Metal Nanoparticles in Ionic Liquids

Abstract

During the last years ionic liquids (ILs) were increasingly used and investigated as reaction media, hydrogen sources, catalysts, templating agents and stabilizers for the synthesis of (monometallic and bimetallic) metal nanoparticles (M-NPs). Especially ILs with 1,3-dialkyl-imidazolium cations featured prominently in the formation and stabilization of M-NPs. This chapter summarizes studies which focused on the interdependencies of the IL with the metal nanoparticle and tried to elucidate, for example, influences of the IL-cation, -anion and alkyl chain length. Qualitatively, the size of M-NPs was found to increase with the size of the IL-anion. The influence of the size of imidazolium-cation is less clear. The M-NP size was both found to increase and to decrease with increasing chain lengths of the 1,3-dialkyl-imidazolium cation. It is evident from such reports on cation and anion effects of ILs that the interaction between an IL and a (growing) metal nanoparticle is far from understood. Factors like IL-viscosity, hydrogen-bonding capability and the relative ratio of polar and non-polar domains of ILs may also influence the stability of nanoparticles in ionic liquids and an improved understanding of the IL-nanoparticle interaction would be needed for a more rational design of nanomaterials in ILs. Furthermore, thiol-, ether-, carboxylic acid-, amino- and hydroxyl-functionalized ILs add to the complexity by acting also as coordinating capping ligands. In addition imidazolium cations are precursors to N-heterocyclic carbenes, NHCs which form from imidazolium-based ionic liquids by in situ deprotonation at the acidic C2-H ring position as intermediate species during the nanoparticle seeding and growth process or as surface coordinating ligand for the stabilization of the metal nanoparticle.

Single LiBH4 nanocrystal stochastic impacts at a micro water|ionic liquid interface

“…Lithium borohydride (LiBH4) and its analogues have been proposed for a variety of energy and synthetic applications, including H2 storage [1][2][3][4], direct borohydride fuel cells [5,6], and as reducing agentsboth molecular and in the formation of metal nanoparticles (NPs) [4,7]. Simultaneously, ionic liquids (ILs) have been used as industrial solvents for chemical processes, where the environmental impact has been reduced relative to molecular solvents, the reactivity enhanced, and with better recovery of catalytic materials [8].…”

“…These materials, either added intentionally or present as impurities, will likely influence IL solvent effectiveness or introduce new reactivity. Interestingly, for the specific case of metal-NP synthesis within an IL the supramolecular nature of the IL produces highly monodisperse particles with sizes ranging as low as 1-2nm [7,[10][11][12][13][14][15] when LiBH4 is used as a reducing agent. In most of these synthetic applications, and for the case of H2 storage, an excess of borohydride is required.…”

Sputtering onto a liquid: interesting physical preparation method for multi-metallic nanoparticles

“…Based on the temperature-dependent viscosity of ILs, stopping the aggregation and growth of Ag NPs after sputtering onto an IL was achieved using low temperature storage, that is below glass transition temperature of IL [54]. The anion and cation effect and the stabilization capability of ionic liquid for NPs have been also investigated and discussed elsewhere [55][56][57]. On the other hand, liquid monomers, which can be polymerized in the succeeding step, or liquid polymers were then used as a capture medium in sputtering [58][59][60][61][62][63].…”

Ionothermal Synthesis of Metal Oxide-Based Nanocatalysts and Their Application towards the Oxidative Desulfurization of Dibenzothiophene

“…ese IL-based nanocatalysts exhibit both homogeneous and heterogeneous catalytic properties, which not only facilitate rapid and selective chemical transformations but also offer enhanced yield and easy separation and recovery of catalysts [27]. In several studies, ILs have demonstrated excellent potential for the synthesis of various inorganic metal and metal oxide NPs [28]. Particularly, the thermal synthesis of nanomaterials using ILs (ionothermal synthesis) has received considerable attention of researchers.…”