Cheap and efficient synthesis of metal selenide nanocrystals using a heterogeneous Se precursor

Following their increasing use, the supply of larger quantities of monodisperse colloidal nanocrystals(NC) necessitates a scaling up of their production. As a result, synthesis cost, tuneability of the NC size at full yield and synthesis reproducibility have become key issues. Finding an optimal approach in this respect is a matter of methodology, involving the use of larger scale or automated batch reactors or continuous flow-line approaches, yet it also concerns a reassessment of the reagents used and the reaction conditions needed. This is especially true for selenium precursors used to synthesize metal selenide nanocrystals such as CdSe. These involve selenium dissolved in either tri-octylphosphine (TOP) [1]- which is expensive and oxygen sensitive - or 1-octadecene, which leads to a precursor (homogeneous ODE-Se) with a low reactivity and a limited reaction yield [2]. Here, we propose an alternative approach to synthesize metal selenide NCU+2019s using a Se precursor that adds a high reactivity to the advantages of homogeneous ODE-Se. The method involves the direct injection of a heterogeneous mixture of selenium powder dispersed in a carrier liquid in a hot solvent containing a metal carboxylate as the cation precursor and excess carboxylic acid. Both in the case of cadmium and zinc carboxylates, we find that the injection of this heterogeneous ODE-Se precursor is followed by the formation of monodisperse nanocrystals, reaching chemical yields up to 80-90% within a few minutes. Moreover, the reaction can be run under ambient conditions without compromising the quality of the end product and the NC diameter reached at close to full yield can be tuned by changing the carboxylic acid chain length. In addition, since the amount of selenium injected is not limited by the solubility of selenium, the reaction can be executed with a high solid load, thus minimizing the amount of solvent needed. Finally, we demonstrate that syntheses involving the heterogeneous Se precursor as proposed here can be reproducibly executed on an automated synthesis platform, thus showing the potential of this novel approach for scaling up the production of colloidal metal selenide nanocrystals. [1] J. Am. Chem. Soc., 2001, 123 (1), pp 183-184 [2] J. Phys. Chem. B, 2005, 109 (44), pp 20665-20668

Publication year:2013