The valorization of coal fines to develop graphene oxide for effective utilization in wastewater treatment through organic dye removal from contaminated waters

The synthesis of graphene oxide (GO)–polystyrene (PS) Pickering emulsions, as environment‐friendly nanostructures suitable for novel applications, has received significant attention in recent years. In this work, the synthesis and characterization of GO–PS nanocomposites through seeded emulsion polymerization and the selective light reflection properties of dry films have been reported. Amphiphilic molecule sulfonated 3‐pentadecyl phenol was used as a co‐surfactant to stabilize GO dispersions during the emulsion polymerization process. The particle size of the dispersions as measured by dynamic light scattering decreases from 540 nm, for PS without any GO, to 88 nm with 1 wt% GO content. Scanning electron microscopy studies show a uniform size distribution of the composite particles prepared with GO. The dried films show a structural color that varies with the GO content. The self‐assembly behavior of the dried film was further studied using reflectance spectroscopy, which shows a red shift of the reflectance maximum from 440 to 538 nm as the GO loading was increased from 0.2 to 0.5 wt%, respectively, indicating a different microstructure. X‐ray diffraction, transmission electron microscopy (TEM) and atomic force microscopy (AFM) were used to study the morphology and structure of the composite particles on drying. The AFM study confirms the non‐spherical shape of the particles. Thermogravimetric analysis shows improved thermal decomposition characteristics of the nanocomposite films. Copyright © 2015 John Wiley & Sons, Ltd.

We report synthesis and characterizations of graphene oxide (GO) reinforced poly(3,4-ethylene dioxythiophene)-tetra methacrylate (PEDOT-TMA)/polymethylmethacrylate (PMMA) based novel composites. The composites were prepared by colloidal blending. The interaction between GO, PEDOT-TMA and PMMA chains were characterized by using UV–Vis spectroscopy, X-ray diffraction, thermogravimetric analysis, Fourier transforms infrared spectroscopy, FT-Raman spectroscopy, atomic force microscopy (AFM) and scanning electron microscopy. The microstructure of composites shows that GO was homogeneously dispersed in the polymer matrix. AFM studies reveal an increase in surface roughness as a function of GO loading. A significant improvement in the thermal stability of composites was observed as a function of GO loading which is due to the presence of high surface area GO in the polymer matrix. The composites show high values of dielectric constant and low values of dielectric loss which resulted from homogeneous dispersion of GO in the polymer matrix. This study suggests that the composites have the potential to be used for suitable electronic applications with desired dielectric properties.

Synthesis and characterization of graphene oxide, tin oxide, and reduced graphene oxide-tin oxide nanocomposites

Graphene oxide (GO) and reduced graphene oxide (rGO) have successfully synthesized using modified Tour’s method with end product having rapid purification rate, hydrophobic condition and conductive material. Prominent green reducing agent namely ascorbic acid has used in the GO sample preparation and act as reductant which help removal of oxygen containing functional group hence, resultant of rGO. In this investigation, the GO purification rate has accelerated by help of sodium hydroxide (NaOH) in function of washing agent with only 3 cycle’s wash. Raman spectroscopy results show that the synthesized GO and rGO samples yield in the range of 1349.33 cm$^{-1}$ (D band) to 1571.35 cm$^{-1}$ (G band) of Raman peak, respectively. A narrow and sharp Raman peak with high intensity of rGO sample has indicates it having a better quality as compared to GO sample. Contact angle measurement reveal the large angle obtained from rGO sample which are 72.8° on left hand side and 65.0° for right side, correspondingly have confirmed it is more hydrophobic than GO which attained contact angle of 52.5° on both sides. Surface morphology examined by Field Emission Scanning Electron Microscope (FE-SEM) show that both samples that diluted with deionized (DI) water have a loose sponge which similar to a thin wrinkle sheet in structure that suggest it has well exfoliated by using modified Tour’s method. On the other hand, produced samples that not diluted with DI water has tightly packed, corrugated and crumpled in form. Results from Energy Dispersive Spectroscopy (EDS) measurement has confirmed that oxygen-containing functional group have been removed from rGO sample by having higher calculated carbon / oxygen (C / O) in quotient with 3.09 as compared to GO sample with 1.43 which based on the atomic percentage of C/O. The significant reduction of resistance value from rGO sample with $33.41 \times 10^{4}\Omega$ as compared to GO with $41.18 \times 10^{6} \Omega$ have leading it to obtained better conductivity with $4.77 \times 10^{-7}$ S / cm in comparison to GO sample with $3.86 \times 10^{-9}$S / cm. Thus, this modified Tour’s method with the usage of green reductant agent has potential to be used in producing sensing device applications.

