Soft, Wet‐Chemical Synthesis of Metastable Superparamagnetic Hexagonal Close‐Packed Nickel Nanoparticles in Different Ionic Liquids

Abstract

The microwave-induced decomposition of bis{N,N'-diisopropylacetamidinate}nickel(II) [Ni{MeC(NiPr) } ] or bis(1,5-cyclooctadiene)nickel(0) [Ni(COD) ] in imidazolium-, pyridinium-, or thiophenium-based ionic liquids (ILs) with different anions (tetrafluoroborate, [BF ] , hexafluorophosphate, [PF ] , and bis(trifluoromethylsulfonyl)imide, [NTf ] ) yields small, uniform nickel nanoparticles (Ni NPs), which are stable in the absence of capping ligands (surfactants) for more than eight weeks. The soft, wet-chemical synthesis yields the metastable Ni hexagonal close-packed (hcp) and not the stable Ni face-centered cubic (fcc) phase. The size of the nickel nanoparticles increases with the molecular volume of the used anions from about 5 nm for [BF ] to ≈10 nm for [NTf ] (with 1-alkyl-3-methyl-imidazolium cations). The n-butyl-pyridinium, [BPy] , cation ILs reproducibly yield very small nickel nanoparticles of 2(±1) nm average diameter. The Ni NPs were characterized by high-resolution transmission electron microscopy (HR-TEM) and powder X-ray diffraction. An X-ray photoelectron spectroscopic (XPS) analysis shows an increase of the binding energy (E ) of the electron from the Ni 2p orbital of the very small 2(±1) nm diameter Ni particles by about 0.3 eV to E =853.2 eV compared with bulk Ni , which is traced to the small cluster size. The Ni nanoparticles show superparamagnetic behavior from 150 K up to room temperature. The saturation magnetization of a Ni (2±1 nm) sample from [BPy][NTf ] is 2.08 A m kg and of a Ni (10±4 nm) sample from [LMIm][NTf ] it is 0.99 A m kg , ([LMIm]=1-lauryl-3-methyl- imidazolium). The Ni NPs were active catalysts in IL dispersions for 1-hexene or benzene hydrogenation. Over 90 % conversion was reached under 5 bar H in 1 h at 100 °C for 1-hexene and a turnover frequency (TOF) up to 1330 mol (mol ) h or in 60 h at 100 °C for benzene hydrogenation and TOF=23 mol (mol ) h .

Nickel nanoparticles supported on a covalent triazine framework as electrocatalyst for oxygen evolution reaction and oxygen reduction reactions

“…In PXRD measurements, both cubic (fcc) and hexagonal (hcp) crystalline phases of nickel [45] were observed in all composites ( Figure 1). When the nickel loading was low (20-22 wt %), the characteristic broad reflections for amorphous CTF could also be seen.…”

Synthesis of plasmonic Fe/Al nanoparticles in ionic liquids

“…55,57 Imidazolium-ILs, in particular with the cation [BMIm] + are well established for the synthesis of small NPs. 18,19,54,[56][57][58][59][60] However, [BMIm] + contains a slightly acidic proton in the C-2 position which can lead to metal-carbene formation. 61 The cation [BPy] + was included here because of the absence of such acidic protons.…”

Nickel Nanoparticles Stabilized by Trisimidazolium Salts: Synthesis, Characterization and Application as Recyclable Catalysts for the Reduction of Nitroarenes

“…The synthesis of nickel nanoparticles has been described in the literature through a thermal or chemical reduction of Ni(II) salts with NaBH 4, LiEt 3 BH or NaEt 3 BH,,,,–, dimethylaminoborane, hydrazine,,,, ethylene glycol, or oleylamine as reducing agents, among others. Moreover, dispersions of Ni NPs in different types of ionic‐liquids have been obtained by auto‐decomposition, or microwave‐induced decomposition of Ni(COD) 2 (COD=1,5‐cyclooctadiene). This zero‐valent organometallic complex has also been used as starting compound for the production of Ni NPs following the Chaudret's organometallic approach,, consisting in the reduction and subsequent displacement of a ligand from a metal(0) organometallic precursor.…”