Oxidation State Of Cu Research Articles

Seeded Growth of Au@CuxO Core-Shell Mesoporous Nanospheres and Their Photocatalytic Properties.

We report a facile synthesis of Au@CuxO core–shell mesoporous nanospheres with tunable size in the aqueous phase via seeded growth. The success of the current work relies on the use of a halide-free copper (Cu) precursor and n-oleyl-1,3-propanediamine as a capping agent to facilitate the formation of a copperish oxide shell with a mesoporous structure and the presence of mixed oxidation states of Cu. By varying the amount of spherical Au seeds while keeping other parameters unchanged, their diameters could be readily tuned without noticeable change in morphology. As compared with commercial Cu2O, the as-prepared Au@CuxO core–shell mesoporous nanospheres exhibit the higher adsorption ability, enhanced activity, and excellent stability toward photocatalytic degradation of methyl orange (MO) under visible light irradiation, indicating their potential applications in water treatment.

Metal–Organic Framework-Derived CuS Nanocages for Selective CO 2 Electroreduction to Formate

Electroreduction of CO2 to target products with high activity and selectivity has techno-economic importance for renewable energy storage and CO2 utilization. Herein, we report a hierarchical CuS h...

A tale of two metal ions: contrasting behaviors of high oxidation states of Cu and Mn in a bicarbonate–H2O2 system

A tale of two metal ions: Cu-bicarbonate–H2O2 efficiently degrades Congo red dye while the corresponding Mn system does not.

Unraveling the Formation Mechanism of a Hybrid Zr-Based Chemical Conversion Coating with Organic and Copper Compounds for Corrosion Inhibition

Corrosion protection is of great importance, since corrosion on metals and alloys happens in a wide range of applications and causes economic and environmental issues. Among various corrosion protection methods, chemical conversion coatings applied by a simple solution immersion process on different metals as a pretreatment has great advantages. The technique is easy to operate and economic. The resulting conversion coatings then act as an effective barrier to corrosion, as well as improving the adhesion between the metal/alloy substrate and the subsequent organic coating. As conventional chromate and phosphate conversion coating treatment has health and environmental issues, there is a strong motivation to develop novel environmentally friendly chemical conversion coatings with comparable functionality. Specifically, zirconium-based (Zr-based) conversion coatings created by immersing alloy substrates in hexafluorozirconic acid (H2ZrF6) solution is an outstanding candidate because of its lower operational cost and fast deposition, while offering good anti-corrosion and adhesion properties.1 Prior works of Zr-based conversion coatings have been focusing on further improving their anti-corrosion performance by controlling the coating deposition parameters including temperature, time, pH value and incorporating organic (silane, phosphonic acids) or inorganic (copper, cerium) compounds. In this study, a novel organic-inorganic hybrid Zr-based conversion coating with copper (Cu) and polyamidoamine (PAMAM).2 Incorporating organic component PAMAM has been shown to enhance the corrosion resistance of the conversion coating, as well as to provide binding media for the subsequent paint coating. Despite evidence showing superior performance, the film growth and reaction mechanisms of the hybrid conversion coatings, when incorporating these additives, is not well understood.Here, we studied the effect of the additive PAMAM concentration in the coating solution on the morphology, structure and chemical composition of the coating by a multimodal X-ray and electron analysis. First, we discovered an inverse relationship between the concentration of PAMAM and the thickness of the coating. A higher PAMAM concentration was also found to reduce the Cu-containing cluster formation. Elemental distribution analysis by Scanning Transmission Electron Microscopy with Energy-dispersive X-ray Spectroscopy revealed different microstructure in the surface cluster formation; Cu-containing nanoparticles formed in coatings without PAMAM additives, whereas a more homogenous distribution of Cu species was found in samples with PAMAM. The atomic ratio of elements characterized by X-ray Photoelectron Spectroscopy (XPS) varied with coating conditions. Notably a higher ratio of organic elements indicated the incorporation of PAMAM into the conversion coating with possibly some further adsorption. High-resolution XPS revealed the existence of amide and amine in the coating and different oxidation states of Cu; the results indicate that the reduction reaction of the Cu ions was suppressed by PAMAM, because the complexation between Cu and PAMAM decreased the reduction potential of Cu. In addition, the corrosion of the hybrid coatings in alkaline environment was characterized by synchrotron X-ray Absorption Near Edge Structure (XANES) Spectroscopy showing a better corrosion resistance of hybrid coating with less dissolution of clusters. Overall, the study discussed the interaction between Cu ions and PAMAM and the subsequent effect on the coating morphology and composition as well as the anti-corrosion property. The work furthers the fundamental understanding on how organic and inorganic additives may synergistically act to enhance the properties of the conversion coating. We intend to shed light on the critical processing-structure-property relationship that need be considered and tailored for applying and designing novel conversion coatings for corrosion protection applications.Figure caption:Surface (top row) and cross-sectional morphology (bottom row) of the conversion coatings with 0 to 200 ppm PAMAM concentration in the coating solution. From the surface view, the cluster visually decreases with increase of PAMAM concentration. The flake-like morphology could be observed on sample with higher PAMAM concentration. From the cross-sectional view, the voids and thickness of the coating decreases with increasing PAMAM concentration.Reference:(1) Xiaoyang Liu, D. V., Hua Jiang, Kim Kisslinger, Xiao Tong, Mingyuan Ge, Evgeny Nazaretski, Bruce Ravel, Kate Foster, Stanislas Petrash, Yu-chen Karen Chen-Wiegart. Environmentally Friendly Zr-Based Conversion Nanocoatings for Corrosion Inhibition of Metal Surfaces Evaluated by Multimodal X-ray Analysis. ACS Appl. Nano Mater. 2019, DOI: 10.1021/acsanm.8b02309.(2) Donald Robb Vonk, T. S. S., Alvaro Bobadilla Thin Corrosion Protective Coatings Incorporating Polyamidoamine Polymers. Feb. 8, 2018. Figure 1

