Room temperature synthesis (RTS) of tetravalent MOFs is a promising strategy to design MOFs and their related (nano)composites. By employing these mild conditions, herein, we report for the first time an efficient sustainable way to form 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 activity under simulated sunlight irradiation are in good agreement with their energy level 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 metals-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 the 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.