Hierarchical Reduced Graphene Oxide Research Articles

Engineering a hierarchical reduced graphene oxide and lignosulfonate derived carbon framework supported tin dioxide nanocomposite for lithium-ion storage

Tin dioxide (SnO2) is widely recognized as a high-performance anode material for lithium-ion batteries. To simultaneously achieve satisfactory electrochemical performances and lower manufacturing costs, engineering nano-sized SnO2 and further immobilizing SnO2 with supportive carbon frameworks via eco-friendly and cost-effective approaches are challenging tasks. In this work, biomass sodium lignosulfonate (LS-Na), stannous chloride (SnCl2) and a small amount of few-layered graphene oxide (GO) are employed as raw materials to engineer a hierarchical carbon framework supported SnO2 nanocomposite. The spontaneous chelation reaction between LS-Na and SnCl2 under mild hydrothermal condition generates the corresponding SnCl2@LS sample with a uniform distribution of Sn2+ in the LS domains, and the SnCl2@LS sample is further dispersed by GO sheets via a redox coprecipitation reaction. After a thermal treatment, the SnCl2@LS@GO sample is converted to the final SnO2/LSC/RGO sample with an improved microstructure. The SnO2/LSC/RGO nanocomposite exhibits excellent lithium-ion storage performances with a high specific capacity of 938.3 mAh/g after 600 cycles at 1000 mA g−1 in half-cells and 517.1 mAh/g after 50 cycles at 200 mA g−1 in full-cells. This work provides a potential strategy of engineering biomass derived high-performance electrode materials for rechargeable batteries.

Fabrication of hierarchical reduced graphene oxide decorated with core-shell Fe3O4@polypyrrole heterostructures for excellent electromagnetic wave absorption

The design of heterostructures with reasonable chemical composition and spatial structure is one of the effective strategies to achieve high performances electromagnetic wave (EMW) absorption. Herein, reduced graphene oxide (rGO) nanosheets decorated with hollow core–shell Fe3O4@PPy (FP) microspheres have been prepared by the combination of hydrothermal method, in situ polymerization method, directional freeze-drying and hydrazine vapor reduction. FP acting as traps can consume EMW trapped into their interior through the magnetic and dielectric losses. RGO nanosheets forming the conductive network are served as multi-reflected layers. Moreover, the impedance matching is optimized by the synergistic effect between FP and rGO. As expected, the synthetic Fe3O4@PPy/rGO (FPG) composite shows excellent EMW absorption performances with the minimum reflect loss (RLmin) of −61.20 dB at 1.89 mm and the effective absorption bandwidth (EAB) of 5.26 GHz at 1.71 mm. The excellent performances for the heterostructure are attributed to the synergistic effect of conductive loss, dielectric loss, magnetic loss, multiple reflection loss, and optimized impedance matching. This work provides a simple and effective strategy for the fabrication of lightweight, thin and high-performances EMW absorbing materials.

Highly dispersed active sites of Ni nanoparticles onto hierarchical reduced graphene oxide architecture towards efficient water oxidation

Herein, we reported a facile route to fabricate the Ni-NPs decorated over reduced graphene oxide (Ni/rGO) nanocomposite by an in-situ reduction method. It has been observed that the Ni/rGO drived the water oxidation at a very low overpotential of 1.42 VRHE (ŋ = 190 mV). Furthermore, the robust catalyst presented an extraordinary porosity and imperious kinetics performance while showing a high time of flight (0.2 s−1), mass activity (28 A/g) and smaller value of Tafel slope (62 mVdec−1) at an applied potential of 0.35 VRHE only. Ni/rGO also exhibited stable current density which leftovers sustained in alkaline water catalysis conducted for a prolonged time without any significant loss in catalytic efficiency. This outstanding catalytic activity of hierarchical Ni/rGO is comparable to avant-garde electrocatalytic material and even much better than the noble and transitional metal-centred eensy-weensy electrocatalytic assemblies with several drawbacks.

