Development of highly faceted reduced graphene oxide-coated copper oxide and copper nanoparticles on a copper foil surface.
ABSTRACT: This work describes the formation of reduced graphene oxide-coated copper oxide and copper nanoparticles (rGO-Cu2ONPs, rGO-CuNPs) on the surface of a copper foil supporting graphene oxide (GO) at annealing temperatures of 200-1000 °C, under an Ar atmosphere. These hybrid nanostructures were developed from bare copper oxide nanoparticles which grew at an annealing temperature of 80 °C under nitrogen flux. The predominant phase as well as the particle size and shape strongly depend on the process temperature. Characterization with transmission electron microscopy and scanning electron microscopy indicates that Cu or Cu2O nanoparticles take rGO sheets from the rGO network to form core-shell Cu-rGO or Cu2O-rGO nanostructures. It is noted that such ones increase in size from 5 to 800 nm as the annealing temperature increases in the 200-1000 °C range. At 1000 °C, Cu nanoparticles develop a highly faceted morphology, displaying arm-like carbon nanorods that originate from different facets of the copper crystal structure.
Project description:A novel dot-like Cu2O-loaded TiO2/reduced graphene oxide (rGO) nanoheterojunction was synthesized via UV light reduction for the first time. Cu2O with size of ca. 5 nm was deposited on rGO sheet and TiO2 nanosheets. The products were characterized by infrared spectroscopy, Raman spectrum, UV-Vis diffuse reflectance spectra, XPS techniques, photoluminescence spectra. The results demonstrated that Cu2O and rGO enhanced the absorption for solar light, separation efficiency of electron-hole pairs, charge shuttle and transfer, and eventually improved photoelectrochemical and photocatalytic performance for contaminants degradation. The reaction time and anion precursor could affect the final copper-containing phase. As extending UV irradiation time, Cu2+ was be first reduced to Cu2O and then transformed to metal Cu. In comparison with CH3COO- (copper acetate), NO3- (copper nitrate) and Cl- (copper chloride), SO42- (copper sulfate) was the optimum for synthesizing pure Cu2O phase.
Project description:Shape-specific copper oxide nanostructures have attracted increasing attention due to their widespread applications in energy conversion, sensing, and catalysis. Advancing our understanding of structure, composition, and surface chemistry transformations in shaped copper oxide nanomaterials during changes in copper oxidation state is instrumental from both applications and preparative nanochemistry standpoints. Here, we report the study of structural and compositional evolution of amorphous copper (II) hydroxide nanoparticles under hydrazine reduction conditions that resulted in the formation of crystalline Cu2O and composite Cu2O-N2H4 branched particles. The structure of the latter was influenced by the solvent medium. We showed that hydrazine, while being a common reducing agent in nanochemistry, can not only reduce the metal ions but also coordinate to them as a bidentate ligand and thereby integrate within the lattice of a particle. In addition to shape and composition transformation of individual particles, concurrent interparticle attachment and ensemble shape evolution were induced by depleting surface stabilization of individual nanoparticles. Not only does this study provide a facile synthetic method for several copper (I) oxide structures, it also demonstrates the complex behavior of a reducing agent with multidentate coordinating ability in nanoparticle synthesis.
Project description:Copper and palladium/copper nanoparticles supported on reduced graphene oxide catalysts were synthesized and evaluated for the selective NO reduction by CO. The catalysts were characterized by XRD, nitrogen adsorption-desorption, TGA, XPS, TPR, in situ XRD, STEM, and HRTEM. The STEM and HRTEM results showed high metal oxide dispersions on the rGO. XPS results showed the presence of Cu and Pd oxide species. The reduction of copper supported on the rGO occurred in two steps for CuO x /rGOc, while that for CuO x -PdO y /rGOc occurred in one step for temperatures lower than 350 °C. Noteworthy is that the in situ XRD results showed that the rGO structure was not affected after reduction at 350 °C. The in situ XRD of reduction revealed the appearance of new phases for copper during the reduction. The catalysts were evaluated in NO reduction by CO. The tests showed that the reduced catalysts presented high performance with NO conversions and N2 selectivity above 85% at 350 °C.
