Hydrothermal Reaction Of Graphene Oxide Research Articles

Enhanced Thermal Performance of Composite Phase Change Materials Based on Hybrid Graphene Aerogels for Thermal Energy Storage.

Thermal conductivity and latent heat are crucial performance parameters for phase change materials (PCMs) in thermal energy storage. To enhance the thermal performance of PCMs, with the help of graphene oxide (GO) acting as a dispersing agent, well-defined hybrid graphene aerogels (HGAs) with a three-dimensional (3D) porous structure were successfully synthesized by hydrothermal reaction of GO and graphene nanoplatelets (GNPs). GNPs, dispersing uniformly along the interconnecting graphene network, acted as thermal conductive fillers and supporting materials. Palmitic acid (PA) was impregnated into the HGA by vacuum forces. It was found that the thermal conductivity of the PA/HGA was enhanced without compromising heat storage capacity. Compared with PA, the PA/HGA with 4.2 wt% GNPs exhibited enhanced thermal conductivity of 2.1 W/mK and high latent heat of 206.2 J/g simultaneously. The PA/HGA with good thermal performance has potential applications in thermal energy storage.

Organic Dye-Derived N, S Co-Doped Porous Carbon Hosts for Effective Lithium Polysulfide Confinement in Lithium-Sulfur Batteries.

Lithium–sulfur batteries are considered as attractive candidates for next-generation energy storage systems originating from their high theoretical capacity and energy density. However, the severe shuttling of behavior caused by the dissolution of lithium polysulfide intermediates during cycling remains a challenge for practical applications. Herein, porous carbon materials co-doped with nitrogen and sulfur atoms were prepared through a facile hydrothermal reaction of graphene oxide and methylene blue to obtain a suitable host structure for regulating the lithium polysulfide shuttling behavior. Experimental results demonstrated that the abundant heteroatom-containing moieties in the carbon frameworks not only generated favorable active sites for capturing lithium polysulfide but also enhanced redox reaction kinetics of lithium polysulfide intermediates. Consequently, the corresponding sulfur composite electrodes exhibited excellent rate performance and cycling stability along with high Columbic efficiency. This work highlights the approach for the preparation of nitrogen and sulfur co-doped carbon materials derived from organic dye compounds for high performance energy storage systems.

The construction of porous graphene tri-doped with B, N and Co for enhanced oxygen reduction reaction

Graphene-based materials are promising nonprecious metal catalysts (NPMCs) for oxygen reduction reaction (ORR). However, this kind of carbon materials are usually suffering from layer stacking and intrinsically lack of highly-efficient active sites for ORR. At present, it is still a huge challenge to develop porous multi-doped graphene. Herein, the B, N and Co tri-doped graphene with hierarchical pores is successfully synthesized via a first hydrothermal reaction of graphene oxide (GO) with Co(II) nitrate, 2-methylimidazole (2MI) and boric acid, subsequent pyrolysis and final acid leaching. The morphology, structure and components of a series of samples are systematically investigated. The as-obtained products possess abundant macro/mesopores and ORR active sites including B-bonded C (CB), pyridinic N, graphitic N, CoNC and defects owing to the formation and decomposition of the Co layered double hydroxides (Co-LDHs). After optimizing hydrothermal temperature, pyrolytic temperature and the amount of GO, the sample exhibits an excellent ORR performance in 0.1 M KOH solution. The activity, durability and methanol tolerance are comparable or even superior to those of the commercial Pt/C catalyst (20 wt%). This work provides a new strategy to construct porous multi-doped graphene as nonprecious ORR catalyst.

