Enhanced Water Adsorption Performance of UiO-66 Modulated with p-Nitrobenzoic or p-Hydroxybenzoic Acid: Introduced Defects and Functional Groups

Abstract

Adding appropriate modulators can effectively improve the porosity and adsorption performance of UiO-66. Herein, UiO-66 samples were synthesized with p-nitrobenzoic acid (PNBA) and p-hydroxybenzoic acid (PHBA) as modulators. All samples exhibited good crystallinity and thermal stability. The polar functional groups (−NO 2 and −OH) and defects were introduced into UiO-66, which significantly improved its water adsorption performance and applications in adsorption heat transformation. With the addition of six equiv PNBA, the saturated water uptake of UiO-66 increased from 0.40 to 0.58 g/g. Also, 4eqPNBA-UiO-66 exhibited the highest water uptake under low relative pressure, which was almost twice that of "low-defect" LD-UiO-66. The addition of PHBA had little effect on the saturated water absorption. However, its highest water uptake at P/P 0 = 0.3 is 0.23 g/g, which is equivalent to that of 4eqPNBA-UiO-66. Ten consecutive adsorption/desorption cycles indicated that these samples had good cycle stability.

Improvement of water adsorption performance of UiO-66 by post-synthetic modification

“…3) is inversely correlated with the defectivity of the UiO-66 samples, and the number of defects can be calculated based on this correlation. The calculation method is based on our previous work 43 and the study by Shearer and co-workers; 36 the results are shown in Table 2. It can be seen that compared with defect-free UiO-66 and LD-UiO-66, the number of BDC 2− linkers relative to each Zr6 cluster for H-UiO-66 is lower (Table 2).…”

“…The adsorption isotherms of all samples exhibit the characteristics of a typical type I isotherm, indicating that there are mainly micropores in these samples. The N 2 adsorption LD-UiO-66 is the sample with low defects that was prepared in our previous work; 43 M Plat is the mass percentage of each sample at T plat (400 °C for PSE samples prepared in this work, 350 °C for LD-UiO-66). HCOO − : NEW : BDC 2− *: the molar ratio between HCOO − , new ligands, and BDC 2− ligands.…”

Commonly Neglected Ester Groups Enhanced Microwave Absorption

“…On the other hand, Oxygen functional groups and structural flaws are invariably present together. The presence of oxygen functional groups that opposed to atoms invariably results in more pronounced irregular flaws in the structure, [15][16][17] favoring in-plane topological defects (dislocations, crystal planes, etc.). These structural flaws induce in situ Gaussian curvature, which modifies the rehybridized electron orbitals and bond lengths and might cause more pronounced electron redistribution.…”