Graphene oxides with different oxidation degrees for Co(II) ion pollution management

Graphene oxide (GO) was synthesized from graphite via a modified Hummer's method, followed by thermal and chemical reductions to produce reduced graphene oxide (RGO) samples at various temperatures. A suite of characterization techniques including Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM), Energy-Dispersive X-ray Spectroscopy (EDS), UV-Visible Spectroscopy, thermogravimetric analysis (TGA), X-ray diffraction (XRD), and Hall effect measurements were employed to assess the structural, morphological, optical, and electrical properties of the samples. FTIR analysis confirmed the successful functionalization of graphite to GO and subsequent reduction to reduced graphene oxide, with peak intensities decreasing as the reduction temperature increased. UV-visible spectroscopy of GO showed a maximum absorption at 235 nm which confirmed the synthesis of GO while the reduction revealed a notable red shift in absorption peaks with increasing annealing temperature, and that signified a reduction in bandgap. XRD analyses demonstrated the removal of oxygen functional groups. The X-ray diffraction (XRD) analysis of GO showed diffraction at 2θ = 10.74° which revealed a fully oxidized graphene oxide with oxygen-containing functional groups, and hence an increase in interlayer spacing (d002) from 3.341 Å (graphite) to 8.228 Å (GO). Upon reduction, there is a gradual decrease in d002 from 8.228 Å (GO) to 3.387 Å (HRGO300), suggesting the gradual removal of intercalated oxygen molecules, and hence the gradual restoration of sp2 hybridisation in graphene. The EDS analysis revealed an increase in the carbon-to-oxygen (C/O) ratio from 1.78 in GO to 2.75 in HRGO300 as the annealing temperature for the reduction process increased which further confirmed the removal of oxygen functional groups. The Hall effect data showed hole mobility of 4.634 x101 (GO), 4.831 x101 (HRGO200), and 5.462 x100 (HRGO300) with conductivities of 8.985 x10-5 (GO), 1.087 x100 (HRGO200) and 1.791 x101 1/Ω cm, suggesting an increase in conductivity as the annealing temperature increased as revealed in the EDS. Out of the three samples identified as hole transport materials, the sample HRGO300 with the highest C/O ratio of 2.75 has the highest conductivity, and hence most suitable for application as hole transport material in perovskite solar cell.

Graphene oxide (GO) sheets are emerging as a new class of carbocatalysts. Conventionally, researchers exfoliate graphite oxide into submicrometer-sized, water-dispersible flakes to produce these sheets. The presence of oxygen functional groups on the aromatic scaffold of GO allows these sheets to mediate ionic and nonionic interactions with a wide range of molecules. GO shows remarkable catalytic properties on its own and when hybridized with a second material. It is a perfect platform for molecular engineering. This Account examines the different classes of synthetic transformations catalyzed by GO and correlates its reactivity with chemical properties. First, we raise the question of whether GO behaves as a reactant or catalyst during oxidation. Due to its myriad oxygen atoms, GO can function as an oxidant during anaerobic oxidation and become reduced at the end of the first catalytic cycle. However, partially reduced GO can continue to activate molecular oxygen during aerobic oxidation. Most importantly, we can enhance the conversion and selectivity by engineering the morphology and functionalities on the G/GO scaffold. GO can also be hybridized with organic dyes or organocatalysts. The photosensitization by dyes and facile charge transfer across the graphene interface produce synergistic effects that enhance catalytic conversion. Using GO as a building block in supramolecular chemistry, we can extend the scope of functionalities in GO hybrids. The presence of epoxy and hydroxyl functional groups on either side of the GO sheet imparts bifunctional properties that allow it to act as a structural node within metal-organic frameworks (MOFs). For example, known homogeneous molecular catalysts can be anchored on the GO surface by employing them as scaffolds linking organometallic nodes. We have demonstrated that porphyrin building blocks with GO can lead to facile four-electron oxygen transfer reactions. We have also evaluated the advantages and disadvantages of GO as a catalytic material relative to other types of catalysts, both metallic and nonmetallic. Researchers would like to increase the potency of GO catalysts because many catalytic reactions currently require high loading of GO. Further research is also needed to identify a low-cost and environmentally friendly method for the synthesis of GO.

