Characterization of PEO/PVP/GO nanocomposite solid polymer electrolyte membranes: microstructural,thermo-mechanical,and conductivity properties

Poly (ethylene oxide) (PEO)/polyvinylpyrrolidone (PVP) blended nanocomposite polymers, incorporating graphene oxide (GO) nano-sheets and embedded with NaIO₄ salt, were prepared using solution casting technique. The as-prepared nanocomposite electrolyte membranes were characterized by SEM, TEM, XRD, and Raman vibrational spectroscopic techniques to confirm the dispersion of GO nano-sheets and to understand the synergistic properties of GO/polymer interactions as a function of GO nano-sheets concentration. GO fillers incorporated electrolyte membranes demonstrated distinctive surface morphology composed of circular-shaped protuberances of different dimensions. The decrease of Raman intensity ratio (I_D/I_G) and in-plane crystallite size (L_a) values of the nanocomposites suggested the good dispersion and confinement of the GO nano-sheets. The optical properties of blend electrolyte films were studied as a function of GO filler concentration using optical absorption and diffuse reflectance spectra. In reference to PEO/PVP/NaIO₄, the resultant PEO/PVP/NaIO₄/GO (0.4% in weight) electrolyte membrane demonstrated both an increase in tensile strength of ca. 42% and in Young’s modulus of ca. 40%, improvements coupled with a maximum fractured elongation of 3%. Through impedance spectroscopy analysis, the role of the GO nano-sheets onto the room temperature conductivity properties of the prepared electrolyte membranes has been probed.     

Synthesis and Characterization of Poly(vinyl pyrrolidone)/Reduced Graphene Oxide Nanocomposite

Poly(vinyl pyrrolidone) (PVP)/reduced graphene oxide (RGO) nanocomposites were synthesized by reducing graphene oxide in the polymer matrix at different temperatures. The effects of the GO content on the properties of the nanocomposites were investigated by Fourier-transform infrared (FTIR) spectroscopy and thermogravimetric analysis (TGA). The degree of dispersion of GO in the PVP matrix was examined by field-emission scanning electron microscopy. The results showed that both GO and RGO were well dispersed in the PVP matrix. Under low filler content, the improvement of onset decomposition temperatures of PVP nanocomposites was not obviously observed, but the amounts of residual char of the PVP nanocomposites were clearly increased. In addition, the decomposition temperature peak values of the PVP nanocomposites were increased, while the peak was broadened.     

Removal of Congo red dye from aqueous solution with nickel-based metal-organic framework/graphene oxide composites prepared by ultrasonic wave-assisted ball milling

Metal-organic frameworks (MOFs) were successfully synthesized by ultrasonic wave-assisted ball milling. In the absence of organic solvent, the coupling effect of ultrasonic wave and mechanical force played an significant role in the synthesis of MOFs. Adsorption of Congo red (CR) was studied in view of adsorption kinetic, isotherm and thermodynamics. The adsorbent was carried out using X-ray diffraction (XRD), thermogravimetric analysis (TGA), N₂ adsorption-desorption isotherms, Raman spectroscopy and scanning electron microscope (SEM) methods. It was found that pseudo-second-order kinetic model and Freundlich adsorption isotherm matched well for the adsorption of CR onto nickel-based metal-organic framework/graphene oxide composites (Ni-MOF/GO). The results of the adsorption thermodynamics indicated that the adsorption process was a spontaneous and endothermic process. The adsorption capacity of graphene oxide/metal-organic frameworks (GO/MOFs) for CR reached 2489 mg/g, much higher than previous reports. It was demonstrated that an increase in the number of active metal sites can dramatically improve the adsorption capacity of dye. A suitable dry temperature is beneficial for the improvement of adsorption capacity for dye. In this paper, the adsorption results indicated that ultrasonic wave-assisted ball milling has a good prospect for synthesis of MOFs with excellent adsorption performance.     

