A Robust Titanium Isophthalate Metal-Organic Framework for Visible Light Photocatalytic CO ₂ Methanation

Abstract

Isophthalic acid (IPA), a feedstock linker, has been considered so far to build series of topical metal-organic frameworks (MOFs) of diverse structures with various di-and trivalent metal ions, such as CAU-10(Al), owing to its facile availability, unique connection angle/mode and a wide scope of functional groups attached. Constructing MOFs from IPA and tetravalent metals, typically Group 4 metals, would be of a great interest due to expected higher chemical stability. In particular, titanium-IPA frameworks possessing photoresponse is alluring, in relation to the known challenge of synthesizing new Ti-MOFs. Here, we have synthesized the first Ti-IPA MOF, denoted as MIP-208, via a solvothermal process that efficiently combines the use of preformed Ti 8 oxoclusters and in situ acetylation of 5-NH 2 -IPA linker. MIP-208 has helical chains of cis-connected corner-sharing TiO 6 polyhedra as the inorganic building units, which are interconnected to each other leading to a 3D ultramicroporous framework. Solid-solution mixed linkers strategy was then successfully applied resulting in a series of multivariate MIP-208 structures with tunable chemical environment and sizable porosity. Finally, the excellent thermal and hydrolytic stabilities of MIP-208 allowed its use for the photocatalytic carbon dioxide (CO 2 ) methanation, showing the best result among the pure MOF catalysts. Ruthenium oxide nanoparticles were further photodeposited on MIP-208 forming a highly active and selective composite catalyst, MIP-208@RuO x , to largely improve the photocatalytic performance, which features a notable visible light response, an excellent stability and recycling ability.

H2S Stability of Metal-Organic Frameworks: A Computational Assessment

“…To that purpose, we first evaluated different plausible degradation mechanisms with MIL-53(Al)-BDC 30 taken as our reference MOF material since it was already proved experimentally to be stable upon exposure to H 2 S. This preliminary stage enabled us to identify the most probable degradation mechanism and to propose the rate constant of the degradation reaction as a reliable descriptor for characterizing the H 2 S stability of MOFs. We further explored a range of MOFs with the objective to evaluate how the stability of this family of materials is affected by the nature of the linkers, with the consideration of several derivatives of MIL-53 [54][55] and CAU-10; [63][64][65] the nature of the functional groups grafted to organic linkers, with the use of functionalized MIL-53(Al)s, [66][67] the pore size with the comparison between the large-pore and narrow-pore forms of MIL-53(Al)-BDC-NH 2 , 67 the metal substitution with the cases of CAU-10(Al) 68 and MIL-160(Al) 69 and their Tianalogues and the presence/nature of coordinatively unsaturated site (CUS) with the consideration of MOF-74 (Ni) 57 and MOF-74(Zn). 52,57 This systematic exploration led to a qualitative H 2 S stability ranking of all these MOFs based on the evaluation of their associated rate constants for the corresponding first-step degradation reaction.…”