Post modification of Oxo-clusters in robust Zirconium-Based metal organic framework for durable SO₂ capture from flue gas

The efficient capture of SO₂ after the combustion of fossil fuels is of great challenge as the low SO₂ concentration (<500 ppm) and coexisting with CO₂, water, O₂ in flue gas. Robust zirconium-based MOFs possessing accessible polar sites usually have high SO₂ adsorption capacity but poor durably in adsorption desulfurization due to the acidic sulfate deposition on the Zr-O cluster. Herein, a Zr-O cluster post-modification method was introduced in a Zr-MOF (MOF-808) to form EDTA-MOF-808 (EDTA, ethylene diaminetetraacetic acid) for selective and durable removal of SO₂. The introduction of EDTA not only improve their SO₂ adsorption capacity, but also sharply increase their SO₂/CO₂ selectivity (57.2 vs 8.9) and SO₂/N₂ selectivity (1915.8 vs 292.7) at low SO₂ partial pressure. Moreover, the synergistic effects of dipole and hydrogen bonding interaction between SO₂ and EDTA in EDTA-MOF-808 make the capture of SO₂ in a reversible manner, which can prevent the formation of S(VI) species in Zr-MOF. DFT calculation confirmed that SO₂ was interacted with EDTA through moderate dipole–dipole interaction (S(SO₂) with N(EDTA)) and hydrogen bonds (H(–COOH) with O(SO₂)). Systematic investigations including thermodynamic SO₂ adsorption, dynamic breakthrough experiments, stability tests and DFT-calculations in both MOF-808 and EDTA-MOF-808 confirmed the efficient performance of post modification of Zr-O clusters with EDTA in Zr-MOFs for durable SO₂ capture.