CuO Particles Research Articles

Thermal hysteresis enhancement and dispersion thermal stability in paraffin actuators: Comparison of pan-nanofibers vs metal oxide nanoparticles use

In this research, the possibility of thermal property enhancement of paraffin actuators with nanofiber and metal oxide nanoparticle addition was experimentally evaluated. Besides pure paraffin compound, paraffin mixed with the CuO, Fe3O4, ZnO, Al2O3, and electrospun polyacrylonitrile (PAN) nanofiber nanoparticles were used, and a significant hysteresis improvement at first-level measurement was observed as 24.6, 26.2, 20.0, 29.2, and 30.8 % sequentially for the samples respectively compared with pure paraffin. Thermal dispersion stability of the nanocomposites was comprehended via computer tomographic (CT) investigation. The excessive precipitation of CuO, Fe3O4, and ZnO particles in the paraffin nanocomposite was observed. Precipitation of PAN Nanofiber- and Al2O3-Paraffin nanocomposite was not visually detectable via CT throughputs. The effect of thermal dispersion stability on the hysteresis performance of the nanocomposites was also investigated to ensure long-term consistent hysteresis performance advantages in paraffin actuators. Thermal dispersion stability effect on hysteresis performance of paraffin actuators with CuO, Fe3O4, ZnO, Al2O3, and PAN nanofiber nanocomposite paraffin compounds showed losses as 14.3, 14.6, 5.8, 4.3 and 2.2 % sequentially for the samples respectively.

Localized Oxidative Catalytic Reactions Triggered by Cavitation Bubbles Confinement on Copper Oxide Microstructured Particles.

Efficient energy transfer management in catalytic processes is crucial for overcoming activation energy barriers while minimizing costs and CO2 emissions. We exploit here a concept of CuO particle design with multiple gas-stabilizing sites, engineered to function as cavitation nuclei and catalysts. This concept facilitates the selective and efficient acoustic energy transfer directly to the catalyst surface, avoiding the undesired dissipation of acoustic energy into the bulk solution while demonstrating superior cavitation properties at lower acoustic pressure amplitudes. Utilizing a chemical thermometric approach, we demonstrate that the local temperature on the surface of our CuO particles during cavitation bubble implosions can create an effective equivalent temperature of about 360°C. This temperature effect facilitates the efficient catalysis of oxidative reactions using an organic probe molecule. Density functional theory (DFT) calculations were used to assess the decomposition of H2O2 and of pollutant probe molecule on CuO (111). Our work represents a significant advance in sonocatalytic systems, promising efficient energy use in catalytic reactions.

Localized Oxidative Catalytic Reactions Triggered by Cavitation Bubbles Confinement on Copper Oxide Microstructured Particles.

Efficient energy transfer management in catalytic processes is crucial for overcoming activation energy barriers while minimizing costs and CO2 emissions. We exploit here a concept of CuO particle design with multiple gas‐stabilizing sites, engineered to function as cavitation nuclei and catalysts. This concept facilitates the selective and efficient acoustic energy transfer directly to the catalyst surface, avoiding the undesired dissipation of acoustic energy into the bulk solution while demonstrating superior cavitation properties at lower acoustic pressure amplitudes. Utilizing a chemical thermometric approach, we demonstrate that the local temperature on the surface of our CuO particles during cavitation bubble implosions can create an effective equivalent temperature of about 360°C. This temperature effect facilitates the efficient catalysis of oxidative reactions using an organic probe molecule. Density functional theory (DFT) calculations were used to assess the decomposition of H2O2 and of pollutant probe molecule on CuO (111). Our work represents a significant advance in sonocatalytic systems, promising efficient energy use in catalytic reactions.

