Selective highly sensitive gas sensing by using the BeP₂C monolayer: a theoretical study

Abstract

Identifying high-performance materials is essential for developing new gas sensors capable of detecting harmful gases. In this study, density functional theory (DFT) and the non-equilibrium Green's function (NEGF) method were employed to investigate the gas-sensitive properties of BeP₂C monolayer films. The structural, electronic, transport and gas sensitivity characteristics of the BeP₂C monolayer were examined for various adsorbed gases, including CO, CO₂, NH₃, NO, NO₂, H₂S, SO₂, H₂O and O₂. Except for CO₂ and O₂, all other gases are bound to the substrate via ionic bonds, with SO₂ additionally forming covalent bonds. Notably, NO, NO₂ and SO₂ have suitable adsorption energy on the BeP₂C monolayer and can change the electronic properties of the material. Current–voltage (I–V) characteristics and transport functions reveal that the BeP₂C monolayer exhibits high sensitivity and selectivity towards NO, NO₂ and SO₂ gases. The relative change in the work function for NO adsorbed on the BeP₂C monolayer is 10.14%, indicating its promising potential as a work-function type gas sensor for detecting NO. The BeP₂C monolayer is a high-performance, reusable gas sensor that can detect NO (2.61 ms) at room temperature and NO₂ (3.83 s) at 400 K. Furthermore, due to its high adsorption energy, the BeP₂C monolayer is also capable of capturing SO₂. This study provides a theoretical foundation for the application of BeP₂C in gas sensor technology.

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1. Introduction

Air quality is intimately connected to human health, with industrial emissions and vehicle exhaust gases posing significant environmental and health risks.¹ Pollutants such as NO₂ and SO₂ contribute to acid rain and can damage the human respiratory system.^1,2 To address these challenges, a variety of gas sensors have been developed to detect harmful gases,^3,4 with semiconductor gas sensors being particularly favored for their low cost and ease of fabrication. These sensors operate by measuring changes in the semiconductor resistance upon exposure to different gases^5,6 and are typically composed of metal oxide materials like NiO and ZnO.^7–11 However, traditional gas-sensitive materials have notable limitations, including high operating temperatures and low sensitivity. Researchers enhance the performance of existing gas sensors through various methods, such as doping and constructing heterostructures.^12–15 In addition, researchers are exploring new materials with superior properties, particularly two-dimensional (2D) materials, which have garnered significant attention for their unique physical and chemical characteristics. These materials are being investigated for a range of applications, including high-performance catalysis, batteries, and gas sensors.

2D materials have been extensively studied due to their unique physical and chemical properties, which have found diverse applications in fields such as high-performance catalysis, batteries, and gas sensors.^16–21 In the field of gas sensors, a variety of 2D materials have the potential to develop into high-performance sensors,^22–26 because 2D materials have considerable prospects due to their large specific surface area, high carrier mobility and large number of adsorption sites.^27–29 For example, the sandwich structure of the MoS₂ monolayer,^30,31 monolayers of metallic stanene,^32,33 and various carbon-based 2D materials have been studied.^34–43 The gas-sensitive properties of various 2D materials, such as C_xN_y,^34–37 B_xC_y,³⁸ C_xP_y,^39,40 and B_xC_yP_z,⁴¹ have been extensively studied. Recently, Azarmi et al. discovered a novel carbon-based 2D material, the BeP₂C monolayer, which demonstrates sensitivity to visible light.⁴² With a structure and band-gap similar to that of the B₃C₂P₃ monolayer,^41,43 the BeP₂C monolayer emerges as a promising candidate for gas sensor applications. However, research into its gas-sensitive properties is still in the early stages. Therefore, it is crucial to investigate the adsorption properties and underlying physicochemical mechanisms of the BeP₂C monolayer to fully realize its potential as a high-performance gas sensor material.

