Magnetite

About: Magnetite is a research topic. Over the lifetime, 10277 publications have been published within this topic receiving 278071 citations.

Iron oxide-gold core-shell nanoparticles and thin film assembly

Abstract: This paper reports findings of an investigation of the synthesis of monolayer-capped iron oxide and core (iron oxide)–shell (gold) nanocomposite and their assembly towards thin film materials. Pre-synthesized and size-defined iron oxide nanoparticles were used as seeding materials for the reduction of gold precursors, which was shown to be effective for coating the iron oxide cores with gold shells (Fe oxide@Au). The unique aspect of our synthesis is the formation of Fe oxide@Au core–shell nanoparticles with controllable surface properties. The novelty of our assembly strategy is the exploitation of the ligand-exchange reactivity at the gold shells for the thin film assembly of the core–shell nanoparticles. The core–shell nanocomposites and assemblies have been characterized using TEM, XRD, XPS, FTIR, TGA, and DCP-AES techniques. In addition to evidence from TEM detection of the change in particle size, UV-Vis observation of the change in the surface plasmon resonance band, and XRD detection of disappearance of the magnetite diffraction peaks after coating the gold shell, the formation of the core–shell morphology was further confirmed by DCP-AES composition analysis of Au and Fe in the molecularly-mediated thin film assembly of Fe oxide@Au particles. The interparticle ligand exchange–precipitation chemistry at the gold shell is to our knowledge the first example demonstrating the inter-shell reactivity for constructing thin films of Fe oxide@Au particles. The results have provided important insights into the design of interfacial reactivities via core–shell nanocomposites for magnetic, catalytic and biological applications.

Investigation on Capacitance Mechanisms of Fe3O4 Electrochemical Capacitors

Abstract: The capacitance mechanisms of magnetite (Fe 3 O 4 ) electrochemical capacitor in Na 2 SO 3 , Na 2 SO 4 , and KOH aqueous solutions have been investigated by electrochemical quartz-crystal microbalance analysis, along with cyclic voltammetry and X-ray photoelectron spectroscopy. The oxide thin-film electrode was prepared by an electroplating method, and exhibits a capacitance of ∼170, 25, and 3 F/g in 1.0 M Na 2 SO 3 (aq), Na 2 SO 4 (aq), and KOH(aq), respectively. Strong specific adsorption of the anion species was evidenced in all solutions. Experimental results indicate that, in Na 2 SO 3 (aq), the capacitive current of magnetite electrode originates from the combination of electric double-layer capacitance (EDLC) and the pseudocapacitance that involves successive reduction of the specifically adsorbed sulfite anions, from SO 2 - 3 through, e.g., S 2 - , and vice versa. In Na 2 SO 4 (aq), the current is due entirely to EDLC. Furthermore, due to the specific adsorption behavior, magnetite exhibits high EDLC, >30 μF/cm 2 , in both Na 2 SO 3 and Na 2 SO 4 solutions. The lowest capacitance of magnetite was observed in KOH, which is attributed to the formation of an insulating layer on the magnetite surface.