-decorated C24 fullerene is observed in the range of 2950e3102 cm 1. fullerene and [He] 2s0.85 2p2.56 and [He] 3s0.47 3p0.98 on the Quantum molecular descriptors analysis also revealed that in- adsorption of SOC with Co-decorated C24 fullerene. The values of crease in the values of global hardness (h) from 0.60 to 0.36 eV DG and DH for SOC adsorbed on Co-decorated C24 fullerene are (before adsorption) to 2.92 and 0.46 eV (after adsorption) for the calculated to be 1.51 and 2.06 eV, while these values for Soman pure and Co-decorated C24 fullerenes, respectively, lead to increase are about 2.15 and 2.68 eV, respectively. When SOF chemisorbed in stability and decrease in reactivity of system [48,49]. Moreover, upon Co-decorated C24 surface, the length of P]O and PeF bonds the same adsorption forms of SAF and SAC resulted to the reduction are equal to 1.513 and 1.611 Ả, respectively, which are different of of values of electron affinity (A) and electrophilicity index (u) the isolated SOF molecule with the values of 1.489 (P]O) and 1.631 which is in well agreement with the results obtained by the DNmax Ả (PeF). Compared to Soman molecule, the length of P]O and PeCl calculation whereas electron transfers occur from the adsorbates to bonds of SOC chemisorbed on Co-decorated C24 surface were adsorbents by SAF and SAC interactions with the pure and Co- approximately 1.526 and 2.064 Ả, respectively, while it was 1.493 decorated C24 fullerenes (see Tables 2 and 3). (P]O) and 2.102 Ả (PeCl) in isolated SOC molecule. The NBO analysis demonstrates that the charges about 0.301 and 0.116 electrons were transferred from SOF and SOC to Co-decorated C 3.3. Adsorption of Soman and Chlorosoman on Co-doped C 24 24 fullerene. The infrared spectra for SOF and SOC are very resembling, showing the similarities in their molecular structure and surface After structure relaxations, we calculated two kinds of ener- bonding energy. After adsorption of SOF and SOC on the surface of getically favorable configurations, in which the Soman (SOF) and Co-decorated C24 fullerene, the bands observed at around 1168 and Chlorosoman (SOC) adsorb over the Co-decorated C fullerene as 24 1121 cm 1 can be attributed to the P]O vibrations and compared displayed in Fig. 2.InTable 3, For SOF and SOC upon the Co- they with the values of the SOF and SOC appears at around 1234 decorated C fullerene, the calculated binding energy for both 24 and 1227 cm 1, respectively [4]. The bands at around 495 and states were about 1.31 and 1.65 eV, and distance of SOF and SOC 789 cm 1 are assigned to the PeCl and PeF stretching vibrations to the Co-decorated C were discovered to be 1.950 and 1.996 Å, 24 (Fig. 3). Davis et al. calculated the band of PeF stretching vibration respectively. The BSSE-corrected binding energies for interaction in related to Sarin adsorbed on silica in the region of 803 cm 1 [4]. between boron-doped C fullerene and Soman molecule was 34 The global hardness values decreased in SOC/C and SOF/C sys- found to be 1.83 eV (from its O head) and 1.65 eV (from it's OF 24 24 tems and increased in SOC/CoeC and SOF/CoeC systems, indi- head) [50]. The obtained results demonstrated a strong chemical 24 24 cating that stability of the recently mentioned systems increased interaction (covalent) with a small distance in SOF or SOC on Co- after adsorptions of SOF and SOC over C24 fullerene while it decorated C24 fullerene. The natural electron configuration of

Fig. 4. Illustrations of FMO, MEP plots and spin density from the cobalt-decorated C24 fullerene. 2154 A. Soltani et al. / Journal of Alloys and Compounds 735 (2018) 2148e2161

Fig. 5. The HOMO and LUMO orbitals of the Sarin and Chlorosarin adsorbed on the surface of Co-decorated C24 fullerene.