Creatinine-induced specific signal responses and enzymeless ratiometric electrochemical detection based on copper nanoparticles electrodeposited on reduced graphene oxide-based hybrids

In this article, a novel and efficient electrochemical sensor of creatinine was facilely constructed on the surface of multifunctional nanohybrids-modified glassy carbon electrode (GCE), integrating creatinine-induced specific signal response and enzymeless ratiometric signal detection strategy. Dopamine hydrochloride as a reducing agent was dispersed in interface layers of graphene oxide. One-step hydrothermal reaction of graphene oxide with dopamine hydrochloride was conducted to prepare reduced graphene oxide (rGO), together with self-polymerization of polydopamine (PDA) attaching on rGO. Nile blue (NB) was loaded on rGO under ultrasonication through π-π stacking interactions between rGO and NB. The resulting PDA-rGO-NB complex was drop-coated on the surface of GCE. Under cyclic voltammetry scanning, copper nanoparticles (CuNPs) were prepared through electrochemical reduction of Cu2+ ions and electrodeposited on PDA-rGO-NB surface to construct a new CuNPs/PDA-rGO-NB/GCE sensing platform. Specific interactions of creatinine with Cu2+ ions from CuNPs surface led to regularly decreased peak current intensities located at –0.05 V (ICu2+) and negligible changes in peak current intensities located –0.325 V from NB (INB). There was a well plotted linear relationship between ICu2+/INB and creatinine concentration in the range from 0.01 to 100 μM, with a low detection limit of 2 nM. This sensing platform enabled highly sensitive and selective responses towards creatinine, over potential interferents. In practical samples, this developed enzymeless ratiometric electrochemical sensor realized efficient detection of creatinine, showing high detection performance.

Amine group induced high activity of highly torn amine functionalized nitrogen-doped graphene as the metal-free catalyst for hydrogen evolution reaction

A metal-free highly torn amine functionalized nitrogen doped graphene (HT-AFNG) used as hydrogen evolution reaction (HER) catalyst is prepared by using a simple synthesis method involving the hydrothermal reaction of graphene oxide in the presence of ammonia and the subsequent ball milling. The metal-free HT-AFNG is efficient for the HER in the acid solution and can deliver an onset potential of 100 mV and an overpotential of 350 mV at the current density of 10 mA cm−2, which is much lower than those of the singly and dually doped graphene reported previously. The amine functionalized and nitrogen doped structure plays an important role in the high catalytic activity of the HT-AFNG, where the amine group can greatly reduce the |ΔGH*| value at both defect and edge sites as well as increases the electron transfer capability of nitrogen dope graphene (NG). Significantly, the highly torn structure also makes a big contribution on the high catalytic activity of the HT-AFNG, since it allows for the good accessibility of the active sites for the HER. The strategy involves the introduction of electron donating groups open a new research pathway towards the improvement of HER catalytic activity of graphene-based materials.

Ultralow Loading Ruthenium Nanoparticles on Nitrogen‐Doped Graphene Aerogel for Trifunctional Electrocatalysis

AbstractA three‐dimensional (3 D) nitrogen‐doped graphene aerogel (NGA) with confined ultrasmall ruthenium nanoparticles (2–4 nm) was prepared through a hydrothermal reaction of graphene oxide (GO), ammonia solution, and ruthenium trichloride hydrate, followed by high‐temperature annealing and oxidation. The reactants self‐assemble into a 3 D porous structure with Ru nanoparticles embedded inside. With ultralow N and Ru contents of 2.40 and 1.21 at %, the introduction of Ru and N in the 3 D graphene aerogel gives rise to multifunctional catalytic performance in oxygen‐ and hydrogen‐involved reactions. Particularly, its performance in the oxygen evolution reaction (OER) surpassed those of commercial Pt/C and RuO2 in terms of both smaller potential (1.62 V vs. RHE) to reach 10 mA cm−2 and larger current densities across the applied potential range of 1 to 2 V (vs. RHE). Structural and chemical characterization revealed that the nanoparticle size and Ru/RuO2 ratio played decisive roles in determining the aerogel's electrocatalytic performance. Hence, this study demonstrates that the synergistic effect of nanosized Ru and a porous NGA can be applied to achieve effective multifunctional electrocatalysis, for which the Ru nanoparticles can be tailored to achieve optimized performance with the lowest‐necessary doping concentration.

Phytic acid induced three-dimensional graphene for the enrichment of phthalate esters from bottled water and sports beverage samples.

