Modeling the Electronic Properties for CNT Interacted with ZnO, CuO and Co3O4

doi:10.21203/rs.3.rs-755424/v1

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Modeling the Electronic Properties for CNT Interacted with ZnO, CuO and Co₃O₄

https://doi.org/10.21203/rs.3.rs-755424/v1

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Because of the wide applications of carbon nanotubes (CNTs) and magic properties of metal oxides, Hartree-Fock (HF)/STO-3G quantum mechanical calculations were applied to study the electronic properties of CNTs and its interaction with ZnO, CuO and Co₃O₄. Calculations were conducted to calculate HOMO/LUMO band gap energy ∆E, moleculare electrostatic potential (MESP) and total dipole moment (TDM) for CNTs, CNT-Zn-O, CNT-Cu-O, CNT-Co-O and CNT-O-Zn, CNT-O-Cu, CNT-O-Co following the two mechanism of interaction as adsorbed and complex state. The calculations show that the interaction of CNTs with metal oxides increases its reactivity where MESP indicated to more distribution charges and an increasing in the TDM value after interaction of CNTs with metal oxides. Where, the interaction of CNT-Co-O as adsorbed state has the highest TDM with lowest band gap ∆E which confirms that CNT-Co₃O₄ can be used in sensing devices.

Electrical Engineering

Atomic and Molecular Physics

Optics/Lasers

Electronic Materials and Devices

HF/STO-3G

CNTs

Metal oxides

HOMO/LUMO band gap energy

MESP

TDM.

Since the discovery of CNTs by Iijma 1991, subject takes agreat attention of scientific research due to it is logical electronic ,physical, and mechanical properties. Where, large surface area, high thermal and electrical conductivity of CNTs make it applicable in several fields of energy storage devices such as solar cell, supercapacitor and sensors applications (Smalley 2003; Scoville et al.1991). There are two main types of CNTs the first is a single wall carbon nanotube (SWCNT) which is considerd as a graphene sheat rolled up to form a single cyllinder in nano scale. While, the second type is called multiwall carbon nanotubes (MWCNT) which are a several multilayer of concentric tubes (Klumpp 2006). Synthesizing process of CNTs is achieved by different methods. The most important and well known methods are arc discharg, laser abliation and chemical vapor deposition (CVD) (Awasthi 2005; Isaacs et al. 2010). Functionalization of CNTs enhances its physical properties and takes nanotubes to a very wide range of applications (Morsy 2015). It must be covalent or non covalent functionalizations. Covalnt functionalization causes change hypridization from SP2 to SP3 and non covalant such as vander waal,s force i.e adsorption of atoms or small molecules on the outer surface of CNTs (Hirsch 2005). While, non covalnt interaction and functionalization is prefred because it conserves the electrical properties and not disturpes π electrons decolization (Speranza 2019). In the recent years the semicoductor metal oxides have agreat attention due to its magic properties of high stability, chemical, physical, electronic and high responsability for sensor applications (Chavali 2019). Researchers found that the combiation between CNTs and metal oxides nanoparticles improves sensor^,s responsabillity (Korotcenkov 2017).

Moleculare modeling is useful to understand the electronic structure ,chemical and physical properties for many molecules. where the computional work attach and simplify the comunication between theoritical and exprimintal results. Moleculare modeling is divided into two branches, the first is called molecular mechanics that predicts the structure of molecule applying the classical physics and studies the interactions acts upon nuclei.The second one is the electronic structure methods that are solving shrodinger equations. Electronic structure methods are divided into two classes which are semi-imperical methods and Ab initio methods. Solving shroudinger equation, total energy and TDM can be obtained from the first derivatve of shroudinger equation while, the vibration frequancy appear in Raman and IR spectroscopy in addition to other physical parameters are obtained from the second derivative (Foresman 1996).

Recently researchers are applying molecular modeling to understrand the structural properties of carbon nanomaterials ( Ezzat 2020; Ezzat et al. 2018 and Elhaes 2018). G. Zollo and F. Gala studied the structure of carbon nano materials with various atomizing methods of gas adsorption one of these methods are HF methods (Zollo 2012). where the interaction configuration in ground state is replaced by linear combination state and the excited state is replaced by virtual molecular orbitals (Young 2001).

The interactions of CNTs with metal oxides and the effect of functionalization on the surface of CNTs are explained by moleculare modeling where the effect of functionalization is very important for certain well applications.

