This work aimed to study cobalt nanoparticles (Co-NPs) preparation using three different methods in order to evaluate the effect of synthesis variables that can influence the nanoparticle size distribution and particle shape. The synthesised nanoparticles were characterised by Transmission Electron Microscopy. The first synthesis employed decomposition of Co2(CO)8, at high temperatures. This procedure resulted in spherical nanoparticles with low size distribution. The size of Co-NPs could be tuned by modification of precursor/surfactant, nevertheless the stirring and injection time influenced the size distribution. Using polyol process, at high temperatures, it was produced undefined-shape nanoparticles. This result suggests that the solution composition, i.e. the amount of trioctylphosphine and oleic acid was not suitable to control both size and shape of nanoparticles. Finally, the method based on reduction with NaBH4 resulted spherical nanoparticles with tiny sizes, indicating that in this case a variation on amount of reductant would be more efficient on the particle size control than a variation in concentration of oleic acid. These results indicated that, for each method, a different variable exists for the control of the distribution size and the shape of the formed particles. © 2014 Copyright Taylor and Francis Group, LLC.94398405Bao, Y., Beerman, M., Krishnan, K.M., Letter to the editor: Controlled self-assembly of colloidal cobalt nanocrystals (2003) J. Magn. Magn. Mater., 266, pp. L245-L249Puntes, V.F., Krishnan, K.M., Synthesis, structural order and magnetic behavior of self-assembled ε-Co nanocrystal arrays (2001) IEEE Trans. Magn., 37 (4), pp. 2210-2212Aiken III, J.D., Finke, R.G., A review of modern transition-metal nanoclusters: Their synthesis, characterization, and applications in catalysis (1999) J. Mol. Catal. A Chem., 145, pp. 1-44Bezemer, G.L., Bitter, J.H., Kuipers, H.P.C.E., Oosterbeek, H., Holewijn, J.E., Xu, X., Kapteijn, F., de Jong, K.P., Cobalt particle size effects in the Fischer-Tropsch reaction studied with carbon nanofiber supported catalysts (2006) J. Am. Chem. Soc., 128 (12), pp. 3956-3964Sun, S., Murray, C.B., Synthesis of monodisperse cobalt nanocrystals and their assembly into magnetic superlattices (invited) (1999) J. Appl. Phys., 85 (8), pp. 4325-4330Zhao, Y.-W., Zheng, R.K., Zhang, X.X., Xiao, J.Q., A simple method to prepare uniform cobalt nanoparticles (2003) IEEE Trans. Magn., 39 (5), pp. 2764-2766Kobayashi, Y.M., Horie, M., Konno, M., Rodriguez-Gonzalez, B., Liz-Marzan, L.M., Preparation and properties of silica-coated cobalt nanoparticles (2003) J. Phys. Chem. B, 107 (30), pp. 7420-7425Wu, N., Fu, L., Su, M., Aslam, M., Wong, K.C., Dravid, V.P., Interaction of fatty acid monolayers with cobalt nanoparticles (2004) Nano Lett., 4 (2), pp. 383-386Su, Y.K., Shen, C.M., Yang, T.Z., Yang, H.T., Gao, H.J., Li, H.L., The dependence of Co nanoparticles sizes on the ratio of surfactants and the influence of different crystal sizes on magnetic properties (2005) Appl. Phys. A, 81, pp. 569-572Martínez, A., Prieto, G., Breaking the dispersion-reducibility dependence in oxide-supported cobalt nanoparticles (2007) J. Catal., 245, pp. 470-476Martínez, A., Prieto, G., The key role of support surface tuning during the preparation of catalysts from reverse