Understanding droplet bridging in ionic liquid-based Pickering emulsions

Copper nanoparticles are prepared in aqueous solution by reducing copper ions with hydrazine hydrate in the presence of cetyl trimethylammonium bromide (CTAB) and polyvinylpyrrolydone (PVP) as stabilizers. With only CTAB was used as stabilizer, copper nanoparticles are aggregated and partially oxidized to Cu(2)O. When both PVP and CTAB were used, dispersed copper nanoparticles with 56 nm diameter were obtained. Copper nanoparticles are simply mixed with poly (3,4-ethylenedioxythiophene)/poly(styrenesulfonate) (PEDOT/PSS) in aqueous solution to form conducting composite. The effect of copper weight percent and surfactants on the conductivity and stability of the composite has been investigated.     

Synthesis and properties of Cu–Pd hydrosol: Hydrogen reduction of Cu<Superscript>2+</Superscript> ions catalyzed by palladium nanoparticles

A method has been developed for obtaining Cu–Pd hydrosols via catalytic reduction of copper ions by hydrogen on seed palladium nanoparticles 2.5 ± 0.3 nm in size. It has been found that reduction of Cu²⁺ to metal proceeds stage-by-stage through the formation of an intermediate Cu⁺ ion. Cu–Pd hydrosol remains stable with respect to sedimentation and aggregation for several weeks. The hydrodynamic size of Cu–Pd nanoparticles increases proportionally to the copper content in particles. It has been shown that this is due to an acidification of the solution as a result of H⁺ ions formation via the reaction of reduction of Cu²⁺ ions by hydrogen.     

Liquid-phase oxidation of toluene to benzaldehyde with molecular oxygen catalyzed by copper nanoparticles supported on graphene

Highly-dispersed copper nanoparticles (Cu NPs) were fabricated on the surface of reduced graphene oxide via direct hydrazine hydrate reduction of Cu²⁺ in aqueous solution. Scanning electron microscope and transmission electron microscope images show that the Cu NPs are distributed on the surface of graphene nanosheets, and the average particle size was about 40 nm. The Cu NPs supported on graphene have high reaction activity for the oxidation of toluene to corresponding benzaldehyde. It was found that the selectivity reached 66.5% and the conversion of toluene reached 11.5%.     

Effect of complexation of poly(acrylic acid) with Cu2+ ions on the size of copper nanoparticles prepared via reduction in aqueous solutions

Sols of zero-valence copper are prepared via the chemical reduction of Cu(II) ions by hydrazine borane in aqueous solutions of high-molecular-mass poly(acrylic acid), which forms stable complexes with copper ions at 20°C in a wide pH range. The study of the composition of coordination centers, the ligand surrounding of metal ions, and the character of distribution of copper ions over poly(acrylic acid) coils in a wide range of solution compositions and pH values shows that the size of copper nanoparticles in the sols can be controlled by varying the ratio between ligand groups (carboxylate anions in poly(acrylic acid)) and copper ions in the reaction system during the synthesis of sols. This effect can be accomplished either by variation in the initial composition of solution or change in pH (the degree of ionization of the initial poly(acrylic acid) in the presence of copper ions).     

Facile solid-state synthesis of oxidation-resistant metal nanoparticles at ambient conditions

A simple and scalable method for the synthesis of metal nanoparticles in the solid-state was developed, which can produce nanoparticles in the absence of solvents. Nanoparticles of coinage metals were synthesized by grinding solid hydrazine and the metal precursors in their acetates and oxides at 25 °C. The silver and gold acetates converted completely within 6 min into Ag and Au nanoparticles, respectively, while complete conversion of the copper acetate to the Cu sub-micrometer particles took about 2 h. Metal oxide precursors were also converted into metal nanoparticles by grinding alone. The resulting particles exhibit distinctive crystalline lattice fringes, indicating the formation of highly crystalline phases. The Cu sub-micrometer particles are better resistant to oxidation and exhibit higher conductivity compared to conventional Cu nanoparticles. This solid-state method was also applied for the synthesis of platinum group metals and intermetallic Cu₃Au, which can be further extended to synthesize other metal nanoparticles.     

