Adsorption of habitat and industry-relevant molecules on the MoSi₂N₄ monolayer

Highlights

• Spin-polarized DFT has been employed to reveal the impact of various adsorbed molecules on the structural, electronic and magnetic properties of MoSi₂N₄ (MSN) monolayer.

• The effect of environmental and industry-relevant gas molecules was studied.

• The interaction between the different molecules with the MSN is a physisorption type.

• Our theoretical studies indicate that MSN-based sensor has a high potential for O₂, NO, NO₂ and SO₂ detection.

Abstract

The adsorption of various environmental gas molecules, including H₂, N₂, CO, CO₂, O₂, NO, NO₂, SO₂ H₂O, H₂S, NH₃ and CH₄, on the surface of the recently synthesized two dimensional MoSi₂N₄ (MSN) monolayer has been investigated by means of spin-polarized first-principles calculations. The most stable adsorption configuration, adsorption energy, and charge transfer have been computed. Due to the weak interaction between molecules studied with the MSN monolayer surface, the adsorption energy is small and does not yield any significant distortion of the MSN lattice, i.e., the interaction between the molecules and MSN monolayer surface is physisorption. We find that all molecules are physisorbed on the MSM surface with small charge transfer, acting as either charge acceptors or donors. The MSN monolayer is a semiconductor with an indirect band gap of 1.79 eV. Our theoretical estimations reveal that upon adsorption of H₂, N₂, CO, CO₂, NO, H₂O, H₂S, NH₃ and CH₄ molecules, the semiconducting character of MSN monolayer is preserved and the band gap value is decreased to $~$1.5 eV. However, the electronic properties of the MSN monolayer can be significantly altered by adsorption of O₂, NO and SO₂, and a spin polarization with magnetic moments of 2, 1, 2 ${\mu }_B$, respectively, can be introduced. Furthermore, we demonstrate that the band gap and the magnetic moment of adsorbed MSN monolayer can be significantly modulated by the concentration of NO and SO₂ molecules. As the concentration of NO₂ molecule increases, the magnetic moment increase from 1 ${\mu }_B$ to 2 and 3 ${\mu }_B$. In the case of the SO₂ molecule with increasing of concentration, the band gap decreases from 1.2 eV to 1.1 and 0.9 eV. Obviously, our theoretical studies indicate that MSN monolayer-based sensor has a high application potential for O₂, NO, NO₂ and SO₂ detection.

Introduction

Two-dimensional materials (2DM) have attracted impressive attention because of their interesting physical and chemical characteristics such as ultrathin thickness, high flexibility, fascinating electronic properties, high miscibility, surface charge state, available active sites, eligible carrier density, excessive lightweight structures, and other attractive quantum properties [1], [2], [3], [4], [5]. Two-dimensional nanodevices with adjustable features due to defects engineering gave rise to large expectations in the field of nanoelectronics, nano-optoelectronics, spintronics, electromagnetic shielding, antennas, supercapacitors, transparent conductive materials [6], [7], [8], [9], [10]. Lately, highly efficient 2D nanodevices based on graphene have been demonstrated [11]. Furthermore, having other seductive features such as a huge surface to volume ratio, negligible electronic screening, appropriate bandgaps, and suitable conductivity give the impression that the structural and electronic properties of a 2DM are affected by environmental factors. The relevant studies clearly confirm that the environmental factors can modify certain properties of the 2D material and in this way to promote the development of a new potential application [12]. Thus, it will be attractive for gas sensing, catalysis, conversion and storage of energy and so on [13], [14].

It has been reported that the adsorption of a gas molecule on the surface of a 2D nanomaterial has slightly changed its carrier concentration and has led to a great variation in the electrical conductivity [15], [16], [17]. Hence, the variation of the 2D nanomaterial properties should be carefully evaluated to enhance the material sensing capabilities [18]. Consequently, the 2D material have received much interest and their tremendous potential in the field of gas sensing application has been demonstrated [19], [20], [21], [22], [23]. The experimental and theoretical studies have indicated that the 2D material are very promising materials for nanosensors with a high efficiency [24], [25]. Generally, sensing of all gas molecules and particularly, those that are polluting our habitat being also toxic is actually vital for human health and biosphere stewardship [2]. Detection of a small amount of gas molecules might be critical for protecting the environment, industrial harm evaluation, cultivation of agricultural products as well as for assessment of medical drugs, etc. [26], [27]. Various theoretical investigations have been carried out to evaluate electronic, magnetic and optical properties of the 2D material impacted by adsorption of adatoms [14]. The adsorption of different molecules on the surface of 2D monolayers such as graphene [28], silicene [29], germanene [30], black phosphorus [31], stanene [32], and the molybdenum disulfide [33] has been studied theoretically.

