The five shades of oleylamine in a morphological transition of cobalt nanospheres to nanorods

Abstract

Understanding of cobalt nanorods’ (Co NRs) formation still remains challenging when it comes to enhancing their anistropic properties applicable in magnetic or catalytic areas. Herein, we propose a mechanism for...

Transforming Cobalt Nanospheres into Co2P Nanorods: The Key Roles of Oleylamine and Organophosphorus Ligands in a Co(I) Precursor Uncovered through X-ray Photoelectron Spectroscopy Analysis

“…For its part, the red-shaded component at 401.4 eV in the spectrum of the 9:1 and 7:3 TD:OAm sphere sample, with spectral weights of ∼20% and 10%, respectively, can be attributed to the ammonium species (R-CH 2 NH 3 + ). This confirms one crucial tenet of the model depicted in The Five Shades (reaction ).…”

“…Second, we must consider that the solidified solution is “vertically” structured (with an OAm propensity for the surface). SAXS measurements indicate that pure OAm is indeed periodically structured . This would create natural “sinks” well below the surface where the organophosphorus ligands accumulate (see Scheme ).…”

“…Particles are prepared in the 7:3 TD:OAm mixture (as for the kinetic study), but a synthesis of spheres in the 9:1 TD:OAm mixture was also examined. The 9:1 mixture is considered by the authors of Five Shades of Oleylamine as much less conducive to the “sphere-to-rod” transformation than the 7:3 one, due to the too limited “reservoir” of oleylamine “fuel”. The XPS spectra are given in Figure (Co 2p), Figure (Cl 2p, P 2s and P 2p), and Figure (N 1s).…”

“…The high aspect ratio of the produced particles is attributed to the templating role of OAm. 8 Even though the model satisfactorily explains the observed growth phenomena, direct spectroscopic evidence of disproportionation was still lacking (i.e., determining the oxidation state of cobalt), as well as signatures of the amine decomposition products, namely, aldimine R2 and ammonium R4. Therefore, after characterizing the precursor (in powder form), we employed X-ray photoelectron spectroscopy (XPS) to monitor nanoparticle growth kinetics by sampling the precursor solution at various times and temperatures.…”

“…A mechanism explaining the sphere-to-rod transition mechanism is proposed in Five shades of Oleylamine . To account for the H 2 yield (Figure ), it is assumed that OAm adsorbs on the metallic Co spheres and breaks to give adsorbed H atoms (H ads ) and the aldimine: R − CH 2 − NH 2 normal ( on the Co surface ) → 2 H ads + R − CH = NH …”