Influence of starch used in the sol-gel synthesis of ZnO nanopowders

The work presents the synthesis and characterization of zinc oxide (ZnO) nanoparticles obtained by the starch-assisted sol-gel route. To observe the influence of the botanical source on the final properties of the nanoparticles, corn, and potato starches were used. After calcination (500°C/2h), the resulting material was analyzed by X-ray Diffraction (XRD) and Fourier-Transform Infrared Spectroscopy (FTIR) to confirm the formation of ZnO. The crystallite size was calculated by two methods, Scherrer and Williamson-Hall. Using the Scherrer method, ZnO nanopowders have been found with 26 nm and 23 nm sizes using corn and potato starches, respectively. By the Williamson-Hall method, the sizes were found 22 nm and 14 nm, using corn and potato starches, respectively. The band gap energies (E_g) were estimated from Diffuse Reflectance Spectroscopy, using the Tauc method (~3.05 to 3.08 eV) and the effective mass model (~3.36 to 3.38 eV). In every case and independently of the method adopted for calculating the crystallite size, the E_g values tend to decrease as the crystallite size increases, which could be associated with the difference in the type of starch used for the synthesis of ZnO. Based on these results, it can be inferred that the type of botanical source used as starch plays a role in the crystallite size, as well as in their optical properties. Therefore, ZnO nanopowders can be obtained by an ecological and low-cost sol-gel route, using starch from botanical sources.