Elsevier

Applied Surface Science

Volume 484, 1 August 2019, Pages 33-38
Applied Surface Science

Full length article
SnSe monolayer: A promising candidate of SO2 sensor with high adsorption quantity

https://doi.org/10.1016/j.apsusc.2019.03.346Get rights and content

Highlights

  • SnSe monolayer could be one of the promising candidates as SO2 sensors with high selectivity and sensitivity.

  • NO2 is chemisorbed on SnSe monolayer while SO2 is physisorption nature. Surprisingly, adsorption quantity of SO2 is 6 times as large as that of NO2.

  • When SO2 and NO2 are mixed, the adsorption quantity of SO2 is not affected, but the adsorption of NO2 is inhibited.

Abstract

Recently, the application of phosphorene structure analogues in gas sensors has been a hot research topic since the appearance of phosphorene. SnSe monolayer as one of them has been proved to be much more stable properties than phosphorene. Based on the density-functional theory, the interaction between gas molecules (CO, CO2, O2, NO, NH3, SO2 and NO2) and SnSe monolayer are theoretically investigated by first-principles calculation. Macroscopically, gas molecules selective adsorption of SnSe monolayer is analyzed by molecular dynamics. Compared to CO, CO2, O2, SnSe monolayer performs stronger affinity for SO2 and NO2, which possesses appropriate adsorption energies (−6.000 eV and −0.759 eV) and elevated charge transfers (−0.239 e and −0.328 e). SnSe monolayer chemical adsorption of NO2, while physically adsorbing SO2, is more suitable for the adsorption mode of SO2 sensors. Surprisingly, the adsorption amount of SO2 is 6 times that of NO2. Therefore, the adsorption of SO2 is more likely to occur compared to other gas molecules. For a mixed environment of SO2 and NO2, the adsorption quantity of SO2 is not significantly affected, while the adsorption of NO2 is inhibited. Therefore, the SnSe monolayer could be a promising candidate as SO2 sensors with high selectivity and sensitivity.

Introduction

With the deterioration of environmental problems, environmental monitoring has become a key means of environmental governance. People attach importance to continuous on-site monitoring of air pollutants to protect human body from harm [1]. Sulfur dioxide (SO2), colorless, corrosive and strong excitant, is one of the typical atmospheric pollutants, which is produced in the combustion of sulfur containing coal and oil, volcanic eruptions and many industrial processes [2]. When sulfur dioxide is dissolved in water, the sulfite is formed; then the further oxidation of sulfite quickly produces sulfuric acid, forming acid rain [2]. SO2 can also lead to some respiratory diseases, lung diseases, cardiovascular diseases and even cancer [3]. Therefore, monitoring SO2 gas is becoming more and more important and its gas monitoring devices have started to be developed. The materials applied in these devices are the vital part of the detection devices [[4], [5]]. Numerous efforts have been devoted to developing the highly sensitive materials for the SO2 sensors, such as solid electrolytes [[6], [7]] or metal oxides (SnO2, FeO2) [3,8]. Although the commercial SO2 gas sensors based on the above materials have occupied a large market, its application effect is still not ideal because of the low sensitivity or high operating temperature [1]. Hence, it is very urgent to find other novel materials to optimize the SO2 sensors.

Recently, a large number of theoretical and experimental researches show that two-dimensional (2D) material, such as graphene and phosphorene, are suitable for gas sensors with excellent quality [[9], [10]]. Yang et al. reported that phosphorene is suitable for SO2 sensors due to great physical adsorption [11]. However, phosphorene is unstable in the air and also restricts its commercial development [12]. We noticed that a new phosphorene structure analogues semiconducting material – Tin selenide (SnSe) monolayer. Compared to cadmium, toxic lead, or mercury containing minerals [13], SnSe monolayer has more outstanding performance in some aspects, such as earth-abundance, less toxicity, and chemical stability [14]. Therefore, SnSe monolayer has been widely used as near-infrared optoelectronic devices [13], memory switching devices [15], solar cells [16], anode materials for rechargeable lithium batteries [17], high performance supercapacitors [18], high thermoelectric performance material [19], etc. Motivated by Yang et al., we take great interest in developing SnSe monolayer as SO2 sensor, since it not only has similar structure and excellent properties comparing to phosphorene, but is more stable for commercial application and promotion [20].

In this study, we combine the first-principles calculations with molecular dynamics to investigate the electrical properties and adsorption capacity of SnSe monolayer, exploring the feasibility of SnSe monolayer for SO2 sensor application. The most favorable adsorption configurations are determined through calculation of adsorption energy, adsorption distance and charge transfer. Electron localization function and electronic structures (total and partial densities of states and charge density difference) have also been calculated to further explain adsorption mechanism. Besides, we consider adsorption quantity as a normative factor to explore suitable gas sensor with the increasing pressure and temperature.

Section snippets

Computational method

The calculation of structure and electronic properties is performed by DMol [3] and CASTEP module, and the calculation of adsorption quantity is implemented in Forcite and Sorption module. We construct a 3 × 3 × 1 supercell of SnSe monolayer, and the lattice constant obtain after optimization is a = 4.24 Å and b = 4.47 Å, which is good consistent with previous research [21]. To avoid the possible interaction between the adjacent layers in the vertical direction of the SnSe monolayer in the

Stability and geometry structure

To confirm the most favorable adsorption configurations, the gas molecule under investigation is placed at different positions with different orientations initially, including above the Sn or Se atom, the center of puckered quadrilateral or Snsingle bondSe bond, the gas molecules being aligned either parallel or perpendicular to the surface. After full relaxation, the most stable adsorption configurations have been shown in Fig. 1. And more details from the simulation, including adsorption energy Ea,

Conclusion

In summary, we have performed first-principles calculations to investigate the structure, electronic properties, and adsorption capacity of SnSe monolayer with the adsorption of CO, CO2, O2, NO, NH3, SO2 and NO2 molecules. Our results demonstrate that the interaction between CO2, O2, CO, NO, NH3 molecules and SnSe monolayer are weak, while NO2 and SO2 exhibit strong reactivity with SnSe monolayer. Physisorption behavior of SO2, rather than NO2 (chemisorption possess), raises the possibility of

Acknowledgments

This work was supported by the National Natural Science Foundation of China under Grant No. 51706029.

This work was supported by the National Key Research and Development Program of China (Grant No. 2016YFE0125200).

This work was supported by the National Natural Science Foundation of China under Grant No. 61874035.

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