Engineering porosity of MIL-101(Cr) using solvation effect

Abstract

Toluene, a kind of volatile organic compounds (VOCs), serves as a vital constituent of PM2.5 and acts as a notable precursor to ozone. To improve the adsorption performance of adsorbents for toluene, MIL-101(Cr)-XmM with high porosity were synthesized using an in-situ growth restriction strategy. This research reveals that the solvation effect influences the rate of crystal nucleation and growth, leading to variations in the ratio of micropores to mesopores and overall porosity in MIL-101(Cr)-XmM. The high porosity of MIL-101(Cr)-1.6 mM facilitates a higher diffusion rate of particles and exposes a greater number of alkaline sites. Consequently, the adsorption performance of MIL-101(Cr)-1.6 mM for toluene demonstrates a remarkable 240% improvement compared to that of MIL-101(Cr)-1.2 mM. Molecular simulations unveils the impact of adsorption temperature, demonstrating the crucial role of van der Waals interactions in the adsorption of toluene, with a noteworthy inhibition of van der Waals interactions observed upon heating. Density functional theory(DFT) simulations show that toluene molecules tend to preferentially adsorb near the benzene ring of the ligand, primarily due to π-π stacking interactions. Simultaneously, the electrophilic channel with greater porosity can gather more nucleophilic groups, thereby enhancing the adsorption performance of toluene.