Enhanced Exfoliation Effect of Solid Auxiliary Agent On the Synthesis of Biofunctionalized MoS2 Using Grindstone Chemistry

Mass production and commercial availability are prerequisites for the viability and wide application of MoS₂. Here, we demonstrate enhanced grindstone chemistry for a one‐step synthesis of biofunctionalized MoS₂. By adding a SiO₂ auxiliary agent the exfoliation efficiency increases from 16.23% to 58.59% and a rapid and high‐yield exfoliation of MoS₂ is seen. SiO₂ exhibits a fragmentation effect, which reduces the lateral size and facilitates the exfoliation of MoS₂, thus inducing a high‐efficient paradigm in the top‐down fabrication of biofunctionalized MoS₂ nanosheets. The as‐prepared MoS₂‐chitosan (MoS₂‐CS) nanosheets display complete disaggregation and homogeneous dispersion, as well as a high content of chitosan (ca. 20 wt%). As a proof‐of‐concept application, the MoS₂‐CS nanosheets act as a biosorbent for Pb^II removal, exhibiting a good adsorption capacity and recyclability. This green and facile enhanced grindstone chemistry with minimal use of organic solvents and high‐throughput efficiency can be extended to the fabrication of other biocompatible inorganic 2D analogues for a variety of applications.     

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.     

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.     

Synthesis of Fluorinated Graphene Oxide and its Amphiphobic Properties

The richly functionalized basal plane bonded to polar organic moieties makes graphene oxide (GO) innately hydrophilic. Here, a methodology to synthesize fluorinated graphene oxide by oxidizing the basal plane of fluorinated graphite, allowing for tunable hydrophobicity of GO, is reported. Fluorine exists as tertiary alkyl fluorides covalently bonded to graphitic carbons, and using magic‐angle spinning (MAS) ¹³C NMR as a primary tool chemical structures for the two types of synthesized fluorinated graphene oxides (FGOs) with significantly different fluorine contents are proposed. The low surface energy of the C–F bond drastically affects GO's wetting behavior, leading to amphiphobicity in its highly fluorinated form. Ease of solution processing enables the fabrication of inks that are spray‐painted on various porous/non‐porous substrates. These coatings maintain amphiphobicity for solvents with surface tensions down to 59 dyn/cm, thus bypassing existing lithographic means to create similar surfaces. The approach towards fluorinating GO and fabricating graphene‐based surfaces with tunable wettability opens the path towards unique, accessible, carbon‐based amphiphobic coatings.     

Real-time monitoring of graphene oxide reduction in acrylic printable composite inks

This work reports the electrical characterization of a water-based graphene oxide/acrylic composite material, which was directly inkjet printed to fabricate dissipative patterns. The graphene oxide filler, which is strongly hydrophilic due to its heavily oxygenated surface and can be readily dispersed in water, was reduced by UV irradiation during photo-curing of the polymeric matrix. The concurrent polymerization of the acrylic matrix and reduction of graphene oxide filler was demonstrated by real-time resistance measurements during UV light irradiation. The presence of graphene filler allowed decreasing the resistance of the pure polymeric matrix by nearly five orders of magnitude. This was explained by the fact that clusters of reduced graphene oxide inside the polymer matrix act as preferential pathways for the mobility of charge carriers, thus leading to an overall decrease of the material’s resistance.     

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.     

Fabrication of Graphene Nanoplatelet/Epoxy Nanocomposites for Lightweight and High‐Strength Structural Applications

Graphene nanoplatelets (GNPs), the most important mass‐produced graphene, are fabricated as a mechanical reinforcement for epoxy matrix nanocomposites. Current performance of GNPs as a reinforcing filler is limited by their agglomeration and weak interfacial interaction with certain polymer matrices. Herein, an approach to produce noncovalently functionalized GNPs (F‐GNPs) is reported that can be extended to the industrial level of mass production. The one‐step functionalization process uses melamine, a low‐cost chemical, to improve the interfacial adhesion and dispersion in an epoxy matrix. The mechanical properties of nanocomposites prepared with the F‐GNP flakes are much better (94.3% and 35.3% enhancements in Young's modulus and tensile strength, respectively) than those of the unfilled pure epoxy. Experimental data are analyzed using the Halpin–Tsai model. The fabrication process developed in this paper provides a strategy to use GNPs at the industrial level in lightweight and high‐strength structural applications.     

