A hydroxyl ion assisted alcohol reduction method has been applied for the preparation of copper nanoparticles with an average diameter of 10.5 nm and narrow size distribution. The addition of specific amounts of hydroxyl ions to the alcoholic solution is the key to enhance the reducing potential of alcohols to obtain metal copper from their salts even with 1-butanol. The synthesis of copper metal was realized through intermediate steps corresponding to the formation of copper oxides (CuO and Cu 2 O). The obtained nanoparticles were coated with necessary surfactants and dispersed in organic solvent such as dodecane to prepare conducting ink. Samples annealed at 250 C in nitrogen and vacuum atmosphere showed electrical resistivity of 26 and 35 mU cm, respectively.

The monoanionic state of ethylene glycol was theoretically and experimentally confirmed to be the active species during reduction reaction of metal salts.

Ideal interaction-free magnetite nanoparticles were prepared, and their magnetic properties were measured to clarify the true nature of magnetic anisotropy of individual magnetite nanoparticles at the nanoscale and to analyze the shape, surface, and crystalline anisotropy contributions. Spherical (17.7 nm), cubic (10.6 nm), and octahedral-shaped magnetite nanoparticles with average sizes ranging from 7.6 to 23.4 nm were synthesized using solution techniques. Then, these nanoparticles were coated with silica at appropriate shell thicknesses to prepare magnetic interaction-free samples, and their noninteractive nature was confirmed through first-order reversal curve diagrams. For these well-isolated nanoparticles, remanent magnetizations of the hysteresis loops are just equal to a half of the saturation magnetization. This result clearly indicates that uniaxial magnetic anisotropy is predominant in each nanoparticle. In order to clarify the details of the uniaxial magnetic anisotropy, the analysis of blocking temperature−switching field distribution diagrams is constructed based on thermal decay curves of isothermal remanent magnetization at various applied fields. The obtained effective magnetic anisotropy constant K eff is distributed around 10−20 kJ/m 3 and has insignificant size dependence. This result seems inconsistent with the inverse proportion relation of K eff with size predicted for surface magnetic anisotropy. The theoretical calculation suggested that the crystalline magnetic anisotropy plays a major role in magnetic properties of the magnetite nanoparticles at lower temperatures. However, it should be noted that K eff seems slightly different for the different shapes. The above study indicates that control size, shape, and interparticle interactions is required to strictly discuss such delicate differences of magnetic anisotropy of individual magnetite nanoparticles for the design of thermal seeds for magnetic hyperthermia.

A modified alcohol reduction process by controlling the complexation and reduction of metallic ions was developed to obtain compositionally and structurally controlled Ni-Pt nanoparticles (NPs) with sizes less than 20 nm in a high yield. The characterization of NPs synthesized under different experimental conditions suggested that the reduction of Pt and subsequent formation of cubic-shaped Ni-Pt NPs were strongly dependent on the formation of Pt-oleylamine (OAm) complexes. Thus, prior to the synthesis of Ni-Pt NPs, the formation and reduction process of Pt complexes in the solution-state were investigated by in situ UV-Visible and X-ray spectroscopies. The complexation of Pt ions along with their reduction prior to the formation of Pt metal and their influence on the size and the elemental distribution of Pt within the Ni-Pt NPs were revealed. Then, the above findings were actively utilized to design and to obtain Pt(core)-Ni(shell), Ni-Pt alloy, and Ni(core)-Pt(shell) nanostructures by regulating the OAm concentration in the system. The specific distribution of Pt on the Ni-Pt surface was confirmed by decolorization of methylene blue. Furthermore, Ni-Pt NPs with a Pt concentration of 10 at.% exhibited a mass activity four times larger than that of commercial Pt during the oxygen reduction reaction (ORR).

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Development of a technology for the synthesis of monometallic or multimetallic nanoparticles is exceptionally vital for the preparation of novel magnetic, optical. and catalytic functional materials. In this context, the polyol process is a safe and scalable method for preparation of metal nanoparticles with controlled sizes and shapes in large scales. However, there is no systematic investigation that discusses the criteria for the selection of metal salt and solvent type that determine the kinetics of reduction reaction that influences the morphology of the particles. Consequently, the design of metallic nanoparticles, which is controlled by the kinetics and thermodynamics of the reduction reaction, has become difficult. In this paper, the selection criterion for metal salt precursor is established based on the presumption that the ligand of the metal precursor promotes the formation of active species of the solvent, and the criterion for the selection of the solvent type is based on the highest occupied molecular orbital (HOMO) energy value estimated using molecular orbital theory. The results suggested that the dissociation constants of metal salt precursors and HOMO energy of the polyol solvent can be tuned to control the kinetics of the reduction reaction. The reduction potential of polyol depends on the number of carbon atoms and the location of hydroxyl ligands within the molecule. Among the polyols considered in this study, 1,4-butanediol had the highest reduction potential. The predictions have been experimentally verified by synthesizing metallic Co and Fe nanoparticles. The findings could be extended to other techniques such as thermal decomposition and alcohol reduction for the synthesis of noble metal-transition metal magnetic and catalytic nanoparticles with novel properties.

The formation process of Pt decorated Ni-Pt nanocubes was investigated by analysing the elemental distribution of Ni and Pt in the particles obtained from time-resolved in situ sampling during the synthesis in the oleylamine-1-heptanol system. The analysis confirmed the formation of Pt(core)-Ni(shell) nanoparticles at the initial stages of the reaction. However, as the reaction time progressed, the Pt atoms at the centre diffused outward and reached the corners and edges of the particle, whose shape changed from nearly spherical at the initial stages of the reaction to a perfect cube at the end of the reaction, forming a Ni rich cube (core)-Pt(cage). The cage obtained by dissolving the Ni rich cube was composed mainly of Pt and the Ni content in the frame was a mere 12%. The catalytic activity of the Pt cage was measured using cyclic voltammetry. The initial measurements suggested that the activity was comparable to some of the commercially available Pt catalysts.

Recently, the development of bimetallic nanoparticles with functional properties has been attempted extensively but with limited control over their morphological and structural properties. The reason was the inability to control the kinetics of the reduction reaction in most liquid-phase syntheses. However, the alcohol reduction technique has demonstrated the possibility of controlling the reduction reaction and facilitating the incorporation of other phenomena such as diffusion, etching, and galvanic replacement during nanostructure synthesis. In this study, the reduction potential of straight-chain alcohols has been investigated using molecular orbital calculations and experimentally verified by reducing transition metals. The alcohols with a longer chain exhibited higher reduction potential, and 1-octanol was found to be the strongest among alcohols considered. Furthermore, the experimental evaluation carried out via the synthesis of metallic Cu, Ni, and Co particles was consistent with the theoretical predictions. The reaction mechanism of metallic particle formation was also studied in detail in the Ni–1-octanol system, and the metal ions were confirmed to be reduced via the formation of nickel alkoxide. The results of this investigation were successfully implemented to synthesize Cu–Ni bimetallic nanostructures (core–shell, wire, and tube) via the incorporation of diffusion and etching besides the reduction reaction. These results suggest that the designed synthesis of a wide range of bimetallic nanostructures with more refined control has become possible.