Researchers at NC State have developed a technique to create nanoparticles with a unique structure: a core of nickel embedded in a silica shell with small orbs of nickel surrounding the core. This leads to an increased nickel surface area, making more of this metal available for catalysis. For more on this work, please see the NC State press release.
Authors: Brian B. Lynch and Joseph B. Tracy, North Carolina State University; Bryan D. Anderson, North Carolina State University and Air Force Research Laboratory; W. Joshua Kennedy, Air Force Research Laboratory
Published: Nov. 28, Nanoscale
Abstract: 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.