Mixed-metal Zr/Ti MIL-173 porphyrinic metal–organic frameworks as efficient photocatalysts towards solar-driven overall water splitting

Abstract

Hydrolytically stable MOFs combining Ti(IV) ions and porphyrin ligands are expected to display outstanding photophysical properties, making them ideal photocatalysts for the overall water splitting reaction under solar light. We...

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

“…7b and, better in the data provided in Table S4, † the amount of evolved O 2 in the gas phase is below that corresponding to the 0.5 stoichiometry expected for ideal overall water splitting, particularly at shorter irradiation times. This fact has been frequently observed in related precedents of OWS using MOFs as photocatalysts [43][44][45] and can be attributed to the operation of various factors having larger contribution at initial reaction times. Among them, the occurrence of 2e − oxidation of H 2 O, building a stationary low concentration of H 2 O 2 that subsequently decomposes to O 2 (the 4e − oxidation product) and saturation of deareated H 2 O by O 2 , much more water-soluble than H 2 , are two major processes to be considered to justify the lower-than-the-stoichiometry O 2 amount measured in the gas phase.…”

“…As it can be observed in Figure 7b and, better in the data provided in Table S4, the amount of evolved O 2 in the gas phase is below that corresponding to the 0.5 stoichiometry expected for ideal overall water splitting, particularly at shorter irradiation times. This fact has been frequently observed in related precedents of OWS using MOFs as photocatalysts [43][44][45] and can be attributed to the operation of various factors having larger contribution at initial reaction times. Among them, the occurrence of 2 e - Regardless these comments, Table S5 in SI summarizes the use of MOF-based photocatalysts for the OWS into H 2 and O 2 .…”

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

“…In this work, the activity of the UiO-66­(Zr)-NH 2 -25@UiO-66­(Ce) photocatalyst (5 mg) was notably higher with the production rates of H 2 and O 2 reaching to 708 and 320 μmol g –1 , respectively, after 22 h. The estimated apparent quantum yield (AQY) using UiO-66­(Zr)-NH 2 -25@UiO-66­(Ce) as photocatalyst for the OWS is 0.034% at 400 nm. For comparison, a mixed-metal Zr/Ti-MIL-173 porphyrin-based MOF exhibited an AQY of 0.11% at 450 nm . Overall, this study shows the possibility of preparing MOF-on-MOF composites based on UiO-66 solids to develop active photocatalysts for the OWS under simulated sunlight irradiation.…”

“…In this context, previous studies in the area of photocatalysis using both inorganic semiconductors − and MOFs , have shown that the size and shape of the particles determine their energy band diagram. Other factors, including structural defects such as oxygen vacancies in inorganic semiconductors or missing linkers or clusters in MOFs, − also influence the resulting energy level band diagram of the solids. Therefore, these are possible explanations for the deviations in energy level diagrams between the UiO-66­(Zr)-NH 2 or UiO-66­(Ce) solids and the MOF-on-MOF composites.…”

“…The somewhat lower oxygen content observed compared to the H 2 O stoichiometry may be due to several reasons, including the partial consumption of the photogenerated holes by spurious electron donor impurities or the in situ reaction of O 2 evolved during the photocatalytic reaction . In fact, several previous studies of photocatalytic OWS using MOFs such as MIL-125­(Ti)-NH 2 , UiO-66­(Zr/Ce/Ti), UiO-66­(Ce)-NH 2 , MIL-173­(Zr/Ti), and IEF-11, among other precedents, have also reported a H 2 to O 2 molar ratio higher than the theoretical value of 2. These observations can be related to several factors with different contributions that include H 2 O oxidation to H 2 O 2 that later could be decomposed to O 2 .…”