Adsorption Behavior of Toxic Carbon Dichalcogenides (CX₂; X = O, S, or Se) on β₁₂ Borophene and Pristine Graphene Sheets: A DFT Study

Abstract

The adsorption of toxic carbon dichalcogenides (CX₂; X = O, S, or Se) on β₁₂ borophene (β₁₂) and pristine graphene (GN) sheets was comparatively investigated. Vertical and parallel configurations of CX₂⋯β₁₂/GN complexes were studied herein via density functional theory (DFT) calculations. Energetic quantities confirmed that the adsorption process in the case of the parallel configuration was more desirable than that in the vertical analog and showed values up to −10.96 kcal/mol. The strength of the CX₂⋯β₁₂/GN complexes decreased in the order CSe₂ > CS₂ > CO₂, indicating that β₁₂ and GN sheets showed significant selectivity for the CSe₂ molecule with superb potentiality for β₁₂ sheets. Bader charge transfer analysis revealed that the CO₂⋯β₁₂/GN complexes in the parallel configuration had the maximum negative charge transfer values, up to −0.0304 e, outlining the electron-donating character of CO₂. The CS₂ and CSe₂ molecules frequently exhibited dual behavior as electron donors in the vertical configuration and acceptors in the parallel one. Band structure results addressed some differences observed for the electronic structures of the pure β₁₂ and GN sheets after the adsorption process, especially in the parallel configuration compared with the vertical one. According to the results of the density of states, new peaks were observed after adsorbing CX₂ molecules on the studied 2D sheets. These results form a fundamental basis for future studies pertaining to applications of β₁₂ and GN sheets for detecting toxic carbon dichalcogenides.

1. Introduction

Recently, the emission of greenhouse gases and toxic molecules into the environment has gathered unprecedented attention from the scholarly community. These molecules might cause severe heart and lung conditions and contribute to the greenhouse impact and the destruction of the ozone layer [1,2,3,4]. Among these harmful molecules, carbon dioxide (CO₂) is a crucial gas because of its high concentration in the atmosphere as a result of the combustion of petroleum, coal, and other fossil fuels [5]. Carbon disulfide (CS₂) is another toxic gas that adversely affects human health. It was documented that exposure to CS₂ gas leads to many problems, including paucity of vitamin B₆ and an increase in heart attack risk [6,7]. In the same vein, the carbon diselenide (CSe₂) molecule is well recognized as a highly toxic molecule with unpleasant properties [8,9]. Because of its high toxicity, the CSe₂ molecule must be handled with utmost care [10]. Many researchers have accordingly focused their efforts on developing various effective sensors for monitoring such toxic molecules.

Two-dimensional (2D) materials are a topic of interest for sensing purposes due to their vital physical and chemical properties. Graphene (GN), the first 2D form of carbon produced experimentally in 2004 [11], has received sustained attention due to its superior optical and mechanical properties [12,13,14,15,16,17]. Based on the electronic properties of 2D materials, the GN sheet was previously nominated as a Dirac material and could be recognized by defining its pseudomobility energy edges, energy spectrum surrounding the Fermi energy, and zero-energy confined state modes [18].

Crucially, GN has been used in many fields such as gas sensors [19], energy production [20], and spintronic devices [21]. The utilization of pristine and doped GN in detecting toxic gases, such as CO, NO, NO₂, and NH₃, has been investigated [14,22,23].

In addition to GN, many 2D materials have been developed, like molybdenum disulfide [24,25,26], phosphorene [27,28], silicene [29,30], and germanene [31,32], as active nanomaterials. Among the new 2D materials, borophene [33] has aroused the interest of the academic community. Indeed, borophene has been well characterized with versatile superior properties, including superconductivity, chemical complexity, low density, large bulk modulus, and high carrier mobility [34,35,36]. Borophene was earlier synthesized on a silver (111) surface in an ultrahigh vacuum [33]. Two phases of borophene have been observed using various deposition temperatures: the β₁₂ phase with 1/6 vacancy concentration and the χ₃ phase with 1/5 vacancy concentration [37]. From the literature, experimental and theoretical studies have revealed that all phases of borophene are metallic and exhibit superb electronic conductivity [37,38]. Further electronic properties of borophene as a Weyl 2D material, including high anisotropy and topological character, were also revealed [39,40].

