New Cu(I) complexes with 2,2′-biquinolyl and 2,2′-quinolyl-pyridine containing polymer ligands as electrocatalysts for O2 activation in the oxidation of aliphatic amines

A series of polynuclear Cu(I) complexes with various types of polymer ligands containing 2,2′-biquinolyl (biQ) or 2,2′-quinolyl-pyridine (QPy) fragments in the polymer backbone was synthesized using sacrificial Cu anode. Cyclic voltammetry investigation of the obtained complexes revealed the formation of two types of Cu(I) coordination units, depending on the polymer's structure and electrolysis conditions. The first type of complexes, with only one biQ ligand per Cu(I) center, showed high oxidase activity in the air oxidation of primary and secondary amines to corresponding aldehydes with concomitant reduction of molecular oxygen to water. The reactions proceed in acetonitrile or N-methylpyrrolidone in the presence of O₂ at a potential of Cu^II/Cu^I electroreduction (−0.55 V vs. Ag/AgCl/KCl) with the high preparative yield and current efficiency. The possible scheme of the electrocatalytic process is discussed.     

New heterobimetallic Cu(I)–Pd(II)-containing polymer complexes: Electrochemical synthesis and application in catalysis

Electrochemical approach to a new electroactive heteropolynuclear catalytic system based on polyamic acids with biquinolyl (biQ) fragments in the polymer backbone capable of coordination to Pd^II and Cu^I-ions was developed using sacrificial Pd and Cu anodes. The order of anode dissolution (first Pd and then Cu) was shown to be important for the synthesis of the heteropolynuclear complex. The opposite order of dissolution resulted in the oxidation of the initially formed Cu^I ions to Cu^II. The redox properties of the obtained heteronuclear polymer complexes containing Cu^I and Pd^II coordination units were characterized by cyclic voltammetry. The catalytic properties of the resultant metal–polymer system were investigated and it showed high catalytic activity in the reaction of aryl halides with phenylacetylene (Sonogashira coupling) at a small Pd loadings (0.1 mol%) yielding 50–90% of arylphenylacetylene depending on the nature of the aryl halide. The proposed catalytic system also exhibits high catalytic activity in cascade cyclisations of 2-iodoaniline and 2-iodophenole in the presence of phenylacetylene yielding synthetically useful 2-phenylindole (90%) and 2-phenylbenzofuran (92%).     

Effect of Pretreatment Atmosphere on CuO/TiO2 Activities in NO + CO Reaction

Using TiO₂ as carrier, CuO/TiO₂ catalysts with different CuO loading were prepared by the impregnation method. The catalytic activities in NO+CO reaction were examined with a micro-reactor gas chromatography reaction system and the methods of TPR, XPS and NO-TPD. It was found that the catalytic activities were affected by pretreatment atmosphere, i.e. H₂ atmosphere > reduction–reoxidation > 10%CO/He > reaction gas (fresh sample). NO decomposition was better by low-valence Cu species than by high-valence Cu species, i.e. Cu⁰>Cu⁺>Cu²⁺. The XPS results indicated that Cu species on CuO/TiO₂ were Cu⁰, Cu⁺, normal Cu²⁺(Cu²⁺(I)) and chain-structured Cu²⁺(Cu²⁺(II)) as –Cu–O–Ti–O–. The activities of Cu²⁺(II) were much higher than that of Cu²⁺(I), but both species were very unstable in the reaction atmosphere and easily reduced by CO, which accounted for the variable activities of fresh catalysts with increasing reaction temperature. In NO+CO reaction, the redox process was a cycle of Cu⁺–Cu²⁺(I) at low reaction temperature but was a cycle of Cu⁰–Cu⁺ at high reaction temperature. As shown by NO-TPD, high catalytic activities could be attributed to the following factors, e.g. oxygen caves on the catalyst’s surface after pretreatment with H₂ and reduction–reoxidation, formation of Cu⁰ after pretreatment with H₂, and increment of Cu species dispersion and formation of Cu²⁺(II) after pretreatment with reduction–reoxidation.     

