Evolution of acid and basic sites in UiO-66 and UiO-66-NH2 metal-organic frameworks: FTIR study by probe molecules

Tailoring Lewis/Brønsted acid properties of MOF nodes via hydrothermal and solvothermal synthesis: simple approach with exceptional catalytic implications

“…3 shows three principal n(CN) vibrational bands at 2307-2311, 2272 and 2261 cm À1 , assigned to the CD 3 CN adsorption on Lewis and Brønsted acid sites and physisorbed acetonitrile, respectively. [42][43][44] The relative ratio between the integrated signals associated with Brønsted and Lewis acid sites (band centered at 2272 and 2307-2311 cm À1 , respectively) is at least two times higher for the Hf-MOF-808_H 2 O sample than for the Hf-MOF-808_DMF sample under the conditions employed for the CD 3 CN-FTIR spectroscopy experiment. This characterization clearly suggests that the Brønsted acidity increases through the introduction of OH groups on the metallic nodes during the hydrothermal synthesis.…”

Synthesis, characterization and application of defective metal–organic frameworks: current status and perspectives

“…99 The participation of the modulator formic acid during the structure formation of the Zr-fumarate MOF was only observed in the DMF-based system, resulting in the formation of structural defects. Besides, FTIR spectra of adsorbed specic probe molecules (e.g., CO, 100,101 CD 3 CN, 80,102 and pyridine 27,81,103 ) have been used to characterize coordinatively unsaturated metal sites, which are associated with missing linker defects. Recently, Gentile et al 104 reported a combination of the FTIR and Raman spectra of the HKUST-1 MOF with an ab initio theoretical analysis of the vibrational spectra to reveal spectroscopic signatures of framework defects.…”

Identifying UiO‐67 Metal‐Organic Framework Defects and Binding Sites through Ammonia Adsorption

“…Structural defects in MOFs are known to dictate the balance between their stabilities and chemical reactivities [9b] . Ideally, the node, or secondary building unit (SBU) of a non‐defective UiO‐67 MOF should contain four μ 3 ‐O groups and Brønsted acid (μ 3 −OH group) sites, bound to 12 BPDC linkers coordinated via carboxylate groups and zero Lewis acid sites (undercoordinated Zr 4+ sites) [32] . However, defects, during synthesis, can arise due to several factors which include reaction temperature, [33] reaction time, [34] and modulator choice and concentration [35] .…”