Valence State Of Copper Research Articles

Impact of adding Na2SiF6 on the crystal phase and copper valence state in glass ceramics made from leftover granite for use as architectural ornamentation

Abstract The accumulation of granite waste can result in the occupation of a considerable amount of land resources. Using granite waste as glass ceramics for architectural decoration represents a potential solution to this issue. The microstructure, valence state, and crystalline phase of copper ions were examined by using X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and X-ray diffraction (XRD). The findings demonstrated that the concentration of Na2SiF6 affects the valence condition of Cu ions in crystallized glass. The crystalline phases of the sample containing 1.84 wt% Na2SiF6 consisted of forsterite (MgSiO3) and diopside (CaMgSi2O6), and the Cu+ accounted for 39.9% of the total Cu ions in the sample which showed a grey-black color. For the sample containing 3.67 wt% Na2SiF6, the crystalline phases consisted of richterite (Na, F) syn (Na (Na, Ca) Mg5Si8O22F2), cuprite (Cu2O), and forsterite, its Cu+ accounted for 39.9%, and the sample appeared orange-red. With the increase of Na2SiF6 content, the percentage of Cu+ in the total Cu ions showed an increasing trend, and the corresponding red color of the samples gradually deepened.

Study of the stoichiometry effect on the structure and loss kinetics of photogenerated current carriers in Cu2-δBaSnS4 (0≤δ≤0.4) quaternary copper compounds

The solid-phase method was applied to synthesize Cu2-δ BaSnS4 (0≤δ ≤ 0.4) polycrystalline powders. The lattice parameters were refined. It was shown that the crystal structure parameters changed. For the first time, Raman spectra were experimentally obtained for copper-deficient samples. It was found that some difference in the position of major peaks is due to the Cu2-δBaSnS4 structure changing with increasing δ, as well as a partial valence change in tin or copper atoms. Using X-ray photoelectron spectroscopy, it was shown that when going from Cu2BaSnS4 to Cu1.6BaSnS4, there was no change in the valence state of copper, but the valence state of tin particularly changed. The lifetimes of the current carriers in the synthesized samples were significantly less than 10 ns.

Recovery of Cu, Co, and Fe from Pyrite Cinder Based on Mineral Phase Reconstruction.

Pyrite cinder (PyC) containing polymetallics is difficult to use due to the low grade of metals and complex mineral phase composition, the low reutilized rate of which causes the wastage of resources. In this paper, a novel approach based on mineral phase reconstruction was proposed to recover Cu, Co, and Fe from PyC. A feasible reduction roasting process was developed for mineral phase reconstruction, followed by leaching with sulfuric acid to recover Cu and Co; finally, the leaching residue was separated by a magnetic tube to recover Fe. The maximum copper and cobalt extract rates of 86.15 and 79.61% were achieved respectively under the optimized conditions of reduction roasting for 30 min at 550 °C and 30% CO/N2 volume fraction, followed by leaching for 4 h at a liquid-solid ratio of 4:1 (mL/g), a mass concentration of 160 g/L sulfuric acid, and a temperature of 70 °C. The iron concentrate can be obtained with 63.08% Fe grade and 98.91% recovery rate by magnetic separation at a magnetic field strength of 28.26 kA/m. The mechanism analysis results of mineral phase reconstruction revealed that the primary copper sulfide in PyC was transformed into free copper oxide, combined copper oxide, and secondary copper sulfide without changing the valence state of copper by reduction roasting, resulting in a higher extraction rate of copper. Meanwhile, cobaltosic oxide and cobalt ferrite in PyC were transformed into cobalt sulfate and cobalt sulfide with the reduction of Co(III) to Co(II), improving the extraction rate of cobalt.