Synthesis of high-concentration Cu nanoparticles in aqueous CTAB solutions

Pure metallic Cu nanoparticles at a high concentration (up to 0.2 M) have been synthesized by the reduction of cupric chloride with hydrazine in the aqueous CTAB solution. The input of extra inert gases was not necessary. The use of ammonia solution for the adjustment of solution pH up to 10 and the use of hydrazine as a reducing agent in a capped reaction bottle are crucial for the synthesis of pure Cu nanoparticles. The reaction solution finally became wine-reddish and its UV/vis absorption spectrum exhibited an absorption band at 574 nm, revealing the formation of metallic Cu nanoparticles. By the analysis of electron diffraction pattern, EDS, XRD, and XPS, the resultant particles were confirmed to be pure Cu with a face-centered cubic (fcc) structure. From the TEM analysis, it was found that the mean diameter of Cu nanoparticles first decreased and then approached a constant with the increase of hydrazine concentration. In addition, the CTAB concentration had not significant influence on the size of Cu nanoparticles. Also, TG analysis indicated that there were two weight-loss steps for the CTAB-capped Cu nanoparticles. It was suggested that a bilayer structure of CTAB was formed on the surface of Cu nanoparticles to prevent from the particle agglomeration. The synthesis method reported in this work might be helpful for the large-scale production of Cu nanoparticles.     

Synthesis of metallic copper nanoparticles coated with polypyrrole

This paper describes a method for polypyrrole (PPy) coating of metallic Cu nanoparticles in aqueous solution in atmosphere. Colloid solution of Cu nanoparticles was prepared by reducing Cu ions with the use of hydrazine in an aqueous solution dissolving citric acid and cetyltrimethylammonium bromide as stabilizers. The PPy coating was performed by polymerizing pyrrole with the use of hydrogen peroxide as an initiator in an aqueous colloid solution of the Cu nanoparticles. Ultraviolet–visible extinction measurements, transmission electron microscopy observation, and X-ray diffraction measurements revealed that the metallic Cu nanoparticles with a size of 27.6 ± 11.1 nm were coated with PPy. The obtained PPy-coated Cu particles were chemically stable even in atmosphere.     

Influence of different copper(II) salts on the oxidation and doping reactions of emeraldine base polyaniline

A spectroscopic investigation of the products formed in the reaction of emeraldine base (EB-PANI) with copper(II) ions in dimethylacetamide (DMA) is presented. It is well known that metal cations can dope emeraldine base polyaniline (EB-PANI) through a pseudo-protonation reaction. Resonance Raman, UV–vis-NIR, and EPR data, obtained for Cu²⁺/EB-PANI solutions prepared using CuCl₂·2 H₂O, Cu(NO₃)₂· 3 H₂O or Cu(CH₃COO)₂·H₂O as Cu²⁺ sources, showed that the species formed in reactions of EB-PANI and Cu²⁺ ions are dependent on the anions of the copper salt employed. EPR spectra pointed out that the environments of Cu²⁺ ions with acetate, chloride or nitrate as anions in DMA solution are distinct. Resonance Raman and UV–vis-NIR data demonstrated that the main reactions are the oxidation of EB-PANI to pernigraniline base (PB-PANI) and doping of EB-PANI to ES-PANI (emeraldine salt) when a direct coordination of Cu²⁺ ions to PANI exists. With nitrate as very weak coordinating anion, ES-PANI is formed preferentially. When copper chloride is used, both oxidation and doping of EB-PANI are verified. Conversely with acetate, the dimeric cage structure of this copper salt is preserved in solution, and oxidation of EB-PANI to PB-PANI is the only observed reaction. These results demonstrate the possibility of modulating the products of reaction between Cu²⁺ ions and EB-PANI in DMA solution by changing the counter ion of the Cu²⁺ source.     

Why the size of copper nanoparticles depends on the nature of the reducing agent in the preparation of sols in a cationic polyelectrolyte solution

The influence of different borane reducing agents (hydrazine borane and sodium borohydride) on the size of copper nanoparticles in sols prepared at 20°C through the reduction of Cu(II) ions in diluted aqueous solutions of high-molecular-mass poly(1,2-dimethyl-5-vinylpyridinium methyl sulfate) is studied. When hydrazine borane is used as a reducing agent, the nanoparticle size (3–14 nm in diameter) is independent of the solution pH. In the case of sodium borohydride, the transition from a highly acidic (pH 2.0) solution to solution with pH 4.5–8.5 during sol synthesis leads to a shift in the size distribution of nanoparticles toward larger diameters (from 3–14 to 10–20 nm). During the reduction of Cu(II) ions with sodium borohydride, the polymer-analogous reaction, which includes the reduction of pyridine rings of the polymer, proceeds simultaneously with the main process. The as-modified polymer is a weak polybase and, therefore, is protonated to a high extent via nitrogen atoms only in a strongly acidic solution. As pH is increased in the range 4.5–8.5, the positive charge of chains is decreased. The relationship between the nanoparticle size and variation in the positive charge of macromolecules is discussed in terms of the concept of the pseudomatrix synthesis of polymer-metal nanocomposite sols.     

