Deep eutectic solvents (DES), a new generation of non-toxic, eco-friendly and biodegradable solvents discovered in 2001 consist of a variety of cations and anions. These new sub-category of ionic liquids present interesting properties due to the hydrogen bonding between their components and are being currently explored for a number of applications such as nanomaterial synthesis, electrodeposition, metal processing etc. Particularly interesting is their use as solvents for the synthesis of nanomaterials. The DES are especially attractive due to the lack of toxic emissions because of their negligible vapour pressure in comparison to the volatile organic compounds. However there is a lack in the understanding on the role played by DES to produce nanomaterials.
Herein, the role of reline, an eutectic mixture of choline chloride and urea, one of the most popular DES, is elucidated during the synthesis of different families such as gold (noble metal), vanadium pentoxide (transition metal oxide), ceria and zirconia (ceramic oxides). The work focuses on gaining a holistic understanding on the interaction of reline with different precursors. It is found that reline can act as an ‘all in one’ platform such as template reagent, reducing agent, solvent platform and morphology directing agent in the synthesis of nanomaterials. It is important to highlight that there is no addition of any external additives in contrast to previously published work.
It is demonstrated here that reline can actively form gold nanoparticles by reducing a salt precursor and simultaneously stabilize the nuclei, delaying their growth, leading to highly monodispersed small gold particles. In the case of metal oxides, the templating role of reline is elucidated to produce different morphologies of vanadium pentoxide upon altering the water ratio in reline. Reline has been also shown to direct the growth of 1D ceria-zirconia nanorods. The effect of reline on the crystal phase of the zirconia nanomaterial is also investigated herein.