Room temperature design of Ce(iv)-MOFs: from photocatalytic HER and OER to overall water splitting under simulated sunlight irradiation.

The development of MOF-based efficient and reusable catalysts for hydrogen production under simulated sunlight irradiation, especially through overall water splitting, remains challenging. This is mainly due to either the inappropriate optical features or poor chemical stability of the given MOFs. Room temperature synthesis (RTS) of tetravalent MOFs is a promising strategy to design robust MOFs and their related (nano)composites. By employing these mild conditions, herein, we report for the first time that RTS leads to the efficient formation of highly redox active Ce(iv)-MOFs that are inaccessible at elevated temperatures. Consequently, not only highly crystalline Ce-UiO-66-NH2 is synthesized, but also many other derivatives and topologies (8 and 6-connected phases) without compromise in space-time yield. Their photocatalytic HER and OER activities under simulated sunlight irradiation are in good agreement with their energy level band diagrams: Ce-UiO-66-NH2 and Ce-UiO-66-NO2 are the most active photocatalysts for the HER and OER, respectively, with a higher activity than other metal-based UiO-type MOFs. Combining Ce-UiO-66-NH2 with supported Pt NPs results finally in one of the most active and reusable photocatalysts for overall water splitting into H2 and O2 under simulated sunlight irradiation, due to its efficient photoinduced charge separation evidenced by laser flash photolysis and photoluminescence spectroscopies.

A Novel Porous Ti-Squarate as Efficient Photocatalyst in the Overall Water Splitting Reaction under Simulated Sunlight Irradiation.

A new porous titanium(IV) squarate metal-organic framework (MOF), denoted as IEF-11, having a never reported titanium secondary building unit, is successfully synthesized and fully characterized. IEF-11 not only exhibits a permanent porosity but also an outstanding chemical stability. Further, as a consequence of combining the photoactive Ti(IV) and the electroactive squarate, IEF-11 presents relevant optoelectronic properties, applied here to the photocatalytic overall water splitting reaction. Remarkably, IEF-11 as a photocatalyst is able to produce record H2 amounts for MOF-based materials under simulated sunlight (up to 672 µmol gcatalyst in 22 h) without any activity loss during at least 10 d.