Synthesis and characterization of ZnO nanoparticles doped with Mg and Ni for the electro-assisted degradation of hazardous 4-nitrophenol

• Mg and Ni doping effectively tuned the structural and optical properties of ZnO nanocomposites. • ZnO/Mg and ZnO/Ni significantly enhanced electrocatalytic degradation of 4-nitrophenol. • The degradation process followed pseudo-first-order kinetics with high efficiency. In this work, pristine ZnO, Mg-doped ZnO, Ni-doped ZnO, and Mg/Ni co-doped ZnO nanocomposites were prepared by the hydrothermal method and tested in an electro-assisted degradation system for the degradation of the toxic compound 4-nitrophenol (4-NP) in alkaline solution. XRD confirmed the hexagonal wurtzite ZnO structure for all samples, while the crystallite size decreased from 33 nm for pristine ZnO to 22 nm for Ni-doped ZnO. SEM showed dopant-induced changes in particle morphology, and the apparent band-gap energy varied from 3.14 to 2.86 eV depending on composition. The degradation experiments were carried out at 21 V using stainless-steel electrodes. Under the tested conditions, the doped samples outperformed pristine ZnO. Mg-doped ZnO showed the highest degradation efficiency at low 4-NP concentration, reaching 97.11% at 5 mg/L with an apparent rate constant of 0.042 min-1, whereas Ni-doped ZnO gave the best result at a higher concentration, achieving 79.56% at 20 mg/L. Among the tested kinetic models, the pseudo-first-order equation gave the best empirical fit. Figure 1: Synthesis flowchart of ZnO/(Mg–Ni) nanocomposites.