Enhanced photocatalytic organic dye removal by Ag-doped ZnO/GO nanocomposites: a combined experimental and DFT study

Abstract

In this work, Ag-doped ZnO/graphene oxide nanocomposites were synthesized by a co-precipitation technique and characterized systematically for their structural, optical, and photocatalytic properties. The XRD study confirmed the wurtzite phase of ZnO, and the successful incorporation of Ag and GO, besides an improvement in crystallinity and enlargement in crystallite size following composite formation. UV-Vis diffuse reflectance spectroscopy showed a reduced band gap from 3.20 eV (pure ZnO) to 3.00 eV (Ag–ZnO/GO), while photoluminescence spectra indicated the suppression of electron–hole recombination. Electron microscopy revealed that the Ag–ZnO nanoparticles are homogeneously distributed on the GO sheets. Under visible light, the photocatalytic efficiency of Ag–ZnO/GO towards Methylene Blue and Methyl Red reaches 99.98 ± 0.02 (n = 3)% and 92%, respectively, showing much higher efficiency compared to pure ZnO and Ag–ZnO. The DFT+U calculations show that the bandgap narrowed, while charge delocalization was improved, along with stronger adsorption of dye molecules on the Ag–ZnO/GO surface, as reflected by E_ads = −1.49 eV for MB and −1.61 eV for MR. The Mulliken charge analysis further confirmed the enhanced charge transfer ΔQ = −0.1573e for MB and −0.1705e for MR because of the synergistic effect of Ag and GO. This study combines experimental and theoretical insights, showing that Ag–ZnO/GO nanocomposites possess efficient charge separation, superior light absorption, and excellent photocatalytic activity, thus presenting great promise for application in wastewater purification and environmental remediation.