Effect of urea on the dispersibility and crystallisation of AZO nanoparticles prepared by sol-gel combustion

Highly dispersive and well crystallised aluminium-doped zinc oxide (AZO) nanoparticles (the mole ratio of Al to Zn was 0.02) were prepared by sol-gel combustion method. Two typical synthesised chemical reagents of urea and citric acid were employed to synthesise the AZO nanoparticles by investigating and comparing the physical properties and micro structural characteristics. The nanoparticles were characterised in detail by thermogravimetry and differential thermal analysis, bulk density measurement, transmission electron microscope and X-ray diffraction (XRD). The XRD patterns of AZO nanoparticles corresponded well to the hexagonal structure of pure ZnO, indicating that the Zn atom was substituted by Al atom. Small amount of urea in the precursor solution tends to generate larger amount of heat when the sol-gel is combusting. With increasing the content of urea in the precursor solution, the size of the prepared AZO nanoparticles varied from 17 to 25 nm. Simultaneously, obvious decrease in bulk density was observed when slightly increasing the ratio of the urea to the citric acid.