MODIFYING CRYPTOMELANE (K-OMS-2) WITH CERIUM (CE): PROGRESS TOWARDS UNDERSTANDING MATERIALS APPLICATIONS AND NATURAL VARIABILITY

Cryptomelane K(Mⁿ³⁺, Mn⁴⁺)₈O₁₆ (K-OMS-2) is known to have excellent surface chemistry due to its unique crystal structure which consists of 2x2 tunnels of MnO₆ octahedra creating a fiber-like particle. This allows researchers to explore doping K-OMS-2 with various elements to increase the surface area and improve the catalytic properties. Cerium (Ce) is of particular interest and has been used to dope K-OMS-2 for multiple applications. Current literature describes the occupancy of Ce to be in the 2x2 tunnel of the crystal structure, replacing the K⁺ ion. This study will explore the various placements of Ce^x+ in the K-OMS-2 crystalline structure when using multiple weight percentages. Synthetic unmodified K-OMS-2 is used as a control to compare the lattices, selected area electron diffraction (SAED), and physical properties. Weight percentages of Ce include 5%, 10%, and 30% using increasing amounts of Ce(NO₃)₃ during synthesis. Transmission electron microscopy (TEM) equipped with an electron dispersive spectrometer (EDS) was used to image each material including structural and low magnification images, map individual particles and aggregates of particles, and collect SAED images to better understand the crystallinity. Preliminary results show Ce-oxide (presumably CeO₂) nano-particles attach to the surface of individual K-OMS-2 in addition to Ce^x+ ions replacing K⁺ ions in the tunnels. As the weight percentage of Ce increases, so does the number of Ce-oxide nanoparticles. At the 30% weight percentage, K-OMS-2 fiber-like particles are difficult to see as they are almost completely covered in Ce-oxide nanoparticles. Although Ce^x+ is in the tunnel of the structure, Ce-oxide nanoparticles are present at every weight percent (5%, 10%, and 30%). Future research is needed to explore the exact weight percent of Ce^x+ that enters the tunnel structure without the presence of Ce-oxide nanoparticles.