Effect of annealing on the conversion of ZnS to ZnO nanoparticles synthesized by the sol-gel method using zinc acetate and thiourea

A systematic study is presented on the conversion of zinc sulfide to zinc oxide nanoparticles as a function of annealing temperature. Zinc acetate dihydrate (Zn(CH₃COO)₂.2H₂O) and thiourea (NH₂CSNH₂) are used as precursors to synthesize ZnS and then ZnO. The aqueous solution of the precursor was refluxed at 90 °C for over 12 h. The synthesized complex was then annealed at 300 °C, 500 °C, 700 °C, and 900 °C in air for one hour. From elemental analyses, it was found that the as-synthesized powder is a mixture of ZnS and ZnO, which annealing later converts to the zinc oxide phase only. The morphological observations revealed spherical particles of various sizes (20 nm to 300 nm) while increasing the annealing temperatures. A drastic change in the vibration bands is noticed with annealing. Photoelectron peaks related to sulfur and carbon are observed for synthesized powder, whereas, these peaks disappeared when annealed at 500 °C.