Rational design and synthesis of highly oriented copper-zinc ferrite QDs/titania NAE nano-heterojunction composites with novel photoelectrochemical and photoelectrocatalytic behaviors.

This work reported that novel highly oriented and vertically aligned stoichiometric copper- and zinc-based ferrites, i.e., Cu0.5Zn0.5Fe2O4 quantum dots (QDs) anchored with TiO2 nanotube array electrode (NAE) composites, with n-n nano-heterojunctions and highly effective simulated solar light harvesting could be successfully achieved via electrochemical anodization followed by a vacuum-assisted impregnation strategy. It has been observed that Cu0.5Zn0.5Fe2O4 QDs/TiO2 NAE composites exhibit distinctly enhanced visible light photoelectrocatalytic (PEC) performance toward the degradation of typical pollutants including sulfamethoxazole (SMX) and methylene blue (MB) as compared to that of pristine TiO2 NAEs, which can be attributed to the synergistic effect of heterostructures with strong interfacial interaction and abundant 1D nanotube array structures to facilitate efficient spatial charge separation and interfacial transfers. The cocatalyst-anchoring of ternary oxides with derived spinel crystal structures onto nanotube arrays forming novel nanocomposites have obviously achieved remarkably enhanced photoelectrochemical (PE) conversion efficiencies, up to a dedicated value of 3.75%, under visible light irradiation as compared to that of 0.88% for aligned standalone TiO2 NAEs. Transient absorption spectroscopy quantitatively indicated long-lived photo-holes with lifetimes exceeding 72.23 μs generated among Cu0.5Zn0.5Fe2O4 QDs/TiO2 NAE nanocomposites. Electron spinning resonance (ESR) demonstrated that more ˙O2- species derived from molecular uptake played the predominant role in the PEC oxidations of SMX and MB species. Moreover, the binding energy of the onset edge (Evf) and Fermi level (Ef) of Cu0.5Zn0.5Fe2O4 QDs/TiO2 NAEs indicated that Cu0.5Zn0.5Fe2O4 QDs modification could considerably enhance the visible light harvesting and adsorption properties of TiO2 NTs. Furthermore, Cu0.5Zn0.5Fe2O4 QDs/TiO2 NAEs achieved up to 50% PEC degradation efficiency and 52.4% COD removal with regard to practical textile wastewater when irradiated by simulated sunlight. This work has provided new insights into the molecular tailing and coupling of multiple spinels with TiO2 NTs possessing remarkable visible light harvesting and sensitization characteristics, which would offer a prospective strategy toward designing highly efficient and easily recyclable photocatalytic materials for environmental remediation and solar energy utilizations and conversions both simultaneously and standalone.