Catalysis with nanostructured solution-processed materials

Solution-processed, nanostructured inorganic materials offer enormous potential in scientific and technological fields including heterogeneous catalysis, photovoltaics, photoelectrochemistry, and inexpensive nanofabrication. This Ph.D. thesis Dissertation focuses on two general concepts in solution-processed inorganic materials: semiconductor photopolymerization reactions and multicomponent inorganic materials for heterogeneous catalysis.

Semiconductor sensitized photopolymerizations that exploit the exceptional material properties of two different systems are examined. In the first case (Chapter 2), the enormous non-linear optical properties of CdS semiconductor quantum dots are used for efficient two-photon induced polymerization. The surface of the CdS quantum dots was modified in order to achieve efficient photoinitiation, and the first successful demonstration of two-photon induced polymerization using semiconductor quantum dots is reported. Second (Chapter 3), mesoporous TiO₂ was utilized for the photo-oxidative polymerization of pyrrole monomer. In this case polypyrrole was polymerized in the pores of the TiO₂, and the process was monitored using a quartz crystal microbalance and thermogravimetric analysis. These two materials systems have applications in three-dimensional nanolithography and photo-electro-catalysis, respectively.

In the second half of this thesis the development of novel inorganic nanostructured materials for heterogeneous catalysis applications such as catalytic oxidation, water gas shift, and NO_x reduction is reported. We sought to address the particularly troublesome phenomenon of catalyst sintering by using multicomponent catalysts with novel geometries. First, we report the development of hollow spheres of cerium oxide, which exhibit microporosity and therefore allow for gas diffusion into the hollow core of the particle (Chapter 4). The hollow spheres are then used to encapsulate metal nanoparticles (gold and silver) in order to prevent sintering (Chapter 5). It is shown that the multicomponent catalysts are active for CO oxidation and are thermally stable up to ∼600°C. In order to increase this temperature stability window further, zirconium was incorporated into the cerium oxide encapsulants (Chapter 6), extending the stability window for the spherical structure beyond 900°C.