Enhanced thermal stability in graphene oxide covalently functionalized with 2-amino-4,6-didodecylamino-1,3,5-triazine

In this study 2-amino-4,6-didodecylamino-1,3,5-triazine (ADDT) was synthesized from cyanuric chloride and covalently functionalized onto graphene oxide nanosheets. The chemical structure of the alkylated melamine and the functionalized graphene oxide (GO) nanosheets were characterized with ¹H NMR, FT-IR, XPS, TGA and TEM. The results indicate that two chlorine atoms on the triazine ring of cyanuric chloride were substituted by two long alkyl chains. Covalent functionalization of ADDT onto the graphene oxide nanosheets was confirmed with both FT-IR and XPS results. The reduced mass loss rate along with enhanced residue formation (TGA results) indicates significant improvement in thermal stability for GO-ADDT compared to GO. Moreover good solubility of GO-ADDT in organic solvents suggests the potential of GO-ADDT as a nanoadditive for polymeric systems.     

Graphene oxide-anchored reactive sulfonated copolymer via simple one pot condensation polymerization: proton-conducting solid electrolytes

A rapid and efficient post-polymerization functionalization of poly(urea-co-urethane) (PUU) onto the graphene oxide (GO) nanosheets has been developed to produce super-acidic polymer/GO hybrid nanosheets. Thus, the surface of GO nanosheets were functionalized with 3-(triethoxysilyl)propyl isocyanate (TESPIC) from hydroxyl groups to yield isocyanate functionalized graphene oxide nanosheets. Then, sulfonated polymer/GO hybrid nanosheets were prepared by condensation polymerization of isocyanate-terminated pre-polyurea onto isocyanate functionalized graphene oxide nanosheets through the formation of carbamate bonds. FTIR and TGA results indicated that TESPIC modifier agent and poly(urea-co-urethane) were successfully grafted onto the GO nanosheets. The grafting efficiency of poly(urea-co-urethane) polymer onto the GO nanosheets was estimated from TGA thermograms to be 205.9%. Also, sulfonated polymer/GO hybrid nanosheets showed a proton conductivity as high as 3.7 mS cm^?1. Modification and morphology of GO nanosheets before and after modification processes were studied by scanning electron microscopy (SEM), atomic force microscopy (AFM) and X-ray diffraction (XRD).     

Chemically Functionalized Graphene Nanosheets and Their Influence on Thermal Stability,Mechanical, Morphological,and Electrical Properties of Poly(methyl methacrylate)/Poly(ethylene Oxide) Blend

Poly(methyl methacrylate)/poly(ethylene oxide) (90/10) blend containing various contents of functionalized graphene was prepared through solution technique and characterized to investigate the effects of functionalized graphene content on mechanical, thermal, and electrical properties of the nanocomposites. Infrared results revealed the interaction between matrix and functionalized graphene. Electron microscopy images of the nanocomposites exhibited a good dispersion of functionalized graphene nanosheets in the blend. The incorporation of functionalized graphene significantly increased the thermal stability and mechanical properties of poly(methyl methacrylate)/poly(ethylene oxide) blend. At electrical percolation threshold achieved at functionalized graphene loading of 4.27?wt%, the conductivity of the nanocomposites was increased by more than eight orders of magnitude.     

磺化石墨烯固体酸催化剂的制备及活性评价

石墨烯是由碳原子以sp₂杂化连接的单原子层构成的新型二维碳原子晶体,由于含有众多具有反应活性的碳碳双键,石墨烯纳米片表面很容易进行化学修饰键合有机官能团而改变其性质。采用改良Hummers法制备氧化石墨烯,通过磺化反应制备磺化石墨烯固体酸催化剂,通过FT-IR、元素分析和XPS等对其结构进行表征。将制备的氧化石墨烯和磺化石墨烯应用于催化纤维二糖的水解反应,以纤维二糖糖苷键的水解反应为模型考察其酸催化性能。结果表明,氧化石墨烯和磺化石墨烯中含有-COOH、-OH和-SO₃H等官能团,磺酸根密度分别为1.0 mmol·g^-1和2.2 mmol·g^-1,氧化石墨烯和磺化石墨烯具有与H₂SO₄相比拟的酸催化活性,尽管酸性强度和密度较低,但催化活性与H₂SO₄相当。     

