Comparative study the impact of single and double vacancy defects in BC 3 nanosheet on the acetaminophen detection

Density functional theory (DFT) calculations was used to investigate the interaction between the prefect and defected boron carbide (BC 3 ) monolayer nanosheet and conventional acetaminophen (AP) drug. The obtained findings indicate no considerable interaction between BC 3 nanosheet and AP drug. Thus, perfect BC 3 is not highly sensitive against AP presence regarding weak interactions. We explored if introducing single vacancy (SV) and double vacancy (DV) defect in prefect BC 3 nanosheet can enhance the interaction with AP drug. The adsorption energy of AP drug on the DV-BC 3 and SV- BC 3 surface were calculated about -15.32 and -23.78 kcal/mol, respectively. After AP adsorption, a considerable change of bang gap and work function of DV-BC 3 and SV-BC 3 was observed while only the electrical bang gap of perfect BC 3 was changed after AP adsorption and the work function change was negligible. It can be concluded that both defected BC 3 sheets can act as both electrical and work function sensor types while the perfect BC 3 can only act as an electrical sensor. The adsorption energy is remarkably changed in media with higher dielectric constant. Additionally, AP adsorption dramatically changes the magnetic properties of DV-BC 3 .


Introduction
Social development criteria such as education, lifestyle, and better medicines have promoted the human health standards during last 50 years [1]. However, there has been an increase in the usage of pharmaceuticals for lengthening life and also to treat a variety of diseases [2]. Acetaminophen (AP) (N-acetyl-P-aminophenol) is a conventional painkillers drug has been widely used to diminish fever and pain [3]. The AP disposal in waste water and ground water has been an environmental concern during last decades [4]. According to analytical chemistry literature, the detection concentration range of AP is about 100-1000 to ng -1 which challenges it an emerging waste water treatment concern worldwide [5][6][7][8][9][10][11]. Additionally, increasing AP value in drinking water has resulted in serious diseases including heart, gastro-intestine, and kidney disorders [12,13]. Furthermore, the AP overdose may lead to health hepato-and nephro-toxic [14,15]. AP detection in water and waste water is of a great deal of importance regarding the mentioned health concerning challenges and a straightforward and simple method of ACE detection is critical.
conventional analytical methods of AP detection pharmaceutical and biological media include spectrophotometry [16], high performance liquid chromatography (HPLC) [17], gas chromatography (GC) [18], titrametry [19], and chemiluminescence [20]. An efficient and appropriate extraction process is a requisite of all above mentioned methods before detection procedure. Although mentioned detection techniques often meet the standard requirements in miscellaneous samples, the intricate procedure and high costs may limit their widespread application. Nanomaterials are the most promising candidates for the detection of chemical species owing to their specificities such as high stability, considerably high specific surface area and high biocompatibility [21][22][23]. According to literature, many studies have been conducted based on their specific adjustable features and their exclusive application [24]. Nanomaterial-based detectors 4 have been widely investigated regarding their high sensitivity, low response time, low cost and capability of direct detection of AP in real-time.
The promising candidate to play effective role in energy storage, sensing, composites are carbon based nanomaterial. In addition to one component carbon based sheets, multicomponent structures of these sheets have been widely reported mainly including boron and nitrogen atoms [25,26].
These BCN monolayers, with elemental stoichiometries such as BN, BC2N, and BC3, show noticeable electronic specificities which can be applied for specific uses [27]. Both experimental (arch-discharge) and first principle methods have been applied to confirm the stability and existence of BC3 nanomaterial [28][29][30]. There are convincing experimental and theoretical evidences that verify the stability and existence of BC3 nanodomains in nanotube and sheet structure upon the replacement of boron atom in CNTs [31,32]. Strictly speaking, similar justifications have been reported to discuss the stability of both BC3 sheet. Several theoretical approaches have been proposed to study the structural and electronic identity of BC3 sheet [33][34][35]. Almost all types of BC3 sheets and also nanotube counterparts such as (n, 0) zigzag and (n, n) armchair, are classified as small-gap semiconductors [36]. Like other nanosheet, some imperfections may be introduced either during the synthesis or because of applied stress in experimentally available BC3 nanosheet [37,38]. Most frequently reported defects include antisites, vacancies, and topological defects. These defects often result in electronic, mechanical, and optical properties of nanotubes. Additionally, an interesting type of defect, obtained by rotation of a chemical bond by 90°, is called Stone-Wales (SW) topological defects mainly reported in CNTs and boron nitride nanotubes (BNNTs) [39][40][41][42][43][44][45].
In the present study, the adsorption behavior of AP drug on both perfect and defected BC3 nanosheet substrates toward AP adsorbate was investigated through density functional theory 5 (DFT) calculations. Considering the feasibility of mentioned sheets to act as sensors is targeted as well. The effect of dielectric constant, as the main factor determining the solvent specificities, on tendency of AP adsorbate toward BC3 sheet. Finally, the mechanistic study of adsorption process was done by applied NICS calculations.