The present work aimed to study CNT and CNT interacted with ZnO, CuO and Co₃O₄ following the two mechanisms of interaction: adsorb and complex states. The electronic properties were studied interms calculated TDM, HOMO-LUMO band gap energy and MESP at HF/ STO-3G level of theory.

All calculations wre carried out using Gaussian 09 program (Frisch 2010) at Spectroscopy Department, National Research Centre (NRC), Cairo, Egypt. Model molecules were subjected to optimization using HF method at STO-3G basis set (Stewart 1970). Then, three physcial parameters namely HOMO/LUMO molecular orbital, TDM and MESP were calculated for all studied structures at the same level of theory.

3.1. Building the molecular modeling:

A model molecule was designed to form structure of CNT. This CNT formed by rolling graphene sheet to obtain a hollow cylinder consists of hexagonal carbon rings of 84 carbon atoms. As shown in Fig. 1 some modifications acts on the surface of CNT throughout the interaction of CNT with different metal oxides like CNT-Zn-O, CNT-Cu-O and CNT-Co-O at the same carbon atom., Fig. 2 described the model structures for the interaction of CNT with metal oxides throughout the oxygen as: CNT-O-Zn, CNT-O-Cu,CNT-O-Co as adsorb state. There is also another interaction mechansim can be studied which is the complex interaction. In this case the CNT can interact with ZnO, CuO and Co₃O₄ as a complex interaction. Also, this interaction can processed throughout the metal atom as shown in Fig. 3 and throughout the oxygen atom as presented in Fig. 4.

3.2. HOMO/LUMO and MESP for CNT:

HOMO and LUMO are the most important orbitals in the molecule where, HOMO is the highest occupied molecular orbital and LUMO is the lowest unoccupied molecular orbital. The difference energy between the HOMO and LUMO orbitals gives the band gap energy where the most excitations occur. HOMO/LUMO band gap calculations are useful to study the electrical properties of the studied structures. MESP is an important parameter to describe the nucleophilic and electrophilic active sites of CNT structure and for CNT interacted with metal oxides. Generally, MESP measures the interactions of charges around the surface. Mapping MESP contours on the surface of nanotube enable us how to activate the CNT surface by illustrating the distribution of charges on the surface of CNT by following a color mapping. The potential is high at red color then followed decrease until blue color to: red > orange > yellow > green > blue (Murray 1996; Şahin et al. 2015).

Figure 5 presented the HOMO/LUMO and MESP for CNT. Firstly, the HOMO and LUMO molecular orbitals are distributed along the surface of CNT. MESP for CNT showed that only yellow color appears refers to the uniform distribution of charges inside and outside the surface of CNT ascribed no changing in the electronegativity. Therefore, it is important to study the interaction of CNT with metal oxides to manipulate its reactivity properties.

3.2.1. HOMO/LUMO and MESP for CNT-metal oxides as adsorb state:

Figure 6 displayed HOMO-LUMO orbitals for CNT-Zn-O, CNT-Cu-O and CNT-Co-O as adsorb state. Figure 6-a. described HOMO/LUMO orbitals distribution in case of interactions of CNT with Zn-O which are approximately the same distributions of CNT structure Fig. 5-a. As shown as Fig. 6-b. HOMO/LUMO orbitals of CNT interacted with Cu-O localized far away from the Cu-O. While, for CNT interact with Co-O, the orbitals distributed around the metal oxide from right and left as shown in Fig. 6-c. Figure 7 showed the calculated MESP for CNT-Zn-O, CNT-Cu-O and CNT-Co-O as adsorb state. There are color changes from red to blue color in the three structures towards the metal oxides position. Such colors indicated to the active sites at the surface of CNT interacted with the three metal oxides individually. The results confirm the same obtained before (Politzer 1986). Therefore, mapping colors demonstrated that the adsorption of metal oxides on the surface of nanotubes manipulate the reactivity of CNT and direct functionalized CNT toward a wide range of applications.

For the interaction of CNT-O-Zn,CNT-O-Cu andCNT-O-Co,the same calculations areapplied at the same carbon atom as adsorb state. HOMO/LUMO orbitals and MESP are also calculated as presented in fig.8 and fig.9 respectively. MESP maps displayedthe electronegativity of CNT increased because ofinteraction of CNT with the different metal oxides through the oxygen atom. The red color appears around the structures represented CNT-O- metal unlike the mapping of MESP of CNT structure. The results confirm that the CNT became more reactive due to the interaction with metal oxides. Also, fig.9 showed that the reactivity of CNT-O-Co model molecule is higher than that of the other models as the intensity of the red color increased within the structure.Meanwhile, there are more charges transfer on CNT surface when the interaction processed via the oxygen atom.

