Jhon L. Cuya Huaman

Copper nanoparticles synthesized by hydroxyl ion assisted alcohol reduction for conducting ink

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 Cu2O). 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 µΩ cm, respectively.

Size-controlled monodispersed nickel nanocrystals using 2-octanol as reducing agent

Size-controlled nickel nanocrystals have been successfully synthesized using 2-octanol as the reducing agent. The elucidation of the reduction mechanism of nickel ions by 2-octanol was monitored by using UV-vis spectrometry, FT-IR spectrometry, X-ray diffractometry and transmission electron microscopy and the formation of intermediate layered hydroxides that subsequently undergoes reduction to metallic nickel was identified. Although, the nickel particles obtained in the 2-octanol–Ni acetate system were irregularly shaped with size in the sub-micrometer range, the addition of surfactants, hydroxyl ions and metal seed particles to the alcoholic system facilitated the synthesis of nanocrystals with controlled size and size distribution. The optimization of the synthesis conditions based on the above analytical data led to the preparation of a toluene-based suspension dispersing Ni nanoparticles with an average particle size of about 16 nm.

Novel standing Ni–Pt alloy nanocubes

The synthesis of novel cubic shaped-standing Ni–Pt alloy nanoparticles is reported. Incorporation of a few percent of Pt atoms in the presence of chloride ions and oleylamine, which helps to control the growth and prevents agglomeration, facilitates the formation of highly monodispersed cubic shaped particles. Furthermore, these cubic-shaped particles stand on their corners, which is believed to be due to the magnetic interaction between particles whose easy axis is in the [111] direction. The formation of these unique shaped particles with different sizes has been realized by using platinum particles as seeds. It should be noted that these particles are highly reproducible and holds great potential for catalytic applications.

Dissolution and reduction of cobalt ions in the polyol process using ethylene glycol: identification of the active species and its role

The polyol process has been used to synthesize metal and alloy nanoparticles over decades. However, though the role of polyol has been identified as a reducing agent, the details have not been clarified fully. In this manuscript, determination of the active polyol species and its role in the synthesis of metal nanoparticles has been attempted both experimentally and theoretically using ethylene glycol (EG) as the medium and cobalt as the metal source. Molecular orbital calculations carried out considering dianion, monoanion and neutral states of ethylene glycol species suggested that the monoanion state of ethylene glycol is the most active form. Subsequently, this was verified experimentally using different types of cobalt salts in ethylene glycol. The cobalt salts that could dissociate easily and the deprotonation of ethylene glycol by its counter anion were vital for the progression of the dissolution and reduction reaction of cobalt ions to form cobalt metal particles. Furthermore, the acceleration of the dissolution and reduction reaction by the addition of hydroxyl ions also confirmed the deprotonation reaction of ethylene glycol. In conclusion, the experimental and theoretical studies have proved that the monoanion of ethylene glycol is the active species that not only assumes a role in the reduction of metal, but also plays an important role in the dissolution and formation of the intermediate metallic complex, which is vital for their subsequent reduction reaction.

Towards a designed synthesis of metallic nanoparticles in polyols – elucidation of the redox scheme in a cobalt–ethylene glycol system

The polyol process has been used to synthesize metal and alloy nanoparticles over a couple of decades. Its potential has been demonstrated through the synthesis of metallic nanoparticles with various sizes and shapes. However, although one of the roles of polyol is to act as a reducing agent, research studies related to the investigation of the redox reaction mechanism have been scarce. In this study, we report the results of a detailed study undertaken to investigate the polyol oxidation and metal reduction for the cobalt(II)–ethylene glycol system with the possible addition of a base (Na) to the system using several physico-chemical techniques such as NMR, FT-IR, ESI-TOFMS and XRD. The results suggested that in the reduction reaction, ethylene glycol first reacts with the base to produce the ethylene glycol monoanion, hereinafter denoted as EG−. This reaction not only occurs between ethylene glycol and the base, but also occurs with Co2+ species. In such a case, the formation of Co alkoxide and the subsequent reduction could progress even in the presence of a weak base such as acetate ion or any other solvent that has a lone pair of electrons such as oxygen in ether. On the other hand, in the case of oxidation of ethylene glycol, first the base attacks one of the two α-protons in Co alkoxide and along with the electron transfer to Co2+, ethylene glycol gets oxidized to aldehyde. Then, the aldehyde thus formed undergoes bond exchange with the neighboring coordinated ethylene glycol and an ester is formed. The above steps are repeated and the hydrogen atoms coordinated with Co get detached with the evolution of hydrogen gas, while ethylene glycol is oxidized to polyglycolic acid. The analytical techniques and the results obtained in this study could be used to enhance the properties of metals and alloy nanoparticles synthesized using the polyol process.

Large-scale synthesis of ITO nanoparticles in an alcohol system assisted by acids

Co-precipitation of indium and tin salts in aqueous media followed by heat treatment of the products provides a versatile route to obtain tin-doped indium oxide (ITO) nanopowders in large quantities. However, the high temperature treatment that is needed to obtain well-crystallized powders provokes particle growth through sintering and leads to poor dispersibility. In this study, ITO nanoparticles (NPs) were obtained by dehydration of the (In, Sn) hydroxide precursor and subsequent crystallization of the same in acidified 2-octanol solution under atmospheric conditions and at low reaction temperature, 180 °C. This process yields grams of well-dispersed ITO nanoparticles with an average size of ∼5 nm and a tin content of ∼10%. In addition, pellets made of ITO nanoparticles and annealed at 200 °C under vacuum exhibited a conductivity of 1.3 Ω cm.