dwindled after adsorptions of SOF and SOC over CoeC24 fullerene 3.4. Electronic properties of the Co-decorated C24 complexes which as the consequence resulted to the diminishment and growth of reactivity of C24 and Co-decorated C24 species, respec- 3.4.1. HOMO-LUMO energy of the complexes tively. Concerning electron transfer studies, both electron afﬁnity In this section, we are reporting on the frontier molecular or- (A) and electrophilicity index (u) values reduced upon the bitals (FMO) of the applied adsorbents before (see Fig. 4) and after adsorption processes except in case of SOF/C24 system where the u adsorption (see Figs. 5 and 6), as it is represented in Fig. 5, the increased from 21.59 to 43.13 eV. This along with the values of occupied (HOMO) and virtual (LUMO) orbitals in both a (alpha) and DNmax as total electron transfer index of the studied systems b (Beta) forms are more situated over the Co-decorated C24 represent that electrons were generally transferred from SOF and fullerene after interactions with SAF and SAC molecules except in b SOC to the adsorbents which coincides well with our previous forms of LUMO where the more orbitals concentrated on Co atom report [41]. and its surrounding atoms. Moreover, the calculations of electronic A. Soltani et al. / Journal of Alloys and Compounds 735 (2018) 2148e2161 2155 properties revealed that the HOMO energy (EHOMO) and LUMO Table 4 Spin polarization terms (m ) of the Co 3d orbitals in four investigated C eCo- energy (ELUMO)ofC24 has some negligible changes after SAF and B 24 chemical agent complexes obtained from Plane-Wave calculations using s ¼ 0.002 SAC adsorptions, while E and E of Co-decorated C HOMO LUMO 24 Ry. changed appreciably after adsorption of the same molecules (see Property 3d2 3d 3d 3d22 3d Spin density Table 2). The value of Eg for C24 fullerene is found to be 1.24 eV at z xz yz x-y xy

PBE functional, which is close to the obtained values by other CoeC24 1.798 1.217 1.847 1.840 1.445 1.413 Sa(Cl)/CoeC 1.771 1.438 1.693 1.600 1.498 1.463 literature [51,52]. When the nano-cage linked to cobalt atom, the Eg 24 e value is reduced to 0.71 eV at alpha form and 0.31 eV at Beta form Sa(F)/Co C24 1.342 1.837 1.739 1.451 1.559 1.106 So(Cl)/CoeC24 1.841 1.552 1.343 1.491 1.707 0.994 which this push down expect is related in the change of HOMO So(F)/CoeC24 1.751 1.518 1.632 1.487 1.614 1.448 energy in comparison with the LUMO energy. Moreover, the

Fig. 6. The HOMO and LUMO orbitals of the Soman and Chlorosoman adsorbed on the surface of cobalt-decorated C24 fullerene. 2156 A. Soltani et al. / Journal of Alloys and Compounds 735 (2018) 2148e2161

Fig. 7. Illustrations of MEP plots and spin density transfer from chemical toxic agents to the cobalt-decorated C24 fullerene.

differences in EHOMO and ELUMO values (DEg)ina forms were 28.17 except b forms of LUMO in both SOF and SOC/Co-decorated C24 (SAF) and 29.58% (SAC) and in b forms were 8.57 (SAF) and 42.86% systems which electrons are more exist on Co atom and areas close (SAC) whereas the EHOMO and ELUMO values in the same parameter to it, occupied and virtual orbitals of both a and b forms were is about zero concerning SAF and SAC adsorptions over C24 uniformly distributed throughout the adsorbents. Again, the fron- fullerene. Fig. 5 demonstrates that b form of LUMO is more localized tier molecular orbitals (FMOs) values of SOF and SOC adsorbed over over the Co atom and C atoms close to it (after SAF interaction with C24 were not changes upon the adsorption process while the HOMO Co-decorated C24), while the occupied and virtual orbitals of both a and LUMO in both a and b forms reduced in both SOC/CoC24 and and b forms were uniformly distributed throughout the adsorbents. SOF/CoC24 systems. As displayed in Table 3, the Eg values of SOC/ Concerning HOMO-LUMO of Co-decorated C24 fullerene before CoC24 and SOF/CoC24 systems are larger than that of the C24 and after interactions with SOF and SOC, Fig. 6 represents that, fullerene (0.71 eV), being 0.91 and 0.92 eV, respectively. It is noticed A. Soltani et al. / Journal of Alloys and Compounds 735 (2018) 2148e2161 2157

Fig. 8. Partial density of states spectrums for (a) chlorosarin and (c) chlorosoman (left) and (b) Sarin and (d) Soman (right) interacting with the Co-decorated C24 fullerene.

