Sol–gel synthesis and characterization of Ni-doping enhanced NixCd0.8−XZn0.2Al0.3Fe1.7O4 nanoparticles with exceptional photocatalytic activity for ciprofloxacin degradation

In this study, the sol–gel synthesis of Ni-doped cadmium zinc aluminum ferrite Ni-doped Ni_xCd_0.8−XZn_0.2Al_0.3Fe_1.7O₄ (X = 0,0.4) nanoparticles and their photocatalytic activity for ciprofloxacin degradation under visible-light irradiation were investigated. The nanoparticles were characterized using XRD, FTIR, SEM, EDX, and BET analyses. XRD revealed cubic spinel structures with crystallite sizes of 39 (undoped) and 30 nm (Ni-doped). FTIR spectra showed peak shifts upon Ni doping, indicating Ni²⁺ ion substitution in the spinel lattice. SEM images showed that the nickel-free sample was porous and had larger, loosely packed grains, whereas the nickel-doped sample was denser and featured smaller, uniformly distributed grains. The Ni-doped sample exhibited a higher BET surface area (37.85 m²/g) and pore volume (1.836 cm³/g) than those of the undoped sample. The photocatalytic degradation of ciprofloxacin was significantly enhanced by Ni doping, achieving 97.88% in 60 min under visible light, which was attributed to the narrowed bandgap (2.1 eV), improved visible light absorption, and increased charge separation. Scavenger studies have identified hydroxyl radicals as primary reactive species. The addition of H₂O₂ (up to 6 mM) enhanced the degradation rate, but higher concentrations decreased the rate. The catalyst exhibited gradual deactivation upon reuse, with the degradation efficiency decreasing from 97.88 (first cycle) to 90.93% (fifth cycle), owing to loss, deactivation, and fouling.