Presence Of Graphene Oxide Sheets Research Articles

GO modification with PANI-PpPDA as support material for Pd-Ni and its application for ethanol electrooxidation

Among different renewable energy sources, fuel cells emerged to be a promising solution. However, due to limitations such as high cost and low stability of current commercial catalysts, several approaches are considered to modify them. Graphene oxide (GO) modification via a facile in-situ polymerization of aniline (ANI) and p-phenylenediamine (pPDA) in the presence of GO sheets is the main goal of this study. Pd and Ni as active metals are chemically deposited on the support material. The prepared substrates and catalysts are examined by various structural and electrochemical tests. This study shows that GO-PANI-PpPDA support material has favorable characteristics with 32.64 % higher surface area compared to GO. High surface area and porosity lead to more loading and uniform distribution of metallic particles. GO-PANI-PpPDA/Pd-Ni exhibited superior eligible properties including 29.28 % higher electrochemically active surface area compared to GO/Pd-Ni. This nanohybrid has the lowest charge transfer resistance, highest current density, stability and durability and it loses 5.67 % of the initial current after 15 h. This method shows promising results as an advanced strategy to synthesize low-cost and high-performance Pd-based electrocatalysts on the modified GO.

Photocatalytic activity of GO/Fe<sub>3</sub>O<sub>4</sub> fabricated by Sri Lankan graphite under visible light irradiation

Graphene oxide (GO) was synthesized using Sri Lankan naturally available graphite and Fe3O4 nanoparticles were successfully incorporated fabricating magnetically separable GO/Fe3O4 nanocomposite. The synthesized nanocomposites were characterized by X-ray diffractometry (XRD), Scanning electron microscopy (SEM), and FT-IR spectroscopy. Crystalline phases of GO and Fe3O4 nanoparticles were identified by XRD patterns, while the presence of functional groups such as –COOH, OH, CH2 was confirmed by FT-IR spectroscopy. SEM images show that Fe3O4 nanoparticles with an average particle size of 107 nm ranging between 56-150 nm are dispersed on GO while restacking and folding of the nanosheets have been observed with incorporation of Fe3O4 nanoparticles. The photocatalytic performance of the photocatalysts was evaluated on photodegradation of methylene blue under visible light irradiation. The GO/Fe3O4 shows better adsorption behavior and excellent photocatalytic activity where it could be successfully used for three cycles without significant activity loss. This is due to the enhanced charge separation resulted due to the presence of GO sheets and better interactions between GO and Fe3O4.

A Facile Approach of Fabricating Electrically Conductive Knitted Fabrics Using Graphene Oxide and Textile-Based Waste Material.

This research investigated a feasible approach to fabricating electrically conductive knitted fabrics using previously wet-spun wool/polyacrylonitrile (PAN) composite fibre. In the production of the composite fibre, waste wool fibres and PAN were used, whereby both the control PAN (100% PAN) and wool/PAN composite fibres (25% wool) were knitted into fabrics. The knitted fabrics were coated with graphene oxide (GO) using the brushing and drying technique and then chemically reduced using hydrazine to introduce the electrical conductivity. The morphological study showed the presence of GO sheets wrinkles on the coated fabrics and their absence on reduced fabrics, which supports successful coating and a reduction of GO. This was further confirmed by the colour change properties of the fabrics. The colour strength (K/S) of the reduced control PAN and wool/PAN fabrics increased by ~410% and ~270%, and the lightness (L*) decreased ~65% and ~71%, respectively, compared to their pristine fabrics. The Fourier transform infrared spectroscopy showed the presence and absence of the GO functional groups along with the PAN and amide groups in the GO-coated and reduced fabrics. Similarly, the X-ray diffraction analysis exhibited a typical 2θ peak at 10⁰ that represents the existence of GO, which was demolished after the reduction process. Moreover, the wool/PAN/reduced GO knitted fabrics showed higher electrical conductivity (~1.67 S/cm) compared to the control PAN/reduced GO knitted fabrics (~0.35 S/cm). This study shows the potential of fabricating electrically conductive fabrics using waste wool fibres and graphene that can be used in different application fields.