Integrating Cu+/Cu0 sites on porous nitrogen-doped carbon nanofibers for stable and efficient CO2 electroreduction to multicarbon products

The Cu+/Cu0 sites of copper-based catalysts are crucial for enhancing the production of multicarbon (C2+) products from electrochemical CO2 reduction reaction (eCO2RR). However, the unstable Cu+ and insufficient Cu+/Cu0 active sites lead to their limited selectivity and stability for C2+ production. Herein, we embedded copper oxide (CuOx) particles into porous nitrogen-doped carbon nanofibers (CuOx@PCNF) by pyrolysis of the electrospun fiber film containing ZIF-8 and Cu2O particles. The porous nitrogen-doped carbon nanofibers protected and dispersed Cu+ species, and its microporous structure enhanced the interaction between CuOx and reactants during eCO2RR. The obtained CuOx@PCNF created more effective and stable Cu+/Cu0 active sites. It showed a high Faradaic efficiency of 62.5% for C2+ products in H-cell, which was 2 times higher than that of bare CuOx (∼31.1%). Furthermore, it achieved a maximum Faradaic efficiency of 80.7% for C2+ products in flow cell. In situ characterization and density functional theory (DFT) calculation confirmed that the N-doped carbon layer protected Cu+ from electrochemical reduction and lowered the energy barrier for the dimerization of *CO. Stable and exposed Cu+/Cu0 active sites enhanced the enrichment of *CO and promoted the C–C coupling reaction on the catalyst surface, which facilitated the formation of C2+ products.

Investigation of Copper Anodization Products with Temperature and Chemical Solution Changes

The rapid breakdown anodization (RBA) process was used to modify the copper surface and produce copper oxide powder. The effects of the temperature and inhibitors like glycerol and ethylene glycol were studied. The rate of corrosion increased dramatically at low temperatures, whereas it decreased at high temperatures. Cubic Cu2O particles were formed on the anode. Their volumes increased with increasing temperatures. Scanning electron microscope (SEM) images show the production of semispherical particles in the powder formed at low temperatures, but these particles congregate and combine at high temperatures. After using the glycerol, octahedron and semispherical Cu2O particles were formed on the anode and cathode, respectively. The findings confirm the concept that the anodizing process's temperature may be utilized for controlling the oxide to metal ratio. Significant slowing of the anodic process occurs at high ratios for both inhibitors.

Facile one-pot synthesis of CuO–Bi2O3/MgAl2O4 catalyst and its performance in the ethynylation of formaldehyde

The CuO–Bi2O3/MgAl2O4 catalyst was synthesized via one-pot synthesis and used to catalyze formaldehyde (HCHO) ethynylation. Coprecipitation using Cu2+, Bi3+, Mg2+, and Al3+ nitrates and NaOH generated Cu and Bi oxides and spinel MgAl2O4 phase. The catalyst precursor was calcined at 450 °C. The catalytic performance of CuO–Bi2O3/MgAl2O4 in the synthesis of 1,4-butynediol via HCHO ethynylation was investigated. The presence of a new spinel phase enhanced the acid–base properties on the catalyst surface and prevented the aggregation of CuO particles. These properties resulted in improved CuO dispersion during calcination and CuO particle growth suppression, affording smaller CuO crystals. The MgAl2O4 support facilitated the reduction of Cu2+ to Cu+ and formation of abundant active species during the reaction. The catalyst exhibited abundant weakly basic, fewer strongly basic, and least acidic sites, which facilitated the adsorption of HCHO and acetylene. The catalytic performance of CuO–Bi2O3/MgAl2O4 demonstrated 97 % conversion and 80 % selectivity after the online monitoring of the ethynylation reaction for 6 h. The leaching of Cu during the reaction, as analyzed by inductively coupled plasma spectroscopy, was extremely low. Moreover, conversion and selectivity did not substantially change after eight cycles. In addition, the catalyst exhibited superior activity and long-term stability in the ethynylation reaction.

Experimental and numerical study on CuO/ZnO-modified aramid fabric for ballistic and UV radiation protection