Morphology,thermal, mechanical,and barrier properties of graphene oxide/poly(lactic acid) nanocomposite films

To improve the physical and gas barrier properties of biodegradable poly(lactic acid) (PLA) film, two graphene nanosheets of highly functionalized graphene oxide (0.3 wt% to 0.7 wt%) and low-functionalized graphene oxide (0.5 wt%) were incorporated into PLA resin via solution blending method. Subsequently, we investigated the effects of material parameters such as loading level and degree of functionalization for the graphene nanosheets on the morphology and properties of the resultant nanocomposites. The highly functionalized graphene oxide (GO) caused more exfoliation and homogeneous dispersion in PLA matrix as well as more sustainable suspensions in THF, compared to low-functionalized graphene oxide (LFGO). When loaded with GO from 0.3 wt% to 0.7 wt%, the glass transition temperature, degree of crystallinity, tensile strength and modulus increased steadily. The GO gave rise to more pronounced effect in the thermal and mechanical reinforcement, relative to LFGO. In addition, the preparation of fairly transparent PLA-based nanocomposite film with noticeably improved barrier performance achieved only when incorporated with GO up to 0.7wt%. As a result, GO may be more compatible with hydrophilic PLA resin, compared to LFGO, resulting in more prominent enhancement of nanocomposites properties.     

磺化聚醚醚酮／氧化石墨复合膜的制备与表征

采用液相氧化法制备了氧化石墨（GO）,以浓硫酸为磺化剂与聚醚醚酮反应制备了磺化聚醚醚酮（SPEEK）。采用溶液共混法制备了不同组成的SPEEK／GO复合膜,并运用FTIR、XRD、DSC、TG对复合膜进行了表征。研究表明,当氧化石墨和磺化聚醚醚酮复合后,氧化石墨的层间距由0．8nm增大至1．1nm,这说明磺化聚醚醚酮极性基团或者高分子链段已经插入到氧化石墨片层之间。DSC结果显示,氧化石墨的加入,在一定程度上降低了SPEEK的结晶性能。TG分析表明,在温度低于300℃,复合膜的热稳定性比磺化聚醚醚酮的略有降低,但当温度高于450℃后,复合膜的热稳定性反而得到提高。     

石墨烯的制备及石墨烯/PVDF合材料介电性能的研究

通过Staudenmaier法制备了完全氧化的氧化石墨(GO),并通过高温热膨胀制备了单层石墨烯(graphene).用FT-IR、TG和XRD对GO的氧化程度、含氧官能团进行了表征;Graphene的XRD测试结果证明了单层石墨的存在.利用超声共混法制备了graphene/PV DF介电纳米复合材料.介电性能的测试表...     

Synthesis and properties of click coupled graphene oxide sheets with three‐dimensional macromolecules

A facile click chemistry approach to the functionalization of three‐dimensional hyperbranched polyurethane (HPU) to graphene oxide (GO) nanosheets is presented. HPU‐functionalized GO samples of various compositions were synthesized by reacting alkyne‐functionalized HPU with azide‐functionalized GO sheets. The morphological characterization of the HPU‐functionalized GO was performed using transmission electron microscopy and its chemical characterization was carried out using Fourier transform‐infrared spectroscopy, nuclear magnetic resonance spectroscopy, and X‐ray photoelectron spectroscopy. The graphene sheet surfaces were highly functionalized, leading to improved solubility in organic solvents, and consequently, enhanced mechanical, thermal, and thermoresponsive and photothermal shape memory properties. The strategy reported herein provides a very efficient method for regulating composite properties and producing high performance materials. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43358.     

