Biosynthesis of enhanced magnetic iron Oxide@ZnO nanocomposites with incorporated Ni species for the photodegradation of dyes

Abstract

The textile industry generates approximately 700 million kilograms of dyes annually, with about 10–20 % improperly discharged into the environment, poing significant risks to aquatic ecosystems and human health. This study reports the sustainable biosynthesis of FeOx@ZnO (FZ) and FeOx@ZnO-Ni (FZNi) nanocomposites using hydroethanolic extract and infusion from Magonia pubescens A. St. Hil. Characterization techniques confirmed their crystalline structure, composition, morphology and optical properties. Photodegradation tests using rhodamine B under visible light for 300 min showed superior efficiency for FZNi (96.8 %) compared to FZ (87.5 %), attributed to enhanced light absorption from Ni doping, which lowers the band gap. Density Functional Theory (DFT) calculations analyzed ZnO(100) and ZnO(101) surfaces. The optimized ZnO(100) surface exhibited a decrease in the c lattice parameter from 5.209 Å to 4.935 Å, while ZnO(1 0 1) displayed triclinic characteristics with a lattice parameter set of a = 3.23 Å, b = 3.07 Å, and c = 6.02 Å. Partial density of states (PDOS) analysis revealed a higher band gap of 1.93 eV for ZnO(1 0 1), than the experimental value of 3.46 eV. Substitutional doping with Ni in ZnO(1 0 1) significantly reduced the band gap energies to 1.08 eV and 1.41 eV, respectively, while introducing new defect states near the valence band due to d-orbital contributions from the doped cations. These theoretical findings, aligned with experimental results, demonstrate that partial Ni doping and the presence of Ni nanoparticles on the material’s surface effectively narrow the band gap in ZnO(1 0 1). Ni-ZnO(1 0 1) exhibits the most significant reduction, enhancing its photodegradation performance.