Massive production of graphene oxide from expanded graphite

In a deviation from the conventional Hummers method, a spontaneous expansion approach was introduced with expanded graphite as the precursors. The intercalating agent (H2SO4) was able to penetrate into the expanded graphite; this had further expanded the graphite and as a result, a foam-like intermediate was produced. The foam-like graphite was more easily oxidized in reaction with the oxidant (KMnO4) to form graphene oxide (GO). Fully exfoliated GO was obtained with expanded graphite having the median diameter ~ 15 {\mu}m as the precursors. This procedure was much safer and productive in scalable applications than the conventional Hummers methods

Effect of encapsulated graphene oxide on alginate-based bead adsorption to remove acridine orange from aqueous solutions

Environmentally-benign high-performance graphene oxide (GO)/alginate-based absorbents were prepared to eliminate acridine orange selected as a typical dye. Characterizations demonstrated GO well encapsulated and its promotion of pore formation on structure. Kinetic studies exhibited that the addition of GO shortened the adsorption equilibrium time, raised the initial rate and the adsorption capacity. Isotherm studies indicated the adsorptive behavior followed Langmuir type, and higher maximum capacity was obtained in the presence of GO. The adsorption positively responded to pH increased from acidic to weakly alkaline. At low pH, GO would contribute dominantly to the adsorption, whereas alginate component was inhibited

CNTs/TiC Reinforced Titanium Matrix Nanocomposites via Powder Metallurgy and Its Microstructural and Mechanical Properties

By using pure titanium powder coated with unbundled multiwall carbon nanotubes (MWCNTs) via wet process, powder metallurgy (P/M) titanium matrix composite (TMC) reinforced with the CNTs was prepared by spark plasma sintering (SPS) and subsequently hot extrusion process. The microstructure and mechanical properties of P/M pure titanium and reinforced with CNTs were evaluated. The distribution of CNTs and in situ formed titanium carbide (TiC) compounds during sintering was investigated by optical and scanning electron microscopy (SEM) equipped with EDS analyzer. The mechanical properties of TMC were significantly improved by the additive of CNTs. For example, when employing the pure titanium composite powder coated with CNTs of 0.35 mass%, the increase of tensile strength and yield stress of the extruded TMC was 157 MPa and 169 MPa, respectively, compared to those of extruded titanium materials with no CNT additive. Fractured surfaces of tensile specimens were analyzed by SEM, and the uniform distribution of CNTs and TiC particles, being effective for the dispersion strengthening, at the surface of the TMC were obviously observed

Facile synthesis of graphene sheets intercalated by carbon spheres for high-performance supercapacitor electrodes

The composites consisting of graphene oxides (GOs) and carbon spheres (CSs), which were hydrothermally derived from the aqueous solution of glucose with average diameter of 200 nm, were mechanically mixed, and the GOs/CSs (GCSs) were thermally treated at high temperatures in the range of 700–900 °C. In the GCS composites, the CSs as spacers located between the GO sheets prevent the aggregation and restacking of graphene sheets. The GCS composites (GO/CS = 1) treated at 800 °C (GCS@800) have the high specific capacitances of 272.8 and 197.5 F g−1 in a three-electrode cell at the current density of 0.2 and 10 A g−1, respectively, in 6 M KOH aqueous solution, and demonstrated high rate capability and good cycling stability. The excellent electrochemical performance of the GCS@800 electrode is attributed to its structure with hierarchical porous structures including overwhelming micropores and a few of macropores. This work provides an effective and simple technique by integrating CSs and graphene sheets into composite structures for high-performance energy storage devices

Phytotoxicity of multi-walled carbon nanotubes on red spinach (Amaranthus tricolor L) and the role of ascorbic acid as an antioxidant

Carbon nanotubes (CNTs) are a novel nanomaterial with wide potential applications; however the adverse effects of CNTs following environmental exposure have recently received significant attention. Herein, we explore the systemic toxicity and potential influence of 0-1000 mg L^[-1] the multi-walled CNTs on red spinach. CNTs exposed plants exhibited growth inhibition and cell death after 15 days of hydroponic culture. CNTs had adverse effects on root and leaf morphology, as observed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Raman spectroscopy detected CNTs in leaves. Biomarkers of nanoparticle toxicity, reactive oxygen species (ROS), and cell damage in the red spinach were greatly increased 15 days post-exposure to CNTs. These effects were reversed when CNTs were supplemented with ascorbic acid (AsA), suggesting a role of ROS in the CNT-induced toxicity and that the primary mechanism of the CNTs' toxicity is oxidative stress

A novel adsorbent obtained by inserting carbon nanotubes into cavities of diatomite and applications for organic dye elimination from contaminated water

A novel approach is described for establishing adsorbents for elimination of water-soluble organic dyes by using multi-walled carbon nanotubes (MWCNTs) as the adsorptive sites. Agglomerates of MWCNTs were dispersed into individual tubes (dispersed-MWCNTs) using sodium n-dodecyl itaconate mixed with 3(N,N-dimethylmyristylammonio)-propanesulfonate as the dispersants. The resultant dispersed-MWCNTs were inserted into cavities of diatomite to form composites of diatomite/MWCNTs. These composites were finally immobilized onto the cell walls of flexible polyurethane foams (PUF) through an in situ PUF formation process to produce the foam-like CNT-based adsorbent. Ethidium bromide, acridine orange, methylene blue, eosin B, and eosin Y were chosen to represent typical water-soluble organic dyes for studying the adsorptive capabilities of the foam-like CNT-based adsorbent. For comparisons, adsorptive experiments were also carried out by using agglomerates of the sole MWCNTs as adsorbents. The foam-like CNT-based adsorbents were found to have higher adsorptive capacities than the CNT agglomerates for all five dyes; in addition, they are macro-sized, durable, flexible, hydrophilic and easy to use. Adsorption isotherms plotted based on the Langmuir equation gave linear results, suggesting that the foam-like CNT-based adsorbent functioned in the Langmuir adsorption manner. The foam-like CNT-based adsorbents are reusable after regeneration with aqueous ethanol solution

Graphene oxide adsorption enhanced by in situ reduction with sodium hydrosulfite to remove acridine orange from aqueous solution

Graphene oxide (GO) is a highly effective adsorbent, and its absorbing capability is further enhanced through its in situ reduction with sodium hydrosulfite as the reductant. Acridine orange is the selected target to eliminate with GO as the adsorbent. Under identical conditions, GO without the in situ reduction showed a maximum adsorption capacity of 1.4 g g^[-1], and GO with the in situ reduction provided a maximum adsorption capacity of 3.3 g g^[-1]. Sodium hydrosulfite converts carbonyl groups on GO into hydroxyl groups, which function as the key sites for the adsorption enhancement

Graphene phytotoxicity in the seedling stage of cabbage, tomato, red spinach, and lettuce

The effects of graphene on root and shoot growth, biomass, shape, cell death, and reactive oxygen species (ROS) of cabbage, tomato, red spinach, and lettuce, were investigated using a concentration range from 500 to 2000 mg/L. The results of the combined morphological and physiological analyses indicate that after 20 days of exposure under our experimental conditions, graphene significantly inhibited plant growth and biomass compared to a control. The number and size of leaves of the graphene-treated plants were reduced in a dose-dependent manner. Significant effects also were detected showing a concentration-dependent increase in ROS and cell death as well as visible symptoms of necrotic lesions, indicating graphene-induced adverse effects on cabbage, tomato, and red spinach mediated by oxidative stress necrosis. Little or no significant toxic effect was observed with lettuce seedlings under the same conditions. The potential effect of graphene largely depends on dose, exposure time, and plant species and deserves further attention