Photocatalytic hydrogen generation of ZnO rod–CdS/reduced graphene oxide heterostructure prepared by Pt-induced oxidation and light irradiation-assisted methods

A synthesis method including Pt-induced oxidation and light irradiation-assisted routes has been developed to prepare a ZnO rod–CdS/reduced graphene oxide (RGO) heterostructure. Here, graphene oxide nanosheets are reduced and loaded onto the surface of Zn spheres using a redox process. ZnO rods are generated from Zn spheres by a Pt-induced oxidation method, and CdS nanoparticles are then loaded onto the surface of RGO via a light irradiation-assisted method. The ZnO rod–CdS/RGO heterostructure exhibits 3.8 times higher photocatalytic hydrogen generation rate from an aqueous solution containing Na₂S/Na₂SO₃ than the reference ZnO rod–CdS heterostructure under simulated solar light irradiation. The optimal contents of RGO nanosheets and CdS nanoparticles are 2 wt% and 20 at.%, respectively.     

One-pot synthesis of CdS sensitized TiO2 decorated reduced graphene oxide nanosheets for the hydrolysis of ammonia-borane and the effective removal of organic pollutant from water

A hybrid material of reduced graphene oxide (RGO) sheets decorated with CdS-TiO₂ NPs was prepared through a facile one-pot hydrothermal method. The assembly of CdS-TiO₂ nanoparticles (NPs) on RGO sheets was in-situ produced. As-synthesized nanocomposites were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), energy disperse X-ray spectrum (EDS), fourier transform infrared spectroscopy (FTIR), and photoluminescence spectroscopy (PL). The obtained nanocomposites exhibited a good photocatalytic activity for the visible-light-induced decomposition of methylene blue (MB) dye and hydrolysis of ammonia borane. The results showed that by incorporation of CdS and TiO₂ NPs on graphene oxide sheets the photocatalytic efficiency was enhanced. The significant enhancement in the photocatalytic activity of CdS-TiO₂/RGO nanocomposites under visible light irradiation can be ascribed to the effect of CdS by acting as electron traps in TiO₂ band gap. Reduced graphene oxide worked as the adsorbent, electron acceptor and a photo-sensitizer to efficiently enhance the dye photo decomposition. Such nanocomposite photocatalyst might find potential application in a wide range of fields, including hydrogen energy generation, air purification, and wastewater treatment.     

Fabrication of Pt–Cu/RGO hybrids and their electrochemical performance for the oxidation of methanol and formic acid in acid media

Pt–Cu/reduced graphene oxide (Pt–Cu/RGO) hybrids with different Pt/Cu ratios were prepared by the reduction of H₂PtCl₆ and CuSO₄ by NaBH₄ in the presence of graphene oxide (GO). The Pt–Cu nanoparticles were characterized by transmission electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy. The reduction of GO was verified by ultraviolet–visible absorption spectroscopy, Raman spectroscopy and X-ray photoelectron spectroscopy. Compared to Pt/RGO, the Pt–Cu/RGO hybrids have superior electrocatalytic activity and stability for the oxidation of methanol and formic acid. Thus they should have potential applications in direct methanol and formic acid fuel cells.     

Activated carbons with metal containing bentonite binders as adsorbents of hydrogen sulfide

Wood-based activated carbon was ground and mixed with 10% bentonite binders containing either iron, zinc or copper cations adsorbed within the interlayer space and/or on the external surface of bentonite flakes. To better understand the role of transition metals, carbon was also impregnated with iron, zinc and copper salts. The structure of materials after modification was determined using nitrogen adsorption. The modification resulted in a decrease in porosity, especially in micropore volume, as a result of combined mass dilution effect and adsorption/re-adsorption of metals in small pores. Introduction of bentonite binders containing adsorbed metal increased the capacity of carbon for hydrogen sulfide only in the case of material containing copper. Copper also significantly increases the performance of carbon as an H₂S adsorbent when impregnation is applied whereas the effects of other metals used in this study are much less pronounced. It is likely that copper present in the small pores acts as a catalyst for oxygen activation causing hydrogen sulfide oxidation. As a result of this process, elemental sulfur is formed which, when present in small pores, is oxidized to weakly adsorbed SO₂. The SO₂ is removed from the surface when continuous reaction with hydrogen sulfide occurs. Thus, even though binding carbon with spent bentonites after copper adsorption increases the capacity of carbon toward H₂S removal, the formation of SO₂, another undesirable pollutant, does detract somewhat from the procedure.     