Aramid fabrics are widely used in bulletproof armor because of their excellent mechanical properties. Previous studies have shown that ultraviolet radiation has a negative effect on the mechanical properties of aramid yarn, so improving the mechanical properties and impact resistance of aramid fabrics under ultraviolet radiation has become a research focus. In this work, aramid fabric was modified with CuO and ZnO particles to improve its ballistic performance under ultraviolet radiation. The ballistic impact resistance response and microscopic failure mechanisms of aramid fabrics under ultraviolet radiation were analyzed in detail. Under ultraviolet radiation, the ballistic limit velocity (vbl) of the CuO/ZnO-modified aramid fabric was 185.1 % greater than that of a neat fabric with a similar areal density. The vbl of the single-layer modified fabric was 45.6 % greater than that of the two-layer neat fabrics. The decrease in the ballistic performance of the aramid fabric under ultraviolet radiation was attributed to surface damage caused by the fracture of the chemical structure of the fibers, which weakened the mechanical properties of the fabric. The numerical simulation results were highly consistent with the ballistic impact test results, and the error between the numerical simulation and experimental results was within 10 %. The effects of changes in the mechanical parameters of the fabrics on the protection mechanism and energy absorption structure during ballistic impact were investigated. The energy dissipation of the modified fabric was at least 147.7 % greater than that of the neat fabric, further explaining the significant improvement in the ballistic performance of CuO/ZnO-modified fabrics under ultraviolet radiation.

Synthesis of undoped and mixed binary transition metals (Ni-Co)-doped cupric oxide nanostructures: Structural characteristics, optical behavior, and biological activity

In this work, co-precipitation-assisted undoped and various concentrations (1%, 3%, and 5%) Ni-Co-doped CuO nanostructures have been synthesized to test the biomedical applications. The structure, optical band gap, zone of inhibition width, hemocompatibility, and free radical scavenging activity of the CuO are significantly varied by introducing various concentrations of co-dopants compared to the undoped CuO. The single phase of monoclinic and heterogeneous crystal systems (monoclinic CuO, hexagonal Co, cubic NiO, and Co3O4) for undoped CuO and all Ni-Co-doped CuO samples was identified by the powder XRD tools. Microstructural properties were tuned in each dopant concentration of Ni-Co in the CuO, which confirmed through FE-SEM analysis. Heterogeneous structures (spherical particles/sheet-like particles) were noticed in the HR-TEM studies of 5% Ni-Co-doped CuO nanostructures. Synthesized compounds related to the elements (Cu, O, Co, and Ni) were traced with the help of the EDX and XPS study. The photoabsorption spectra and optical band gap values of the undoped CuO and co-doped CuO samples were significantly varied. Antimicrobial studies of the undoped CuO and Ni-Co co-doped CuO against E. coli and S. mutans bacterial strains were performed, and their outcomes of the zone of inhibition (ZOI) values have been discussed in detail. The synthesized undoped and various concentrations of CuO particles were taken to investigate their compatibility via hemolytic study. Hemolysis results showed that both the synthesized undoped CuO and Ni-Co doped CuO nanostructures are highly hemocompatible. In addition, compatibility natures are varied with increasing concentrations from 1% to 5% Ni-Co dopant in the CuO samples. The DPPH assay was employed to evaluate the antioxidant properties of the synthesized particles by determining their free radical scavenging (FRS) activity percentages. It was observed that Ni-Co-doped CuO exhibited better antioxidant properties than undoped CuO due to the higher FRS percentage.

Highly selective alginate/CuO mixed matrix membranes for efficient dehydration pervaporation of various organic solvents

Pervaporation is an energy-efficient technique for dehydrating organic solvents from aqueous mixtures. To develop a highly selective pervaporation membrane with broad usage, we incorporated three types of CuO particles (solid CuO-S, sea urchin-like CuO-U, and porous CuO-P) into sodium alginate (Alg) for fabricating the Alg/CuO mixed matrix membranes (MMMs). The CuO syntheses and membrane preparation are simple and eco-friendly. The synthesized particles and membranes were systematically characterized. The improved hydrophilic feature of Alg/CuO MMMs was validated from the reduced water contact angle and higher water swelling ratio with increasing CuO wt%. When the Alg/CuO MMMs were applied to the pervaporation of 30 wt% water/isopropanol (IPA) at 25 ℃, both the permeation flux and separation factor were enhanced significantly compared to the pure Alg membrane. The separation efficiency followed the order of Alg/CuO-S MMMs < Alg/CuO-U MMMs < Alg/CuO-P MMMs, in good agreement with their water swelling tendency. The incorporation of 3 wt% porous CuO-P particles in MMM achieved the optimal dehydration efficacy (normalized total flux of 3.5 kg m-2h−1, separation factor of ca. 5000, and water purity of 99.96 wt%, with a stable performance over 168 h). A further larger loading wt% led to a decreased separation selectivity due to more void formation from particle aggregation. With an increase in feed temperature, both the permeation flux and separation factor were improved; however, the increase in feed water concentration deteriorated the separation selectivity while enhancing the flux. Furthermore, the high selectivity and broad applicability of Alg/3% CuO-P MMM were fruitfully demonstrated by exhibiting superior separation efficiencies in dehydrating various polar aprotic solvents compared with several membranes discussed in the literature.

