Adsorption of greenhouse gases (methane and carbon dioxide) on the pure and Pd-adsorbed stanene nanosheets: A theoretical study

Abstract

We have examined the adsorption of methane (CH₄) and carbon dioxide (CO₂) molecules on the perfect and Pd-adsorbed stanene nanosheets using the first-principles computations. Since CH₄ and CO₂ molecules represent weak physisorption on the pure stanene, we have placed the Pd adatom on the hollow site of stanene sheet to enhance the interaction between stanene and methane molecule. The band structure diagram of the Pd-adsorbed stanene clearly reveals the semiconductor property of the system, being beneficial for gas sensing. Our calculations showed that CH₄ adsorption on the Pd-adsorbed stanene is stronger than that on the perfect system. The Pd site of the Pd-stanene system strongly seizes the CH₄ molecule. The electron accumulation was also observed along the Pd-Sn bonds, which represents the covalent character of the interaction between Pd and Sn atoms. Besides, after the adsorption of CH₄ and CO₂ molecules on the perfect and Pd-adsorbed stanene sheets, the systems still continue to be semiconductor with a little band gap. Hence, our theoretical results suggested an excellent potential for Pd-adsorbed stanene nanosheets as promising CH₄ and CO₂ sensing material.

Introduction

In recent years, two-dimensional (2D) nanomaterials have motivated considerable research interests owing to their unique structure and large surface-to-volume ratio [1], [2], [3], [4], [5], [6], [7], [8], [9], [10]. Due to these unique properties, 2D nanomaterials have a high capability for use in an extensive range of technological applications [11], [12], [13]. Most of 2D layered nanostructures such as graphene, boron-nitride (BN) and transition metal dichalcogenides such as MoS₂ have recently been constructed from the bulk nanomaterials representing weak van der Waals (vdW) interactions between the stacked layers. Since the number of these bulk nanomaterials is restricted, the monolayers that should be obtained from these structures are also significantly limited. To tackle this issue, a new type of two-dimensional materials with new capabilities has been introduced, which is produced without the need for initial bulk materials. Over the past few years, numerous honeycomb-like layered materials such as stanene, germanene and silicene have been fabricated and grown on suitable substrates [14], [15], [16], [17], [18].

Several methods have been tested and investigated for modulating the electronic and magnetic properties of 2D nanomaterials after their synthesis including elemental doping, surface adsorption with transition metals or molecules, and electric field/strain effects [19], [20], [21], [22], [23], [24]. Among these proposed approaches, surface adatom adsorption is of particular importance in engineering the electronic and magnetic properties of nanomaterials [9, 12]. A large number of theoretical studies have been published, which examine the adsorption of external adatoms on the 2D monolayers. For example, Chan et al. surveyed the binding of foreign metals on the graphene nanosheets using the DFT calculations [25]. Sahin group also inspected the effects of the adsorption of the different metals including alkali, alkali-earth and transition metals on silicene monolayers [26]. In the case of germanene and stanene monolayers, some reported studies have focused on the metal adatom adsorptions on the surface [27, 28].

Nowadays, the environmental damages and climate changes caused by greenhouse gas emissions is one of the biggest human concerns. Methane (CH₄) is one of the most important gas molecules among the all greenhouse gases. It is capable of absorbing and trapping heat with high capability from the Earth's atmosphere. Sensing harmful gas molecules is of substantial importance due to the destructive effects that these gases have on human, animal and plant health. Thus, efficient approaches and consequently highly sensitive sensors should be designed for gas adsorption and sensing especially greenhouse gases [29, 30]. Thiefelder et al. [31] studied the adsorption of methane molecule on the graphene nanosheets using the dispersion corrected density functional theory calculations. Kaloni et al. [32] examined the interaction of organic molecules including methane with silicene nanosheets. Their results suggested that the band gap of silicene can be significantly increased upon the adsorption of methane.

In this work, density functional theory (DFT) calculations were applied to inspect the CH₄ and CO₂ adsorption on stanene nanosheets functionalized with palladium adatoms. Our results indicated that introducing palladium significantly improves the absorption of CH₄ and CO₂ gases on the stanene nanosheets. Thus, the palladium decorated stanene monolayer can be exploited as a robust and promising gas sensor for CH₄ and CO₂ detection.