Preparation of polyimide/siloxane‐functionalized graphene oxide composite films with high mechanical properties and thermal stability via in situ polymerization

An effective approach to prepare polyimide/siloxane‐functionalized graphene oxide composite films is reported. The siloxane‐functionalized graphene oxide was obtained by treating graphene oxide (GO) with 1,3‐bis(3‐aminopropyl)‐1,1,3,3‐tetra‐methyldisiloxane (DSX) to obtain DSX‐GO nanosheets, which provided a starting platform for in situ fabrication of the composites by grafting polyimide (PI) chains at the reactive sites of functional DSX‐GO nanosheets. DSX‐GO bonded with the PI matrix through amide linkage to form PI‐DSX‐GO films, in which DSX‐GO exhibited excellent dispersibility and compatibility. It is demonstrated that the obvious reinforcing effect of GO to PI in mechanical properties and thermal stability for PI‐DSX‐GO is obtained. The tensile strength of a composite film containing 1.0 wt% DSX‐GO was 2.8 times greater than that of neat PI films, and Young's modulus was 6.3 times than that of neat PI films. Furthermore, the decomposition temperature of the composite for 5% weight loss was approximately 30 °C higher than that of neat PI films. © 2015 Society of Chemical Industry     

Synthesis and characterisation of hydrophilic and organophilic graphene nanosheets

Hydrophilic graphene nanosheets were rapidly synthesized by reacting graphene oxide nanosheets with poly(sodium 4-styrene sulfonate) and simultaneously reducing by hydrazine hydrate under hydrothermal conditions. Organophilic graphene nanosheets were prepared by reacting with octadecylamine and reduction by hydroquinone through a reflux process. Ultraviolet-visible spectroscopy and Fourier transform infrared spectroscopy measurements confirmed the attachment of organic molecules to the graphene nanosheets to achieve hydrophilic and organophilic affinity. X-ray diffraction, Raman spectroscopy, and transmission electron microscopy analysis indicated that the crystal structure of the graphene nanosheets was maintained intact after chemical functionalisation.     

Convenient method for preparation of a new absorbent based on biofunctionalized graphene oxide hydrogels using nitrene chemistry and click reaction

A new graphene oxide (GO)-based hydrogel was synthesized through cross-linking of biofunctionalized graphene oxide nanosheets by di-alkyne polyethylene glycol as cross-linking agent. In this respect, nitrene chemistry as a convenient and straightforward protocol was developed for biofunctionalization of GO using an azido-starch as an eco-friendly, biodegradable and cost-effective material. In the next step, 1,3-dipolar cycloaddition chemistry, a green and highly efficient approach was utilized in cross-linking of functionalized GO by PEG through click reaction between remaining azido groups of starch on the surface of GO sheets and terminal alkyne groups of polyethylene glycol. Formation of aziridine and triazole rings during functionalization and cross-linking in this method could evidently improve biological activities of the obtained hydrogel compared to the conventional methods. The antibacterial activity of the new compounds was explored. The synthesized hydrogel showed antibacterial properties against Gram-positive and Gram-negative bacteria due to the presence of triazole rings. Also, the resulting hydrogel exhibited high dye removal efficiency and it can be utilized in water treatment effectively. The adsorption kinetics was analyzed through the effects of adsorption time and the dye concentration on the adsorption capacity. Kinetic data were accurately described by a pseudo-second-order model.     

Graphenes prepared by Staudenmaier, Hofmann and Hummers methods with consequent thermal exfoliation exhibit very different electrochemical properties