Graphene oxide reinforced poly (4-styrenesulfonic acid)/polyvinyl alcohol blend composites with enhanced dielectric properties for portable and flexible electronics

The development of active and stable heterogeneous Fenton-like catalysts have emerged as an alternative to overcome the practical limitations related to the homogeneous Fenton catalyst, where various iron species and/or iron oxides are immobilised within the structure of different catalyst supports. Clay, alumina, zeolite and carbonaceous materials such as activated carbon and carbon nanotubes have been used as catalyst supports of choice by the scientific community. However, there is a knowledge gap associated with using high aspect ratio 2D (dimension) graphene oxide (GO) as an alternative catalyst support. Of particular interest, it is postulated that the structure and functionalities of GO as a support confers to the resultant catalyst overall catalytic activity beyond the conventional Fenton catalysts. In this thesis, the structural and physicochemical properties of resultant catalyst with their corresponding catalytic activity were systematically investigated. To this end, the synergistic interaction between GO and immobilised iron oxide nanoparticles (Fe3O4 NPs) was proposed for an oxidative degradation of synthetic dye acid orange 7 (AO7), which is a major water pollutant from textile production. The GO‒Fe3O4 nanocomposites were initially synthesised through a facile one-pot method by co-precipitating irons salts onto GO sheets in a basic solution. The formation of GO‒Fe3O4 was postulated as follows: (i) Fe3+/ Fe2+ ions are adsorbed and coordinated by the carboxyl groups (C=O) of GO sheets, (ii) hydrolysed ions form nanoclusters on GO sheets when NaOH is introduced, (iii) followed by condensation of the nanoclusters to form Fe3O4 nuclei, and (iv) further nucleation and growth of Fe3O4 crystallites on GO sheets were due to the redox reaction as the pH is increased to 10. The incorporation of GO led to an enhancement on the catalytic activity of the nanocomposites with 76% AO7 removal over the control catalysts of Fe3O4 NPs and GO sheets, which corresponds to 48 and 22%, respectively. Further improvements on the catalytic activity of GO‒Fe3O4 were performed by modifying the synthesis through pre-hydrolysing iron salts prior to GO addition at pH 4 with various GO loadings. The key finding of this new method is the formation of two sets of different mesoporous structure. At low GO loadings ≤10 wt%, GO–Fe3O4 nanocomposites resulted in high surface area up to 409 m2 g-1, in tandem with high 92‒98% degradation of AO7. By contrast, GO loadings >10 wt% led to reduced surface area and lower GO‒Fe3O4 activity (60%). The presence of strong interfacial interactions (Fe–O–C bonds) in the nanocomposites contributed to the superior degradation of AO7, in tandem with structural-morphological features. The operational conditions of heterogeneous Fenton-like reaction were evaluated and modelled as a function of nanocomposites dosage, pH, temperature, oxidant and dye concentrations. Best results showed a fast 80% degradation in ~20 min, whilst ~98% of AO7 was successfully removed after 180 min of reaction time. Optimal conditions were determined for nanocomposites (GO(5wt%)‒Fe3O4) at the catalyst dosage of 0.2 g L-1, initial pH of 3 and 22 mM of H2O2 concentration at 298 K. The kinetics for the oxidative degradation of AO7 was found to be a pseudo-first-order reaction following the Langmuir-Hinshelwood mechanism. A noteworthy finding was the high activity (>98%) and recyclability of GO‒Fe3O4 over 7 cycles whilst the Fe3O4 NPs exhibited a severe loss of activity (~0%) at the 5th cycle. It was found that the ratio of Fe3+/Fe2+ for GO‒Fe3O4 remained almost constant over the 7 cycles, contrary to Fe3O4 NPs which underwent a significant Fe2+ decrease. The synergistic effect of GO in the GO‒Fe3O4 nanocomposite was able to accelerate the ≡Fe3+/≡Fe2+ redox cycles for the fast reduction of ≡Fe3+ to ≡Fe2+ which is actively participating in the decomposition of adsorbed H2O2 into HO• radicals during catalysis. The X-ray photoelectron spectroscopy (XPS) analysis of spent GO‒Fe3O4 showed that the sp2 carbon domains (C=C) slightly decreased after every cycle, thus suggesting some degree of oxidation of the carbon basal plane. It is therefore postulated that the unusual stability in the GO‒Fe3O4 is attributed to a donor-acceptor mechanism of the nanocomposites, in which the electrons donated from the oxidation of the GO are used for the regeneration of ≡Fe2+ and thus maintaining the Fe3+/Fe2+ ratio. Finally, the partial substitution of zinc (Zn) into Fe3O4 in the presence of GO was investigated, in view of the UV photocatalyst properties of zinc oxides. A slight change on the physicochemical properties of GO–Fe3-xZnxO4 lead to an increase in photocatalytic activity, where x=0.2 gave the higher degradation of AO7 in the UV-assisted Fenton-like reactions at 60 min reaction. It was found that the activity of the catalyst without GO always gave lower values ~30% of AO7 removal. Therefore, GO has proven again its beneficial use as an active component in the case of UV-assisted Fenton-like reaction as well.

