ZnO nanoparticles (ZnO-NPs) were successfully fabricated by soft chemical technique from zinc acetate di-hydrate (Zn(CH(3)COO)(2)center dot 2H(2)O) and octadecylamine (CH(3) (CH(2))(17)NH(2)). The crystallinity of the grown product was analyzed by the XRD technique revealing the as-prepared nanoparticles (NPs) have hexagonal wurzite structure. Their morphology was investigated by FE-SEM and TEM, which showed that well dispersed spherical particles of 10 +/- 4 nm in diameter had been formed. The optical property of ZnO-NPs was confirmed by the photoluminescence spectroscopy showing an intense room temperature photoluminescence in the violet region of 382 nm. Furthermore, the synthesized ZnO-NPs showed a better photo-catalytic activity than that of commercial Degussa P-25 powder during photochemical degradation of methyl orange (MO) dye. Also, the Zn(2p1/2), Zn(2p3/2), and O(1s) peaks in XPS clearly suggest that the grown nanoparticles are ZnO. Additionally, liquid chromatography mass spectroscopy (LC-MS) was applied to observe the degradated compounds from photo-catalytic degradation of methyl orange (MO) dye in presence of ZnO-NPs. (C) 2011 Elsevier B.V. All rights reserved.