Chemical immobilization of amino acids into robust metal–organic framework for efficient SO₂ removal

Abstract

Adsorptive removal of trace SO2 emissions from flue‐gases can significantly reduce energy and water consumption and minimize the amount of unmanageable waste, however, this remains a great challenge. Herein, we report a universal strategy of chemical immobilization of amino acids into a robust metal–organic framework to enhance deep desulfurization. The grafted amino acid resulted in the formation of pores with compatible pore sizes and created abundant N‐containing moieties for selective SO2 adsorption. MOF‐808‐His (His = l‐histidine) exhibited a top‐ranking SO2 uptake (10.4 mmol g−1) with an excellent SO2/CO2 selectivity (90.5) under ambient conditions; furthermore, MOF‐808‐His could be easily regenerated. Breakthrough curves verified its excellent separation performances with water vapor and real flue‐gas compositions. Computational simulations confirmed the vital role of immobilized amino acids in improving the SO2 capture ability and selectivity. As a proof‐of‐concept, five natural amino acids were immobilized into MOF‐808; all samples displayed improved adsorptive desulfurization performances.

Dense open metal sites in a microporous metal–organic framework for deep desulfurization with record‐high sulfur dioxide storage density

“…To estimate the affinity between SO 2 molecule and MOF frameworks, the coverage‐dependent isosteric heats ( Q st ) were calculated based on the SO 2 adsorption isotherms at 273, 298, and 323 K using the Clausius‐Clapeyron equation (Figures S8 and S11), and the Langmuir–Freundlich equation was applied to perform the global fitting (Figure S12). At zero coverage, the Q st on Cu‐ATC is calculated to be 60 kJ mol −1 (Figure 3B), which is higher than that of MOF‐808‐His (52 kJ mol −1 ), 7 NH 2 ‐MIL‐125(Ti) (53 kJ mol −1 ), 38 MFM‐300(Sc) (36.2 kJ mol −1 ), 40 and MIL‐101(Cr)‐4F (54 kJ mol −1 ) 9 . In sharp contrast, the Q st value at zero coverage declined to 48 kJ mol −1 on Cu 2 (ATC)∙2H 2 O, also suggesting that the exposed Cu OMSs are strong binding sites for SO 2 .…”

“…The ideal adsorbed solution theory (IAST) was applied to access the separation selectivity of SO 2 /CO 2 (10/90 and 0.2/99.8, v / v ), SO 2 /CH 4 (10/90, v / v ), and SO 2 /N 2 (10/90, v / v ) mixtures. Notably, as shown in Figure 2E, Cu‐ATC showed exceptionally high SO 2 /CO 2 (10/90, v / v ) IAST selectivity of 114 at 1.0 bar and 298 K, superior to SIFSIX‐2‐Cu‐i (87.1), 21 MOF‐808‐His (90.5), 7 and MFM‐300(In) (50), 37 and comparable to top‐ranking benchmarks including MFM‐520 (125), 31 MIL‐160 (124), 38 and Co‐gallate (143) 35 . Besides, the IAST selectivity for SO 2 /CO 2 (0.2/99.8, v / v ) reached 88 at 298 K and 1.0 bar (Figure S9).…”

“…For instance, Cui et al 21 reported a series of microporous anion‐pillared MOFs with steep SO 2 adsorption of 4.16 mmol g −1 at 0.01 bar due to strong S δ+ ···F δ− electrostatic and O δ− ···H δ+ dipole–dipole interactions. Our group also demonstrated the amino‐acid immobilization strategy to decorate the pore environment of MOF‐808, and the optimized MOF‐808‐His (His = l ‐histidine) showed a leading SO 2 separation capacity of 10.4 mmol g −1 and SO 2 /CO 2 selectivity of 90.5 at 298 K and 1 bar 7 …”

“…Furthermore, the wet FGD technology consumes large amounts of energy and water, as well as generates bulky slurry wastes 5,6 . In addition, the regeneration of solvents for SO 2 capture is energy‐consuming because of the irreversible chemisorption with strong acidic gas molecules 7,8 . Therefore, dry physisorption using readily regenerable adsorbents is considered as the promising alternative to eliminate trace SO 2 with reduced energy demands for pressurization 9,10 …”

Multi-Level Computational Screening of in Silico Designed MOFs for Efficient SO2 Capture

“… 25 One strategy to render such MOFs efficient for SO 2 capture is functionalization, as exemplified by MOF-808-His, underlining the importance of investigating the functionalized MOFs whose bare forms may not show significant gas uptake or separation capability. 25 Through functionalization, the pores may provide stronger host–guest interactions as they can be narrower (leading to stronger confinement effects) or grafted favorable interaction sites for sorbates.…”