Reduced Graphene Oxide Microspheres Research Articles

Tuning the aggregation structure and surface composition of reduced graphene oxide microspheres for high-rate supercapacitors

Tuning the aggregation structure and surface composition of reduced graphene oxide microspheres for high-rate supercapacitors

Bifunctional ZnMn2O4/reduced graphene oxide microspheres with a needle-like surface architecture as effective electrodes for energy storage

The synthesis procedure of the ZNMO/rGO composites.

Macroporous vanadium dioxide–reduced graphene oxide microspheres: Cathode material with enhanced electrochemical kinetics for aqueous zinc-ion batteries

Aqueous zinc-ion batteries are being extensively investigated owing to their safe operating conditions. Therefore, the search for cathode materials with optimum composition and nanostructure that enable high zinc-ion storage performance is underway. This study introduces a procedure for the formation of vanadium dioxide-nanoflake-reduced graphene oxide composite (P-VO2@rGO) microspheres with open pores through spray pyrolysis. Spherical cathode materials are formed by spray pyrolysis through the addition of polystyrene nanobeads and graphene oxide nanosheets in the spray solution. This enabled the formation of porous and crumpled graphene oxide microspheres, wherein thin VO2 nanoflakes are anchored. As a cathode for zinc-ion batteries, P-VO2@rGO exhibits a high rate capability (159 mA h g−1; current density = 5.0 A g−1) and stable cycle performance for the 300 cycles at 1.0 A g−1. To discern the synergistic effect of the reduced graphene oxide (rGO) and 3D-porous structure with a small crystal size on the zinc-ion storage, control samples (VO2-rGO composite and porous VO2 microspheres) are synthesized and tested as cathodes for zinc-ion batteries. The synergistic effect of compositing rGO and introducing porous structure with small crystal size enables high reversible capacity and enhances electrochemical kinetics of the electrode.

Nanoconfined vanadium nitride in 3D porous reduced graphene oxide microspheres as high-capacity cathode for aqueous zinc-ion batteries

Aqueous zinc-ion batteries (ZIBs) are receiving considerable research highlights owing to their high safety and environment-friendliness. To implement this promising technology for grid-scale energy storage, effective cathode materials with high capacity, cycle stability, and electrochemical kinetics should be developed. Herein, the synthesis of uniquely structured porous VN-reduced graphene oxide composite (VN-rGO) microspheres through a facile spray pyrolysis process and their application as cathodes for ZIBs are introduced. The electrochemical reaction mechanism of VN-rGO microspheres with zinc ions is investigated through various in situ and ex situ analyses. During the initial charge process, VN phase transforms into the Zn3(OH)2V2O7·2H2O (ZVOH) phase. From the second cycle and on, the ZVOH phase undergoes zinc-ion ingress and egress processes. VN-rGO microspheres exhibit an unprecedented high capacity (809 mA h g−1 at 0.1 A g−1), high energy density (613 W h kg−1), and good rate capability (467 mA h g−1 at 2.0 A g−1). The cathode delivers a reversible capacity of 445 mA h g−1 after 400 cycles at 1.0 A g−1, which ascertains the robustness of the structure. The 3D porous rGO matrix to which VN nanocrystals are homogenously anchored accelerates the zinc-ion storage kinetics and endows the cathode with structural robustness.

Two-Birds-One-Stone: Tuning the Aggregation Structure and Chemical Composition of Reduced Graphene Oxide Microspheres with Nacl

Two-Birds-One-Stone: Tuning the Aggregation Structure and Chemical Composition of Reduced Graphene Oxide Microspheres with Nacl

Oil-Water Separation Performance of Electrospray Reduced Graphene Oxide Microspheres with a Local Radially Aligned and Porous Structure

Oil-Water Separation Performance of Electrospray Reduced Graphene Oxide Microspheres with a Local Radially Aligned and Porous Structure

Mulberry-like hollow rGO microspheres decorated with CoO nanoparticles as efficient polysulfides anchoring for Li-S batteries