Graphene Modified Lipophilically by Stearic Acid and its Composite With Low Density Polyethylene

Graphene, prepared by the thermal reduction of graphite oxide (GO), was modified with stearic acid to enhance its lipophilicity. A novel method, using the intrinsic epoxy groups on the graphene, was utilized for reaction with stearic acid to minimize the negative impact of the normal functionalization method on the π-electronic system of graphene. Gravimetric analysis, thermogravimetric analysis (TGA), Fourier transform infrared (FTIR) spectroscopy, and X-ray photoelectron spectroscopy (XPS) showed that the stearic acid was effectively attached to the graphene. In addition, Raman spectroscopy and electric conductivity of the graphene showed that this novel modification method, utilizing intrinsic defects, did not damage the π-electronic system of the sp² bonded carbons. The dispersion of graphene in a low density polyethylene (LDPE) matrix was enhanced; consequently, the reinforcing effect in tensile testing was improved by the lipophilic modification. The crystallization behavior observed by differential scanning calorimetry (DSC) showed that the crystallization of LDPE was hindered by dispersed graphene, more evidently when dispersed uniformly.     

Synthesis,mechanical, and barrier properties of LDPE/graphene nanocomposites using vinyl triethoxysilane as a coupling agent

Precise interface control and dispersal of graphene nanosheets in polymer hosts are challenging to develop high performance graphene-based nanocomposites due to their strong interlayer cohesive energy and surface inertia. Here, we firstly report an efficient and novel method to functionalize graphene nanosheets with vinyl triethoxysilane (VTES) and successfully blend them with low density polyethylene (LDPE) to prepare nanocomposites. Fourier transforms infrared spectra (FTIR), Raman spectra, and thermogravimetric analysis (TGA) proved that the graphene sheets were covalently bonded with VTES. The resulting nanocomposites obtained the increases of up to 27.0 and 92.8% in the tensile strength and Young’s modulus, respectively, compared to neat LDPE. The VTES–graphene not only remarkably improved the tensile strength of the composites, but also enhanced its toughness by 17.7%. Oil permeability measurements showed that the absorption ratio of toluene by the LDPE/graphene composites decreased from 56 to 39%, and its barrier properties have obviously been improved. This study opens a new route to optimize interface structures and improve the comprehensive performances of graphene–polymer nanocomposites.     

Probing disorder and charged impurities in graphene by Raman spectroscopy

Disorder and doping can strongly affect the properties of graphene. Here we analyze these effects on several samples by Raman spectroscopy. In particular, we show that pristine and unprocessed graphene samples deposited on silicon, covered with a thin silicon oxide layer, show strong variations in their Raman spectra, even in absence of disorder. The variation in the Raman parameters is assigned to charged impurities. This shows that as‐deposited graphene is unintentionally doped, reaching charge concentrations up to 10¹³ cm^–2 under ambient conditions. The doping varies from sample to sample and the charges are inhomogeneously distributed on a submicron scale. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Improved Dielectric Breakdown Strength of Covalently-Bonded Interface Polymer–Particle Nanocomposites

Interfacial covalent bonding is an effective approach to increase the electrical resistance of a polymer–particle composite to charge flow and dielectric breakdown. A bifunctional tether reagent bonded to an inorganic oxide particle surface assists with particle dispersion within a thermosetting epoxy polymer matrix but then also reacts covalently with the polymer matrix. Bonding the particle surface to the polymer matrix resulted in a composite that maintained the pure polymer glass transition temperature, compared to modified or unmodified particle dispersions that lacked covalent bonding to the polymer matrix, which depressed the polymer glass transition to lower temperatures. The added interfacial control, directly bonding the particle to the polymer matrix, appears to prevent conductive percolation across particle surfaces that results in a reduced Maxwell–Wagner relaxation of the polymer–particle composite and a reduced sensitivity to a dielectric breakdown event. The inclusion of 5 vol% particles of higher permittivity produces a composite of enhanced dielectric constant and, with surface modification to permit surface cross-linking into the polymer, a polymer–particle composite with a Weibull E ₀ dielectric breakdown strength of 25% greater than that of the pure polymer resulted. The estimated energy density for the cross-linked interface composite was improved 260% compared to the polymer alone, 560% better than a polymer–particle composite synthesized using bare particles, and 80% better than a polymer–particle composite utilizing bare particles with a dispersant.     

