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Rh-doped MoTe2 Monolayer as a Promising Candidate for Sensing and Scavenging SF6 Decomposed Species: a DFT Study

Abstract

In this work, the adsorption and sensing behaviors of Rh-doped MoTe2 (Rh-MoTe2) monolayer upon SO2, SOF2, and SO2F2 are investigated using first-principles theory, wherein the Rh doping behavior on the pure MoTe2 surface is included as well. Results indicate that TMo is the preferred Rh doping site with Eb of − 2.69 eV, and on the Rh-MoTe2 surface, SO2 and SO2F2 are identified as chemisorption with Ead of − 2.12 and − 1.65 eV, respectively, while SOF2 is physically adsorbed with Ead of − 0.46 eV. The DOS analysis verifies the adsorption performance and illustrates the electronic behavior of Rh doping on gas adsorption. Band structure and frontier molecular orbital analysis provide the basic sensing mechanism of Rh-MoTe2 monolayer as a resistance-type sensor. The recovery behavior supports the potential of Rh-doped surface as a reusable SO2 sensor and suggests its exploration as a gas scavenger for removal of SO2F2 in SF6 insulation devices. The dielectric function manifests that Rh-MoTe2 monolayer is a promising optical sensor for selective detection of three gases. This work is beneficial to explore Rh-MoTe2 monolayer as a sensing material or a gas adsorbent to guarantee the safe operation of SF6 insulation devices in an easy and high-efficiency manner.

Introduction

SF6 insulation devices, in high even ultra-high voltage power systems, are one kind of the most important and expensive equipment [1,2,3], except electrical transformers [4, 5], to guarantee the safe operation of the whole system. These contributions attribute to the strong arc-extinguishing property and high electronegativity of SF6 gas that behaves as an insulation media in such devices [6]. However, in a long-running one, SF6 could still be decomposed into several low-fluorine sulfides by the power of partial discharge caused by inevitable inner defects of the equipment [7, 8]. Moreover, these by-products will further interact with the surrounding trace water and oxygen, forming some stable chemicals such as SO2, SOF2, and SO2F2 and instead deteriorating the insulation behavior of SF6 [9]. Therefore, detecting these decomposed species has been regarded as an effective manner to evaluate the decomposing status of SF6 and to reflect the operation status of related insulation devices [10].

With the growing attention of transition metal dichalcogenides (TMDs), MoS2-based sensors have been proposed for detection of SF6 decomposed species [11,12,13]. These reports have demonstrated the appropriateness and superiority of transition metal (TM)-doped MoS2 monolayer for sensing components including SO2 and SOF2. Besides, a theoretical study on the sensing characteristic of pristine MoTe2 monolayer upon SF6 decomposed species proves its suitability for sensing SO2 [14]. Moreover, recent advancements in chemical vapor deposition (CVD) used for large-scale synthesis of TMDs largely accelerate the development of MoTe2 monolayer for gas sensing applications [15,16,17]. As reported, MoTe2 monolayer possesses outstanding carrier mobility, large bond length, and low binding energy, which provides it with high sensitivity upon gas interactions at room temperature [18]. Thus, it is hopeful that MoTe2 monolayer is quite a promising candidate for gas sensing, and its application for detection of SF6 decomposed species should be further explored.

It is well proved that TM-doped 2D nanomaterials possess stronger adsorption performance and sensing behavior upon gaseous molecules compared with pristine surfaces [19,20,21,22]. This is because of the admirable chemical activity and catalytic behavior of TM whose d orbital can strongly hybridize with those adsorbed molecules, facilitating the chemisorption and enlarging the charge transfer [23,24,25]. When it comes to the MoTe2 monolayer, to the best of our knowledge there have few theoretical reports on the TM-doping behavior on its monolayer; meanwhile, related adsorption and sensing behaviors of TM-doped MoTe2 monolayer upon gases are also less explored. Among the TM elements, rhodium (Rh) with strong catalytic performance has been demonstrated as a desirable TM dopant on other nano-surfaces for gas adsorption [26, 27]. Especially, ref. [26] investigates the Rh doping behavior on the MoSe2 monolayer and its enhanced performance for toxic gas adsorption. From this regard, it would be interesting using the first-principles theory to study the Rh doping behavior on the less explored MoTe2 monolayer to compare their geometric property and give a better understanding of Rh doping on the TMDs. Beyond that, the adsorption and sensing performances of Rh-doped MoTe2 (Rh-MoTe2) monolayer upon three SF6 decomposed species, namely, SO2, SOF2, and SO2F2, were theoretically simulated as well to explore its potential sensing application in some typical areas. The electronic and optical behaviors of Rh-MoTe2 monolayer upon gas adsorption provide the basic sensing mechanisms for its exploration as a resistance-type or optical gas sensor to realize the detection of SF6 decomposed species. The desorption behavior verifies the potential of Rh-MoTe2 monolayer as a gas scavenger to remove these noxious gases in SF6 insulation devices, which from another aspect guarantees the safe operation of the power system. This work would be meaningful to propose novel nano-sensing material and its application for evaluating the operation status of SF6 insulation devices in an easy and high-efficiency manner.