Crucial roles of graphene oxide in preparing alginate/nanofibrillated cellulose double network composites hydrogels

In this study, a novel strategy to prepare sodium alginate (SA)/nano fibrillated cellulose (NFC) double network (DN) hydrogel beads with the aid of graphene oxide (GO) was developed. In comparison with the multi-step freezing-thawing method, this study employs a facile one-step freeze drying method with the presence of GO sheets. The crucial roles of GO were highlighted as an efficient nucleating agent of NFC and a reinforcer for the hydrogel. The adsorption property of the DN hydrogel towards crystal violet (CV) was also studied. Results indicated that the introduction of GO could greatly facilitate the formation of double networks. Furthermore, the as-prepared DN hydrogel beads exhibited an efficacious adsorption property towards CV. The maximum adsorption capacity of the hydrogels for CV was observed as 665 mg g−1. Therefore, our approach here represents a facile method for the preparation of crystalline polymer based DN hydrogels to replace the awkward freezing-thawing process, giving inspiration for DN hydrogels design and preparation. Moreover, due to its efficient adsorption capacity, the hydrogels hold great promise for the water pollution control materials.

Reduced graphene oxide nanosheets doped by Cu with highly efficient visible light photocatalytic behavior

Abstract Graphene oxide (GO) and reduced graphene oxide (RGO) exhibit good electrochemical properties due to their semiconducting nature, large surface area, high concentration of functional groups and unique layered structure. They have been used widely for the removal of heavy metal ions, dyes and other organic contaminants from water. In the present study, a modified Hummer’s method was used to prepare GO while Cu-doped RGO which was obtained by employing a simple hydrothermal process. X-ray diffraction analysis confirmed the presence of GO sheets and Cu-doped RGO in the synthesized product. Examination with field emission scanning and high resolution transmission electron microscopes revealed an ultrathin, porous and layered structure of GO nanosheets while RGO sheets appeared as a well-defined, layered and non-agglomerated sponge. Dispersion of Cu within RGO sheets was also confirmed during microstructural study. Optical properties, such as absorption of light and bandgap width, were studied using UV–visible spectroscopy. Photoluminescence characterization showed maximum emission between 300 and 350 nm (UV region) caused by the presence of vacancies and surface defects in synthesized sheets. In aqueous media, methylene blue (MB) pollutant was photodegraded up to 91% within 80 min when Cu-doped RGO photocatalyst was employed under visible light irradiation. The present work shows the ability of Cu-doped RGO to degrade aqueous pollutants in an efficient manner. In conclusion, this product can find potential application in the removal of organic pollutants from wastewater.

Electron-transfer mechanisms for confirmation of contact-electrification in ZnO/polyimide-based triboelectric nanogenerators

Abstract Zinc oxide (ZnO) acting as a versatile material for electronic and optoelectronic devices shows promising applications in triboelectric nanogenerator (TENG)-based self-powered electronics. However, the output performances of ZnO-based TENG are relatively low and the origin of contact-electrification in the ZnO-based TENG is unclear. Here, we fabricate a TENG by using ZnO film and polyimide (PI) acting as positive and negative friction layers, respectively. The work function of the ZnO film is modified by doping with elemental Al, and the conductivity of the ZnO film is additionally enhanced by the presence of graphene-oxide sheets. The output performance is greatly improved and it is sensitive to the work function of ZnO film. These results reveal that electron transfer is the dominant process in contact-electrification for ZnO-based TENGs. This work provides significant insight into understanding the contact-electrification properties of ZnO, thus allowing optimization of ZnO-based self-powered devices.