Effect of minor phase (CuO) on sinterability, grain size, and dielectric properties of CaCu3Ti4O12 ceramics

CaCu3Ti4O12 (CCTO) electro ceramic was prepared by a solid-state reaction technique. The formation of CCTO was confirmed by X-ray diffraction (XRD). Pellets of calcined powder were sintered at different temperatures for two different durations, i.e., 2 and 10 h (h). The morphology and grain size of the samples were observed using scanning electron microscopy (SEM). SEM images showed that the minor phase (CuO) plays an important role in the growth of grain size. It seems that higher sintering temperatures led to change in the oxidation states of Cu and Ti, which increase the volume fraction of the CuO minor phase. Dielectric studies show that the dielectric constant is increasing with increasing sintering temperature, holding time, and presence of the CuO phase. The highest dielectric constant of ~ 41,000 was observed for CCTO samples sintered at 1100 °C for 10 h. The present samples find application in the energy storage devices.

The State of Trace Elements (In, Cu, Ag) in Sphalerite Studied by X-Ray Absorption Spectroscopy of Synthetic Minerals

The oxidation state and local atomic environment of admixtures of In, Cu, and Ag in synthetic sphalerite crystals were determined by X-ray absorption spectroscopy (XAS). The sphalerite crystals doped with In, Cu, Ag, In–Cu, and In–Ag were synthesized utilizing gas transport, salt flux, and dry synthesis techniques. Oxidation states of dopants were determined using X-ray absorption near edge structure (XANES) technique. The local atomic structure was studied by X-ray absorption fine structure spectroscopy (EXAFS). The spectra were recorded at Zn, In, Ag, and Cu K-edges. In all studied samples, In was in the 3+ oxidation state and replaced Zn in the structure of sphalerite, which occurs with the expansion of the nearest coordination shells due to the large In ionic radius. In the presence of In, the oxidation state of Cu and Ag is 1+, and both metals can form an isomorphous solid solution where they substitute for Zn according to the coupled substitution scheme 2Zn2+ ↔ Me+ + In3+. Moreover, Ag K-edges EXAFS spectra fitting, combined with the results obtained for In- and Au-bearing sphalerite shows that the Me-S distances in the first coordination shell in the solid solution state are correlated with the ionic radii and increase in the order of Cu < Ag < Au. The distortion of the atomic structure increases in the same order. The distant (second and third) coordination shells of Cu and Ag in sphalerite are split into two subshells, and the splitting is more pronounced for Ag. Analysis of the EXAFS spectra, coupled with the results of DFT (Density Function Theory) simulations, showed that the In–In and Me+–In3+ clustering is absent when the metals are present in the sphalerite solid solution. Therefore, all studied admixtures (In, Cu, Ag), as well as Au, are randomly distributed in the matrix of sphalerite, where the concentration of the elements in the “invisible” form can reach a few tens wt.%.

Structure functionality relationship of flavonoids (myricetin, morin, taxifolin and 3′,4′-dihydroxyflavone). A computational study via the cupric ion probe

