Materials libraries of binary alloy nanoparticles (NPs) are synthesized by combinatorial co‐sputter deposition of Cu and Au into the ionic liquid (IL) 1‐butyl‐3‐methylimidazolium bis(trifluoromethylsulfonyl)imide ([C1C4im][Tf2N]), which is contained in a micromachined cavity array substrate. The resulting NPs and NP‐suspensions are investigated by transmission electron microscopy (TEM), X‐ray diffraction (XRD), UV‐Vis measurements (UV‐Vis), and attenuated total reflection Fourier transformed infrared (ATR‐FTIR) spectroscopy. Whereas the NPs can be directly observed in the IL using TEM, for XRD measurements the NP concentration is too low to lead to satisfactory results. Thus, a new NP isolation process involving capping agents is developed which enables separation of NPs from the IL without changing their size, morphology, composition, and state of aggregation. The results of the NP characterization show that next to the unary Cu and Au NPs, both stoichiometric and non‐stoichiometric Cu–Au NPs smaller than 7 nm can be readily obtained. Whereas the size and shape of the alloy NPs change with alloy composition, for a fixed composition the NPs have a small size distribution. The measured lattice constants of all capped NPs show unexpected increased values, which could be related to the NP/surfactant interactions.

Recently we developed an access to metal- and metal-oxide colloids based on thermal evaporation of metals into ionic liquids (ILs). Here we present systematic studies on the long-time stability of gold and copper nanoparticles (NPs) in different ILs. The influence of metal concentration and temperature on the ripening of the as-prepared gold NPs in different ILs was investigated by transmission electron microscopy (TEM) and UV-vis absorption measurements. Short alkyl chain-length-methyl-imidazolium salts with weakly coordinating perfluorinated counter anions (PF(6), BF(4) or Tf(2)N, bis(trifluoromethanesulfonyl)amide) were found to be better stabilizers compared to ILs with cations bearing long alkyl chains (trihexyltetradecylphosphonium, 1-octyl-3-methylimidazolium) and anions of higher coordination strength (DCA, dicyanamide). In the latter ILs fast particle growth and agglomeration was observed. In the well-stabilizing ILs initially very small NPs form which undergo a similar ripening process at room temperature as at higher temperatures. The final particle size depends largely on the used IL and the metal and to a minor extent on the temperature. The metal concentration seems to be an unimportant factor.

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Ionic liquids (ILs) offer outstanding possibilities as media for manufacturing nanoparticles. Synthesis conditions with high reaction and nucleation rates are achievable leading to the formation of extremely small particles. The IL itself can act as an electronic as well as a steric stabiliser preventing particle growth and particle aggregation. In addition, as highly structured liquids, ILs have a strong effect on the morphology of the particles formed. We have developed two synthesis techniques for the generation of metal nanoparticles that take advantage of the unique properties that ILs offer when compared to conventional volatile organic solvents (VOCs): microwave (MW) synthesis and physical vapour deposition (PVD). The ionic character and high polarisability of the IL renders it highly susceptible to energy uptake via MWs and extreme heating and reaction rates can be achieved. To make full use of the possibilities that ILs offer we have designed a set of reducing ILs which can be used as direct reaction partners for the generation of metal nanoparticles. The negligible vapour pressure of many ILs makes experiments under high vacuum possible and allows for the PVD of metals into ILs. magnified imagePhysical vapour deposition (left) and microwave synthesis of metal nanoparticles in ILs.

The environmentally friendly ionic liquid N-(2-hydroxyethyl)ammonium formate works as a reaction medium, reducing and templating agent in the mild microwave synthesis (5 min, 80 degrees C) of a macroporous silver framework from AgNO(3).