Effect of Oxide Content of Graphene Oxide Membrane on Remarkable Adsorption for Calcium Ions

Graphene oxide membranes(GOMs), as one of the most promising novel materials, have gained great interest in the field of adsorption. However, the oxygen content of graphene oxide is directly related to its adsorption properties, such as suspension stability, adsorption capacity, and reusability of GOMs. Here, a series of reduced GOMs with oxygen content from 28% to 12% were conveniently prepared by the thermally reduced and the corresponding interlayer spacing of these membranes changed from 8.0 ? to 3.7 ?. These prepared GOMs have remarkable Ca~(2+) adsorption capacity, which increases with the oxygen content or interlayer spacing of GOMs.Importantly, the max adsorption capacity of the mass ratio between adsorbed Ca~(2+)and pristine GOMs can reach up to 0.481 g/g, which is about one order of magnitude higher than the adsorption capacity of activated sludge,magnetic Fe_3 O_4, functionalized silica, zeolite molecular sieve, and other reported previously. Moreover, GOMs show excellent stability and the Ca~(2+) can be easily desorbed by water, so that the GOMs can be reused. Our previous theoretical analysis suggests that this remarkable adsorption is attributable to the strong interactions between Ca~(2+) and GO sheets, including the ion- interactions between Ca~(2+) and aromatic graphitic rings as well as the electrostatic interaction between Ca~(2+) and oxygen-containing groups.     

Synthesis of graphene oxide-poly(2-hydroxyethyl methacrylate) composite by dispersion polymerization in supercritical CO2: adsorption behavior for the removal of organic dye

The use of a biocompatible and thermoresponsive polymer, poly(2-hydroxyethyl methacrylate) (PHEMA) grafted onto the surface of graphene oxide (GO) as an adsorbent for the removal of a cationic dye (methylene blue [MB]) from an aqueous solution is examined in this work. GO–PHEMA forms a hydrogel in water thus overcoming the problem faced by carbon-based adsorbent materials during post-treatment (i.e., separation of adsorbent from the aqueous phase). The GO–PHEMA composite was synthesized using a green approach through dispersion polymerization in supercritical CO₂. The successful preparation of this composite was confirmed by a series of characterization techniques. The adsorption behavior of the composite toward MB such as the effect of the adsorbent dosage, pH, contact time, dye concentration, and recyclability were observed. In addition, the adsorption isotherm, kinetics and thermodynamics were investigated. According to the experimental data, the adsorption parameters were found to fit well into the Freundlich adsorption isotherm with a correlation coefficient of 0.975 and a maximum predicted adsorption capacity of 39.41 mg g^?1 at 25 °C. The adsorption kinetics studies showed that the adsorption behavior followed a pseudo-second-order reaction. On the other hand, the thermodynamics studies showed that the adsorption of MB on GO–PHEMA composite followed spontaneous and endothermic adsorption process with an efficient adsorption temperature at 45 °C. The experimental results also showed that the GO–PHEMA composite could remove 99.8% of the dye in 45 min. Therefore, GO–PHEMA composite is a favorable green adsorbent for environmental applications.     

不同尺度的蛋白质在纯石墨烯及氧化石墨烯表面的吸附比较

Using all-atom molecular dynamics (MD) simulations, we have investigated the adsorption stability and conformation change of different proteins on the surface of pristine graphene (PG) and graphene oxide (GO). We find that: (i) with the cooperation of the electrostatic interactions between proteins and oxygen-containing groups, GO shows better adsorption stability than PG; (ii) the peptide loses its secondary structure on both PG and GO surface, and the a-helix structure of the protein fragment is partially broken on PG surface, but is well preserved on GO surface, while the secondary structure of globular protein has no distinct change on both PG and GO surface. In general, GO presents better biocompatibility than PG. Our results are of significant importance to understand the interactions between proteins and PG/GO and the applications of PG/GO in biotechnology and biomedicine.     

Molecular responses of cells to 2-mercapto-1-methylimidazole gold nanoparticles (AuNPs)-mmi: investigations of histone methylation changes

Reduced graphene oxide (RGO) sheet was functionalized with nanocrystalline cellulose (NCC) via click coupling between azide-functionalized graphene oxide (GO-N₃) and terminal propargyl-functionalized nanocrystalline cellulose (PG-NCC). First, the reactive azide groups were introduced on the surface of GO with azidation of 2-chloroethyl isocyanate-treated graphene oxide (GO-Cl). Then, the resulted compounds were reacted with PG-NCC utilizing copper-catalyzed azide-alkyne cycloaddition. During the click reaction, GO was simultaneously reduced to graphene. The coupling was confirmed by Fourier transform infrared, Raman, DEPT135, and ¹³C NMR spectroscopy, and the complete exfoliation of graphene in the NCC matrix was confirmed with X-ray diffraction measurement. The degree of functionalization from the gradual mass loss of RGO-NCC suggests that around 23 mass % has been functionalized covalently. The size of both NCC and GO was found to be in nanometric range, which decreased after click reaction.     

