Highly antibacterial rGO/Cu2O nanocomposite from a biomass precursor:Synthesis,performance,and mechanism

Reduced graphene oxide(rGO)has been widely used to fabricate electronics,sensors,photodetectors,and in other applications.However,the antibacterial performance of pristine rGO is relatively weak.The application of rGO in biomedical devices,smart food packaging,and water desalination membranes requires further improvement of rGO’s antibacterial abilities.Copper(I)oxide(Cu2O)is an effective antibacterial agent,which denatures protein and enhances the permeability of cell membranes.In this work,we report a simple method of synthesizing a highly antibacterial rGO/Cu2O nanocomposite from cellulose acetate,a derivative of abundant natural cellulose.The synthesized rGO/Cu2O nanocomposite was thoroughly characterized by Raman spectroscopy,X-ray powder diffraction(XRD),X-ray photoelectron spectroscopy(XPS),atomic force microscopy(AFM),scanning electron microscopy(SEM),high-resolution transmission electron microscopy(HRTEM),and scanning transmission electron microscopy(STEM).Then,the antibacterial abilities of rGO/Cu2O nanocomposite were evaluated and a bactericidal mechanism was revealed from the molecular biology perspective.Results indicate that our synthesized rGO/Cu2O nanocomposite owns strong antibacterial activity,mainly stemming from the uniformly incorporated Cu2O nanocrystals with a lateral size of 5–40 nm.

Preparation of in-situ Cu/NbC nanocomposite and its functionally graded behavior for electrical contact applications

Cu–15%NbC (volume fraction) powder was synthesized using the starting powders of Cu, Nb and graphite in a high energy vibratory disc mill for 7 h of milling under argon atmosphere. A composite sample and a Cu/NbC functionally graded material (FGM) sample were produced by using the two-step press and sintering at 900 °C for 1 h under vacuum. The microstructure and physical and mechanical properties of the specimens were investigated. The field emission scanning electron microscopy, energy dispersive X-ray and X-ray diffraction analysis confirmed the synthesis of the nanostructure matrix of 18–27 nm with the nanoparticles reinforcement of 42 nm after sintering, verifying the thermal stability of this composite at high temperature. The hardness of Cu–15%NbC was five times greater than that of the pure Cu specimen. The volume reduction of the sample after the wear test decreased in comparison with the pure Cu specimen. The electrical conductivity of the composite specimen decreased to 36.68% IACS. The FGM specimen exhibited high electrical conductivity corresponding to 75.83% IACS with the same hardness and wear properties as those of the composite sample on the composite surface. Thus, Cu/NbC FGM with good mechanical and electrical properties can be a good candidate for electrical contact applications.

Enhanced mechanical and electrical properties of multi-walled carbon nanotubes reinforced Cu/Ti_(3)SiC_(2)/C nanocomposites via high-pressure torsion

In order to achieve combined mechanical and electrical properties,multi-walled carbon nanotubes(MWCNTs)reinforced Cu/Ti_(3)SiC_(2)/C nanocomposites were further processed by high-pressure torsion(HPT).The maximum microhardness values of central and edge from the composites with 1 wt.%MWCNTs reached HV 130.0 and HV 363.5,which were 43.9%and 39.5%higher than those of the original samples,respectively.With the same content of MWCNTs,its electrical conductivity achieved 3.42×10^(7) S/m,which was increased by 78.1%compared with that of original samples.The synergistic improvement of mechanical and electrical properties is attributed to the obtained microstructure with increased homogenization and refinement,as well as improved interfacial bonding and reduced porosity.The strengthening mechanisms include dispersion and refinement strengthening for mechanical properties,as well as reduced electron scattering for electrical properties.