In this study, the gas-sensitive properties of the BeP₂C monolayer were investigated using first-principles calculations. The BeP₂C monolayer was modeled, and its interactions with eight common gas molecules were examined. We analyzed energy band diagrams, density of states diagrams, and electron local density distributions to assess the effects of gas adsorption on the material's structure and electronic properties. Additionally, we calculated the I–V characteristic curves and transmission spectra of the gas-adsorbed monolayer using the non-equilibrium Green's function method to further validate our findings. The results show that the BeP₂C monolayer functions as a work function sensor for NO, effectively detects NO at room temperature and NO₂ at 400 K, and is suitable for SO₂ capture, providing a preliminary theoretical basis for future research and applications.

2. Computational details and models

In this paper, the Vienna ab initio simulation package (VASP) code was used for first-principles calculations, employing the projector-augmented wave (PAW) method.^44,45 The visualization software VESTA was used to construct the model.⁴⁶ The truncation energy of the material was set to 500 eV. We tested the structural energy at various cutoff energies and determined that 500 eV was appropriate, as shown in Fig. S1 of the ESI.† The long-range dispersion forces were factored by using the D4-Grimme correction (DFT-D4) scheme.^47,48 The electron exchange energy and correlation energy are calculated using the Perdew–Burke–Ernzerhof (PBE) functional in generalized gradient approximation (GGA).^49–51 For sampled Brillouin zone (BZ) calculations, the 5 × 5 × 1 k-point grids were used for geometry optimization and the 10 × 10 × 1 k-points grids were used for electronic structure calculations by the means of Monkhorst–Pack (MP) methods.⁵² To test k-point convergence, we calculated the total energy of the BeP₂C monolayer with different k-point meshes and found that 5 × 5 × 1 and 10 × 10 × 1 meshes are sufficient to ensure calculation accuracy, as shown in Fig. S1 of the ESI.† The vacuum region of 20 Å was added to the structure to prevent interlayer interactions. The corresponding threshold values of 10⁻⁶ eV, 10⁻² eV Å⁻¹ and 5 × 10⁻³ Å were chosen for convergence tolerance of energy, maximum force and maximum system. The HSE06 hybrid functional with norm-conserving pseudopotentials was used to calculate the material's band gap.⁵³ In addition, we calculated the electron localization function (ELF) to analyze the adsorption type and used the climbing image nudged elastic band (CINEB) method^54,55 to calculate the diffusion barrier of the gases, with a convergence criterion of 0.02 eV Å⁻¹, as implemented in the VASP procedure. The non-equilibrium Green's function (NEGF) method was employed to compute the transmission characteristics using the Nanodcal code.^56–58 The behavior of all elements was described using double-zeta polarized atomic orbital basis sets (DZP), with the PBE functional employed. For self-consistency and transmission coefficient calculations, a k-point grid of 1 × 1 × 1 was used. The electron transmission spectrum at zero bias voltage, the transmission spectra at 0–1 V bias, and the I–V curve were calculated.

The adsorption energy (E_ads) that describes the adsorption stability of molecule on the BeP₂C monolayer was defined as follows:

E_ads = E_T − E_P − E_G (1)

where E_T, E_P, and E_G represents the total energy of the adsorbed compound, pure BeP₂C monolayer, and isolated gas molecule, respectively. The electrical current (I) through the scattering region at a finite bias voltage (V) was calculated using the Landauer–Buttiker formula as follows:⁵⁹where μ_L and μ_R are the chemical potentials of left and right electrodes, respectively, while f_L(E,μ_L) and f_R(E,μ_R) are electronic Fermi–Dirac distribution functions of left/right electrodes.⁶⁰T_σ(E,V) is the transmission probability that can be calculated as follows:

T(E) = Tr[Γ_R(E,V)G^R(E,V)Γ_L(E,V)G^A(E,V)] (3)

where G^R and G^A are the retarded and advanced Green's function, respectively, while Γ_L and Γ_R is the imaginary part of the self-energies known as coupling functions induced by interaction of channel areas with electrodes.

