Colloidal Copper Research Articles

Drop-on-Demand Direct Printing of Colloidal Copper Nanoparticles by Electrohydrodynamic Atomization

Electrohydrodynamic inkjet printing technology has recently become attractive in many industrial fabrication fields mainly due to its advantage of smaller drop generation as compared to the diameter of the delivery nozzle. In this article, drop-on-demand (DoD) printing of colloidal solution containing copper nanoparticles through electrohydrodynamic atomization (EHDA) is investigated. By applying a novel forward multistep waveform (FMSW) superimposed on dc biased voltage, charged fluid drops containing copper nanoparticles are deposited on glass substrate. The main focus of this study is to generate uniform droplets of conductive copper ink in a controlled fashion by varying amplitude and frequency of the applied waveform. The deposited patterns show a series of uniform-sized drops with regular spacing. Using this DoD printing technique, it is feasible to print a variety of patterns of dots and conductive continuous or discontinuous lines.

Supported Copper Catalysts Prepared from Colloidal Copper for the Water‐Gas Shift Reaction

Al2O3-supported copper nanoparticles prepared from cetyltrimethylammonium bromide (CTAB) capped copper nanoparticles are effective water-gas shift catalysts. High activity can be explained by the presence of well-dispersed Cu nanoparticles on the alumina support due to strong interaction between CTAB and the Cu nanoparticles. Detailed facts of importance to specialist readers are published as ”Supporting Information”. Such documents are peer-reviewed, but not copy-edited or typeset. They are made available as submitted by the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

The influence of solvents and surfactants on the preparation of copper nanoparticles by a chemical reduction method

A chemical reduction method for preparing colloidal copper nanoparticles in water and ethylene glycol (EG) is reported. The obtained copper nanoparticles were characterized by powder x-ray diffraction (XRD), transmission electron microscopy (TEM) and UV-visible spectrophotometry (UV-vis). Surface plasmon resonance peaks immediately after the synthesis appeared at 579 and 551 nm for the colloidal copper in water and EG, respectively. The stability of colloidal copper in EG was longer than that in water. The color of solution in water changed from light-red to black and the nanoparticles mostly precipitated after 22 days, which is attributed to the oxidation of copper nanoparticles in copper oxide (I), as was confirmed by optical absorption measurements. In EG, copper nanoparticles were red and stable even after 2 months. Ascorbic acid plays a role as antioxidant for colloidal copper, due to its ability to scavenge free radicals and reactive oxygen molecules. Polyvinyl pyrrolidone works both as size controller and polymeric capping agent because it hinders the nuclei from aggregation through the polar groups, which strongly absorb the copper particles on the surface with coordination bonds.

Solvent-Dependent Surface Plasmon Response and Oxidation of Copper Nanocrystals

We report the synthesis of monodisperse colloidal copper nanocrystals and subsequent solvent-dependent oxidation to form copper(I) oxide nanoparticles. The oxidation process was monitored by optical spectroscopy in the visible spectrum with the Cu nanocrystals exhibiting a surface plasmon feature that was replaced over time by an excitonic feature corresponding to the band gap of the Cu2O nanocrystals. The initial intensity of the copper plasmon was strongly dependent on the properties of the solvent used to form the nanocrystal dispersion; solvents with π-bonds significantly reduced (by >3-fold) the plasmon intensity and this effect was attributed to electron sharing between the solvent and the copper surface. The damped plasmon only recovered to its solvent-independent intensity once the nanocrystal surface oxidized and eliminated the solvent−Cu surface interactions. Solvents without π-bonds induced only a very small damping of the plasmon, and at longer time scales all solvents caused similar changes in the optical properties as oxidation converted the nanocrystals from metallic copper to semiconducting copper oxide.

Structure and IRR spectra of copper-exchanged soda-lime silica glass

Multi-component soda lime silica glass (SLSG) specimens, with composition from the miscibility gap in the SiO2-Na2O system, were investigated after the substitution of copper for sodium and after thermal treatment of the exchanged samples in gaseous hydrogen. The behaviour of the obtained composite materials was studied by infrared reflection spectroscopy (IRRS). Some optical absorption micro-spectrophotometry (OAMS) measurements and X-ray-diffraction (XRD) analyses complemented these investigations. It has been stated that after exchange in the CuCl molten bath, the dopant was present in the glassy matrix in the form of cuprous and cupric ions. The cuprous ions participate in the formation of semiconducting Cu2O nanoparticles. Hydrogenation of the exchanged specimens leads to the formation of metallic copper atoms which due to the van der Waals interactions precipitate in the form of colloidal copper nanoparticles. Changes of the matrix morphology are mainly related with the presence of cupric ions which behave as glass forming cations and such as these participate in the formation of mixed copper-sodium silicates. The effectiveness of these processes is substantially dependent on the exchange and hydrogenation parameters.