Electro-derived Cu-Cu2O nanocluster from LDH for stable and selective C2 hydrocarbons production from CO2 electrochemical reduction

Recently,CO2 conversion by electrochemical tool into value-added chemicals has been considered as one of the most promising strategies to offer sustainable development in energy and environment.In this contribution,we investigated electro-derived composites from Cu-based layered double hydroxide(LDH)for CO2 electrochemical reduction.The Cu-Cu2O based nanocomposite(HPR-LDH)were derived by using electro-strategy from LDH having the stability up to 20 h and selectivity toward C2H4 with faraday efficiency up to 36%by significantly suppressing CH4 and H2 with respect to bulk Cu foil.A highly negative reduction potential derived catalyst(HPR-LDH)maintained long-term stability for the selective production of ethylene over methane,and a small amount of Cu2O was still observed on the catalyst surface after CO2 reduction reaction(CO2RR).Moreover,such unique strategy for electro-derived composite from LDH having small nanoparticles stacked each other grown on layered structure,would provide new insight to improve durability of O-Cu combination catalysts for C-C coupling products during electrochemical CO2conversion by suppressing HER.The XRD,SEM,ESR,and XPS analyses confirmed that the long-term ethylene selectivity of HPR-LDH is due to the presence of subsurface oxygen.The designed composite catalyst significantly enhances the stability and selectivity,and also decreases the over potential for CO2 electroreduction.We predict that the new designed LDH 2D-derived composites may attract new insight for transition metal and may open up a new direction for known structural properties of selective catalyst synthesis regarding effective CO2 reduction reaction.

Morphology-dependent structures and catalytic performances of Au nanostructures on Cu_2O nanocrystals synthesized by galvanic replacement reaction

Au nanostructures were prepared on uniform Cu2O octahedra and rhombic dodecahedra via the galvanic replacement reaction between HAuCl 4 and Cu2O. The compositions and structures were studied by Scanning Electron Microscope (SEM), Transmission Electron Microscope (TEM), High-Resolution Transmission Electron Microscope (HRTEM), X-Ray Diffraction (XRD), X-Ray Absorption Spectroscopy (XAS), X-ray Photoelectron Spectroscopy (XPS) and in-situ DRIFTS spectroscopy of CO adsorption. Different from the formation of Au-Cu alloys on Cu2O cubes by the galvanic replacement reaction (ChemNanoMat 2 (2016) 861-865), metallic Au particles and positively-charged Au clusters form on Cu2O octahedra and rhombic dodecahedra at very small Au loadings and only metallic Au particles form at large Au loadings. Metallic Au particles on Cu2O octahedra and rhombic dodecahedra are more active in catalyzing the liquid phase aerobic oxidation reaction of benzyl alcohol than positively-charged Au clusters. These results demonstrate an obvious morphology effect of Cu2O nanocrystals on the liquid-solid interfacial reactions and prove oxide morphology as an effective strategy to tune the surface reactivity and catalytic performance. (C) 2016 Science Press and Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier B.V. and Science Press. All rights reserved.

Biosynthesis of copper nanoparticles supported on manganese dioxide nanoparticles using Centella asiatica L. leaf extract for the efficient catalytic reduction of organic dyes and nitroarenes

In this study we designed a novel,cost‐efficient and green method for the synthesis of copper nanoparticles(Cu NPs)supported on manganese dioxide(MnO2)NPs,using Centella asiatica L.leaf extract as a naturally‐sourced reducing agent,without stabilizers or surfactants.This synthetic process is environmentally‐friendly and avoids the use of toxic reducing agents.Phenolic hydroxyl groups in the leaf extract are believed to reduce Cu2+in solution to generate Cu NPs that are subsequently stabilized on the MnO2NP surfaces.The resulting Cu/MnO2nanocomposite was fully characterized using X‐ray diffraction,transmission electron microscopy,field emission scanning electron microscopy,energy‐dispersive X‐ray spectroscopy and Fourier transform infrared spectroscopy.This material was found to function as a highly active,efficient and recyclable heterogeneous catalyst for the reduction of Congo red,rhodamine B and methylene blue as well as nitro compounds such as2,4‐dinitrophenylhydrazine and4‐nitrophenol in the presence of NaBH4in aqueous media at ambient temperature.The high stability of the Cu/MnO2nanocomposite also allows the catalyst to be separated and reused several times without any significant loss of activity.?2018,Dalian Institute of Chemical Physics,Chinese Academy of Sciences.Published by Elsevier B.V.All rights reserved.