3. Results and discussion

3.1 Structural and electronic properties of gases on the BeP₂C monolayer

The BeP₂C monolayer, composed of beryllium, phosphorus, and carbon, is a two-dimensional graphene-like material. Its 4 × 2 × 1 supercell structure is illustrated in Fig. 1a. The lattice parameters of the BeP₂C monolayer are a = 3.25 Å and b = 5.50 Å, with bond lengths of 1.76 Å (Be–C), 1.64 Å (C–P), 2.21 Å (Be–P), and 2.13 Å (P–P). These results are consistent with previous data, confirming the accuracy of our structure.⁴² In the work of Azarmi et al.,⁴² the phonon spectrum of the BeP₂C monolayer was calculated. Additionally, we conducted ab initio molecular dynamics (AIMD) simulations of the BeP₂C monolayer, as shown in Fig. S2 of the ESI.† The NVT ensemble was adopted, and the system temperature was set to 300 K and 400 K. The molecular dynamics simulations were performed at the Gamma point and lasted for 10.0 ps, with a time step of 1 fs. These results indicate that the BeP₂C monolayer exhibits excellent stability at 400 K, with even better stability at 300 K.

Fig. 1 (a) The structure of the BeP₂C monolayer and (b) its band structure calculated using the HSE06 method. The brown, green, and gray balls represent the C, Be, and P atoms, respectively. Bond lengths are given in Å.

We further calculated the band structure and density of states (DOS) to determine the fundamental properties, as shown in Fig. 1b. The band-gap calculated using the PBE method is 1.462 eV, while the HSE06 method yields a band-gap of 2.217 eV, both of which are in general agreement with previous studies.⁴² The energy band structure obtained using the PBE method is presented in Fig. S3 of the ESI.†Fig. 1b shows that the conduction band minimum (CBM) and valence band maximum (VBM) are both located between the Γ and X points, with a difference of 0.06 eV. This indicates that the BeP₂C monolayer is an indirect band-gap semiconductor.

To investigate the gas-sensitive properties of the BeP₂C monolayer, we adsorbed eight common gas molecules (CO, CO₂, NH₃, NO, NO₂, H₂S, SO₂, H₂O and O₂) onto its surface. The BeP₂C monolayer offers numerous adsorption sites, including four top sites (Be, P, and C atoms), four bridge sites (Be–C, C–P, P–P, and Be–P bonds), and two hollow sites. Additionally, the orientation of gas molecule adsorption can vary. Considering these factors, we constructed various adsorption configurations for each gas. After structural optimization, we identified the most stable adsorption configuration for each gas molecule on the monolayer, as depicted in Fig. 2.

Fig. 2 The most stable configurations of the BeP₂C monolayer adsorbed with each molecule: (a) CO, (b) CO₂, (c) NH₃, (d) NO, (e) NO₂, (f) H₂S, (g) SO₂, (h) H₂O, and (i) O₂. The blue, red, white, and yellow balls represent the N, O, H, and S atoms, respectively.

Our results indicate that the optimal adsorption sites for most gas molecules are near the Be atom, except CO₂, which adsorbs on a hollow site. Except for CO₂ and O₂, the adsorption of other gases slightly deforms the BeP₂C monolayer. Moreover, the adsorption distances are relatively short; except CO₂ and H₂S, the distances between the gases and the BeP₂C monolayer range from 1.65 to 1.79 Å. The adsorption energies vary among the gases, reflecting differences in adsorption distances. Notably, NH₃, NO₂, and SO₂ exhibit the largest adsorption energies, with values of −1.083 eV, −1.079 eV, and −1.494 eV, respectively. The adsorption energies of CO₂ and O₂ on the BeP₂C monolayer are −0.198 eV and −0.114 eV, respectively. The adsorption energies of the other gases range from −0.504 eV to −0.721 eV. Detailed data are presented in Table 1. In addition, we calculated the diffusion barriers of nine gases on the BeP₂C monolayer, as shown in Fig. S4 (ESI†). The largest diffusion barrier is for CO (1.309 eV), while NH₃ (0.975 eV), NO₂ (0.864 eV), and SO₂ (1.270 eV) also have relatively high barriers. The smallest barrier is for O₂ (0.027 eV). This indicates that the diffusion of CO, NH₃, NO₂, and SO₂ on the BeP₂C monolayer is more difficult, while O₂ diffusion encounters minimal hindrance.