Computational details
Quantum chemical calculations were done through density functional theory (DFT) by GAMESS program package [46]. All studied nanotube structures were geometrically optimized at the level of M06-2X/6-31G (d) [47]. Also, the aromaticity of the nanotubes was analyzed in GIAO-M06-2X/6-31G (d) level by nucleus independent chemical shift (NICS) value at the center of molecule as well as the nanotube axes to investigate the shielding effect of the whole tube. The adsorption energy (Ead) upon complexation between the BC3 nanosheet and AP drug is defined as: Ead=Esheet-AP -Esheet-EAP +δBSSE (1) In which Esheet and EAP are the total energy of BC3 nanosheet and AP drug, respectively. Esheet-AP is also, the total energy of the BC3-AP complex. We used counterpoise method to predict δ (BSSE, basis set superposition error).

3.1.Adsorption of AP drug on the perfect BC3 nanosheet
The interaction of AP drug with perfect BC3 surface was investigated to study the adsorption behavior of adsorbent. The adsorption behavior of BC3 toward AP species can elucidate whether this nanotube can effectively adsorb and detect this AP drug. Similar to main 2D grapheme and BN sheets, BC3 sheet has a hexagonal lattice. As can be seen in Fig.1, BC3 unit cell consists of six 6 C atoms and two B atoms. According to optimized geometry data, the B-C bond and C-C bond lengths are 1.56 and 1.42 Å, respectively. Also, the band gap of the BC3 monolayer is obtained about 2.33 eV as shown in Fig. 1, which is in agreement with the reported bond distance values reported at literature [36]. Considering the adsorption of AP drug onto BC3 substrate, the most feasible interaction configuration is considered of O atoms of adsorbates close to the boron atom of BC3. The BC3-AP complex is schematically shown in Fig. 2

3.2.Adsorption of AP drug on the defected BC3 nanosheet
As mentioned before, the interaction and adsorption of perfect BC3 nanosheet is not strong enough to capture AP effectively which is strictly needed for sensing and monitoring of AP drug.
Therefore, the tendency of BC3 substrate toward AP adsorbent and consequently the adsorption ability should be promoted. For this purpose, the effect of structural defects on the enhancement of potential adsorption of adsorbent was investigated. Experimentally, different detects have been applied in this type of materials such as: Stone-Waals and single and double vacancy and etc. [44]. 7 Vacancy defects have been widely studied as point defect types and their effects have on physicochemical nature of nanomaterials have been examined [40]. when an atom is missing from a lattice sites, the defect is known as a "vacancy" also known as a Schottky [40]. The single vacancy (SV) and double vacancy (DV) are the importance defect in which an atom is missing from its regular atomic site. It can be noted that vacancies are often created within solidification as a result of the vibration and local rearrangement of atoms [40].
As shown in Fig.3 Table 1. The optimized of AP drug on the SV-BC3 and SV-BC3 surface as shown in Fig.4. A significant enhancement of adsorption energy, -15.32 and -23.78 kcal/mol, were observed for AP on the SV-BC3 and SV-BC3 surface, respectively. According to obtained data, it can be noted that the adsorption of AP on DV-BC3 are stronger than the SV-BC3 and perfect BC3.
It was clearly found that the adsorbed molecule was attached closer to the DV-BC3 surface compared to SV-BC3 and perfect BC3.
Total charge density changes were monitored to investigate the interaction process. Fig. 5(a-b) shows the calculated total charge density of most stable structure for AP species on both DV-BC3 and perfect BC3 sheets. The picture shows that there is charge accommodation between the interaction region of AP molecule and DV-BC3. Contrarily, no evidence is found in AP drug and which σ and σ0 are the electrical conductivity signals of the DV-BC3 after and before of AP drug, respectively. From Eq. (3), one can write: Using Eq. (4), the response of the DV-BC3 and SV-BC3 were predicted to be 54323 and 80291, respectively and indicating sensitivity of the DV-BC3 to AP because of a high response value. It should be noted that absolute value of ΔEg is used for calculation of sensing responses. Therefore, it can be a promising electronic sensor for monitoring of AP drug.

