A Novel Ti12-based Metal-Organic Framework for Photocatalytic Hydrogen Evolution

Constructing titanium-based metal-organic frameworks (Ti-MOFs) is an effective way towards upgrading TiOx and the enhancement of their photocatalytic performance throughout higher accessibility to active sites and better tunability of photophysical properties. In this regard, Ti-MOFs have attracted much attention as photocatalyst candidates owing to their porosity and tunability in terms of chemical composition and pore engineering. However, Ti-MOFs remain still one of the least developed sub-class of MOF materials because of the complexity of titanium chemistry in solution hampering their rational design, despite recent progresses. Here, we present a new microporous Ti-MOFs with acs topology, labeled MIP-209(Ti) (MIP stands for Materials from Institute of Porous Materials of Paris) constructed by a nitro terephthalate ligand and Ti12O15 oxo-clusters, as revealed by continuous rotation electron diffraction (cRED). MIP-209(Ti) can be obtained using various terephthalate (1,4-BDC2-) derivatives such as NO2-BDC and 2Cl-BDC using an eco-friendly solvent, suggesting the ability of Ti12-MOFs for isostructural chemistry. Alternatively, it is also possible to tune the composition of its Ti-oxo-cluster, similarly to MIP-177(Ti)-LT bearing the same Ti12O15 sub-unit. Typically, low percentage Cr3+ doping (≤ 5 at%) in MIP-209(Ti) favorably enhances the water stability. Interestingly, photocatalytic hydrogen evolution from water splitting reaction (HER) were measured for MIP-209(Ti-Cr)-NO2 and a significant hydrogen production rate, with good reusability and stability under simulated solar light irradiation, were revealed. It showed enhanced photocatalytic hydrogen production performances under simulated solar light irradiation compared to the benchmark Ti-MOF IEF-11 with a fourfold enhanced hydrogen production in HER in 5h in presence of methanol (5812 µmol of H2/gcat against 1391 µmol of H2/gcat) as well as, without any noble metal co-catalyst, a 6-fold enhanced overall water splitting production (681 and 325 µmol/gcat of H2 and O2, respectively for MIP-209, against 94 and 53 µmol/gcat of H2 and O2, respectively, for IEF-11). This work represents a leap forward in the synthesis of Ti-MOFs and their practical photocatalytic applications.