3.2.2. HOMO/LUMO and MESP for CNT-metal oxides as a complex:

HOMO/LUMO orbitals and MESP calculations revealed an observed difference between the two mechanisms of interaction between CNT and metal oxides when the interaction is complex. Figure (10-a, b and c) presents the HOMO/LUMO molecular orbitals of CNT complexed with Zn-O, Cu-O and with Co-O respectively. MESP maps are presented in Fig. (10-d, e and f) for complex CNT-Zn-O, CNT-Cu-O and CNT -Co-O respectively. It is clear from the figures that the intensity of red color is nearly identical for the three structures but, it is still less than that observed within the adsorbed structures of CNT-Zn-O, CNT-Cu-O and CNT -Co-O. Meanwhile, Fig. (11-a, b and c) showed the HOMO/LUMO orbitals of CNT-O-Zn, CNT-O-Cu and CNT-O-Co as complex state respectively. The figures showed that the distribution of electrons within the orbitals for CNT complexed with Cu-O is identical to that complexed with O-Cu. In contrast, for CNT-O-Zn and CNT-O-Co, the electrons distribution within the HOMO/LUMO orbitals differs from that for CNT-Zn-O and CNT -Co-O as complex. While Fig. (11-d, e and f) showed the MESPs for complexed CNT interacted with the three metal oxides under study through the oxygen atom. Similarly, for the complex interactions processed through the oxygen atom, the red color is distributed equally within the models represent CNT-O-Zn, CNT-O-Cu and CNT-O-Co. As presented in Fig. (9-a, b and c) and Fig. (11-d, e and f), it is clear that the electronegativity for the adsorbed interaction processed through oxygen is higher than that for the complex interaction. This means that the reactivity of the oxygenated adsorbed interaction is higher than that of the complexed one.

3.3. TDM and energy gap ∆E calculation for CNT- metal oxides as adsorb:

The reactive property of CNT structure and the interaction of CNT with metal oxides is determined by the two physical parameters: total dipole moment TDM and ∆E value. Where the reactivity increased when the total dipole moment increased, and the energy gap decreased. The minimum ∆E means that the material becomes more conducting and subsequently increasing interactions around the surface (Bayoumy 2020). Table 1 presents the values of both TDM and ∆E for CNT and its interaction with metal oxides as adsorb state where the interaction processed through the metal atom. The calculated TDM of CNT is 0.43 Debye while, ∆E value is 1.94 eV. As a result of interaction with metal oxides, TDM value became: 3.62, 12.35 and 21.1 Debye for CNT-Zn-O, CNT-Cu-O and CNT-Co-O respectively. However, as presented in the table, the band gap energy increased as a result of interaction with the defferent metal oxides. Where, it takes values 4.45, 3.51 and 2.66 eV for CNT-Zn-O,CNT-Cu-O and CNT-Co-O respectively. The results indicated that CNT-Co-O has the highest TDM with the lowest band gap energy compared with CNT-Cu-O then CNT-Zn-O.

Table 1

HF/Sto-3G calculated TDM as (Debye) and HOMO/LUMO band gap energy (∆E) as (eV) for CNT and CNT-Zn-O, CNT-Cu-O and CNT-Co-O as adsorb state.
Structure		TDM (Debye)	∆E (eV)
CNT		0.43	1.94
CNT-Zn-O	3.62		4.45
CNT-Cu-O		12.35	3.51
CNT-Co-O		21.1	2.66

Regarding the TDM and ∆E for CNT-O- metals as adsorb state, Table 2 presents the TDM and band gap energy of CNT-O-Zn, CNT-O- Cu and CNT-O- Co. For CNT interact with O-Zn and O-Cu, TDM equals 5.38 and 1.00 Debye while ∆E equals 4.21 and 5.60 eV respectively. Meanwhile, TDM and band gap energy equals 1.37 Debye and 6.61 eV for CNT interact with O-Co. These results indicated that the composite CNT-O-Zn has the highest TDM with lowest ∆E and prove that CNT-O-Zn higher reactive than CNT-O-Co and CNT-O-Cu. Comparing the results of Table 1 and 2, it is concluded that the interaction between CNT and the different metal oxides is often adsorbed. Where, the CNT-Zn-O, CNT-Cu-O and CNT-Co-O studied structures possess the highest TDM and lowest band gap values when the interaction is supposed to be adsorbed. The results of TDM and band gap energy confirm the MESP results that the model molecule represents CNT-Co-O is the most reactive one. Additionally, this result confirms that CNT-Co-O model molecule can be used in sensing devices.

