Spherical Copper Nanoparticles Research Articles

Silica SBA-15 Template Assisted Synthesis of Ultrasmall and Homogeneously Sized Copper Nanoparticles

The synthesis of spherical copper nanoparticles with extremely narrow size distribution by electroless copper deposition on mesoporous silica support is described. The materials were characterized by nitrogen sorption, transmission electron microscopy, x-ray diffractometry and Fourier transform infrared spectroscopy. The copper nanoparticles have a cubic crystalline structure and an average particle size of 5.5 +/- 0.8 nm. The copper nanoparticles are stable, without detectable oxidation or further agglomeration under ambient conditions even after months. These results demonstrate that electroless copper reduction can be conducted and constrained within the mesoporous silica framework, which pave the way for engineered mesoreactors.

Synthesis and Ultrasonic Characterization of Cu/PVP Nanoparticles-Polymer Suspensions

A polymer colloidal solution having dispersed nanoparticles of Cu metal has been developed using a novel chemical method. Colloidal solutions of representative concentrations of 0.2 to 2.0 wt% Cu-nanoparticles con-tents in the primary solutions were prepared to study the modified ultrasonic attenuation and ultrasonic velocity in polyvinyl alcohol (PVP) polymer molecules on incorporating the Cu-nanoparticles. The synthesized copper metal nanoparticles dispersed in the polymer solutions were characterized by UV-Visible absorption spectros-copy, X-ray diffraction (XRD) and Transmission electron microscopy (TEM). The nanofluid sample showed a symmetrical peak at 592 nm due to the surface plasmon resonance of the copper nanoparticles. XRD results confirmed that copper nanoparticles were crystalline in the colloidal solution. The TEM micrograph revealed spherical copper nanoparticles having diameter in the range 10 - 40 nm. A characteristic behaviour of the ultra-sonic velocity and the attenuation are observed at the particular temperature/particle concentration. It reveals that the colloidal suspension occurs in divided groups in the small micelles. The results are discussed in correlation with the thermophysical properties predicting the enhanced thermal conductivity of the samples.

Copper Nanofluids: Synthesis and Thermal Conductivity

A novel one-step chemical reduction method is developed to fabricate nanofluids with very tiny spherical copper nanoparticles. Their chemical and colloidal stability is studied by adjusting their pH value with citric acid. Their thermal conductivity is also measured by the transient hot-wire method. The particle size can be varied from 6.4 nm to 2.9 nm by changing the surfactant concentration. The thermal conductivity data show the existence of a critical particle size below which the nanoparticles cannot significantly enhance fluid conductivity due to the particle conductivity reduction and the solid-liquid interfacial thermal resistance increase as the particle size decreases. By considering these two factors, we have also made some theoretical analysis to find the possible critical particle size.

Molecular dynamics simulation on flow behavior of nanofluids between flat plates under shear flow condition

Molecular dynamic model of nanofluid between flat plates under shear flow conditions was built. The nanofluid model consisted of 12 spherical copper nanoparticles with each particle diameter of 4 nm and argon atoms as base liquid. The Lennard–Jones (LJ) potential function was adopted to deal with the interactions between atoms. Thus, the motion states of nanoparticles during the process of flowing were obtained and the flow behaviors of nanofluid between flat plates at different moments could be analyzed. The simulation results showed that an absorption layer of argon atoms existed surrounding each nanoparticle and would accompany with the particle to move. The absorption layer contributed little to the flow of nanoparticles but much to the heat transferring in nanofluids. Another phenomenon observed during shear flowing process was that the nanoparticles would vibrate and rotate besides main flowing with liquid argon and these micro-motions could strengthen partial flowing in nanofluids.

Photo- and radiation-induced preparation of nanocrystalline copper and cuprous oxide catalysts

Spherical copper nanoparticles have been prepared by photo- or radiation-induced reduction of aqueous solutions containing 10−3 mol.dm−3 copper sulphate or formate, 1.3 mol.dm−3 propan-2-ol and polyvinyl alcohol as a stabilizer. Increase of initial copper concentration to 10−2 mol.dm−3 resulted in formation of different reaction product—octahedral cuprous oxide nanoparticles. Solutions were irradiated by means of electron beam, 60Co γ rays (dose rate 70 Gy.h−1) or by 400 W medium-pressure mercury lamp and were characterised by UV-Vis spectrophotometry, X-Ray Powder Diffraction, TEM and SEM. Pink to violet colour of colloidal copper solutions corresponded to measured copper surface plasmon band at circa 580 nm and has been found to be very sensitive to oxygen, which causes dissolution of particles. Therefore, the influence of purging by nitrogen gas prior to irradiation was thoroughly examined and has been found to only hinder, not alter irradiation effects. Moreover, the evolution of absorption spectrum of colloidal copper solution in contact with air has been measured, revealing interesting non-monotonous dependence on the air exposure time, probably caused by formation of protective oxide layer. Catalytic activity of prepared cuprous oxide has been measured by catalytic decomposition of hydrogen peroxide and has been found to be higher or comparable to commercial cuprous oxide.