Large-scale fabrication of graphene is highly important for industrial and academic applications of this material. The most common large-scale preparation method is the oxidation of graphite to graphite oxide using concentrated acids in the presence of strong oxidants and consequent thermal exfoliation and reduction by thermal shock to produce reduced graphene. These oxidation methods typically use concentrated sulfuric acid (a) in combination with fuming nitric acid and KClO(3) (Staudenmaier method), (b) in combination with concentrated nitric acid and KClO(3) (Hofmann method) or (c) in the absence of nitric acid but in the presence of NaNO(3) and KMnO(4) (Hummers method). The evaluation of quality and applicability of the graphenes produced by these various methods is of high importance and is attempted side-by-side for the first time in this paper. Full-scale characterization of thermally reduced graphenes prepared by these standard methods was performed with techniques such as transmission and scanning electron microscopy, Raman spectroscopy and X-ray photoelectron spectroscopy. Their applicability for electrochemical devices was further evaluated by means of cyclic voltammetry techniques. We showed that while Staudenmaier and Hofmann methods (methods that do not use potassium permanganate as oxidant) generated thermally reduced graphenes with comparable electrochemical properties, the graphene prepared by the Hummers method which uses permanganate as oxidant showed higher heterogeneous electron transfer rates and lower overpotentials as compared to graphenes prepared by the Staudenmaier or Hofmann methods. This clearly shows that the methods of preparations have dramatic influences on the materials properties and, thus, such findings are of eminent importance for practical applications as well as for academic research.     

Nanoparticles@rGO membrane enabling highly enhanced water permeability and structural stability with preserved selectivity

Developing advanced membranes with high separation performance and robust mechanical properties is critical to the current water crisis. Herein, a general and scalable fabrication of nanoparticles (NPs)@reduced graphene oxide (rGO) membranes with significantly expanded nanochannels meanwhile ordered laminar structures using in situ synthesized NPs@rGO nanosheets as building blocks is reported. Size‐ and density‐controllable NPs were uniformly grown on the regularly stacked rGO nanosheets through coordination, followed by filtration‐deposition on inner surface of porous ceramic tubes. The NPs bonded rGO building blocks enabled the as‐prepared membranes 1–2 orders of magnitudes higher water permeance than the counterparts while keeping excellent rejections for various organic matters and ions. Moreover, the industrially preferred GO‐based tubular membrane exhibited an extraordinary structural stability under high‐pressure and cross‐flow process of water purification, which is considered as a notable step toward realizing scalable GO‐based membranes. © 2017 American Institute of Chemical Engineers AIChE J, 2017     

Influence of Sulfonated Graphene Oxide on Sulfonated Polysulfone Membrane for Direct Methanol Fuel Cell

Novel proton exchange membranes consisting of an inorganic filler, namely sulfonated graphene oxide, embedded in sulfonated polysulfone were fabricated. The membrane performance depended on the sulfonated graphene oxide content possessed the functional groups to provide the interfacial interaction with sulfonated polysulfone through ionic channels and blocking effect. The membrane with 3% v/v sulfonated graphene oxide content embedded in the matrix was shown to be suitable for direct methanol fuel cell applications. The membrane exhibited the highest proton conductivity of 4.27?×?10^?3 S cm^?1 which was higher than that of Nafion117. Moreover, the membrane provided the lowest methanol permeability of 3.48?×?10^?7?cm²/s which was lower than that of Nafion117.     

Allyl-Functionalization enhanced thermally stable graphene/fluoroelastomer nanocomposites

Development of new elastomers with novel functionality has continued since their discovery in order to meet industrial and defense needs in harsh environments. The recent advance of carbon nanomaterials inspired innovative material design strategies and enable more effective production of high-performance elastomers. In this paper, the free radical initiated crosslinking reaction in graphene/fluoroelastomer nanocomposites was studied and the effects of chemical functionalization of graphene nanosheets were analyzed. It indicated that graphene oxide (GO) enhanced fluoroelastomer nanocomposites demonstrated poor high-temperature stability due to the pyrolysis at around 200 °C. In contrast, reduced graphene oxide (RGO) enhanced fluoroelastomer exhibited good thermal stability, but RGO didn't participate in the crosslinking, resulting in very limited improvement in mechanical properties. In this paper, reduced allyl functionalized graphene was studied for the first time to enhance free radical initiated elastomers. The reduced allyl functionalization of graphene was demonstrated to impart superior thermal stability and enhanced mechanical properties to the elastomer matrices. The study of vulcanization kinetics provided insights that the allyl functional groups participated in and accelerated the crosslinking. These results indicated a scalable method to incorporate the advantages of graphene into polymer matrices through free radical reaction. The discovery is very promising to be used in the industry to fabricate gaskets, o-rings, and membranes for high temperature applications.     