A three-dimensional graphene was synthesized through a hydrothermal reaction of graphene oxide with phytic acid. The microstructure and morphology of the phytic acid induced three-dimensional graphene were investigated by nitrogen adsorption-desorption isotherms, scanning electron microscopy, and transmission electron microscopy. With a large surface area and three-dimensional structure, the graphene was used as the solid-phase extraction adsorbent for the extraction of phthalate esters from bottled water and sports beverage samples before high-performance liquid chromatographic analysis. The results indicated that the graphene was efficient for the solid-phase extraction of phthalate esters. The limits of detection (S/N=3) of the method for the analytes were 0.02-0.03ng/mL for the water samples and 0.03-0.15ng/mL for the sports beverage sample. The limits of quantitation (S/N=9) for the analytes were 0.06-0.09ng/mL for water samples and 0.09-0.45ng/mL for sports beverage sample. The calibration curves for the phthalate esters by the method had a good linearity from 0.1 to 80.0ng/mL with correlation coefficients larger than 0.9997. The recoveries of the analytes for the method fell in the range of 86.7-116.2% with the relative standard deviations between 1.5 and 6.8%.

Enhanced adsorbability and photocatalytic activity of TiO2-graphene composite for polycyclic aromatic hydrocarbons removal in aqueous phase

Photodegradation via titanium dioxide (TiO2) has been used to remove polycyclic aromatic hydrocarbons (PAHs) from environmental media broadly. In this study, a series of TiO2-graphene composites (P25-GR) with different GR weight ratios were synthesized via hydrothermal reaction of graphene oxide (GO) and P25. Their structures were characterized and the proprieties were tested in aqueous phase. Phenanthrene (PHE), fluoranthene (FLAN), and benzo[a]pyrene (BaP) were selected as models of PAHs. The experiment indicated that P25-2.5%GR exhibited enhancement in both adsorption and photodegradation, ∼80% of PAHs were removed after 2h photocatalysis. The influence of photodegradation rate was studied, including PAHs initial concentration and pH. Aromatic intermediates were identified during the reaction process and the degradation pathways were portrayed. This work explored the enhanced photocatalysis performance was attributed to the PAH-selective adsorbability and the strong electron transfer ability of the composite. The analysis of the degradation intermediates confirmed that the reaction proceeded with the formation of free radicals, leading to the gradual PAH mineralization.

Facile synthesis of Co3O4 with different morphologies loaded on amine modified graphene and their application in supercapacitors

A simple and scalable method has been developed for the growth of Co3O4 on amine modified graphene (NH2-Gs), synthesized from the hydrothermal reaction of graphene oxide in the presence of ammonia. It shows that the relative NH3 content could alter the elemental composition and the relative percentages of functional groups in NH2-Gs, and the Co3O4 particles on the NH2-Gs with a relatively higher amount of amine groups exhibit a relatively small sizes. The obtained Co3O4/NH2-Gs can then be used as an active electrode material for supercapacitors. Among the synthesized samples, Co3O4/NH2-G(2) (the weight ratio of ammonia to GO is 5) exhibits the highest capacitive performance, 2108.4 F g−1 at 1 A g−1 and 1356.7 F g−1 at 15 A g−1, which is much higher than that of Co3O4 based materials reported previously. The electrode also has a satisfactory cycling performance with capacity retention of 64% after 800 cycles at 5 A g−1. The enhanced electrochemical performances of Co3O4/NH2-G(2) are ascribed to the higher specific surface area, the smaller Co3O4 particle sizes, the strong interaction between Co3O4 and NH2-G(2), and the higher conductivity. The excellent electrochemical performance makes the resultant composite materials to be a promising candidate for supercapacitor electrode application.