Table 1 Adsorption energy (E_ads), band-gap (E_g), charge transfer (Q), and recovery time (τ) of the BeP₂C monolayer due to the adsorption of nine common gases

System	E ads (eV)	E g (eV)^a	Q (eV)	τ (s) (300 K)	τ (s) (400 K)
a The values of band gaps obtained using the PBE method (out of parentheses) and the HSE06 method (in parentheses).
CO	−0.583	1.324 (2.073)	−0.203	6.10 × 10^−3	2.18 × 10^−5
CO2	−0.198	1.456 (2.210)	−0.030	2.11 × 10^−9	3.11 × 10^−10
NH3	−1.083	1.351 (2.086)	−0.439	1.5 × 10^6	4.30
NO	−0.561	0.745 (1.900)	−0.314	2.61 × 10^−3	1.15 × 10^−5
NO2	−1.079	0.104 (0.513)	−0.852	1.29 × 10^6	3.83
H2S	−0.504	1.335 (2.075)	0.004	2.88 × 10^−4	2.21 × 10^−6
SO2	−1.494	1.104 (1.730)	−0.850	1.19 × 10^13	6.41 × 10^6
H2O	−0.721	1.398 (2.142)	−0.019	1.26	1.19 × 10^−3
O2	−0.114	0.835 (2.214)	−0.046	8.19 × 10^−11	2.72 × 10^−11

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Based on adsorption distances and energies, we can infer that CO, NH₃, NO, NO₂, SO₂, and H₂O are not physically adsorbed on the BeP₂C monolayer. To more accurately determine the type of adsorption, we calculated the electron localization function (ELF) diagrams, as shown in Fig. 3. The ELF analysis reveals that, with the exception of CO₂ and O₂, all gases are ionically bonded to the Be atom of the BeP₂C monolayer. For NO₂ and SO₂, the two oxygen atoms are ionically bonded to Be, while the sulfur atom in SO₂ is covalently bonded to the carbon atom of the substrate, which accounts for the high adsorption energy of SO₂ on the BeP₂C monolayer.

Fig. 3 ELF plots of (a) CO, (b) CO₂, (c) NH₃, (d) NO, (e) NO₂, (f) H₂S, (g) SO₂, (h) H₂O, and (i) O₂ adsorbed on the BeP₂C monolayer.

We further calculated the energy band structure and density of states (DOS) diagrams for the gas-adsorbed configurations, as shown in Fig. 4. The variation in the band gap due to gas adsorption can be determined using the following equation:

where E_gas and E_pure represent the band gaps before and after adsorption of gases, respectively. The adsorption of CO, CO₂, NH₃, H₂S and H₂O has a minimal impact on the band gap of the BeP₂C monolayer, of which the ΔE_g is less than 7%, as calculated in conjunction with Table 1. The PDOS diagrams (Fig. 4) further confirm that no impurity states appear near the Fermi energy level for these gases, indicating that the BeP₂C monolayer is insensitive to them.

However, after NO adsorption, selective spin splitting occurs, resulting in a spin-up band gap of 1.340 eV and a spin-down band gap of 0.745 eV. This phenomenon arises because spin-down NO introduces impurity states both above and below the Fermi level, thereby reducing the band gap, as depicted in Fig. 4d. Similarly, NO₂ adsorption induces spin polarization in the BeP₂C monolayer, producing a band gap of 0.104 eV for spin-down electrons and 1.380 eV for spin-up electrons (Fig. 4e). The PDOS analysis reveals that the spin-down peak near the Fermi energy level is not due to NO₂, which might be attributed to the deformation of the BeP₂C monolayer caused by NO₂ adsorption. Additionally, since O₂ is a polar molecule, spin polarization occurs in the system, resulting in the generation of spin-down impurity states below the conduction band, which reduces the band gap of the BeP₂C monolayer to 0.835 eV, as depicted in Fig. 4i.