Enhanced photocatalytic CO2 reduction to methanol by modulating valence states of copper in CuSrTiO3

Manipulating the oxidation states of transition metals is an ideal solution to achieve selective generation of different products and copper is widely used in CO2 photocatalytic reduction to methanol. However, the understanding on the effects of valence states of copper species in SrTiO3 on its structure and the selectivity of the corresponding product in CO2 photocatalysis are currently still limited. Here, copper-doped SrTiO3 nanofibers with different controllable ratios of Cu+/Cu2+ and Cu+/Cu0 were prepared by the combination of the electrospinning with the in-situ reduction method. The proportion of copper with different valence states (Cu+/Cu2+ and Cu+/Cu0) was changed by rationally adjusting the time of hydrogen reduction. The presence of monovalent copper facilitated the generation of reactive intermediates, thereby enhancing its photocatalytic activity. The copper-doped SrTiO3 nanofibers obtained after 3 h of hydrogen reduction (STCu0.08-H-3 h) had the highest proportion of Cu+/Cu2+ and Cu+/Cu0 with the highest methanol yield (6.96 μmol·g−1·h−1). Methanol generation rate and Cu+/Cu2+ ratio of STCu0.08-H-xh (x = 1, 2, 3, 4,5) with different hydrogen reduction time were proven to be linearly positively correlated. Furthermore, theoretical investigation and in-situ CO2 infrared spectrum deeply understood the difference of CO2 adsorption behavior and CO2 activation over Cu2+ and Cu+ of STCu0.08-H-3 h photocatalyst and the reaction intermediates involved in the photocatalytic CO2 reduction to methanol.

Mechanistic insights into temperature hysteresis in CO oxidation on Cu-TiO2 mesosphere

This study employs in-situ X-ray absorption spectroscopy (XAS) and operando Raman to explore the reaction mechanism of copper/titanium dioxide microspheres (CuTMS) in CO oxidation. A temperature-dependent hysteresis behavior was observed during catalytic CO oxidation, which can be divided into two distinct regions. In the low-temperature region, the transformation of CuO → Cu2O → Cu2O/Cu on the surface of CuTMS is detected via in-situ XAS, highlighting the pivotal role of surface-adsorbed oxygen in initiating this conversion process. Conversely, in the high-temperature region, analysis of Raman peak areas suggests a variation in the {001} and {101} facets of anatase. Specifically, a decrease in the {001} facets from 17% to 10% indicates TiO2-mediated oxygen transportation, which facilitates the reoxidization of reduced Cu species. This integrated approach showcases significant potential for unraveling the mechanistic studies of catalytic reaction mechanisms in copper/titanium systems, including surface copper valence state changes, oxygen replenishment, and crystal structure distortion.

Effect of fluorine on terrace-ledge-kink morphology and valence state of copper and titanium ions in CaCu3Ti4O12

Ceramic CaCu3Ti4O12 (ССТО), Ca0.98Cu3Ti4O11.96F0.04 (CΔCTOF), and CaCu3Ti4O11.92F0.08 (CCTOF) were synthesized by the solid-state reaction technique. Fluorine stimulates the formation of Cu-depleted grains, Cu3+ ions, and Cu-rich composites CuO-xCCTO-yTiO2-zSiO2-wСaF2 (w < z < y < x < 1), which include parts of grinding bodies. The observed structures are distinct from simple grain boundaries of the perovskite phase. They exhibit a terrace-ledge-kink (TLK) morphology and, in some cases, the presence of twinning planes, both independent of fluorine content. They are responsible for the nanoscale barrier layer capacitance (NBLC) component of the dielectric response of both CCTO and CuO ceramics. Changes in the unit cell parameter a, and titanium and copper valences indicate that Ca2+ ions occupy part of Cu vacancies in the grains of CCTO and CCTOF. In CΔCTOF, Ti3+ ions in the copper sublattice were found for the first time using NMR. The maximum ε′1kHz = 6.9 × 104 demonstrates CΔCTOF and the minimum tan δ = 0.045 is characteristic of CCTOF.

Different Valence States of Copper Ion Delivery against Triple-Negative Breast Cancer.