Computational Details

All the results were obtained in the Dmol3 package [28] based on the first-principles theory. The DFT-D method proposed by Grimme was adopted [29] to better understand the van der Waals force and long-range interactions. Perdew-Burke-Ernzerhof (PBE) function with generalized gradient approximation (GGA) was employed to treat the electron exchange and correlation terms [30]. Double numerical plus polarization (DNP) was employed as the atomic orbital basis set [31]. The Monkhorst-Pack k-point mesh of 7 × 7 × 1 was defined for supercell geometry optimizations, while a more accurate k-point of 10 × 10 × 1 was selected for electronic structure calculations [32]. The energy tolerance accuracy, maximum force, and displacement were selected as 10− 5 Ha, 2 × 10− 3 Ha/Å, and 5 × 10− 3 Å [33], respectively. For static electronic structure calculations, self-consistent loop energy of 10− 6 Ha, the global orbital cut-off radius of 5.0 Å to ensure the accurate results of total energy [34].

A MoTe2 monolayer with supercell of 4 × 4 and vacuum region of 15 Å containing 16 Mo and 32 Te atoms was established to perform the whole calculation below. It has been proved that a 4 × 4 supercell is large enough to conduct the gas adsorption process while a 15 Å slab is proper to prevent the interaction between adjacent units [35]. Apart from that, the Hirshfeld method [36] was employed throughout this work to analyze the atomic charge of Rh dopant (QRh) and molecular charge of adsorbed molecules (QT). Therefore, a positive value of QRh (QT) represents that the Rh dopant (gas molecule) is an electron donator, while a negative QRh or QT indicates the related electron-accepting behavior. Only the most favorable configurations of Rh-MoTe2 monolayer and adsorption systems are plotted and analyzed in the following parts.

Results and Discussion

Analysis of Rh-MoTe2 Monolayer

Upon Rh-MoTe2 monolayer, four possible adsorption sites are considered, traced as TH (above the center of the hexagonal ring of MoTe2), TMo (at the top of the Mo atom), TTe (at the top of Te atom), and TB (the bridge site between two Te atoms), respectively. The binding energy (Eb) for Rh doping onto the MoTe2 monolayer is formulated as:

$$ {E}_{\mathrm{b}}={E}_{\mathrm{Rh}\hbox{-} {\mathrm{MoTe}}_2}-{E}_{\mathrm{Rh}}-{E}_{{\mathrm{MoTe}}_2} $$
(1)

where\( {E}_{\mathrm{Rh}\hbox{-} {\mathrm{MoTe}}_2} \),ERh, and\( {E}_{{\mathrm{MoTe}}_2} \)represent the energies of the Rh-MoTe2 monolayer, Rh atoms, and pristine MoTe2 monolayer, respectively.

Based on this definition, the most stable configuration (MSC) with the lowest Eb in line with related electron deformation density (EDD) of Rh-MoTe2 monolayer is depicted in Fig. 1. One can see that the Rh dopant is trapped on the TMo site, forming three covalent bonds with neighboring Te atoms on the upper layer of MoTe2 monolayer. Three Rh-Te bonds are measured equally as 2.54 Å, shorter than the sum of covalent radii of Rh and Te atoms (2.61 Å [37]), indicating the formation of chemical bonds for Rh doping on the MoTe2 layer. The calculated Eb of this configuration is − 2.69 eV, much larger than those of − 2.14 eV for TH site, − 1.28 eV for TTe site, and − 2.55 eV for TB site. It is worth noting that the Rh-Te bonds in Rh-MoTe2 monolayer are longer than those of Rh-Se bonds in Rh-MoSe2 monolayer and the Eb for Rh doping is smaller on the MoTe2 surface in comparison with that of MoSe2 counterpart. These indicate the stronger binding force of Rh-Se than Rh-Te bonds. Based on the Hirshfeld method, the Rh dopant behaves as an electron acceptor during doping process, which receives 0.045 e from the MoTe2 surface proving its electron-accepting behavior in surface doping [26]. This is in accordance with the EDD in which the Rh atom is mainly surrounded by electron accumulation.