Fig. 4 The band structures and partial density of states (PDOS) of (a) CO, (b) CO₂, (c) NH₃, (d) NO, (e) NO₂, (f) H₂S, (g) SO₂, (h) H₂O and (i) O₂ adsorbed on the BeP₂C monolayer. In the band structures of NO, NO₂, and O₂, the red and black lines indicate spin-up and spin-down, respectively. In the PDOS the red and black lines represent the contributions of gases and BeP₂C monolayer, respectively.

The extent of charge transfer can indicate the degree to which the gas alters the properties of the BeP₂C monolayer. As shown in Table 1, the maximum charges obtained by NO₂ and SO₂ from the BeP₂C monolayer are 0.852 e and 0.850 e respectively, which may be due to the strong interaction between the two gases and the BeP₂C monolayer, which changes the structure of the substrate and accumulates electrons, while only H₂S loses 0.04 e. These gases almost all gain electrons from the BeP₂C monolayer. We believe this is simply because the material is more prone to losing electrons due to the presence of the element beryllium. To further visualize charge transfer, we plotted the charge differential density (CDD), as shown in Fig. 5. The analysis reveals that, for most gases, the yellow regions (indicating electron gain) are larger than the blue regions, except in the cases of CO₂ and H₂S. This suggests that these gases generally gain electrons, which aligns with the results of the Bader charge analysis. Additionally, a yellow charge region appears between the gases and the Be atoms of the BeP₂C monolayer, except for CO₂ and O₂, confirming that these gases form ionic bonds with Be atoms. Notably, NO₂ and SO₂ exhibit the highest levels of electron gain. This could be attributed to the fact that two oxygen atoms of NO₂ and all three atoms of SO₂ are adsorbed on the BeP₂C monolayer. In contrast, for other gases such as NO, only interaction with the Be atoms of the substrate occurs, resulting in weaker interactions, as shown in Fig. 5. The stronger interactions of NO₂ and SO₂ with the substrate lead to higher adsorption energies and greater charge transfer.

Fig. 5 CDD plots of (a) CO, (b) CO₂, (c) NH₃, (d) NO, (e) NO₂, (f) H₂S, (g) SO₂, (h) H₂O, and (i) O₂ adsorbed on the BeP₂C monolayer.

We also calculated the work functions of the BeP₂C monolayer and the adsorption system; detailed data are shown in Fig. 6. The work function is a measurable quantity that indicates the energy required to move an electron from the Fermi level to the vacuum level, and a work function-based gas sensor can be developed based on changes in the surface work function.^61,62 The work function of a pure BeP₂C monolayer is 5.591 eV. The adsorption of SO₂ and O₂ has a minimal effect on the work function of the material. Only the adsorption of NO₂ increased the work function of the BeP₂C monolayer, increasing it to 5.778 eV. In contrast, the adsorption of other gases reduces the work function of the material to varying degrees. The most significant reduction occurs with the adsorption of NO, which lowers the work function of the BeP₂C monolayer to 5.024 eV, resulting in a change rate of 10.14%, while the changes in the work function for other gases are less than 4.50%. Therefore, the BeP₂C monolayer shows promise as a work function-based gas sensor for NO.

Fig. 6 The work function of the BeP₂C monolayer adsorbed with nine gases. The dashed blue line represents the work function of the pure BeP₂C monolayer.

For gas sensors, the most critical performance metrics are sensitivity and recovery time. Experimentally, sensitivity is measured by observing changes in a material's resistance before and after gas adsorption. Theoretically, sensitivity can be approximated by evaluating the change in the material's band gap, as a larger band gap shift generally corresponds to a more significant change in resistance or conductivity, thereby indicating higher sensitivity. In the following section, we will calculate the transport properties of the material to provide a more precise assessment of its sensitivity. The band gap value calculated by the HSE06 method is more accurate than that by the PBE method, so we use the band-gap value obtained by this method to calculate ΔE_g. The ΔE_g of BeP₂C monolayer to NO, NO₂, SO₂ and O₂ is 14.30%, 76.85%, 21.97% and 42.90%, respectively, while ΔE_g < 7% of other gases, indicating that BeP₂C single-layer film is sensitive to these three gases. The recovery time is determined using the following equation:

