The role of reduced graphene oxide capping on defect induced ferromagnetism of ZnO nanorods

Photocatalytic degradation of dissolved organic matter in landfill leachate by heterostructural ZnO-rGO composite catalysts

The dissolved organic matter (DOM) in landfill pollutes not only the landfill and surroundings, but also the environment far away from the landfill by infiltrating into the soil and/or flowing on the ground surface. Developing an efficient photocatalyst to degrade DOM is an interesting topic. Herein, the catalysts composed of ZnO and reduced graphene oxide (ZnO-rGO) with different morphologies were fabricated with a two-step hydrothermal method. The phase composite and microstructure were analyzed, and the degradation efficiency of the DOM under ultraviolet light was investigated. Three kinds of ZnO-rGO composite catalysts with different morphologies were successfully synthesized, and rGO was coated on the ZnO surface to form heterostructural composite catalysts. The catalyst powders have similar Raman and FT-IR spectra, but have different specific surface areas and band gaps. The degradation efficiency of DOM by ZnO-rGO composites is higher than that of pure ZnO powder. Compared to pure ZnO, ZnO-rGO composite catalysts contain more oxygen vacancies and a narrower band gap, and the heterostructure is beneficial for accelerating electron separation, inhibiting electron recombination.

Observation of critical magnetic behavior in 2D carbon based composites

Two dimensional (2D) carbonaceous materials such as graphene and its derivatives, e.g., graphdiyne, have enormous potential possibilities in major fields of scientific research. Theoretically, it has been proposed that the perfect atomic lattice arrangement of these materials is responsible for their outstanding physical and chemical properties, and also for their poor magnetic properties. Experimentally, it is difficult to obtain a perfect atomic lattice of carbon atoms due to the appearance of structural disorder. This structural disorder is generated during the growth or synthesis of carbon-related materials. Investigations of structural disorder reveal that it can offer both advantages and disadvantages depending on the application. For instance, disorder reduces the thermal and mechanical stability, and deteriorates the performance of 2D carbon-based electronic devices. The most interesting effect of structural disorder can be seen in the field of magnetism. Disorder not only creates magnetic ordering within 2D carbon materials but also influences the local electronic structure, which opens the door for future spintronic devices. Although various studies on the disorder induced magnetism of 2D carbon materials are available in the literature, some parts of the above field have still not been fully exploited. This review presents existing work for the future development of 2D carbon-based devices.

Study of Optical and Magnetic Properties of Graphene-Wrapped ZnO Nanoparticle Hybrids

In this work, we report a one-step method for the preparation of graphene-wrapped zinc oxide (ZnO) nanoparticle (NP) (ZnO@G) hybrids. These hybrids are characterized by transmission electron microscopy, X-ray diffraction, Raman spectroscopy, optical absorption measurements, photoluminescence (PL) emission spectroscopy, and M-H hysteresis measurements. All results reveal that the ZnO NPs are entirely covered with graphene sheets. In the PL spectra, the quenching of the band gap emission and the enhanced green emission serve as evidence of the electron transfer from the ZnO NPs to the graphene layer. The increase of the room-temperature magnetization of the hybrid, compared to pure ZnO NPs, is due to the increasing defect concentration. We suggest a band diagram model that accounts for these observations. We present the simple wet-chemical synthesis procedure to open a new way for the synthesis of NP-graphene hybrid systems having magnetic properties giving the large manifold potential application.

Organochloride pesticides modulated gut microbiota and influenced bile acid metabolism in mice

Organochlorine pesticides (OCPs) can persistently accumulate in body and threaten human health. Bile acids and intestinal microbial metabolism have emerged as important signaling molecules in the host. However, knowledge on which intestinal microbiota and bile acids are modified by OCPs remains unclear. In this study, adult male C57BL/6 mice were exposed to p, p'-dichlorodiphenyldichloroethylene (p, p'-DDE) and β-hexachlorocyclohexane (β-HCH) for 8 weeks. The relative abundance and composition of various bacterial species were analyzed by 16S rRNA gene sequencing. Bile acid composition was analyzed by metabolomic analysis using UPLC-MS. The expression of genes involved in hepatic and enteric bile acids metabolism was measured by real-time PCR. Expression of genes in bile acids synthesis and transportation were measured in HepG2 cells incubated with p, p'-DDE and β-HCH. Our findings showed OCPs changed relative abundance and composition of intestinal microbiota, especially in enhanced Lactobacillus with bile salt hydrolase (BSH) activity. OCPs affected bile acid composition, enhanced hydrophobicity, decreased expression of genes on bile acid reabsorption in the terminal ileum and compensatory increased expression of genes on synthesis of bile acids in the liver. We demonstrated that chronic exposure of OCPs could impair intestinal microbiota; as a result, hepatic and enteric bile acid profiles and metabolism were influenced. The findings in this study draw our attention to the hazards of chronic OCPs exposure in modulating bile acid metabolism that might cause metabolic disorders and their potential to cause related diseases in human.