Molecular simulations of phenol and ibuprofen removal from water using multilayered graphene oxide membranes

We present here non-equilibrium molecular dynamic simulations concerning the separation of phenol and ibuprofen as impurities compounds (ICs) in water by novel graphene oxide (GO) membranes. The coupling between water permeability and impurity rejection is studied as a function of membrane thickness and concentration, focusing on the underlying molecular phenomena. Results show that water permeability decreases as the number of layers increases. Moreover, molecular sieving can be achieved by tuning the number of GO layers and the surface chemistry of the sheet: water flow through layers is up to 20% faster than that in graphene layers, because of strong hydrogen bonded interactions with the oxygenated groups. Analysis of the simulation results suggests that upon adsorbing on the GO surface, the translational motion of ICs in water would be supressed. Nevertheless, hydrophilicity affects the permeability for membranes with high O/C ratio, owing to these strong hydrogen bonds. Furthermore, 100% rejection for the ICs can be obtained for most of the GO membranes with four layers. This study elucidates the important role of hydrophilic interactions in GO membranes to become ideal candidates for removal of organic pollutants from water, showing the applicability of molecular simulations to obtain molecular insights into this problem.     

Self-assembly between graphene sheets and cationic poly(methyl methacrylate) (PMMA) particles: preparation and characterization of PMMA/graphene composites

In this study, we presented a simple approach to prepare poly(methyl methacrylate) (PMMA)/graphene composites based on the self-assembly between graphene oxide (GO) sheets and cationic PMMA emulsion particles. Briefly, cationic PMMA emulsion particles were first synthesized by a soap-free emulsion polymerization process, in which methacryloyloxyethyl trimethyl ammonium chloride was used as the emulsifier, and then blended with the aqueous solution of GO. Through electrostatic attraction, the exfoliated GO sheets were tightly adhered on the PMMA particles. The GO sheets could be reduced in situ into graphene sheets by a chemical method, without the aggregation. The structure of the prepared composites and the influences of GO and graphene sheets on the properties of PMMA were investigated. Both GO and graphene sheets can increase the glass transition temperature and storage modulus of PMMA. Moreover, graphene sheets provided a more significant reinforcement effect.     

Microwave-assisted covalent modification of graphene nanosheets with chitosan and its electrorheological characteristics

Biofunctionalization and manipulating of graphene nanosheets (GNS) are important for biomedical research and application. Chitosan (CS) modified graphene nanosheets have been successfully prepared under microwave irradiation in N,N-dimethylformamide medium, which involved the reaction between the carboxyl groups of graphene oxide nanosheets (GONS) and the amido groups of chitosan followed by the reduction of graphene oxide nanosheets into graphene nanosheets using hydrazine hydrate. The as-prepared graphene nanosheets-chitosan (GNS-CS) nanocomposites have been characterized by FTIR, TEM, FESEM, XRD and TG. The results showed that chitosan was covalently grafted onto the surface of graphene nanosheets via amido bonds. Solubility measurements indicated that the resultant nanocomposites dispersed well in aqueous acetic acid. Especially, the electrorheological (ER) properties of the GNS-CS nanocomposites have been investigated. It is believed that this new nanocomposites may be promising for biomedical applications.     

Electro‐optic switching with liquid crystal graphene

Graphene oxide (GO) particles in aqueous dispersions can form liquid crystal (LC) phases at extremely low concentrations due to the extremely high aspect ratio of the flakes and noticeably, they possess an extremely large Kerr coefficient attractive for low power consumption electro‐optic devices. Reduced graphene does not easily form LC phases in water due to its hydrophobic nature but here we show that stable dispersions of reduced graphene oxide can be realized with surfactants and that they exhibit birefringence upon shearing as well as under application of electric fields. The performance of the system is largely superior to GO LC possessing longer time stability and drastically improved electro‐optic properties with an induced birefringence twice as large at the same field strength thanks to the almost recovery of graphene properties upon reduction. (© 2016 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Synthesis of phosphonic acid silver-graphene oxide nanomaterials with photocatalytic activity through ultrasonic-assisted method

In this article, phosphonic acid silver-graphene oxide nanomaterials (Nano-PAS-GO) was synthesized from silver nitrate (AgNO₃) solution and phosphoric graphene oxide (PGO) via the convenient ultrasonic-assisted method, and the structure and morphology were characterized, and the photocatalytic activity and recyclability were evaluated through photocatalyzing degradation of Rhodamin B (RhB) aqueous solution, and the possible photocatalytic mechanism was also discussed. Based on those, it was confirmed that Nano-PAS-GO has been synthesized from AgNO₃ solution and PGO colloidal suspension under ultrasonic-assisted condition, and Nano-PAS-GO has consisted of phosphoric acid silver nanoparticles and GO with 2D lattice (2D GO lattice) connected in the form of C-P bonds, and the photodegradation rate of Nano-PAS-GO for RhB aqueous solution has reached 93.99%, and Nano-PAS-GO has possessed the nicer recyclability when the photocatalytic time was 50 min. From those results, the strong and stable interface _.between PAS nanoparticles and 2D GO lattice connected in the form of the covalent bonds has effectively inhibited the occurrence of the photocorrosion phenomenon.     