Fig. 9. Contour plots of charge density for the Sarin and Chlorosarin adsorbed on the surface of cobalt-decorated C24 fullerene. 2158 A. Soltani et al. / Journal of Alloys and Compounds 735 (2018) 2148e2161 that, a large Eg can be related to kinetic and structural stability electrophilic site with red color is defined as the most electroneg- [53e58]. The values of DEg increased from both a and b forms of ative electrostatic potential (Co-decorated C24 fullerene). Hence, SOC/CoC24 and SOF/CoC24 systems while it was again close to zero MEP maps indicate that the all chemical toxic agents acts as an in case of SOC/C24 and SOF/C24 systems. electron donor and Co-decorated C24 fullerene acts as an electron As shown in Table 4, in the cobalt-decorated C24 nano-cage, five acceptor. 3d subshells are highly polarized with the dominance of spin-up fi 22 states. Among ve 3d subshells, 3dyz and 3dx-y are the most 3.4.2. Total densities of states (TDOSs) of the complexes fi polarized orbital, while we also notice signi cant spin polarizations The total density of state (TDOS), partial density of state (PDOS), in 3dxz and 3dxy. For all the other species, high positive spin po- and overlap population density of state (OPDOS) were computed larization terms were found in all 3d subshells which resulted in a for stable configurations of considered complexes adsorbed upon more severe distortion for the species (see Table 4). Therefore, the the Co-decorated C24 fullerene. All the TDOS, PDOS, and OPDOS plane-wave calculations predicted that the structures gave anti- plots for each complex are displayed in Fig. 8. PDOS plots of first ferromagnetic contributions. The spin-up states in the 3d subshells (fullerene) and second (chemical toxic agents) fragments indicate and polarizations show the effect of strong chemical toxic agent's with the red and blue colors of specified complexes. According to dispersion interactions. According to the data presented we can see the partial density of state demonstrated in the figure we can also e e that the total magnetic moment of the SAF/Co C24 and SAC/Co C24 see that the HOMO and LUMO states of the Co-decorated C states e 24 complexes have slightly increased in comparison with Co C24 host interacting with chemical toxic agents are significantly altered. This e e cage. However in the case of the SAF/Co C24 and SOC/Co C24 the suggests the chemical toxic agents are chemically adsorbed total magnetic moment have also a slightly decline (Fig. 7). As (chemisorption) upon the outer surfaces of Co-decorated C fi 24 presented in Fig. 5 the Co atom spin polarization is signi cant and fullerene and consequently, charge transfer does happen between the Co-3d orbitals charge polarization has remarkable role in adsorbent and adsorbate. As a result decoration of C24 surface with induced magnetic moment to the systems. cobalt can leads to a significant reduces in Eg of the fullerene after The molecular electrostatic potential (MEP) maps for all chem- the interacting with SAF and SOF in both alpha and beta forms, ical toxic agents (in the most stable states) interacting with Co- which can resulting from overlapping of HOMO or LUMO orbital of decorated C24 fullerene are displayed in Figs. 4 and 7. MEP maps chemical toxic agents with CoeC24 orbital hybridization [59,60]. represent nucleophilic sites with blue color for the most positive Also in all considered systems, the overlap population density of electrostatic potential (chemical toxic agents) and the positions of states (OPDOS) indicates bonding interaction (green color) between