Copper Azide Confined Inside Templated Carbon Nanotubes

AbstractThe currently used primary explosives, such as lead azide and lead styphnate, present serious health hazards due to the toxicity of lead. There is a need to replace them with equally energetic but safer‐to‐handle and more environmentally friendly materials. Copper azide is more environmentally acceptable, but very sensitive and detonates easily from electrostatic charges during handling. If the highly sensitive copper azide is encapsulated within conducting containers, such as anodic aluminum oxide (AAO)‐templated carbon nanotubes (CNTs), its sensitivity can be tamed. This work describes a technique for confining energetic copper azide within CNTs. ∼5 nm colloidal copper oxide nanoparticles are synthesized and filled into the 200 nm diameter CNTs, produced by template synthesis. The Cu‐O inside the CNTs is reduced in hydrogen to copper, and reacted with hydrazoic acid gas to produce copper azide. Upon initiation, the 60 μm long straight, open‐ended CNTs guide decomposition gases along the tube channel without fracturing the nanotube walls. These novel materials have potential for applications as nano‐detonators and green primary explosives; they also offer new opportunities for understanding the physics of detonation at the nanoscale.

Effect of Nanosized Colloidal Copper on Cotton Fabric

This research deals with the synthesis of nanosized copper as colloidal solution and its application to cotton fabric. Copper nano colloids were prepared by chemical reduction of copper salt using sodium borohydride as reducing agent in presence of tri-sodium citrate. The size and size distribution of the particles were examined by particle size analyzer and the morphology of the synthesized particles was examined by SEM and AFM techniques. X-ray fluorescence spectroscopy detected the presence of copper in the treated fabric. The results of particle size analysis showed that the average particle size varied from 60 nm to 100 nm. The nano copper treated cotton was subjected to soil burial test for the assessment of its resistance towards microbial attack. SEM images of treated fabric indicate copper nano particles are well dispersed on the surface of the specimens. The treatments of nano copper colloidal solution on cotton not only improve its antimicrobial efficiency but also influenced the tensile strength of the fabric sample positively. The treatment was found to enhance the color depth and fastness properties of direct dyed cotton fabric samples.

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.

One-pot synthesis and self-assembly of colloidal copper(I) sulfide nanocrystals

A simple one-pot method is developed to prepare size- and shape-controlled copper(I) sulfide (Cu2S) nanocrystals by thermolysis of a mixed solution of copper acetylacetonate, dodecanethioland oleylamine at a relatively high temperature. The crystal structure, chemicalcomposition and morphology of the as-obtained products are characterized bypowder x-ray diffraction (PXRD), x-ray photoelectron spectroscopy (XPS),Auger electron spectroscopy (AES), transmission electron microscopy (TEM)and scanning electron microscopy (SEM). The morphology and size of theCu2S nanocrystals can be easily controlled by adjusting the reaction parameters. TheCu2S nanocrystals evolve from spherical to disk-like with increasing reaction temperature. The sphericalCu2S nanocrystals have a high tendency to self-assemble into close-packed superlattice structures. The shapeof the Cu2S nanodisks changes from cylinder to hexagonal prism with prolonged reaction time,accompanied by the diameter and thickness increasing. More interestingly, the nanodisksare inclined to self-assemble into face-to-face stacking chains with different lengths andorientations. This one-pot approach may extend to synthesis of other metal sulfidenanocrystals with different shapes and sizes.

Effect of Particle Size on Copper Oxychloride Transport through Saturated Sand Columns

Understanding the mechanisms behind the transport of particulate contaminants in porous media is crucial with a view to evaluating their potential impact on the environment. Much of the copper used in agriculture is sprayed as colloidal copper oxychloride, and despite its potential environmentally adverse consequences, colloidal transport of particulate formulations of copper remains poorly understood. In this work, transport of copper colloids from a commercial copper oxychloride based fungicide formulation was studied by measuring its breakthrough in saturated quartz sand columns. The influence of ionic strength and flow rate on the test results suggests that retention of copper oxychloride based colloids is governed by weak forces. The particle deposition dynamics of the studied copper formulation was consistent with a two-site kinetic attachment model. The proposed colloid retention mechanisms are highly sensitive to the fungicide particle size. A comparison of our test results with reported data for other copper oxychloride wettable powder fungicide formulations revealed that transport of copper oxychloride is strongly influenced by its particle size. This is consistent with the theory of Derjaguin, Landau, Verwey, and Overbeek (DLVO), but only if binding occurs at the secondary minimum in the potential, where attachment is less favorable with small particles. The influence of particle size is also consistent with the results of previous studies where deposition was ascribed to retention at a secondary minimum. The mobility of colloidal formulations of these copper-based fungicides in saturated porous media increases with increasing particle size.

