MOF-on-MOF Composites with UiO-66-Based Materials as Photocatalysts for the Overall Water Splitting under Sunlight Irradiation

There is a large interest in the sustainable conversion of H2O into H2 and O2, assisted by sunlight. In recent times, metal–organic frameworks (MOFs) have evolved as promising photocatalysts for this reaction. In the present study, a number of novel MOF-on-MOF composites possessing UiO-66 topologies, namely UiO-66(Ce), UiO-66(Zr)-NH2, UiO-66(Zr)-NH2@UiO-66(Ce), and UiO-66(Ce)@UiO-66(Zr)-NH2, are prepared, and their photocatalytic activity is examined in the overall water splitting under simulated sunlight irradiation. Among these photocatalysts, promising activity is observed with the UiO-66(Zr)-NH2@UiO-66(Ce) photocatalyst, exhibiting 708 and 320 μmol g–1 at 22 h for H2 and O2, respectively. This enhanced photocatalytic activity of UiO-66(Zr)-NH2@UiO-66(Ce) is associated with its adequate energy band diagram and ability for photoinduced charge separation, as revealed by several spectroscopic measurements, such as photoluminescence and transient absorption spectroscopy together with specific photocatalytic measurements. This study is an illustrative investigation showing the photocatalytic activity of MOF-on-MOF composites for the overall water splitting under simulated sunlight irradiation.