The role of structural and fluidic aspects of room temperature ionic liquids in influencing the morphology of CdSe nano/microstructures grown in situ

Abstract

RTILs as media to synthesize a variety of nanomaterials are gaining momentum owing to their unique physicochemical properties. However, the fundamental questions regarding the role of the inherent structure of the IL in directing the morphology and the growth mechanism of the nanoparticles are still unexplored. Therefore, an attempt was made in this respect wherein CdSe nanoparticles were synthesized in a neat room temperature ionic liquid (RTIL), 1-ethyl-3-methyl imidazolium ethylsulfate ([EMIM][EtSO₄]), under ambient conditions. The IL was found to play three roles, as a solvent, as a stabilizing agent and as a shape directing template. The primary nanoparticles were of the sizes in the range of 2–5 nm, as determined by HR-TEM. These primary nanoparticles grow into nanoflake-like units which further self-assemble and transform into a mixture of anisotropic nanostructures (predominantly 2D sheets and flower-like 3D patterns) as revealed by the SEM studies. The co-existence as well as the stability of these nanomorphologies point towards the intrinsic microheterogeneity prevailing in the IL. Furthermore, the vibrational spectroscopic studies comprising of FT-IR and Raman spectroscopy clearly indicate a sort of accord involving the π–π stacked aromatic geometry and the hydrogen bonding network (between the cation and the anion) of the IL with the CdSe nanoparticles. Therefore, a suitable mechanism has been provided for the resulting anisotropic nanostructures on the basis of the structural and the fluidic aspects of the IL in conjunction with the surface properties of the transient morphologies involved in the process. To further supplement this, control experiments were facilitated by diluting the IL with different amounts of water and the morphology of the CdSe nanostructures was examined at respective mole fractions of water as well as at different time intervals.