The antioxidant and/or prooxidant properties of flavonoids are strongly dependent on their redox metal chelating capacity as well as on the number and positions of hydroxyl groups. In this work the interaction between Cu(II) ion and the set consisting of four flavonoids (myricetin, morin, taxifolin and 3′,4′-dihydroxyflavone) is investigated using density functional theory (DFT) and quantum theory of atoms in molecules (QTAIM). Several potential Cu(II) acceptor sites are considered with respect to the number and positions of hydroxyl (and keto) functional groups within the particular flavonoid moiety. Suitability of the particular Cu(II) acceptor site is discussed from the energetics point of view, i.e. overall stability and interaction energies, electronic transitions are characterized and compared to experimental UV–Vis spectra in DMSO. The nature of the formed Cu-flavonoid chemical bonds is inspected using the bond critical point (BCP) analysis under the formalism of Bader's QTAIM method and the oxidation state of Cu is estimated with respect to the localized d-orbitals and d-populations. An impact of explicit DMSO solvent effects are considered as well.

Direct Hydrogenation of Nitroaromatics at Room Temperature Catalyzed by Magnetically Recoverable Cu@Fe2O3 Nanoparticles

Metal embedded in metal oxide nanoparticles are active as catalyst in plethora of industrially important reactions. Herein, embedded Cu@Fe2O3 nanoparticles was synthesized via a one step hydrothermal strategy which selectively catalyzes the hydrogenation of diverse nitroaromatics in H2O at room temperature. The remarkable catalytic performance is due to the successful hybridization of metallic Cu and Fe2O3 which in turn allows easy electroflipping between various oxidation states of Cu and Fe. Azo‐ and azoxy‐compounds are not formed during the catalyzed process. This evidently establish that the hydrogenation of nitroaromatics proceeds via direct route with >99% selectivity to the corresponding anilines.

Deactivation of Cu-Exchanged Automotive-Emission NH3 -SCR Catalysts Elucidated with Nanoscale Resolution Using Scanning Transmission X-ray Microscopy.

To gain insight into the underlying mechanisms of catalyst durability for the selective catalytic reduction (SCR) of NOx with an ammonia reductant, we employed scanning transmission X‐ray microscopy (STXM) to study Cu‐exchanged zeolites with the CHA and MFI framework structures before and after simulated 135 000‐mile aging. X‐ray absorption near‐edge structure (XANES) measurements were performed at the Al K‐ and Cu L‐edges. The local environment of framework Al, the oxidation state of Cu, and geometric changes were analyzed, showing a multi‐factor‐induced catalytic deactivation. In Cu‐exchanged MFI, a transformation of CuII to CuI and CuxOy was observed. We also found a spatial correlation between extra‐framework Al and deactivated Cu species near the surface of the zeolite as well as a weak positive correlation between the amount of CuI and tri‐coordinated Al. By inspecting both Al and Cu in fresh and aged Cu‐exchanged zeolites, we conclude that the importance of the preservation of isolated CuII sites trumps that of Brønsted acid sites for NH3‐SCR activity.

