Graphene Oxide In Organic Solvents Research Articles

Hyperbranched lutecium phthalocyanines grafted ethylenediamine@graphene oxide with enhanced nonlinear optical properties

To enhance the nonlinear optical properties of graphene oxide in organic solvent and polymeric matrix, lutecium phthalocyanines (LuPc) and hyperbranched lutecium phthalocyanines (HBLuPc) have been grafted on the surface of graphene oxide, respectively. After the surficial modification, the electron transfer process between phthalocyanines and graphene oxide has been also facilitated, resulting in significant fluorescence quenching. Given the combination of nonlinear scattering, two-photon absorption with reverse saturable absorption and the photo-induced electron or energy transfer from the electron donor (phthalocyanine moiety) to the acceptor (graphene oxide), stronger nonlinear optical properties can be realized based on graphene oxide hybrids compared with graphene oxide and phthalocyanines. Furthermore, graphene oxide hybrid modified by hyperbranched lutecium phthalocyanines exhibits the best optical limiting response and the highest nonlinear extinction coefficient at 532 nm in both organic solvent and polymeric matrix. Interestingly, we also find that it could exhibit better optical limiting properties than those possessed by pure phthalocyanine at 1064 nm.

Effect of Annealing Treatment on Optical and Electrical Properties of PCDTBT:Graphene Hybrid Structure for Photovoltaic Application

Indium tin oxide (ITO)/poly[N-9′-heptadecanyl-2,7-carbazole-alt-5,5-(4,7-di-2-thienyl-2′,1′,3′-benzothiadiazole)] (PCDTBT):graphene/Al structures have been elaborated. By applying a specific elaboration method, we succeeded in dispersing expandable graphene oxide in organic solvent (N,N-dimethylformamide, DMF) to obtain graphene oxide and insert it into a PCDTBT matrix. The effect of annealing treatment of PCDTBT:graphene films on the optical and electrical properties were studied. The obtained results showed a remarkable effect of the annealing treatment on the optoelectronic properties. The ultraviolet–visible (UV–Vis) spectra showed that the light harvesting was increased and the orderly stacking of the polymer chains was enhanced. The photoluminescence results showed a red-shift of about 10 nm in case of heat treatment at 150°C, related to an increase of the conjugation length of the polymer chains. The electrical parameters, such as the series resistance (Rs), ideality factor (n), and barrier height (ϕb), were calculated. We found that thermal annealing reduced both the series resistance Rs and barrier height value ϕb, significantly. These results indicate that annealing treatment improves the transport phenomenon in the active layer. In addition, the Log(J)–Log(V) curves suggested that the charge transport is governed by a space-charge-limited mechanism current. The effective carrier mobility (μeff) was on the order of 10−5 cm2/V.

Enhanced mechanical and thermal properties of polyurethane/functionalised graphene oxide composites by in situ polymerisation

ABSTRACTIsocyanate-functionalised graphene (iGO) was prepared and incorporated into a thermoplastic polyurethane via an in situ polymerisation. Firstly, graphene oxide was successfully modified using a mixture of isocyanate- and diisocyanate-containing compounds, leading to the formation of good dispersions of resulting functional graphene oxide in organic solvents, such as N,N-dimethylacetamide and N,N-dimethylformamide. The addition of iGO into polyurethane matrix improved both mechanical and thermal properties in the polyurethane/iGO composites relative to neat polyurethane. An addition of only 0.03 wt-% of functionalised graphene into the polyurethane increased Young’s modulus by 1.4 times and tensile strength by two times. Meanwhile, the elongation at break was similar to that of the neat polymer. In addition, dynamic mechanical analysis also confirmed the improvement in storage modulus of the polymer composites especially at high-temperature range. We believe that the developed modification approach for graphene oxide and polyurethane/graphene composites presented herein could be useful in polymer/graphene composite development.

Imidazolium Ionic Liquid Modified Graphene Oxide: As a Reinforcing Filler and Catalyst in Epoxy Resin.

Surface modification of graphene oxide (GO) is one of the most important issues to produce high performance GO/epoxy composites. In this paper, the imidazole ionic liquid (IMD-Si) was introduced onto the surface of GO sheets by a cheap and simple method, to prepare a reinforcing filler, as well as a catalyst in epoxy resin. The interlayer spacing of GO sheets was obviously increased by the intercalation of IMD-Si, which strongly facilitated the dispersibility of graphene oxide in organic solvents and epoxy matrix. The addition of 0.4 wt % imidazolium ionic liquid modified graphene oxide (IMD-Si@GO), yielded a 12% increase in flexural strength (141.3 MPa), a 26% increase in flexural modulus (4.69 GPa), and a 52% increase in impact strength (18.7 kJ/m2), compared to the neat epoxy. Additionally the IMD-Si@GO sheets could catalyze the curing reaction of epoxy resin-anhydride system significantly. Moreover, the improved thermal conductivities and thermal stabilities of epoxy composites filled with IMD-Si@GO were also demonstrated.