Fig. 1
figure1

The MSC (a) and related EDD (b) of Rh-MoTe2 monolayer. In EDD, the green (rosy) areas indicate electron accumulation (depletion). The isosurface is 0.005 e/Å3

The band structure (BS) and density of state (DOS) of Rh-MoTe2 system are depicted in Fig. 2 to better understand the caused change in electronic behavior of MoTe2 surface by Rh doping. It is reported that pristine MoTe2 monolayer has a direct bandgap of 1.10 eV [38]. In Fig. 2a, the bandgap of Rh-MoTe2 monolayer is obtained as 0.937 eV according to the calculations. This indicates that the Rh dopant induces several impurity states within the bandgap of MoTe2 system, narrowing the bandgap of the whole system accordingly. Besides, the top of the valence band is localized on the Г point and the bottom of the conduction band is on the K point, implying the indirect semiconducting property for Rh-MoTe2 system. In Fig. 2b, it is seen that the states of Rh dopant contribute largely to the top of the conduction band of pristine MoTe2 monolayer and forming several novel DOS peaks around the Fermi level. These peaks seemingly change the electronic behavior of the whole system, reducing its electrical conductivity accordingly. Because the Rh dopant is trapped on the TMo site forming bonds with Te atoms, the atomic DOS of Rh and Te atoms are plotted to understand the electron hybridization behavior between them. As shown in Fig. 2c, the Rh 4d orbital is strongly hybrid with the Te 5p orbital from − 5 to 2 eV, accounting for the significant bonding interaction that leads to the formation of chemical bonds of Rh-Te.

Fig. 2
figure2

a BS of Rh-MoTe2 monolayer; b DOS comparison between pristine and Rh-doped MoTe2 monolayer; and c orbital DOS of bonding Rh and Te atoms. The Fermi level is 0

Gas Adsorption Configurations of Rh-MoTe2 Monolayer

Based on the relaxed structure of Rh-MoTe2 monolayer, the adsorption of SO2, SOF2, and SO2F2 molecules onto its surface around the Rh center are fully simulated. Before that, the geometric structures of the three gas molecules should also be optimized as well, as exhibited in Additional file 1: Figure S1. The adsorption energy (Ead) is used to determine the most stable configuration of each system, formulated as:

$$ {E}_{\mathrm{ad}}={E}_{\mathrm{Rh}\hbox{-} {\mathrm{MoTe}}_2/\mathrm{gas}}-{E}_{\mathrm{Rh}\hbox{-} {\mathrm{MoTe}}_2}-{E}_{\mathrm{gas}} $$
(2)

in which the \( {E}_{\mathrm{Rh}\hbox{-} {\mathrm{MoTe}}_2/\mathrm{gas}} \) and \( {E}_{\mathrm{Rh}\hbox{-} {\mathrm{MoTe}}_2} \) are the total energy of Rh-MoTe2 monolayer before and after adsorption, whereas Egas is the energy of isolated gas molecule. According to this definition, the MSC with the lowest Ead could be identified.

To better understand the charge-transfer behavior during gas adsorption, EDD is also calculated for each configuration. Detailed information for SO2, SOF2, and SO2F2 adsorption could be seen in Figs. 3, 4, and 5, respectively. In addition, the adsorption parameters including Ead, charge-transfer (QT), and bond length (D) are listed in Table 1.

