Sulfur hexafluoride (SF6) is among the most potent greenhouse gases causing global warming. In fact, its warming potential is 23.500 times greater than that of carbon dioxide, attributed to its long atmospheric lifetime and high radiative efficiency. Upon reaction with atmospheric oxygen and water, SF6 decomposes into four main components: sulfur dioxide (SO2), sulfuryl fluoride (SO2F2), hydrogen sulfide (H2S) and thionyl fluoride (SOF2). These SF6 components are highly reactive, corrosive and toxic, posing a great threat to human life and environmental quality.
Developing effective strategies for monitoring and controlling the decomposition and emission of SF6 components is imperative. The efficiency of different materials in detecting and capturing SF6 decomposition species has been demonstrated in many studies. Among them, 2D phthalocyanine (Pc) materials have attracted considerable research due to their diverse and unique morphologies and properties like excellent charge transfer and high specific surface area. These advantages have also enabled their application in other fields like photovoltaic and optoelectronics. Despite the numerous benefits of phthalocyanine materials, their poor sensing, selectivity and sensitivity performance restrict their practical application scope.
One way of overcoming these limitations is by modifying Pc with transition metal (TM) atoms on the surface to improve sensing performance. Recently, Pc doped with TM atoms has been shown to detect common gas molecules like CO, NO and O2. In particular, manganese phthalocyanine (MnPc) and iron phthalocyanine (FePc) exhibit remarkable catalytic activity toward CO2 and oxygen reduction. Lately, MnPc and FePc monolayers have been identified as promising sensing materials for detecting SF6 components though there are still limited experimental results to prove such assertions.
Inspired by the previous findings, Kunming University researchers: Professor Zhifeng Nie, Ms. Chen Wang, Ms. Rou Xue and Professor Gang Xie in collaboration with Dr. Huihui Xiong from Jiangxi University of Science and Technology investigated the sensing performance of FePc and MnPc monolayers toward the four SF6 decomposition components via first-principles calculations. The electronic properties, structures and adsorption behaviors of the SF6 of the four gas molecules were investigated and analyzed. Furthermore, the feasibility of using FePc and MnPc for SF6 decomposition gas detection was validated by evaluating their sensing performance, adsorption strength and recovery time. Their work is currently published in the journal, Applied Surface Science.
The authors demonstrated the semi-metallic features of both MnPc and FePc monolayers, suggesting they are dynamically and thermodynamically stable. Compared to MnPc, the adsorption energy analysis showed that FePc monolayers have a stronger affinity for SOF2, SO2 and H2S molecules attributed to strong orbital hybridization between the S-sp and Fe-d gas molecules. Consequently, the MnPc nanosheet possesses desirable capture ability for SOF2 and SO2, achieving adsorption energy of -0.57 eV and -0.53 eV due to the orbital hybridizations between S-sp and Mn-d of SO2/SOF2.
Charge density difference, density of states, Hirshfeld charge and electron density distribution were analyzed to provide more insights into the microcosmic mechanism of the gas-adsorbent interaction. Due to the obvious changes in magnetism and electrical conductivity, the monolayers exhibited excellent sensitivity to SOF2, H2S and SO2F2. At room temperature, the recovery time for MnPc toward SOF2 and SO2 gas molecules was 4.33 ms and 0.91 ms, extremely shorter than that for FePc. In contrast, FePc had a relatively shorter recovery time at higher temperatures.
In summary, the suitability of MnPc and FePc monolayers as sensing materials for SF6 decomposition components was investigated. Based on capture ability and recovery time values, FePc monolayer emerged as the most suitable monolayer for application as a disposal gas sensor for SOF2, H2S and SO2 at room temperature and high temperatures. Similarly, the MnPc monolayer was regarded as the best recyclable gas sensor for SOF2 and SO2 detection. In a statement to Advances in Engineering, Professor Zhifeng Nie the first and corresponding author explained that the findings would contribute to developing effective sensors for detecting and removing SF6 components.
Nie, Z., Wang, C., Xue, R., Xie, G., & Xiong, H. (2023). Two-dimensional FePc and MnPc monolayers as promising materials for SF6 decomposition gases detection: Insights from DFT Calculations. Applied Surface Science, 608, 155119.