Hybride Self-Assemblies Of Iron, Cobalt Catalysts And CdTe Quantum Dots For Light-Driven Hydrogen Production

Direct conversion of solar energy into chemical fuels such as hydrogen, an energy-dense molecule, by photoinduced water splitting is one of the promising solutions to meet globally ever-increasing energy demands. The key issue for approaching this target is to develop highly efficient, robust, and cheap photocatalytic systems. It has been found that the integration of molecular catalysts with inorganic light harvesting materials is an effective method to construct highly efficient and robust photocatalytic systems.In this thesis, two types of hybrid photocatalytic systems were constructed by using cobalt or iron complexes,[(bme-dach)M(NO)](1, M=Co;3, M=Fe; H2bme-dach=N,N’-bis(2-mercaptoethyl)-1,4-diazacycloheptane) and [(bme-dach)M]2(2, M=Co;4, M Fe), containing a N2S2tetradentate ligand as catalysts,2-thioglycolic acid-stabilized CdTe (TGA-CdTe) quantum dots (QDs) as light harvester, and ascorbate as sacrificial electron donor. Among these systems, the two sulfur atoms of the N2S2ligand in the mononuclear complex [(bme-dach)M(NO)] can be coordinately anchored to the Cd2+-rich surface of water soluble TGA-CdTe QDs, forming a self-assembly; while the dimeric complex [(bme-dach)M]2cannot have such interaction with TGA-CdTe QDs because its sulfur atoms are already coordinatively saturated. UV-vis and IR spectroscopic studies show that there is a ground-state interaction between [(bme-dach)Co(NO)] and QDs. ICP analyses of the solid samples indicate that about0.21%(w/w) of1is grafted on CdTe QDs while only negligible amount of2is adsorbed on QDs. The photoinduced electron transfer from QDs to cobalt catalyst was studied by fluorescence spectroscopy, which verified that a static quenching occurred in the system comprising [(bme-dach)M(NO)] and TGA-CdTe QDs, and a dynamic quenching dominantly took place in the system containing [(bme-dach)M]2and QDs. The TGA-CdTe-1hybrid assembly formed by coordinative anchoring of1to semiconducting nanoparticles is highly efficient and robust for photochemical H2production in water, giving TON higher than2.3×104based on catalyst over70-h irradiation with a quantum efficiency of5.32%at400nm. Under identical conditions, the homogeneous system containing [(bme-dach)Co]2and TGA-CdTe displays a TON of3600over20-h irradiation with a quantum efficiency of1.49%. Iron complexes3and4are less efficient for catalytic H2production than analogous cobalt complexes. Under optimal conditions, TGA-CdTe/[(bme-dach)Fe(NO)] assembly exhibits a TON of4800over30-h irradiation, while the TON of H2evolution with [(bme-dach)Fe]2as catalyst is2900.