Enhanced malachite green dye degradation using Ni-doped ZnO nanoparticles: a combined experimental and theoretical approach

Abstract Pure and Ni-doped ZnO nanoparticles were synthesized using a simple co-precipitation method for malachite green (MG) dye removal. Structural and compositional analyses (scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction, Fourier transform infrared spectroscopy) confirmed the successful incorporation of Ni2+ into the ZnO lattice, resulting in a morphological transition from spherical to mixed spherical/rod-like forms and a reduction in crystallite size (from 18.49 nm for pure ZnO to 17.36 nm for Ni-doped ZnO). Photocatalytic tests revealed that Ni-doped ZnO achieved 99% MG degradation under UV light in 60 min, compared to 62% for pure ZnO. Enhanced activity is attributed to Ni2+-induced impurity levels that act as electron traps, improving charge separation and reducing recombination. Density functional theory calculations supported these findings, showing that Ni doping narrows ZnO’s band gap via localized Ni-3d states and promotes strong Ni-3d–O-2p hybridization, increasing carrier density. Optical simulations predicted a red shift in the absorption edge and increased optical conductivity, aligning with experimental results. The combined experimental and theoretical study demonstrates the potential of Ni-doped ZnO for efficient environmental remediation.