where ν₀, k_B, and T represent the attempted molecule frequency that is 10¹² s⁻¹ in the visible light region,⁶³ the Boltzmann constant, and the temperature, respectively. As can be seen from their work, the recovery time calculated theoretically is in excellent agreement with the experimental value.⁶³ It is observed that, at the same temperature, the recovery time is related to the adsorption energy, with an optimal recovery time achieved at an appropriate adsorption energy. Table 1 shows that CO, NO, and H₂O have suitable recovery times of 6.10 × 10⁻³ s, 2.61 × 10⁻³ s, and 1.26 s, respectively, at room temperature. CO₂, H₂S, and O₂ exhibit low adsorption energies, leading to short recovery times. In contrast, NH₃, NO₂, and SO₂ have excessively long recovery times, rendering the BeP₂C monolayer less suitable for detecting these gases at room temperature. However, at a high temperature of 400 K, the BeP₂C monolayer exhibits suitable recovery times of 4.30 s and 3.83 s for NH₃ and NO₂, respectively. Furthermore, due to its high adsorption energy for SO₂ (E_ads = −1.494 eV), the BeP₂C monolayer has a long recovery time (1.19 × 10¹³ s at room temperature), making it more effective for capturing SO₂. In summary, the BeP₂C monolayer is a high-performance gas sensor for detecting NO at room temperature and NO₂ at 400 K, and it is also a promising material for capturing SO₂.

3.2 Transport properties of the BeP₂C monolayer with gas adsorption

Additionally, we investigated the transport properties of the BeP₂C monolayer. The device model used for this study is depicted in Fig. 7 and consists of two electrode regions, two screening regions, and a central scattering region. For 2D materials, it is standard practice to use the electrodes themselves, and we introduced a substantial number of electrons to enhance electrode conductivity, thereby achieving more accurate results.⁴⁰ To mitigate the adverse effects of the electrodes, we incorporated a 19.5 Å electrode extension area, which is adequate for such 2D materials. To assess the impact of gas adsorption on the transport properties of the BeP₂C monolayer, we analyzed the transmission spectra and current–voltage characteristic curves for both the pure monolayer and those adsorbed with NO, NO₂, H₂S, and SO₂ gases.

Fig. 7 The front view and side views of the two-probe system with the left and right electrode regions (in shade) and the central scattering region for detection gas molecules.

The transmission spectrum at zero bias voltage is illustrated in Fig. 8. The pure BeP₂C monolayer exhibits two peaks near the Fermi level. After gas adsorption, these peaks decrease to varying extents. Specifically, the adsorption of NO induces spin polarization in the BeP₂C monolayer and significantly diminishes the peak on the left side of the Fermi level. Similarly, NO₂ adsorption also causes spin polarization, which reduces the left-side peak and shifts the downward spin component towards the right side of the peak near the Fermi level. The adsorption of H₂S has a minimal effect on the transmission spectrum of the BeP₂C monolayer, whereas SO₂ adsorption slightly reduces the peak on the right side of the Fermi level. Overall, the reduction in electron transmittance after gas adsorption is attributed to changes in the material's charge distribution, which impedes electron transmission. Additionally, the spin polarization effects of NO and NO₂ further influence electron transport.

Fig. 8 Transmission spectra of pure BeP₂C monolayer and BeP₂C monolayer adsorbed with NO, NO₂, H₂S, and SO₂ under zero bias voltage.

We investigated the current–voltage (I–V) characteristics of various gases adsorbed on the BeP₂C monolayer, as depicted in Fig. 9a. We observed a negative differential resistance (NDR)^64–66 effect at a bias voltage of 0.6 to 1 V, which also occurs when adsorbing NO₂, H₂S and SO₂. However, the NDR of the BeP₂C monolayer was inhibited following NO adsorption, indicating that NO can be detected through this phenomenon. Furthermore, gas adsorption typically reduces the current of the BeP₂C monolayer, except in cases where the monolayer adsorbs H₂S (between 0.6 and 0.8 V) and NO (at 1 V), which results in increased current.