Lithium-sulfur batteries (LSB) became recently one of the most promising next-generation energy storage devices due to their high energy density and low cost. However, its large-scale commercial application is hindered by severe shuttle-effect and insulation of the sulfur. Herein, in order to overcome these disadvantages, mulberry-like three-dimensional hollow reduced graphene oxide microspheres modified with cobalt oxide nanoparticles (CoO/MGra) were designed as sulfur host. CoO/MGra possesses not only excellent electrical conductivity but also provides sufficiently large space for the storage of sulfur. The three-dimensional hollow structures can also significantly alleviate the volume expansion of sulfur during the cycling process. At the same time, the shuttle effect is suppressed due to the efficient chemical adsorption towards lithium polysulfide by CoO nanoparticles. As a result, excellent cycle stability (1010 mAh g−1 after 150 cycles at 0.2C) and outstanding rate performance (745 mAh g−1 at 3C) are achieved when using the S-CoO/MGra cathode.

Hollow Graphene-Based Microspheres Adsorbents for Removal of Gaseous Formaldehyde

Two type of hollow graphene microspheres were investigated for the adsorption performance of gaseous formaldehyde. Hollow gently reduced graphene oxide microspheres (HgRGOS) were synthesized by using the polystyrene microspheres as sacrificial template and gently reducing graphene oxide with NH2NH2. Hollow amine modified graphene microspheres (DETA-HgRGOS) were synthesized by DETA-treatment following the before-mentioned steps. The materials were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffractometry, Fourier transform infrared and X-ray photoelectron spectroscopies. This was followed by formaldehyde adsorption tests. The results showed that HgRGOS and DETA-HgRGOS were characterized to have adsorption capacities of 24.54 and 17.18 mg/g. The amine-modified material can interacts with HCHO more easily than the material eith carboxyl and epoxy groups on the surface. The reaction mechanism was discussed according to FTIR and XPS analysis.

Self-Assembly of Antisite Defectless nano-LiFePO4 @C/Reduced Graphene Oxide Microspheres for High-Performance Lithium-Ion Batteries.

LiFePO4 @C/reduced graphene oxide (rGO) hierarchical microspheres with superior electrochemical activity and a high tap density were first synthesized by using a Fe3+ -based single inorganic precursor (LiFePO4 OH@RF/GO; RF=resorcinol-formaldehyde, GO=graphene oxide) obtained from a template-free self-assembly synthesis followed by direct calcination. The synthetic process requires no physical mixing step. The phase transformation pathway from tavorite LiFePO4 OH to olivine LiFePO4 upon calcination was determined by means of the in situ high-temperature XRD technique. Benefitting from the unique structure of the material, these microspheres can be densely packed together, giving a high tap density of 1.3 g cm-3 , and simultaneously, defectless LiFePO4 primary nanocrystals modified with a highly conductive surface carbon layer and ultrathin rGO provide good electronic and ionic kinetics for fast electron/Li+ ion transport.

Size-controlled synthesis of urchin-like reduced graphene oxide microspheres with highly packed density by emulsion-assisted in-situ assembly and their supercapacitor performance

We report a facile water-in-oil (W/O) emulsion method to fabricate urchin-like reduced graphene oxide microspheres (UrGOMSs) with tunable sizes and structures. The success of this synthesis relies on the use of polyethyleneimine and ethylenediamine, acted as an emulsifier and weak crosslinker, respectively, to assist the formation of graphene hydrogel in emulsion droplets, followed by thermal treatment to remove the water. The diameter of the UrGOMSs could be controlled in the range of 2.30–4.58 μm by varying the water-oil ratio and thus the size of emulsion droplets. The UrGOMSs show crumpled surface and urchin-like structure with assembly of graphene nanosheets, which can supply large amount of accessible surface area and efficient ion diffusion pathways. The specific surface area of the structures is up to 356.33 m2 g−1 with high pack density of 1.37 g cm−3. When used as electrode materials in supercapacitors, the UrGOMSs exhibit high volumetric capacitance of 527.6 F cm−3 at 10 mV s−1 and 452.1 F cm−3 at 0.2 A g−1. Furthermore, they also exhibit excellent long-term cycling stability. After 5000 cycles, the capacity retention is around 99.43%. These results indicate the feasibility of the novel strategy for designing densely assembled graphene microspheres for supercapacitors.