Synthesis of PtNFs/PANI/NG with enhanced electrocatalytic activity towards methanol oxidation

A novel Pt nanoflowers/polyaniline/nitrogen-doped graphene (PtNFs/PANI/NG) electrocatalyst was prepared by dispersing Pt nanoflowers (PtNFs) onto a polyaniline (PANI) grafted N-doped graphene (NG) matrix through a two-step electrochemical process. Firstly, NG was prepared by a hydrothermal reaction of graphene oxide (GO) with urea, and then electrochemical polymerization of aniline at NG was carried out. Secondly, PtNFs was dispersed onto the film of PANI/NG by electrochemical reduction of H2PtCl6. The as-prepared composites were characterized by SEM, XRD, and Raman spectra. Compared with PtNFs/PANI/G, PtNFs/PANI, and PtNFs/NG catalysts, the novel PtNFs/PANI/NG catalyst exhibits more advantages such as high catalytic activity, excellent poisoning tolerance, and stability characteristic towards methanol electro-oxidation, which is attributed to not only the good dispersion of PtNFs on PANI/NG but also the strong interactions between metal particles and conducting polymer matrixes. The results suggest that the PtNFs/PANI/NG catalyst can be a promising alternative for catalyst in direct methanol fuel cells (DMFCs).

Fabrication of 3-Dimensional Porous Graphene Materials for Lithium Ion Batteries

A 3-dimensional porous graphene material (PGM) has been synthesized using a simple two-step process: hydrothermal reaction and calcination. Hydrothermal reaction of graphene oxide (GO) in the presence of resorcinol and glutaraldehyde leads to covalent grafting of partially reduced GO with glutaraldehyde and the deposition of phenolic resin. Subsequent calcination of the composite consisting of phenolic resin deposited on partially reduced GO in the presence of KOH produces structurally stable, highly porous graphene material with a specific surface area of ∼1,066±2m2g−1. When used as an active electrode material in a lithium battery, the PGM exhibits an initial discharge capacity of ∼1,538 mAh g−1, which is significantly higher than those of graphite and other carbonaceous materials reported previously. More importantly, when cycled at higher discharge/charge rates, the PGM-based electrodes still deliver large capacities and excellent cycling performance, demonstrating great potential for high-performance lithium-ion batteries. The attractive electrochemical performance of the PGM is attributed to its unique porous structure with large specific surface area and the presence of more disordered carbon atoms produced by the KOH activation.

Hydrothermal synthesis of TiO2–RGO composites and their improved photocatalytic activity in visible light

Composites of titanium dioxide–reduced graphene oxide (TiO2–RGO) have been prepared via an efficient and facile hydrothermal reaction of graphene oxide and Ti(OH)4 in a ethanol–water solvent. The structure and composition of the composites have been characterized by X-ray diffraction, Scanning electron microscopy, Brunauer–Emmett–Teller specific area analysis, X-ray photoelectron spectroscopy and ultraviolet-visible diffuse reflectance spectroscopy. The results showed that the TiO2–RGO composites exhibited a layered structure with well-dispersed anatase TiO2 on the surface of the reduced graphene oxide. Compared with the pure TiO2 nanoparticles, the composites had larger surface area, and extended the photoresponse range to the visible light region. The photocatalytic activity of the composites was much higher than that of TiO2 in the photodegradation of methyl orange (MO) under visible light irradiation.

Nitrogen-Doped Graphene:Effects of nitrogen species on the properties of the vanadium redox flow battery

Nitrogen-doped graphene nanosheets (NGS), prepared by a simple hydrothermal reaction of graphene oxide (GO) with urea as nitrogen source were studied as positive electrodes in vanadium redox flow battery (VRFB). The synthesized NGS with the nitrogen level as high as 10.12 atom% is proven to be a promising material for VRFB. The structures and electrochemical properties of the materials are investigated by scanning electron microscopy, X-ray photoelectron spectroscopy, cyclic voltammetry and electrochemical impendence spectroscopy. The results demonstrate that not only the nitrogen doping level but the nitrogen type in the NGS are significant for its catalytic activity towards the [VO]2+/[VO2]+ redox couple reaction. In more detail, among four types of nitrogen species (pyridinic-N, pyrrolic-N, quaternary-N, oxidic-N) doped into the graphene lattice, quaternary-N play mainly roles for improving the catalytic activity toward the [VO]2+/[VO2]+ couple reaction.

