Iridium (Ir) nanoparticles (NPs) of variable shapes have been synthesized via the reduction of Ir(III) ions in CTAB micellar media containing alkaline 2,7-DHN under 4 h of UV-irradiation. The one-step process generates different shapes, such as nano-spheres, nano-chains, nano-flakes, and nano-needles. The synthesized It NPs are stable for more than a month in ambient conditions. The particles' morphology can be tuned by simply changing the surfactant-to-metal ion molar ratios and altering other reaction parameters. The mechanisms of the Ir particle formation and effects of different reaction parameters were studied in detail. The Ir nano-needles serve as a good catalyst for the reduction of organic dye molecules in presence of NaBH4. The catalysis rate was compared by considering the electron transfer process during the reduction of the dye molecules. The present method would lead to a quick process for the synthesis of other mono-metallic, composite, and semiconductor particles with variable shapes. The It NPs will find promising applications in different types of organic and inorganic catalysis reactions, nanoelectronics, and biomedical applications. (C) 2010 Elsevier Inc. All rights reserved.