Versatile fabrication and characterization of Cu-doped ZrO₂ nanoparticles: enhanced photocatalytic and photoluminescence properties

Pristine ZrO₂ and molar ratios of Cu-doped ZrO₂ nanoparticles were synthesized by chemical precipitation. The XRD pattern of pristine ZrO₂ and Cu-doped ZrO₂ nanoparticles shows the formation of t-tetragonal phase and shifting of tetragonal phase to monoclinic phase. The average crystallite sizes of the pristine ZrO₂ and Cu-doped ZrO₂ nanoparticles were calculated as 2.9, 4.65, 4.76, 5.02, and 4.96 nm, respectively. The Cu (0.06 M)-doped ZrO₂ nanoparticles are present as spherical morphology and high agglomeration was confirmed by FE-SEM and TEM analyses. The XPS spectra affirmed the presence of Cu²⁺, Zr⁴⁺, and oxygen ions in the Cu (0.06 M)-doped ZrO₂ nanoparticles. The Cu-doped ZrO₂ nanoparticles exhibit two energy gaps at 5.30 and 3.05 eV, 5.21 and 2.22 eV, 4.65 and 2.11 eV, and 4.44 and 2.65 eV. The surface defects and oxygen vacancies were analyzed by PL and ESR spectroscopy. The ESR spectra are clearly asymmetric in shape and contain a peak signal related to the presence of the copper species (Cu²⁺) in the distorted tetragonal coordination of ZrO₂. The photocatalytic activities of Cu (0.06 M)-doped ZrO₂ nanoparticles were successfully sought on degradation of the two azo dyes: methyl violet and methyl blue under sunlight irradiation. Cu (0.06 M)-doped ZrO₂ showed complete degradation at 70 min. The reusability of Cu (0.06 M)-doped ZrO₂ nanoparticles shows maximum degradation efficiency for six successive runs.