Sulfur hexafluoride (SF6) [1] is an inert gas with non-toxic properties that is extensively employed in gas-insulated switchgear (GIS) [2], gas-insulated lines (GIL) [3] and gas circuit breaker (GCB) [4]. SF6 also possesses exceptional insulating properties with impressive dielectric [5], chemical and thermal stability. However, defects present within the equipment due to persistent operation results in high energy discharges which causes SF6 to decompose into various sulfides (SF4, SF3, SF2 and S2F10) [6–8]. These sulfides generate corrosive decomposed products (H2S, HF, SO2, SOF2 and SO2F2) through an irreversible reaction with micro-water, micro-oxygen, and traces of impurities [9, 10]. As a consequence, these gases significantly damage the materials inside the equipment, and also create a potential hazard to industrial employees and people living nearby when the gases are released [11]. It is very difficult for inspection worker to assess the faults found within the equipment. Hence, an on-line detection method is highly sought after to accurately measure the insulation status automatically in real times which can protect the equipment, environment and human beings [12–14].
In the past few decades, there has been an active exploration of various gas sensors, which include carbon-based nanomaterials (CNTs), metal oxide semiconductors, transition metal dichalcogenides (TMDs), graphene-like nanomaterials, and other 2D materials [15]. Pristine CNTs showed high sensitivities towards various gases except towards O2 and NO2 [16], meanwhile, pristine graphene exhibits weak interaction with SO2 gas and other sulfides [17]. Such poor sensitivity was attributed to the weak van der Waals interaction between the adsorbent and gas molecules. Impurity doping on the system has led to enhanced adsorption performance resulting better electrical response. For instances, Co-doped CNT showed better adsorption with SOF2 and SO2F2 than SO2 and H2S, Pd- and Ni-doped CNT are a good detector towards the SO2 gas whereas Ag-doped graphene showed enhanced sensing properties towards SO2F2 [18, 19]. The sensing performance was further enhanced by decorating the CNTs with hybrid metals and metal clusters. Compared to single metal doped CNTs, stronger chemisorption to SOF2 was observed in PtnPdn co-doped CNTs (n = 1–2) [20]. Similarly, a PtN3-doped CNT showed stronger chemisorption to SO2F2 [21] and CNTs doped with Pt4 or Pd4 clusters exhibited overall enhanced adsorption properties [22, 23].
Metal oxide semiconductors like SnO2 [24], ZnO [25–27], TiO2 [28] are affordable and effective gas sensors. Research has shown that modifying these materials, either by doping them with metals (like copper) or combining them with other materials (like carbon nanotubes), can improve their sensitivity and selectivity towards specific gases like SO2 [29] and H2S [30, 31]. However, challenges like irreproducibility and weak interactions with certain gases remain. Doping TiO2 with metals [32, 33] or non-metals [34, 35] has shown promise in enhancing its adsorption capabilities for different SF6 decomposition gases, with potential for further improvement through co-doping strategies.
Recently, 2D nanomaterials are also considered to be ideal gas sensing devices as consequence of their extremely large surface-to-volume ratios and active surfaces [36–38]. Owing to their chemical inertness [39], transition metal doping is necessary to enhance their chemical activity and gas sensitivity [40–42]. Si- and Co-doped MoS2 showed stronger binding interaction with SO2F2 over H2S and SOF2 as revealed through DFT studies [43, 44] while Pt-doped MoS2 demonstrate good sensing performance with SO2, SOF2 and SO2F2 gases [10]. Zhang et al. successfully proved the sensing properties of metal-doped MoS2 towards SO2 gas experimentally [45]. Pristine, Ni-, Fe- and Co-doped MoS2 were synthesized and investigated as sensor at room temperature. Findings reveal that Ni-doped MoS2 possesses the highest sensitivity with good reusability. DFT calculations were performed which strongly supported the experimental studies indicating strong chemisorption on the Ni-doped surface due to the strong hybridization between the Ni 3d and S 2p orbitals. Several other TMDs such as MoTe2 [46, 47], PtSe2 [48] and AsSb [49] have been utilized to study the SF6 decomposed species. Generally, their results conclude that SO2 is the most sensitive species to be detected by the 2D nanomaterials compared to other SF6 decomposed gases.
Despite these advancements, the development of novel nanomaterial-based gas sensors with superior sensitivity and selectivity remains an ongoing challenge. In this context, nanorings [50], a class of nanomaterials with unique structural and electronic properties, have emerged as promising candidates for gas sensing applications. However, their potential for detecting SF6 decomposition gases has not been fully explored. In this study, we present the first investigation of the Al8P8 double nanoring [51] as a novel material for the detection of SF6 decomposed gases (SO2, H2S, HF, SOF2 and SO2F2). This work encompasses a comprehensive theoretical analysis, including geometric optimization, interaction energy calculations, analyses of HOMO LUMO energy gap, NBO charge transfer, density of states, non-covalent interactions, conductivity, sensitivity, and recovery time, with a focus on the response of the Al8P8 double nanoring to the adsorbed gases.