3D graphene-Ni microspheres with excellent microwave absorption and corrosion resistance properties

In this study, we report a simple and efficient two-step method consisting of water-in-oil (W/O) emulsion technique and subsequent annealing process for synthesizing the hollow reduced graphene oxide microspheres embedded with Ni nanoparticles (Air@rGO€Ni). The microspheres showed good electromagnetic properties because of the coexistence of magnetic loss and dielectric loss to microwaves. The minimum reflection loss (RLmin) value of Air@rGO€Ni microsphere reaches up to − 59.7 dB at 11.6 GHz with a thickness of 2.7 mm and an absorption bandwidth (lower than − 10 dB) is 4.8 GHz (9.4–14.2 GHz). Their resistance to chemical corrosion is amazingly, after treatment in hydrochloric acid for 5 days, the saturation magnetization (Ms) values of Air@rGO€Ni microsphere has fallen only six percentage points. More interestingly, we can easily controll the microwave absorbing properties of the microspheres by changing the ratio of the two components in the composites. The unique 3D structure and excellent electromagnetic match at the corresponding resonance peaks for dielectric and magnetic loss play an important role in improving microwave absorption property. Our study provides a good potential method for preparation of lightweight microwave absorbing materials.

Self-assembly of ternary hollow microspheres with strong wideband microwave absorption and controllable microwave absorption properties

In this study, we report a simple and efficient two-step method consisting of water-in-oil (W/O) emulsion technique and subsequent annealing process for synthesizing the hollow reduced graphene oxide microspheres embedded with Co nanoparticles (Air@rGO€Co). The microspheres showed good electromagnetic properties because of the coexistence of magnetic loss and dielectric loss to microwaves. The minimum reflection loss (RLmin) value of S1.5 reaches −68.1 dB at 13.8 GHz with a thickness of 2.2 mm, and the absorption bandwidth (lower than −10 dB) is 7.1 GHz covering from 10.9 GHz to 18.0 GHz. More interestingly, we can easily controll the microwave absorbing properties of the microspheres by changing the ratio of the two components in the composites. The excellent electromagnetic match at the corresponding resonance peaks for dielectric and magnetic loss play an important role in improving microwave absorption property. Our study provides a good potential method for preparation of lightweight microwave absorbing materials.

Facile Synthesis of Mesoporous Reduced Graphene Oxide Microspheres with Well-Distributed Fe2O3 Nanoparticles for Photochemical Catalysis

In this study, we report the fabrication of hollow reduced graphene oxide microspheres with well-distributed Fe2O3 nanoparticles (Fe-rGOS) via a spray-drying methodology. l-Ascorbic acid was employed to reduce graphite oxide (GO) and improve velocity of electrons transfer. Because of l-ascorbic acid and the spray-drying procedure, the in situ Fe2O3 nanoparticles with a mean size of 5–10 nm were uniformly deposited on rGO support and the rGO migrated to the surface of the drop to form microspheres. The well dispersed nanoparticles not only generated more active sites and interface contact which was beneficial to enhance the stability of catalysts but also acted as pillars between the rGO layers to achieve mesoporous structure. The formed mesoporous frameworks enhanced mass transfer to a large extent and led to the much better catalytic efficiency. Therefore, the prepared Fe-rGOS exhibited a remarkable photocatalytic activity in a wide pH range and superior recyclability with low leaching of iron ions.