Effect of cyclic oxidation temperature on compressive strength of Cu-based brake pad for high-speed train

The cyclic oxidation tests of Cu-based brake pads at temperatures of 25, 300, 400, 500, 550, 600, 650 and 700 °C were conducted to simulate the oxidation of the friction surface under different braking speeds. Furthermore, the effect of cyclic oxidation temperature on the compressive strength was investigated. The results show that the cyclic oxidation process of Cu-based brake pads can be divided into three stages: mild oxidation (≤400 °C), moderate oxidation (500–600 °C) and severe oxidation (≥650 °C). Mild oxidation results in the formation of spherical Cu2O particles. The surface is covered by Cu2O and Fe2O3 nanosheets for moderate oxidation. Severe oxidation is characterized by a continuous thick CuO film, Fe2O3 nanosheets, and eroded graphite particles. The compressive strength and toughness of Cu-based brake pads show a declining trend as the cyclic oxidation temperature rises. The compressive strength of the Cu-based brake pad after oxidized at 700 °C, recorded at 30.56 MPa, is considerably lower than that of the original samples, which was 132.2 MPa. This reduction in compressive strength is attributed to the embrittlement of the metallic matrix and the formation of pores from graphite oxidation.

Restructuring of Cu-based Catalysts during CO Electroreduction: Evidence for the Dominant Role of Surface Defects on the C2+ Product Selectivity.

CO is the key reaction intermediate in the Cu-catalyzed electroreduction of CO2 to products containing C-C bonds. Herein, we investigate the impact of the particle size of CuO precursors on the direct electroreduction of CO (CORR) to C2+ products. Flame spray pyrolysis was used to prepare CuO particles with sizes between 4 and 30 nm. In situ synchrotron wide-angle X-ray scattering (WAXS), quasi-in situ X-ray photoelectron spectroscopy, and transmission electron microscopy demonstrated that, during CORR, the CuO precursors transformed into ∼30 nm metallic Cu particles with a crystalline domain size of ∼17 nm, independently of the initial size of the CuO precursors. Despite their similar morphology, the samples presented different Faradaic efficiencies (FEs) to C2+ products. The Cu particles derived from medium-sized (10-20 nm) CuO precursors were the most selective to C2+ products (FE 60%), while those derived from CuO precursors smaller than 10 nm displayed a high FE to H2. As the oxidation state, the particle and the crystallite sizes of these samples were similar after CORR, the differences in product distribution are attributed to the type and density of surface defects on the metallic Cu particles, as supported by studying electrochemical oxidation of the reduced Cu particles during CV cycling in combination with synchrotron WAXS. Cu particles derived from <10 nm CuO contained a higher density of more under-coordinated defects, resulting in a higher FE to H2 than Cu particles derived from 10 to 30 nm CuO. Bulk oxidation was most prominent and stable for Cu particles derived from medium-sized CuO, which indicated the more disordered nature of their surface compared to Cu particles derived from 30 nm CuO precursors and their lower reactivity compared to Cu particles derived from small CuO. Cu particles derived from <10 nm CuO initially displayed intense redox behavior, quickly fading during subsequent CVs. Our results evidence the significant restructuring during the electrochemical reduction of CuO precursors into Cu particles of similar size. The differences in CORR performance of these Cu particles of similar size can be correlated to different surface structures, qualitatively resolved by studying surface and bulk oxidation, which affect the competition between CO dimerization to yield C2+ products and undesired H2 evolution.