Fig. 3
figure3

MSC (a) and EDD (b) of Rh-MoTe2/SO2 system. In EDD, the green (rosy) areas indicate electron accumulation (depletion), with isosurface as 0.005 e/Å3

Fig. 4
figure4

Same as Fig. 3 but for Rh-MoTe2/SOF2 system

Fig. 5
figure5

Same as Fig. 3 but for Rh-MoTe2/SO2F2 system

Table 1 Adsorption parameters of Rh-MoTe2 monolayer upon SO2, SOF2, and SO2F2

For SO2 adsorption on the Rh-MoTe2 monolayer, one can find from Fig. 3 that the SO2 molecule is basically parallel to the MoTe2 layer with one O atom and one S atom trapped by the Rh dopant. As listed in Table 1, the newly formed Rh-O and Rh-S bonds are measured as 2.16 and 2.36 Å, respectively, indicating the strong binding force between Rh dopant and SO2 molecule. Besides, the Ead is obtained as − 1.65 eV implying the chemisorption for the SO2 system, and the QT is obtained as − 0.333 e implying the electron-withdrawing behavior of SO2. After adsorption, the Rh dopant is negatively charged by 0.017 e, which means it contributes 0.028 e to the adsorbed SO2 and the other part of charge (0.305) comes from the MoTe2 monolayer. Compared with the adsorption parameters in the MoTe2/SO2 system (Ead = − 0.245 eV; QT = − 0.086 e; D = 3.44 Å [14]), one can infer that Rh doping largely enhances the reacting behavior and electronic redistribution for the MoTe2 monolayer upon SO2 adsorption, making the adsorbent much desirable for gas interaction. Moreover, the S-O bonds in the SO2 molecule are separately elongated to 1.50 and 1.58 Å after adsorption, from that uniform 1.48 Å in the gas phase; the three Rh-Te bonds in the Rh-MoTe2 monolayer are elongated to 2.58, 2.58, and 2.64 Å, respectively. These deformations imply the geometric activation during adsorption for both nano-adsorbent and gaseous adsorbate, which further confirms the strong chemisorption here. From the EDD distribution, it is found that the SO2 molecule is surrounded by electron accumulation, which agrees with the Hirshfeld analysis; and electron accumulation largely surrounds the Rh-S and Rh-O bonds, suggesting the electron hybridization in the formation of new chemical bonds.

In the Rh-MoTe2/SOF2 system presented in Fig. 4, the SOF2 molecule preferred to approach the Rh dopant by the O-end position and the plane made of the S atom and two F atoms are almost parallel to the MoTe2 layer. However, there has no obvious evidence suggesting the formation of new bonds between Rh dopant and SOF2 molecule. The nearest distance of Rh-O is measured to be 2.25 Å, a little longer than that in the SO2 system, and the SOF2 molecule does not undergo large geometric deformation after interaction. These findings manifest the relatively weaker adsorption performance of Rh-MoTe2 monolayer upon SOF2 in comparison with SO2. As presented in Table 1, the Ead is calculated as − 0.46 eV supporting the physisorption again [39] and the QT is obtained as 0.040 e implying the electron-donating behavior of SOF2. According to the EDD, one can see that the electron accumulation is mainly localized on the area between the SOF2 molecule and Rh dopant, which implies somewhat hybridization between them, while the electron depletion on the SOF2 molecule agrees with the Hirshfeld analysis.

In terms of the SO2F2 adsorption system, as depicted in Fig. 5, it is found that after optimization, the SO2F2 molecule tends to be resolved to be a F atom and a SO2F group. Both are captured by the Rh dopant forming a Rh-F bond and a Rh-S bond, respectively, with related bond length of 2.02 and 2.26 Å. The newly formed bonds indicate the strong binding force between Rh dopant and SO2F2 molecule, which combined with the calculated Ead of 2.12 eV evidence the chemisorption nature for Rh-doped surface upon SO2F2 adsorption, similar as that in the SO2 system. From the EDD, the electron accumulation is significantly localized on the SO2F2 molecule, in agreement with the result of QT (− 0.753 e) based on Hirshfeld analysis. On the other hand, a large number of electron depletion is localized on the Rh dopant and a little is on the MoTe2 monolayer. In other words, the Rh dopant contributes largely to the charge-transfer to the adsorbed SO2F2 molecule, manifesting its high electron mobility and strong chemical reactivity [40]. At the same time, the overlap of electron accumulation and electron depletion on the Rh-S and Rh-F bonds suggest the electron hybridization in their formation.

Based on the analysis of adsorption configuration and parameters, one can conclude that the Rh-MoTe2 monolayer possesses the best performance upon SO2F2 molecule, followed by SO2 and the last one comes to SOF2. In the meanwhile, the Rh dopant can largely affect the electron distribution of this system and therefore dramatically alter the electronic behavior of the Rh-MoTe2 monolayer.

