Se nanoparticles (NPs) of predominantly
amorphous phase (α-Se)
have been prepared in room-temperature ionic liquids (RTILs). The
effects of ion-pair combination and −OH functionalization of
RTILs on the size and phase stability of Se NPs were investigated.
The RTILs used were 1-ethyl-3-methyl imidazolium boron tetrafluoride
([EMIM][BF4]), 1-(2-hydroxyethyl)-3-methyl imidazolium
boron tetrafluoride ([EOHMIM][BF4]), and 1-ethyl-3-methyl
imidazolium methane sulfonate ([EMIM][MS]). The size of Se NPs@[EOHMIM][BF4] was found to be the smallest (∼32 nm), followed by
Se NPs@[EMIM][BF4] (∼57 nm) and Se NPs@[EMIM][MS]
(∼60 nm), respectively. Interestingly, the stability studies
revealed minimal size variations for Se NPs@[EMIM][MS], followed by
Se NPs@[EOHMIM][BF4] and Se NPs@[EMIM][BF4],
respectively. The observed trends could be correlated with the strength
of interionic interactions in the respective RTILs, as well as their
packing order (density). Importantly, the RTILs played the role of
a solvent, a stabilizer, and an in situ source of reducing species.
Pulse radiolysis study revealed imidazolium-originated radical species-driven
formation of Se NPs. Further, anticancer efficacy studies demonstrated
the role of NP size, wherein Se NPs@[EOHMIM][BF4] exhibited
the highest cancer cell killing, followed by Se NPs@[EMIM][BF4] and Se NPs@[EMIM][MS]. Another significant highlight of
this work is the reuse of the spent RTILs for the synthesis of the
next batch of Se NPs.