Graphene oxide with zinc partially substituted magnetite (GO–Fe1−xZnxOy) for the UV-assisted heterogeneous Fenton-like reaction

A series of graphene oxide (GO) and zinc partially substituted magnetite GO–Fe_1−xZn_xO_y (0 ≤ x ≤ 0.285) catalysts were synthesised through a precipitation-oxidation method.

Zinc Oxide-Containing Porous Boron-Carbon-Nitrogen Sheets from Glycine-Nitrate Combustion: Synthesis, Self-Cleaning, and Sunlight-Driven Photocatalytic Activity

We developed a single-step thermal method that enables successful inclusion of ZnO components in the porous boron-carbon-nitrogen (BCN) framework to form a new class of functional hybrid. ZnO-containing BCN hybrids were prepared by treating a mixture of B2O3, glycine, and zinc nitrate at 500 °C. Glycine-nitrate decomposition along with B2O3 acts as a source for ZnO-BCN formation. The incorporation of ZnO onto BCN has extended the photoresponse of ZnO in the visible region, which makes ZnO-BCN a preferable photocatalyst relative to ZnO upon sunlight exposure. It is interesting to note that as-prepared 2D ZnO-BCN sheets dispersed in PDMS form a stable coating over aluminum alloys. The surface exhibited a water contact angle (CA) of 157.6° with 66.6 wt % ZnO-BCN in polydimethylsiloxane (PDMS) and a water droplet (7 μL) roll-off angle of <6° and also demonstrates oil fouling resistant superhydrophobicity. In brief, the present study focuses on the gram scale synthesis of a new class of sunlight-driven photocatalyst and also its application toward the development of superhydrophobic and oleophobic coating.

Deciphering the underlying mechanisms of oxidation-state dependent cytotoxicity of graphene oxide on mammalian cells

The promising broad applications of graphene oxide (GO) derivatives in biomedicine have raised concerns about their safety on biological organisms. However, correlations between the physicochemical properties, especially oxidation degree of GOs and their toxicity, and the underlying mechanisms are not well understood. Herein, we evaluated the cytotoxicity of three GO samples with various oxidation degrees on mouse embryo fibroblasts (MEFs). Three samples can be internalized by MEFs observed via transmission electron microscopy (TEM), and were well tolerant by MEFs at lower doses (below 25μg/ml) but significantly toxic at 50 and 100μg/ml via Cytell Imaging System. More importantly, as the oxidation degree decreased, GO derivatives led to a higher degree of cytotoxicity and apoptosis. Meanwhile, three GOs stimulated dramatic enhancement in reactive oxygen species (ROS) production in MEFs, where the less oxidized GO produced a higher level of ROS, suggesting the major role of oxidative stress in the oxidation-degree dependent toxicity of GOs. Results from electron spin resonance (ESR) spectrometry showed a strong association of the lower oxidation degree of GOs with their stronger indirect oxidative damage through facilitating H2O2 decomposition into OH and higher direct oxidative abilities on cells. The theoretical simulation revealed the key contributions of carboxyl groups and aromatic domain size of nanosheets to varying the energy barrier of H2O2 decomposition reaction. These systematic explorations in the chemical mechanisms unravel the key physicochemical properties that would lead to the diverse toxic profiles of the GO nanosheets with different oxygenation levels, and offer us new clues in the molecular design of carbon nanomaterials for their safe applications in biomedicine.

In situ and ex situ carbon coated Zn2SnO4 nanoparticles as promising negative electrodes for Li-ion batteries

Zinc stannate, Zn₂SnO₄ nanoparticles are successfully synthesized by a facile hydrothermal method.

