Fei Xu

Water nanodroplets act as microreactors, driving critical processes in atmospheric chemistry, pollutant degradation, and aerosol formation. This study utilizes ab initio molecular dynamics (AIMD) simulations to unravel the thermally induced behavior of hydroxyl (OH) radicals within water nanodroplets across temperatures ranging from 300 K to 400 K. Elevated temperatures significantly weaken the hydrogen-bonding network, enhance OH radical mobility, and promote interfacial reactivity. The energy barriers for hydrogen transfer events decrease from ~ 4 kcal/mol at 300 K to ~ 2.5 kcal/mol at 400 K, facilitating rapid migration of OH radicals from the droplet interior to the air-water interface. Thermal energy also induces droplet deformation, as reflected by an increase in the asphericity parameter, further amplifying interfacial dynamics. Despite these thermal perturbations, OH radicals maintain a consistent orientation at the interface, stabilized by interfacial forces and localized hydrogen bonding. These findings provide molecular-scale insights into temperature-dependent radical dynamics with broad implications for atmospheric oxidation, plasma-liquid interactions, and environmental chemistry.

The interaction of nitrate radicals (NO₃) with the air–water interface is a critical aspect of atmospheric chemistry, influencing processes such as secondary organic aerosol (SOA) formation, pollutant transformation, and nighttime oxidation. This study investigates the behavior of NO₃ radicals at the air–water interface and in bulk water environments through ab initio molecular dynamics simulations, directly comparing them with Cl and ClO radicals. Three distinct configurations of NO₃ in water droplets were analyzed: surface-parallel, surface-perpendicular, and bulk-phase. The results reveal environment-dependent dynamics, with surface-localized NO₃ radicals exhibiting fewer but more flexible hydrogen bonds compared to bulk-solvated radicals. Analysis of radial distribution functions, coordination numbers, and population distributions demonstrates that NO₃ radicals maintain distinct interfacial and bulk-phase preferences, with rapid equilibration in both environments. Electronic structure analysis shows significant modulation of spin density and molecular orbital distributions between surface and bulk environments. The comparative analysis with Cl and ClO radicals highlights how the unique planar geometry and delocalized π-system of NO₃ influence its hydration patterns and interfacial activity. These results offer fundamental molecular-level insights into NO₃ radical behavior at the air–water interface and in aqueous environments, enhancing our understanding of their role in heterogeneous atmospheric processes and nocturnal chemistry.

Gas-insulated switchgear (GIS) employs sulfur hexafluoride (SF₆) as an insulating medium to shield electrical gadget. However, SF₆ can decompose under sure situations, generating dangerous sulfur-based totally compounds which include SO₂, SOF₂, and SO₂F₂. These byproducts pose enormous dangers to both protection and environmental integrity. Efficiently adsorbing and disposing of those compounds is critical for ensuring operational reliability and reducing environmental dangers. This study investigates the adsorption and degradation mechanisms of SF₆ decomposition compounds (SO₂, SOF₂, and SO₂F₂) on boron nitride nanocones (BNNCs) using density functional theory (DFT) and ab initio molecular dynamics (AIMD) simulations. Our comprehensive analysis covers five distinct systems, exploring individual and combined adsorption scenarios. The findings reveal that the apex of BNNCs plays a crucial role in the adsorption process, showing high efficiency in adsorbing SO₂ (adsorption energy − 1.22 eV) and facilitating the catalytic breakdown of SOF₂ (adsorption energy − 1.57 eV). The positively charged potential at the nanocone’s apex significantly influences the dissociation and subsequent adsorption of fluorine atoms, with an energy barrier for F dissociation at the apex (1.8 kcal/mol) much lower than at the sidewall (5.3 kcal/mol). In gas mixtures, SO₂ preferentially binds to the apex region of BNNCs, with a bond length of approximately 1.38 Å. BNNCs demonstrate superior adsorption capabilities for SO₂ and SOF₂ compared to other boron nitride nanostructures, with adsorption energies up to 89% higher. The electron transfer analysis reveals that BNNC complexes act as potent electron donors, particularly in the case of BNNC@3SO₂F₂. Additionally, BNNCs show significant potential as sensors for detecting SO₂F₂, with a rapid recovery time of 4.67 ps and a notable decrease in the Fermi level energy to -4.97 eV upon adsorption. The study also provides insights into the angular distribution and charge density difference profiles, offering a detailed understanding of the adsorption mechanisms. These findings have important implications for improving the safety and efficiency of gas-insulated switchgear (GIS) and contribute to the development of more effective environmental protection solutions in electrical power systems.