Synthesis of crystalline Cu2O nanoparticles using long chained alcohol

The successful synthesis of highly crystallized cuprous oxide nanoparticles using long chained alcohol reduction method is reported. The purity of copper oxide obtained by this method greatly depends on the synthesis conditions such as reaction temperature, reaction duration, and hydroxyl ion concentration that assist the reduction kinetics. By optimizing the above parameters, cubic cuprous oxide with particle sizes controllable in the range of 10–30 nm were synthesized. The x-ray diffraction analysis confirmed the single-phased nature of Cu2O crystal. Furthermore, the ratio between copper and oxygen atoms in the product was determined to be 1.96 using the Rietveld analysis and confirmed the purity of Cu2O nanoparticles. In addition, I–V characteristics suggested that the nanoparticles function as semiconductor and indicated the use of these cuprous nanocrystals as a functional material for the preparation of solar devices.

In situ spectroscopic studies of the one-pot synthesis of composition-controlled Cu–Ni nanowires with enhanced catalytic activity

Here, an alcohol reduction method for preparing composition controlled Cu–Ni nanowires (NWs) in high yields is proposed through the selection of an appropriate combination of metallic precursors, alcohol type and surfactant. Also, the mechanism of NW formation was elucidated using morphological, structural and in situ UV-visible and X-ray absorption spectroscopic measurements. In the initial stages of the reaction, the metallic precursors coordinated with amine groups to form complexes. When the temperature of the reactants was increased, Ni formed hydroxide structures such as layered Ni(OH)2, while Cu was partially reduced to Cu+ and coordinated with Cl− ions. At higher temperatures, the Ni2+ ions were reduced to metallic Ni before the formation of metallic Cu. Subsequently, the metallic Ni seeds donated electrons to Cu+ through a galvanic reaction forming Cu seeds. Then, the unidirectional growth progressed due to the etching of the Cu seeds by the chloride ions and the preferential adsorption of the capping agent on the [100] planes of Cu. After the consumption of the Cu ions to form metallic Cu NWs, the Ni ions that remained in the solution were reduced and deposited on the Cu NW surface. The average diameter and length of the Ni-coated Cu NWs were 70 nm and 30 μm, respectively and the composition of Ni varied between 2 and 80 wt%. The catalytic activity of the Cu–Ni NWs was studied through the decoloration reaction of methylene blue, and nanowires with 58 wt% Ni were the most active. These results could be ascribed to the efficient interaction between the Cu core and the Ni sheath.

Large-Scale Cu Nanowire Synthesis by PVP-Ethylene Glycol Route

Cu nanowire (NW) is a promising cost-benefit conducting material that could be considered for the development of transparent conducting films (TCF). However, the development of Cu NW as an alternating material for Ag or Au is not only limited by its stability in atmospheric conditions in the nanometer range but also due to the nonavailability of a simple synthetic route to produce them in high yields and in large-scale. Here, a scheme to synthesize Cu NWs by reducing Cu nitrate in a Cl− ion-polyvinylpyrrolidine- (PVP-) ethylene glycol (EG) system is proposed. Cu NWs with average diameter around 60 nm and average length of about 40 μm was obtained under optimized experimental conditions. Furthermore, the formation of Cu NW was elucidated to be through the progression of the following sequential reduction steps: at first, Cu ions underwent partial reduction to form spherical Cu2O. Then, the spherical Cu2O particles were redissolved and reduced to metallic Cu0 atoms that subsequently formed the Cu seeds. Thereafter, Cu seeds underwent etching to form multiply-twinned particles (MTP). Finally, these Cu MTP grew unidirectionally to form metallic Cu NWs.

Design of monoalcohol – Copolymer system for high quality silver nanowires

Research to improve the dimensional properties of silver nanowires (Ag NWs) for transparent conductive film (TCF) applications are being carried out intensively. However, the protocol for the designed synthesis of high-quality Ag NWs is yet to be developed due to the inadequacy of knowledge on the role of parameters. Here, we attempt to elucidate the role played by the parameters and propose a monoalcohol-copolymer based system for the designed synthesis of Ag NWs superior in quality to the one synthesized using conventional ethylene glycol (EG)-polyvinylpyrrolidone (PVP) system. The key findings of the study are as follows: (1) the solubility of Ag source and the partially formed AgCl particles in monoalcohols was found to play an important role not only in the reduction to metallic Ag but also on the uniaxial growth, (2) the adsorption of capping agents on Ag NWs was carried through O and N atoms in the base molecule and their binding energies indicated that the strength is the key parameter to obtain Ag NWs with high aspect ratio, (3) the properties of nanowire could be enhanced through copolymerization of VP and base molecules that have O- and N-based ligands, and (4) the influence of copolymerization on the physical and chemical properties of the surface active agent has been theoretically and experimentally verified. Consequently, we succeeded in the development of a new technique to synthesize high yield of Ag NWs with improved aspect ratio than EG-PVP system by using benzyl alcohol as reducing solvent and N-vinylpyrrolidone/N,N-diethylaminoethyl metacrylate copolymer as a capping agent. The optical transmittance and electrical resistivity of TCFs prepared using the Ag NWs with an average diameter of 43 nm, and an average length of 13 μm were 98.6% and R: 49.1 Ω/□, respectively.