Folded graphene reinforced nanocomposites with superior strength and toughness:A molecular dynamics study

Toughness and strength are important material parameters in practical structural applications.However,it remains a great challenge to achieve high toughness and high strength simultaneously for most materials.Here,we report a folded graphene(FG)reinforced copper(Cu)nanocomposite that overcomes the long-standing conflicts between toughness and strength.Intensive molecular dynamics simulations show that the 10%pre-strain-induced four-wave-patterned FG(1.09 wt%)reinforced Cu nanocomposite exhibits simultaneous enhancement in toughness(~13.59 J/m^(2)),ductility(~32.38%),and strength(~9.52 GPa),corresponding to 38.53%,58.88%,and 2.26%increase,respectively when compared with its counterpart reinforced by pristine graphene(PG).More importantly,the mechanical properties of FG/Cu nanocomposites can be effectively tuned by changing the pre-compressive strain,wave number,and peak number of FG.The toughening and strengthening mechanisms are applicable to other metal materials reinforced by other 2 D nanomaterials,opening up a new avenue for developing tough and strong metal nanocomposites.

Cu2O-Au Nanocomposites with Novel Structures and Remarkable Chemisorption Capacity and Photocatalytic Activity

The decomposition of Cull nanoparticles in aqueous solution has been successfully developed as a novel method for the preparation of Cu2O nanoparticles. In particular, we found that the decomposition of Cull nanoparticles in aqueous solution could be catalyzed by Au colloids, forming CU2O-Au nanocomposites. The composition and structure of the resulting Cu2O-Au nanocomposites have been characterized in detail by inductively coupled plasma atomic emission spectroscopy, powder X-ray diffraction, N2 adsorption-desorption isotherms, infrared spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy and transmission electron microscopy. Their visible-light-driven photocatalytic activity toward various dye molecules has also been investigated. Depending on the Au：Cu ratio, Cu20-Au nanocomposites exhibit different novel nanostructures including a beautiful flower-like nanostructure that consists of polycrystalline Cu2O, amorphous Cu2O and Au colloids. We propose that the rapidly-generated bubbles of H2 during the course of the catalytic decomposition reaction drive the simultaneously-formed Cu2O to form amorphous curved thin foils and might also act as a template to assemble curved thin foils of amorphous Cu2O, polycrystalline Cu2O and Au colloids into uniform nanostructures. A Cu2O-Au nanocomposite with a Cu：Au ratio of 40 exhibits remarkable chemisorption capacity and visible-light-driven photocatalytic activity towards methyl orange and acid orange 7 and is a promising chemisorption-photocatalysis integrated catalyst. The catalytic decomposition of the metal hydride might open up a new approach for the fabrication of other metal/metal oxide nanocomposites with novel nanostructures and properties.

Influence of N-doping on dielectric properties of carbon-coated copper nanocomposites in the microwave and terahertz ranges

Carbon-coated Cu nanocomposites (Cu@C NCs) consisting of core-shell nanoparticles and nanorods weresynthesized by arc discharge plasma under an atmosphere of He and H_(2) gas, and the N-doping of themwas achieved by a post-treatment process using ureal as the precursor. The concentration of N in the Ndoped samples varies in the range of 0.62%-2.31 % (in mole), with a transformation from pyrrolic N tographitic N when increasing the relative content of ureal. Dielectric properties of the NCs without or withN-doping in the microwave and THz bands were investigated. The N-doped samples achieve theenhanced dielectric loss in both microwave and THz bands. In the microwave band, dielectric loss wasdominated by interfacial polarization, dipolar polarization, and conduction loss, while in the THz band,plasma resonance, ionic polarization and conduction loss are responsible for the dielectric loss, with astrong absorption characteristic dominated by conductive effect.