Table 2

HF/Sto-3G calculated TDM as (Debye) and HOMO/LUMO band gap energy (∆E) as (eV) for CNT-O -Zn, CNT-O -Cu and CNT-O -Co as adsorb.
Structure	TDM (Debye)	∆E (eV)
CNT-O-Zn	5.38	4.21
CNT-O-Cu	1.00	5.60
CNT-O-Co	1.37	6.61

3.3.1. TDM and ∆E calculation for CNT- metal oxides as complex state:

For CNT- Metal- O interaction, Table 3 presents the calculated TDM and band gap energy for CNT-Zn-O, CNT-Cu-O and CNT-Co-O. Where, TDM equals 4.43, 0.81 and 13.91 Debye for CNT-Zn-O, CNT-Cu-O and CNT-Co-O, respectively. Meanwhile, the ∆E takes values of 4.54, 5.75 and 4.81 eV for the same sequence. The obtained results confirmed that the reactivity of CNT-Co-O model molecule is higher than that of CNT-Zn-O and CNT-Cu-O because of the highest TDM. However, TDM and HOMO/LUMO energy for complexed CNT-O-Zn, CNT-O-Cu and CNT-O-Co are tabulated in Table 4. Where, its values are 19.79, 3.38 and 1.37 Debye and 3.84, 5.36 and 6.61 eV respectively for CNT-O-Zn, CNT-O-Cu and CNT-O-Co. This result deduced the structure of CNT-O-Zn and CNT-O-Cu are more reactive than that processed through the metal atom in contrast CNT-O-Co structure.

Table 3

HF/Sto-3G calculated TDM as (Debye) and HOMO/LUMO band gap energy (∆E) as (eV) for CNT-Zn-O, CNT-Cu-O and CNT-Co-O as complex.
Structure	TDM(Debye)	∆E (eV)
CNT-Zn-O	4.43	4.54
CNT-Cu-O	0.81	5.75
CNT-Co-O	13.91	4.81

Table 4

HF/Sto-3G calculated TDM as (Debye) and HOMO/LUMO band gap energy (∆E) as (eV) for CNT-O -Zn, CNT-O -Cu and CNT-O -Co as complex.
Structure	TDM (Debye)	∆E (eV)
CNT-O-Zn	19.76	3.84
CNT-O-Cu	3.38	5.36
CNT-O-Co	1.37	6.61

Finally, as shown in Table 4. the interaction of ZnO from oxgen atom as complex differ from the expected result. This is because the ZnO is a n-type smiconductor where valance band related to 2p level in oxygen and the conduction bands comes from 4s level of zinc atom, electrons move from valance bands to conduction bands leave holes in valance band (Li 2020; Harun et al. 2016). Therefore in case of the strong interaction between CNT and ZnO, holes directed to transfere between from Oxygen to CNT that introduced positive charge transfere around CNT surface. This charge transfere inhanced the reactivity of the compsite surface (Gupta 2011; Boscarino et al. 2019).

HF/Sto-3G method is suitable for studying the molecular structure of CNT and the interaction of CNT with ZnO, CuO and Co₃O₄. The TDM value, ∆E, MEP are studied at the same level of theory. The MESP studies showed the distribution of charges and presence of electrophilic-nucleophilic charges in the interaction between CNT and metal oxides comparison with CNT that is a neutral. This indicates that the interaction of CNT with metal oxides enhances its reactivity. Also, Results of calculated TDM confirm the MESP results, where TDM of CNT increased due to the interaction of CNT with metal oxides. The results showed that the highest reactivity and highest dipole moment belongs to CNT-Co -O as adsorb state because of the more vacancies present in cobalt oxide. Additionally, ∆E results showed that CNT-Co -O as adsorb state has the lowest value of energy gap and the most reactive one in comparison with the other structures. This makes CNT-Co-O suitable for application as sensor. The results confirm also that the adsorption state is better than complex state when interactions through metal atom.

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Editorial decision: Minor revisions
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Modeling the Electronic Properties for CNT Interacted with ZnO, CuO and Co₃O₄

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1. Introduction

2. Calculations Details

3. Results And Discussion