Tuning the physio-chemical properties of ZnO nanoparticles through annealing process and their photocatalytic activity for dye degradation

Hexagonal phase zinc oxide nanostructures were synthesized via hydrothermal method and annealed at different temperatures viz., 200, 400, 600, 800 and 1000°C. The prepared nanostructures were characterized by XRD, FTIR, FESEM, HR-TEM and UV-DRS techniques. The annealing seems to have a profound effect on the crystallinity, morphology and properties of nanostructures. The lattice strain (ε) is calculated from Williamson-Hall (W-H) plot; for nanostructure with small crystallite size the strain is caused by compressive force (intercept is negative) whereas for the large crystallite size tensile force (intercept is positive) determines the lattice strain. The photocatalytic performances were studied by analyzing the degradation of methylene blue (MB) in an aqueous solution. ZnO annealed at 1000°C exhibited better photocatalytic activity due to enhanced crystallinity, comparatively lower bandgap and high oxygen vacancy. Thus, ZnO nanostructures prepared here provide a potential solution to general wastewater treatment and drinking water purification.