Surfactant-treated graphene oxide in organic solvents and its application in photovoltaic cells

In this paper, a simple and non-poisonous “surfactant treatment” method to prepare graphene oxide (GO) in organic solvents with good dispersibility was presented. As the surfactant molecules, didodecyldimethyla-mmonium bromide (DDAB) was attached onto the GO sheets via ionic interactions by mild sonication, the obtained GO:DDAB nanocomposites were then blended into copolymer Poly(3-hexylthiophene-2,5-diyl) (P3HT) [6,6]:-Phenyl C61 butyric acid methyl ester (PC61BM) as the active layer to fabricate bulk-heterojunction (BHJ) organic solar cells ITO/PEDOT:PSS/P3HT:PC61BM:(GO:DDAB)/Ca/Al. The concentration of GO:DDAB in the active layer, a maximum power conversion efficiency (PCE) of 3.67% was obtained by blending 0.5 mg/mL GO:DDAB in the active layer, showing an efficiency increment of 13.35% as compared with that of the control device without doping GO:DDAB. The optimized OPVs with PTB7:PC71BM by adding GO:DDAB shows the PCE of 7.96%. Therefore, it paves a way to get high efficiency organic photovoltaic cells by directly blending surfactant-treated graphene oxide in organic solvent.

Thermal Reduction of Graphene Oxide in Organic Solvents for Producing Colloidal Suspensions of Reduced Graphene Oxide Sheets

A new method for preparing graphene colloidal suspension is studied by thermal reducing graphene oxide in N-methylpyrrolidone (NMP) and γ-Butyrolactone (GBL) at 200°. Without assistance of polymeric or surfactant stabilizers, thermal reduction and dispersion of reduced graphene sheets are performed in one pot, and stable suspensions are confirmed by transmission electron microscope (TEM) and atomic force microscope (AFM) technic. Experimental results such as thermal gravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS) and Raman indicate bulk cleavage of oxygen-containing functional groups and restoration of graphite structure on reduced graphene oxide sheets. The study contributes to the preparation of graphene-based nanocomposites using this quick and low-cost processing technique.

Improved dispersibility of graphene oxide in o-dichlorobenzene by adding a poly(3-alkylthiophene)

The dispersibility of graphene oxide (GO) in o-dichlorobenzene was improved by adding poly(3-hexylthiophene) (P3HT). The resulting GO dispersion was stable for up to one week. Transmission electron microscopy, UV–Vis spectroscopy, Raman spectroscopy and photoluminescence spectroscopy indicated that the crystallization of P3HT molecules on the GO surface prevented GO sheets from strong π–π interactions, and thus greatly increased the dispersibility of GO in organic solvent. The crystallization of P3HT molecules is a physical and reversible process, and it is time and temperature dependent. The crystallization process becomes remarkable with prolonged aging time and decreasing temperature. Other conjugated polymers, including poly(3-butylthiophene) and poly(3-hexylthiophene)-b-poly(ε-caprolactone), were further examined by the same method, and similar phenomena were also observed, indicating that the simple method of using a poly(3-alkylthiophene) to improve GO dispersibility in organic solvent is universal.

Electrochemical reduction of graphene oxide in organic solvents

Graphene oxide (GO) cast on conductive substrates was electrochemically reduced in some organic solvents. The amount of electricity required for the almost complete reduction of GO was 2.0 C for 1 mg GO, corresponding to attaching of a one-electron reducible species to each benzene ring in graphene. The electrochemically reduced GO film gave an electrical conductivity of about 3 S cm −1 and exhibited a relatively high specific capacitance of 147.2 F g −1 in propylene carbonate. The electrochemical reduction of GO was feasible on Al foils as well.

Organo- and Water-Dispersible Graphene Oxide−Polymer Nanosheets for Organic Electronic Memory and Gold Nanocomposites

A solution-processable graphene oxide (GO)−polymer complex, consisting of GO nanosheets with covalently grafted poly(tert-butyl acrylate) (PtBA) brushes, was prepared via surface-initiated atom transfer radical polymerization (ATRP). The grafted hydrophobic polymer brushes substantially enhance the solubility of GO in organic solvents, and the GO-g-PtBA nanosheets can form a uniform and stable dispersion in toluene. The functionalized GO nanosheets can also be integrated into an electroactive polymer matrix. Bistable electrical conductivity switching behavior and a nonvolatile electronic memory effect were demonstrated in a composite thin film of poly(3-hexylthiophene) (P3HT) containing 5 wt % GO-g-PtBA in an Al/GO-g-PtBA+P3HT/ITO sandwich structure (ITO = indium−tin oxide). Hydrolysis of GO-g-PtBA produces water-dispersible GO-g-PAAc (PAAc = poly(acrylic acid)) nanosheets and allows the preparation of gold nanoparticle-decorated GO-g-PAAc nanofilms from aqueous dispersions.