(25h) Investigating Mechanisms of Bimetallic Nanocrystal Formation with Liquid Phase Transmission Electron Microscopy
AIChE Annual Meeting
Monday, November 16, 2020 - 9:30am to 9:45am
Here we establish ranges of LP-TEM experimental conditions that are representative of flask-based nanocrystal synthesis. We investigate Au/Cu bimetallic nanoparticle synthesis as a model system due to its promising application as a CO2 reduction electrocatalyst.3 Controllable synthesis of alloyed bimetallic nanocrystals is difficult due to differing kinetics and thermodynamics of precursor reduction of different metal species.4 We utilized poly(ethylene glycol) methyl ether thiol (PEG-thiol, Mw=800 g/mol) to complex Au/Cu metal salts into prenucleation complexes (PNC) prior to nanoparticle synthesis.5 Our results showed that flask-based synthesis using sodium borohydride to reduce PNCs formed ~2-3 nm Au/Cu alloy nanocrystals. LP-TEM synthesis, which utilizes radiolysis to produce aqueous electrons and hydrogen radicals as reducing agents,6 formed 3 - 7 nm nanocrystals at low electron dose rates. Imaging at high electron dose rates (high image magnification and beam current) formed irregular aggregated particles. High electron dose rates increase the nucleation rate and create more oxidizing radical species,7 which oxidizes the sulfur group on the PEG-thiol ligand, leading to formation of uncapped aggregated particles. Our study identified key differences between flask-based and LP-TEM synthesis methods, giving important guidance on how to set experimental conditions during LP-TEM to study nanocrystal formation mechanisms at conditions relevant to flask-based synthesis.
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