Synergistic effect of vanadium pentoxide and graphene oxide in polyvinyl alcohol for energy storage application

Tuning sound absorbing properties of open cell polyurethane foam by impregnating graphene oxide

Synthesis, characterization and toxicity profiling of graphene oxide-metformin hydrogel as a sustained release system for metformin in-vitro

Facile one pot synthesis of graphene oxide (GO) by sonication assisted mechanochemical approach has been reported here. The amalgamation of ultrasonication and mechanical stirring has assisted the synthesis of GO in a short time duration of only 4 hours with good reaction yield. The structural characterization of GO was performed by X-ray diffraction spectroscopy (XRD), Fourier transform infrared spectroscopy (FTIR), UV-Visible spectroscopy and Raman spectroscopy. Atomic force microscopic (AFM) analysis manifested the flake like morphology of GO with average sheet thickness ~1.5 nm. AFM also provides important information about the surface roughness. Transmission electron microscope (TEM) analysis gave clear visualization of well exfoliated structure of GO in the form of thin flakes. The field emission scanning electron microscope (FESEM) analysis revealed a crimpling surface morphology of GO. The average size of GO flake as revealed through various morphological as well as light scattering techniques was around 3 μm. Moreover, important surface chemistry of the synthesized GO was well ascertained through contact angle analysis, AFM analysis and zeta potential analysis.

Surface modification by using citric acid (CA) in the graphene is a process to modify the physicochemical properties of graphene oxide. The strategy that has been proposed depends upon the electrochemical exfoliation of reduced graphene oxide (rGO), and simultaneously, the surface modification of rGO with CA carried out in accordance with the green technique. The synthesis of graphene oxide that has been doped with CA was accomplished via an electrochemical process in an aqueous medium containing fresh lime juice and sulphuric acid (electrolyte heating aided method at [Formula: see text]C) as an electrolyte. The electrolyte has been prepared using CA & H2SO4 (sulphuric acid), and both were mixed in a proportion of 1:2. In order to dilute the H2SO4 and perform the sonication, the water that has been pasteurized (according to the USP standards for irrigation) was used. The crystallite size, structural disorder, structure and surface morphology of the CA-doped graphene oxide were identified through X-ray diffraction (XRD) analysis, Raman spectroscopy, Field emission scanning electron microscope (FE-SEM). The presence of oxygen-containing functional group and adsorption has been analyzed using Fourier transform infrared (FTIR), and UV–Vis spectroscopy. The thermal stability of the CA-doped, and without CA-doped thermally reduced graphene oxide (TRGO) has been analyzed via thermogravimetric analysis (TGA). A green, simple, and environmentally friendly method has been demonstrated for the synthesis of CA-doped TRGO by electrochemical synthesis method by using natural dopant.

Membrane treatment for wastewater treatment is one of the promising solutions to affordable clean water. It is a developing technology throughout the world and considered as the most effective and economical method available. However, the limitations of membranes’ mechanical and chemical properties restrict their industrial applications. Graphene Oxide (GO) is one of the materials that have been recently investigated in membrane water treatment sector. In this work, ultrafiltration polysulfone (PSF) membranes with high antifouling properties were synthesized by incorporating different loadings of GO. High-oxidation degree GO had been synthesized using modified Hummers’ method. The synthesized GO was characterized using different analytical techniques including (FTIR-UATR), Raman spectroscopy, and CHNSO elemental analysis that showed high oxidation degree of GO represented by the its oxygen content (50 wt.%). Morphology and hydrophilicity of membranes were investigated using SEM, AFM and contact angle analyses and showed clear effect of GO on PSF morphology and better hydrophilicity of GO-based membranes caused by the hydrophilic nature of GO and its high oxygen content. Separation properties of the prepared membranes were investigated using a cross-flow membrane system. Biofouling and organic fouling resistance of membranes were tested using bovine serum albumin (BSA) and humic acid (HA) as model foulants. It has been found that GO based membranes exhibit higher antifouling properties compared to pure PSF. When using BSA, the flux recovery ratio (FRR %) increased from 65.4 ± 0.9 % for pure PSF to 86.9 ± 0.1 % with loading of 0.1 wt.% GO in PSF. When using HA as model foulant, FRR increased from 87.8 ± 0.6 % to 95.6 ± 4.2 % with 0.1 wt.% of GO in PSF. The pure water permeability (PWP) decreased with loadings of GO from 181.7 L.m-2.h-1.bar-1 of pure PSF to 181.1 and 167.4 L.m-2.h-1.bar-1 with 0.02 and 0.1 wt.% GO respectively. Furthermore, GO based membranes exhibited effective antibacterial performance against Halomonas aquamarina compared to pristine PSF. It can be concluded from the obtained results that incorporating low loading of GO could enhance the antifouling and antibacterial properties of PSF hence improving its lifetime and reuse.