Role of trapped water on electroresponsive characteristic of silica-graphene oxide composite microspheres

Electroresponsive microspheres containing nanosilica and graphene oxide (GO) sheets have been achieved by the one-step evaporation induced assembly of mixed colloids using spray drying. The interlocking of the nanostructured constituents by the attractive capillary force during drying of dispersion droplets results in the formation of powder grains with correlated nanoparticles and nanosheets. The presence of GO sheets arrests the buckling of the drying droplets during evaporative assembly and results in well-defined spherical shaped grains. Interestingly, this approach of random jamming in colloidal droplets is capable of preventing the spontaneous stacking of the GO sheets and, therefore, facilitates a way to confine the atomic-thick GO sheet in the solid matrix. A plausible mechanism for the formation of silica-GO binary composite microspheres is elucidated. Microspheres dispersed in insulating oil show interesting electroresponsive characteristics where the microspheres form a chainlike percolation path under the applied electric field. It has been established that the adsorbed water in the microspheres plays a profound role as far its electroresponsive behavior is concerned. GO sheets in the microspheres allow for tuning of electroresponse strength owing to the increased interaction of water molecules to the oxygen-containing functional groups anchored on the GO sheets.

New insights into oxygen surface coverage and the resulting two-component structure of graphene oxide

Abstract Elucidating the essential details of the structure of graphene oxide (GO) is still a challenge. There is no consensus in the increasingly abundant literature, especially relating to the epoxy groups as the main surface complexes in the basal plane, as well as the simultaneous presence of GO sheets and oxidative debris (OD), with a large difference in their oxygen content. In the present work we characterized the base-washed GO (bwGO) sheets, the OD and the humic fraction of the OD obtained by base digestion, when the parent GO was dispersed by applying sonication, a routine procedure when starting from dried graphite oxide. When sonication is not applied, the amount of OD detected is considerably lower, indicative of its formation before base digestion. The presence of lactols and carboxylic anhydrides as the dominant surface complexes at graphene edges is consistent with all the characterization results, as well as with the general knowledge of surface chemistry of carbon materials ranging from coal to graphite. These findings suggest that the Hummers-Offeman reaction produces a chemical scissor effect during the water/hydrogen peroxide quenching step, yielding a broad size distribution of GO sheets, with little in-plane oxidation and the vast majority of edges being oxidized to form oxepinone-type functionalities.

New insight into the aggregation of graphene oxide in synthetic surface water: Carbonate nanoparticle formation on graphene oxide

Graphene oxide (GO), used in a wide variety of applications, is increasingly being introduced into aquatic environments; this situation calls for research on GO aggregation and sedimentation to regulate the environmental behaviors and risks. Many studies have investigated the aggregation and the mechanism of GO in water with a single background salt (monosalt system); however, this may not reflect real water environments where multiple salts coexist (multisalt system). A typical synthetic surface water (soft water) with representative multisalts was therefore used to study the aggregation and sedimentation of GO. The GO concentration-dependent aggregation (low concentration aggregation, high concentration stability) was observed in the soft water, and this concentration-dependent aggregation is opposite to the aggregation in monosalt systems (NaCl or CaCl2 solutions). The presence of GO sheets induced the formation of amorphous CaMg(CO3)2 nanoparticles on the GO surfaces in the soft water, and the formed nanoparticles promoted the aggregation and sedimentation of low concentrations of GO through bridging action. Neutral and alkaline conditions were favorable for the formation of CaMg(CO3)2 nanoparticles and the induced GO aggregation. These findings show a new mechanism of GO aggregation in environmentally relevant waters and help us to better evaluate the environmental fate of GO.

Simultaneous Silicon Oxide Growth and Electrophoretic Deposition of Graphene Oxide.

