Reduced Graphene Oxide In Composites Research Articles

Cadmium sulfide composite reduced graphene oxide for selective oxidation of 5-hydroxymethylfurfural to 2.5-diformylfurans

In this study, the Cadmium sulfide composite reduced graphene oxide photocatalyst (CdS/xrGO) was successfully synthesized to enhance the conversion of photocatalytic oxidation of 5-hydroxymethylfurfural (HMF). The conversion of 5-hydroxymethylfurfural and the yield of 2.5-diformylfurans (DFF) were 71.18 % and 69.72 %, respectively under optimum conditions, and the selectivity of DFF was significantly higher of about 97.94 %. Compared with CdS as a catalyst, HMF conversion and the DFF yield were roughly double. The excellent photocatalytic performance can be found through various characterization results because specific surface area of rGO is larger which provides many numbers of reaction sites for the reaction, reducing the clustering of CdS and allowing better contact between the photocatalyst and the substrate. Meanwhile, photogenerated electrons were easily transferred to the surface of rGO, which results in improving the separation potential of photogenerated carriers inhibited its complexation and resulting in enhanced photocatalytic performance.

Facilitated water transport in composite reduced graphene oxide pervaporation membranes for ethanol upgrading

High purity ethanol is one of the most sought-after renewable energy sources. However, standard production methods yield ethanol of insufficient quality. Membrane processes such as pervaporation are recognized as a viable method for upgrading ethanol. Their performance and selectivity depend solely on membrane employed. Hydrophilic polyvinyl alcohol (PVA) membranes are used industrially for this purpose, but there is a trade-off between selectivity and permeability. Among other materials, chemically converted graphene attracts particular attention due to its exceptional water transport properties, however its application is limited by the fabrication of free-standing membranes. In this study, a composite reduced PVA/graphene oxide (rGO) membranes with different rGO content (up to 49 wt%) was synthesized. Polyvinyl alcohol acted as a mediator to improve the mechanical stability of membrane layers by crosslinking rGO flakes with hydrogen bonds. The resulting membranes were fully characterized by scanning electron microscopy, X-ray diffraction, Fourier-transform infrared spectroscopy, water contact angle and mechanical tests. Pervaporation tests with water/ethanol mixtures (10/90 wt%) at temperatures between 20 and 50 °C demonstrated an excellent selectivity (over 12000) of membranes and satisfactory flux, even at high temperatures. The total permeate flux for membranes varied slightly as a function of operating temperature, demonstrating a good thermostability of the reduced graphene oxide-based membranes. The pervaporation separation index (PSI) of synthesized membrane exceed 5000 and surpassed majority of rGO containing membranes reported in the literature. Results indicate that rGO membranes noncovalently strengthened with PVA are a promising material for selective ethanol dehydration via pervaporation.

Enhanced interfacial solar steam generation with composite reduced graphene oxide membrane

Solar steam generation, as a high efficiency photo-thermal conversion method, has enormous potential for many industrial applications. In this work, a reduced graphene oxide (rGO) composite membrane with high light absorption was prepared to enhance the steam generation of water successfully. Through different experimental tests, the evaporation rate and efficiency reached 0.9 kg·h−1·m−2 and 45.1% at 1 sun, even with a small amount of rGO (0.76 g/m2). Furthermore, a simple composite enhanced system (CES) based on the rGO composite membrane was fabricated to further improve the evaporation efficiency. The evaporation rate and efficiency reached 1.37 kg·h−1·m−2 and 85.6% at 1 sun when the same amount of rGO was used in our novel CES. This was due to the decrease in the thermal conductivity and capillary enhancement of the supply water. Comparing the different methods of steam generation, it was observed that the evaporation efficiency of CES was higher than that of other systems, due to the decreased thermal loss. Finally, an integrated distillation and power generation device was assembled to demonstrate the practical application of CES and it exhibited great performance. It was of great significance for large-scale steam generation in distillation, sewage treatment, and other applications.

Hydrothermal preparation of NaTaO3/rGO composite photocatalyst to enhance UV photocatalytic activity

NaTaO3 and graphene oxide (GO) were prepared by hydrothermal method and modified Hummers method, respectively, then NaTaO3/reduced graphene oxide (rGO) composite photocatalysts were synthesized by hydrothermal method, and were characterized by XRD, FESEM, UV–Vis DRS. On this basis, photocatalytic activity of the composite photocatalyst was studied using methylene blue (MB) synthetic wastewater as the target. The results show that the degradation rate of synthetic wastewater can be promoted by about 15% within the same treatment time after NaTaO3 compounded 1.5 wt% reduced graphene oxide. When irradiated with 8 W UV light source, the degradation rate of synthetic wastewater can reach more than 95% after 90 min treatment. The composite reduced graphene oxide can effectively improve the UV catalytic activity of NaTaO3 photocatalyst.