Controlled synthesis of organic ligand passivated ZnO nanostructures and their photocatalytic activity under visible light irradiation

Zinc oxide (ZnO) nanostructures were synthesized and their photocatalytic activity was evaluated using methylene blue (MB) as a model pollutant.

Graphene activating room-temperature ferromagnetic exchange in cobalt-doped ZnO dilute magnetic semiconductor quantum dots

Control over the magnetic interactions in dilute magnetic semiconductor quantum dots (DMSQDs) is a key issue to future development of nanometer-sized integrated "spintronic" devices. However, manipulating the magnetic coupling between impurity ions in DMSQDs remains a great challenge because of the intrinsic quantum confinement effects and self-purification of the quantum dots. Here, we propose a hybrid structure to achieve room-temperature ferromagnetic interactions in DMSQDs, via engineering the density and nature of the energy states at the Fermi level. This idea has been applied to Co-doped ZnO DMSQDs where the growth of a reduced graphene oxide shell around the Zn(0.98)Co(0.02)O core turns the magnetic interactions from paramagnetic to ferromagnetic at room temperature, due to the hybridization of 2p(z) orbitals of graphene and 3d obitals of Co(2+)-oxygen-vacancy complexes. This design may open up a kind of possibility for manipulating the magnetism of doped oxide nanostructures.

Fabrication of 3D structured ZnO nanorod/reduced graphene oxide hydrogels and their use for photo-enhanced organic dye removal

Hybrid 3-dimensional (3D) structures composed of zinc oxide (ZnO) nanorods and reduced graphene oxide hydrogel (rGOH) were fabricated by chemical reaction between Zn ions and GO followed by in-situ lateral growth of ZnO nanorods using Zn ions as seed points. The 3D networked ZnO nanorod-rGOH (ZNR-rGOH) fabricated in this study exhibited excellent methylene blue (MB) removal efficiency due to efficient physical adsorption of dye molecules because of electrostatic attractive forces and enhanced photocatalytic activity by the laterally grown ZnO nanorods. The Langmuir-Hinshelwood rate constant of ZNR-rGOH was 4-fold higher than that of pristine rGO due to the enhanced photocatalytic effects obtained by incorporating laterally grown ZnO nanorods inside the rGOH network.

The role of ionic electrolytes on capacitive performance of ZnO-reduced graphene oxide nanohybrids with thermally tunable morphologies

In the present work, the role of the reaction temperatures on the morphologies of zinc oxide-reduced graphene oxide (ZnO-RGO) nanohybrids and their supercapacitive performance in two different aqueous electrolytes (1.0 M KCl and Na2SO4) were investigated. The ZnO-RGO nanohybrids were synthesized at two different temperatures (ca. 95 and 145 °C) by solvothermal method and labeled as ZnO-RGO-1 and ZnO-RGO-2, respectively. The structure and composition of ZnO-RGO nanohybrids were confirmed by means of X-ray diffraction, electron microscopes (scanning and transmission), X-ray photoelectron, photoluminescence, and Raman spectroscopy. These results show that the temperature allows a good control on loading and morphology of ZnO nanoassemblies in ZnO-RGO nanohybrids and at elevated temperature of 145 °C, ZnO nanoassemblies break and get completely embedded into RGO matrices. The electrochemical performance of ZnO-RGO nanohybrids was examined by cyclic voltammograms (CVs), galvanostatic charge-discharge (chronopotentiometry) and electrochemical impedance spectroscopy (EIS) in 1.0 M KCl and Na2SO4 aqueous electrolytes respectively. Combining the EIS and zeta potential behavior, a direct link between the charge transfer resistance and electrical double layers is established which is responsible for excellent capacitive performance of ZnO-RGO-2. The ZnO-RGO-2 displays high specific capacitance (107.9 F/g, scan rate = 50 mVs(-1)) in 1.0 M KCl and exhibits merely 4.2% decay in specific capacitance values over 200 cycles.

Chemically derived defects in zinc oxide nanocrystals and their enhanced photo-electrocatalytic activities

Schematic illustration of ZnO NCs synthesized in DMF (ZnO-1), NMP (ZnO-2) and DMSO (ZnO-3), their charge–discharge behavior as well as degradation performance.