During electrophoretic deposition of graphene oxide (GO) sheets on silicon substrates, not only deposition but also simultaneous anodic oxidation of the silicon substrate takes place, leading to a three-layered material. Scanning electron microscopy images reveal the presence of GO sheets on the silicon substrate, and this is also confirmed by X-ray photoelectron spectroscopy (XPS), albeit that the carbon portion increases with increasing emission angle, hinting at a thin carbon layer. With increasing applied potential and increasing conductivity of the GO solution, the carbon signal decreases, whereas the overall thickness of the added layer formed on top of the silicon substrate increases. Through XPS spectra in which the Si 2p peaks shifted under those conditions to 103–104 eV, we were able to conclude that significant amounts of oxygen are present, indicative of the formation of an oxide layer. This leads us to conclude that GO can be deposited using electrophoretic deposition, but that at the same time, silicon is oxidized, which may overshadow effects previously assigned to GO deposition.

Structure and interaction of silk fibroin and graphene oxide in concentrated solution under shear

Considering the high biocompatibility of regenerated silk fibroin (RSF) and the good enhancement effect of graphene oxide (GO), various RSF/GO composite materials have been previously investigated, and found that GO plays a vital role in the fabrication of high-performance RSF/GO materials. However, its effects on the structure of RSF solution are unclear. Therefore, in this work, we studied the rheological and optical properties, as well as the aggregation behavior of concentrated RSF/GO solution in response to applied shear. The results demonstrated that the presence of GO sheets in RSF solution increased the shear resistance, while delayed the sol–gel transition. Moreover, GO sheets were not favorable to the formation of the ordered structures of RSF. The results from small angle X-ray scattering (SAXS) of RSF/GO solution also showed that the shear process promoted the formation of RSF/GO interface. The data also provided insights into the structural evolution within the mixture solutions, which can be beneficial to the future design and fabrication of nanofiller-reinforced high-performance materials.

Graphene Oxide Sheathed ZIF-8 Microcrystals: Engineered Precursors of Nitrogen-Doped Porous Carbon for Efficient Oxygen Reduction Reaction (ORR) Electrocatalysis.

Nitrogen containing mesoporous carbon obtained by the pyrolysis of graphene oxide (GO) wrapped ZIF-8 (Zeolitic Imidazolate Frameworks-8) micro crystals is demonstrated to be an efficient catalyst for the oxygen reduction reaction (ORR). ZIF-8 synthesis in the presence of GO sheets helped to realize layers of graphene oxide over ZIF-8 microcrystals and the sphere-like structures thus obtained, on heat treatment, transformed to highly porous carbon with a nitrogen content of about 6.12% and surface area of 502 m2/g. These catalysts with a typical micromeso porous architecture exhibited an onset potential of 0.88Vvs RHE in a four electron pathway and also demonstrated superior durability in alkaline medium compared to that of the commercial Pt/C catalyst. The N-doped porous carbon derived from GO sheathed ZIF-8 core-shell structures could therefore be employed as an efficient electrocatalyst for fuel cell applications.

Rational construction of graphene oxide with MOF-derived porous NiFe@C nanocubes for high-performance microwave attenuation

Exploring lightweight microwave attenuation materials with strong and tunable wideband microwave absorption is highly desirable but remains a significant challenge. Herein, three-dimensional (3D) porous hybrid composites consisting of NiFe nanoparticles embedded within carbon nanocubes decorated on graphene oxide (GO) sheets (NiFe@C nanocubes@GO) as high-performance microwave attenuation materials have been rationally synthesized. The 3D porous hybrid composites are fabricated by a simple method, which involves one-step pyrolysis of NiFe Prussian blue analogue nanocubes in the presence of GO sheets. Benefiting from the unique structural features that exhibit good magnetic and dielectric losses as well as a proper impedance match, the resulting NiFe@C nanocubes@GO composites show excellent microwave attenuation ability. With a minimum reflection loss (RL) of–51 dB at 7.7 GHz at a thickness of 2.8 mm and maximum percentage bandwidth of 38.6% for RL <–10 dB at a thickness of 2.2 mm, the NiFe@C nanocubes@GO composites are superior to the previously reported state-of-the-art carbon-based microwave attenuation materials.