The most stable type of borophene was reported to be β₁₂ borophene (β₁₂) [37,41]. Therefore, the sensing and trapping of greenhouse gases and other atmospheric pollutants (e.g., CO_x, CH₄, NH₃, and NO_x) using the β₁₂ sheet has grown significantly [42,43,44,45].

Hence, this work was accordingly designed in order to deeply understand the potentiality of β₁₂ and GN sheets to adsorb CX₂ toxic molecules by employing density functional theory (DFT) calculations. In that spirit, the CX₂⋯β₁₂/GN complexes (CX₂; X = O, S, or Se) were characterized in both vertical and parallel configurations (Figure 1). The geometric structures of CX₂⋯β₁₂/GN complexes were first subjected to relax calculations to obtain the minimum structures. The adsorption energies were then computed upon the relaxed structures of all the complexes under study. For most stable CX₂⋯β₁₂/GN complexes, charge transfer, electronic band structure, and density of state (DOS) analyses were performed to clearly elucidate the effect of the adsorption process on the features of the inspected 2D sheets. The findings of this study form a basis for future studies relevant to the applications of β₁₂ and GN.

2. Computational Methods

Geometric optimization and energy calculations of the CX₂⋯β₁₂/GN complexes (CX₂; X = O, S, or Se) were carried out in accordance with density functional theory (DFT) [46,47] via the Quantum ESPRESSO 6.4.1 package [48,49]. To describe the electronic interactions, the Perdew–Burke–Ernzerhof (PBE) exchange-correlation functional of the Generalized Gradient Approximation (GGA) was applied [50]. Ultrasoft pseudopotential was adopted for describing the interaction of valence electrons and the atomic cores [51]. The Grimme (DFT-D2) algorithm [52] was applied to correct the dispersion energy of the van der Waals interactions. In all the executed computations, the energy cutoff was set to 50 Ry, and the charge density cutoff was 500 Ry. The structures were optimized at energy and force convergence of 10⁻⁵ eV and 10⁻⁴ eV/Å, respectively. To sample and analyze the first Brillouin zone (BZ), Monkhorst–Pack grids were utilized with 6 × 6 × 1 k-points for geometric optimization and adsorption energy calculations. For the electronic structure calculations, 12 × 12 × 1 k-points were utilized. The Marzari–Vanderbilt smearing technique was performed to speed up the convergence [53]. To avoid interactions between neighboring atoms in the z-direction of the β₁₂ and GN sheets, a vacuum layer with 20 Å was used. Supercells of 3 × 4 × 1 and 6 × 5 × 1 were modeled to calculate the adsorption energy of β₁₂- and GN-containing complexes, respectively, containing 60 atoms in both sheets. For the CX₂⋯β₁₂/GN complexes, both vertical and parallel configurations were considered, as depicted in Figure 1. The adsorption energy (E_ads) of all the studied complexes was computed using Equation (1):

$$E_{\mathrm{ads} }=E_{{\mathrm{CX}}_2\cdots 2\mathrm{D}\mathrm{sheet}}-\left(E_{{\mathrm{CX}}_2}+E_{2\mathrm{D}\mathrm{sheet}}\right)$$

(1)

where $E_{{\mathrm{CX}}_2\cdots 2\mathrm{D}\mathrm{sheet}}$, $E_{{\mathrm{CX}}_2}$, and $E_{2\mathrm{D}\mathrm{sheet}}$ represent the energies of complexes, adsorbed CX₂ molecules, and 2D sheets, respectively. The charge density difference (∆ρ) calculations were estimated using Equation (2):

$$\Delta \rho ={\rho }_{\mathrm{total}}-\left({\rho }_{{\mathrm{CX}}_2}+{\rho }_{2\mathrm{D}\mathrm{sheet}}\right)$$