Hollow TiO2 modified reduced graphene oxide microspheres encapsulating hemoglobin for a mediator-free biosensor

Hollow TiO2 modified reduced graphene oxide microspheres (hollow TiO2-rGO microspheres or H-TiO2-rGO MS) have been synthesized and then be used to immobilize hemoglobin (Hb) to fabricate a mediator-free biosensor. The morphology and structure of hollow TiO2-rGO microspheres were characterized by scanning electron microscopy, transmission electronic microscopy and X-ray diffraction. Results of spectroscopy and electrochemistry tests revealed that hollow TiO2-rGO microsphere is an excellent immobilization matrix with biocompatibility for redox protein, affording good protein bioactivity and stability. The hollow TiO2-rGO microspheres with special structure and component enhance the immobilization efficiency of proteins and facilitate the direct electron transfer, which result in the better H2O2 detection performance-the wide linear range of 0.1–360μM for H2O2 (sensitivity of 417.6 μA mM−1 cm−2) and the extremely low detection limit of 10nM for H2O2. Moreover, the hollow microsphere can provide a protective microenvironment for Hb to make the as-prepared biosensor improve long-term stability. The as-prepared biosensor retains 95.4% of the initial response to H2O2 after 60-d storage. Hence, this work suggests that if can be fabricated a mediator-free biosensor, hollow TiO2-rGO microspheres will find wide potential applications in environmental analysis and biomedical detection.

Capacitive properties of reduced graphene oxide microspheres with uniformly dispersed nickel sulfide nanocrystals prepared by spray pyrolysis

Nickel sulfide-reduced graphene oxide (RGO) composite powders with spherical shapes are prepared by a one-pot spray pyrolysis process. The optimum mole ratio of nickel nitrate and thiourea to obtain nickel sulfide–RGO composite powders with high initial capacities and good cycling performance is 1:8. The bare nickel sulfide and nickel sulfide–RGO composite powders prepared directly by spray pyrolysis have mixed crystal structures of hexagonal α-NiS and cubic Ni3S4 phases. The bare nickel sulfide powders are prepared from the spray solution without graphene oxide sheets. The nickel sulfide–RGO composite powders have sharp mesopores approximately 3.5nm in size. The discharge capacities of the nickel sulfide–RGO composite powders for the 1st and 200th cycles at a current density of 1000mAg−1 are 1046 and 614mAhg−1, respectively, and the corresponding capacity retention measured from the second cycle is 89%. However, the discharge capacities of the bare nickel sulfide powders for the 1st and 200th cycles at a current density of 1000mAg−1 are 832 and 16mAhg−1, respectively. The electrochemical impedance spectroscopy (EIS) measurements reveal the high structural stability of the nickel sulfide–RGO composite powders during cycling.

Sodium ion storage properties of WS₂-decorated three-dimensional reduced graphene oxide microspheres.

Layered WS2 nanosheet-decorated three-dimensional reduced graphene oxide (3D-RGO) microspheres are prepared as anode materials for sodium ion batteries. WO3 nanocluster-decorated 3D RGO microspheres are transformed into multi-layered WS2-3D RGO microspheres by a simple sulfidation process. The WS2-3D RGO microspheres show Na(+) storage properties superior to those of the WO3-3D RGO microspheres.

Hollow reduced graphene oxide microspheres as a high-performance anode material for Li-ion batteries

Hollow reduced graphene oxide (RGO) microspheres are successfully synthesized in large quantities through spray-drying suspension of graphene oxide (GO) nanosheets and subsequent carbothermal reduction. With this new procedure, blighted-microspherical GO precursor is synthesized through the process of spray drying, afterwards the GO precursor is subsequently calcined at 800°C for 5h to obtain hollow RGO microspheres. A series of analyses, such as X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM) and Fourier transform infrared spectroscopy (FTIR) are performed to characterize the structure and morphology of intermediates and as-obtained product. The as-obtained hollow RGO microspheres provide a high specific surface area (175.5 m2g−1) and excellent electronic conductivity (6.3 S cm−1), and facilitated high electrochemical performance as anode material for Li-ion batteries (LIBs). Compared with the RGO nanosheets, the as-obtained hollow RGO microspheres exhibit superior specific capacity and outstanding cyclability. In addition, this spray drying and carbothermal reduction (SDCTR) method provided a facile route to prepare hollow RGO microspheres in large quantities.