ZnO Nanostructures Doped with Various Chloride Ion Concentrations for Efficient Photocatalytic Degradation of Methylene Blue in Alkaline and Acidic Media

In this study, chloride (Cl-) ions were successfully doped into ZnO nanostructures by the solvothermal method. The effect of various Cl- concentrations on the photocatalytic activity of ZnO towards the photodegradation of methylene blue (MB) under the illumination of ultraviolet light was studied. The as-prepared Cl--doped ZnO nanostructures were analyzed in terms of morphology, structure, composition and optical properties. XRD data revealed an average crystallite size of 23 nm, and the XRD patterns were assigned to the wurtzite structure of ZnO even after doping with Cl-. Importantly, the optical band gap of various Cl ion-doped ZnO nanostructures was successively reduced from 3.42 to 3.16 eV. The photodegradation efficiency of various Cl- ion-doped ZnO nanostructures was studied for MB in aqueous solution, and the relative performance of each Cl ion-doped ZnO sample was as follows: 20% Cl--doped ZnO > 15% Cl--doped ZnO > 10% Cl--doped ZnO > 5% Cl--doped ZnO > pristine ZnO. Furthermore, the correlation of the pH of the MB solution and each Cl ion dopant concentration was also investigated. The combined results of varying dopant levels and the effect of the pH of the MB solution on the photodegradation process verified the crucial role of Cl- ions in activating the degradation kinetics of MB. Therefore, these newly developed photocatalysts could be considered as alternative materials for practical applications such as wastewater treatment.

Automated summary

In this study, chloride ions were doped into ZnO nanostructures through the solvothermal method to investigate their effect on the photocatalytic activity of ZnO towards the degradation of methylene blue. The results showed that doping with chloride ions effectively reduced the optical band gap of ZnO and improved its photodegradation efficiency. The study also revealed a correlation between the pH of the methylene blue solution and the concentration of chloride ions, highlighting the crucial role of chloride ions in activating the degradation kinetics of methylene blue.