Different valence states of copper (Cu) ions are involved in complicated redox reactions in vivo, which are closely related to tumor proliferation and death pathways, such as cuproptosis and chemodynamic therapy (CDT). Cu ion mediated Fenton-like reagents induced tumor cell death which presents compelling attention for the CDT of tumors. However, the superiority of different valence states of Cu ions in the antitumor effect is unknown. In this study, we investigated different valence states of Cu ions in modulating tumor cell death by Cu-chelated cyanine dye against triple-negative breast cancer. The cuprous ion (Cu+) and copper ion (Cu2+) were chelated with four nitrogen atoms of dipicolylethylenediamine-modified cyanine for the construction of Cu+ and Cu2+ chelated cyanine dyes (denoted as CC1 and CC2, respectively). Upon 660 nm laser irradiation, the CC1 or CC2 can generate reactive oxygen species, which could disrupt the cyanine structure, achieving the rapid release of Cu ions and initiating the Fenton-like reaction for CDT. Compared with Cu2+-based Fenton-like reagent, the CC1 with Cu+ exhibited a better therapeutic outcome for the tumor due to there being no need for a reduction by glutathione and a shorter route to generate more hydroxyl radicals. Our findings suggest the precision delivery of Cu+ could achieve highly efficient antitumor therapy.

N-modulated Cu0-Cu+ sites for C1/C2 selectivity regulation of carbon dioxide electrocatalytic reduction

Controlling the valence states of copper is pivotal in determining the selectivity of products in CO2 electroreduction. In this study, we developed a Cu doped carbon catalyst (CuNC) derived from a metal-organic framework (MOFs) through a straightforward solution reaction and calcination method. The N-modulated Cu0-Cu+ sites exhibited adjustable C1 and C2 selectivity in electrocatalytic CO2 reduction (CER). Specifically, the CuNC-700 demonstrated an impressive C2 Faradaic efficiency (FE) of 56.0% at − 1.0 V vs reversible hydrogen electrode (RHE), and a remarkable C1 FE of 56.7% with a total current density of 600 mA/cm2 at − 1.6 V vs RHE. In the entire potential range, the CuNC-700 consistently maintained high FE values of > 92% for CER, while the FE values for hydrogen evolution reaction is below 8%. This study unveiled the correlation between the selectivity and the valence states of copper. At low applied potentials, the abundance of N-modulated Cu0-Cu+ sites led to the predominant production of the C2 products. The Cu0 played a primary role in activating CO2 and facilitating subsequent electron transfer, while the Cu+ enhanced the adsorption of *CO, further promoting the C-C coupling. Under high applied potentials, both Cu2+ and Cu+ were converted to Cu0, favoring the methanation process. This research paves the way for future design of Cu-based MOF-derived materials, enabling precise regulation of C1/C2 selectivity in CER.

Conductivity-mediated in situ electrochemical reconstruction of CuOx for nitrate reduction to ammonia.

The electrocatalytic nitrate reduction reaction (NO3RR) is an ideal NH3 synthesis route with ease of operation, high energy efficiency, and low environmental detriment. Electrocatalytic cathodes play a dominant role in the NO3RR. Herein, we constructed a carbon fiber paper-supported CuOx nanoarray catalyst (CP/CuOx) by an in situ electrochemical reconstruction method for NO3--to-NH3 conversion. A series of characterization techniques, such as X-ray diffraction (XRD) and in situ Raman spectroscopy, unveil that CP/CuOx is a polycrystalline-faceted composite copper nanocatalyst with a valence composition containing Cu0, Cu+ and Cu2+. CP/CuOx shows more efficient NO3--to-NH3 conversion than CP/Cu and CP/Cu2O, which indicates that the coexistence of various Cu valence states could play a dominant role. CP/CuOx with a suitable Cu2+ content obtained by adjusting the conductivity during the in situ electrochemical reconstruction process exhibited more than 90% faradaic efficiencies for the NO3RR in a broad range of -0.3 to -1.0 V vs. RHE, 28.65 mg cm-2 h-1 peak ammonia yield, and stable NO3RR efficiencies for ten cycles. These findings suggest that CP/CuOx with suitable copper valence states obtained by fine-tuning the conductivity of the electrochemical reconstruction may provide a competitive cathode catalyst for achieving excellent activity and selectivity of NO3--to-NH3 conversion.

