Synthesis and Characterization of Surface-modified FePt Nanocrystals by Supercritical Hydrothermal Method

Abstract

We have synthesized single nanosized FePt nanocrystals (NCs) by supercritical (sc-) hydrothermal synthesis. The synthesized FePt NCs were characterized by X-ray diffraction (XRD), transmission electron micrography (TEM), electron diffraction (ED), superconducting quantum interference device magnetometry (SQUID), and Fourier transform infrared spectroscopy (FTIR). Surface modification with oleic acid was also successful, and it gave spherical FePt NCs that had average particle size (APS) of 5.0 « 1.5 nm. In addition, the surfacemodified FePt NCs showed good dispersition into organic solvents. A dispersion in tetrahydrofuran (THF) was stable for at least 3 days. The dried surface-modified FePt NCs were easily oxidized in the atmosphere. This high reactivity to oxygen makes the characterization difficult and, at the same time, may indicate that quite a small amount of Fe NC is included in the reaction products.Alloys possibly exhibit benefits of all the contained metals. Sometimes alloy exhibits original unique properties that pure metals do not. These properties are attractive in terms of reduction of rare and noble metals usage. In addition, alloying may help the synthesis of nanoparticles (NPs) which consist of easily oxidized metals. Therefore, a lot of alloys, including their NPs, have been invented and applied as beneficial materials. Among them, FePt alloy which contains close to equal atomic percentage of Fe and Pt is an important class of magnetic materials. 1 3 For instance, FePt NPs can be a magnetic recording material with quite high storage density. There have been a lot of studies to synthesize fine FePt NPs. 4 8 However, a method for large-scale production of fine FePt NPs is still awaited.When one thinks about metal NPs synthesis, the technique to avoid oxidation can be a key issue. Because metal NPs have very high surface/volume ratio, they easily aggregate to reduce total surface area and are rapidly oxidized to metal oxide NPs. In order to solve these problems, surface control of metal NPs and in situ surface-controlled synthesis of metal NPs are quite important issue to be studied. Recently, surface protection of metal NPs by graphite and/or graphene sheet seems promising to avoid oxidation of the surface of metal NPs. 9 11 Further modification method of the graphite surface of the core shell NPs to introduce functional reagent on them have been developed. 12,13 Although this process is suitable to synthesize oxidation-resistant metal NPs, it is a dry process so that good control of the NPs size and morphology as well as dispersion of the NPs is difficult. At this point, the development of the solution-state synthesis of metal NPs seems still important.Hydrothermal synthesis is a promising method to synthesize inorganic NPs, especially for metal oxides, with controlled size, morphology, and surface. 14 We have developed in situ surfacemodified supercritical (sc-) hydrothermal synthesis of metal oxide NPs. 15,16 Since sc-hydrothermal reaction is very fast, it suits large-scale production of NPs, ...

Synthetic versatility of nanoparticles: A new, rapid, one-pot, single-step synthetic approach to spherical mesoporous (metal) oxide nanoparticles using supercritical alcohols

“…However, these techniques generally require long reaction times (several hours) and complex multistep operations [1-43, 47, 48]. Recently, supercritical fluids have been applied in the synthesis of size-and morphology-controlled inorganic-organic hybrid metal and MO NPs [49][50][51][52][53][54][55][56][57][58][59][60][61]. All of these reported NP syntheses occur rapidly in supercritical fluids (several seconds to several minutes) [56][57][58][59][60][61].…”

Versatility of one-pot, single-step synthetic approach for spherical porous (metal) oxide nanoparticles using supercritical alcohols

“…Recently, sizeand morphology-controlled inorganic-organic hybrid metal and metal oxide nanoparticles have been synthesized in supercritical fluids. Supercritical ethanol (scEtOH) yields monodisperse metal nanoparticles [29], supercritical methanol (scMeOH) [30,31] or supercritical water (SCW) [32] yields zinc oxide (ZnO) nanoparticles, while SCW alone yields CeO 2 [33], TiO 2 [34], and magnetite (Fe 3 O 4 ) [35] nanoparticles. All of these reactions proceed in a short reaction time (several seconds to several minutes) [36][37][38][39][40][41].…”

Chemistry in supercritical fluids for the synthesis of metal nanomaterials

“…However, H2O cannot act as a reducing agent and thus the participation of additional reducing agents is indispensable. In this regard, several types of reductants have been studied including formic acid/formate anion, 103,108,109,[112][113][114]157 polyvinylpyrrolidone (PVP), 96,158,159 1-hexanethiol, 104 formaldehyde, 105 hydrazine, 110,160 glucose, 116 and glycerol. 97 Formic acid is convenient to use as it is in liquid form and totally miscible with H2O under ambient conditions, and its thermal decomposition in an aqueous environment yields mostly CO2 and H2.…”

“…For instance, oleic acid-modified FePt and Fe NPs of 5 nm synthesized by the reductive supercritical hydrothermal method were extremely flammable and the whole powder exploded when it was exposed to air. 157 Nevertheless, surface modification appears to be an effective way to protect the fresh assynthesized metal NPs from being oxidized by H2O. Hexanoic acid was introduced to the reductive supercritical hydrothermal synthesis of Fe NPs.…”