Dielectric and dye adsorption properties of luminescent-superparamagnetic MFe2O4 (M = Mn,Mg)/reduced graphene oxide composites

MFe₂O₄ (M = Mn, Mg)/reduced graphene oxide (MFe₂O₄/RGO) nanocomposites were synthesized through a simple and novel pressure cooker assisted solvothermal method. The nanocomposites were characterized using x-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), UV–Vis absorption and photoluminescence spectroscopy, transmission electron microscopy (TEM) and x-ray photoelectron spectroscopy (XPS). The optical analyses showed that, the MFe₂O₄/RGO materials have good photoluminescence (PL) with excitation dependent PL properties while magnetic characterization indicated that, the as-synthesized MFe₂O₄/RGO nanocomposites exhibits superparamagnetic behavior. Dielectric spectroscopy analysis showed enhanced dielectric constant, dielectric loss and AC conductivity for MFe₂O₄/RGO, compared to graphite oxide (GO). The study on methyl blue (MB) dye adsorption revealed that, the as-prepared nanocomposites have strong and recyclable adsorption for MB.     

H2S oxidation by multi-wall carbon nanotubes decorated with tungsten sulfide

Tungsten sulfide catalysts decorated on single and multiwall carbon nanotubes (SWNTs & MWNTs) and activated carbon were synthesized, and XRD, ICP, SEM, TEM and ASAP analyses were employed to acquire the characteristics of each catalyst. Afterwards a gas flow containing 5,000 ppm of H₂S was passed over the catalyst in gas hour space velocity (GHSV) of 5,000 h^?1, temperature of 65 °C, steam volume percent of 20 and O₂/H₂S ratio equal to 2. The results revealed that the catalyst supported on MWNTs exhibited higher conversion amongst its counterparts. Then effects of GHSV, steam volume percent in the feed, catalyst loading and temperature were investigated on conversion of hydrogen sulfide to elemental sulfur for tungsten sulfide catalyst decorated on MWNTs.     

Modification of polypropylene filter with metal oxide and reduced graphene oxide for water treatment

A hydrothermal method for the synthesis of reduced graphene oxide/titanium dioxide filter (RGO/TiO₂) and reduced graphene oxide/zinc oxide filter (RGO/ZnO) by using polypropylene (PP) porous filter is reported. Field emission scanning electron microscopy illustrated that the nanoparticles were uniformly distributed on the reduced graphene oxide nanosheets. Flexural tests showed that the physical properties of the modified filters have greater strength than the original filter. Thermogravimetric analysis revealed that the thermal property of the modified filters is the same as that of the original filter. Under a halogen lamp, the modified filter exhibited excellent photocatalytic degradation of methylene blue. The RGO/TiO₂ filter maintained its ability to degrade MB efficiently, even after five cycles of photocatalysis.     