Activating p-type conduction and visible transparency in delafossite CuAlO2 films: The critical role of the copper valence state transition

P-type oxide semiconductors with high p-type conductivity and visible transparency are highly desired for various electronic devices. However, achieving these two demands is challenging due to the localized oxygen 2p orbitals and compensating donors in oxides. This is seen in the representative delafossite CuAlO2, despite tremendous theoretical and experimental efforts in perfecting the lattice quality and physical properties. Here, we reveal the critical role of the copper valence state transition in activating high p-type conduction and visible transparency in CuAlO2. A two-step synthesis strategy is developed to fabricate c-axis-oriented CuAlO2 films with similar crystallinity but with very different Cu2+/Cu+ proportions on sapphire substrates. In combination with structural and transport characterizations, this study distinguishes the key impact of the cooper valence state from the more commonly noticed lattice crystallization, for simultaneously achieving a room-temperature p-type conductivity of >1 S/cm and visible transmittance of >75 %. We further demonstrate that the strategy of obtaining high-performance CuAlO2 films is applicable to n-type SiC substrates for fabricating pn heterojunction diodes with a rectifying ratio of 106. This study provides critical insights into designing and synthesizing high-performance p-type oxide semiconductors.

Adsorption behavior and mechanism of ethyl mercaptan in natural gas on Cu-modified hexaniobate nanotubes

The presence of sulfur compounds in natural gas seriously affects the yield of hydrogen production from natural gas reforming and the lifespan of catalysts. This study aims to clarify the characteristics and mechanism of the removal of ethyl mercaptan (EM) in equilibrium CH4 by Cu-modified hexaniobate nanotubes (Cu-HNT-450), which was synthesized through a method of copper ions exchange-flocculation-calculation. The EM breakthrough adsorption experiments and the valence state of copper and the types of sulfur on Cu-HNT-450 during dynamic tests were investigated. The removal of EM is mainly achieved through the chemical adsorption of CuO, Cu2O and oxygen on Cu-HNT-450. In the process of EM removal, catalytic oxidation, sulfonate formation and reactive adsorption lead to the formation of sulfide, copper sulfonate and copper thiolate, respectively. Cu-HNT-450 has the highest breakthrough adsorption capacity for EM, reaching 103.6 mg/g at 50 °C. The exhausted Cu-HNT-450 can also be regenerated by thermal treatment at different temperatures under nitrogen atmosphere. However, due to the strong chemical adsorption of sulfur containing compounds, the recovery of nitrogen thermal regeneration removal efficiency is limited. This research work provides guidance for the design of mercaptans removal catalysts and deepens the understanding of the reaction mechanism of mercaptans removal.

Flexible regulation of persulfate activation mechanisms through tuning Cu valence in CuBTC-derived copper oxide catalysts for improved pollutant degradation

Radical and nonradical dominated persulfate activation processes have pros and cons in the degradation of pollutants. It is challenging to flexibly tune the contribution ratios of radicals and nonradicals in a persulfate activation process for improved pollutant degradation. Herein, we successfully synthesize copper oxide catalysts derived from metal-organic frameworks. By varying the annealing temperature, valence states of copper can be regulated in the catalyst, thereby enabling the switching between radical and nonradical mechanisms for persulfate activation. Copper oxides annealed at 300 °C (CuBTC-300) demonstrate high performance in peroxydisulfate (PDS) activation for the degradation of bisphenol A (BPA), with the synergy of radical and nonradical mechanisms. The surface activated PDS-catalyst complex and OH are identified as the reactive oxidative species involved in this process. On one hand, PDS undergoes a one-electron transfer reaction with Cu(I) sites in Cu2O, generating SO4−, which subsequently converts into OH for BPA degradation. On the other hand, the combination of PDS molecules with CuO forms surface-activated complexes, depriving electrons from BPA. The increased content of Cu(II) in the catalyst gradually directs PDS activation towards the nonradical pathway. As the annealing temperature increases from 300 °C to 500 °C, the contribution of nonradical oxidation to BPA degradation increases from 58.65 % to 100 %. This work provides new insights into flexibly regulating persulfate activation mechanisms via rational catalysts design.