Fig. 9 (a) I–V characteristics of the BeP₂C monolayer and its adsorption with NO, NO₂, H₂S, and SO₂. (b)–(f) Transmission spectra of gas adsorbed onto the BeP₂C monolayer under varying bias pressures.

To elucidate the voltammetry characteristic curve, we plotted the transmission spectra at various bias voltages, as shown in Fig. 9b to f. The bias window is represented by the area within the blue dashed lines in the figure, indicating the range that contributes to the current. Each transmission peak within these windows contributes to the current. We observed that the integral area of electron transmission increased from 0 V to 0.6 V, signifying a rise in electron transmission channels and, consequently, an increase in current. However, between 0.8 V and 1 V, the transmission peak decreases for all gases adsorbed on the BeP₂C monolayer, except for NO. This results in a reduction in current, leading to a negative differential resistance phenomenon. Second, we observe that the charge transfer is inconsistent with the current change. For example, H₂S shows yellow regions (indicating electron gain) that are not larger than those of SO₂, yet the current change with voltage is more pronounced, as shown in in Fig. 5. We believe that this is due to the fact that CDD can clearly capture the charge movement and the polarization direction of the bonding electrons during the coupling process, while the current is related to the electron transmission spectrum. Therefore, the current of the BeP₂C monolayer with adsorbed H₂S molecules is higher than that with adsorbed SO₂ molecules, possibly due to the increased current density within the bias window caused by the presence of H₂S molecules.

4. Conclusions

In conclusion, we systematically investigated the gas-sensitive properties of the BeP₂C monolayer by examining its adsorption, structural changes, and electronic and transport properties in response to various gas molecules (CO, CO₂, NH₃, NO, NO₂, H₂S, SO₂, H₂O and O₂) using a combination of density functional theory (DFT) and the non-equilibrium Green's function (NEGF) method. Analysis of adsorption energy, charge transfer, adsorption distance, electron localization function (ELF), and charge density difference (CDD) revealed that, except for CO₂, the other molecules form ionic bonds with the Be atoms of the substrate, while SO₂ also exhibits chemical adsorption. The ΔE_g value of the BeP₂C monolayer to NO, NO₂ and SO₂ is 14.30%, 76.85% and 21.97%, respectively, indicating that these gases have a significant effect on the electronic properties of BeP₂C monolayers. In addition, the adsorption of NO changes the work function of the material by 10.14%. These findings demonstrate the high sensitivity and selectivity of the BeP₂C monolayer for these gases, further supported by electron transport properties such as current–voltage (I–V) characteristics and transmission spectra. At room temperature, the recovery time for NO is moderate (2.61 ms), while at 400 K, the recovery time for NO₂ is 3.83 s. However, the recovery time for SO₂ is excessively long, limiting its use for SO₂ detection. These results highlight the potential of the BeP₂C monolayer as a high-performance gas sensor capable of detecting NO at room temperature and functioning as a work-function-based sensor. The BeP₂C monolayer can also detect NO₂ at 400 K and serves as a candidate for SO₂ capture. Our research provides a theoretical basis for the development of high-performance gas sensors, contributing to the sustainable development of society and the improvement of human health.

Data availability

The data that support the findings of this study are available from the authors upon request.

Conflicts of interest

The authors declare that there are no competing interests.

Acknowledgements

This work was supported by the National Natural Science Foundation of China (No. 12204134), the Hainan Provincial Natural Science Foundation of China (123RC397 and 121QN167) and the Start-up Research Foundation of Hainan University (KYQD(ZR)-20093). We thank HZWTECH company for help and discussions regarding this study.

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Footnote

† Electronic supplementary information (ESI) available. See DOI: https://doi.org/10.1039/d4nj03925d

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