A simple way of preparing high-concentration and high-purity nano copper colloid for conductive ink in inkjet printing technology

Copper nanoparticles in conductive ink are being given great attractive interest due to their growing application in printed electronics industry. In this study, copper nanoparticles used for conductive ink were synthesized using a relatively high-concentration (0.1 M), short reactive time (not more than 5 min) process which used double protective agents to obtain stable and homogeneous colloid. Cu nanoparticles had a diameter between 10–80 nm by varying the amount of CTAB, PVP, reducing agent or reaction temperature, separately. The nano copper colloid was purified through electrodialysis, avoiding centrifugation and re-dispersion process in order to prevent oxidation and agglomeration. Transmission electron microscopy (TEM) images revealed the size and distribution of the synthesized nanoparticles, the X-ray analysis confirmed the formation of metallic copper and the element analysis suggested the high rate of purity of the Cu nanoparticles colloid.

Poly(allylamine)-Stabilized Colloidal Copper Nanoparticles: Synthesis, Morphology, and Their Surface-Enhanced Raman Scattering Properties

Poly(allylamine)-stabilized spherical- and rod-shaped copper nanoparticles are synthesized by a simple chemical reaction. The synthesis is performed by the reduction of copper(II) salt with hydrazine in aqueous solution under atmospheric air in the presence of poly(allylamine) (PAAm) capping agent. Noteworthy of the advantages of the synthetic method includes its production of water dispersible copper nanoparticles at room temperature under no inert atmosphere, making the synthesis more environmentally friendly. The resulting copper nanoparticles are investigated by UV-vis spectroscopy and transmission electron microscopy (TEM). The results demonstrate that the amount of NaOH used is important for the formation of the copper nanoparticles while the reaction time and concentration of PAAm play key roles in controlling the size and shape of the nanoparticles, respectively. The resulting colloidal copper nanoparticles exhibit large surface-enhanced Raman scattering (SERS) signals.

Anisotropic Shape Evolution of Large-Size Cu Nanocrystals Prepared in Nonionic Microemulsion Media

We report the anisotropic shape evolution of colloidal copper nanocrystals (Cu NCs) in nonionic microemulsion media by adopting tetraethylammonium hydroxide as a reactant and capping agent in water phase. Relatively large-size Cu NCs were synthesized to confine the growth of Cu NCs below 100 nm. TEM images showed the triangular and hexagonal morphologies of Cu NCs ranging over 55-70 nm after 28 h, while they showed the spherical NCs dominantly under higher concentration of a reducing agent. The surface plasmon resonance (SPR) absorption band of anisotropic Cu NCs was centered at 571 nm with signal enhancement over time. The formation kinetics revealed that the gradual conversion of the Cu seeds into larger NCs during 28 h at room temperature. The NCs were characterized to be Cu rather than CuO or Cu2O by electron diffraction patterns, exhibiting relevant d-spacing figures consistent with the bulk Cu crystal.

Photochemical synthesis of copper nanoparticles in aqueous polystyrene dispersions

Photochemical deposition of copper nanoparticles onto polystyrene surface under monochromatic (λ 254 nm) and unfiltered irradiation was studied. The kinetic parameters of this process depending on the concentration of copper(II) coordination compound and the size of polystyrene microspheres were determined. A procedure was tested for the preparation of monodisperse copper nanoparticles from colloidal copper chemically synthesized in ethylene glycol matrix in the presence of polystyrene with a microsphere size of 100 nm.

Transmission electron microscopy characterization of colloidal copper nanoparticles and their chemical reactivity

A colloidal synthesis method was developed to produce face centered cubic (fcc) Cu nanoparticles in the presence of surfactants in an organic solvent under an Ar environment. Various synthetic conditions were explored to control the size of the as-prepared nanoparticles by changing the precursor, varying the amount of surfactants, and tuning the reaction temperature. Transmission electron microscopy (TEM), selected-area electron diffraction, and high-resolution TEM were used as the main characterization tools. Upon exposure to air, these nanoparticles are oxidized at different levels depending on their sizes: (1) an inhomogeneous layer of fcc Cu(2)O forms at the surface of Cu nanoparticles (about 30 nm); (2) Cu nanoparticles (about 5 nm) are immediately oxidized into fcc Cu(2)O nanoparticles (about 6 nm). The occurrence of these different levels of oxidization demonstrates the reactive nature of Cu nanoparticles and the effect of size on their reactivity. Furthermore, utilization of their chemical reactivity and conversion of spherical Cu nanoparticles into CuS nanoplates through the nanoscale Kirkendall effect were demonstrated. The oxidization and sulfidation of Cu nanoparticles were compared. Different diffusion and growth behaviors were involved in these two chemical transformations, resulting in the formation of isotropic Cu(2)O nanoparticles during oxidization and anisotropic CuS nanoplates during sulfidation.