Graphene nanocomposites of CdS and ZnS in effective water purification

The present work deals with syntheses of CdS/graphene and ZnS/graphene nanocomposites by hydrothermal reaction of graphene oxide and morpholine-4-carbodithioate complex of Cd and Zn, respectively. The corresponding nanocomposites has been investigated separately as photocatalyst in the decomposition of methylene blue in the presence of UV light and also as adsorbents in the removal of Cd(II) and Pb(II) ions in contaminated water. These studies have established that CdS/graphene and ZnS/graphene are effective photocatalyst as well as effective adsorbents in the removal of Cd(II) and Pb(II) ions to an extent of 97 and 99 % by ZnS/graphene and CdS/graphene nanocomposite, respectively, under 1 g L−1 of adsorption dose and at pH ~7. Further studies also established Langmuir model befitting for the adsorption of Pb(II) and Cd(II) ions on CdS/graphene and ZnS/graphene, respectively. The presence of interfering ions on extent of Cd(II) and Pb(II) removal has also been reported.

Synthesis and photocatalytic activity of graphene based doped TiO2 nanocomposites

The nanocomposites of reduced graphene oxide based nitrogen doped TiO2 (N–TiO2–RGO) and reduced graphene oxide based nitrogen and vanadium co-doped TiO2 (N, V–TiO2–RGO) were prepared via a facile hydrothermal reaction of graphene oxide and TiO2 in a water solvent. In this hydrothermal treatment, the reduction of graphene oxide and the intimate contact between nitrogen doped TiO2 (N–TiO2) or nitrogen and vanadium co-doped TiO2 (N,V–TiO2) and the RGO sheet is achieved simultaneously. Both N–TiO2–RGO and N,V–TiO2–RGO nanocomposites exhibit much higher visible light photocatalytic activity than N–TiO2 and N,V–TiO2, and the order of visible light photocatalytic activity is N,V–TiO2–RGO>N–TiO2–RGO>N,V–TiO2>N–TiO2>TiO2. According to the characterization, the enhanced photocatalytic activity of the nanocomposites is attributed to reasons, such as enhancement of adsorption of pollutants, light absorption intensity, minimizing the recombination of photoinduced electrons and holes and more excited states of these nanocomposites under visible light irradiation. Overall, this work provides a more marked contrast of graphene based semiconductor nanocomposites and a more comprehensive explanation of the mechanism.

Controllable synthesis of RGO/FexOy nanocomposites as high-performance anode materials for lithium ion batteries

We have developed a simple, efficient, and environmentally benign approach to the synthesis of reduced graphene oxide (RGO)/metal oxide composites via hydrothermal reaction of graphene oxide and metal powder under mild reaction conditions.

Methanol electrocatalytic oxidation on Pt nanoparticles on nitrogen doped graphene prepared by the hydrothermal reaction of graphene oxide with urea

A facile hydrothermal reaction of graphene oxide with urea was used to produce nitrogen doped graphene, and Pt nanoparticles were deposited on the obtained nitrogen doped graphene by the NaBH4 reduction route. The morphology and microstructure of the synthesized catalysts were characterized by transmission electron microscopy, X-ray powder diffraction and X-ray photoelectron spectroscopy, while the functional groups on the surface of the catalysts were investigated by the Fourier transform infrared spectroscopy and ultraviolet-visible absorption spectra. Cyclic voltammetry, chronoamperometry and electrochemical impedance techniques were carried out to evaluate the methanol electrocatalytic oxidation activity and durability of Pt catalysts supported on the nitrogen doped graphene. The results showed that nitrogen doping and reduction of GO were achieved simultaneously by the facile hydrothermal reaction, which had beneficial effects for the deposition process and electrocatalytic activity of Pt nanoparticles. The Pt catalysts supported on the nitrogen doped graphene substrate presented excellent activity and durability of methanol oxidation reaction, which might be promising for application in direct methanol fuel cells.

