Aliphatic amine decorating metal–organic framework for durable SO2 capture from flue gas

The efficient capture of SO 2 using porous adsorbents is of great significance in flue gas desulfurization (FGD) process as the reversible physical adsorption can avoid solvents/water consumption and minimize waste generation. Metal organic frameworks (MOFs) are interesting and promising candidates to sequestrate SO 2 in flue gas as their high porosities, regular pore sizes and easy functionalization. However, the coordination bond nature of MOFs makes stably and persistently capture acidic SO 2 gas remains a challenge in MOF. Herein, an aliphatic amine decorating strategy was introduced in a MOF (MIL-101(Cr)) with open metal sites for reversible and durable SO 2 capture. The successful synthesis of N,N'-dimethylethylenediamine (mmen) decorated MIL-101(Cr) named mmen-MIL-101(Cr), was confirmed by powder X-ray diffraction (PXRD), Fourier transform-infrared spectroscopy (FTIR), scanning electron microscopy (SEM), energy-dispersive spectra (EDS) and nitrogen adsorption–desorption isotherm. Compared with chemisorption of SO 2 on open Cr sites in MIL-101(Cr), the SO 2 adsorption sites are transferred from Cr to N atom in mmen-MIL-101(Cr), leading to reversible SO 2 adsorption and desorption. The dipole–dipole interaction between N atom and S(SO 2 ) atom, combining with hydrogen bonding interaction between O(SO 2 ) and H in mmen can increase the SO 2 absorption capacity of mmen-MIL-101(Cr) under low SO 2 partial pressure. The SO 2 adsorption capacity and cycle stability properties were studied in detail by adsorption isotherm and dynamic breakthrough measurement. An unprecedented high SO 2 adsorb capacity (upto 4.27 mmol·g −1 ) at SO 2 partial pressure (0.5 mbar) is achieved in mmen-MIL-101(Cr), which is a great improvement compared to 2.92 mmol·g −1 SO 2 adsorption capacity for primordial MIL-101(Cr) under the same condition. Moreover, mmen-MIL-101(Cr) manifests reversible SO 2 adsorption–desorption performance while MIL-101(Cr) gradually loses its adsorption capacity during dynamic breakthrough cycles. The high SO 2 sorption capacity in low partial pressure and impressive cycle stability of mmen-MIL-101(Cr) demonstrate aliphatic amine decorating strategy is an efficient way to improve MOF’s SO 2 capture capability, which also can extend to other porous adsorbents for low concentration FGD process.