Ionic-liquid mediated synthesis of molybdenum disulfide/graphene composites: An enhanced electrochemical hydrogen evolution catalyst

The ionic liquid (IL, [BMIM]BF4) is employed to mediate the preparation of molybdenum disulfide/graphene composites by hydrothermal route in the presence of graphene oxide sheets. The effects of ionic liquid on the microstructure and hydrogen evolution reaction performances of molybdenum disulfide/graphene are investigated. The molybdenum disulfide/graphene composite (MoS2/G-IL10) prepared with 1.0 mL of ionic liquid displays numerous de-layered molybdenum disulfide sheets with short slab length and discontinuous crystal fringes on the surface of grapheme. Due to the rich exposed edge sites, as well as the synergetic effect of de-layered molybdenum disulfide and graphene sheets, the MoS2/graphene composite prepared by IL-mediated hydrothermal method shows excellent electrocatalytic performance for hydrogen evolution reaction with a small Tafel slope of 52 mV/dec in acidic medium.

Covalently bonded sulfonic acid magnetic graphene oxide: Fe3O4@GO-Pr-SO3H as a powerful hybrid catalyst for synthesis of indazolophthalazinetriones

Multistep synthesis of covalently sulfonated magnetic graphene oxide was achieved by starting from Hummer’s method to produce graphene oxide (GO) from chemical oxidation of graphite. Then, GO nanosheets were applied to support Fe3O4 nanoparticles (Fe3O4@GO) using co-precipitation method in the presence of GO sheets. This strategy led to formation of uniform particles of Fe3O4 on the surface of GO sheets. Then, it was sulfonated (Fe3O4@GO-Pr-SO3H) through modification with 3-mercaptopropyltrimethoxysilane (MPTMS) and subsequent oxidation with hydrogen peroxide (H2O2). In comparison, the covalently bonded propyl sulfonic acid groups were more prevailing rather to sulfonic acids of GO itself. The proposed catalyst was more active and recyclable at least for 11 runs.

Regulation of biphasic drug release behavior by graphene oxide in polyvinyl pyrrolidone/poly(ε-caprolactone) core/sheath nanofiber mats

One of the key issues for drug delivery systems is to develop a drug carrier with a time-programmed, biphasic release behavior. Using vancomycin hydrochloride (VAN) as a model drug, polyvinyl pyrrolidone (PVP) blended with graphene oxide (GO) sheets as the core matrix, and poly(ε-caprolactone) (PCL) as the sheath polymer, core/sheath PVP/PCL nanofiber mats were fabricated via a coaxial electrospinning process. We hypothesized that the addition of GO sheets would lead to their molecular interactions with VAN molecules, thereby adjusting the VAN release behavior. Field emission scanning electron microscopy and transmission electron microscopy of the fiber mats revealed their nanofibrous structure and clear core/sheath boundary. Raman analysis demonstrated the presence of GO sheets in the PVP/PCL nanofiber mats. Fourier transform infrared spectroscopy indicated the formation of hydrogen bonds between GO sheets and VAN molecules. In vitro studies showed that the PVP/PCL nanofiber mats were biocompatible, despite the addition of GO sheets, and exhibited typical biphasic drug release profiles, which were tailored by adjusting the content of GO sheets. Furthermore, an antimicrobial test showed different antimicrobial activities of the medicated nanofiber mats, depending on the GO content. Collectively, the results of the present study provide a simple approach to obtaining time-programmed drug release profiles.