Graphene–TiO2(B) nanowires composite material: Synthesis, characterization and application in lithium-ion batteries

A novel nanostructure graphene–TiO2(B) nanowires composite material was obtained through a green approach by hydrothermal reaction of graphene oxide (GO) hybrid titania gel in 10M NaOH aqueous solution systems. The GO reducing process was accompanied by generation of TiO2(B) nanowires. Results show that the TiO2(B) to anatase phase transformation temperature was increased and the nanotube to nanowire transformation process accelerated after hybridized with graphene, which revealed the enhancement thermostabilities of the composite material. The prepared composite exhibited high surface area (270m2/g). Electrochemical analysis indicated that the composite electrode displayed a high initial discharge capacity of 304mAhg−1 at 30mAg−1 and a good cyclability with a capacity loss of 7% after 60 cycles at 150mAg−1. The graphene modified TiO2(B) nanowires composite could improve the electrochemical performance of TiO2(B) for lithium-ion batteries.

Synthesis of graphene–ZnO nanorod nanocomposites with improved photoactivity and anti-photocorrosion

A series of graphene–ZnO (GR–ZnO) nanorod nanocomposites with different weight addition ratios of graphene (GR) have been prepared via a facile hydrothermal reaction of graphene oxide (GO) and ZnO nanorods. X-ray diffraction (XRD), UV-vis diffuse reflectance spectra (DRS), field-emission scanning electron microscopy (FE-SEM), electrochemical impedance spectroscopy (EIS), photoluminescence (PL) spectra, and electron spin resonance (ESR) spectra are employed to determine the properties of the samples. It is found that GR–ZnO nanorod nanocomposites with a proper addition amount of GR exhibit higher photocatalytic activity and improved anti-photocorrosion than ZnO nanorods toward liquid-phase degradation of dye under ultraviolet (UV) light irradiation. The improved photoactivity and anti-photocorrosion of GR–ZnO nanorods can be ascribed to the integrative synergistic effect of enhanced adsorption capacity, the prolonged lifetime of photogenerated electron–hole pairs and effective interfacial hybridization between GR and ZnO nanorods. This study also shows that graphene sheets act as electronic conductive channels to efficiently separate the photogenerated charge carriers from ZnO nanorods. It is hoped that our current work could promote increasing interest in designing the nanocomposites of one-dimensional (1D) semiconductor and two-dimensional (2D) graphene for different photocatalytic applications.

Nitrogen-doped graphene with high nitrogen level via a one-step hydrothermal reaction of graphene oxide with urea for superior capacitive energy storage

Nitrogen-doped graphene nanosheets (NGS) with the nitrogen level as high as 10.13 atom% were synthesized via a simple hydrothermal reaction of graphene oxide (GO) and urea. N-doping and reduction of GO were achieved simultaneously under the hydrothermal reaction. In the fabrication, the nitrogen-enriched urea plays a pivotal role in forming the NGS with a high nitrogen level. During the hydrothermal process, the N-dopant of urea could release NH3 in a sustained manner, accompanied by the released NH3 reacting with the oxygen functional groups of the GO and then the nitrogen atoms doped into graphene skeleton, leading to the formation of NGS. The nitrogen level and species could be conveniently controlled by easily tuning the experimental parameters, including the mass ratio between urea and GO and the hydrothermal temperature. Remarkably, in 6 M KOH electrolyte, the synthesized NGS with both high nitrogen (10.13 atom%) and large surface area (593 m2 g−1) exhibits excellent capacitive behaviors (326 F g−1, 0.2 A g−1), superior cycling stability (maintaining initial capacity even) and coulombic efficiency (99.58%) after 2000 cycles. The energy density of 25.02 Wh kg−1 could be achieved at power density of 7980 W kg−1 by a two-electrode symmetric capacitor test. A series of experiments results demonstrated that not only the N-content but also the N-type are very significant for the capacitive behaviors. In more detail, the pyridinic-N and pyrrolic-N play mainly roles for improving pseudo-capacitance by the redox reaction, while quaternary-N could enhance the conductivity of the materials which is favorable to the transport of electrons during the charge/discharge process. Hence, the approach in this work could provide a new way for preparing NGS materials which could be used as advanced electrodes in high performance supercapacitors.