(2)

where ${\rho }_{\mathrm{total}}$, ${\rho }_{{\mathrm{CX}}_2}$, and ${\rho }_{2\mathrm{D}\mathrm{sheet}}$ are the charge densities of complexes, adsorbed CX₂ molecules, and 2D sheets, respectively. The Visualization for Electronic and Structural Analysis (VESTA) package was used to generate the ∆ρ maps [54]. Analysis of the Bader charge [55] was utilized to determine the charge transfer (Q_t) to or from the 2D sheets according to Equation (3):

$$Q_{\mathrm{t}}=Q_{\mathrm{combined}2\mathrm{D}\mathrm{sheet}}-Q_{\mathrm{isolated}2\mathrm{D}\mathrm{sheet}}$$

(3)

where Q_{combined 2D sheet} indicates the total charge of the 2D sheets after the adsorption process, and Q_{isolated 2D sheet} represents the total charge of the 2D sheets before the adsorption process. To elucidate the electronic properties, the electronic band structure and the total and projected density of states (TDOS and PDOS) calculations were determined for the inspected 2D sheets. For the band structure calculations, high-symmetry points—namely, Г (0.0, 0.0, 0.0), Y (0.5, 0.0, 0.0), S (0.5, 0.5, 0.0), and X (0.0, 0.5, 0.0)—were selected, and 50 points were taken between each high-symmetry point.

3. Results and Discussion

3.1. Geometric Structures

The structures of the β₁₂ and GN sheets were fully relaxed prior to the adsorption of the CX₂ molecules on their surfaces, and the obtained structures are given in Figure 2.

After the relaxation of the β₁₂ and GN sheets, the optimized lattice parameters of their primitive cells were a = 5.06 Å and b = 2.93 Å for β₁₂ sheets (Figure 2), while a and b had a similar value of 2.47 Å in the case of GN sheets. The obtained findings were compatible with experimental and theoretical evidence [33,37,56,57].

According to the equilibrium structures displayed in Figure 2, four probable adsorption sites were identified in the β₁₂ sheet—namely, top (T), hollow (H), and two bridge (Br1 and Br2) sites. For GN sheets, the top (T), bridge (Br), and hollow (H) sites were located above the carbon atom, C–C bond, and center of the hexagonal ring, respectively.

3.2. Adsorption Energy Calculations

The adsorption process within the vertical and parallel configurations of the CX₂⋯β₁₂/GN complexes (where X = O, S, or Se) was unveiled at variant sites (Figure 2). The CX₂⋯β₁₂/GN complexes were first relaxed, and the obtained structures are given in Figure S1. The adsorption energies (E_ads) for all relaxed complexes were then assessed and are gathered in

Table 1. Adsorption energies (E_ads, kcal/mol) and equilibrium distances (d, Å) for the vertical and parallel configurations of the CX₂⋯β₁₂/GN complexes (where X = O, S, or Se), in addition to the charge transfer differences (Q_t, e) for the investigated 2D sheets after adsorbing the CX₂ molecules.