Improved interfacial mechanical properties between PZT piezoelectric ceramic and Ag metallization layer by in-situ-formed CuO nanoparticles

In-situ-formed CuO nanoparticles were used to improve the interfacial mechanical properties between lead zirconate titanate (PZT) ceramic and metallization layer. The effects of CuO particles on the mechanical properties of PZT/Ag interfaces were studied, and the damage evolutions of the PZT-CuO/Ag interfaces were analyzed. The results showed that both the maximum peeling stress σmax and shear stress τmax of the PZT-CuO/Ag interfaces increased by approximately 200 %, while the critical fracture energy GIC of the interface was increased at most by seven times. The enhanced mechanical properties of the PZT-CuO/Ag interfaces originated from the high bonding strength between CuO and Ag layer and the effective stress concentration relief. Crack deflection and crack pinning effects promoted the enhancement of interfacial fracture toughness. The optimal size of the CuO particles at the PZT/Ag interface was approximately 100 nm. Notably, the electron transport between the PZT ceramic and Ag layer was not degraded with the introduction of CuO nanoparticles.

Copper decorated cuprous oxide–carbon nitride plasmonic p-n heterojunction with high-efficiently charge transfer for photodegradation of tetracycline

In this work, a novel copper decorated cuprous oxide–carbon nitride (Cu@Cu2O-g-C3N4) plasmonic p-n heterojunction was prepared by solvothermal method using pre-synthesized carbon nitride and Cu@Cu2O precursors as raw materials. The morphology observation for the sample exhibits that Cu2O precursor is dispersed from micrometer octahedrons to the particles with the sizes of 20 ∼ 200 nm under action of dimethylformamide, forming a close contact between Cu nanoparticles, Cu2O particles and g-C3N4 stacking flakes. The results of photodegradation shown that 96.4 % of 10 mg·L−1 tetracycline (TC) solution was decomposed within 60 min and degradation rate decreased by 9.2 % after five cycles. Photoelectrochemical characterizations indicated that photocatalytic performance of Cu@Cu2O-g-C3N4 was attributed to high-efficiently charge transfer base on the synergistic effect of heterojunction and plasmon resonance. The formation of p-n type built-in electric field between Cu@Cu2O and g-C3N4 enhances photocatalytic oxidative and reductive ability of the catalyst, and dual coupling effects induced by the localized surface plasmon resonance of Cu nanoparticles promote the amount of photogenerated electrons. This work provides a strategy for preparing efficient p-n heterojunction photocatalysts with plasma coupling effects by reconstructing the junction interface using facile solvothermal method.

Transformation of Cu2O into Metallic Copper within Matrix of Carboxylic Cation Exchangers: Synthesis and Thermogravimetric Studies of Novel Composite Materials.

In order to systematize and expand knowledge about copper-containing composite materials as hybrid ion exchangers, in this study, fine metallic copper particles were dispersed within the matrix of a carboxyl cation exchanger (CCE) with a macroporous and gel-type structure thanks to the reduction of Cu2O particles precipitated within the matrix earlier. It was possible to introduce as much as 22.0 wt% Cu0 into a gel-type polymeric carrier (G/H#Cu) when an ascorbic acid solution was used to act as a reducer of Cu2O and a reagent transforming the functional groups from Na+ into the H+ form. The extremely high shrinkage of the porous skeleton containing -COOH groups (in a wet and also dry state) and its limited affinity for water protected the copper from oxidation without the use of special conditions. When macroporous CCE was used as a host material, the composite material (M/H#Cu) contained 18.5 wt% Cu, and copper particles were identified inside the resin beads, but not on their surface where Cu2+ ions appeared during drying. Thermal analysis in an air atmosphere and under N2 showed that dispersing metallic copper within the resin matrix accelerated its decomposition in both media, whereby M/H#Cu decomposed faster than G/H#Cu. It was found that G/H#Cu contained 6.0% bounded water, less than M/H#Cu (7.5%), and that the solid residue after combustion of G/H#Cu and M/H#Cu was CuO (26.28% and 22.80%), while after pyrolysis the solid residue (39.35% and 26.23%) was a mixture of carbon (50%) and metallic copper (50%). The presented composite materials thanks to the antimicrobial, catalytic, reducing, deoxygenating and hydrophobic properties of metallic copper can be used for point-of-use and column water/wastewater treatment systems.

