Adsorption of NH3 and NO2 molecules on the carbon doped C3N monolayer: A first principles study

https://doi.org/10.1016/j.comptc.2020.113075Get rights and content

Highlights

  • Adsorption of NO2 and NH3 molecules on the carbon doped C3N monolayers was studied.

  • The carbon doped C3N system represents semiconductor property.

  • Both NH3 and NO2 gas molecules are weakly physisorbed on the carbon doped C3N monolayers.

Abstract

In this work, we investigated the optimized structures and electronic properties of novel C3N monolayers doped with carbon atoms at the central hexagon site. The C3N monolayer is an indirect band gap semiconductor with a small band gap at the Fermi level. After substituting carbon atoms, the electronic properties and structures of the nanosystems can be modulated. Interestingly, the new carbon doped C3N structure shows semiconducting behavior. The total electron density profiles show the distribution of charge densities over the whole domain doped nanostructures. The adsorption energy of NO2 molecule on the doped C3N system is higher than that of NH3 molecule, indicating that NO2 molecule strongly interacts with the C3N system. The electron density difference plots show that the charge densities were mainly accumulated at the central carbon doped hexagon site. Both NH3 and NO2 gas molecules are weakly adsorbed on the carbon substituted C3N monolayers.

Introduction

In the past few years, two-dimensional (2D) nanomaterials, such as transition metals dichalcogenides [1], [2], [3], silicene [4], [5], germanene [6], [7], stanene [8], [9], and graphene [10], [11] have attracted considerable interests. They possess atomic thickness and excellent electronic, optical and magnetic properties.

Graphene, a typical 2D material with unique properties has aroused significant scientific attentions since its successful realization in 2004 [10]. Graphene monolayers have been extensively used in a wide range of applications such as gas sensors and storage devices. However, the lack of band gap in graphene has dramatically limited its effectiveness for applications in nanoelectronic devices [11], [12]. Recently, various high-efficiency electronic and spintronic devices have been fabricated based on these 2D nanostructures especially graphene [13], [14], [15], [16].

Numerous strategies have been tested to modify the electronic and magnetic properties of 2D layered nanomaterials. These strategies include substitutional doping, defect formations, embedding of adatoms, and electric field/strain applying [17], [18], [19], [20], [21], [22]. Among these methods, the substitutional doping can be considered as a strong approach, which has been extensively applied on a large number of 2D materials.

Several theoretical studies have been performed to examine the effects of adsorption of adatoms on the electronic, magnetic and optical properties of 2D monolayers. For example, Chan et al. studied the binding of foreign elements to the graphene sheets by using DFT calculations [23]. The adsorption of metallic adatoms on the silicene nanosheets was also investigated by Sahin et al. [24].

They found that the reactivity of silicene monolayer functionalized with metal adatoms cannot be compared to that of graphene due to the buckled geometry and the excellent surface reactivity [24]. Adsorption characteristics of stanene, germanene, MoS2, and graphene monolayers interacting with different external adatoms including alkaline-earth, alkali, transition metals, and nonmetallic elements have been widely examined [25], [26], [27], [28], [29].

More recently, two-dimensional polyaniline (C3N) has been successfully fabricated by using the direct pyrolysis of hexaaminobenzene (HAB) trihydrochloride single crystals. It has been also realized via scanning tunneling microscopy [30]. Recently, several studies regarding the gas molecules adsorption on the C3N monolayers have been performed [31], [32], [33]. Zhao et al. [34] studied the adsorption of NO2 molecule on the C3N monolayer using the DFT calculations. Faye group also examined the enhanced capability of carbon nitride (C3N) nanosheets as promising materials for H2S and NH3 elimination [35]. In the present work, we conducted a density functional theory study to examine the effects of carbon doping on the electronic structures of C3N monolayers. The density of states, band structures and structural parameters were also calculated. Subsequently, the adsorption of NH3 and NO2 gas molecules on the carbon doped C3N systems were investigated. Our results showed that the novel carbon doped C3N monolayers could be a potential candidate for future gas sensor devices. Fig. 1 displays a schematic model for the adsorption of NH3 molecule on the carbon doped C3N monolayer as a typical gas sensor. This work aims at providing a theoretical basis for potential application of carbon doped C3N monolayers as promising gas sensors for NO2 and NH3 detection.

Section snippets

Methods and calculation models

The density functional theory calculations were performed to gain insights into the electronic and geometrical properties of the novel carbon doped C3N monolayers [36], [37] as implemented in the SIESTA package [38], [39]. For visualization of the atomic configurations of the pristine and carbon doped C3N monolayers, GDIS program was used [40]. The cutoff energy in our calculations was set to 450 eV, because a higher value slightly affects the calculated results. The adsorption configurations

Structural and electronic properties of pristine graphene and C3N monolayers

As a preliminary test, we first considered the pristine C3N monolayers and calculated the optimized lattice constants. In this work, we found the lattice parameter of graphene is 2.456 Å after relaxation, which is in good agreement with the theoretical works [44]. This value is also consistent with the experimental value of 2.46 Å reported by Baskin et al [45]. The optimized structure of the C3N monolayer was shown in Fig. 2. As can be seen from this figure, in the honeycomb structure of C3N

Conclusions

In this paper, we examined the optimized structures and electronic properties of the carbon doped C3N monolayers using the density functional theory calculations. The C3N monolayer shows semiconducting behavior with an indirect band gap. By substituting two carbon atoms at the center of the monolayers, the electronic structure of the C3N monolayer was modulated. The total electron density plots show the electron exchange and therefore interaction between the carbon atoms and C3N system. Based

CRediT authorship contribution statement

Yuping Lv: Investigation, Project administration, Methodology, Software, Validation. Yaojie Wang: Writing - review & editing, Software, Conceptualization, Data curation. Haiming Zhang: Visualization, Investigation, Writing - review & editing. Chunfeng Dai: Software, Supervision, Project administration, Writing - original draft.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

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