Recent advancements in nanomaterials and surface science have enabled fabrication of controlled surfaces. Here, colloid and thin film surfaces serve as systems to assist in the elucidation of mechanisms in two systems: ethanol steam reforming on Ni/CeO₂ catalysts and the synergistic role of Ag-Cu in antibacterial processes. CeO₂nanocubes were controlled on thin film Ni samples to investigate the conversion of ethanol into hydrogen gas during the ethanol steam reforming reaction. At a specific submonolayer CeO₂ coverage on Ni, a tenfold increase in the rate of H₂ production, with no deactivation was observed. HR-TEM analysis show filamentous carbon growth, with Ni grains at filament tips, forming an active Ni@CFIL phase. AP-XPS analysis showed that carbon gradients were necessary for filament growth and the formation of the active Ni@CFIL phase. HR-TEM analysis further revealed that filament growth was induced by carbon gradients, originating near mesoscale CeO₂ domains that appeared at specific submonolayer CeO₂ coverages on Ni. These domains played a vital role in templating the formation of the highly active Ni@CFIL phase. Utilizing a similar approach, we employed simple Cu colloid nanoparticles on Ag thin film planar surfaces to investigate the antibacterial activity resulting from the synergistic effects of Ag and Cu. HR-TEM analysis unveiled Cu nanoparticles surrounded by a thin Cu₂O shell at their core. Deposition of these nanoparticles onto Ag thin films led to the formation of a heterostructure with Ag₂O on the surface of the Ag film. Z-scheme electron transfer at the Ag₂O-Cu₂O interface was confirmed by XPS analysis oxidizing Ag to Ag²⁺, while metallic Cu increased, accompanied by the observation of a Cu(OH)₂phase. These three phases have previously been associated with the release of antibacterial reactive oxygen species (ROS). To further substantiate that the interface is the active phase of the surface, an inverse surface system was created where Ag nanocubes were synthesized and deposited at submonolayer concentrations on Cu thin films using Langmuir-Blodgett deposition. Experimental results show antibacterial activity scaling in proportion to the Ag-Cu interface, underscoring the role of the active interface. These studies demonstrate that well-controlled model surfaces can serve as potent tools for investigating surface phenomena, particularly in systems characterized by high degrees of heterogeneity.

Nathan Pimental

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