Electronic Behaviors of Rh-MoTe2 Monolayer upon Gas Adsorption

The band structure (BS) and density of state (DOS) of three adsorption systems are exhibited in Fig. 6 to comprehend the electronic behavior of Rh-MoTe2 monolayer in gas adsorption. As above analyzed, Rh-MoTe2 monolayer has the best performance upon SO2F2 adsorption. Thus, from Fig. 6 (c2), it is seen that the molecular DOS of SO2F2 experiences pronounced deformations, which is integrally left-shifted and some of the states combine to a large one below the Fermi level. From Fig. 6 (c3) where the orbital DOS is shown, it is seen that the Rh 4d orbital is highly hybrid with the F 2p orbital, and is somewhat hybrid with S 3p orbital. From this aspect, it is presumed that Rh-F bond is stronger than that of Rh-S. In the SO2 system, the Rh 4d orbital is highly hybrid with the O 2p orbital and followed by the S 3p orbital in Fig. 6 (a3), and one could also presume that Rh dopant has stronger binding force with the O atom rather than the S atom. Due to such hybridization, the molecular DOS of SO2 in Fig. 6 (a2) suffers remarkable deformation. As for the SOF2 system, one can see in Fig. 6 (b3) that the Rh dopant has little orbital hybridization with the nearest O atom, which supports the weak interaction for SOF2 adsorption.

Fig. 6
figure6

BS and DOS of various systems. (a1)–(a3) SO2 system; (b1)–(b3) SOF2 system; and (c1)–(c3) SO2F2 system. In DOS, the dash line is the Fermi level

Along with the change of orbital and molecular DOS, the whole state of the gas adsorbed system would be automatically changed compared with the pure Rh-MoTe2 system. From Fig. 6 (a1)–(c1) where the BS of the adsorbed system are portrayed, one can see that the BS in the SOF2 system does not experience significant deformation in comparison with that of isolated Rh-MoTe2 system, while those in the SO2 and SO2F2 system are different, in which some novel states are emerged around the Fermi level, thus narrowing the bandgap largely. Detailedly, the bandgap of the Rh-MoTe2 is reduced to 0.863, 0.913, and 0.675 eV after adsorption of SO2, SOF2, and SO2F2, respectively. This provides the basic sensing mechanism for Rh-MoTe2 monolayer as a possible resistance-type gas sensor.

Frontier Molecular Orbital Analysis

To confirm the results based on the BS analysis, the frontier molecular orbital theory is performed to analyze the distribution and energies of frontier molecular orbitals (FMO) of isolated and gas adsorbed Rh-MoTe2 surface. The FMO contains highest occupied molecular (HOMO) and lowest unoccupied molecular orbital (LUMO), and the energy gap between them can evaluate the electrical conductivity of the analyzed system [41]. To obtain the accurate results of the energies of FMO, the smearing in this part of calculations is set to 10− 4 Å. The distributions and energies of FMO of Ru-MoTe2 monolayer before and after gas adsorptions are described in Fig. 7.

Fig. 7
figure7

Distributions and energies of FMO in a Rh-MoTe2 system, b SO2 system, c SOF2 system, and d SO2F2 system

From Fig. 7a, one can observe that the HOMO and LUMO are mainly localized at the Rh dopant, suggesting its high reactivity in the surroundings. The energies of HOMO and LUMO are obtained as − 4.885 and − 3.927 eV, respectively, with the calculated bandgap of 0.958 eV. After adsorption of three gas species, as seen in Fig. 7b–d, the FMO distributions of Rh-MoTe2 surface are afflicted with different degrees of deformations, where the reaction occurs resulting in the convergence of the electron cloud. Along with these deformations, the energies of FMO have changed accordingly. It is found that the energies of FMO are decreased to different degrees after adsorption of three gases, in which those in SOF2 system experience the largest decreases. However, the energy gap in SOF2 system undergoes the smallest change in comparison with that of pure Rh-MoTe2 system. Specifically, the energy gap of Rh-MoTe2 monolayer (0.958 eV) is decreased by 0.044 eV after SOF2 adsorption, while is reduced by 0.061 and 0.281 eV after SO2 and SO2F2 adsorption, respectively. These findings indicate that the electrical conductivity of Rh-MoTe2 monolayer will decrease after adsorption of three gases and the decrease is the most significant in the SO2F2 system, which agree with the conclusions from BS analysis. Besides, the energy gaps from frontier molecular orbital theory is basically close to those of bandgaps from BS results, implying the good accuracy of our calculations.