The hierarchical TiO2 hollow microspheres with exposed high-energy {001} crystal facets composite reduced graphene oxide and its photocatalytic activity

A two-step hydrothermal method was used to prepare a hierarchical TiO2 hollow microspheres with exposed high-energy {001} crystal facets composite reduced graphene oxide nanocomposite with a hydrothermal temperature of 180 °C for 10 h. {001} crystal facets and hierarchical TiO2 hollow microspheres were controlled by F ions and Ostwald Ripening, and the reduced graphite oxide (rGO) is composited on the surface of the TiO2 hollow microspheres by high temperature and high pressure in a closed vessel. The hierarchical hollow microsphere structure can not only enhance the light absorbing ability by light scattering, but also reduce the charge transmission distance and thereby suppress the recombination of photogenerated electron–hole pairs. When rGO is composite, the specific surface area of the composite is increased, thereby providing lots of reactive sites and accelerating the surface reaction. Rhodamine B (RhB) was used as a simulated pollutant to detect the photocatalytic activity of the prepared sample. When the {001} crystal facets-exposed hierarchical TiO2 hollow microspheres composite rGO, it exhibited excellent photocatalytic activity, and 15 mg L−1 of RhB can be degraded by 90.08% in 90 min.

Synergistic Enhancement of H2and CH4Evolution by CO2Photoreduction in Water with Reduced Graphene Oxide–Bismuth Monoxide Quantum Dot Catalyst

Photocatalytic water splitting or CO2 reduction is one of the most promising strategies for solar energy conversion into hydrogen-containing fuels. However, these two processes typically compete with each other, which significantly decreases the solar energy conversion efficiency. Herein, we report for the first time this competition can be overcome by modulation of reactive sites and electron transfer pathway of heterogeneous photocatalysts. As a prototype, BiO composite reduced graphene oxide quantum dots (RGO-BiO QDs) were synthesized, which can provide large amounts of photogenerated electrons as well as individual reactive sites for H+ and CO2 reduction. The productivity of H2, CH4, and CO by the RGO-BiO QDs catalyst were 102.5, 21.75, and 4.5 μmol/(g·h), respectively, in pure water without the assistance of any cocatalyst or sacrificial agent. The apparent quantum efficiency at 300 nm reached to 4.2%, which is more than 10 times higher than that of RGO-TiO2 QDs (0.28%) under the same conditions. In situ DRIFT, ESR, and photoelectrochemical studies confirmed that the unique circled electron transfer pathway (Evb(BiO) → Ecb(BiO) → Ef(RGO) → EVo•(BiO)) and the large amount of separated different reactive sites are responsible for the highly efficient simultaneous H2 evolution and CO2 reduction performance.

SiO2 particle-supported ultrathin graphene hybrids/polyvinylidene fluoride composites with excellent dielectric performance and energy storage density

Polymer composites of polyvinylidene fluoride (PVDF) filled with SiO2–reduced graphene oxide (RGO) hybrids were fabricated and their dielectric properties and energy storage performance were systematically investigated. Hybrid SiO2–RGO with core-cell were prepared by using of SiO2 particles as rigid template and the thermal reduction of the electrostatic assembled SiO2–GO hybrids, in which the inside rigid particles could support the uniform dispersion of ultrathin RGO sheets in the PVDF matrix and thus leading to a much lower percolation threshold (0.141 vol% for RGO in composite) than those of most reported graphene/polymer composites. Only a small amount of RGO in composites lead to high dielectric permittivity (72.94) and low dielectric loss (0.059) which should be ascribed to the increase of interfacial polarization between filler and matrix. More importantly, the composites with high breakdown strength (2438 kV/cm), energy density (0.301 J/cm3) and charge–discharge efficiency (91.2%) can be achieved by incorporation of 10 wt% filler loading. This study provides a special pathway to ensure the dispersion and highly efficient usage of ultrathin graphene sheets in the polymer matrix and achieve graphene/polymer composite with excellent dielectric performance and energy storage density.

Synthesis and application of rGO/CoFe2O4 composite for catalytic degradation of methylene blue on heterogeneous Fenton-like oxidation

A high-specific surface-area, monodisperse and highly active magnetic composite reduced graphene oxide rGO/CoFe2O4 were synthesized using one-pot solvothermal reaction. Concretely, Fe(acac)3 and CoCl2∙6H2O used as starting materials were grown on graphene oxide at 200℃ to prepare rGO/CoFe2O4 composite. Graphene oxide was reduced to graphene, and CoFe2O4 microspheres were simultaneously generated on the carbon basal planes under the conditions generated in the solvothermal system. The morphology and structure of the prepared nanocomposite were characterized by transmission electron microscopy (TEM), N2 adsorption–desorption isotherms, X-ray photoelectron spectroscopy (XPS), vibration sample magnetometer (VSM), and X-ray diffraction (XRD), respectively. Moreover, the heterogeneous catalytic activity and degradation ability were investigated by degrading methylene blue (MB) experiment of Fenton-like reaction. The satisfactory results demonstrated that the rGO/CoFe2O4 showed excellent catalytic degradation ability toward MB than CoFe2O4 in water phase, thereby suggesting that rGO played an important role in rGO/CoFe2O4 for the decomposition of MB. Optimal degradation was achieved (nearly 100% within 15min) using initial concentrations of 3.0mmol/l H2O2, 5.0mmol/l NH2OH and 20mg/lMB. In addition, the nanocomposite can serve as an effective catalyst for decomposition aromatic amines in industrial effluent sample, which indicated its potential for practical applications in water pollutant removal and environmental cleanup.