Facile synthesis of Ag/Zn1-xCuxO nanoparticle compound photocatalyst for high-efficiency photocatalytic degradation: Insights into the synergies and antagonisms between Cu and Ag

By carefully balancing synergies and antagonisms that arise from incorporating Cu and Ag within a single ZnO-based catalytic platform, the photocatalytic activity of Ag/ZnO based on three-dimensional modified ceramic structures can be further significantly enhanced. The performance of Ag/ZnO heterostructure (Z0) was significantly improved by only 0.2 mol% Cu incorporation (Z0.2) and the first-order degradation kinetics constants (K) of Z0.2 were 2 and 1.5 times higher than that of Z0 under simulated sunlight and UV light. The synergies between Cu dopants and metallic Ag were mainly the significantly enhanced visible light absorption capacity and the prolonged photo-excited charge lifetime. However, with the excessive introduction of Cu precursors, the surface Cu²⁺ was found to inhibit the interfacial charge transfer between Ag and ZnO NPs under UV and visible light irradiation, but the transformation from Cu²⁺ to Cu⁺ was also presumed to be a driving factor for the improvement of photocatalytic efficiency. These interactions may provide a useful pathway for enhancing photocatalytic efficiency of low-cost ZnO-based catalytic platforms.     

CuO and CuO-ZnO catalysts supported on CeO2 and CeO2-LaO3 for low temperature water-gas shift reaction

This paper describes an investigation on CuO and CuO-ZnO catalysts supported on CeO₂ and CeO₂-La₂O₃ oxides, which were designed for the low temperature water-gas shift reaction (WGSR). Bulk catalysts were prepared by co-precipitation of metal nitrates and characterized by energy-dispersive spectroscopy (EDS), X-ray diffraction (XRD), surface area (by the BET method), X-ray photoelectron spectroscopy (XPS), and in situ X-ray absorption near edge structure (XANES). The catalysts' activities were tested in the forward WGSR, and the CuO/CeO₂ catalyst presented the best catalytic performance. The reasons for this are twofold: (1) the presence of Zn inhibits the interaction between Cu and Ce ions, and (2) lanthanum oxide forms a solid solution with cerium oxide, which will cause a decrease in the surface area of the catalysts. Also the CuO/CeO₂ catalyst presented the highest Cu content on the surface, which could influence its catalytic behavior. Additionally, the Cu⁰ and Cu¹⁺ species could influence the catalytic activity via a reduction-oxidation mechanism, corroborating to the best catalytic performance of the Cu/Ce catalyst.     

Temperature-induced evolution of reaction sites and mechanisms during preferential oxidation of CO

Active sites responsible for the preferential oxidation of carbon monoxide were investigated using 4 wt.% Cu–CeO₂ catalysts prepared by flame spray pyrolysis. Surface redox properties of the catalyst were assessed using a series of temperature-programmed reduction (CO, H₂ and mixed) experiments, as well as operando infrared spectroscopy. It was demonstrated that CO and H₂ react at identical surface sites, with CO₂ formation proceeding simultaneously via three distinct Cuⁿ⁺–CO carbonyl species. The origin of high catalytic selectivity towards CO at below 150 °C stems from the carbonyl stabilization effect on the catalyst surface, preventing adsorption and subsequent oxidation of H₂. Under non-selective conditions at higher temperatures, a gradual red-shift and loss of intensity in the carbonyl peak was observed, indicating reduction of Cu⁺ to Cu⁰, and the onset of an alternate redox-type oxidation mechanism where CO and H₂ compete for the oxidation sites. These results for Cu–CeO₂ suggest that improved low-temperature catalytic activity will only be achieved at the expense of reduced high-temperature selectivity and vice versa.     

One unexpected mixed-valence Cu(I,II)-cyanide coordination polymer in situ originating from the cleavage of acetonitrile

Solvothermal reaction of CuCl₂·2H₂O and 2-(4-pyridyl)benzimidazole (PyHBIm) in a acetonitrile-water mixed solvent afforded a mixture of [Cu^I₂Cu^II(CN)₂(PyHBIm)₂Cl₂]_n (1) and [Cu^II(PyH₂BIm)₂Cl₄] (2). Complex 1 is a mixed-valence 1D ribbon Cu(I,II)-cyanide coordination polymer. One Cu(II) center linearly links two Cu(I) ions via two μ₂-CN bridges. XPS spectrum and bond valence sum (BVS) analysis have confirmed the mixed-valence characteristics. Cu(II) ion adopts a centrosymmetric square-planar geometry surrounded by two cyanides and two pyridyl groups. Cu(I) ions adopt a trigonal geometry coordinated by cyanide, imidazole group and Cl⁻ anion. The cyanide ligand is in situ generated from the cleavage of acetonitrile solvent, which indicates that acetonitrile is an environmentally friend cyanating agent. The mechanism of acetonitrile in situ cleavage under solvothermal condition is explained. Complex 2 is a centrosymmetric mononuclear Cu(II) compound. Four equivalent Cl⁻ anions lie on the equatorial plane. The protonated PyH₂BIm⁺ cation as a monodentate ligand coordinates to Cu(II) center via pyridyl terminal.     