Self-supported copper selenide nanosheets for electrochemical carbon dioxide conversion to syngas with a broad H2-to-CO ratio

Production of syngas from carbon dioxide (CO2) and water (H2O) is greatly attractive but very challenging for accomplishing tuneable/wide range of H2-to-CO ratios at current density. Herein, the anion-regulated self-supported Cu3Se2 with a hierarchical structure of nanosheet-assembled fibers, enabling multiple copper valence states and abundant in situ formed copper boundaries simultaneously regulating electrochemical CO2 reduction reaction (CO2RR) and H2 evolution reaction (HER). As a consequence, the delicate design of Cu3Se2 catalyst results in an outstanding electrocatalysis of syngas generation with a tuneable/wide range of H2-to-CO ratios (0.8 to 6.0), and high turnover frequency of 1303 h−1, which can achieve a high current density much higher than Cu foam and stable electrolysis with negligible attenuation of Faraday efficiency and current. The superior performance is attributed to the multiple copper valence states for activation of CO2, and the abundant boundaries for modifying the binding energy of intermediate for *COOH formation and *CO desorption and hydrogen adsorption for HER process. Therefore, the design of anion-regulated electrocatalysts with self-supported Cu3Se2 nanosheet-assembled fibers show great potential for the investigation of value-added chemicals/fuels from CO2RR.

Insight into the Role of Copper in the Transformation of a [Ag25(2,5-DMBT)16(DPPF)3]+ Nanocluster: Doping or Oxidation.

Structural transformation in nanoclusters is important not only in obtaining functional nanoclusters controllably but also in understanding their structural evolution. This study investigated the role of Cu2+ ions in structural transformation. It was revealed that Cu2+ exhibits two different functions, doping and oxidation, in determining the final products. Starting with a new silver nanocluster, [Ag25(2,5-DMBT)16(DPPF)3]+ (Ag25), a doping process would occur when no more than 0.5 equiv of Cu2+ was added, resulting in the formation of [Ag25-xCux(2,5-DMBT)16(DPPF)3]+ (Ag25-xCux). When 1 equiv of Cu2+ was introduced to Ag25, a structural transformation process would occur instead, forming [Ag22-xCux(2,5-DMBT)12(DPPF)4Cl4]2+ (Ag22-xCux). Considering the similar Cu doping amounts in Ag25-xCux and Ag22-xCux, an oxidation process induced by Cu2+ in the solution can account for this transformation process, which was further demonstrated by the addition of other oxidant substitutions. On the other hand, the role of other valence states of copper in the transformation of the Ag25 cluster was explored. It was found that copper powder can hardly change Ag25 and Cu+ can only proceed the doping process, both of which are different from the role of Cu2+. Overall, this work explores the role of copper in the transformation of the Ag25 cluster in detail, including its concentrations and valence states.

Valence State of Copper in CuI–AgI–As2Se3 Chalcogenide Films and Membrane Surface Composition of Ion-Selective Electrodes According to the Data of X-Ray Photoelectron and Auger-Electron Spectroscopy

Valence State of Copper in CuI–AgI–As2Se3 Chalcogenide Films and Membrane Surface Composition of Ion-Selective Electrodes According to the Data of X-Ray Photoelectron and Auger-Electron Spectroscopy

Cu-Based Multicomponent Metallic Compound Materials as Electrocatalyst for Water Splitting.

In this study, Cu-based multicomponent metallic compound materials M-Cu (M = Mn, Fe, Co, Ni, and Pt) were studied as electrocatalytic materials for water splitting. Different metal materials attached to the copper foam substrate can change the valence states of copper and oxygen, resulting in the change of electronic structure of the materials, thus changing its catalytic activity.

Role of oxygen partial pressure of synthesis environment in tuning the dielectric properties of Nd2CuTiO6

Dielectric studies were carried out on Nd2CuTiO6 samples prepared by high temperature solid-state reaction followed by annealing under different oxygen partial pressures. X-ray diffraction studies revealed that the orthorhombic (Pnma) structure of Nd2CuTiO6 is retained in all the samples. The room temperature permittivity at 100Hz was found to be about 200 in the air-annealed sample, and it increased considerably to about 3000 upon annealing in argon atmosphere. The electrical conductivity in the argon-annealed compound was found to be an order of magnitude higher than that for the air-annealed sample. On annealing in oxygen, both permittivity and electrical conductivity of the sample were found to be significantly reduced. The variation in dielectric properties could be attributed to the induction or annihilation of mixed valence state of copper and oxygen vacancies, which was supported by X-ray photoelectron and diffuse reflectance spectroscopy data. The analysis of temperature and frequency dependent conductivity and dielectric data showed that the overlapping large polaron tunnelling (OLPT) mechanism is responsible for the observed dielectric relaxations and conduction. The observed systematic dependence of properties on the oxygen partial pressure of the annealing environment suggests a simple method to tune the electrical properties of Nd2CuTiO6.