Plasma-catalytic direct oxidation of methane to methanol over Cu-MOR: Revealing the zeolite-confined Cu2+ active sites

Efficient methane conversion to methanol remains a significant challenge in chemical industry. This study investigates the direct oxidation of methane to methanol under mild conditions, employing a synergy of non-thermal plasma and Cu-MOR (Copper-Mordenite) catalysts. Catalytic tests demonstrate that the Cu-MOR IE-3 catalyst (i.e., prepared by three cycles of ion exchange) exhibits superior catalytic performance (with 51 % methanol selectivity and 7.9 % methane conversion). Conversely, the Cu-MOR catalysts prepared via wetness impregnation tend to over-oxidize CH4 to CO and CO2. Through systematic catalyst characterizations (XRD, TPR, UV–Vis, HRTEM, XPS), we elucidate that ion exchange mainly leads to the formation of zeolite-confined Cu2+ species, while wetness impregnation predominantly results in CuO particles. Based on the catalytic performance, catalyst characterizations and in-situ FTIR spectra, we conclude that zeolite-confined Cu2+ species serve as the active sites for plasma-catalytic direct oxidation of methane to methanol.

Innovative insights into nanofluid-enhanced gear lubrication: Computational and experimental analysis of churn mechanisms

This study offers unique insights into the churn lubrication mechanism in gear transmission systems through the utilization of nanofluids for the first time. Various performance parameters of the prepared nanofluid lubrication oil are measured, along with the discussion of suspension stability. Based on the overset mesh method and VOF multiphase flow model, a rotating fluid domain calculation model considering the nanofluid-air two-phase is proposed. The high-speed nanofluid lubrication experiment platform is established to track churn phenomena and identify the oil volume fraction on the gear surface. Comparing simulation results with experimental data confirms the calculation accuracy in depicting oil flow and churn lubrication. Result shows that the interaction between droplets and the gear surface involves splash, rebound, adhesion, and diffusion. The nanofluid exhibits improved adsorption, resulting in a higher oil volume fraction. When the rotation speed is increased, intensified oil spatter and atomization are observed. The ranking of nanofluid lubrication performance is Al2O3, SiO2, Fe3O4, CuO, and TiO2 particles, which are approximately aligned with contact angle magnitudes. For 3 % nanoparticles concentration, less oil is swung off, more is drawn into the gear meshing zone, and subsequently squeezed out. Image recognition results align with numerical simulation, indicating that the oil distribution of nanofluid is better than that of base fluid lubrication. This work serves as a foundational exploration for future nanofluid lubrication and heat dissipation, offering insights into preventing oil film rupture, tooth surface wear, gluing and other failure mechanisms.

Fabrication of Cu2O plated carbon fabrics via electrochemical deposition method

Functional fabrics have many advanced applications to meet the expectations of the end-user industry. There is a variety of approaches to impart functional properties to the fabrics including coatings, the addition of functional fillers, surface modifications, etc. Metallization techniques are also a good candidate to impart functionalities to textile fabrics. On the other hand, Cu2O is a diamagnetic solid that has a variety of applications from flexible electronics to gas sensing. In this study, one of the simplest plating techniques, the electroplating method, was applied to carbon fabric to provide Cu2O coating on the surface which can add the advantages of metal oxides on carbon fabric. The Cu2O particles were observed on the surface of carbon fabric using SEM and the elemental composition of the surface was investigated using the EDS method. The crystal structure of the coating was identified using the X-ray diffraction technique and Raman spectroscopy. To confirm the achieved structure, FTIR analysis was performed as well. The newly fabricated structure can be a promising candidate for supercapacitors, electromagnetic shielding materials, dielectric surfaces, etc.

Synthesis and Catalytic Performance of Bimetallic Oxide-Derived CuO-ZnO Electrocatalysts for CO2 Reduction.

Steering the selectivity of electrocatalysts toward the desired product is crucial in the electrochemical reduction of CO2. A promising approach is the electronic modification of the catalyst's active phase. In this work, we report on the electronic modification effects on CuO-ZnO-derived electrocatalysts synthesized via hydrothermal synthesis. Although the synthesis method yields spatially separated ZnO nanorods and distinct CuO particles, strong restructuring and intimate atomic mixing occur under the reaction conditions. This leads to interactions that have a profound effect on the catalytic performance. Specifically, all of the bimetallic electrodes outperformed the monometallic ones (ZnO and CuO) in terms of activity for CO production. Surprisingly, on the other hand, the presence of ZnO suppresses the formation of ethylene on Cu, while the presence of Cu improves CO production of ZnO. In situ X-ray absorption spectroscopy studies revealed that this catalytic effect is due to enhanced reducibility of ZnO by Cu and stabilization of cationic Cu species by the intimate contact with partially reduced ZnO. This suppresses ethylene formation while favoring the production of H2 and CO on Cu. These results show that using mixed metal oxides with different reducibilities is a promising approach to alter the electronic properties of electrocatalysts (via stabilization of cationic species), thereby tuning the electrocatalytic CO2 reduction reaction performance.

