Effects of ligand monolayers on catalytic nickel nanoparticles for synthesizing vertically aligned carbon nanofibers

Synthesis and chemical transformation of Ni nanoparticles embedded in silica

Ni nanoparticles (NPs) catalyze many chemical reactions, in which they can become contaminated or agglomerate, resulting in poorer performance. We report deposition of silica (SiO₂) onto Ni NPs from tetraethyl orthysilicate (TEOS) through a reverse microemulsion approach, which is accompanied by an unexpected etching process. Ni NPs with an average initial diameter of 27 nm were embedded in composite SiO₂-overcoated Ni NPs (SiO₂-Ni NPs) with an average diameter of 30 nm. Each SiO₂-Ni NP contained a ∼7 nm oxidized Ni core and numerous smaller oxidized Ni NPs with diameters of ∼2 nm distributed throughout the SiO₂ shell. Etching of the Ni NPs is attributed to use of ammonium hydroxide as a catalyst for deposition of SiO₂. Aliquots acquired during the deposition and etching process reveal agglomeration of SiO₂ and Ni NPs, followed by dissociation into highly uniform SiO₂-Ni NPs. This etching and embedding process may also be extended to other core materials. The stability of SiO₂-Ni NPs was also investigated under high-temperature oxidizing and reducing environments. The structure of the SiO₂-Ni NPs remained significantly unchanged after both oxidation and reduction, which suggests structural durability when used for catalysis.

Mechanistic Investigations of the Synthesis of Size-Tunable Ni Nanoparticles by Reduction of Simple NiII Diamide Precursors

Herein, we present a detailed study of the conversion of a nickel(II) diamide precursor to size-tunable, monodisperse nickel nanoparticles (NPs). The thermal decomposition of nickel(II) dioleylamide, synthesized either independently or in situ, resulted in the formation of Ni NPs without the coproduction of water. Mechanistic studies were conducted on the stability and reduction pathway of the Ni^II precursor, and on the consequent particle formation. Variations in the ratio of trioctylphosine (TOP) to nickel allowed size tunability, which resulted in nanoparticles that ranged in size from 4 to 11 nm in diameter. The DFT calculations support a mechanistic pathway that involves nickel reduction by imine formation. This water-free method was extended to the synthesis of water-sensitive M⁰ NPs (M=Fe, Co).

High yield, controlled synthesis of graphitic networks from dense micro emulsions

We propose a new synthesis method to produce hyper-branched carbon nano structures that we call carbon nano networks. These porous, graphitic materials directly grow into a networked structure, do not require the use of an inorganic support, and can be tailored by experimental conditions to better suit their application.

Coating alumina on catalytic iron oxide nanoparticles for synthesizing vertically aligned carbon nanotube arrays

To synthesize long and uniform vertically aligned carbon nanotube (VACNT) arrays, it is essential to use catalytic nanoparticles (NPs) with monodisperse sizes and to avoid NP agglomeration at the growth temperature. In this work, VACNT arrays were grown on chemically synthesized Fe(3)O(4) NPs of diameter 6 nm by chemical vapor deposition. Coating the NPs with a thin layer of Al(2)O(3) prior to CNT growth preserves the monodisperse sizes, resulting in uniform, thick and dense VACNT arrays. Comparison with uncoated NPs shows that the Al(2)O(3) coating effectively prevents the catalyst NPs from sintering and coalescing, resulting in improved control over VACNT growth.