Hierarchical porous hollow N-doped Cu-based MOF derivatives as highly sensitive electrochemical sensing platform for pesticides detection

Pesticides have long posed serious threats to human health, and the development of efficient sensors for ultratrace pesticides detection is urgently needed. In this work, a class of hierarchical porous hollow N-doped Cu-based nanocages (HPH-N-Cu NCs) is reported as a highly sensitive electrochemical sensing platform for organophosphates pesticide detection. Due to their unique micro-/mesoporous structures, the changeable valence state of copper and heteroatom doping, HPH-N-Cu NCs show more exposed active sites, multiple reaction interfaces and enhanced conductivity, which result in high electrocatalytic ability toward the oxidation of electroactive products. Accordingly, the acetylcholinesterase (AChE) biosensor based on HPH-N-Cu NCs shows a smaller Michaelis-Menten constant of 126 μM for acetylthiocholine chloride, while achieving a low detection limit of 2.58 × 10−11 g/L (S/N = 3) and a wide detection range of 1.00 × 10−9 to 1.00 × 10−3 g/L for methamidophos. Moreover, the prepared biosensor exhibits good stability and high accuracy in real sample detection. The HPH-N-Cu NCs electrode materials may serve as promising tools for the sensitive monitoring of multiple pollutants.

The promotion effect of iron to Cu/ZSM‐5 catalyst for NOx removal by NH3‐SCR

AbstractThe Cu/ZSM‐5 and Cu‐Fe/ZSM‐5 catalysts (ZSM‐5 with Si:Al ratio of 25:1) were created utilizing the liquid ion‐exchange technique. The effects of Fe on the physical and chemical characteristics of Cu/ZSM‐5 catalysts were investigated using X‐ray diffraction, field‐emission scanning electron microscopy, energy‐dispersive X‐ray spectroscopy, nitrogen adsorption/desorption, and temperature‐programmed ammonia desorption. The coordination and valence state of copper and iron elements at intersections or in channels of ZSM‐5 was determined by the electron paramagnetic resonance technique. The effects of metal doping on the structure and catalytic activity of all catalysts were comprehensively investigated for NOx removal utilizing selective catalytic reduction with ammonia (NH3‐SCR). The results indicated that the promotion of iron significantly increased the NOx conversion and N2 selectivity of the Cu/ZSM‐5 catalyst for NH3‐SCR in the temperature range from 200 to 600 °C, and catalysts were highly resistant to high space velocity. This article describes a simple and uncomplicated method for synthesizing the commercially viable catalyst used in NH3‐SCR technology to reduce NOx emissions.

Investigating the Effect of the Initial Valence States of Copper on CO2 Electroreduction

AbstractAbstract: The valence states of copper always play an important role for the most studied copper‐based catalysts in CO2 electroreduction (CO2ERR). In this work, distinct Cu, Cu2O, and CuO nanoparticles with similar particle size on active carbon are synthesized via carbonthermal reduction. Although all CuOx nanoparticles are reduced to metallic Cu during CO2ERR, their different initial valence states result in particle‐size variations and different CO2ERR performances. Cu nanoparticles in Cu/C evolve into smaller particles, while those derived from Cu2O/C and CuO/C agglomerate into larger ones. The optimal CO production potential of CO drops with decreasing particle size and is as low as −0.7 V (vs. the eversible hydrogen electrode) on Cu/C. Furthermore, Cu nanoparticles in Cu/C expose much more active sites with higher electrochemical active area and stronger CO adsorption, which further promote C−C coupling to produce C2+ products while inhibiting competitive hydrogen evolution.