Surface functionalization of porous ZrO2-TiO2 membranes using γ-aminopropyltriethoxysilane in palladium electroless deposition

A pre-treatment technique was developed to facilitate the electroless deposition of Pd layers onto ZrO₂-TiO₂ ceramic membrane surfaces in the preparation of novel multi-functional porous membranes. Surface functionalization using an aqueous solution of γ-aminopropyltriethoxysilane (γ-APTES) aided the surface immobilization of the Pd activation particles and the subsequent electroless deposition of metal layers onto the hydroxyl-rich membrane surface. The attractiveness of γ-APTES functionalization, in the electroless deposition of metal layers, was thus demonstrated. Characterization techniques employed in the structural study of the surface-modified membranes included SEM, EDS, dynamic analysis in micro-PIXE, and XRD. Special membrane techniques such as electrokinetic analysis and single-gas permeation measurements were also used in the study of surface modification. These membranes were developed for application in tasks associated with the hydrogen economy.     

氧化石墨烯/壳聚糖复合薄膜材料的制备及其非线性光限幅效应的研究

石墨烯及其衍生物作为新型碳纳米结构,由于其优异的光限幅性能而受到广泛关注,但现有的工作多侧重于其在液相体系中光限幅效应及其起因研究.本文以壳聚糖为成膜基质,将氧化石墨烯(GO)与壳聚糖(CS)在液相中均匀共混后成膜,对比研究GO溶液和GO-CS复合膜的光限幅效应及其起因.结果表明在线性透过率相同的情况下,GO在固相基质中表现出比液相基质更强的光限幅效应和更弱的非线性散射.这说明不同于碳纳米管简单的非线性散射,在GO中可能存在多种非线性光学效应.     

Surface-modified zeolite-filled chitosan membranes for pervaporation dehydration of ethanol

Surface-modified zeolite-filled chitosan (CS) membranes were prepared by incorporating 3-mercaptopropyltrimethoxysilane (MPTMS)-modified H-ZSM-5 zeolite into chitosan for pervaporation dehydration of aqueous ethanol solution. The physicochemical characterization by XPS, FT-IR, XRD, DMA and SEM showed that -SO₃H group was readily grafted on the surface of H-ZSM-5 with the mediation of MPTMS and hydrogen peroxide, and the accompanying ion-ion interaction between -SO₃H group on surface-modified H-ZSM-5 and -NH₃⁺ group on chitosan substantially eliminated the nonselective voids at the chitosan-H-ZSM-5 interface of the filled membranes. The experimental results also revealed that H-ZSM-5 exhibited desirable size-selective and preferential adsorption effects for aqueous ethanol solution. As a result, modified H-ZSM-5 filled membranes showed higher swelling degree and permeation flux, and improved selectivity for aqueous ethanol solution. In comparison between chitosan control membrane (permeation flux 54.18 g/(m² h) and separation factor 158.02 for 90 wt.% aqueous ethanol solution at 80 °C), the modified H-ZSM-5 filled membrane with 8 wt.% filling content exhibited a remarkably improved pervaporation performance with permeation flux 278.54 g/(m² h) and separation factor 274.46 under the identical experimental condition.     

Synthesis and characterization of nanocomposites films with graphene oxide and reduced graphene oxide nanosheets

Graphene oxide (GO) and reduced graphene oxide (CRGO), as a graphene derivatives, possess unique properties and a high aspect ratio, indicating great potential in nanocomposite fields. The present work reports the fabrication of the nanocomposite films by a simple and environmentally friendly process using aqueous solution and optimized time sonication for better exfoliation of the graphene sheets within Poly(Vinyl alcohol) (PVA) as matrix. The films were characterized using high-resolution TEM (HRTEM), X-ray diffraction (XRD), Microtensile testing, Differential scanning calorimetry (DSC) and Thermogravimetric analysis (TGA). The TEM images revealed a successfully exfoliation of the GO/CRGO nanosheets. XRD combined with TGA and DSC measurements showed an improvement in the thermal stability and tunable thermal properties. In addition, the Young's modulus and tensile yield strength of the composite films containing 1 wt% GO were obtained to be 4.92 GPa and 66 MPa respectively. These excellent reinforcement effects were achieved by the strong interaction between the components.     

