Au-Mediated Charge Transfer Process of Ternary Cu₂O/Au/TiO₂-NAs Nanoheterostructures for Improved Photoelectrochemical Performance

Based on a facile three-step preparation method, Cu₂O/Au/TiO₂-NAs ternary heterojunction nanocomposites have been successfully synthesized by electrodepositing a Cu₂O layer on the surface of Au nanoparticles (NPs) decorated highly ordered TiO₂ nanotube arrays (NAs). The structure, surface morphology, chemical composition, and optical and intrinsic defects properties of the as-prepared samples are characterized by transmission and scanning electron microscopy (TEM and SEM), X-ray diffraction (XRD), UV-vis light absorbance spectra, Raman scattering, and X-ray photoelectron spectroscopy (XPS). Simultaneously, the Cu₂O/Au/TiO₂-NAs ternary nanohybrids exhibited progressively improved photoelectrocatalytic (PEC) performance compared with the dual Cu₂O/TiO₂-NAs type-II nanoheterojunctions, confirming by the photocurrent density versus testing time curve (amperometric I-t curve), open-circuit potential versus testing time curve (V _oc-t curve), and electrochemical impedance spectroscopy (EIS) measurements, which were mainly ascribed to the synergistic effect of reduced interfacial charge transfer resistance and boosted energetic charge carriers generation associated with embedding Au NPs. Furthermore, the self-consistent charge transfer mechanism of Z-scheme and interband transitions mediated with Au NPs for Cu₂O/Au/TiO₂-NAs triple nanocomposites is proposed, which was evaluated by nanosecond time-resolved transient photoluminescence (NTRT-PL) spectra excited by 266 and 400 nm, respectively. Following this scheme, UV-vis light photocatalytic activities of Cu₂O/Au/TiO₂-NAs ternary nanohybrids were elaborated toward photodegradation of methyl orange (MO) in aqueous solution, and the photodegradation rate of optimum triple nanocomplex was found to be 90%.