DFT-based, Monte Carlo and Grand Canonical Monte Carlo simulations of nitro-organic pollutants 4-nitrophenol, 2-nitrophenol, 9-nitroanthracene and nitrogen trifluoride interacting with water in zeolite imidazole framework (ZIF-8)

We report in this study the behaviour of adsorbed Nitrogen-volatile organic compounds (NVOCs) such as 2NP (2-Nitrophenol), 4NP (4-Nitrophenol), 9NAnt (9-Nitroanthracene), NF₃ (Nitrogen trifluoride) with and without water in Zinc-Imidazolate Framework (ZIF-8) using the Density Functional Theory (DFT). The work considers both single and multiple molecular capture of different species of pollutants, along with theoretical research based on force fields to determine the maximum number of molecules that can be loaded inside the material. Negative adsorption energy is obtained when each pollutant is considered separately or in mixtures. The values range from −2.6 kJ/mol to −137.1 kJ/mol depending on the size of adsorbed species. Modelling of the adsorbed pollutants on ZIF-8 towards the use of the code CASTEP show the possible interaction with the imidazole rings of the bulk crystal. The interaction energy (E_int) indicates that the capture of 2NP and 4NP is more favourable with H₂O than 9NAnt and NF₃. More specifically, E_int corresponding to one water molecule with one pollutant (4NP, 2NP, 9NAnt, NF₃) is −0.473, −5.580, +0.588, and +8.307 kJ/mol, respectively. The Connolly surface was calculated to gain a better understanding of the volume and surface accessibility of ZIF-8, which helps to predict and support CASTEP results. Finally, an isotherm study was conducted using a Monte Carlo simulation, which proved useful in interpreting the most probable mechanism of the competing mixed capture. The results obtained were similar to those provided by Density Functional Theory (DFT).