2D Sheet	Adsorption Site a	Carbon Dichalcogenides (CX2)
		CO2			CS2			CSe2
		Eads (kcal/mol)	d (Å)	Qt b (e)	Eads (kcal/mol)	d (Å)	Qt b (e)	Eads (kcal/mol)	d (Å)	Qt b (e)
Vertical Configuration c
β12	T	−2.05	3.24	−0.0117	−3.54	3.35	−0.0219	−5.35	3.30	−0.0127
	H	−1.76	3.14	−0.0122	−4.25	3.09	−0.0199	−6.73	3.04	−0.0036
	Br1	--- d	--- d	--- d	--- d	--- d	--- d	--- d	--- d	--- d
	Br2	−2.13	3.17	−0.0120	−3.47	3.34	−0.0233	−5.04	3.33	−0.0189
GN	T	−1.77	3.16	−0.0055	−3.13	3.31	−0.0077	−4.39	3.31	−0.0051
	H	−1.95	3.03	−0.0059	−3.28	3.23	−0.0097	−4.49	3.26	−0.0072
	Br	−1.79	3.14	−0.0055	−3.14	3.29	−0.0072	−4.39	3.30	−0.0040
Parallel Configuration c
β12	T	−2.86	3.41	−0.0213	−5.49	3.49	0.0044	−8.54	3.43	0.0513
	H	−4.42	3.17	−0.0271	−6.53	3.32	0.0139	−10.96	3.26	0.0724
	Br1	−3.78	3.22	−0.0304	−6.29	3.38	−0.0039	−9.54	3.34	0.0335
	Br2	−2.96	3.37	−0.0225	−5.69	3.44	0.0044	−8.74	3.39	0.0484
GN	T	−3.64	3.19	−0.0155	−5.17	3.46	−0.0010	−6.81	3.49	0.0063
	H	−3.29	3.26	−0.0114	−4.83	3.52	0.0008	−6.45	3.55	0.0118
	Br	−3.77	3.14	−0.0146	−5.31	3.42	−0.0019	−6.91	3.47	0.0068

^a All adsorption sites on the β₁₂ and GN surfaces are shown in Figure 2. ^b Q_t was estimated using Equation (3). ^c Figure S1 displays all relaxed structures of the CX₂⋯β₁₂/GN complexes. ^d No favorable adsorption was observed.

. The most desirable relaxed structures of the CX₂⋯β₁₂/GN complexes are provided in Figure 3.

Apparently, the relaxed structures of the CX₂⋯β₁₂/GN complexes showed the ability of the β₁₂ and GN sheets to adsorb toxic CX₂ molecules (Figure S1), resulting in significant negative adsorption energies (Table 1). From Figure 3 and Table 1, the CX₂ β₁₂ and GN equilibrium distances were found to be in the ranges 3.04–3.49 and 3.03–3.55 Å, respectively.

For adsorption of the CX₂ molecules on the β₁₂ sheet in the vertical configuration, the CS₂⋯ and CSe₂⋯H@β₁₂ complexes exhibited the most significant negative adsorption energies with values of −4.25 and −6.73 kcal/mol, respectively. For the CO₂⋯β₁₂ complexes, the most favorable adsorption energy value of −2.13 kcal/mol was obtained at the Br2 adsorption site of the β₁₂ sheet (Table 1). In the parallel configuration, it was observed that the most favorable adsorption site on the β₁₂ sheet for adsorbing all the CX₂ molecules was the H@β₁₂ site (Figure 3). Notably, the CSe₂⋯H@β₁₂ complex had the largest negative adsorption energy, followed by the CS₂⋯H@β₁₂ and CO₂⋯H@β₁₂ complexes, with values of −10.96, −6.53, and −4.42 kcal/mol, respectively (Table 1).

Similar to the CX₂⋯β₁₂ complexes, the most considerable negative adsorption energies were generally observed in the case of CSe₂⋯GN complexes. In the case of the vertical configuration, the E_ads values of the studied complexes were noticed to decrease in the order CX₂⋯H@GN > ⋯Br@GN > ⋯T@GN, showing the favorability of the H@GN site. Numerically, the E_ads values of CS₂⋯H@GN, CS₂⋯Br@GN, and CS₂⋯T@GN were found to be –3.28, –3.14, and –3.13 kcal/mol, respectively. For the parallel configuration, the favorability of the CX₂⋯GN complexes increased in the order of CX₂⋯H@GN < CX₂⋯T@GN < CX₂⋯Br@GN. It was also observed that the CSe₂⋯Br@GN complex with an equilibrium distance of 3.47 Å had the most significant E_ads, with a value of −6.91 kcal/mol (Table 1).

Ultimately, all the studied carbon dichalcogenides (CX₂; X = O, S, or Se) showed negative values of E_ads, indicating greater preferentiality of the parallel configuration of the CX₂⋯β₁₂/GN complexes compared with the vertical one.