A DFT Study and Microkinetic Simulation in Propylene Oxidation on the “29” CuxO/Cu(111) Surface

The propylene epoxidation reaction in a rich variety of other industrially important catalytic processes was used for synthesis of many value-added products. As an attractive and environmentally friendly process for direct epoxidation of propylene by Cu-based catalysts, the active oxidation states of Cu (Cu0, Cu+, or Cu0/Cu+) in the epoxidation reaction were widely studied. Herein, “29” CuxO/Cu(111) was chosen to act as a precursor to bulk oxidation, as it can be observed in special oxide phases of Cu (Cux+). In our work, the crucial competitive reactions of dehydrogenation versus the epoxidation using the lattice oxygen (Olatt*) and adsorbed molecular oxygen as the oxidants were investigated on “29” CuxO/Cu(111) surface by virtue of the periodic density functional theory computational method. Because of the higher energy barriers of the key steps for the lattice oxygen (Olatt*) as the oxidant, there are two active species in the whole reaction processes of propylene oxidation with O2 as oxidant: the molecular O2* species and the atomic O* species. It was found that the molecular oxygen is difficult to dissociate on the surface directly, while the atomic O* species can be produced via the C3H6* + Olatt* + OO* = C3H5* + Olatt* + OOH* = C3H5Olatt* + O* + OH* mechanism or by the mechanism of C3H6* + OO* = dioxametallacycle = oxametallacycle + O*. It was found that the O* mechanism is preferred for the PO formation as compared to that of O2* on pure “29” CuxO/Cu(111) surface. Promising results in terms of selectivity were achieved for PO formation, which can reach 49% with the apparent activation energy of only 0.62 eV by microkinetic simulation. Therefore, “29” CuxO/Cu(111) surface involving the Cux+ active phase is expected to show an efficient PO selectivity, which is much higher that of Cu+ of Cu2O(111) and similar to that of metallic Cu0. It is hoped that the present study could provide a theoretical guide for the further development of catalysts for propylene epoxidation.

Investigating the Origin of Enhanced C2+ Selectivity in Oxide-/Hydroxide-Derived Copper Electrodes during CO2 Electroreduction.

Oxide-/hydroxide-derived copper electrodes exhibit excellent selectivity toward C2+ products during the electrocatalytic CO2 reduction reaction (CO2RR). However, the origin of such enhanced selectivity remains controversial. Here, we prepared two Cu-based electrodes with mixed oxidation states, namely, HQ-Cu (containing Cu, Cu2O, CuO) and AN-Cu (containing Cu, Cu(OH)2). We extracted an ultrathin specimen from the electrodes using a focused ion beam to investigate the distribution and evolution of various Cu species by electron microscopy and electron energy loss spectroscopy. We found that at the steady stage of the CO2RR, the electrodes have all been reduced to Cu0, regardless of the initial states, suggesting that the high C2+ selectivities are not associated with specific oxidation states of Cu. We verified this conclusion by control experiments in which HQ-Cu and AN-Cu were pretreated to fully reduce oxides/hydroxides to Cu0, and the pretreated electrodes showed even higher C2+ selectivity compared with their unpretreated counterparts. We observed that the oxide/hydroxide crystals in HQ-Cu and AN-Cu were fragmented into nanosized irregular Cu grains under the applied negative potentials. Such a fragmentation process, which is the consequence of an oxidation-reduction cycle and does not occur in electropolished Cu, not only built an intricate network of grain boundaries but also exposed a variety of high-index facets. These two features greatly facilitated the C-C coupling, thus accounting for the enhanced C2+ selectivity. Our work demonstrates that the use of advanced characterization techniques enables investigating the structural and chemical states of electrodes in unprecedented detail to gain new insights into a widely studied system.