Accumulation of Cu(II) cations in poly(3,4-ethylenedioxythiophene) films doped by hexacyanoferrate anions and its application in Cu-selective electrodes with PVC based membranes

Electrochemical properties of poly(3,4-ethylenedioxythiophene) doped with hexacyanoferrate(II,III) ions (PEDOT(HCF)) were studied in the presence of Cu²⁺ ions. Voltammetric and EDAX studies revealed retention of hexacyanoferrate anions in the polymer film and accumulation of Cu(II) cations, as well as formation of solid copper hexacyanoferrate near the polymer surface.Accumulation of Cu²⁺ ions was found to be advantageous from the point of view of PEDOT(HCF) applications as a solid contact (ion-to-electron transducer) in all-solid-state Cu²⁺-selective electrodes with solvent polymeric polyvinyl chloride (PVC) based membrane, containing Cu²⁺-selective ionophore. Binding of Cu²⁺ ions in the conducting polymer layer results in analyte ions flux into the transducer phase. Thus, pronounced enhancement of selectivity of the all-solid-state Cu²⁺-selective electrode or lower detection limit of the potentiometric response range was achieved, reaching under optimised conditions 10⁻⁷ M CuSO₄.     

Effect of Cu(II) ligands on electroless copper deposition rate in formaldehyde solutions: An EQCM study

The electroless copper deposition rate for 6 Cu^II complexes decreases in the ligand sequence: nitrilotriacetic acid (NTA) > N,N,N′,N′-tetrakis-(2-hydroxypropyl)-ethylenediamine (Quadrol) > glycerol > L(+)-tartrate ~ sucrose > -tartrate. Both Cu^II complex stability and specific ligand effects were found to influence the Cu deposition process. The specific ligand effects are most obvious in the case of Quadrol (high kinetic activity at a high Cu^II complex stability), glycerol and sucrose (additional reaction of Cu₂O formation by interaction of Cu^II with ligand). According to the EQCM data for 11 Cu^II complexes (including data from the former study) the higher kinetic activity is demonstrated by complexes with ligands containing amino groups; this factor is more important for Cu deposition rate than copper complex stability. A potential dependence of the Cu reduction partial current on the electrode potential has been extracted from the EQCM data in the complete electroless plating bath. An increase in Cu^II reduction rate was found to occur in electroless plating solution for Cu^II complexes with NTA and Quadrol compared with that in formaldehyde-free solutions. Possible reasons for the acceleration of the partial Cu^II reduction reaction and the overall process kinetics are discussed using a hypothetical reaction sequence involving intermediate copper oxy-species and active Cu* formation as well as development of the preferred Cu surface structure.     

Chitosan functionalized with 2[-bis-(pyridylmethyl) aminomethyl]4-methyl-6-formyl-phenol: equilibrium and kinetics of copper (II) adsorption

The complexation agent 2[-bis-(pyridylmethyl) aminomethyl]-4-methyl-6-formyl-phenol (HL) was immobilized in chitosan in order to obtain a new adsorbent material to be employed in studies on adsorption and pre-concentration of Cu(II). The chitosan modified by the complexation agent was characterized by infrared spectroscopy, DSC and TGA. The studies were conducted as a function of the pH of the medium and the mechanism of Cu(II) adsorption in the solid phase was analyzed utilizing several kinetic models. The parameters for the adsorption of Cu(II) ions by chitosan-HL were determined with a Langmuir isotherm, the maximum saturation capacity of the monolayer being 109.4 mg of Cu(II) per gram of polymer. Electron paramagnetic resonance spectroscopy revealed that Cu^II ions coordinate to the donor atoms of the HL ligand anchored to the surface of the polymer forming a stable chelate complex in the solid state.     