Project description:Human oral exposure to copper oxide nanoparticles (NPs) may occur following ingestion, hand-to-mouth activity, or mucociliary transport following inhalation. This study assessed the cytotoxicity of Cupric (II) oxide (CuO) and Cu2O-polyvinylpyrrolidone (PVP) coated NPs and copper ions in rat (intestine epithelial cells; IEC-6) and human intestinal cells, two- and three-dimensional models, respectively. The effect of pretreatment of CuO NPs with simulated gastrointestinal (GI) fluids on IEC-6 cell cytotoxicity was also investigated. Both dose- and time-dependent decreases in viability of rat and human cells with CuO and Cu2O-PVP NPs and Cu2+ ions was observed. In the rat cells, CuO NPs had greater cytotoxicity. The rat cells were also more sensitive to CuO NPs than the human cells. Concentrations of H2O2 and glutathione increased and decreased, respectively, in IEC-6 cells after a 4-h exposure to CuO NPs, suggesting the formation of reactive oxygen species (ROS). These ROS may have damaged the mitochondrial membrane of the IEC-6 cells causing a depolarization, as a dose-related loss of a fluorescent mitochondrial marker was observed following a 4-h exposure to CuO NPs. Dissolution studies showed that Cu2O-PVP NPs formed soluble Cu whereas CuO NPs essentially remained intact. For GI fluid-treated CuO NPs, there was a slight increase in cytotoxicity at low doses relative to non-treated NPs. In summary, copper oxide NPs were cytotoxic to rat and human intestinal cells in a dose- and time-dependent manner. The data suggests Cu2O-PVP NPs are toxic due to their dissolution to Cu ions, whereas CuO NPs have inherent cytotoxicity, without dissolving to form Cu ions.
Project description:Cuprous oxide and copper have been synthesized via the solvothermal process using basic copper carbonate as the source of copper. Pure Cu2O or Cu could be afforded by simply varying the solvent while keeping the temperature and time constant. In this study, copper-based materials were coated on jute stick pieces (JSP) in situ. Cu2O-coated JSP (Cu2O-JSP) and Cu-coated JSP (Cu-JSP) were characterized by powder X-ray diffraction (PXRD) and scanning electron microscopy (SEM). Cu2O-JSP and Cu-JSP were found to be active against Escherichia coli NCIM 2931 (Gram-negative bacteria) and Staphylococcus aureus (Gram-positive bacteria). The antibacterial nature of the material and the buoyant nature of Cu2O-JSP and Cu-JSP were exploited to develop beaded necklace-like strands that could be floated on potable water to effectively prevent aerial contamination. Leaching of copper from both Cu2O-JSP and Cu-JSP into water was found to be below the permissible limit for copper in drinking water.
Project description:A quantitative and analytical investigation on the conduction mechanism in p-type cuprous oxide (Cu2O) thin films is performed based on analysis of the relative dominance of trap-limited and grain-boundary-limited conduction. It is found that carrier transport in as-deposited Cu2O is governed by grain-boundary-limited conduction (GLC), while after high-temperature annealing, GLC becomes insignificant and trap-limited conduction (TLC) dominates. This suggests that the very low Hall mobility of as-deposited Cu2O is due to significant GLC, and the Hall mobility enhancement by high-temperature annealing is determined by TLC. Evaluation of the grain size and the energy barrier height at the grain boundary shows an increase in the grain size and a considerable decrease in the energy barrier height after high-temperature annealing, which is considered to be the cause of the significant reduction in the GLC effect. Additionally, the density of copper vacancies was extracted; this quantitatively shows that an increase in annealing temperature leads to a reduction in copper vacancies.
