Application Of Imidazolium Based Ionic Liquids For Reduction Of Metal Ions Using Glow Discharge Plasma

Plasma reduction is an effective green chemistry reduction process. Comparing to conventional chemical reduction,plasma reduction requires no hazardous reducing agents. The supported catalysts after plasma reduction have higher dispersions and show better catalytic activities. Ionic liquids, be composed of entire organic ionics and in liquid state in room temperature, are playing a more and more important role in chemical reactions or electrochemical depositions. Because of some unique properties, such as invotalizability, wide electrochemical windows and high thermal stability, ionic liquids were called green solvents. In this paper we combine plasma technology with ionic liquids to develop liquid plasma techniques. We intended to synthesize nanoparticles in ionic liquids via plasma reduction, and prepare highly dispersive supported ionic liquid catalysts.As ionic liquids have been developed for a relatively short time, people are not familiar with all of their properties. We investigated the stability of ionic liquids under glow discharge plasma for the first time. Three imidazolium based ionic liquids, [bmim]Cl, [bmim][BF4] and [bmim][PF6] showed their characteristic peaks in 1H NMR and FTIR. Only chemical shifts of [bmim]Cl in NMR changed a little but that was not an evidence of structure change. FTIR results confirmed that three ionic liquids were stable. All processes were at room temperature according to Infrared images. [bmim][BF4] was used as solvent, in which glow discharge reduced HAuCl4 and PdCl2 to prepare nanosized Au and Pd particles. Au nanoparticles formed in this process were little aggregated. The average particle size was 32.7 nm. The prepared Pd particles were well dispersed spherical particles in TEM results. The average size was 4.9 nm.Further more, Hypo-atmospheric pressure glow discharge (HAPGD) was used to reduce Pd(NO3)2 in [bmim][BF4]. The surface modification of plasma to the glass was observed during this process. [bmim][BF4] keep unchanged after HAPGD treatment, according to FTIR results. Pd nanoparticles reduced in ionic liquids were uniform and spherical, with an average size around 5 nm.Poly(vinyl pyrrolidone) (PVP) was imported into ionic liquids to control the Au nanoparticles formed after plasma reduction. The sizes and shapes were quite different with different reduction time. The products were mainly separate particles with various shapes after 1 minute or 5 minutes plasma reduction. In the processes with longer reduction time, peanut-like structures and irregular nanowires were formed. These nanostructures are connected through Au (111) planes, according to HRTEM results. The angles between two Au (111) planes varied from 0o to 180o. The action between PVP and Au clusters made these reduced Au clusters array along linear PVP molecules. Thus Au clusters had more chances to contact with each other to form linear shapes. XRD results showed that these irregular shapes were typical face-centered cubic structure. The concentration of surfactant was another important influencing factor to the Au particle sizes and shapes. We can reduce Au particles with uniform size through adjusting the PVP concentration.We produced supported ionic liquid catalysts on SBA-15 with plasma reduction for the first time. Dispersive Au nanoparticles on SBA-15 were formed after plasma reduction with [bmim][PF6] impregnated on the support. The particle sizes increased along with higher Au loading, up to 5%. Very few short nanowires could be found on the support. This was quite different from that without [bmim][PF6]. The Pd nanoparticles in supported ionic liquid catalysts produced after plasma reduction was also smaller than that without supported ionic liquid. XRD results confirmed that these nanoparticles were all face-centered cubic structures. Pd-[bmim][PF6]/SBA-15 catalysts showed good catalytic activities in Suzuki reactions. A series of catalysts were prepared with different precursors and ionic liquids impregnating sequences. Impregnating Pd(NO3)2 before ionic liquid [bmim][PF6], the catalyst prepared in this way showed the best activity.