Conditions for the formation of copper nanoparticles by reduction of copper(II) ions with hydrazine hydrate solutions

Optimal conditions were found for the preparation of copper nanoparticles in aqueous solution via reduction of copper(II) ions with hydrazine hydrate. The effects of ligand environment of copper(II) in the initial solution (hydrate, ammonia, citrate, and glycine complexes), concentration, pH, surfactants, temperature, and mode of heating were examined. The obtained colloidal systems were studied by optical spectroscopy, X-ray photoelectron spectroscopy, X-ray powder diffraction, and atomic force microscopy. The examined colloids were found to contain generally spherical copper nanoparticles with a diameter of about 10 nm, which were coated with a copper(I) or copper(II) oxide and hydroxide film.

Metallic Copper Nanostructures Synthesized by a Facile Hydrothermal Method

A facile hydrothermal route has been developed for the synthesis of nearly spherical copper nanoparticles, copper nanocubes and ribbon-like network nanostructures. The as-prepared copper nanostructures were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution TEM (HRTEM), and UV-vis spectrum analysis. These copper products were fabricated in the presence of surfactant sodium dodecyl benzenesulfonate (SDBS) acting not only as stabilizer but also as size and shape controller via hydrothermal reduction process. HRTEM revealed that the surface of the copper nanostructures was packed with a thin layer of impurities such as oxide combined surfactant or amorphous surfactant. The influence of surfactant concentration and temperature on the resultant copper nanostructures was investigated in details. UV-vis spectra indicated that strong red shift existed for the copper ribbon-like network nanostructures due to the novel morphology as well as the presence of impurities on the surface.

Copper electrocrystallization on titanium electrodes: Controlled growth of copper nuclei using a potential step technique

Copper nanoparticles were synthesized using a pulsed sonoelectrochemical (20 kHz, 78 Wcm−2) method. Two electrolytes used were a copper salt dissolved in Na2SO4 (pH=3.80) or H2SO4 (pH=0.6). For both electrolytes and in the absence of any surfactant, monodispersed spherical copper nanoparticles were strongly aggregated in three-dimensional clusters of about 200nm. The particle size is controlled by varying reaction parameters such as duration of the experiment, current density, temperature and ultrasound power. A potential step technique is proposed to synthesize copper nanoparticules. Under potentiostatic conditions the aim is to control and decrease the nanoparticle size and reduce production costs by avoiding gas evolution and other adverse reactions.

Controlled synthesis of copper nano/microstructures using ascorbic acid in aqueous CTAB solution

This paper describes a low-temperature green chemical synthesis of various morphologies of copper nano/microstructures. These syntheses achieved high yields in aqueous solution using ascorbic acid as a reductant and the cationic surfactant cetyltrimethylammonium bromide (CTAB) as a capping agent. The resulting copper particles were characterised by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), and UV–Vis. absorption spectroscopy techniques. From the SEM analysis, it was found that different morphologies of copper particles, including submicron polyhedrons, micrometer rods, spherical nanoparticles, and nanowires were obtained by varying factors such as the molar ratio of reactants (ascorbic acid and CuSO 4·5H 2O), pH, reaction time, and temperature. Increasing the molar ratio of ascorbic acid to precursor salt and increasing the pH led to a decrease in the size of copper particles formed. At short reaction times, spherical copper nanoparticles with an average diameter of 90 nm are obtained. When the reaction time was prolonged, the nanoparticles transformed into nanowires with diameters in the range of 100–250 nm, and lengths of up to 6–8 μm. When the reaction temperature was decreased, Cu mixed with Cu 2O particles were obtained instead of Cu particles. The resultant copper particles were confirmed by EDX and XRD to be pure Cu, with face-centred cubic (fcc) structures.

PVP-Stabilized Copper Nanoparticles: A Reusable Catalyst for “Click” Reaction between Terminal Alkynes and Azides in Nonaqueous Solvents

Highly stable poly(N-vinyl-2-pyrrolidone) (PVP) protected copper nanoparticles were prepared using a simple chemical reduction route in different solvents {N, N-dimethyl formamide (DMF) and formamide (FA)} under aerated condition. The particles were characterized using TEM, SEM, XRD, and UV−visible spectroscopic techniques. Copper nanostructures of varying shapes and sizes were obtained using hydrazine hydrate as the reducing agent in both DMF and FA. However, reducing by ascorbic acid in FA leads to formation of mostly spherical copper nanoparticles with a narrow size distribution. The Cu nanoparticles serve as effective catalyst for 1,3-dipolar cycloaddition reactions between terminal alkynes and azides to synthesize 1,2,3-triazoles in excellent yields under mild reaction conditions. The nanocatalysts can be recycled and reused several times without significant loss of their catalytic activity.