Ultrasound assisted synthesis of Sn nanoparticles-stabilized reduced graphene oxide nanodiscs

Sn nanoparticles-stabilized reduced graphene oxide (RGO) nanodiscs were synthesized by a sonochemical method using SnCl₂ and graphene oxide (GO) nanosheets as precursors in a polyol medium. TEM and XPS were used to characterize the Sn-stabilized RGO nanodiscs.     

Highly concentrated, stable nitrogen-doped graphene for supercapacitors: Simultaneous doping and reduction

In this work, we developed a concentrated ammonia-assisted hydrothermal method to obtain N-doped graphene sheets by simultaneous N-doping and reduction of graphene oxide (GO) sheets. The effects of hydrothermal temperature on the surface chemistry and the structure of N-doped graphene sheets were also investigated. X-ray photoelectron spectroscopy (XPS) study of N-doped graphene reveals that the highest doping level of 7.2% N is achieved at 180 °C for 12 h. N binding configurations of sample consist of pyridine N, quaternary N, and pyridine-N oxides. N doping is accompanied by the reduction of GO with decreases in oxygen levels from 34.8% in GO down to 8.5% in that of N-doped graphene. Meanwhile, the sample exhibits excellent N-doped thermal stability. Electrical measurements demonstrate that products have higher capacitive performance than that of pure graphene, the maximum specific capacitance of 144.6 F/g can be obtained which ascribe the pseudocapacitive effect from the N-doping. The samples also show excellent long-term cycle stability of capacitive performance.     

Enhanced photocatalytic degradation of organic dyes by ultrasonic-assisted electrospray TiO2/graphene oxide on polyacrylonitrile/β-cyclodextrin nanofibrous membranes

Polyacrylonitrile (PAN)/β-cyclodextrin (β-CD) composite nanofibrous membranes immobilized with nano-titanium dioxide (TiO₂) and graphene oxide (GO) were prepared by electrospinning and ultrasonic-assisted electrospinning. Scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), transmission electron microscopy (TEM), and X-ray diffraction (XRD) confirmed that TiO₂ and GO were more evenly dispersed on the surface and inside of the nanofibers after 45 min of ultrasonic treatment. Adding TiO₂ and GO reduced the fiber diameter; the minimum fiber diameter was 84.66 ± 40.58 nm when the mass ratio of TiO₂-to-GO was 8:2 (PAN/β-CD nanofibrous membranes was 191.10 ± 45.66 nm). Using the anionic dye methyl orange (MO) and the cationic dye methylene blue (MB) as pollutant models, the photocatalytic activity of the nanofibrous membrane under natural sunlight was evaluated. It was found that PAN/β-CD/TiO₂/GO composite nanofibrous membrane with an 8:2 mass ratio of TiO₂-to-GO exhibited the best degradation efficiency for the dyes. The degradation efficiency for MB and MO were 93.52 ± 1.83% and 90.92 ± 1.52%, respectively. Meanwhile, the PAN/β-CD/TiO₂/GO composite nanofibrous membrane also displayed good antibacterial properties and the degradation efficiency for MB and MO remained above 80% after 3 cycles. In general, the PAN/β-CD/TiO₂/GO nanofibrous membrane is eco-friendly, reusable, and has great potential for the removal of dyes from industrial wastewaters.     

In situ growth of ultrashort rice-like CuO nanorods supported on reduced graphene oxide nanosheets and their lithium storage performance

A facile refluxing strategy in aqueous solution was engaged to synthesize ultrashort rice-like CuO nanorods/reduced graphene oxide (CuO-NRs/rGO) composite. The result of the high-resolution transmission electron microscopy shows that the as-synthesized rice-like CuO nanorods have a uniform size of about 8 nm in width and 28 nm in length and are homogenously dispersed on rGO nanosheets. The CuO nanorods are uniformly dispersed and immobilized by the graphene nanosheets reduced from GO. The resultant CuO-NRs/rGO composite as anode material for lithium-ion batteries displays better electrochemical properties than those of pure CuO-NRs and rGO nanosheets. The high reversible capacity and good stability can be ascribed to the presence of rGO nanosheets.