Highly efficient synthesis of graphene/MnO2 hybrids and their application for ultrafast oxidative decomposition of methylene blue

A highly efficient method has been reported to fabricate the reduced graphene oxide/MnO₂ (RGO/MnO₂) hybrid materials, a kind of catalysts for oxidative decomposition of methylene blue (MB). The pristine suspension of graphene oxide/manganese sulfate (GO/MnSO₄) produced by the modified Hummers method is in situ transformed into GO/MnO₂ composites in combination with KMnO₄, and then further into RGO/MnO₂ composites by means of glucose-reduction. It is found that MnO₂ nanoparticles with the size of 20–30 nm are uniformly distributed in the structure of RGO. A series of composites with different mass ratios of RGO to MnO₂ has been proved superior catalytic activities, much higher than that of the bare MnO₂ for decomposition of MB dye in the presence of H₂O₂. Typically, 50 mL of MB (50 mg L⁻¹) can be completely decolorized and nearly 66% mineralized at 50 °C in 5 min with 10 mg of the RGO/MnO₂ hybrid. According to the adsorption–oxidation–desorption mechanism, the high activity of RGO/MnO₂ composites for decomposition of MB is closely related to the positive synergistic effect of RGO and MnO₂ with the assistance of H₂O₂.     

One pot preparation of reduced graphene oxide (RGO) or Au (Ag) nanoparticle-RGO hybrids using chitosan as a reducing and stabilizing agent and their use in methanol electrooxidation

An environment-friendly approach to synthesizing reduced graphene oxide (RGO) was developed by using chitosan (CS) as both a reducing and a stabilizing agent. Factors that affect the reduction of graphene oxide (GO), such as the ratio of CS/GO, pH and temperature, were explored to obtain optimum reaction conditions. The RGO was characterized with UV visible absorption spectroscopy, Fourier transform infrared spectroscopy, Raman spectroscopy, X-ray diffraction spectroscopy, thermo-gravimetric analysis, and X-ray photoelectron spectroscopy and transmission electron microscopy. Analysis shows that CS macromolecules can efficiently reduce GO at a comparatively low temperature and their adsorption onto the RGO nanosheets allows a stable RGO aqueous dispersion to be formed. Since CS is a natural, nontoxic and biodegradable macromolecule, this approach provides a new green method for GO reduction that would facilitate the large scale production of RGO, which has great value for graphene applications. Moreover, CS can reduce GO and AgNO₃ (or HAuCl₄) in one pot to obtain Ag nanoparticle-RGO hybrids or Au nanoparticle-RGO hybrids that exhibit good electrochemical activity.     

Interaction of hydrogen sulfide with the pristine and B&N-doped beryllium oxide nanotube: DFT study

ABSTRACT

In this study, hydrogen sulfide interaction with pristine, B-, N-, and B&N atom-doped beryllium oxide nanotube (BeONTs) is investigated by the density functional theory (DFT) method. At the first step, we considered different configuration models for the adsorption of H₂S on the surface of nanotube and then we selected 12 stable models for this study. The structures of all selected models are optimized and the quantum properties, thermodynamic parameters, natural bond orbitals (NBO), reduced density gradient (RDG), molecular electrostatic potential (MEP), and atom in molecule (AIM) parameters are calculated at the cam–B3LYP level of theory with 6–31G (d) base set. The obtained E_ads for the exterior surface of nanotube is exothermic and is in the range –3.15 to –28.34?Kcal mol^–1, and that for the interior surface is endothermic and is in the range 19.17 to 27.17?kcal mol^–1. The gap energy for pure, B-doped, N-doped, and B&N-doped BeONTs is 10.11, 10.03 (α spin), 10.13 (α spin), and 9.35?eV, respectively. The results of thermodynamic parameters, such as ΔG and ΔH values for the adsorption of H₂S, on the surface of B-doped BeONTs are more negative than other models and favorable in thermodynamic approach. The NBO, MEP, NMR, and HOMO–LUMO results confirm that the electron charge transfer occurs from H₂S molecule toward BeONTs, as a result the bonding type of H₂S?…?BeONTs is weak ionic.     

