Rare-Earth-Based MIS Type Core-Shell Nanospheres with Visible-Light-Driven Photocatalytic Activity through an Electron Hopping-Trapping Mechanism.

A bilayered rare-earth-based metal-insulator-semiconductor, DyO@SiO@ZnO core-shell nanospheres, was synthesized by a stepwise synthesis for enhanced visible photocatalytic activity. The prepared material was characterized by Fourier transform infrared spectroscopy, X-ray diffraction, ultraviolet-visible diffuse reflectance spectroscopy, field-emission scanning electron microscopy, energy-dispersive spectroscopy, high-resolution transmission electron microscopy, selected area electron diffraction, atomic force microscopy, X-ray photoelectron spectroscopy, Brunauer-Emmett-Teller, and electron paramagnetic resonance techniques. DyO@SiO@ZnO core-shell nanospheres were found be in a spherically arranged cauliflower-like morphology (40-60 nm). The high-resolution transmission electron microscopy analysis proved the core-shell morphology of the prepared material with a single DyO core and two shells comprising SiO and ZnO. The material possessed a surface roughness of 4. 98 nm (2 × 2 μm area) and a band gap energy of 2.82 eV. The in situ generation of OH radicals was confirmed by electron paramagnetic resonance. Electron hopping through the SiO layer from ZnO to DyO played a major role in trapping electrons in the f-shells of lanthanides, thus, preventing the recombination of electron-hole pair. X-ray photoelectron spectroscopy studies proved the band alignment of the material. Brunauer-Emmett-Teller analysis further showed the core-shell surface area was 14 m/g. The visible photocatalytic activity was tested against 2,4-D (2,4-dichlorophenoxyacetic acid), an endocrine disruptor. The kinetic studies showed that the photocatalytic degradation process followed a pseudo-first-order pathway. The photocatalyst was found to be reusable even up to the third cycle.