A porous coordination polymer was prepared using pyrazine-2,3-dicarboxylate (pzdc) and a dipyridyl ligand that contains −CH2CH2CH2– as a spacer, namely, 1,3-bis­(4-pyridyl)­propane (bpp). The material was thoroughly tested for determination of textural and adsorption properties in an attempt to elucidate structural flexibility in the absence of a gate opening pressure phenomenon. The periodic framework (monoclinic, P21/c, a = 13.300(3), b = 13.112(7), c = 10.808(5) Å, β = 101.28(4)°) composition is Cu2(pzdc)2­(bpp))­·4H2O, with an overall structural arrangement similar to those present in other two-dimensional copper + pzdc based coordination polymers, but showcasing a heavily distorted, parallelogram-shaped gallery along c. The structure appears stable up to 510 K based on thermogravimetric analysis and in situ high temperature X-ray diffraction data; complete elimination of water takes place at 373 K. Upon activation, the material effective surface area and pore volume are much smaller than those of other Cu2(pzdc)2 structures, probably because of the constricted void space. Still, a corrected Horvath–Kawazoe pore size distribution analysis method points to a 4.2 Å average pore size. Uptake of CO2 at 194.5 K revealed a hysteretic adsorption–desorption phenomenon, probably due to a concomitant pore width expansion process that is analogous to the one reported for Cu2(pzdc)2­(bpy) (bpy: 4,4′-bipyridine). The phenomenon is amplified at 298 K and remains at pressures up to 50 atm of CO2. Furthermore, it appears that the dynamics of structural changes are slower compared to those of the adsorption process; equilibrium seems to take place at an equilibration time interval of at least 120 s. In contrast with isostructural Cu2(pzdc)2­(dpyg) (dpyg: 1,2-di­(4-pyridyl)-glycol), Cu2(pzdc)2­(bpp) appears to have a stronger interaction with CO2 as evidenced by the isosteric heats of adsorption profiles and probably due to the flexibility introduced by the bpp ligand.

A composite adsorbent (CMOF) based on in situ growth of MIL-100Fe (MOF) within the macro-and mesopores of a Darco-KB-G activated carbon (AC) was prepared for the efficient adsorption of a set of contaminants of emerging concern (CECs), namely, caffeine (CFN), carbamazepine (CBZ), clofibric acid (CA), 10,11-epoxycarbamazepine (Ep-CBZ), naproxen (NPX), o-desmethylnaproxen (o-DMN), paraxanthine (PXN), and salicylic acid (SA), from water. The properties of the composite and that of the parent materials were evaluated via X-ray diffraction, scanning electron microscopy, nitrogen porosimetry, thermal gravimetric analysis (TGA), and X-ray photoelectron microscopy. Mass balances indicate that the composite contains about 46 wt % MOF, while a comparison of pore size distributions and TGA corroborated that the vast majority of the crystalline material resides within the macro/mesopores of the AC. Zeta potential measurements revealed that the acid media used during the in situ growth of the MOF resulted in a CMOF surface charge profile (isoelectric point (IEP) = ∼3.2) that is generally more negative than that of the MIL-100(Fe) (IEP = ∼4.2) and the nonacid treated AC (IEP = ∼5.5). Single and multicomponent CEC equilibrium adsorption tests were performed at room temperature, neutral pH conditions, and low CEC concentrations (∼μg L −1 ). Single component adsorption data show that the composite adsorbs 10-fold more CEC molecules compared to the MOF alone, with a selectivity that increases as follows: CA < SA < o-DMN < PXN < NPX < CFN < Ep-CBZ < CBZ. The effect of competition among the CECs on the adsorption capacity of CMOF was not as significant, only about 9% smaller compared to single component adsorption data. Uptake improvements seen in the CMOF appear to be the result of interactions based on a combination of hydrophobicity (from the AC core) and enhanced electrostatic level forces as well as π-complexation and π−π stacking interactions.

Aiming to elucidate guest-induced structural changes in the coordination polymer CPL-2, grand canonical Monte Carlo (GCMC) simulations were used to predict CO loadings in this material, and the results were compared with experimental isotherms. Our calculations suggest that CPL-2 exhibits more pronounced CO-induced structural changes than previously reported. As the initial evidence, the isotherm simulated in the previously reported CPL-2 structure (experimentally resolved from X-ray diffraction in the "as-synthesized" CPL-2) underestimated the measured CO loadings at high pressure, indicating that CPL-2 might undergo structural changes that enable higher pore volumes at high pressure. GCMC simulations in CPL-2 structures considering moderate unit cell expansions reported in the literature still underestimated high-pressure experimental loadings. However, considering an incremental rotation of the CPL-2 bipyridyl pillars with increasing CO pressure, we were able to trace the measured isotherm with the simulation data. Computational analysis shows that ligand rotation in CPL-2 enables higher pore volumes, which, in turn, accommodate more CO as the gas pressure increases. Desorption measurements suggest that hysteresis in the CO isotherm of CPL-2 may also be linked to ligand rotation, and the measured adsorption/desorption cycles show that the rotation is reversible. Based on our simulations for CPL-4 and CPL-5 and previously reported experimental data, it is likely that these materials, which differ from CPL-2 in the bipyridyl ligand, behave similarly in the presence of CO. Our results help understand the behavior of these materials, which present the kind of structural changes that could be potentially exploited to enhance the CO working capacity of ultra-microporous materials for carbon capture applications.

Flexible metal-organic frameworks (MOF) can show exceptional selectivity and capacity for adsorption of CO2. The incorporation of CO2 into flexible MOFs that have Cu2+ coordination centers and organic pillar ligands...