Fig. 10. Contour plots of charge density for the Soman and Chlorosoman adsorbed on the surface of cobalt-decorated C24 fullerene. A. Soltani et al. / Journal of Alloys and Compounds 735 (2018) 2148e2161 2159

Fig. 11. ELF plots of Sarin (I) and Chlorosarin (II) adsorbed on cobalt-decorated C24 fullerene. adsorbate and adsorbent. for all cases demonstrate that the interaction between the cobalt atom of the nano-cage and the oxygen atom of chemical warfare agents (CoeO bond) is a strong negative covalent potential in na- 3.4.3. Electron charge density differences ture, exhibited of high polarization, and in agreement with the high We demonstrate in Figs. 9 and 10 contour plots of the electron dipole moment of all the systems. charge density distribution belong to SAC (I),SAF(II), SOC (III), and SOF (IV) interacting with Co-decorated C24 fullerene. As it is explicit from Figs. 9 and 10, the electron charge density distribution is 4. Summary obviously centralized around the cobalt atom and the oxygen atom of the complex and indicated a signiﬁcant overlapped charge The interaction of Soman, Chlorosoman, Sarin, and Chlorosarin density in agreement with covalent interaction scheme leading to over the pure and cobalt-decorated C fullerenes have been the chemical adsorption and high binding energy of the chemical 24 studied theoretically using DFT calculations to investigate the effect warfare agents to the Co-decorated C fullerene. 24 of cobalt atom in the binding energies and the electronic properties in the mentioned systems. The results are as follows: 3.4.4. Electron localization function differences To study further the performance of cobalt atom, we have (1) In the interaction between the chemical warfare agents and distinguished the isosurface plots of the electron localization the cobalt-decorated C24 fullerene, the adsorption resulted in function (ELF) for the SAC (I), SAF (II), SOC (III), and SOF (IV) chemical strong CoeO bonding and charge transfer from adsorbed on cobalt-decorated C24 fullerene. Figs. 11 and 12 adsorbate to adsorbent. demonstrate in all cases, the electron localization is signiﬁcant (2) The results demonstrated that the energy gap between the between oxygen atom of chemical warfare agents and Co atom of HOMO and LUMO orbitals of the mentioned systems de- adsorbent surface as the electrons more localized on the oxygen creases quite rapidly as the chemical warfare agents ap- atom of adsorbate interact considerably with the vacant orbitals of proaches the cobalt-decorated C24 fullerene. the Co atom, suggesting that Co facilities the adsorption of chemical (3) The reported harmonic frequencies of the chemical warfare warfare agents over the surface of C24 fullerene. In Figs. 11 and 12 agents interacting with cobalt-decorated C24 fullerene 2160 A. Soltani et al. / Journal of Alloys and Compounds 735 (2018) 2148e2161

Fig. 12. ELF plots of Soman, and Chlorosoman adsorbed on cobalt-decorated C24 fullerene.