micellar-synthesized metal nanoparticles (2007) Catal. Commun., 8, pp. 1479-1486Osuna, J., Decaro, D., Amiens, C., Chaudret, B., Snoeck, E., Respaud, M., Broto, J.M., Fert, A., Synthesis, characterization, and magnetic properties of cobalt nanoparticles from an organometallic precursor (1996) J. Phys. Chem., 100 (35), pp. 14571-14574Dassenoy, F., Casanove, M.J., Lecante, P., Verelst, M., Snoeck, E., Mosset, A., Ely, T.O., Chaudret, B., Experimental evidence of structural evolution in ultrafine cobalt particles stabilized in different polymers - from a polytetrahedral arrangement to the hexagonal structure (2000) J. Chem. Phys., 112 (18), pp. 8137-8145Puntes, V.F., Krishnan, K.M., Alivisatos, A.P., Synthesis, self-assembly, and magnetic behavior of a two-dimensional superlattice of single-crystal ε-Co nanoparticles (2001) Appl. Phys. Lett., 78 (15), pp. 2187-2189Puntes, V.F., Krishnan, K., Alivisatos, A.P., Synthesis of colloidal cobalt nanoparticles with controlled size and shapes (2002) Top. Catal., 19 (2), pp. 145-148Ribeiro, R.U., Liberatori, J.W.C., Winnishofer, H., Bueno, J.M.C., Zanchet, D., Zanchet, D., Colloidal Co nanoparticles supported on SiO2: Synthesis, characterization and catalytic properties for steam reforming of ethanol (2009) Appl. Catal. B Environ., 91, pp. 670-678Murray, C.B., Sun, S., Gaschler, W., Doyle, H., Betley, T.A., Kagan, C.R., Colloidal synthesis of nanocrystals and nanocrystal superlattices (2001) IBM J. Res. Dev., 45 (1), pp. 47-56Lisiecki, I., Size, shape, and structural control of metallic nanocrystals (2005) J. Phys. Chem. B, 109 (25), pp. 12231-12244Wang, C., Fang, J., He, J., O'Connor, C.J., Synthesis of one-dimensional magnetic Co nanoparticles in a novel solution system (2003) J. Colloid Interf. Sci., 259, pp. 411-413Cha, S.I., Mo, C.H., Kim, K.T., Hong, S.H., Ferromagnetic cobalt nanodots, nanorices, nanowires and nanoflowers by polyol process (2005) J. Mater. Res., 20 (8), pp. 2148-2153Puntes, V.F., Zanchet, D., Erdonmez, C.K., Alivisatos, A.P., Synthesis of hcp-Co nanodisks (2002) J. Am. Chem. Soc., 124 (43), pp. 12874-12880Chakroune, N., Viau, G., Ricolleau, C., Fiévet-Vincent, F., Fiévet, F., Cobalt-based anisotropic particles prepared by the polyol process (2003) J. Mater. Chem., 13, pp. 312-318Wilcoxon, J.P., Abrams, B.L., Synthesis, structure and properties of metal nanoclusters (2006) Chem. Soc. Rev., 35, pp. 1162-1194Rotstein, H.G., Tannenbaum, R., Cluster coagulation and growth by surface interactions with polymers (2002) J. Phys. Chem. B, 106, pp. 146-151Murray, C.B., Sun, S., Doyle, H., Betley, T., Monodisperse 3d transition-metal (Co, Ni, Fe) nanoparticles and their assembly into nanoparticle superlattices (2001) MRS Bull, pp. 985-991Glavee, G.N., Klabunde, K.J., Sorensen, C.M., Hadjipanayis, G.C., Sodium borohydride reduction of cobalt ions in nonaqueous media. Formation of ultrafine particles (nanoscale) of cobalt metal (1993) Inorg. Chem., 32, pp. 474-477Glavee, G.N., Klabunde, K.J., Sorensen, C.M., Hadjipanayis, G.C., Borohydride reduction of cobalt ions in water. Chemistry leading to nanoscale metal, boride, or borate particles (1993) Langmuir, 8, pp. 771-773Lisiecki, I., Pileni, M.P., Synthesis of well-defined and low size distribution cobalt nanocrystals: The limited influence of reverse micelles (2003) Langmuir, 19, pp. 9486-9489