Date of Award
Doctor of Philosophy
With the goal of creating efficient visible light photocatalysts for water photolysis, in this work we are exploring the synthesis of new porous oxide materials derived from potassium triniobate (KNb3O8) and titanium niobium oxide (KTiNbO5), which are layered wide band gap semiconductors. Generating hydrogen via direct water photolysis holds promise as a way to lower the cost of hydrogen gas production so it can be used as a renewable and clean alternative fuel. My group has demonstrated that layered semiconductor materials have the potential to enable the synthesis of new types of photocatalyst composites with customizable characteristics. In this work, porous oxide materials were synthesized from metal oxide nanosheet colloids by agglomerating or restacking them with specific cations. This new technique created disordered porous solids with open-pore structures and greatly improved surface areas. Using acids in water, the interlayer of potassium ions in KNb3O8 and KTiNbO5 were ion-exchanged for H+, leading to the formation of HNb3O8 and HTiNbO5, which in turn were exfoliated into nanosheets colloids using tetrabutylammonium hydroxide. To create visible light-sensitized photocatalysts, nanosheet niobate colloids were restacked with the cationic dye, tris(2,2'-bipyridyl)ruthenium(II), abbreviated as Ru(bpy)32+. In these studies, a series of novel composites were synthesized, resulting in the formation of catalytic solids with a striking, deep orange color. In order to enhance the hydrogen production activity, the surfaces of these composites were treated with photo-deposited metallic platinum or gold. The hydrogen generation kinetics of all of the newly developed photocatalysts were then measured under visible light. The full characterization of the catalysts using XRD, TEM, SEM, ICP-OES, and UV-Vis revealed valuable insights for optimizing the properties and photo efficiency of the catalysts. Successful hydrogen generation from water resulted from visible light irradiation of the new porous metal oxide photocatalysts, which contained deposited Pt and Au nanoparticle co-catalysts. The visible light photo depositions of the co-catalysts were carried out with different percentages of Pt and Au. Stability tests were conducted over five consecutive five-hour photolysis experiments, and the rates of hydrogen evolution only fell by 3-4% from beginning to end, indicating the robustness of this system. Additionally, quantum efficiency calculations showed that 41.2% of the incident photons were effectively utilized to produce hydrogen from water. The sensitizer loadings of restacked visible photocatalysts synthesized from KNb3O5 were systematically varied, and the catalyst with the highest sensitizer loading produced the best hydrogen evolution kinetics. The novel visible light deposition of the Pt on the surfaces of the metal oxide produced an exceptional distribution of nanoparticles in sizes smaller than 3 nm. This new approach of sensitizing metal oxides by restacking nanosheets holds promise as a technique to produce stable and highly efficient visible light photocatalysts.
Recieved from ProQuest
Cassandra Idona MonÃ¡rrez-Grendahl
Monárrez-Grendahl, Cassandra Idona, "Niobate Nanosheet Catalysts For Cationic Dye Intercalation And Solar-Driven Water Photolysis" (2023). Open Access Theses & Dissertations. 4000.
Available for download on Friday, December 19, 2025