Project description:Monodisperse Cu2O of different microstructures, such as cubes, flower-like, and microspheres, have been extensively synthesized by a simple polyol reduction method using different copper salts, i.e. (Cu(acac)2, Cu(OH)2, and Cu(Ac)2·H2O). The effects of copper salts on the morphology of Cu2O were investigated in details through various characterization methods, including X-ray diffraction, transmission electron microscopy, scanning electron microscopy and UV-Vis absorption spectra. The effects of morphology on the electrochemical properties were further studied. Among the different structures, Cu2O with the microspheric morphology shows the highest specific capacitance and the best cycling stability compared with those of the other two structures, thus bear larger volume charge during the electrochemical reaction due to the microspheres of small nanoparticles.
Project description:Nanocomposites and a composite based on poly(butylene adipate-co-terephthalate) (PBAT) were synthesized using commercial copper nanoparticles (Cu-NPs), copper/cuprous oxide nanoparticles (Cu|Cu2O-NPs), and copper sulfate (CuSO4), respectively. The Cu|Cu2O-NPs were synthesized using chemical reduction and characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The synthesis of Cu|Cu2O-NPs yielded a mixture of Cu and Cu2O, with metal Cu having a spherical morphology of approximately 40 nm in diameter and Cu2O with a diameter of 150 nm. To prepare the nanocomposites (NCs) and the composite material (MC), the NPs and the CuSO4 salt were incorporated into the PBAT matrix in concentrations of 1, 3, and 5% p/p via an ex situ method. Fourier transform infrared spectroscopy (FTIR), a tensile test, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and agar diffusion assays were used for structural, thermomechanical, and antimicrobial characterization. Results showed that the reinforcements did not modify the chemical structure of the PBAT and only slightly increased the percentage of crystallization. The mechanical and thermal properties of the PBAT did not change much with the addition of fillers, except for a slight increase in tensile strength and thermal stability, respectively. The agar diffusion antimicrobial assays showed that the NCs and MCs had good inhibitory responses against the nonresistant strains Enterococcus faecalis, Streptococcus mutans, and Staphylococcus aureus. The MCs based on CuSO4 had the highest biocidal effect, even against the resistant bacteria Acinetobacter baumannii.
Project description:Cu has recently received great interest as a potential candidate for glucose sensing to overcome the problems with noble metals. In this work, reduced graphene oxide-encapsulated Cu nanoparticles (Cu@RGO) have been prepared via an electrostatic self-assembly method. This core/shell composites were found to be more stable than conventional Cu-decorated graphene composites and bare copper nanoparticles in an air atmosphere because the graphene shell can effectively protect the Cu nanoparticles from oxidation. In addition, the obtained Cu@RGO composites also showed an outstanding electrocatalytic activity toward glucose oxidation with a wide linear detection range of 1 ?M to 2 mM, low detection limit of 0.34 ?M (S/N = 3), and a sensitivity of 150 ?A mM-1 cm-2. Moreover, Cu@RGO composites exhibited a satisfactory reproducibility, selectivity, and long effective performance. These excellent properties indicated that Cu@RGO nanoparticles have great potential application in glucose detection.
Project description:The rapid oxide formation on pristine unprotected copper surfaces limits the direct application of Cu nanomaterials in electronics and sensor assemblies with physical contacts. However, it is not clear whether the growing cuprous (Cu2O) and cupric oxides (CuO) and the formation of core-shell-like Cu-Cu2O/CuO nanowires would cause any compromise for non-contact optical measurements, where light absorption and subsequent charge oscillation and separation take place such as those in surface plasmon-assisted and photocatalytic processes, respectively. Therefore, we analyze how the surface potential of hydrothermally synthetized copper nanowires changes as a function of time in ambient conditions using Kelvin probe force microscopy in dark and under light illumination to reveal charge accumulation on the nanowires and on the supporting gold substrate. Further, we perform finite element modeling of the optical absorption to predict plasmonic behavior of the nanostructures. The results suggest that the core-shell-like Cu-Cu2O/CuO nanowires may be useful both in photocatalytic and in surface plasmon-enhanced processes. Here, by exploiting the latter, we show that regardless of the native surface oxide formation, random networks of the nanowires on gold substrates work as excellent amplification media for surface-enhanced Raman spectroscopy as demonstrated in sensing of Rhodamine 6G dye molecules.