Systematic Size Control in the Synthesis of Zero-Valent Iron Nanoparticles

摘要

A novel synthetic method for the production of highly magnetic, low size-dispersity nanoparticles through reversible magnetic agglomeration is introduced and studied in detail. Initially, a weakly coordinating surfactant (3-octadecyl-2,4-pentanedione) is employed to produce a wide range of nanoparticle sizes ranging from 8 to 20 nm in diameter. The kinetics faced in these reactions by cheap and widely available iron complex precursors can be avoided in this method with the introduction of thermodynamic control, which occurs in the form of a magnetic precipitation event that essentially halts nanoparticle growth. Utilizing this synthetic method, the length of the alkyl chain on the surfactant can be modified to shorter lengths to ultimately control the size to which the particles can grow by varying the degree of steric stabilization. Surfactants increasing in alkyl chain length from the bare surfactant (2,4-pentanedione) to 4 and 10 carbons long (3-butyl-2,4-pentanedione and 3-decyl-2,4-pentanedione, respectively) were used to further provide fundamental insight into the surfactant nanoparticle relationship. Through this relationship our research could also elaborate on the factors that influence and control nanoparticle nucleation, growth, and stabilization.;Post-processing techniques on the as-synthesized nanoparticles are also introduced, opening numerous opportunities for further customization of nanoparticle properties for a given system. The magnetization saturation can be drastically enhanced and the collective blocking temperature altered through simple hydrogenation procedures. It was discovered through these techniques that the nanoparticles can also behave as active catalysts for the hydrogenation of alkenes with a high prospect for many other substrates.;The magnetic properties of the nanoparticles were studied using a superconducting quantum interference device (SQUID) magnetometer and the physical characteristics were analyzed using transmission electron microscopy (TEM), small angle X-ray scattering (SAXS), and X-ray diffraction (XRD). Nuclear magnetic resonance (NMR) assisted in the identification of the custom-synthesized surfactants as well as the substrate conversion progress in the alkene hydrogenation reactions.