Supramolecular assembly of one-dimensional channels and two-dimensional brick-wall networks from asymmetric dithioether ligands and copper(I) iodide

Two asymmetric dithioether ligands with cyclohexyl (L¹) and phenyl (L²) end-groups were synthesized. Reaction of L¹ with copper(I) iodide afforded a 1D channel-type coordination polymer {[Cu₄I₄(L¹)₂](CH₃CN)_0.5}_n (1) interconnected by cubane-type tetranuclear Cu₄I₄ cluster units. Whereas, a 2D brick-wall-type coordination polymer [CuI(L²)]_n (2) with rhomboid dinuclear Cu–I₂–Cu nodes was isolated from the reaction of L² with copper(I) iodide.     

Polarographic studies on the effect of thiourea on deposition of copper in the presence of 2M H2SO4

Results of polarographic studies on the Cu(II)-thiourea-2M H₂SO₄ and equilibria resulting in that system are presented. The formation of both anodic and cathodic waves due to the copper(I)formamidine disulphide complex adsorption, anodic-cathodic waves of thioureadisulphide and copper deposition from the [Cu(CSN₂H₄)_x]⁺²(x = 2–4) complex are discussed. The reduction of the adsorbed complex leads to the catalytic hydrogen evolution. The influence of depolarizers charge and that of the electrode surface on electrode processes are discussed also.     

Synthesis of novel copper ion-selective material based on hierarchically imprinted cross-linked poly(acrylamide-co-ethylene glycol dimethacrylate)

A novel hierarchically imprinted cross-linked poly(acrylamide-co-ethylene glycol dimethacrylate) using a double-imprinting approach for the Cu²⁺ selective separation from aqueous medium was prepared. In the imprinting process, both Cu²⁺ ions and surfactant micelles (cetyltrimethylammonium bromide – CTAB) were employed as templates. The hierarchically imprinted organic polymer named (IIP-CTAB), single-imprinted (IIP-no CTAB) and non-imprinted (NIP-CTAB and NIP-no CTAB) polymers were characterized by SEM, FTIR, TG, elemental analysis and textural data from BET (Brunauer–Emmett–Teller) and BJH (Barrett–Joyner–Halenda). Compared to these materials, IIP-CTAB showed higher selectivity, specific surface area and adsorption capacity toward Cu²⁺ ions. Good selectivity for Cu²⁺ was obtained for the Cu²⁺/Cd²⁺, Cu²⁺/Zn²⁺ and Cu²⁺/Co²⁺ systems when IIP-CTAB was compared to the single-imprinted (IIP-no CTAB) and non double-imprinted polymer (NIP-CTAB), thereby confirming the improvement in the polymer selectivity due to double-imprinting effect. For adsorption kinetic data, the best fit was provided with the pseudo-second-order model for the four materials, thereby indicating the chemical nature of the Cu²⁺ adsorption process. Cu²⁺ adsorption under equilibrium was found to follow dual-site Langmuir–Freundlich model isotherm, thus suggesting the existence of adsorption sites with low and high binding energy on the adsorbent surface. From column experiments 600 adsorption–desorption cycles using 1.8 mol L⁻¹ HNO₃ as eluent confirmed the great recoverability of adsorbent. The synthesis approach here investigated has been found to be very attractive for the designing of organic ion imprinted polymer and can be expanded to the other polymers to improve performance of ion imprinted polymers in the field of solid phase extraction.     

Electroreduction of nitrate ions on Pt(1 1 1) electrodes modified by copper adatoms