Electrically conductive and mechanically tough graphene nanocomposite hydrogels with self‐oscillating performance

Conventional hydrogels are extremely brittle, fragile and poorly conductive, which limits their applications in a variety of aspects. In this study, we fabricated a novel kind of nanocomposite self‐oscillating hydrogel poly(AA‐co‐Fe(phen)₃)/PVA/RGO with high conductivity and good mechanical strength by dispersing reduced graphene oxide (RGO). Due to the synergetic effect of RGO dispersed in the hydrogels or dry gels and Fe metal which is the reduction product of the Fe(phen)₃ moiety by RGO, the hydrogels have a high conductivity of 18.2 S m^?1 with 0.67 wt% RGO content. The dispersed RGO in the hydrogels combined with the network structure by means of hydrogen bonding, π–π stacking and electrostatic interaction and was demonstrated to enhance the mechanical properties of the hydrogels. The elastic modulus achieves 65.2 kPa (1020% of the tensile strength) and 236.4 kPa (with 70% compression), respectively. In addition, the prepared hydrogels exhibit a self‐oscillating behavior in a Belousov–Zhabotinsky solution free of catalyst. These results can be broadly applied in the future in the development of an autonomous on–off switching, flexible/stretchable, graphene‐based soft electronic device. © 2019 Society of Chemical Industry     

Wood Pulp Fiber Wrapped by Fish-Scale Graphene as Flexible and Free-Standing Supercapacitor Electrode

Poplar wood pulp was adopted as both frame and precursor for the synthesis of pulp fiber (PF)/reduced graphene oxide composite via a simple and low-cost method. In this method, the PF based on graphene (PFG) composite film electrode was prepared by a simple vacuum filtration process with various ratios (PF: reduced graphene oxide (RGO)?=?5:1, PF:RGO?=?5:2, PF:RGO?=?5:3, PF:RGO?=?5:4, PF:RGO?=?5:5). In terms of special structures, the PFG can be used as electrodes without metal-collector, adhesives, and additives. The optimal ratio (PF:RGO?=?5:4) film electrode displayed a high areal-specific capacitance of 683 mF/cm² at 1?mA/cm² with a mass of 5.3?mg/cm² (specific capacitance of 129?F/g) and good cycling stability (87.5% capacitance retention after 10,000 cycles at 5?mA/cm²) as well as excellent rate capability and high flexibility (suitable for any angle, even 180°). Moreover, the device could possess a maximum energy density of 47.71?μWh/cm² and a maximum power density of 1251?μW/cm². These results suggest that the composite PGF film is a promising electrode material.     

Ultra-high compression and wear resistant hybrid filled polyimide composite: Synergistic effect of Fe2O3 decorated RGO

Herein, the tribological performance, thermal and compression resistance behavior of polyimide (PI) reinforced by Fe₂O₃ decorated reduced graphene is systematically investigated. The remarkable synergistic effect of Fe₂O₃ decorated reduced graphene oxide (RGO) is demonstrated in its PI wear resistance, and PI/RGO/Fe₂O₃ composites show good thermal stability and much higher compression resistant ability than PI, PI/RGO, and PI/Fe₂O₃ composites when the filling contents are same. Additionally, the PI/RGO/Fe₂O₃ composites also exhibited ultra-wear-resistant properties under high load condition, and the lowest wear rate is 3.18 × 10⁻⁸ mm³N⁻¹ m⁻¹, which is an order of magnitude lower than that of pure PI. The investigation of its tribological mechanism also showed strong synergistic effect and interface force of Fe₂O₃ decorated RGO, which contribute to its high-performance friction-reducing behaviors. These findings give an inside view to Fe₂O₃ decorated RGO and its polyimide composites, and open an avenue for the graphene oxide (GO) based composite to act as compression wear-resisting solid fillers and lubricants when polymer composite with excellent compressive, thermal and tribological properties is required.     