Probing the role of hydrolytically stable, 3-aminopropyl triethoxysilane crosslinked chitosan/graphene oxide membrane towards Congo red dye adsorption

In this investigation, the practicability of utilizing 3-aminopropyl triethoxysilane (3-APTES) crosslinked chitosan (Ch)/graphene oxide (GO) membranes were explored for adsorptive removal of anionic dyes from aqueous medium. Membranes were successfully fabricated through solution casting technique. Strong interactions amongst matrix (chitosan), 3-APTES, polyvinylpyrrolidone (PVP) and GO were confirmed by Infrared spectroscopy. Thermal stability of the chitosan was improved by adding graphene oxide and results were verified via thermogravimetric (TGA) analysis. Swelling and hydrolytic results confirmed that 2 %-Ch/PVP was a stable membrane while increasing the amount of 3-APTES in the chitosan nanocomposites membrane decreased its stability in aqueous medium. The adsorption characteristics of the membranes were evaluated by the adsorption of Congo red (CR) dye from aqueous medium. The adsorbent can remove 80% of CR from aqueous medium and follows second order kinetics. This study outlines the possibility of exploring green membranes which can be easily fit in various flow systems.     

Facile Fabrication of Bicomponent CoO/CoFe2O4‐N‐Doped Graphene Hybrids with Ultrahigh Lithium Storage Capacity

A facile strategy is developed to fabricate bicomponent CoO/CoFe₂O₄‐N‐doped graphene hybrids (CoO/CoFe₂O₄‐NG). These hybrids are demonstrated to be potential high‐performance anodes for lithium‐ion batteries (LIBs). The CoO/CoFe₂O₄ nanoplatelets are finely dispersed on the surface of N‐doped graphene nanosheets (CoO/CoFe₂O₄‐NG). The CoO/CoFe₂O₄‐NG electrode exhibits ultrahigh specific capacity with 1172 mA h g^?1 at 500 mA g^?1 and 970 mA h g^?1 at 1000 mA g^?1 as well as excellent cycle stability due to the synergetic effects of N‐doped graphene and CoO/CoFe₂O₄ nanoplatelets. The well‐dispersed bicomponent CoO/CoFe₂O₄ is responsible for the high specific capacity. The N‐doped graphene with high specific surface area has dual roles: to provide active sites for dispersing the CoO/CoFe₂O₄ species and to function as an electrical conducting matrix for fast charge transfer. This method provides a simple and efficient way to configure the hybridized electrode materials with high lithium storage capacity.     

Photovoltaic activity in a ZnSe/PEO–chitosan blend electrolyte junction

Thin films of ZnSe and PEO–chitosan blend polymer doped with NH₄I and iodine crystals were prepared to form the two sides of a semiconductor electrolyte junction. ZnSe was electrodeposited on indium tin oxide (ITO) conducting glass. The polymer is a blend of 50 wt% chitosan and 50 wt% polyethylene oxide. The polymer blend was complexed with ammonium iodide (NH₄I), and some iodine crystals were added to the polymer–NH₄I solution to provide the I⁻/I³⁻redox couple. The room temperature ionic conductivity of the polymer electrolyte is 4.32 × 10⁻⁶ S/cm. The polymer film was sandwiched between the ZnSe semiconductor and an ITO glass to form a ZnSe/polymer electrolyte/ITO photovoltaic cell. The open circuit voltage (V _oc) of the fabricated cells ranges between 200 to 400 mV and the short circuit current between 7 to 10 μA.     

Ecofriendly Route for the Synthesis of Highly Conductive Graphene Using Extremophiles for Green Electronics and Bioscience

Highly conductive biocompatible graphene is synthesized using ecofriendly reduction of graphene oxide (GO). Two strains of non‐pathogenic extremophilic bacteria are used for reducing GO under both aerobic and anaerobic conditions. Degree of reduction and quality of bacterially reduced graphene oxide (BRGO) are monitored using UV–vis spectroscopy, X‐ray photoelectron spectroscopy, and Raman spectroscopy. Structural morphology and variation in thickness are characterized using electron microscopy and atomic force microscopy, respectively. Electrical measurements by three‐probe method reveal that the conductivity has increased by 10⁴–10⁵ fold from GO to BRGO. Biocompatibility assay using mouse fibroblast cell line shows that BRGO is non‐cytotoxic and has a tendency to support as well as enhance the cell growth under laboratory conditions. Hereby, a cost effective, non‐toxic bulk reduction of GO to biocompatible graphene for green electronics and bioscience application is achieved using halophilic extremophiles for the first time.     

