Silver Oxide Reduction Chemistry in an Alkane Environment

The in situ reduction of silver oxide to metallic silver is of technological relevance for various applications, from conductive welding in electronics to silver (Ag) nanoparticle generation in reactive melt extrusion. This study revisits the redox reaction mechanisms involved in forming metallic silver particles through the reduction of silver(I) oxide (Ag₂O) in an alkane and polymer melt environment and sheds light on the obtained particulate morphology. Liquid pentadecane was selected as a model alkane, and the observed redox chemistry and particle morphology were compared to the reactive melt extrusion in polyethylene. Unlike the well-studied reduction of metal salts in the presence of oxygen-containing organic materials, the reduction occurring in a pure alkane environment, namely the different particle morphology, is poorly understood. Our findings revealed that the primary byproducts of the reaction between Ag₂O and pentadecane were CO₂ and H₂O, with minor products including alkenes and oxidized alkanes. The reduction process was not linear, with Ag₂O acting both as a radical initiator and a source of oxygen. Gas chromatography detected CO₂ formation at a rather low temperature, as low as 70 °C during the reaction between Ag₂O and pentadecane, indicating a highly oxidative process resembling catalyzed combustion. Analytical techniques, including electron paramagnetic resonance (EPR) spectroscopy, confirmed that radicals were involved in the redox process via ROO• and HOO• radical species typically found in hydrocarbon oxidation under oxygen conditions. We hypothesize that the reaction is predominantly a complete oxidation, with only a small fraction of incomplete oxidation. Our observations also indicated that the metallic Ag formed directly on the surface of Ag₂O in what appeared to be a solid-solid surface reaction, leading to a final Ag morphology resembling fused particles. While the resulting morphology may seem suboptimal regarding particle dispersion and homogeneity, it still offers a large contact area percolated structure that is advantageous for applications such as electronics welding. We thus conclude that in a pure alkane environment, the redox reactions are confined to the surface of the original particles.