Sensing Response and Recovery Property

The changes in the bandgap of Rh-MoTe2 monolayer after gas adsorption manifest its change in electrical conductivity in related gas atmosphere [42], which can provide the basic sensing mechanism for exploration of Rh-MoTe2 monolayer as a resistance-type gas sensor. Besides, the larger change in electrical conductivity would account for a higher sensitivity for gas detection. To identify the possibility of Ru-MoTe2 monolayer as a sensor, its conductivity (σ) and sensitivity (S) upon three typical gases are calculated using the following formulas [43, 44]:

$$ \sigma =\mathrm{A}\cdot {e}^{\left(-{B}_g/2 kT\right)} $$
(3)
$$ S=\frac{\frac{1}{\sigma_{\mathrm{gas}}}-\frac{1}{\sigma_{\mathrm{pure}}}}{\frac{1}{\sigma_{\mathrm{pure}}}}=\frac{\sigma_{\mathrm{pure}}\hbox{-} {\sigma}_{\mathrm{gas}}}{\sigma_{\mathrm{gas}}} $$
(4)

In formula 3, A is a constant, Bg is the bandgap of the analyzed system, k is the Boltzmann constant, and T is the working temperature. In formula 4, σgas and σpure respectively mean the conductivity of analyzed adsorption system and isolated Rh-MoTe2 monolayer. According to such two formulas, it is found that the S of certain surface could be obtained just with its bandgap before and after gas adsorption. After calculation, the sensitivities of Rh-MoTe2 monolayer upon SO2, SOF2, and SO2F2 detection at 298 K are 76.3, 37.3, and 99.4%, respectively. These findings suggest that the Rh-MoTe2 monolayer possess the most admirable sensing behavior upon SO2F2, followed by the SO2 and the last one comes to SOF2. This order is in accordance with those analysis of adsorption parameter and electronic behavior. Based on these results, it is hopeful that Rh-MoTe2 monolayer could realize sensitive detection of SO2 and SO2F2 at room temperature.

The recovery property is also important to evaluate the reusability of the gas sensor, and to reduce the recovery time (τ) of gas desorption from certain surfaces, heating technique is usually considered since the recovery time is related to the temperature (T), formulated as [45] \( \tau ={A}^{-1}{e}^{\left(-{E}_a/{K}_BT\right)} \). In this formula, A is the attempt frequency referring to 1012 s− 1 [46], Ea is the potential barrier, determined as equivalent as Ead in this work, and KB is the Boltzmann constant (8.318 × 10− 3 kJ/(mol·K)).

Based on the formula, the recovery behavior of Rh-MoTe2 monolayer at 298, 448, and 598 K is portrayed in Fig. 8. It can be seen from this figure that the desorption of SO2F2 and SO2 at room temperature are extremely difficult, while for SOF2 the recovery time is quite short due to its weak binding force with the Rh-doped surface. Through heating, the recovery time for SO2F2 or SO2 desorption is pronouncedly reduced, and when the temperature increases to 598 K, the recovery time in SO2 system (79.48 s) becomes favorable which allow its reusability in several minutes. This supports the potential of Rh-MoTe2 monolayer as a reusable gas sensor for detecting SO2. On the other hand, the long recovery time for SO2F2 desorption at 598 K (7.24 × 105) also reflects the strong chemisorption here. Although continuing to increase the temperature can further reduce the recovery time, the thermostability of the sensing material and the high energy consumption in sensing application would be another problem. Given all these, Rh-MoTe2 monolayer is not suitable as a sensor for SOF2 detection. However, it provides us another thought to propose Rh-MoTe2 monolayer as a gas adsorbent to scavenge this noxious gas in SF6 insulation devices, thus guaranteeing their safe operation. Moreover, this part of analysis from another aspect reveals the inappropriateness to explore Rh-MoTe2 monolayer as a SO2F2 sensor given the weak interaction with the surface.

