Nanostructured Cu2O is a model photocathode for the reduction of protons or carbon dioxide and can also catalyze or photocatalyze various organic transformations. The performance of Cu2O nanomaterials in these applications depends crucially on their surface chemistry and optical properties. Here, we demonstrate that the absorption spectrum of colloidal Cu2O nanocrystals depends strongly on the oxidation states of surface copper species. Both ground state and transient absorption spectra of pristine Cu2O nanoparticles are very similar to the analogous spectra of colloidal metallic Cu nanoparticles and are therefore consistent with behavior expected of a localized surface plasmon resonance (LSPR). X-ray photoelectron and Auger spectroscopy indicate that the observation of an LSPR feature in pristine Cu2O nanoparticles correlates with the presence of Cu0 atoms on their surfaces. This work reveals localized redox chemistry in Cu2O nanoparticles that is distinct from the behavior of Cu2E (E = S, Se, Te) nanoparticles, and demonstrates the significant role surface redox chemistry plays in determining the optical properties of colloidal Cu2O nanocrystals. Finally, we demonstrate the utility of these spectroscopic features as a diagnostic tool to investigate the mechanisms by which Cu2O nanocrystals catalyze organic cross-coupling reactions.

Correlation between surface chemistry and the optical properties of colloidal Cu2O nanoparticles: Implications for characterization of catalytic processes

ACS Fall 2021

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