3.3. Band Structure Calculations

To trace the influence of the adsorbed CO₂, CS₂, and CSe₂ molecules on the electronic features of the β₁₂ and GN sheets, electronic band structure analysis was performed for the pure and combined 2D sheets. The PBE functional was used to calculate the band structure on the high-symmetry path of the BZ. The Г-Y-S-X-Г and Y-S-X-Г-Y paths were selected for band structures of the β₁₂ and GN sheets, respectively. Figure S2 illustrates the band structures of the pure β₁₂ and GN sheets. The electronic band structure calculations of the adsorbed CX₂ molecules at the most favorable adsorption sites on the β₁₂ and GN sheets were plotted and are shown in Figure 4.

According to Figure S2, the electronic band structure of the pure β₁₂ surface showed a metallic character that was attributed to the presence of many bands that crossed the Fermi level along the high-symmetry path. In comparison, the Dirac point on the pure GN surface between points X and Г indicated that the GN exhibited a semiconductor amplitude that was consistent with that in previous work [17].

Figure 4 shows that the electronic properties of 2D sheets were marginally affected by the adsorption of the CO₂ molecule in both studied configurations on the surfaces of the β₁₂ and GN sheets (see Figure S2). Such an observation outlines that β₁₂ and GN cannot be highly effective CO₂ sensors, which agrees with evidence from previous studies [44,58]. In contrast, the adsorption of the CS₂ and CSe₂ molecules in vertical and parallel configurations on the β₁₂ and GN sheets resulted in the appearance of many new bands in valence and conduction regions, as illustrated in Figure 4. The band structure plots showed that the bands of β₁₂ moved far away from each other after adsorbing CS₂ and CSe₂ molecules, confirming the strong adsorption of these molecules on the β₁₂ sheet. In detail, the resultant band structures after the adsorption of CS₂ molecules on β₁₂ showed extra conduction bands in the vertical and parallel configurations at around 2.3 and 1.8 eV, respectively. Besides this, new valence bands were noticed at –1.8 and –2.0 in the vertical and parallel configurations, respectively. For CS₂⋯GN complexes, additional conduction and valence bands in both configurations were found at 1.5 and –2.5 eV, respectively. The band structures of the CSe₂⋯β₁₂ complexes strongly affirmed the more evident impact of the adsorbed CSe₂ molecules on the electronic characteristics of the β₁₂ sheet in the parallel configuration compared with the vertical analog. For adsorption of the CSe₂ molecule in the parallel configuration at the H@β₁₂ site, new bands were observed at 1.35, 1.55, and 1.65 eV in the conduction region. In addition, new bands at −0.4, −0.65, and −1.75 eV appeared in the valence region, as depicted in Figure 4.

Conspicuously, the results regarding the band structure demonstrated that the CSe₂⋯β₁₂ complexes were more favorable than the CS₂⋯β₁₂ complexes, as revealed by the bands that moved toward the Fermi level. To sum up, the electronic characteristics of the studied 2D sheets after adsorbing CX₂ molecules were improved in the order CO₂⋯β₁₂/GN < CS₂⋯β₁₂/GN < CSe₂⋯β₁₂/GN, which is consistent with the results regarding the adsorption energies (Table 1). The appearance of new valence and conduction bands indicates the interaction of the CX₂ molecules with the investigated 2D sheets. In addition, the presence of the Dirac point was not affected by the adsorption of CX₂ molecules on the GN sheet, confirming the physical adsorption of CX₂ on the GN sheet.

3.4. Charge Transfer Calculations

Bader charge analysis is considered an informative method for deducing the charge transfer throughout the adsorption process [55,59]. Thus, the charge transfer (Q_t) was calculated for the vertical and parallel configurations of the CX₂⋯β₁₂/GN complexes at variant sites, and the results are given in Table 1. Negative and positive signs of the Q_t values indicate the transference of charge from the CX₂ molecules to the 2D sheet and from the 2D sheet to the adsorbed CX₂ molecules, respectively.