Synthesis and size control of monodisperse copper nanoparticles by polyol method

We describe herein the synthesis of metallic copper nanoparticles in the presence of poly(vinylpyrrolidone), employed as a protecting agent, via a polyol method in ambient atmosphere. The obtained copper particles were confirmed by XRD to be crystalline copper with a face-centered cubic (fcc) structure. We observed monodisperse spherical copper nanoparticles with a diameter range 45 ± 8 nm . The particle size and its distribution are controlled by varying the synthesis parameters such as the reducing agent concentration, reaction temperature, and precursor injection rate. The precursor injection rate plays an important role in controlling the size of the copper nanoparticles. On the basis of XPS and HRTEM results, we demonstrate that the surface of the copper is surrounded by amorphous CuO and that poly(vinylpyrrolidone) is chemisorbed on the copper surface.

Size-dependent melting of spherical copper nanoparticles embedded in a silica matrix

We report size-dependent melting of spherical copper nanoparticles embedded in a silica matrix. Based on the temperature dependence of the surface-plasmon resonance energy and its width, we observe two distinct melting regimes. For particles smaller than $20\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$, the absorption spectrum changes monotonically with the temperature, and this allows us to assume the gradual solid-liquid phase transition (melting) of the nanoparticles or the existence of superheated solid nanoparticles. In contrast, for nanoparticles larger than $20\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$, we observe a jumplike increase of the bandwidth and a nonmonotonic shift of surface-plasmon band with the increase of temperature below the bulk melting point. This indicates that the melting of large nanoparticles is a first-order phase transition similar to the melting of bulk copper.

Influence of annealing conditions on size and optical properties of copper nanoparticles embedded in silica matrix

Copper nanoparticles have been grown in silica matrix by annealing of the sol–gel prepared porous matrix impregnated with the copper nitrate. The annealing has been performed in air, successively in air and hydrogen, and in hydrogen. An annealing in air results in copper oxide nanoparticles (Cu 2O) growth as well. Transmission electron microscopy proves the formation of the spherical copper nanoparticles in size range of 2–65 nm depending on annealing conditions. Optical spectroscopy of the copper nanoparticles has been performed. The surface plasmon peak has been observed clearly in absorption spectra of Cu nanoparticles. Surface plasmon peak in absorption spectra of Cu nanoparticles demonstrates slight blue shift with decrease of the particle size. The bandwidth of the surface plasmon peak decreases appreciably at the lowering of temperature from 293 K to 77 and 4.2 K that is due to strong electron–phonon interaction. The low-frequency Raman scattering data are in agreement with electron microscopy and absorption data. Photoluminescence from the copper nanoparticles has been observed. Efficiency of the luminescence increases appreciably at the decrease of particle size. The observed increase is explained by the coupling of the excited incoming and outgoing emitted photons with surface plasmon.

Synthesis, characterization and catalytic activity of metal nanoparticles in the selective oxidation of olefins in the gas phase

Shape controlled metal nanoparticles were studied in the epoxidation of olefins. PVP mediated polyol processes were employed to generate silver nanowires/rods, nanocubes and nanopolyhedra. Spherical copper nanoparticles were also obtained by the polyol process. The mean diameter of the silver nanoparticles was around 150 nm. Furthermore, Cu nanoparticles were synthesized in an ethanol solution using CTAB as surfactant and as reducing agent. Additionally Au nanoparticles were synthesized by a phase-transfer system irradiated with 254 nm UV light. The mean diameter of these Au and Cu nanoparticles was around 10 nm. The catalytic activity of these nanoparticles on several supports such as α-Al2O3, CaCO3 and spherical particles of TiO2 obtained by the Stöber method was investigated in the epoxidation of a no-allylic olefin such as styrene, as well as for an allylic olefin, such as propene, using molecular oxygen and N2O as oxidants. The effect of Cs promotion in the styrene epoxidation was also investigated. The type of metal, the particle size, the support and the oxidant, as well as the addition of promoters such as Cs, showed a strong influence towards the formation of selective oxidation products. The metal nanoparticles were characterized employing various techniques such as X-ray diffraction (XRD), temperature programmed reduction (TPR), UV-visible spectroscopy, transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and ICP-AES.