Synthesis of CoNi/SiO2 core-shell nanoparticles decorated reduced graphene oxide nanosheets for enhanced electromagnetic wave absorption properties

In this research, the nanocomposites, CoNi/SiO₂ core-shell nanoparticles decorated reduced graphene oxide (RGO) nanosheets, are successfully synthesized via liquid-phase reduction reactions combined with a sol-gel route. The structures, morphologies, chemical composition and magnetic properties of CoNi nanoparticles, CoNi/SiO₂ core-shell nanoparticles and RGO/CoNi/SiO₂ nanocomposites have been investigated in exhaustive detail. The electromagnetic (EM) parameters of RGO/CoNi/SiO₂ nanocomposites are measured using a vector network analyzer. The results reveal that the RGO/CoNi/SiO₂ nanocomposites display enhanced EM wave absorption properties with the maximum reflection loss (R_L) of ??46.3?dB at 6.2?GHz with a matching thickness of 4.2?mm. Additionally, the absorption bandwidth corresponding to the R_L less than ??10?dB is up to 14.3?GHz (3.7–18.0?GHz) with a matching thickness range of 2.0–5.0?mm. To comprehensively consider the absorption bandwidth and the maximum R_L, the integrational method which defines ΔS as the integration area of R_L (R_L < ??10?dB) and R_E as EM wave absorption efficiency is adopted to reveal that the RGO/CoNi/SiO₂ nanocomposites exhibit the excellent absorption properties with the matching thickness of only 2.0?mm. Accordingly, the as-prepared RGO/CoNi/SiO₂ nanocomposites could be applied as promising EM wave absorption materials.     

Sub-20 nm anatase particles uniformly anchored on graphene oxide and reduced graphene oxide nanosheets and their photocatalytic oxidation and Li-ion storage capabilities

Nanosized anatase TiO₂ particles anchored on nanocarbon substrates have great potential for practical applications in high-performance lithium ion batteries and efficient photocatalysts. The synthesis of this material usually utilizes calcination to crystallize amorphous titania, which normally causes the formation of aggregates and some side effects. In this work, we demonstrated that sub-20 nm anatase particles uniformly anchored on graphene oxide and reduced graphene oxide nanosheets in aqueous solution at a temperature of 90 °C and atmospheric pressure, without further calcination. The photocatalytic oxidation activity and electrochemical properties of graphene oxide/anatase TiO₂ (GO/A) and reduced graphene oxide/anatase TiO₂ (RGO/A) were comparatively investigated. We found that GO/A showed higher photocatalytic oxidation activity than RGO/A under UV light irradiation. Graphene oxide accepted electrons and suffered reduction, which finally decreased GO/A’s photocatalytic oxidation activity to an extent similar to RGO/A. We also found that, as anode material for Li-ion battery, the specific capacity of RGO/A was nearly three times that of GO/A at the same current rate. This study will inspire better design of metal oxide/nanocarbon nanocomposites for high performance lithium ion battery and photocatalysis applications.     

Large scale production of highly conductive reduced graphene oxide sheets by a solvent-free low temperature reduction

A novel one-pot process that can produce freestanding reduced graphene oxide (RGO) sheets in large scale through a mechanochemical method is presented, which is based on a 1:1 adduct of hydrazine and carbon dioxide (H₃N⁺NHCO₂⁻, solid hydrazine). We were able to synthesize RGO sheets by grinding solid hydrazine with graphene oxide (GO), followed by storing the mixed powder at 50 °C for 10 min. No solvents, nor large vessels, nor post-annealing at high temperatures are required. The resulting RGO sample was characterized by elemental analysis, X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy, Brunauer–Emmett–Teller measurement, thermo gravimetric analysis, Fourier transform infrared spectroscopy, solid state nuclear magnetic resonance spectroscopy, and conductivity measurement. It exhibits excellent conductivity and possesses a high specific surface area. This reduction method was successfully applied for the fabrication of inkjet-printed RGO devices on a flexible substrate.     