Controlling the Oxidation State of the Cu Electrode and Reaction Intermediates for Electrochemical CO2 Reduction to Ethylene.

Understanding the role of the oxidation state of the Cu surface and surface-adsorbed intermediate species in electrochemical CO2 reduction is crucial for the development of selective CO2-to-fuel electrocatalysts. In this study, the electrochemical CO2 reduction mechanism over the Cu catalysts with various oxidation states was studied by using in situ surface-enhanced infrared absorption spectroscopy (SEIRAS), in situ soft X-ray absorption spectroscopy (Cu L-edge), and online gas chromatography measurements. The atop-adsorbed CO (COatop) intermediate is obtained on the electrodeposited Cu surface which primarily has the oxidation state of Cu(I). COatop is further reduced, followed by the formation of C1 product such as CH4. The residual bridge-adsorbed CO (CObridge) is formed on the as-prepared Cu surface with Cu(0) which inhibits hydrocarbon formation. In contrast, the CV-treated Cu electrode prepared by oxidizing the as-prepared Cu surface contains different amounts of Cu(I) and Cu(0) states. The major theme of this work is that in situ SEIRAS results show the coexistence of COatop and CObridge as the reaction intermediates during CO2 reduction and that the selectivity of CO2-to-ethylene conversion is further enhanced in the CV-treated Cu electrode. The Cu catalysts modulated by the electrochemical method exhibit different oxidation states and reaction intermediates as well as electrocatalytic properties.

Impediment to growth and yeast-to-hyphae transition in Candida albicans by copper oxide nanoparticles

The effects of two prominent copper oxide nanoparticles (CuO-NP and Cu2O-NP), with the oxidation state of Cu++ (cupric) and Cu+ (cuprous), on Candida albicans were evaluated. CuO-NP and Cu2O-NP were synthesized and characterized by XRD, FESEM, HR-TEM and Zeta potential. At sub-MIC (50 µg ml−1), both cupric and cuprous oxide NPs prevented yeast-to-hyphae switching and wrinkling behaviour in C. albicans. The mechanism for the antifungal action of the two NPs differed; CuO-NP significantly elicited reactive oxygen species, whereas membrane damage was more pronounced with Cu2O-NP. Real time PCR analysis revealed that CuO-NP suppressed the morphological switching of yeast-to-hyphae by down-regulating cph1, hst7 and ras1 and by up-regulation of the negative regulator tup1. In comparison, Cu2O-NP resulted in down-regulation of ras1 and up-regulation of the negative regulators nrg1 and tup1. Between the two NPs, CuO exhibited increased antifungal activity due to its stable oxidation state (Cu++) and its smaller dimensions compared with Cu2O-NP.

Quantitatively Unraveling the Redox Shuttle of Spontaneous Oxidation/Electroreduction of CuO x on Silver Nanowires Using in Situ X-ray Absorption Spectroscopy.

Oxide-derived copper catalysts have been shown to enhance CO2 reduction reaction (CO2RR) activity with high selectivity toward hydrocarbon products. However, the chemical state of oxide-derived copper during the CO2RR has remained elusive and is lacking in situ observations. Herein, a two-step process was developed to synthesize Ag nanowires coated with various thicknesses of a CuOx layer for the CO2RR. By employing in situ X-ray absorption spectroscopy, a strong correlation between the chemical state under reaction conditions and the CO2RR product profile can be revealed to validate another competing reaction (i.e., the spontaneous oxidation of Cu(0) in aqueous electrolyte) that significantly governs the chemical state of active centers of Cu. In situ Raman spectroscopy reveals the existence of reoxidation behavior under cathodic potential, and the quantification analysis of reoxidized behavior is revealed to indicate that the reoxidation rate is independent of surface morphology and strongly proportional to the electrochemically surface area. The steady oxidation state of Cu in an in situ condition is the paramount key and dominates the products’ profile of the CO2RR rather than other factors (e.g., crystal facets, atomic arrangements, morphology, elements) that have been investigated in numerous reports.