Colloidal copper and peculiarities of its reaction with silver ions in aqueous solution

Interactions between colloidal copper and silver ions lead to the formation of silver nanoparticles. The reaction proceeds through the intermediate stage of the formation of a copper-silver contact pair. The formation of bimetallic AgcoreCushell nanoparticles is observed in the presence of the “seeding” silver nanoparticles and upon the simultaneous radiochemical reduction of Ag+ and Cu2+ ions.

Contaminant mobilization by metallic copper and metal sulphide colloids in flooded soil

Colloids, such as submicrometre mineral particles or bacterial cells, can act as carriers enhancing the mobility of poorly soluble contaminants in subsurface environments. Spectroscopic and microscopic analysis of flooded soils suggests that copper colloids and metal sulphide colloids increase the concentration of contaminants in waterlogged soils.

Synthesis and Characterization of Monodispersed Copper Colloids in Polar Solvents

A chemical reduction method for preparing monodispersed pure-phase copper colloids in water and ethylene glycol has been reported. Owing to the reduction property of ethylene glycol, the reaction rate in ethylene glycol is higher than that in water. In addition, the amount of reducing agent can be reduced largely. Ascorbic acid plays roles as reducing agent and antioxidant of colloidal copper, due to its ability to scavenge free radicals and reactive oxygen molecules. Thermogravimetric results reveal that the as-prepared copper nanoparticles have good stability, and they begin to be oxidized at above 210 °C. Polyvinyl pyrrolidone works both as size controller and polymeric capping agents, because it hinders the nuclei from aggregation through the polar groups, which strongly absorb the copper particles on the surface with coordination bonds.

Detachment of sprayed colloidal copper oxychloride–metalaxyl fungicides by a shallow water flow

Flow shear stress induced by rainfall promotes the loss of the pesticides sprayed on crops. Some of the factors influencing the losses of colloidal-size particulate fungicides are quantified by using a rotating shear system model. With this device it was possible to analyse the flow shear influencing washoff of a commercial fungicide formulation based on a copper oxychloride-metalaxyl mixture that was sprayed on a polypropylene surface. A factor plan with four variables, i.e. water speed and volume (both variables determining flow boundary stress in the shear device), formulation dosage and drying temperature, was set up to monitor colloid detachment. This experimental design, together with sorption experiments of metalaxyl on copper oxychloride, and the study of the dynamics of metalaxyl and copper oxychloride washoff, made it possible to prove that metalaxyl washoff from a polypropylene surface is controlled by transport in solution, whereas that of copper oxychloride occurs by particle detachment and transport of particles. Average losses for metalaxyl and copper oxychloride were, respectively, 29 and 50% of the quantity applied at the usual recommended dosage for crops. The key factors affecting losses were flow shear and the applied dosage. Empirical models using these factors provided good estimates of the percentage of fungicide loss. From the factor analysis, the main mechanism for metalaxyl loss induced by a shallow water flow is solubilisation, whereas copper loss is controlled by erosion of copper oxychloride particles.

The formation of colloidal copper nanoparticles stabilized by zinc stearate: one-pot single-step synthesis and characterization of the core–shell particles

A highly efficient one-step process to generate Cu-Zn colloids was developed, in which the colloidal particles were synthesized from Cu and Zn stearates by reduction with H(2) in a continuously operated stirred tank reactor. The resulting spherical, well separated particles have a size of 5-10 nm, consisting of a crystalline Cu(0) core (fcc) stabilized by a Zn stearate shell without long-range order. In situ attenuated total reflection FTIR spectroscopy was used to monitor the shift of the C-O stretching vibration of adsorbed CO as a function of temperature and pressure. The absence of the CO rotation-vibration bands of dissolved CO allowed us to obtain FTIR spectra at a CO pressure of 1.0 MPa at 473 K resulting in three shifted CO bands at 2030-2025, 1979-1978, and 1920 cm(-1). These bands indicate the presence of reduced coadsorbed Zn species on the metallic Cu surface. Cyclic CO adsorption experiments demonstrated the dynamics of the interaction between the Cu core and the Zn stearate shell.