ABSTRACT
P2W18Co4@MOF-545, which contains the sandwich-type polyoxometalate (POM) [(PW9O34)2Co4(H2O)2]10- (P2W18Co4) immobilized in the porphyrinic metal-organic framework (MOF), MOF-545, is a "three-in-one" (porosity + light capture + catalysis) heterogeneous photosystem for the oxygen-evolution reaction (OER). Thin films of this composite were synthesized on transparent and conductive indium tin oxide (ITO) supports using electrophoretic (EP) or drop-casting (DC) methods, thus providing easy-to-use devices. Their electro- and photocatalytic activities for OER were investigated. Remarkably, both types of films exhibit higher turnover numbers (TONs) than the original bulk material previously studied as a suspension for the photocatalytic OER, with TONs after 2 h equal to 1600 and 403 for DC and EP films, respectively, compared to 70 for the suspension. This difference of catalytic activities is related to the proportion of efficiently illuminated crystallites, whereby a DC thin film offers the largest proportion of POM@MOF crystallites exposed to light due to its lower thickness when compared to an EP film or crystals in suspension. Such devices can be easily recycled by simply removing them from the reaction medium and washing them before reuse. The films were fully characterized with extended X-ray absorption fine structure (EXAFS) and X-ray absorption near edge structure (XANES) spectroscopies, Raman, scanning electron microscopy, and electrochemistry before and after catalysis. The combination of all of these techniques shows the stability of both the POM and the MOF within the composite upon water-oxidation reaction.
ABSTRACT
A unique polyoxometalate complex made up of a tetradecanuclear nickel bisphosphonate cluster capping a {SiW9} unit has been characterized. This stable compound exhibits a high hydrogen evolution reaction photocatalytic activity under visible light irradiation via a reductive quenching mechanism.
ABSTRACT
The luminescent [EuW10O36]9- polyoxometalate has been introduced into the cavities of the highly porous zirconium luminescent metal-organic framework UiO-67 via a direct synthesis approach, affording the EuW10@UiO-67 hybrid. Using a combination of techniques (TGA, BET, elemental analysis, EDX mapping, ) this new material has been fully characterized, evidencing that it contains only 0.25% in europium and that the polyoxometalate units are located inside the octahedral cavities and not at the surface of the UiO-67 crystallites. Despite the low amount of europium, it is shown that EuW10@UiO-67 acts as a solid-state luminescent sensor for the detection of amino-acids, the growth of the emission intensity globally following the growth of the amino-acid pKa. In addition, EuW10@UiO-67 acts as a sensor for the detection of metallic cations, with a high sensitivity for Fe3+. Noticeably, the recyclability of the reported material has been established. Finally, it is shown that the dual-luminescent EuW10@UiO-67 material behave as a self-calibrated-ratiometric thermometer in the physiological range.
ABSTRACT
The sandwich-type polyoxometalate (POM) [(PW9O34)2Co4(H2O)2]10- was immobilized in the hexagonal channels of the Zr(IV) porphyrinic MOF-545 hybrid framework. The resulting composite was fully characterized by a panel of physicochemical techniques. Calculations allowed identifying the localization of the POM in the vicinity of the Zr6 clusters and porphyrin linkers constituting the MOF. The material exhibits a high photocatalytic activity and good stability for visible-light-driven water oxidation. It thus represents a rare example of an all-in-one fully noble metal-free supramolecular heterogeneous photocatalytic system, with the catalyst and the photosensitizer within the same porous solid material.
