Formation of silver nanoparticles from ionic liquids comprising N-alkylethylenediamine: Effects of dissolution modes of the silver(I) ions in the ionic liquids

Abstract

Silver nanoparticles (AgNPs) were prepared from ionic liquids (ILs) of silver(I) N-alkylethylenediamine (N-alkyl=N-2-ethylhexyl, N-octyl, and N-dodecyl) complexes (=AgILs) and from protic ionic liquids (PILs) of N-alkylethylenediamines containing dissolved silver(I) nitrate (=AgNO3-PILs) and the two methods were compared. The difference between the silver(I) ion–ligand interaction modes of the AgIL and AgNO3-PIL systems was distinctly reflected in the formation of the AgNPs. The effects of the molecular structures of the AgILs and PILs, such as the effects of the alkyl chains in the cationic unit and the counter anion, on the shape and size distribution of the AgNPs were also examined using transmission electron microscopy (TEM), visible (VIS) absorption spectra, and extended X-ray absorption fine structure (EXAFS). The effect of the ethyl-branch of the alkyl chains on the physicochemical properties of the AgILs is drastic. The AgILs generally provided a more favorable reaction field for AgNP production than the AgNO3-PIL. The preparation of AgNPs depends on the concentration of AgNO3 in the PILs; at approximately 0.01molkg−1 of AgNO3 in the PILs, the PILs were capable of preventing the aggregation of silver(0) particles to allow the formation of AgNPs, while at higher AgNO3 concentrations (0.05molkg−1), even in the long-chained dodecyl-PIL system, larger continuous-shaped aggregates were detected. The bis(fluorosulfonyl)amide (FSA) anion is effective on decreasing the transition temperature for the formation of the liquid states, but not appropriate for the preparation of the AgNPs when combined with the N-2-ethylhexylethylenediamine-AgIL cationic unit, compared to the NO3 and trifluoroacetate (TFA) salts.