Synthesis of Superparamagnetic ZnFe₂O₄-Core/Ag-Deposited ZnO-Shell Nanodiscs for Application as Visible Light Photocatalyst.

Nanodiscs with ZnFe₂O₄ core and Ag-deposited ZnO shell have been synthesized by hydrothermal method. Scanning electron microscopy (SEM) shows the morphology as nanodiscs. X-ray diffractometry (XRD), selected area electron diffractometry (SAED) and Raman spectroscopy reveal cubic ZnFe₂O₄, hexagonal ZnO and face centered cubic Ag as the constituents of the synthesized nanodiscs. Energy dispersive X-ray spectroscopy (EDS) provides the atomic percentage of Ag as 0.6. High resolution transmission electron microscopy (HRTEM) displays the core-shell structure of the synthesized nanodiscs. The specific surface area, pore volume and pore radius of the nanodiscs are 26.83 m² g, 0.082 cm³ g and 4.88 nm, respectively. The charge-transfer resistance () of precursor ZnFe₂O₄ nanoparticles, determined by solid state impedance spectroscopy, is very much smaller than that of pristine ZnO and ZnFe₂O₄/Ag-ZnO and the of ZnFe₂O₄/Ag-ZnO is larger than that of ZnO. The capacitance () of ZnFe₂O₄/Ag-ZnO is very much smaller than that of ZnFe₂O₄ and ZnO and the of ZnFe₂O₄ is much larger than that of ZnO. ZnFe₂O₄/Ag-ZnO nanodiscs as well as ZnFe₂O₄ nanopowder are superparamagnetic. ZnFe₂O₄/Ag-ZnO exhibits surface plasmon resonance (SPR) in the visible region. The emission spectrum of ZnFe₂O₄/Ag-ZnO is similar to that of pristine ZnO and shows violet, blue, blue-green and green emissions due to different crystal defects in ZnO lattice. The synthesized nanodiscs display visible light photocatalysis, degrade dye completely and are reusable visible light photocatalyst. The mechanism of visible light photocatalysis is addressed.