A simple approach to synthesize nanosized sulfur/graphene oxide materials for high-performance lithium/sulfur batteries

We report on a simple and facile synthesis route for the sulfur/graphene oxide composite via ultrasonic mixing of the nano-sulfur and graphene oxide aqueous suspensions followed by a low-temperature heat treatment. High-resolution transmission and scanning electronic microscopy observations revealed the formation of a highly porous structure consisting of sulfur with uniform graphene oxide coating on its surface. The resulting sulfur/graphene oxide (S/GO) composite exhibited high and stable specific discharge capacities of 591 mAh g^?1 after 100 cycles at 0.1 C and good rate capability. This enhanced electrochemical performance could be attributed to the effective confining the polysulfides dissolution and accommodation of the volume changes during the Li-S electrochemical reaction by the functional groups on the graphene oxide coating layer. Furthermore, the highly developed porous structure of S/GO composite favors the enhanced ion transport and electrolyte diffusion.     

Thermodynamic approach to enhance the dispersion of graphene in epoxy matrix and its effect on mechanical and thermal properties of epoxy nanocomposites

Graphene-reinforced polymer nanocomposites are under intense investigation in recent years. In this work, graphene nanosheets have been prepared using chemical reduction method of graphene oxide. Graphene-reinforced epoxy nanocomposites show an enhancement in mechanical and thermal properties at 0.05 wt.% of graphene in epoxy matrix. Modification of graphene with polyvinylpyrrolidone (PVP) shows the significant enhancement in mechanical and thermal properties of epoxy nanocomposites. PVP-modified graphene nanosheets reduces the gap of enthalpic and entropic penalties and facilitates improved dispersion of graphene in epoxy matrix. In addition, enhanced dispersion of PVP-modified graphene in epoxy matrix results in better load transfer across graphene–epoxy interface. Glass transition temperature (T_g) of PVP-modified graphene epoxy nanocomposites increases as compared to pure epoxy because there exist an interaction between epoxy and PVP. Fractography study reveals the localized ductile fracture.     

Near‐3‐MeV protons from target‐normal‐sheath‐acceleration femtosecond laser irradiating advanced targets

Advanced targets based on graphene oxide and gold thin film were irradiated at high laser intensity (10¹⁸–10¹⁹ W/cm²) with 50‐fs laser pulses and high contrast (10⁸) to investigate ion acceleration in the target‐normal‐sheath‐acceleration regime. Time‐of‐flight technique was employed with SiC semiconductor detectors and ion collectors in order to measure the ion kinetic energy and to control the properties of the generated plasma. It was found that, at the optimized laser focus position with respect to the target, maximum proton acceleration up to about 3 MeV energy and low angular divergence could be generated. The high proton energy is explained as due to the high electrical and thermal conductivity of the reduced graphene oxide structure. Dependence of the maximum proton energy on the target focal position and thickness is presented and discussed.     

Preparation and properties of kenaf dust-filled chitosan biocomposites

Kenaf dust filled chitosan biocomposites have been prepared using a solution blending method. Diluted acetic acid was used as medium to dissolve the chitosan powder. Kenaf dust particles were dispersed in the chitosan solution using a high speed homogenizer. Chitosan biocomposites with five different compositions of kenaf loading (w/w) were prepared. The biocomposites were evaluated in terms of mechanical, chemical and micro-structural properties. The maximum tensile strength, tensile strain and toughness values were obtained from biocomposites containing 28% of kenaf dust, while pure chitosan film exhibit the lowest value as expected. Morphological study on the tensile fracture surface of the biocomposites under FESEM showed the interconnected structure of chitosan matrix with fine distribution of kenaf dust. From the FT-IR spectrum, the finger print peak of chitosan was detected (3233 cm^?1) as well as the increasing in intensity of typical functional groups (aldehyde, primary amine and ammonium ions), indicating a strong interaction between kenaf dust and chitosan matrix.     

Influence of covalent and non-covalent modification of graphene on the mechanical,thermal and electrical properties of epoxy/graphene nanocomposites: a review

Abstract

Graphene is emerged as a highly sought after reinforcing filler for epoxy matrix in view of its superior electrical, mechanical and thermal properties. Dispersion of low concentration of graphene can significantly enhance the epoxy/graphene nanocomposites properties. Dispersion of graphene in epoxy matrix depends on processing protocols used, and interfacial interaction between epoxy matrix and graphene. Interfacial interaction between epoxy matrix and graphene can be achieved by covalent and non-covalent modification of graphene. This paper comprehensively review the influence of different processing protocols adopted for the processing of epoxy/graphene nanocomposites, and its effect on mechanical, thermal and electrical properties. In addition, covalent and non-covalent strategies adopted for modification of graphene, and its influence on mechanical, thermal and electrical properties of epoxy/graphene nanocomposites are extensively discussed. The future challenges associated with graphene reinforced epoxy nanocomposites processing have been discussed.