Spray drying induced engineering a hierarchical reduced graphene oxide supported heterogeneous Tin dioxide and Zinc oxide for Lithium-ion storage

In this work, a hierarchical reduced graphene oxide (RGO) supportive matrix consisting of both larger two-dimensional RGO sheets and smaller three-dimensional RGO spheres was engineered with ZnO and SnO2 nanoparticles immobilized. The ZnO and SnO2 nanocrystals with controlled size were in sequence engineered on the surface of the RGO sheets during the deoxygenation of graphene oxide sample (GO), where the zinc-containing ZIF-8 sample and metal tin foil were used as precursors for ZnO and SnO2, respectively. After a spray drying treatment and calcination, the final ZnO@SnO2/RGO-H sample was obtained, which delivered an outstanding specific capacity of 982 mAh·g−1 under a high current density of 1000 mA·g−1 after 450 cycles. Benefitting from the unique hierarchical structure, the mechanical strength, ionic and electric conductivities of the ZnO@SnO2/RGO-H sample have been simultaneously promoted. The joint contributions from pseudocapacitive and battery behaviors in lithium-ion storage processes bring in both large specific capacity and good rate capability. The industrially mature spray drying method for synthesizing RGO based hierarchical products can be further developed for wider applications.

Graphene Aerogels with Ultrahigh Pore Volume for Organic Dye Adsorption and High-Energy Lithium Batteries

Three-dimensional (3D) hierarchical reduced graphene oxide (rGO) aerogel with a finely tuned C/O ratio of 11.8 can be used for various applications because of its high specific surface area (925.27...

Electrocatalytic polysulfide transformation for suppressing the shuttle effect of Li-S batteries

We report a method based on 2,4-dihydroxybenzoic acid-formaldehyde (RF-COOH) microsphere hard templates to prepare core-shelled Fe2O3 microspheres, which were then added to graphene oxide to obtain hierarchical reduced graphene oxide, ultimately dropping Fe2O3 (Fe2O3@rGO) by Vitamin C reduction and freeze drying. When used as cathode materials for lithium-sulfur batteries, Fe2O3@rGO shows a high specific capacity of 400.5 mAh g−1 at 2 C after 500 cycles. The prominent performance is due to the collaborative assembly of rGO, which provides stablestructural support and favourable conductivity, and core-shelled Fe2O3 microspheres, which are certified to have a strong interaction with polysulfides. Theloose and stable skeletons of highly electroconductive rGO can offer a conductive framework for rapid ion/electron transport. Meanwhile, the unique core-shelled structure of Fe2O3 with the ample void space can anchor polysulfides through the strong chemical adsorption and buffer the mechanical stresses caused by volume expansion during the charge and discharge processes. Moreover, Fe2O3 promotes the transformation of polysulfides to insoluble LiPSs during the discharging process, effectivelyalleviating the shuttling of the polysulfides.

Hierarchical Reduced Graphene Oxide Ridges for Stretchable, Wearable, and Washable Strain Sensors.

Recently, flexible and wearable devices are increasingly in demand and graphene has been widely used due to its exceptional chemical, mechanical and electrical properties. Building complex buckling patterns of graphene is an essential strategy to increase its flexible and stretchable properties. Herein, a facile dimensionally controlled four-dimensional (4D) shrinking method was proposed to generate hierarchical reduced graphene oxide (rGO) buckling patterns on curved substrates mimicking different parts of the uniforms. The reduced graphene oxide ridges (rGORs) generated on the spherical substrate seem isotropic, while those generated on the cylindrical substrate are obviously more hierarchical or oriented, especially when the cylindrical substrate are shrinking via two steps. The oriented rGORs are superhydrophobic and strain sensitive but obviously anisotropic along the axial and circumferential directions. The sensitivity of rGORs along the axial direction is much higher than those along the circumferential direction. In addition, the intrinsic solvent barrier property of graphene enables the crack-free rGORs an excellent chemical protective performance, withstanding DCM immersion for more than 2.5 h. The flexible rGORs-based strain sensors can be used to detect both large and subtle human motions and activities by achieving high sensitivity (maximum gauge factor up to 48), high unidirectional stretchability (300-530%), and ultrahigh areal stretchability (up to 2690%). Excellent durability was also demonstrated for human motion monitoring with resistance to hand rubbing, ultrasonic cleaning, machine washing, and chemical immersion.

Three-Dimensional Hierarchical Architecture of the TiO2/Ti3C2Tx/RGO Ternary Composite Aerogel for Enhanced Electromagnetic Wave Absorption

Tunable and high-efficiency electromagnetic wave (EMW) absorption materials composed of a three-dimensional (3D) hierarchical reduced graphene oxide (RGO) aerogel network entrapped with TiO2/Ti3C2Tx hybrids were fabricated by a hydrothermal method and a mild chemical reduction treatment. The incorporation of the TiO2/Ti3C2Tx micronanoheterostructure and construction of the 3D well-designed hierarchical interconnected network can significantly reduce the agglomeration of RGO sheets together with the beneficial effect of a better impedance match. When the filler loading is 10 wt %, the maximum reflection loss of the composite aerogel reaches up to −65.3 dB with a matching thickness of 2.5 mm. Meanwhile, the effective absorption bandwidth (RL < −10 dB) is 4.3 GHz with the coating thickness of only 2.0 mm, and the tunable absorption bandwidth achieves at 13.74 GHz via modulating the absorber thicknesses in a range from 1.5 to 5.0 mm. The enhanced EMW absorbing performance is closely related to highly porous c...