Fig. 8
figure8

Recovery time of Rh-MoTe2 monolayer at various temperatures

Optical Behavior of Rh-MoTe2 Monolayer upon Gas Adsorption

Given the desirable optical property of MoTe2 monolayer, the calculation of the dielectric function of Rh-MoTe2 monolayer upon gas adsorption is conducted, as displayed in Fig. 9, to illustrate its possibility as an optical gas sensor.

Fig. 9
figure9

Dielectric function of Rh-MoTe2 monolayer

From Fig. 9, it is seen that there have three main adsorption peaks for the isolated Rh-MoTe2 monolayer, localizing at 148, 389, and 1242 nm, among which the former two distance are in the range of ultraviolet ray and the last one is in the range of infrared ray. After gas adsorption, the peaks in ultraviolet range suffer small deformation and that in infrared range undergoes significant deformation. Detailedly, the peak intensity at 1242 nm decreases after SOF2 adsorption whereas increases after SO2 and SO2F2 adsorption, and the blue shift could also be identified in the SOF2 system. Therefore, it could be assumed that Rh-MoTe2 monolayer is a promising optical sensor for sensitive and selective detection of three gases by infrared device.

In short, it is worth adding that this work makes a progressive research for proposing novel nanomaterials to realize the detection of SF6 decomposed species through various techniques, which would be significant to fulfil the evaluation of SF6 insulation devices in an easy and high-efficiency manner.

Conclusions

In this paper, the potential application of Rh-MoTe2 monolayer as a gas sensor for detection of SF6 decomposed species is explored, which mainly contains two aspects: (1) Rh doping behavior on the intrinsic MoTe2 monolayer and (2) adsorption and sensing behaviors of Rh-MoTe2 monolayer upon SO2, SOF2, and SO2F2. It is found that the Rh dopant prefers to be doped on the MoTe2 surface through the TMo site with Eb of − 2.69 eV, exerting great electron hybridization with the Te atoms. The adsorption performance of Rh-MoTe2 monolayer upon three gases are in order as SO2F2 > SO2 > SOF2, in which chemisorption is identified in SO2F2 and SO2 systems while physisorption in SOF2 system, as further supported by the DOS analysis. Rh-MoTe2 monolayer is a promising resistance-type gas sensor for recycle detection of SO2 with a response of 76.3%, is a desirable adsorbent for SO2F2 removal from the SF6 insulation device, and is promising as an optical sensor for selective detection of three gases. All in all, Rh-MoTe2 monolayer is a potential sensing material for detection of SF6 decomposed species. This work is meaningful to propose novel nano-sensing material and to realize the effective evaluation of SF6 insulation devices in an easy and high-efficiency manner.

Methods Section

This work means to explore novel 2D sensing materials using first-principle theory for application in electrical engineering, through detecting the SF6 decomposed species to evaluate the operation status of high-voltage insulation devices.

Availability of Data and Materials

The data at present cannot be shared because they are still in study in our following research.

Abbreviations

TMDs:

Transition metal dichalcogenides

TM:

Transition metal

CVD:

Chemical vapor deposition

PBE:

Perdew-Burke-Ernzerhof

GGA:

Generalized gradient approximation

DNP:

Double numerical plus polarization

Q Rh :

Atomic charge of Rh dopant

Q T :

Molecular charge of adsorbed molecules

E b :

Binding energy

MSC:

Most stable configuration

EDD:

Electron deformation density

BS:

Band structure

DOS:

Density of state

E ad :

Adsorption energy

D :

Bond length

FMO:

Frontier molecular orbitals

HOMO:

Highest occupied molecular

LUMO:

Lowest unoccupied molecular orbital

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Acknowledgments

We acknowledge the financial support from the National Natural Science Foundation of China (no. 11572065), and Fundamental Research Funds for the Central Universities (grant no. SWU120001).

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Hongliang Zhu: writing; Hao Cui: editing and guidance; Dan He and Ziwen Cui: polishing; Xiang Wang: data analysis. Hao Cui and Hongliang Zhu contribute equally to this work. The author(s) read and approved the final manuscript.

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Zhu, H., Cui, H., He, D. et al. Rh-doped MoTe2 Monolayer as a Promising Candidate for Sensing and Scavenging SF6 Decomposed Species: a DFT Study. Nanoscale Res Lett 15, 129 (2020). https://doi.org/10.1186/s11671-020-03361-6

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Keywords

  • Rh-MoTe2 monolayer
  • First-principles theory
  • SF6 decomposed species
  • Gas sensor