indicated a positive vibration mode, suggesting that the [10] Z. Zhang, C.H. Turner, J. Phys. Chem. C 117 (17) (2013) 8758e8766. e complexes are stable. Also, the obtained results by thermo- [11] W. An, C.H. Turner, Chem. Phys. Lett. 482 (2009) 274 280. [12] C. Tian, Z. Wang, M. Jin, W. Zhao, Y. Meng, F. Wang, W. Feng, H. Liu, D. Ding, dynamic parameters demonstrated the interaction between D. Wu, Chem. Phys. Lett. 511 (2011) 393e398. adsorbate and adsorbent is exothermic and energetically [13] S.S. Han, H.M. Lee, Carbon 42 (2004) 2169e2177. favorable. [14] S.H. Friedman, D.L. Decamp, R.P. Sijbesma, G. Srdanov, F. Wudl, G.L. Kenyon, Inhibition of the HIV-1 protease by fullerene derivatives: model building studies and experimental veriﬁcation, J. Am. Chem. Soc. 115 (1993) Acknowledgments 6506e6509. [15] H. Kato, Y. Kanazawa, M. Okumura, A. Taninaka, T. Yokawa, H. Shinohara, J. Am. Chem. Soc. 125 (2003) 4391e4397. We would like to thank the clinical Research Development Unit [16] M.T. Baei, Heteroat. Chem. 24 (2013) 516e522. (CRDU), Sayad Shirazi Hospital, Golestan University of Medical [17] A. Soltani, M.T. Baei, M. Ramezani Taghartapeh, E. Tazikeh Lemeski, S. Shojaee, Sciences, Gorgan, Iran. Struct. Chem. 26 (2015) 685e693. [18] J.A. Rather, K. De Wael, Sens. Actuators B 176 (2013) 110e117. [19] Z. Shariatini, S. Shahidi, J. Mol. Graph. Model. 52 (2014) 71e81. References [20] Q. Sun, H.-B. Xie, J. Chen, X. Li, Z. Wang, L. Sheng, Chemosphere 92 (2013) 429e434. [1] C.P. Holstege, M. Kirk, F.R. Sidell, Crit. Care Clin. 13 (1997) 923e942. [21] A.M. El Mahdy, Appl. Surf. Sci. 383 (2016) 353e366. [2] Y. Tokuda, M. Kikuchi, O. Takahashi, G.H. Stein, Resuscitation 68 (2006) [22] L. Xu, C. Li, F. Li, X. Li, S. Tao, Spectrochim. Acta Part A 98 (2012) 183e189. 193e202. [23] M.T. Baei, P. Torabi, H. Mohammadian, H. Saeedeh, Fuller. Nanotub. Carbon [3] T.M. Alam, C.J. Pearce, J.E. Jenkins, Comput. Theor. Chem. 995 (2012) 24e35. Nanostruct. 23 (2015) 874e877. [4] E.D. Davis, W.O. Gordon, A.R. Wilmsmeyer, D. Troya, J.R. Morris, J. Phys. Chem. [24] E.D. Davis, W.O. Gordon, A.R. Wilmsmeyer, D. Troya, J.R. Morris, J. Phys. Chem. Lett. 5 (2014) 1393e1399. Lett. 5 (2014) 1393e1399. [5] V. Stengl, J. Bludska, F. Oplustil, T. Nemec, Mater. Res. Bull. 46 (2011) [25] V.M. Bermudez, J. Phys. Chem. C 113 (2009) 1917e1930. 2050e2056. [26] A. Michalkova, J. Martinez, O.A. Zhikol, L. Gorb, O.V. Shishkin, D. Leszczynska, [6] V.M. Bermudez, J. Phys. Chem. C 111 (2007) 3719e3728. J. Leszczynski, J. Phys. Chem. B 110 (2006) 21175e21183. [7] Q. Zhao, G. Liu, H. Zhang, F. Zhou, Y. Li, W. Cai, J. Hazard. Mater. 324 (2017) [27] V.S. Vaiss, I. Borges Jr., A.A. Leitao, J. Phys. Chem. C 115 (2011) 24937e24944. 194e202. [28] M. Frisch, G. Trucks, H. Schlegel, G. Scuseria, M. Robb, J. Cheeseman, et al., [8] H. Kroto, J. Heath, S. Obrien, R. Curl, R. Smalley, Nature 318 (1985) 162e163. Gaussian 03, Revision D. 01, Gaussian Inc, Wallingford, CT, 2004. [9] S.W. de Silva, A. Du, W. Senadeera, Y. Gu, Beilstein J. Nanotechnol. 5 (2014) [29] J.P. Perdew, K. Burke, M. Ernzerhof, Phys. Rev. Lett. 77 (1996) 3865e3868. 413e418. [30] H.-S. Wu, F.-Q. Zhang, X.-H. Xu, C.-J. Zhang, H. Jiao, J. Phys. Chem. A 107 (2003) A. Soltani et al. / Journal of Alloys and Compounds 735 (2018) 2148e2161 2161