Pulsed Sonoelectrochemical Synthesis of Size-Controlled Copper Nanoparticles Stabilized by Poly(N-vinylpyrrolidone)

A novel sonoelectrochemical method for the size-controlled synthesis of spherical copper nanoparticles in an aqueous phase was developed. In this study, poly(N-vinylpyrrolidone) (PVP) was used as the stabilizer for the copper clusters. The copper nanoparticles were characterized by XRD, UV-vis, IR, DLS, TEM, and HRTEM. The PVP was found to greatly promote the formation rate of copper particles and to significantly reduce the copper deposition rate, thereby making monodispersed copper nanoparticles. We could control the particle size by adjusting various parameters such as current density, deposition, temperature, and sonic power, and improve the homogeneity of the copper particles. The results also showed that the transfer rate of PVP-stabilized copper clusters from the cathodic vicinity to the bulk solution played an important role in the preparation of the monodispersed nanoparticles.

Synthesis of oleate capped Cu nanoparticles by thermal decomposition

A method has been introduced to produce monodispersed copper nanoparticle using thermal decomposition of Cu-oleate complex, which was prepared by the reaction of CuCl 2 with sodium oleate in water solution. Sodium oleate acts as a stabilizer of the Cu nanoparticles and protector of oxidation of Cu nanoparticles in various concentrations. We also found that no extra inert gases for protecting the oxidation of Cu nanoparticles were necessary. By TGA measurement, thermal decompositions of Cu-oleate complexes were observed. TEM data show that at 0.05 M oleate concentration, spherical copper nanoparticles are prepared, but at high concentration (0.3 M), large lumps are formed. This method can be easily increased scale up for industrial purpose. We confirm that these nanoparticles are very pure copper.

A method for the synthesis of spherical copper nanoparticles in the organic phase

In this paper, stable metallic copper nanoparticles protected by bis(ethylhexyl)hydrogen phosphate (HDEHP) were prepared in the organic phase. In the synthesis of copper nanoparticles, the bis(ethylhexyl)hydrogen phosphate (HDEHP) acted as both a phase-transfer agent and a particle protector. It was also found that the protective ability of HDEHP was different with different diluent polarities. Despite zero valent Cu initially forming in all the solvents studied, it has been found that the zero valent Cu can easily transform into oxides in those solvents with high dipole moments under ambient conditions. Only in those nonpolar solvents, the metallic copper nanoparticles are stable in air. In addition, theoretical analyses were made in order to interpret the interaction mode between the copper nanoparticles and the surfactant HDEHP.

Synthesis and Characterization of Copper-Doped Carbon Aerogels

We have prepared carbon aerogels (CAs) doped with copper through sol−gel polymerization of formaldehyde with the potassium salt of 2,4-dihydroxybenzoic acid, followed by ion exchange with Cu(NO3)2, supercritical drying with liquid CO2, and carbonization at 1050 °C under a N2 atmosphere. The materials were characterized by elemental analysis, nitrogen adsorption, high-resolution transmission electron microscopy, and X-ray diffraction. Results obtained indicate that this approach is an effective method for controlling both the amount and the distribution of a desired metal species within the carbon framework. We also found that carbonization of the copper-doped organic aerogels results in the formation of spherical copper nanoparticles within the carbon framework of the aerogel. The copper nanoparticles have a cubic crystalline structure and range in size from 10 to 50 nm. The Cu-doped CAs retain the overall open cell structure of metal-free CAs, exhibiting high surface areas and pore diameters in the micro- and mesoporic region.

Ozone plus radiation on aqueous solution of DNA—A suggestion for treatment of waste water

A series of copper(II) azo complexes having the formula [CuL1–4(nH2O)]·OAc·xH2O where (n = 1–2) and (x = 0–1) have been synthesized using azo dyes containing the triazol and thiadiazole moieties. The azodyes and their metal complexes were characterized by elemental analysis, molar conductance, IR, electronic, mass, ESR spectra, magnetic moment measurements, and thermal analyses. IR spectra showed that the ligands having triazole moiety were coordinated with the copper(II) ion in a tridentate manner with ONN donor sites of the naphthyl OH, N-atoms of azo group, and triazole moiety while azodyes having thiadiazole moiety were coordinated with the copper(II) ion in a bidentate manner with ON donor sites of the naphthyl OH and the N-atom of the group. The thermodynamic activation parameters such as ΔE*, ΔH*, ΔS*, and ΔG* were calculated from the TG curves. Prepared spherical copper nanoparticles were characterized using UV–Vis spectroscopy and transition electron microscope (TEM). The spectral data showed the formation of surface complex between azo-dye ligands and colloidal copper nanoparticles through (OH) anchoring group. The stability constant of the prepared copper nanoparticles complexes is higher compared with the corresponding bulk ones due to the larger surface area of copper nanoparticles.