According to the Q_t values recorded in Table 1, adsorption of the CX₂ molecules in the vertical configuration at different adsorption sites on the β₁₂ sheet was noticed with negative values of Q_t. For instance, the CO₂⋯, CS₂⋯, and CSe₂⋯β₁₂ complexes at the T site exhibited Q_t values of –0.0117, –0.0219, and –0.0127 e, respectively. These negative values demonstrate that the β₁₂ sheet behaved as an electron acceptor.

The adsorption of the CO₂ molecule on the β₁₂ sheet, in the case of the parallel configuration, had negative values of Q_t, demonstrating the electron donor character of the CO₂ molecule. Moreover, the adsorption of the CS₂ and CSe₂ molecules on the β₁₂ sheet showed positive Q_t values, proposing that the CS₂ and CSe₂ molecules acted as electron acceptors. Numerically, Q_t values of 0.0044 and 0.0513 e were shifted from the β₁₂ sheet toward the CS₂ and CSe₂ molecules at the T@β₁₂ site, respectively. In line with the adsorption energy results, the CSe₂⋯H@β₁₂ complex, the most favorable adsorption system in the parallel configuration, was found to have the largest positive Q_t value of 0.0724 e.

For the vertical configuration of the CX₂⋯GN complexes, the H@GN site showed the highest negative Q_t values, consistent with its energetic preferentiality. Notably, all the CX₂⋯GN complexes showed negative values of Q_t, illustrating the potent ability of the GN sheet to accept electrons from the CX₂ molecules.

Negative Q_t values were observed for the parallel configuration of the CO₂⋯T/H/Br@GN complexes, while both negative and positive Q_t values were found at the studied adsorption sites in the case of the CS₂⋯GN complexes. For adsorption of the CSe₂ molecule, it can be seen that the charge was transferred from the GN sheet to the adsorbed CSe₂, as indicated by the positive Q_t values shown in Table 1.

At the most favorable energetic sites, the charge density difference (∆ρ) maps of the CX₂⋯β₁₂/GN complexes were plotted and are depicted in Figure 5.

As seen in Figure 5, the ∆ρ maps of the CX₂⋯β₁₂ complexes in the vertical configuration showed that the CX₂ molecules acted as electron donors, as demonstrated by the negative Q_t values (Table 1). In the case of the parallel configuration, the charges were shifted from the CO₂ to the β₁₂ sheet, as seen from the charge accumulation region existing below the CO₂ (cyan region) and corroborated by the negative Q_t value in Table 1 (−0.0271 e). A depletion region (i.e., yellow color) was clearly observed above the β₁₂ sheet in the case of the adsorption of CS₂ and CSe₂ molecules in the parallel configuration, which was consistent with the positive Q_t values stated in Table 1. This observation emphasized that CS₂ and CSe₂ molecules have the potential to draw charge from the β₁₂ sheet.

For the vertical configuration of the CX₂⋯GN complexes, the existence of regions with accumulated charge ensures the adsorption of CX₂ molecules on the β₁₂ and GN sheets. The accumulated charge above the GN sheet within the CO₂⋯ and CS₂⋯GN complexes in the parallel configuration indicated that electrons were transferred from the CO₂ and CS₂ molecules to the GN sheet (Figure 5). In comparison, the depletion region above the GN sheet in the case of adsorption of the CSe₂ molecule revealed the ability of the molecule to attract charge from the sheet.

To recapitulate, the Bader charge findings revealed that the charge was transferred from the CX₂ molecules to the studied 2D sheets in the vertical configuration, indicating the electron-donating character of the CX₂ molecules. The CO₂⋯β₁₂/GN complexes in the case of parallel configuration had the largest negative Q_t values, followed by CS₂⋯β₁₂/GN, then CSe₂⋯β₁₂/GN complexes. The small Q_t values confirmed physical adsorption between the CX₂ molecules and the investigated 2D sheets. Consistent with the literature, the electronic properties of the β₁₂ and GN sheets were changed by transferring electronic charge to or from the adsorbed molecules, indicating their potential for use as sensors [60,61,62].

