Defective cubic-ZrO₂ nanomaterials stabilized with calcium under microwave irradiation

The present study focuses on the sustainable synthesis of zirconium dioxide (zirconia, ZrO2) nanopowders using calcium (Ca) as a stabilizing element and microwave irradiation, eliminating the need for any post-synthesis treatment. The addition of different amounts of calcium (3, 7, and 10 mol%) influenced the ZrO2 phase transformation and further stabilization of cubic ZrO2. The synthesized nanopowders have been analyzed by X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and scanning transmission electron microscopy (STEM), as well as by ultraviolet-visible (UV-VIS) and photoluminescence (PL) spectroscopies. Defective cubic ZrO2 nanocrystals (∼6 nm) were observed (10 mol% of Ca), featuring atomic lattice distortions and surface step defects. The higher amount of Ca also revealed an additional yellow luminescence band on PL, which can be related to intrinsic defects or impurities. The defective ZrO₂ nanopowder exhibited an enhanced specific surface area of 151.62 m2/g, which was attributed to the presence of smaller nanocrystals associated with structural defects. As a proof of concept, the nanopowder with 10 mol% Ca was impregnated into commercial water filters to be evaluated as sustainable and cost-effective photocatalysts for the removal of tetracycline from water under solar radiation.