204e209. [45] A.E.T. Kuiper, J.J.G.M. van Brokhoven, J. Medema, J. Catal. 43 (1976) 154e167. [31] A. Soltani, M. Bezi Javan, RSC Adv. 5 (2015) 90621e90631. [46] M.D. Elkin, S.I. Tatarinov, E.Y. Stepanovich, J. Appl. Spectrosc. 77 (4) (2010) [32] A. Soltani, A. Sousaraei, M. Bezi Javan, M. Eskandaric, H. Balakheyli, New J. 479e483. Chem. 40 (2016) 7018e7026. [47] E.H. Braue Jr., M.G. Panella, Appl. Spectrosc. 44 (9) (1990) 1513e1520. [33] D.S. Sabirov, R.G. Bulgakov, Comput. Theor. Chem. 963 (2011) 185e190. [48] N. Saikia, R.C. Deka, Comput. Theor. Chem. 964 (2011) 257e261. [34] GaussView 4.1.2, Gaussian Inc., Wallingford, CT, 2004. [49] N. Saikia, R.C. Deka, Chem. Phys. Lett. 500 (2010) 65e70. [35] R.G. Parr, R.A. Donnelly, M. Levy, W.E. Palke, J. Chem. Phys. 68 (1978) [50] S. Arshadi, A.R. Bekhradnia, F. Abbasi Alaei, Phosphorus Sulfur Silicon 190 3801e3807. (2015) 2051e2061. [36] R.G. Parr, L. Szentpaly, S. Liu, J. Am. Chem. Soc. 121 (1999) 1922. [51] Y. Yue, X.J. Li, Int. J. Quant. Chem. 111 (2009) 96e102. [37] T. Koopmans, Über die Zuordnung von Wellenfunktionen und Eigenwerten [52] S. Peng, Y. Zhang, X.J. Li, Y. Ren, D.X. Zhang, Spectrochim. Acta A 74 (2009) zuden Einzelnen Elektronen Eines Atoms, Physica 1 (1933) 104. 553. [38] Mohammad T. Baei, A.S. Ghasemi, E. Tazikeh Lemeski, Alireza Soltani, [53] D. Bucher, Chem. Phys. Lett. 534 (2012) 38e42. Niloofar Gholami, J. Clust. Sci. 27 (2016) 1081e1096. [54] S. Peng, X.J. Li, Spectrochim. Acta A 73 (2009) 67. [39] M. Bezi Javan, A. Soltani, E. Tazikeh Lemeski, A. Ahmadi, S. Moazen Rad, [55] X.J. Li, J. Mol. Struct. (THEOCHEM) 896 (2009) 25. Superlattices Microstruct. 100 (2016) 1e14. [56] S. Peng, Y. Zhang, X.J. Li, Y. Ren, D.X. Zhang, Spectrochim. Acta A 74 (2009) [40] A. Soltani, S. Ghafouri Raz, V. Joveini Rezaei, A. Dehno Khalaji, M. Savar, Appl. 553. Surf. Sci. 263 (2012) 619e625. [57] Z. Sun, X. Li, M. Tian, G. Zhao, J. Li, B. Ma, J. Mol. Struct. (THEOCHEM) 913 [41] M. Bezi Javan, A. Soltani, A.S. Ghasemi, E. Tazikeh Lemeski, N. Gholami, (2009) 265. H. Balakheyli, Appl. Surf. Sci. 411 (2017) 1e10. [58] D.E. Manolopoulos, J.C. May, S.E. Down, Chem. Phys. Lett. 181 (1991) 105. [42] M.T. Baei, A. Soltani, P. Torabi, F. Hosseini, Monatsh. Chem. 145 (2014) [59] O. Leenaerts, B. Partoens, F. Peeters, Phys. Rev. B 77 (2008) 125416e125421. 1401e1405. [60] H. Pinto, R. Jones, J.P. Goss, P.R. Briddon, J. Phys. Condens. Matter 21 (2009) [43] D. Manna, A. Sirohiwal, T.K. Ghanty, J. Phys. Chem. C 118 (2014) 7211e7221. 402001e402003. [44] N. Sharma, R. Kakkar, J. Comput. Sci. 10 (2015) 225e236.