An amperometric sensor for hydrazine based on nano-copper oxide modified electrode

A sensitive hydrazine sensor has been fabricated using copper oxide nanoparticles modified glassy carbon electrode (GCE) to form nano-copper oxide/GCE. The nano-copper oxide was electrodeposited on the surface of GCE in CuCl₂ solution at −0.4 V and was characterized by Scanning electron microscopy and X-ray diffraction. The prepared modified electrode showed a good electrocatalytic activity toward oxidation of hydrazine. The electrochemical behavior of hydrazine on nano-copper oxide/GCE was explored. The oxidative current increased linearly with improving concentration of hydrazine on nano-copper oxide/GCE from 0.1 to 600 μM and detection limit for hydrazine was evaluated to be 0.03 μM at a signal-to-noise ratio of 3. The oxidation mechanism of hydrazine on the nano-copper oxide/GCE was also discussed. The fabricated sensor could be used to determine hydrazine in real water.     

Lateral flow nucleic acid biosensor for Cu2+ detection in aqueous solution with high sensitivity and selectivity

A lateral flow nucleic acid biosensor based on copper-dependent DNA-cleaving DNAzyme and gold nanoparticles has been developed for the visual detection of copper ions (Cu(2+)) in an aqueous solution with a detection limit of 10 nM.     

Spacer layer screening effect: a novel fluorescent film sensor for organic copper(II) salts

A fluorescent film sensor was prepared by chemical assembly of pyrene on a glass plate surface via a long flexible spacer. It was found that the film is highly selective for some organic Cu2+ salts, such as copper acetate and copper propionate. The presence of inorganic Cu2+ salts and other metal(II) acetates, including Ni2+, Co2+, Pb2+, Cd2+, Zn2+, etc., had little effect upon the sensing behavior of the film for copper acetate or copper propionate. The observation was explained by employing a proposed "two-dimensional solution" model. The quenching by copper acetate of the emission of the film is static in nature due to complexation of the spacers to the metal ions. Furthermore, the response of the film sensor to copper acetate is fully reversible. To the best of our knowledge, this film sensor may be the first one that can differentiate greasy copper salts from inorganic copper salts.     

Stabilization of copper nanoparticles prepared by reduction from solutions of poly(acrylic acid) complexes with Cu2+ ions and poly(ethylene glycols)

Copper sols are prepared via the reduction of copper ions with hydrazine borane in dilute aqueous solutions of mixtures of the PAA-Cu²⁺ complex and poly(ethylene glycols) of various molecular masses at PEG: PAA = 0.25 base-mol/base-mol and PAA: Cu²⁺ = 10 base-mol/mol in the pH range 4.0–7.0. The stability of sols against oxidation (dissolution) or aggregation (enlargement) of metal nanoparticles is much higher than that of sols prepared in the absence of PEG. With an increase in the initial pH or a decrease in the molecular mass of PEG, the formed copper nanoparticles are much larger (no less than 20 nm in diameter) than copper nanoparticles occurring in the sol prepared in a solution of the PAA double complex with Cu²⁺ ions and high-molecular-mass PEG at a low initial pH (3–10 nm in diameter). Copper nanoparticles in sols prepared in solutions of complexes based on the high-molecular-mass PEG do not aggregate during exposure, thereby indicating the high stability of polymer screens on their surfaces.     

EPR analysis of copper particles in aqueous systems

Experimental and theoretical EPR spectra of nanodispersed copper synthesized by the reduction of copper dichloride in aqueous solutions, thin films of electrolytic copper, and copper ions are analyzed. It is established that the reduction of copper dichloride in an aqueous solution in the presence of a surfactant yields copper nanoparticles. The EPR spectra are shown to be sensitive to the oxidation of copper nanoparticles in both an aqueous medium and in thin copper films prepared by electrolytic deposition.     

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.     

