Sol-gel-assisted cobalt doping in the ZnO lattice and the decoration of silver for enhanced dye degradation

Doping and heterojunctions are found to improve the optical property of host materials. In this study, materials with improved optical properties have been synthesized via the sol-gel solution combustion approach. The thermal stability of the silver-decorated cobalt-doped ZnO nanocomposite crystal (Ag@CZ NCs)-PVA complex was studied. Based on the DTA-TGA stability analysis, 370 °C has been used as the optimum calcination temperature for further analysis. The XRD analysis indicated the existence of a peak shift for Ag@CZ relative to pure ZnO peaks due to cobalt ion doping. The presence of a separate silver metal crystal peak was also attested using the XRD pattern analysis, indicating the development of close contact between the Ag and ZnO crystals. The declining of an indirect band gap energy for Ag@CZ (2.93 eV) compared to ZnO NPs (3.15 eV) confirms improved visible light absorption efficiency for Ag@CZ NCs. The reduction in intensity and emission wavelength shift on the PL analysis confirms the successful doping of cobalt ions and the formation of Ag/ZnO heterojunction. FESEM/EDS investigation shows a porous morphology and only the existence of expected elements. The decent spreading of dopants on the host (ZnO) surface was confirmed from the EDS layered image analysis. The HR-TEM image confirms the formation of a heterojunction through lattice fringe analysis of Ag (0.233 nm) and ZnO (0.262 nm). The EIS and cyclic voltammetric methods of analysis verified the existence of a smaller electron-hole recombination property on Ag@CZ NCs. The Ag@CZ NCs exhibited improved photocatalytic activities (k = 0.107 min⁻¹) and decent stability compared to ZnO (k = 0.026 min⁻¹). The improvement in photocatalysis potential is associated with the enhancement of light absorption and charge transfer ability.