Density functional theory (DFT) is one of the state-of-the-art methods of theoretical evaluation. DFT is a computational quantum mechanical modeling that is used to estimate the atomic and electronic structure of materials through first-principles [34], [35], [36], [37], [38], [39], [40]. In addition, it was effectively employed to predict and explain the sensing behavior of 2DM [41]. For the first time, the sensing abilities of the 2D material have been attributed to graphene, and the research is still ongoing with newly developed 2D material possessing higher capabilities and better performance [42]. Up to now, exploitation of these materials is hindered by some drawbacks such as: the inappropriate bandgap value of graphene, the unsuitable carrier mobility of molybdenum disulfide and the instability of phosphorene in air. Hence, to overcome the mentioned above disadvantages and to enhance the sensing capability, it is essential to discover novel 2D material with improved performance [43].

Among all 2DM, MXenes belong to a novel transition metal compounds (carbide/nitride) group. They have exhibited great promising applications partly revealed in Ref. [44]. Recently, a new 2D MXene, has been successfully fabricated by chemical vapor deposition. Lately, the MSN monolayer has been disclosed as a semiconductor with remarkable strength, stability and a moderate bandgap [45]. It has been reported that the carrier mobility of the MSN monolayer is much larger than that of the MoS₂ one [46]. The fascinating features of the MSN monolayer such as moderate bandgap, appropriate mobility, and high stability make it suitable for utilization in nanoelectronics and nano-optoelectronics. After the successful fabrication of the MSN monolayer, numerous efforts have been made to divulge its palette of interesting properties ranging from electronic, magnetic, mechanical, optical, photocatalytic, piezoelectric, thermal conducting, and stiffness properties to electrically contacting with metals, valley polarization, and its different heterostructures [47], [48], [49], [50], [51], [52], [53], [54], [55]. Although, the study of a material as a sensor can be considered as an application by itself, and we try to discuss the possibility of the MSN monolayer as a gas sensor, that is, whether the MSN monolayer can exhibit a better performance or not; but there are some points about the importance of these specific gases. Generally gases are classified into three groups: oxidizers (e.g. O₂, NO, NO₂), inert gases (e.g. N₂, CO₂) and flammable gases (e.g. CH₄, H₂, CO, NH₃, H₂S). We have evaluated the impact of some gasses of each group, which have been considered important for the environment and our daily life. Furthermore, about the importance of each gas can be discussed on its own. For example, in the case of NO and NO₂, which have made the most changes on MSN monolayer surface; it can be said that NO is a nonflammable, extremely toxic, oxidizing gas with a sharp sweet odor. NO can be released by the reaction of nitric acid with metals. The most hazardous effect of NO is on the lungs. NO₂ is highly toxic, oxidizer, corrosive. It has a strong harsh odor, similar to chlorine, and may exhibit a vivid orange color. The main effect of breathing high levels of NO₂ is an increased risk of respiratory problems [56].

In this article, we present an inclusive investigation of the adsorption of various molecules (including H₂, N₂, CO, O₂, CO₂, NH₃, NO, NO₂, CH₄, H₂O, H₂S, and SO₂) on the MSN surface using first-principles calculation based on DFT. The orientations and binding energies of these molecules on the MSN surface have been assessed. The results reveal that adsorption of different molecules affects the electronic and magnetic properties of the MSN monolayer, which facilitates its utilization as a gas sensor with a large application potential. To the best of our knowledge a study on the adsorption of different molecules on the surface of the MSN monolayer as well as its impact on the MSN monolayer properties is still lacking. Therefore, the purpose of this paper is to fulfill the lack of knowledge in this field.