New Findings for the Composition and Structure of Ni Nanoparticles Protected with Organomercaptan Molecules

Abstract

Here we explore the synthesis of alkanethiol-coated Ni NPs following the one-phase reaction method by Brust et al. The reduction of NiCl2 with NaBH4 in the presence of dodecanethiol (C12SH) yields a complex product that is difficult to identify as illustrated in the figure of merit. We synthesized Ni(II) dodecanethiolate (C12S) (without the addition of NaBH4) for comparison and performed an exhaustive characterization with TEM, HR-TEM, AFM, MFM, XPS, XRD, UV-vis, magnetism, and FT-IR. It is found that the organic coating is not quite a well-organized self-assembled monolayer (SAM) surrounding the Ni cluster as previously reported. XPS and XRD data show slight differences between both syntheses; however, Ni(II) thiolate appears to be more stable than reduced Ni when exposed to ambient air, indicating the propensity of metallic Ni to oxidize. It has been shown that irradiating with TEM electrons over various metal thiolates leads to nanoparticle formation. We irradiated over Ni(II) thiolate and observed no evidence of NP formation whereas irradiating a reduced Ni sample exhibited an ~3.0 nm nanoparticle diameter. Magnetism studies showed a difference between both samples, indicating ferromagnetic character for the reduced Ni sample. According to our results, the product of the synthesis is comprised of ultrasmall metallic clusters embedded in some form of Ni(II) C12S. In this work, we open a discussion of the chemical nature of the core and the shell in the synthesis of Ni NPs protected with organomercaptan molecules.

Crystal-Bound vs Surface-Bound Thiols on Nanocrystals

“…48 In the staples, Au atoms are removed from the Au cluster surface to so that the thiolates have a gold coordination number of two. The decomposition of thiols on metal atoms to give metal sulfide nanocrystals has been well established for Cu, 49 Pd, 50 and Ni, 51 and it is possible that high coordination number binding of thiols also occurs in these cases.…”

Quinone‐Rich Poly(dopamine) Magnetic Nanoparticles for Biosensor Applications

“…[61,62] In fact, MFM imaging has been successfully used to characterize the magnetic properties shown by bidimentional self-assembled melanin-iron biofilms and Ni-aggregated nanoparticles both supported on a HOPG basal plane. [63,64] In this context, the size of the magnetic particle is a significant factor that has a surprisingly strong effect on its magnetic properties. Thus, magnetite particles ranging from 35 to 80 nm in diameter must be considered to be single-domain magnets.…”

Self-assembled monolayers of thiolates on metals: a review article on sulfur-metal chemistry and surface structures

“…202,203 Recently a detailed analysis of DT-protected NiNPs (~4 nm in 10 diameter according to TEM) prepared by the one-phase Brust-Schiffrin method 204 reveals, as in the case of thiolate SAMs on planar Ni, a large excess of S that include Ni(II)-thiolate, and free thiols as shown in Figure 12c. 205 Also, the Ni 2p peak shows evidence of Ni(II)-thiolate ( Figure 12d). IR data indicate that the 15 DT-protected NiNPs exhibit more disordered alkyl chains than those found for DT-protected AuNPs of the same size.…”