The role of ammonia hydroxide in the formation of ZnO hexagonal nanodisks using sol-gel technique and their photocatalytic study

ZnO nanomaterials with large surface area are desired particularly for the gas sensor, biosensor and photocatalyst applications. In this study, ZnO hexagonal nanodisks with thickness to diagonal aspect ratio (similar to 1/80) were successfully synthesised via sol-gel approach. By using aluminium sulphate as a complexing agent and carefully controlling the amount of ammonia hydroxide, zinc oxide hexagonal nanodisks were produced. The ZnO nanodisks had perfect hexagonal shape with about 4 mu m in diagonal and 50nm in thickness. The growth of the nanodisks was favoured along the six symmetric directions of +/-[1i00], +/-[01i0] and +/-[10i0]. The growth mechanism of ZnO hexagonal nanodisks is proposed as follows. The formation of ZnO hexagonal nanodisks was mediated by the adsorption of aluminate ions, Al(OH)(4)(-), on the polar surface of ZnO. The Al(OH)(4)(-) ions were produced as a result of reaction between Al-2(SO4)(3) and NH4OH. The Al(OH)(4)(-) ions were bonded to the positively charged Zn2+-terminated (0001) polar surface of ZnO. This suppressed the preferential growth of ZnO along [0001] direction but allowed the lateral growth of ZnO in . Eventually, ZnO hexagonal nanodisks with +/-(0001) top/bottom surfaces and {1i00} side surfaces were formed. The size of the ZnO hexagonal nanodisks could be adjusted via the synthesis duration and the amount of ammonia hydroxide. The photocatalytic study indicates that ZnO hexagonal nanodisks were a good photocatalyst for the degradation of Rhodamine B under ultraviolet light irradiation with a rate constant of 0.036min(-1).