Structure, binding energy and optoelectrical properties of p-type CuI thin films: The effects of thickness

Ultra-high transparent p-type copper iodide (CuI) thin films were fabricated by solid iodization of evaporated Cu precursor layers at room temperature. The effect of the thickness on microstructure, binding energy and optoelectrical properties is systematically studied. X-ray diffraction measurements show the polycrystalline nature of the CuI thin films with zincblende type structure. The X-ray photoelectron spectroscopy (XPS) analysis indicates that the oxidation state of Cu is +1 and the estimated value of [Cu]/[I] at 100 nm is 0.87. Excess iodide ions trap considerable holes, causing CuI thin films to exhibit the p-type conductivity, which is consistent with the results of the Hall effect measurement and the non-linear characteristics of the CuI/ITO structure. Moreover, the CuI thin films with thickness of 100 nm exhibits an ultra-high optical transmittance of 95.5% in the wavelength of 380–780 nm and an excellent conductivity of 34 S/cm. These results prove the great potential of CuI as a promising p-type optoelectronic material.

Combinatorial Tuning of Structural and Optoelectronic Properties in CuxZn1−xS

Summary P-type transparent conductors (TCs) are important enabling materials for optoelectronics and photovoltaics, but their performance still lags behind n-type counterparts. Recently, semiconductor CuxZn1−xS has demonstrated potential as a p-type TC, but it remains unclear how properties vary with composition. Here, we investigate CuxZn1−xS across the entire alloy space (0 ≤ x ≤ 1) using combinatorial sputtering and high-throughput characterization. First, we find a metastable wurtzite alloy at an intermediate composition between cubic endpoint compounds, contrasting with solid solutions or cubic composites (ZnS:CuyS) from the literature. Second, structural transformations correlate with shifts in hole conductivity and absorption; specifically, conductivity increases at the wurtzite phase transformation (x ≈ 0.19). Third, conductivity and optical transparency are optimized within a "TC regime" of 0.10

Room temperature ferromagnetism in ZnO:Cu and ZnO:Ag co-doped with Al

Abstract The room temperature ferromagnetism in doped and co-doped ZnO is reported here. X-ray photoelectron spectroscopy revealed the mixed oxidation states of Cu and Ag in ZnO:Cu and ZnO:Ag films, respectively. However, co-doping of Cu and Ag with Al does not alter their bonding characteristics in ZnO. Al in +3 oxidation state indicates that substitution of Al to Zn site gives an extra electron which increases the conductivity of ZnO:Ag and ZnO:Cu films. Mott variable range hopping dominates the conduction in ZnO:Cu and ZnO:Ag films whereas thermally activated conduction dominates in Al co-doped ZnO:Ag and ZnO:Cu films. We show that Ruderman–Kittel–Kasuya–Yosida mechanism is not responsible for ferromagnetism in Cu and Ag doped ZnO as the increase in carrier concentration due to Al co-doping does not enhance the ferromagnetism. Finally, possible mechanism behind the ferromagnetism is discussed.

Comparative Studies of Some Novel Cu2+ and Fe3+ Chelates Derived From Tricine (L1) by Single Crystal X‐ray, Spectroscopic and Biological Data: Applications to Investigate Antitumor Activity

Novel Cu2+ and Fe3+ chelates derived from L1 were synthesized and characterized by single crystal X‐ray diffraction. The results indicate that the Fe (III) crystal, [Fe(L1‐H)Cl2], has an orthorhombic structure of the type pc2b while the dimeric Cu (II) crystal, [Cu(L1‐H)Cl … ClCu(L1‐H)], has a monoclinic with space group Cc. X‐ray diffraction and spectroscopic studies revealed that L1 acts as monobasic tetradentate with octahedral geometry in Fe (III) crystal while it behaves as dibasic tetradentate with distorted‐octahedral in the Cu (II) crystal. Also, the two chelates were characterized by spectral, magnetic and thermal analyses. DFT parameters were used to prove the liberation of a proton from COOH rather than NH groups. The kinetic and thermodynamic parameters of Fe (III) chelate were determined by Coats‐Redfern and Horowitz‐Metzger methods. Cyclic voltammogram provides information about the oxidation states of Cu (II) and Fe (III) chelates. Antitumor activity against Epitheliod carcinoma (Hela), breast cancer (MCF‐7) and antibacterial activities of chelates were investigated.

