Square-octagon arsenene nanosheet as chemical nanosensor for M-xylene and toluene – A DFT outlook
Graphical abstract
Introduction
Worldwide the solid waste generated per year is about 1.3 billion tons and is expected to double in the next two decades [1]. Utmost, these landfills suffer poor management or open environment [2], leading to microbial degradation and the emission of odorous gases directly to the atmosphere [3]. A major component of this odorous gas is methane and carbon dioxide, along with a substantial amount of benzene, toluene, xylenes, and ethylbenzenes [4]. These gases being volatile organic compounds (VOCs) impose negative health effects on the environment and human health causing sensory and respiratory issues [1]. Among several VOCs, toluene and M-xylene are the most common VOCs accompanying with municipal solid waste [4]. Quite a lot of approaches have been implemented to manage the discharge of these VOCs into the environment, which includes chemical, biological, and physical treatments but owing to costly chemicals and high operational costs there is a need for solid-state sensors [5]. However, to work upon operational costs, realising the quantity of VOCs generated for specific amounts of the landfill is vital and for which several processes and products are emerging [6], [7], [8]. Regardless of emerging materials, the evaluation of quantification between measured and calculated gases and also the final chemical composition is not fully explored. Chuandong Wu et al. addressed this issue by measuring VOCs of landfills from Beijing, China [9]. Besides, gases were quantified using gas chromatography and olfactometer. With motivation from this work, we explored based on density functional theory (DFT) insights on adsorption of toluene and M-xylene on 2D square-octagon arsenene nanosheet (O-AsNS). Toluene and M-xylene are the aromatic hydrocarbons, benzene ring decorated with one and two methyl groups, respectively. M-xylene is one of the three isomers of xylene with two methyl groups in the meta position.
Nearly six decades ago, variations in electronic features of semiconductor materials due to changes in the surrounding atmosphere were reported by Brattain [10] and Sandler et al. [11]. Several metal oxides based sensors are used to detect hazardous gas molecules such as NO2, NO, N2O, NH3, H2S, CO, CH4, CO2, and SO2 [12]. Since then sensing heavy metals and hazardous gases have been scrutinised by several researchers. A contribution of graphene-like 2D materials such as reduced graphene oxides, germanene, phosphorene, MXenes, and transition metal dichalcogenides to the world of gas sensing is craved for their good adsorbing ability for organic molecules [13], [14], [15], [16], [17], [18], [19], [20], [21], [22]. Tang et al. [23] reported silicon doped graphene, which act an excellent catalyst for CO oxidation. W. Ju and D. Ma group [24], [25], [26] have studied the magnetic properties of monolayer silicene material including structural stability, electronic properties, and adsorption behaviour of transition metal atom on InSe and MoS2 using the DFT method. The layered structure of 2D materials offers a high surface-to-volume ratio with huge active sites along with the surface diffusion of the gas molecule into the host molecule that facilitates the adsorption process [27]. Arsenene nanosheet (AsNS) is one such 2D material theoretically proposed in 2015 by Kou et al. [28]. Nevertheless, the sensing abilities of pristine, B, and N-doped As towards SO2 and NO2 were investigated by Chen et al. [29]. Liu et al. [30] reported arsenese as a chemical sensor for N2, CO, CO2, NH3, NO, and NO2 gas molecules based on the first-principles analysis.
AsNS is an isoelectronic group-VA arsenic elemental monolayer, with a stable honeycomb, non-honeycomb, porous structures and many allotropic forms such as α, β, ε, ξ, η, θ, tricycle-type and square-octagon arsenene structures [31]. The bandgap variations for these structures was between ~1 eV to ~2.5 eV and higher anisotropic carrier mobilities up to several hundred suitable for the base substrate for the chemical sensor. Besides, the efficacy of Al-doped ε-AsNS for aniline adsorption [32] and Kagome AsNS for methyl and ethyl mercaptan adsorption were reported [33]. The various arsenene nanostructures are used to detect toxic vapours by our group [34], [35], [36]. Herein, we stretch out the studies to probe the sensitivity of newly predicted square-octagon arsenene (O-AsNS) towards prominent VOCs, toluene, and M-xylene. The research discloses the DFT insights to speculate the fundamental structure and electronic features of O-AsNS before and after toluene and xylene vapours adsorption.
Section snippets
Calculation particulars
All the calculation in the present study is carried out based on DFT-method using Atomistic Toolkit – Virtual Nanolab (ATK-VNL) [37]. Importantly, we studied the possibility of utilising O-AsNS as a leading material for sensing the toluene and xylene vapours. The hybrid GGA/B3LYP exchange-correlation functional was applied to study the geometrical firmness and electronic characteristics of O-AsNS [38], [39]. For geometrical optimisation and van der Waals (vdW) interactions, semi-empirical
Geometrical parameters for stable O-AsNS and band structure analysis
An acquaintance of geometrical and structural bounds of probing material is essential and finds a topmost basic study. Herein, we first investigated the stable structural parameters of O-AsNS and then progressed towards probing target VOCs. Square-octagon arsenene NS, as the name indicates, the monolayer of O-AsNS is made of arsenic atoms organised into square and octagon rings and would be symbolised as (4–8)-As, bearing 8 atoms per unit cell belonging to space group P4/nbm [31]. Pristine
Finishing notes
We investigated the geometric firmness and electronic properties of O-AsNS with the framework of density functional theory. The energy bandgap of 1.348 eV is observed for O-AsNS indicating semiconductor nature. Hence, O-AsNS is deployed as a base substrate to adsorb M-xylene and toluene vapours. The adsorption energy owing to adsorption of M-xylene and toluene molecules on O-AsNS shows exothermic and physisorption type of adsorption. Also, the electron density variation and charge transfer
CRediT authorship contribution statement
M.S. Jyothi: Data curation, Formal analysis, Investigation, Methodology, Resources, Validation, Visualization, Writing - original draft. V. Nagarajan: Formal analysis, Investigation, Methodology, Resources, Software, Validation, Visualization, Writing - original draft. R. Chandiramouli: Data curation, Investigation, Funding acquisition, Project administration, Resources, Software, Supervision, Writing - review & editing.
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.
Acknowledgement
The authors wish to express their sincere thanks to Nano Mission Council, Department of Science & Technology, India (No. SR/NM/NS-1011/2017(G)) for financial support.
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