Solar-assisted CO₂ conversion into fuels and chemical products involves a range of technologies aimed at driving industrial decarbonization methods. In this work, we report on the development of a series of multifunctional metal-organic frameworks (MOFs) based on nitro- or amino-functionalized UiO-66(M) (M: Zr or Zr/Ti) supported RuO_x NPs as photocatalysts, having different energy band level diagrams, for CO₂ hydrogenation under simulated concentrated sunlight irradiation. RuO_x(1 wt %; 2.2 ± 0.9 nm)@UiO-66(Zr/Ti)-NO₂ was found to be a reusable photocatalyst, to be selective for CO₂ methanation (5.03 mmol g^-1 after 22 h;, apparent quantum yield at 350, 400, and 600 nm of 1.67, 0.25, and 0.01%, respectively), and to show about 3-6 times activity compared with previous investigations. The photocatalysts were characterized by advanced spectroscopic techniques like femto- and nanosecond transient absorption, spin electron resonance, and photoluminescence spectroscopies together with (photo)electrochemical measurements. The photocatalytic CO₂ methanation mechanism was assessed by operando FTIR spectroscopy. The results indicate that the most active photocatalyst operates under a dual photochemical and photothermal mechanism. This investigation shows the potential of multifunctional MOFs as photocatalysts for solar-driven CO₂ recycling.

There is an increasing interest in developing cost-effective technologies to produce hydrogen from sustainable resources. Herein we show a comprehensive study on the use of metal–organic frameworks (MOFs) as heterogeneous photocatalysts for H₂ generation from photoreforming of glycerol aqueous solutions under simulated sunlight irradiation. The list of materials employed in this study include some of the benchmark Zr-MOFs such as UiO-66(Zr)-X (X: H, NO₂, NH₂) as well as MIL-125(Ti)-NH₂ as the reference Ti-MOF. Among these solids, UiO-66(Zr)-NH₂ exhibits the highest photocatalytic H₂ production, and this observation is attributed to its adequate energy level. The photocatalytic activity of UiO-66(Zr)-NH₂ can be increased by deposition of small Pt NPs as the reference noble metal co-catalyst within the MOF network. This photocatalyst is effectively used for H₂ generation at least for 70 h without loss of activity. The crystallinity of MOF and Pt particle size were maintained as revealed by powder X-ray diffraction and transmission electron microscopy measurements, respectively. Evidence in support of the occurrence of photoinduced charge separation with Pt@UiO-66(Zr)-NH₂ is provided from transient absorption and photoluminescence spectroscopies together with photocurrent measurements. This study exemplifies the possibility of using MOFs as photocatalysts for the solar-driven H₂ generation using sustainable feedstocks.

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.