Study of adsorption interactions between nitrous oxide and Zeolitic Imidazolate framework-8 (ZIF-8) by molecular modeling

Abstract

Nitrous oxide (N2O) is a greenhouse gas (GHG) mainly issued from agriculture and waste management activities. Since N2O has a global warming potential 298 times higher than CO2 and an annual emission equivalent to 5.1 % v/v of total GHG emissions, the control of its emissions becomes essential. One of the main challenges to control N2O emissions is to capture them under the main sources’ conditions, i.e. atmospheric pressure and ambient temperature. The available technologies to control N2O emissions operate presently at medium/high pressure, being high energy consuming.The development of new and specific adsorbents for capturing N2O is important. Molecular modeling is a helpful tool to develop engineered adsorbents, generating virtual molecular interactions as a prior adsorbate-adsorbent system before experimental studies. Zeolitic Imidazolate Framework-8 (ZIF-8) has been selected in this study as an adsorbent because of its easy and reproducible synthesis, thermal stability, flexible structure, hydrophobicity and high adsorption capacity of gases, including GHGs.In the present study, the interactions between N2O and ZIF-8 were studied by molecular modeling methods, PM6 and DFT. Optimized geometries of N2O and ZIF-8, adsorption energy and ligand point length parameters were analyzed as part of a physical adsorption process. Three adsorption sites were identified on the four-membered and six-membered windows of ZIF-8. The two possible N2O interaction configurations (–ONN and –NNO) were simulated and compared in order to determine the most probable behavior of N2O. The study showed that the –ONN configuration produces more stable interactions with ZIF-8 than –NNO configuration. The six-membered window of ZIF-8 seems to be the pore where the most stable interactions occur based on the adsorption energy and the approach distance. The present study was concentrated on the interactions of one N2O molecule and a fragment of the ZIF-8, and it will be the basis for molecular dynamics simulations of adsorption with a control volume, containing several N2O molecules and a representative surface of ZIF-8 under different pressures and temperatures.