Rational Fine-Tuning of MOF Pore Metrics: Enhanced SO2 Capture and Sensing with Optimal Multi-Site Interactions

Abstract

Selective capture of sulfur dioxide (SO₂), important in the context of environmental protection, is reachable by specially tailored porous materials endowed with physisorptive complementarity. Metal–organic frameworks (MOFs) can potentially be leading materials for physisorptive SO₂ capture due to their excellent tailorability. Here, a series of highly stable DMOFs, [Ni₂L₂(DABCO)], where L = 1,4-benzenedicarboxylate (BDC), 1,4-naphthalenedicarboxylate (NDC), 2,6-naphthalenedicarboxylate (2,6-NDC), 9,10-anthracendicarboxylate (ADC), and 1,4-diazabicyclo[2,2,2]octane (DABCO) aiming at optimal SO₂ physisorption characteristics, is reported. The extension of the aromatic core by conjugated benzene rings allows to reach an optimal pore diameter at 4–5 Å in the case of the DMOF-ADC, maximizing the multi-site MOF···SO₂ interactions, which improve the SO₂ binding at low concentrations, as revealed by density-functional theory (DFT) calculations. The improved SO₂ separation performance of DMOF-ADC is demonstrated by single SO₂ and SO₂/CO₂-mixed-component adsorption (a SO₂/CO₂ selectivity >100 is reached at 0.01 bar, which is significantly better than the value for the benchmark DUT-8 material) and dynamic breakthrough experiment. The use as a chemiresistive sensor for SO₂ sensing is demonstrated for the best performing DMOF-ADC at low concentrations (doubled resistive response at 100 ppm and T < 120 °C).