Silica (SiO₂), accounting for the main component of fly ash, plays a vital role in the heterogeneous formation of polychlorinated thianthrenes/dibenzothiophenes (PCTA/DTs) in high-temperature industrial processes. Silica clusters, as the basic units of silica, provide reasonable models to understand the general trends of complex surface reactions. Chlorothiophenols (CTPs) are the most crucial precursors for PCTA/DT formation. By employing density functional theory, this study examined the formation of 2-chlorothiophenolate from 2-CTP adsorbed on the dehydrated silica cluster ((SiO₂)₃) and the hydroxylated silica cluster ((SiO₂)₃O₂H₄). Additionally, this study investigated the formation of pre-PCTA/DTs, the crucial intermediates involved in PCTA/DT formation, from the coupling of two adsorbed 2-chlorothiophenolates via the Langmuir–Hinshelwood (L–H) mechanism and the coupling of adsorbed 2-chlorothiophenolate with gas-phase 2-CTP via the Eley–Rideal (E–R) mechanism on silica clusters. Moreover, the rate constants for the main elementary steps were calculated over the temperature range of 600–1200 K. Our study demonstrates that the 2-CTP is more likely to adsorb on the termination of the dehydrated silica cluster, which exhibits more effective catalysis in the formation of 2-chlorothiophenolate compared with the hydroxylated silica cluster. Moreover, the E–R mechanism mainly contributes to the formation of pre-PCTAs, whereas the L–H mechanism is prone to the formation of pre-PCDTs on dehydrated and hydroxylated silica clusters. Silica can act as a relatively mild catalyst in facilitating the heterogeneous formation of pre-PCTA/DTs from 2-CTP. This research provides new insights into the surface-mediated generation of PCTA/DTs, further providing theoretical foundations to reduce dioxin emission and establish dioxin control strategies.

Aluminum nitride nanocones (AlNNCs) efficiently adsorb and degrade SF ₆ decomposition byproducts, where the sidewall of the AlNNC plays a significant role, and SO ₂ F ₂ exhibits the highest selectivity.

In the marine boundary layer (MBL), chlorine (Cl) and chlorine monoxide (ClO) are powerful oxidants with high concentrations. The gas–liquid interface is also ubiquitous in the MBL as a favorable site for atmospheric reactions. Understanding the role of water in Cl/ClO radical chemistry is essential for predicting their behavior in the atmosphere and developing effective strategies for mitigating their harmful effects. However, the research studies on the system of Cl/ClO radicals on the surface of water droplets are still insufficient. In previous studies, we have found unique results related to the hydroxyl radical at the interface using ab initio molecular dynamics (AIMD). In this work, we have used AIMD to investigate interactions between Cl/ClO radicals and water molecules at the gas–liquid interface. Radical mobility, radial distribution functions, coordination, and population analyses were conducted to investigate the surface preference, bonding pattern, and track Cl/ClO radicals in the water droplets. In addition, density functional theory (DFT) analysis was conducted to compare the results at the gas–liquid interface with those in the gas phase. We found that Cl/ClO radicals tend to remain near the gas–liquid interface in water droplet systems and outside of water clusters in gas phase systems. The ClO radical can form O*–H and Cl–O bonds with water molecules; however, neither the O*–O hemibond nor the Cl–H bond was detected in all systems. Different dominant structures were obtained for ClO in the interface and gas phase. The ClO radical can be bonded to one water molecule from its oxygen side, (H₂O)₀–Cl–O*–(H₂O)₁ at the interface, or to two water molecules from the chlorine and oxygen sides, (H₂O)₁–Cl–O*–(H₂O)₁ in the gas phase. Meanwhile, the Cl radical can only form a dominant structure like Cl*–(H₂O)₁ at the gas–liquid interface by making a Cl*–O hemibond. Providing a thorough explanation of the Cl/ClO radical behavior at the gas–liquid interface, this study will improve our understanding of the MBL's oxidizing capacity and pollution causes.