Toward Highly Dispersed Mesoporous Bioactive Glass Nanoparticles With High Cu Concentration Using Cu/Ascorbic Acid Complex as Precursor.

Copper (Cu) ions have a variety of advantageous biological functionalities, such as proangiogenic and bactericidal activities. Given the intrinsic biodegradability and biocompatibility, silicate-based mesoporous bioactive glass nanoparticles (MBGNs) are considered as promising platforms for the delivery of Cu ions. However, effective incorporation of Cu into MBGNs still faces challenges, e.g., particle aggregation, the formation of insoluble crystalline Cu-based nanoparticles, and a low loading amount of Cu. We report a novel method to synthesize chemically homogenous and highly dispersed Cu-containing MBGNs (Cu-MBGNs) with tunable Cu concentration by using ascorbic acid/Cu complexes as the precursor of Cu in a microemulsion-assisted sol-gel approach. Cu-MBGNs exhibited a sphere-like shape with a particle size between 100 and 300 nm while their pore size varied from 2 to 10 nm. The inclusion of Cu, regardless of the incorporated concentration, did not significantly affect the morphology of particles. ICP-AES results indicated that the concentration of Cu in the particles could be conveniently tuned from 0 to ~6 mol% by controlling the amount of ascorbic acid/Cu complexes added, while the formation of crystalline Cu-based nanoparticles was avoided. The amorphous feature of Cu-MBGNs was proved by XRD, while the predominant oxidation state of Cu was evidenced to be Cu2+ by XPS. The incorporation of Cu did not inhibit the apatite-forming ability (bioactivity) of the particles in contact with simulated body fluid. Cu-MBGNs exhibited the capability of releasing Cu, Si, and Ca ions over time in the physiological fluid. The concentration of released Cu ions could be controlled by selecting specific Cu-MBGNs of different Cu contents. The dissolution products of most Cu-MBGNs at the dosage of 1, 0.1, and 0.01 mg/mL did not exhibit cytotoxicity, while only 7Cu-MBGN was cytotoxic at the dosage of 1 mg/mL. This study provided a feasible strategy to synthesize highly dispersed amorphous Cu-MBGNs with high Cu concentrations for biomedical applications. The particles exhibit great potential as building blocks for developing composite 3D scaffolds, coatings, and drug carriers, particularly when a large amount of particles incorporated may compromise the properties of (polymer) matrix materials while a relatively high concentration of released Cu ions is still required.

Formation mechanism of Cu2O particles using layered CaSi2 as a reduction/oxidation mediator

AbstractWe demonstrate that Cu2O particles can be produced along with siloxene formation by simply dispersing layered CaSi2 into an aqueous solution of CuCl2 and HCl at room temperature. The Cl− ions induce oxidative extraction of Ca from CaSi2 to form siloxene and trigger the reductive deposition of Cu particles. All particles are then gradually oxidized to form Cu2O particles under optimized conditions as follows. A trace amount of residual CaSi2 is dissolved in the solution, which provides OH− ions, and a portion of the formed Cu particles are dissolved as [Cu(OH)4]2− ions. Accordingly, Cu2O particles would be formed through the comproportionation reaction between Cu and [Cu(OH)4]2− ions in the solution. However, under conditions with an excess amount of Cl− ions results in further oxidation of Cu to also form Cu2Cl(OH)3. Thus, CaSi2 acts as an effective reduction and/or oxidation mediator to tune the number of Cl− and OH− ions and control the oxidation state of Cu.