Hazardous industrial gases (HIGas), including cyanogen chloride (CNCl), formaldehyde (CH2O), cyanogen (C2N2), hydrogen cyanide (HCN), dichloroacetylene (C2Cl2), and phosgene (COCl2), comprise a category of acutely toxic and highly reactive compounds that present substantial occupational safety concerns and operational risks in petrochemical processing environments. Their broad industrial application, along with the possibility of accidental release, endangers worker safety, industrial operations, and adjacent ecosystems due to rapid atmospheric dispersion and pronounced toxicity at minimal concentrations [[1], [2], [3]].

These hazardous gases emerge as byproducts from numerous industrial activities, particularly chemical synthesis, water treatment, and metal processing operations. Particularly noteworthy, CNCl and phosgene hold dual significance as both industrial chemicals and historically employed chemical warfare agents, emphasizing their extreme toxic potential [1,4]. Formaldehyde (CH2O) is a widely used industrial compound and known human carcinogen. It is emitted from combustion processes, synthetic materials, and industrial resins. Chronic exposure is associated with cancer and respiratory effects, necessitating strict exposure control and monitoring [3]. Cyanogen chloride occurs as a volatile byproduct of water chlorination processes, while C2N2 and HCN form during chemical manufacturing and metallurgical operations [1,5]. Dichloroacetylene, an unstable and explosive compound, generates during vinylidene chloride synthesis or thermal decomposition of chlorinated hydrocarbons such as trichloroethylene, and associates with considerable neurological and renal toxicity [6,7]. Phosgene, a potent pulmonary agent, evolves from combustion processes involving chlorinated materials, presenting lethal hazards even at low concentration levels [4]. Exposure to these compounds may induce respiratory failure, neurological dysfunction, and systemic intoxication, emphasizing the crucial requirement for advanced detection and monitoring methodologies [1,8].

The detection of HIGas presents considerable challenges, primarily due to their low permissible exposure limits, high reactivity, and the demanding requirements for rapid, sensitive, and portable monitoring solutions [3,9]. For example, cyanogen chloride (CNCl) is commonly identified using gas chromatography-mass spectrometry (GC-MS), a method that offers high analytical accuracy but is laboratory-bound and unsuitable for real-time, field-based applications [1]. Similarly, hydrogen cyanide (HCN) and phosgene demand sensor technologies capable of sub-parts-per-million sensitivity; however, existing approaches such as fluorescence-based probes are often compromised by environmental interference and slow kinetic response [4,10]. The detection of dichloroacetylene is particularly complicated by its high instability and explosive nature. Conventional methods like infrared spectroscopy suffer from inadequate sensitivity and frequently require sophisticated instrumental setups, further limiting their practicality [6,11]. These collective shortcomings underscore the critical necessity for novel sensing mechanisms that enable real-time, highly sensitive, and selective detection under realistic industrial and environmental conditions [5].

Porphyrin nanostructures like nanorings are excellent for gas sensing due to their tunable electronic properties and extensive π-conjugation, which enables efficient light-harvesting and signal transduction [[12], [13], [14]]. Magnesium-porphyrin nanorings (NR4P4Mg4) provide high stability, a large surface area, and numerous coordination sites for gas adsorption [15,16]. Synthesis relies on advanced templating. Vernier templating creates larger nanorings with up to 50 porphyrin units for enhanced optoelectronics [17,18], while shadow mask templating allows for site-selective demetalation [18,19]. The properties of these structures depend on porphyrin count and bridge type. Butadiyne (C4) bridges, for instance, enable greater charge delocalization than Ethyne (C2), making them ideal for electronics and catalysis [13,15]. Aromaticity is key to their function. Local porphyrin aromaticity stabilizes charge, while global aromaticity boosts energy transfer efficiency [[20], [21], [22]]. In NR4P4Mg4, the extended π-conjugation causes analyte-specific spectral shifts, enabling sensitive real-time gas detection [23]. This combination of porosity and tunable electronics makes these nanostructures highly effective for hazardous gas monitoring [23,24].

Previous investigations into porphyrin gas sensors have primarily examined one- and two-dimensional systems [[25], [26], [27], [28], [29]], leaving the three-dimensional architecture of the Mg-porphyrin nanoring (NR4P4Mg4) largely uncharacterized. This unique spherical framework, with its four symmetrically arranged Mg2+ sites, promises enhanced adsorption capacity and synergistic effects beyond the capabilities of lower-dimensional analogs. The specific sensing mechanisms and performance of this nanoball for hazardous industrial gases, however, are still unknown. This work addresses this knowledge gap via a comprehensive DFT investigation, demonstrating its remarkable sensing properties.

This study evaluates the NR4P4Mg4 nanoring as a prospective sensing platform for the detection of hazardous industrial gases, with particular emphasis on the adsorption behavior and associated electronic and structural reconfigurations induced by gas uptake. The work further examines the resulting modifications to critical electronic parameters, including band gap and charge transport properties, which directly dictate the sensing efficacy and response characteristics of the material.

A critical performance metric for any deployable sensor is its recovery time, which was a key focus of this investigation into the NR4P4Mg4 nanoring's viability as a high-speed detection platform [30]. Concurrently, we elucidate the fundamental alterations to the system's structural and electronic properties, with a non-negligible contribution from dispersion interactions, precipitated by the adsorption of HIGas molecules. Our findings collectively underscore the nanoring's exceptional sensitivity, pronounced reversibility, and rapid response kinetics, affirming its strong potential for integration into next-generation gas sensing technologies. The successful implementation of such sensors could prove transformative for industrial applications, providing critical data for mitigating environmental impact and optimizing emission control protocols to advance sustainable manufacturing. The translation of these in silico predictions into functional devices, however, necessitates addressing interdisciplinary challenges spanning materials synthesis, nanofabrication, and integrated signal processing. The computational framework established herein provides a foundational basis for guiding subsequent experimental validation and systematic performance optimization across these domains.