Toxicants in cigarette smoke adsorbed on red phosphorene nanosheet: A first-principles insight
Graphical abstract
Introduction
The sensing ability of two-dimensional (2D) substances are characterized due to the exceptional modifications that are observed in the electronic attributes of the chief component upon external surface assimilation of organic molecules (either toxic or non-toxic). This spectacular feature is attributed to the rapid synthesis of complex structures from the simple 2D nanomaterials. So far, the two-dimensional nanomaterials that have fascinated the scientific research community are graphene, BN (boron nitride), MoS2 sheet, phosphorene, stanene, transition metal oxide, graphitic carbon nitride, silicene, antimonene and arsenene [1], [2]. Among them, our research focuses on phosphorene, a monolayer of group VA exfoliated from bulk phosphorus. The crystalline form of phosphorus produces a vapor made up of P4 molecules upon sublimation. The vapor form is condensed to naturally generate white phosphorus. Due to the fragile nature of the available P4 molecules in white phosphorus, the well-known allotropes namely the red and black phosphorus (BP) are obtained from white phosphorus with the aid of light, heat or x-rays (in case of red-form 1) and at an elevated temperature of 200 °C and pressure of 12,000 atmospheres (in case of black) [3]. There are six forms of red phosphorus, among which only two are widely popular among the research community. They are violet or Hittorf’s phosphorus (VP) and fibrous red phosphorus (RP). VP is obtained from inadequate crystallization of molten lead [4], and RP is attained from consistent crystallization [5]. The VP is manifested in the monoclinic form, which has pentagonal cross-sectioned tubes [6]. Though the physical attributes of RP resemble that of VP, RP has the distinct crystalline configuration. The astonishing attributes of RP are its distinguished specific capacity, the shallow redox potential of less than 0.4 V, etc. The fascinating characteristics of violet phosphorene are its eminent mobility (3000–7000 cm2 V−1 s−1) and immense direct band gap (2.5 eV). The configuration of black phosphorus is orthorhombic in nature, and the noticeable features of BP are its admirable carrier mobility, thickness-based band gap, potent in-plane anisotropy, etc., Black phosphorene which is procured from BP is known for its puckered honeycomb configuration [7], direct band gap (1.5 eV), carrier mobility (10,000 cm2 V−1 s−1) [8], negative Poisson ratio [9], etc., However, the fabrication of black phosphorene is quite complicated. Moreover, another allotrope named A7 phase is acquired from black phosphorus at superior pressures [10], which yields blue phosphorene with an indirect band gap of 2.9 eV [11]. The chemically inert phosphorene can be fabricated by mechanical exfoliation methods without compromising its stability [12]. Molecular-beam epitaxy technique was employed in synthesizing a new form of phosphorous – blue phosphorous on Au (1 1 1) substrate, which has been remarked by Zhang et al. [13] to be an indirect gap semiconductor (Band gap – 2 eV). Layer based reaction produced by phosphorene nanosheets were investigated by S. Cui et al. [14]. Indranil Lahiri group [15] reported the synthesis and applications of two-dimensional black phosphorene. The response of phosphorene as p-type or n-type semiconductor when doped or decorated with calcium was scrutinized by Lalitha et al. [16].
In general, the outstanding properties showcased by phosphorene are conditioned band gap (1.88 ± 0.24 eV) [17], high specific capacity (2596 mAh/g in theory), intense hole carrier mobility (103 cm2Vs−1), supreme mechanical pliability, high on-off current ratio (105) and noble anisotropic characteristics [18]. It is employed in various domains like optoelectronics, biomedicine as photothermal and photodynamic agents [19], chemo sensors, field effect transistors [20]. Habio Zeng group [21], [22], [23], [24], [25], [26] extensively studied the synthesis, electronic properties, and band structure studies of various two-dimensional materials. Kaloni team and other researchers successfully synthesized the ultrathin group-IV and group IV-VI compounds such as monochalcogenides, which shows similar electronic properties like black phosphorene. Besides, group-IVA and group IV-VI possess important features with regard to strong electrical and optical anisotropies, high carrier mobility with native p-type conductivity [27], [28], [29], [30], [31], [32], [33], [34], [35]. Besides, T. Zhao et al. [36] have predicted the red phosphorene by way of restructuring the black and blue phosphorenes. The authors confirmed its dynamic and thermodynamic stabilities based on first-principles studies. Owing to sp3 hybridization, RP exhibits semiconductor behavior. Moreover, for chemical sensor applications, the semiconductor material is a required one, so RP satisfies this criterion. Hence, we have chosen RP as a base substrate to adsorb cigarette toxicants.
Cigarette and tobacco smoke is regarded to be a serious issue among the people in increasing the mortality rate. Nearly 6 million people suffer (die) owing to tobacco consumption. Moreover, the death rate of smokers is noticed to be approximately three times more profuse than non-smokers. In addition, the toxic vapors released from the tobacco smoke and cigarette is found to affect both the children and non-smokers [37]. The main objective of the intended framework is to utilize the chemosensing ability of red phosphorene nanosheets to detect the toxic vapor molecules like acrolein, acrylamide, and nicotine, which is extensively present in the tobacco smoke and cigarettes.
