The Chemical Catalysis Program supports the efforts of Professor Felix N. Castellano for the investigation of both heterogeneous and homogeneous approaches to photocatalytic hydrogen production from water. The effort targets the photochemical preparation, characterization, and photocatalytic properties of titanium dioxide (TiO2) materials decorated with highly dispersed metallic platinum and palladium nanoparticles. Photocatalysis is evaluated in aqueous solutions using bandgap excitation in the presence of hole scavengers and in the analogous visible-light sensitized materials using select surface bound ruthenium(II) and osmium(II) complexes in the presence of appropriate sacrificial electron donors. Various cobalt compounds are tested for their hydrogen-producing ability in concert with "charged" TiO2 in aqueous solutions. Homogeneous photocatalysis schemes exploit reductive quenching pathways that have recently led to significant enhancements in catalytic turnovers. The use of alternative sacrificial electron donors in these homogeneous schemes has led to unprecedented catalytic turnovers while greatly expanding the inventory of potentially useful sensitizers.
This project addresses interdisciplinary research that contributes to the fundamental knowledge base of converting solar light to an environmentally-friendly, non-carbon based, combustible chemical fuel. The photocatalytic systems considered in this research project offer better atom economies and the potential for much higher efficiencies than other systems. The project fosters the scientific and professional education of undergraduate and graduate students as well as postdoctoral associates and visiting scientists. Professor Castellano participates in various K-12 STEM education efforts including the Imagination Station of Toledo and the annual "High School Science Days" that take place on the Bowling Green campus.
The generation of hydrogen gas from water using solar photons remains a formidable challenge and requires multi-faceted approaches in order to develop new photocatalytic molecular compositions and materials, in addition to understanding their functional details. The proposed research activities developed both homogenous (molecular) and heterogeneous (materials) hydrogen-generating photocatalytic compositions, while evaluating their performance metrics in parallel using combinatorial photochemistry while seeking a detailed understanding of mechanisms of action through a battery of static and dynamic spectroscopic techniques. The wide bandgap semiconductor TiO2 bearing surface-anchored Pt(dcbpy)Cl2 [dcbpy = 4,4’-dicarboxylic acid-2,2’-bipyridine] prepared with systematically varied loadings produces Pt0 nanoparticles under bandgap illumination in the presence of methanol hole scavengers, leading to impressive H2 evolution metrics. In parallel, the cobalt phosphate "CoPi" oxygen evolving catalyst (OEC) was photochemically grown on the surface of TiO2 photoanodes short-circuited to a Pt wire under bandgap illumination in the presence of Co(NO3)2 and sodium phosphate (NaPi) buffer. Extended photodeposition using a handheld UV lamp readily permitted quantitative structural and electrochemical/photoelectrochemical characterization of the photochemically deposited CoPi OEC on titania. Collaborative work in heterogeneous materials supported by this award focused on the evaluation of Stark effects in dye-sensitized titania as well as solar fuels generation from core-shell semiconductor nanoparticles. Another important facet of this project involved developing new combinations of homogeneous-based visible light absorbing photocatalysis compositions for the generation of hydrogen from water. These included the development of numerous Pt(II), Cu(I), Ru(II), and Ir(III) sensitizers in conjunction with molecular cobalt hydrogen evolution catalysts as well as the associated high-throughput screening techniques necessary to evaluate numerous photocatalytic compositions in parallel. These combined experimental studies yielded unprecedented stabilities and efficiencies of hydrogen evolution photocatalysis from water. In total, 41 peer reviewed research articles have been published under the auspices of this NSF Award. Eight students graduated from the Castellano group since 2010 (5 Ph.D., 3 M.S.) notably three of them are female scientists and two others are African-American. All of these individuals are currently practicing chemistry. Ten former postdoctoral associates from the laboratory since 2010 have also secured professional positions. Seven different undergraduate researchers were financially supported under this award since 2010, two of which are currently enrolled in doctoral degree programs in Chemistry. The PI was actively engaged in numerous professional, educational, and outreach activities. The PI co-organized an entire international scientific conference (ISPPCC 20 in 2013), organized a major symposium in catalysis (2014 ACS Dallas Meeting) and co-organized a symposium in Pacifichem 2010. Since 2010, the PI has served as an Invited Visiting Professor three times, has given over 70 invited lectures at professional meetings and Universities, and has produced a SlideShare presentation for J. Phys. Chem. Lett. He also served as an invited participant in a Royal Society Discussion on triplet excitons in September of 2014. The PI also published a newly conceived laboratory experience for J. Chem. Ed. in 2013. The PI served as an extramural doctoral dissertation examiner on 4 different occasions and has collaborated with numerous faculty members from undergraduate institutions. The PI hosted an African-American high school junior in the summer of 2014 under the auspices of the ACS Project SEED program and will host this student again during the summer of 2015.