Kinetics and mechanism of nitrate ion reduction on Pt(1 1 1) and Cu-modified Pt(1 1 1) electrodes have been studied by means of cyclic voltammetry, potentiostatic current transient technique and in situ FTIRS in solutions of perchloric and sulphuric acids to elucidate the role of the background anion. Modification of platinum surface with copper adatoms or small amount of 3D-Cu crystallites was performed using potential cycling between 0.05 and 0.3 V in solutions with low concentration of copper ions, this allowed us to vary coverage θ_Cu smoothly. Following desorption of copper during the potential sweep from 0.3 to 1.0 V allowed us to estimate actual coverage of Pt surface with Cu adatoms. Another manner of the modification was also applied: copper was electrochemically deposited at several constant potentials in solutions containing 10⁻⁵ or 10⁻⁴ M Cu²⁺ and 5 mM NaNO₃ with registration of current transients of copper deposition and nitrate reduction.It has been found that nitrate reduction at the Pt(1 1 1) surface modified by copper adatoms in sulphuric acid solutions is hindered as compared to pure platinum due to induced sulphate adsorption at E < 0.3 V. Sulphate blocks the adsorption sites on the platinum surface and/or islands of epitaxial Cu(1 × 1) monolayer thus hindering the adsorption of nitrate anions and their reduction. The extent of inhibition weakly depends on the copper adatom coverage. Deposition of a small amount of bulk copper does not affect noticeably the rate of nitrate reduction.Nitrate reduction on copper-modified Pt(1 1 1) electrodes in perchloric acid solutions occurs much faster as compared to pure platinum. The steady-state currents are higher by 4 and 2 orders of magnitude at the potentials of 0.12 and 0.3 V, respectively. The catalytic effect of copper adatoms is largely caused by the facilitation of nitrate adsorption on the platinum surface near Cu_ad and/or on the islands of the Cu(1 × 1) monolayer (induced nitrate adsorption).Hydrogen adatoms block the adsorption sites on platinum for NO₃⁻ anion adsorption and inhibit reactions of nitrate reduction even at moderate surface coverage.The products of nitrate reduction in sulphuric and perchloric acids are essentially the same (NO and ammonia) irrespective of the presence or absence of Cu on the platinum surface.     

Copper incorporation in Mn2+-doped Sn2S3 nanocrystals and the resultant structural,optical, and electrochemical characteristics

Sn₂S₃ nanocrystals (NCs) with both Mn²⁺ doping and Cu²⁺ incorporation were synthesized using a chemical bath deposition method. The Cu²⁺ ions formed an anorthic Mn²⁺-doped Cu₂SnS₃ structure with E_g =?1.44?eV, which altered the material's optical and photo/electrochemical properties. After coating the bare Nb₂O₅ electrode with Mn²⁺-doped Sn₂S₃ or Mn²⁺-doped Cu₂SnS₃ NCs, the photoluminescence spectrum was blue-shifted to 411.13?nm from 411.69?nm. Compared to the sample without Cu²⁺, the Cu²⁺-incorporated sample showed a slightly stronger emission at the same position, possibly due to disorder in the crystalline structure based on variations at the interface of Mn²⁺-doped Cu₂SnS₃ NCs. Electrochemical analysis showed a lower charge transfer resistance in the Mn²⁺-doped Cu₂SnS₃, which is related to its larger electroactive surface area. The larger electroactive surface area is attributed to the Faradaic redox processes at the electrode surface, which suppresses the carrier recombination. The coexistence of Cu²⁺ and Mn²⁺ ions shortened the electron transport pathway at the interface and improved the carrier diffusion coefficient and diffusion length, leading to a higher specific capacitance that implies higher energy storage performance. Finally, the I-V characteristics of the Mn²⁺-doped Cu₂SnS₃-coated Nb₂O₅ electrode under various light illumination conditions indicated its better efficiency in photoresponse, electron generation, and charge collection, owing to a superior charge transport mechanism. Detailed results were obtained about the charge dynamics in the as-prepared photo/electrochemical devices with Cu²⁺ incorporation in the Mn²⁺-doped SnS₃ electrode.     

Hydrothermal synthesis,crystal structure and strong blue fluorescence of a novel 3D coordination polymer containing copper and zinc centers linked by isonicotinic acid ligands

The first mixed metal Zn/Cu coordination polymer, [Zn₃Cu₂(IN)₈] (1) (HIN = isonicotinic acid) was synthesized under hydrothermal conditions. The three dimensional structure of 1 has a novel topological metal-organic framework, which is built up by Zn²⁺, Cu⁺ and ligands IN to generate an open-framework with an unusual helical [–Zn(Cu)-IN–]_n chains along the b axis. The very strong blue fluorescence for 1 can be observed in the solid state.     

