Finding new adsorbents for the desulfurization of flue gases is a challenging task but is of current interest, as even low SO2 emissions impair the environment and health. Four Zr- and eight Al-MOFs (Zr-Fum, DUT-67(Zr), NU-1000, MOF-808, Al-Fum, MIL-53(Al), NH2-MIL-53(Al), MIL-53(tdc)(Al), CAU-10-H, MIL-96(Al), MIL-100(Al), NH2-MIL-101(Al)) were examined toward their SO2 sorption capability. Pore sizes in the range of about 4–8 Å are optimal for SO2 uptake in the low-pressure range (up to 0.1 bar). Pore widths that are only slightly larger than the kinetic diameter of 4.1 Å of the SO2 molecules allow for multi-side-dispersive interactions, which translate into high affinity at low pressure. Frameworks NH2-MIL-53(Al) and NH2-MIL-101(Al) with an NH2-group at the linker tend to show enhanced SO2 affinity. Moreover, from single-gas adsorption isotherms, ideal adsorbed solution theory (IAST) selectivities toward binary SO2/CO2 gas mixtures were determined with selectivity values between 35 and 53 at a molar fraction of 0.01 SO2 (10.000 ppm) and 1 bar for the frameworks Zr-Fum, MOF-808, NH2-MIL-53(Al), and Al-Fum. Stability tests with exposure to dry SO2 during ≤10 h and humid SO2 during 5 h showed full retention of crystallinity and porosity for Zr-Fum and DUT-67(Zr). However, NU-1000, MOF-808, Al-Fum, MIL-53(tdc), CAU-10-H, and MIL-100(Al) exhibited ≥50–90% retained Brunauer–Emmett–Teller (BET)-surface area and pore volume; while NH2-MIL-100(Al) and MIL-96(Al) demonstrated a major loss of porosity under dry SO2 and MIL-53(Al) and NH2-MIL-53(Al) under humid SO2. SO2 binding sites were revealed by density functional theory (DFT) simulation calculations with adsorption energies of −40 to −50 kJ·mol–1 for Zr-Fum and Al-Fum and even above −50 kJ·mol–1 for NH2-MIL-53(Al), in agreement with the isosteric heat of adsorption near zero coverage (ΔH ads 0). The predominant, highest binding energy noncovalent binding modes in both Zr-Fum and Al-Fum feature μ-OHδ+···δ−OSO hydrogen bonding interactions. The small pores of Al-Fum allow the interaction of two μ-OH bridges from opposite pore walls with the same SO2 molecule via OHδ+···δ−OSOδ−···δ+HO hydrogen bonds. For NH2-MIL-53(Al), the DFT high-energy binding sites involve NHδ+···δ−OS together with the also present Al-μ-OHδ+···δ−OS hydrogen bonding interactions and C6-πδ−···δ+SO2, Nδ−···δ+SO2 interactions.
Herein, we report ap re-synthetic pore environment design strategy to achieve stable methyl-functionalized metalorganic frameworks (MOFs) for preferential SO 2 binding and thus enhanced low (partial) pressure SO 2 adsorption and SO 2 / CO 2 separation. The enhanced sorption performance is for the first time attributed to an optimal pore sizeb yi ncreasing methyl group densities at the benzenedicarboxylate linker in [Ni 2 (BDC-X) 2 DABCO] (BDC-X = mono-, di-, and tetramethyl-1,4-benzenedicarboxylate/terephthalate;D ABCO = 1,4-diazabicyclo[2,2,2]octane). Monte Carlo simulations and first-principles density functional theory (DFT) calculations demonstrate the key role of methyl groups within the pore surface on the preferential SO 2 affinity over the parent MOF. The SO 2 separation potential by methyl-functionalized MOFs has been validated by gas sorption isotherms,i deal adsorbed solution theory calculations,s imulated and experimental breakthrough curves,and DFT calculations.
To develop potential metal-organic frameworks (MOFs) for 2,4,6-trinitrophenol (TNP) detection, an amino-functionalized Zn-MOF, [NH(CH)][ZnO(bpt)(bdc-NH)]·5DMF (where Hbpt = biphenyl-3,4',5-tricarboxylate, Hbdc-NH = 2-aminoterephthalic acid, and DMF = N,N-dimethylformamide), has been designed theoretically and synthesized experimentally. Its structure is composed of ZnO(CO) secondary building units linked by mixed ligands, exhibiting a three-dimensional framework. Fluorescence exploration revealed that the amino-functionalized Zn-MOF shows high selectivity and sensitivity for TNP, which agrees well with the predictions of theoretical simulations. This work provides a suitable means to develop new potential MOFs for TNP detection performance with a combination of experimental and theoretical perspectives.
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