Acrolein (2-propenal) which is extremely electrophilic in nature is α, β-unsaturated aldehyde. It is a metabolic product of cyclophosphamide [38] and is generated from both endogenous and exogenous root. It is found to be immensely available in tobacco smoke, industrial waste, oil-foods, fruits, and beverages. Partial combustion of wood, plastic, and petrol [39] contributes to the release of acrolein. Further, the lipid peroxidation process of DNA, proteins, and polyunsaturated fatty acids results in the production of acrolein [40]. The ill-effects caused in human beings as a result of exposure to acrolein are bronchial hyperactivity, reduction in the antioxidant enzyme activities [41], nasal irritation, disturbance in cellular antioxidative defence, mucus production [42], lung cancer, stimulated neurotoxicity in primary cortical neurons, hippocampal cells and dorsal root ganglionic neurons [43]. Moreover, acrolein is given a supreme priority in the catalog of toxic chemicals established by the United States Environmental Protection Agency. The exposure limit set by OSHA (Occupational Safety and Health Administration) is 0.1 ppm (for 8 hr TWA – time-weighted average) and 0.3 ppm (for 15 min STEL – short term exposure limit). The only admirable application of acrolein is its use as a biocide for inhibiting the rampant growth of weed, algae, mollusk, in marshy regions.
Acrylamide (CH2 = CH-CONH2), which is a constituent of polyacrylamide polymers, is categorized under the group of genotoxic and carcinogenic compounds (according to the World Health Organization) [44]. Other than tobacco smoke, root vegetables holding asparagine amino acid content and carbohydrate-rich foods are observed to release acrylamide vapors when cooked at high temperatures (above 120 °C), which is known as Maillard reaction [45]. The released vapor is ingested by humans and is circulated swiftly to heart, brain, liver, and thymus, resulting in several harmful neurological disorders [46], abdominal pain, sore throat, cough, and eye irritation. It is also the main factor in inducing cancer and obesity [47]. The recommended exposure limit fixed by OSHA is 0.03 mg/m3 (for 8 hr TWA), and the permissible limit is set to be 0.3 mg/m3 TWA. In addition, the beneficial use of acrylamide (2-propenamide – C3H5NO) is its utility as concrete in building, houses, and dams.
Nicotine (C5H4NC4H7NCH3) is a strong oxidizer that is either ingested or inhaled from tobacco smoke and cigarette. In general, it affects the cardiovascular system, reproductive system, and central nervous system. Exposure of nicotine leads to neural plasticity, which augments behavioral responses to conditioned stimuli [48], thereby serving as an addiction to continuous use towards tobacco smoke and cigarette, despite the smoker trying to quit it. Further, nicotine leads to elevated angiogenesis, cell proliferation, cell growth [49], and alleviated locomotor activity [50]. The geometry and the role of nicotinic receptors are modified owing to the continuous availability of nicotine in the brain. The personality behaviors, brain development, and genetic traits are adversely affected due to the presence of nicotine [51]. The skin exposure limit recommended by OSHA is 0.5 mg/m3 (for 8 hr workday). Overall, nicotine serves as a powerful constituent of tobacco smoke/cigarette, thereby causing untimely death. Moreover, the motivation behind the suggested model is initiated by the recorded framework of Mehdi Yoosefian group [52], [53], where the authors presented the acrolein adsorption on carbon nanotubes (CNT) and tobacco-specific nitrosamines adsorption on CNT. As mentioned before, the three toxic cigarette vapor molecules acrolein, acrylamide, and nicotine (that are released from the tobacco smoke and cigarette) are employed as target vapor in the present study. Moreover, the chemosensing ability of the red phosphorene nanosheets is investigated in the current work with the aid of the above-mentioned target vapors.
Section snippets
Estimation details
The structural and electronic features of red phosphorene nanosheet (P-NS) are scrutinized with the aid of SIESTA package [54] based on density functional theory (DFT) framework. The generalized gradient approximation (GGA) and Perdew-Burke-Ernzerhof (PBE) exchange–correlation functional [55], [56] are applied in scrutinizing the surface assimilation of poisonous vapors (acrolein, acrylamide, and nicotine) on red P-NS and also to investigate the electron transmission taking place between them.
Geometric configuration and electronic attributes of red phosphorene nanosheet
The single layer of red phosphorene nanosheet contains phosphorus atoms in layers built from Pbcm (57) space group [36]. Owing to the sp3 hybridization, buckling is noticed in red phosphorene nanosheets. The corresponding lattice constant of a, b and c for fully optimized red phosphorene nanosheet is found to be 20.00, 9.02 & 3.297 Å. Importantly, the red phosphorene nanosheet possesses two dissimilar P-atoms that leads to form three different bond distance between P-atoms with the value of
Acknowledgments
The authors wish to express their sincere thanks to Nano Mission Council (No.SR/NM/NS-1011/2017(G)) Department of Science & Technology, India for the financial support.
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