PEDOT-supported Pd nanoparticles as a catalyst for hydrazine oxidation

Composite poly-3,4-ethylenedioxythiophene (PEDOT)/palladium (Pd) films were obtained by chemical deposition of dispersed palladium nanoparticles into PEDOT conducting polymer matrix. The amounts of palladium particles incorporated into PEDOT films were estimated by electrochemical quartz crystal microbalance measurements. It was shown that palladium loading depends on the time a PEDOT film is exposed in the solution, containing Pd(II)-ions, on the concentration of Pd(II) ions and the film thickness. X-ray photoelectron spectroscopy data have confirmed the presence of metallic palladium in the polymer. The morphology of pristine and composite films as well as the size of Pd nanoparticles and their distribution were characterized using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). From SEM images, it was found that Pd particles decorated PEDOT globular structures as quasi-spherical particles, and their mean size was dependent on synthesis conditions. The nanoparticles were non-uniformly dispersed on the polymer surface. The comparison of TEM images of composite PEDOT/Pd films obtained for different times of metal loading was made. The remarkable effect of loading time on the size of particles has been established: the mean size of dominating palladium particles was close to 6–10 nm for 30 s of metal deposition, and it was getting larger with the increase of deposition time (close to 15–30 nm for 120 s). It is most likely that with prolongation of synthesis time, the deposition of palladium predominantly proceeds on the already deposited palladium clusters, resulting in the extension growth of their size. Catalytic properties of PEDOT/Pd composite films were studied in respect to hydrazine oxidation by cyclic voltammetry and voltammetry on rotating disk electrode. The obtained data allow to conclude that the process of hydrazine oxidation on PEDOT/Pd composites takes place predominantly on palladium particles, located on the surface or in the near-surface layers of the polymer. The diffusion nature of the limiting current of hydrazine oxidation on composite PEDOT/Pd film in phosphate buffer solution рН = 6.86 was confirmed, and hydrazine diffusion coefficient was calculated. The increase of the limiting currents of hydrazine oxidation with the increase of Pd deposition time was observed, resulting from the increase of the active surface area of palladium particles, acting as microelectrodes. The electroanalytical applications of these nanocomposite materials for the determination of hydrazine were demonstrated.     

Synthesis of β-Bromo-Substituted Cu(II) Tetraphenylporphyrinates

Bromination reactions of Cu(II) 5,10,15,20-tetraphenylporphyrinate with N-bromosuccinimide in chloroform and chloroform–dimethylformamide mixture and complexation of 2-bromo-5,10,15,20-tetraphenylporphyrin and 2,3,12,13-tetrabromo-5,10,15,20-tetraphenylporphyrin with copper(II) acetate in dimethylformamide have been studied. Mono-, tetra-, and octabromo-substituted Cu(II) porphyrinates have been synthesized. Obtained compounds have been identified by electronic absorption spectroscopy, IR spectroscopy, mass spectrometry, and elemental analysis.     

Alkane hydroperoxidation with peroxides catalysed by copper complexes

Various copper(I) and copper(II) derivatives, both "simple" ones (copper acetate, perchlorate and a complex with CH3CN) and compounds containing N,O-chelating ligands, catalyse very efficient (turnover numbers attain 2200) oxidation of saturated hydrocarbons with peroxyacetic acid (PAA) or tert-butyl hydroperoxide (TBHP) in acetonitrile solution at 60 degrees C. Alkyl hydroperoxide, alcohol and ketone are formed, the main product being an alkyl hydroperoxide in the oxidation with PAA and an alcohol for the case of TBHP. It has been proposed that the oxidation with PAA is induced via the attack of species r* [HO* or CH3C(=O)O*] on the alkane, RH. A competitive attack of r* on the solvent, CH3CN, also occurs. It has been assumed that in the case of the reaction catalysed by complex Cu(CH3CN)4BF4, copper is present mainly in the form of Cu+ cation, and the rate-limiting step of the oxidation process is the formation of r* via reaction (1): CH3C(=O)OOH + Cu+ --> CH3C(=O)O* + HO- + Cu2+ or/and CH3C(=O)OOH + Cu+ --> CH3C(=O)O- + HO* + Cu2+ with initial rate W1 = k1[PAA][Cu(CH3CN)4BF4] and k1 = 1.7 mol(-1) dm3 s(-1) at 60 degrees C. The activity of the Cu-catalyst is dramatically changed on a small modification of N,O-chelating ligands in the catalyst.     

Catalytic Hydrogenation of Halosteroidal Derivatives by Bipyridine or Phenanthroline Complexes of Copper(II) in Hydrazine Aqueous Media

We report two synthetic systems, Cu(Bpy)²⁺ and Cu(Phen)²⁺, for catalytic hydrogenation of steroidal haloalkenes in the presence of hydrazine and air. Thesestudies demonstrated that the selective hydrogenation is faster for the 1,10‐phenanthroline–Cu(II) system because forming more stable copper complex are formed, leaving fewer free copper ions in solution. Evidence also supports that the catalytic power of Cu(II) ions can be tuned moderately through the addition of bidentate ligand, Bpy or Phen.