Poly(diallyldimethylammonium chloride)-assisted synthesis of MoS2/graphene composites with enhanced electrochemical performances for reversible lithium storage

The MoS2/graphene composites were synthesized by a hydrothermal route in the presence of graphene oxide sheets with assistance from poly(diallyldimethylammonium chloride) (PDDA). The results of characterizations show that the MoS2/graphene composites exhibit a graphene-like morphology with interconnected network, in which single- or few-layer MoS2 sheets are homogenously dispersed and well anchored on the graphene surface. The robust heterostructure and morphology of MoS2/graphene composites can not only provide more sites and channels for lithium ion accommodation and diffusion, but also facilitate electrolyte access. The heterostructure also maximizes the synergistic effects between MoS2 and graphene. Therefore, MoS2/graphene composites exhibit significantly improved electrochemical performances for reversible lithium storage. In particular, the MoS2/graphene composite prepared with monomer concentration of PDDA being 0.02molL−1 exhibits a reversible capacity of 1100mAhg−1 with enhanced rate capability. The reversible capacity of 856mAhg−1 after 900 cycles at 500mAg−1 can be remained, indicating its excellent cyclic stability.

L-Cysteine-assisted hydrothermal synthesis of nickel disulfide/graphene composite with enhanced electrochemical performance for reversible lithium storage

NiS2/graphene composite is synthesized by a facile hydrothermal reaction between NiCl2 and l-cysteine in the presence of graphene oxide sheets. l-Cysteine serves as both the sulfur source for NiS2 and reductant for reduction of graphene oxide sheets. The reduced graphene oxides can be used as a platform for growth of NiS2 particles and restrain NiS2 from agglomerating during hydrothermal process. The results of characterizations show that the sphere-like NiS2 particles exhibit smaller sizes and are well dispersed on the surface of reduced graphene sheets. The electrochemical measurements demonstrate that the NiS2/graphene composite delivers a reversible capacity as high as 1200 mAh g−1 at a current density of 100 mA g−1 and enhanced high-rate capability of 740 mAh g−1 at a high current density of 1000 mA g−1. After 1000 cycles, the NiS2/graphene still preserves the reversible capacity about 810 mAh g−1 at a current density of 500 mA g−1, indicating its excellent cyclic stability.

Preparation and characterization of a composite hydrogel with graphene oxide as an acid catalyst.

In this study, a facile method for synthesizing a novel graphene oxide/pyrrole-formaldehyde (GOP-1) composite hydrogel was developed via in situ polymerization of pyrrole and formaldehyde in the presence of graphene oxide sheets without any additional catalyst. During the polymerization, graphene oxide can act as a two-dimensional template to regulate the aggregation state of polymer and as an acid catalyst to accelerate the reaction rate of pyrrole and formaldehyde. The morphology and microstructure were investigated by scanning electron microscopy, transmission electron microscopy, and X-ray diffraction, respectively. The chemical properties were analyzed via X-ray photoelectron spectroscopy, infrared spectroscopy, and Raman spectroscopy. The freeze-dried GOP-1 composite hydrogel exhibited a large specific surface area, high nitrogen content, and three-dimensional network structure. Based on the above features, the freeze-dried GOP-1 composite hydrogel used as a gas adsorbent showed a high carbon dioxide uptake capacity at 1.0 bar and 273 K (11.1 wt%), in sharp contrast to that of graphene oxide (7.4 wt%). Furthermore, the as-prepared composite hydrogel may possess attractive potential in the fields of electrode material, tissue engineering, and water treatment.

Advanced ZnO–graphene oxide nanohybrid and its photocatalytic Applications

A nanohybrid of Zinc oxide (ZnO)–graphene oxide (GO) was synthesized by chemical route and utilized as an effective photocatalyst for the photodegradation of crystal violet (Cv) dye. The substantially mixed ZnO–GO nanohybrid was formed by the introduction of GO during the synthesis of ZnO. Prepared ZnO–GO nanohybrid showed the better optical properties and exhibited the good interaction between GO and ZnO. The photocatalytic activity of ZnO–GO nanohybrid was analyzed by performing the photodegradation of Cv-dye under light illumination. Enormously high degradation of Cv-dye by ∼95% within 80min was observed over the surface of advanced ZnO–GO nanohybrid, which might attribute to the presence of GO sheets as a supporting material and high e−–h+ pair separation under light illumination.