3.4.NICS investigation
In compounds with π-electron systems with an applied external magnetic field, The induced ring current results in generation of an induced magnetic field in the opposite direction of the exerted magnetic field at the aromatic ring center [48]. Regarding the fact that the aromaticity cannot be observed by many examinations, acquiring any data about it should be provided from magnetic specificities [48]. Among most known magnetic methods to study the aromaticity, Nuclear magnetic resonance (NMR) chemical shifts and diamagnetic susceptibilities are the most conventional and straightforward ones. Diatropic compounds are defined as aromatic chemicals with noticeably high diamagnetic susceptibility while paratropic compounds are antiaromatic. In magnetic study of carbon nanotubes, the observed magnetic field inside the tube is resulted from diamagnetism and can be attributed to the ring currents in the molecular orbitals. Among all conventional magnetic parameters, the nucleus independent chemical shift (NICS) has been reported as a straightforward and applicable probe to consider the aromaticity of most compounds.
The characterization of aromaticity of molecules by NICS has been validated by many studies. highest negative NICS value compared to the rest of the systems which indicates that DV-BC3 is able to detect AP at the presence of a magnetic field of specific intensity. It can be concluded that the lone pair O atom electrons of AP molecule modify the uniformity in ring current and the πresonance system, exhibiting an ordered π-resonance in the parent DV-BC3, increases. The aromaticity was increased and negative NICS value was obtained during the adsorption process of AP drug.

3.5.Effect of solvents dielectric on the adsorption behavior of AP drug
The As can be seen, the value of Ead was decreasing significantly by decreasing the dielectric constant solvent. As mentioned above, Ead increases with the increasing dielectric constant. The solubility of AP increases as the dielectric constant is increased which is attributed to the solvent cage effect.

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In other words, by increasing solvent polarity, the solubility of AP molecules has increased and the value of adsorption energy has consequently increased.

3.6.Work function
The work function variation of defect and perfect BC3 were investigated for further evaluation of AP sensing. According to empirical investigations, the mechanism of the Φ-type gas sensors is defined based on the Kelvin process in which a Kelvin oscillator device is applied to evaluate Φ of the sample before and after the adsorption of AP on BC3. If AP drug adsorption substantially alters the Φ of the adsorbent, it can shift the gate voltage resulting in producing an electrical noise that facilitates the AP detection eventually [49]. In sensor-related studies, the minimum energy required to extract one electron from the Fermi level of a material to an infinite distance is often represented as Φ: Eq.5 defines the electron electrostatic potential energy as Vel (+∞) which is relatively far from the material surface and is presumed to be negative, and EF is Fermi level energy. By Assuming Vel (+∞) = 0, according to the Eq. 5, Φ = -EF, the Fermi level energy is estimated as: Having considered the Richardson Dushman relation (Eq.7), there is a relationship between the Φ value and the current densities of the electron, hence the Fermi level varies as a function of Φ variation, which is related to the the field emission change [50]: 12 here A is the constant of Richardson (A/m 2 ), and T is the absolute temperature (K).
Correspondingly, the electron current density released from the BC3 surface has a significantly change and the nanosheet can be regarded as an AP adsorption Φ-type sensor. The work function of AP drug adsorbed on the DV-BC3, SV-BC3 and BC3 decreases to 4.49 to 3.54 eV, 4.81 to 3.65 eV and 5.32 to 4.94 eV, respectively. The reduction of DV-BC3 and SV-BC3 work function after AP drug adsorption is about 33.50% higher compared to perfect BC3. As a result, the DV-BC3 and SV-BC3 are both electrical and work function sensor for AP detection, while the perfect BC3 is only electrical sensor.

3.7.Recovery time
The recovery time of a sensing material is often considered as an important factor to evaluate the applicability of a gas sensor and is defined according to a conventional transition state theory as follows [51]: Here, υ -1 is the attempt frequency. According on this equation, a considerably increased (more negative) energy corresponds to a much longer recovery time. The recovery time of AP drug on DV-BC3 was measured about 769 ms. This low recovery time value shows a short recovery time of AP drug from DV-BC3 surface.

Conclusion
DFT calculations were applied to study the tendency of both perfect and defected BC3 nanosheet toward the interaction of AP drug in gas and solvent media. The main conclusions are as follows: i) Both vacancy defect in BC3 sheet were improved the interaction with AP drug based on the adsorption energy value. 13 ii) The DV-BC3 and SV-BC3 sheet can act are both electrical and work function type sensors, while the perfect BC3 is the only an electrical sensor.
iii) It can be used the magnetic properties as an in another parameter for sensing of AP drug on the DV-BC3 sheet.
iv) The value of Ead was decreased significantly by decreasing the dielectric constant solvent.

Conflicts of Interest: None
Funding: None Ethical Approval: Not required