Investigation of structural and optical properties of TM-doped CuO NPs: Correlation with their photocatalytic efficiency in sunlight-induced pollutant degradation

The presence of non-biodegradable, toxic, and harmful organic pollutants in various environmental mediums poses significant threats to ecosystems and human health. This study investigates the impact of transition metal (TM) doping on the photocatalytic performance of copper oxide nanoparticles (CuO NPs) in degrading methylene blue (MB) dye under sunlight irradiation. CuO NPs are synthesized using the co-precipitation method. X-ray diffraction (XRD) analysis revealed a monoclinic structure with space group C2/c for undoped and TM–doped CuONPs, with crystalline sizes ranging from 13 nm for undoped to 36 nm for Zn-doped CuO. Based on UV–Visible Spectroscopy data, the band gap energies and the nature of electronic band transitions are determined using a new simplified calculation method. Accordingly, direct band gap energy exhibits a slight red-shift as a result of doping with Ni, Mn or Fe, from 1.427 eV for undoped to 1.402 eV for Fe-doped CuO. While Co or Zn doping, induces a trivial blue-shift to 1.468 eV and 1.434 eV respectively. The CuO particles show a heterogenous distribution size and shape. The mean grain size raised from 34.3 nm for undoped to about 100 nm for TM-doped CuONPS, excluding the Co-doped CuO for which the mean grain size reached 154.532 nm with highest standard deviation heterogeneity of 125.737 nm. Furthermore, photocatalytic experiments demonstrated that TM-doping significantly enhanced the degradation rate of MB dye under sunlight irradiation. Co-doped CuO is the most efficient catalyst. This makes TM-doping a promising pathway for the use of CuO NPs in wastewater decontamination applications.

Robust, high-performance Cu-impregnated ZSM-5 zeolites for hydrocarbon removal during the cold-start period: Quantitative elucidation of effects of H+ and Na+ ions on performance and stability

Cu-containing zeolites are suitable for active hydrocarbon (HC) traps. Crucially, physicochemical properties of the zeolite could be finely tuned by varying the ion contents, though such approach has not been used intensively for HC trapping. Therefore, in this study, we adjusted the ratio of Na+ to H+ ions in ZSM-5 zeolites from 1 to 0 and, subsequently, wet-impregnated these zeolites with Cu. A low Na/Al ratio (≤0.4) resulted in marked cold-start test (CST) performance for HC removal in the fresh state (HC removal efficiency of 60.2 %-69.5 %). However, a hydrothermally treated counterpart having an optimal Na+ content (Na/Al ratio of 0.4) could well preserve the original active Cu+ ions along with zeolite structure and, accordingly, show the best CST performance after hydrothermal treatment (HT) at 800 °C (HC removal efficiency of 24.4 % vs. 10.8 % for the conventional H+-form-based one). Furthermore, we investigated adsorption behavior of water and HCs at a deep level and, further, revealed a clear correlation between the HC adsorption ability and CST performance and the representative physicochemical properties (mainly related to Cu+ ions) at all Na+ contents. Additionally, tiny CuO particles on the outer surface of the Cu-impregnated ZSM-5 zeolites having Na/Al ratios of 0–0.4 showed good low-temperature HC oxidation ability (ca. 175–182 °C). Although this HC oxidation ability was reduced after HT, an optimal Na/Al of 0.4 led to preservation of the original ability (ca. 283 °C vs. 320 °C for pure large CuO particles). Finally, we demonstrated a synergistic relationship between Na+ and H+ ion contents (Na/Al ratio of 0.4) that favored the formation of the desired Cu species, thus achieving marked HC adsorption and oxidation after HT.