## 1 Introduction  
The detection and monitoring of hazardous gases plays a crucial role in safeguarding both the environment and human life [1, 2]. The release of environmentally harmful gases from various natural sources, industrial processes, and vehicular emissions poses serious threats to air quality and human health [3, 4, 5]. Environmental monitoring is crucial for understanding the impact of hazardous gases on air quality and the ecosystem. The early detection of gas leaks or abnormal gas concentrations in industrial settings can prevent accidents and protect workers' safety. Furthermore, monitoring of air quality in urban areas can aid in implementing timely public health interventions to reduce the adverse effects of pollution on respiratory and cardiovascular health. To address these challenges, researchers have been actively exploring advanced gas sensing technologies, particularly chemical gas sensors, to detect and quantify several hazardous gases [2, 6, 7]. Currently, significant progress has been achieved in the development of chemical gas sensors for detecting various hazardous gases. These gas sensors enable selective and sensitive detection of specific gas molecules. Furthermore, advances in nanotechnology and materials science have led to the creation of miniaturized, low-power, and cost-effective gas sensors. This, in turn, facilitates their integration into various environmental monitoring systems and wearable devices [8; 9]. Typically, gas sensors rely on various sensing materials that exhibit distinct gas-sensing properties. These include metal oxides [2], metal-organic frameworks (MOFs) [10], conductive polymers [7], and two-dimensional (2D) materials like graphene and transition metal dichalcogenides (TMDs) [11]. Among these materials, 2D materials have emerged as promising candidates for gas sensing applications due to their exceptional characteristics. These encompass a high surface-to-volume ratio, impressive mechanical and chemical stability, and the potential for miniaturization [12]. TMDs constitute a group of compounds that display appealing sensing properties for various gases, such as inorganic gases with compact structures and volatile organic compounds (VOC) [13; 14]. Unlike graphene, which lacks a bandgap, most TMDs possess an adjustable bandgap of approximately 1-2 eV [15]. WS\({}_{2}\), a well-known TMD, exhibits a high mobility of about 140 cm\({}^{2}\)V\({}^{-1}\)S\({}^{-1}\) and an excellent on/off ratio of about 1 \(\times\) 10\({}^{8}\)[16]. This has led to the innovation of novel field-effect transistors (FET) and optical devices. When WS\({}_{2}\) is employed as a gas sensing material, it often demonstrates p-type semiconductor properties. This implies that when detecting oxidizing gases, its resistance decreases, and vice versa [17]. With these characteristics, WS\({}_{2}\) can differentiate between different gas types by detecting changes in resistance, such as NO\({}_{2}\) and NH\({}_{3}\)[18; 19; 20]. However, pristine WS\({}_{2}\) often fails to meet the requirements for sensitivity and selectivity, promoting the application of various modification methods. Several effective methods have proven successful in enhancing the sensing properties of WS\({}_{2}\). These methods include the construction of composite structures, such as composites with graphene [21; 22], carbon nanotube [23], and metal oxide [24; 25; 26], as well as surface modification using transition metal (TM) nanostructures [27; 28]. TM nanostructures introduce active sites onto WS\({}_{2}\), and these active sites exhibit varying adsorption and catalytic effects on different gases, thereby contributing to selectivity [29]. Previous theoretical studies have indicated that the adsorption strength of several inorganic molecules on intrinsic WS\({}_{2}\) is relatively weak, with adsorption energies not exceeding 0.42 eV [30; 31; 32]. Via the introduction of TM active sites via doping, interactions can be intensified, and the selectivity for specific gases can be achieved.