3.5. Density of State Calculations

For pure and combined 2D sheets, density of state (DOS) analysis was carried out in terms of total and projected DOS (TDOS and PDOS). The TDOS and PDOS of the pure β₁₂ and GN surfaces are illustrated in Figure S3.

From the data in Figure S3, the TDOS peaks of the pure β₁₂ sheet at the Fermi level had high DOS, demonstrating that the β₁₂ sheet had a metallic property. In the case of the GN surface, the TDOS peaks reached zero at the Fermi level, showing the presence of the Dirac point on the pure GN surface. The DOS results confirmed the band structures in Figure S2. For β₁₂ and GN surfaces before adsorbing CX₂ molecules, the major contributions to the DOS were ascribed to the PDOS of B_p and C_p, respectively.

Figure 6 shows the TDOS and PDOS for the β₁₂ and GN sheets within the vertical and parallel configurations of the CX₂⋯β₁₂/GN complexes (where X = O, S, or Se) at the most favorable energetic sites. For adsorption of the CO₂ molecule on the β₁₂ sheet in both configurations, a significant hybridization between the PDOS of O_p and B_p peaks was observed in the valence region between −3.9 and −4.5 eV. In addition, the TDOS and PDOS peaks of adsorption of the CO₂ molecule on the GN sheet in both configurations demonstrated the occurrence of a weak physical adsorption process. Hence, the appearance of the PDOS of O_p peaks within the CO₂⋯GN complexes in both configurations was noticed in the valence and conduction regions ranging from –4.5 to –5.6 eV and from 3.5 to 4.0 eV, respectively.

Conspicuously, the PDOS of S_p was the major contributor to the adsorption within both modeled configurations of the CS₂⋯β₁₂/GN complexes. For both configurations of CS₂⋯β₁₂ and ⋯GN complexes, the appearance of the PDOS of S_p peaks was observed in the valence region with values from −1.5 to −2.5 eV and from −2.0 to −3.0 eV, respectively.

For both configurations of CSe₂⋯β₁₂/GN complexes, the PDOS of Se_p peaks appeared in the valence region in the range from −1.0 to −2.2 eV within the CSe₂⋯β₁₂ complexes and from −1.5 to −2.3 eV within the CSe₂⋯GN complexes.

Overall, the DOS results outlined that the electronic properties of the β₁₂ and GN sheets were changed after adsorbing the CX₂ molecules in vertical and parallel configurations. The appearance of the new DOS peaks indicated the occurrence of adsorption of the CX₂ molecules on the investigated 2D sheets.

4. Conclusions

The adsorption of toxic carbon dichalcogenides (CX₂; X = O, S, or Se) on β₁₂ and GN sheets was assessed via DFT calculations. After geometric relaxation, adsorption energy calculations and electronic analyses were carried out for vertical and parallel configurations of all CX₂⋯β₁₂/GN complexes. The favorability of CX₂⋯β₁₂/GN complexes was more obvious in the parallel configuration compared with the vertical one. The CSe₂⋯H@β₁₂ complex in the parallel configuration was the most promising complex, with an adsorption energy value of –10.96 kcal/mol. The electronic properties of the β₁₂ and GN surfaces were notably changed after the adsorption of CS₂ and CSe₂ molecules. In comparison, the electronic characteristics of the β₁₂ and GN surfaces were slightly changed after adsorbing the CO₂ molecule. Based on Bader charge analysis, an electron-donating character was observed for all the CX₂ molecules in vertical configuration within the CX₂⋯β₁₂/GN complexes. In comparison, the CS₂ and CSe₂ molecules acted as electron acceptors within the parallel configuration of the CS₂⋯ and CSe₂⋯β₁₂/GN complexes. The results of the electronic band structure, TDOS, and PDOS demonstrated that adsorption of the CX₂ molecules on the β₁₂ and GN sheets boosted their electronic properties. The appearance of new bands and DOS peaks affirmed the interaction of the CX₂ molecules with the investigated 2D sheets. Based on the findings of the present study, it appears promising to use the β₁₂ and GN sheets as a suitable sensor for CX₂ molecules, particularly CS₂ and CSe₂ molecules.