Ultrasonic assisted synthesis of TiO2–reduced graphene oxide nanocomposites with superior photovoltaic and photocatalytic activities

In this work, TiO₂–reduced graphene oxide (RGO) nanocomposites were successfully produced by an ultrasonication-assisted reduction process. The reduction of graphene oxide (GO) and the formation TiO₂ crystals occurred simultaneously. The synthesized nanocomposite was characterized by SEM, EDX, Raman spectroscopy, FTIR, XRD, XPS, UV–vis spectroscopy, photoluminescence spectrometer and electrochemical impedance spectroscopy. As a result of the introduction of RGO, the light absorption of octahedral TiO₂ was markedly improved. The photocatalytic results revealed that weight percent of RGO has substantial influence on degradation of Rhodamine B under visible light irradiation. The enhancement of the photocatalytic activity can be attributed to the enhancement of the visible-light irradiation harvesting and efficiently separation of the photogenerated charge carriers. Meanwhile, upon the RGO loading, the photoelectric conversion efficiency of TiO₂–RGO nanocomposite modified electrode was also highly improved.     

The electrocatalytic oxidative polymerization of o-phenylenediamine by reduced graphene oxide and properties of poly(o-phenylenediamine)

The electrocatalytic oxidative polymerization of o-phenylenediamine (o-PD) was performed on a reduced graphene oxide (RGO)/glassy carbon (GC) electrode. The electrolysis of o-PD was carried out using cyclic voltammetry and potentiostatic and galvanostatic methods. The experimental results demonstrated that the reduced graphene oxide (RGO) has a pronounced catalytic ability for the electrochemical oxidative polymerization of o-PD in a 0.60 M H₂SO₄ solution compared to the bare GC electrode; however, graphene oxide has only a slight catalytic ability for the electrochemical oxidative polymerization of o-PD. The above three electrochemical techniques confirmed that there is a considerable discrepancy between the characteristics of the electrocatalytic oxidation of a species and the characteristics of the electrocatalytic oxidative polymerization of o-PD. This effect occurs because the charges passed during the electrolysis of o-PD on the bare GC electrode were mainly consumed for the formation of the soluble oligomer; however, RGO plays an important role in suppressing the formation of the soluble oligomer. An unexpected result was obtained: two or three pairs of the redox peaks of poly(o-phenylenediamine) (PoPD), synthesized using RGO as a catalyst, occur on the cyclic voltammogram in a wider potential range, depending on the polymerization conditions; however, only one pair of redox peaks occurs on the cyclic voltammogram of the conventional PoPD in a narrow potential range under exactly the same experimental conditions. The NMR and ESR spectra of the PoPD polymerized on the RGO/GC electrode are presented in this paper.     

Ordered mesoporous Co3O4 nanospheres / reduced graphene oxide composites for rutin detection

The ordered mesoporous Co₃O₄ nanospheres encapsulated with reduced graphene oxide (denoted as meso-Co₃O₄ / RGO) were synthesized via electrostatic interaction and firstly for the electrochemical detection of rutin with good sensing effects. The resultant meso-Co₃O₄ / RGO nanocatalyst not only possesses more active sites due to the high surface area deriving from the mesoporous structure, but also has benign conductibility due to the presence of RGO, both of which enhance the sensing properties for the electrochemical detection of rutin. The developed sensor displays low detection limit (0.03?μM) and large sensitivity (74.85?μA?μM^?1 cm^?2). Besides, the rutin sensor possesses good selectivity, stability and reproducibility.     

H2S adsorption/oxidation on unmodified activated carbons: importance of prehumidification

Three microporous activated carbons supplied by Norit^® (of peat and bituminous coal origin) were used in this study as hydrogen sulfide adsorbents. Their surface properties were evaluated by means of nitrogen adsorption, Boehm titration, potentiometric titration, and thermal analysis. The results show that the carbons significantly differ in their pore structure and surface chemistry. This is reflected in their hydrogen sulfide breakthrough capacity. The breakthrough capacity is underestimated when not enough water is adsorbed on the carbon surface. The performance follows the expectations after extensive humidification of the sorbents’ surfaces. Moderately low pH in the acidic range of coal-based carbon, Vapure 612, promotes the oxidation of H₂S to sulfur oxides which is important from the point of view of water regeneration. The high pH of peat-based carbon, RB 4, results in H₂S oxidation to elemental sulfur.