In situ polymerization of polyimide‐based nanocomposites via covalent incorporation of functionalized graphene nanosheets for enhancing mechanical,thermal, and electrical properties

In this study, we report an effective method to fabricate high‐performance polyimide (PI)‐based nanocomposites using 3‐aminopropyltriethoxysilane functionalized graphene oxide (APTSi‐GO) as the reinforcing filler. APTSi‐GO nanosheets exhibit good dispersibility and compatibility with the polymer matrix because of the strong interfacial covalent interactions. PI‐based nanocomposites with different loadings of functionalized graphene nanosheets (FGNS) were prepared by in situ polymerization and thermal imidization. The mechanical performance, thermal stability, and electrical conductivity of the FGNS/PI nanocomposites are significantly improved compared with those of pure PI by adding only a small amount of FGNS. For example, a 79% improvement in the tensile strength and a 132% increase in the tensile modulus are achieved by adding 1.5 wt % FGNS. The electrical and thermal conductivities of 1.5 wt % FGNS/PI are 2.6 × 10^?3 S/m and 0.321 W/m·K, respectively, which are ～10¹⁰ and two times higher than those of pure PI. Furthermore, the incorporation of graphene significantly improves the glass‐transition temperature and thermal stability. The success of this approach provides a good rationale for developing multifunctional and high‐performance PI‐based composite materials. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42724.     

磺化聚酰亚胺的合成及其膜性能研究

采用2,2'-双苯氧基对二氨基联苯(PHOB)制备了2,2'-双(4-磺酸基苯氧基)对二氨基联苯(2,2′-BSPOB),以2,2′-BSPOB、1,3-双(4-氨基苯氧基)苯(BAPBz)和1,4,5,8-萘四甲酸二酐(NTDA)为原料,经缩聚反应生成磺化聚酰亚胺(SPIs)。以间甲酚为溶剂,通过溶液浇铸法成膜,研究了合成聚合物膜的吸水率、尺寸变化、机械性能和质子导电率。NTDA-BSPOB-BAPBz(3/2/1)聚合物膜在水中的质子导电率达到了198.3 mS/cm。     

One-pot synthesis of graphene–BiOBr nanosheets composite for enhanced photocatalytic generation of reactive oxygen species

Graphene oxide (GO), BiOBr and graphene–BiOBr nanosheets composites (BiOBr–RG) were synthesized and characterized. It can be found that except for BiOBr nanosheets with pure tetragonal phase were grown uniformly on the graphene surface, little graphene layer also can load on the surface of BiOBr evenly. And we found that the graphene can change the conduction band (CB) and valence band (VB) of BiOBr toward enhanced photocatalytic activity for reactive oxygen species (ROS) generation than that of BiOBr under visible-light irradiation.     

Synthesis of enhanced hydrophilic and hydrophobic graphene oxide nanosheets by a solvothermal method

We report that the hydrophilic affinity of graphene oxide nanosheets can be significantly increased by reacting with allylamine. High resolution transmission electron microscopy and electron diffraction analysis confirmed that the graphene oxide nanosheets were amorphous in structure. Hydrophobic graphene oxide nanosheets were also prepared via functionalising with phenylisocynate (C₆H₅NCO) through a solvothermal synthesis process. Hydrophobic graphene oxide nanosheets can be used as additives in polymer-based composites and other functional applications.     

pH-Mediated fine-tuning of optical properties of graphene oxide membranes

We demonstrate a pH-mediated fine-tuning method for the transmittance and optical properties of graphene oxide membranes (GOMs) which are assembled at liquid/air interface starting from graphene oxide (GO) hydrosols. The transmittance of GOM continuously decreases with the increase of the pH value of the parent hydrosol. The size and surface chemistry of GO nanosheets are discussed to how to influence the transmittance of GO hydrosol and the optical properties of the resulting membrane since a size classification occurs in acidic condition and a deoxygenate reaction is initiated by basic environment. This study indicates an easy strategy for precisely adjusting the optical properties of graphene-based membrane, which is very important for developing novel optical devices.