An unusual 3-D asymmetric mixed valence copper-azido complex with pyrazinecarboxylate as co-ligand showing rare net topology: Hydrothermal synthesis,structure and magnetic properties

A new 3-D mixed valence copper-azido coordination polymer, [Cu^I · Cu^II(N₃)(pzc)₂ (H₂O)]_n1, has been synthesized and characterized, and its magnetic properties studied. In this compound, the azide acts as rare asymmetric μ_1,1,3 bridging mode. The azide ligands and the Cu(2) ions act as 3-connecting nodes, and the Cu(1) ions act as 4-connecting nodes. The overall net takes rare topology with the Schläfli symbol of (6.8²)(6.8²)(6.8⁵).     

Copper(I/II), α/β‐Synuclein and Amyloid‐β: Menage à Trois?

Copper binding to α‐synuclein (aS) and to amyloid‐β (Ab) has been connected to Parkinson's and Alzheimer's disease (AD), respectively, because Cu ions can modulate the peptide aggregation, and these Cu ? peptide complexes can catalyse the production of reactive oxygen species (ROS). In a significant proportion of AD brains, aggregation of aS and Ab has been detected, and it was proposed that Ab and aS interact with each other. Thus, we investigated the potential interactions of Ab and aS through their binding of copper(I) and copper(II). Additionally, β‐synuclein (bS) was investigated, due to its additional methionine residue, a potential Cu^I ligand. We found that: 1) the peptides containing the Cu‐binding domains Ab1–16, aS1–15 and bS1–15 have similar affinities towards Cu^II and towards Cu^I, with Ab1–16 being slightly stronger, 2) in the case of Cu^I, the additional Met residue in bS1–15 increased the affinity slightly, 3) the exchange of Cu^I/II between the two peptides is rapid (≤ms), 4) a/bS1–15 and Ab1–16 form a heterodimeric complex with Cu^II, 5) Cu^I probably promotes a transient ternary complex, 6) the different Cu^I/II coordination of Ab1–16, aS1–15 and bS1–15 impacts the capacity to produce ROS and to oxidise catechol, and 7) when Ab1–16, aS1–15 and Cu are present, the ROS production more closely resembles that by Ab1–16. The work gives insights into the coordination chemistry of these related peptides, and the relevance of coordination differences, the ternary complex and ROS production are discussed.     

Synthesis of poly[dimethylsiloxane-block-oligo(ethylene glycol) methyl ether methacrylate]: an amphiphilic copolymer with a comb-like block

AB amphiphilic comb-like block copolymers of poly(oligo[ethylene glycol] methyl ether methacrylate) and polydimethylsiloxane were synthesised with a methodology based on atom transfer radical polymerization (ATRP). The anionic ring opening polymerisation of hexamethylcyclotrisiloxane followed by reaction with 3-(chlorodimethylsilyl) propyl 2-bromo-2-methylpropanoate propyldimethylchlorosilane gave suitable macroinitiators for the ATRP of oligo[ethylene glycol] methyl ether methacrylate. The latter synthetic procedure was optimised by performing a number of syntheses varying the reaction solvent, catalytic complex and the temperature used. Copolymers with relatively high polydispersity indices (M_w/M_n>1.3) could be synthesised at room temperature by employing a Cu(I)Br:N,N,N′,N′,N″-pentamethyldiethylenetriamine complex in n-propanol with Cu(II)Br. The optimum reaction conditions employed a Cu(I)Cl:N-(n-propyl)-2-pyridyl(methanimine) complex with an n-propanol/water mixture or toluene as solvent at 90 °C. This gave block copolymers of the desired molecular weights and polydispersity indices of less than 1.1. The block copolymers were characterised with ¹H NMR and ¹³C NMR spectroscopy and size exclusion chromatography.     

Synthesis and characterization of Cu-doped ceria nanopowders

Nanopowdered solid solution Ce_1−xCu_xO_2−γ samples (0 ≤ x ≤ 0.15) were synthesized by self-propagating room temperature synthesis (SPRT). Raman spectroscopy and XRD at room temperature were used to study the vibration properties of these materials as well as the Cu solubility in ceria lattice. The solubility limit of Cu²⁺ in CeO₂ lattice was found to be lower than published in the literature. Results show that obtained powders with low dopant concentration are solid solutions with a fluorite-type crystal structure. However, with Cu content higher than 7.5 mass%, the phase separation was observed and two oxide phases, CeO₂ and CuO, coexist. All powders were nanometric in size with high specific surface area.