3D superhydrophobic reduced graphene oxide for activated NO2 sensing with enhanced immunity to humidity

3D SPS-synthesized, superhydrophobic and hierarchical reduced graphene oxide is exploited for high-performance NO2 detection with good immunity to humidity.

Hierarchical reduced graphene oxide supported dealloyed platinum–copper nanoparticles for highly efficient methanol electrooxidation

Exploiting highly efficient electrocatalysts through simple methods is very critical to the development of energy conversion technologies. Herein, we develop a hierarchical reduced graphene oxide supported dealloyed platinum–copper nanoparticle catalyst (Pt–Cu/RGO) by a facile one-step electrodeposition of graphene oxide in the presence of H2PtCl6 and copper ethylenediamine tetraacetate. The nanostructure and composition were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and Raman spectroscopy. Meanwhile, the electrocatalytic performance was investigated by cyclic voltammetry and chronoamperometry, showing that the Pt–Cu/RGO catalyst not only equips with an outstanding electrocatalytic activity for the methanol oxidation reaction (2.3 times that of commercial Pt/C catalyst), but also shows a robust durability and superior tolerance to CO poisoning. The excellent electrocatalytic performance could be attributed to the three-dimensional hierarchical structure, porous dealloyed nanoparticles and synergistic effect between each component.

Three-dimensional reduced graphene oxide foam modified with ZnO nanowires for enhanced microwave absorption properties

Flexible and high-performance electromagnetic absorbing materials of three-dimensional (3D) hierarchical reduced graphene oxide (RGO) foams decorated with in-situ grown ZnO nanowires (ZnOnws) were realized by a direct freeze-drying and hydrothermal process. The unique structure not only effectively reduces agglomeration of RGO and the density of composites, but also makes great contributions to impedance match, dielectric loss and inner scattering, achieving enhanced microwave absorption performance. When RGO foam is 0.8 mg/mL, the ZnOnws/RGO foam/PDMS composite with 3.3 wt% absorber loading attains a minimum reflection loss value of −27.8 dB at 9.57 GHz with a thickness of 4.8 mm, and a wide effective absorption bandwidth of 4.2 GHz covering the whole X band (8.2–12.4 GHz). The fundamental microwave absorption mechanism of the composites is discussed. These results demonstrate a promising method to fabricate an economical, lightweight, broadband and highly efficient microwave absorption material.

Surface and Interface Engineering of Graphene Oxide Films by Controllable Photoreduction.

We report herein the engineering of the surface/interface properties of graphene oxide (GO) films by controllable photoreduction treatment. In our recent works, typical photoreduction processes, including femtosecond laser direct writing (FsLDW), laser holographic lithography, and controllable UV irradiation, have been employed to make conductive reduced graphene oxide (RGO) microcircuits, hierarchical RGO micro-nanostructures with both superhydrophobicity and structural color, as well as moisture-responsive GO/RGO bilayer structures. Compared with other reduction protocols, for instance, chemical reduction and thermal annealing, the photoreduction strategy shows distinct advantages, such as mask-free patterning, chemical-free modification, controllable reduction degree, and environmentally friendly processing. These works indicate that the surface and interface engineering of GO through controllable photoreduction of GO holds great promise for the development of various graphene-based microdevices.

The confinement of SnO2nanocrystals into 3D RGO architectures for improved rate and cyclic performance of LIB anode

In this study, we demonstrate the synthesis of a composite with SnO2 nanoparticles anchored on three-dimensional (3D) reduced graphene oxide (RGO) as an anode for Li ion batteries (LIBs). SnO2 nanoparticles were uniformly deposited on the surface of RGO sheets and the resulting RGO–SnO2 architecture had an interconnected hierarchical structure. This hierarchical RGO–SnO2 architecture exhibited outstanding electrochemical performance with a high reversible capacity of 810 mAh g−1 at 0.1 A g−1 and a high rate capacity of 210 mAh g−1 at 2 A g−1. Moreover, this architecture achieves 99% capacity retention even after 150 cycles at 0.1 A g−1. The improved performance of the RGO–SnO2 architecture is attributed to the uniform dispersion of SnO2 nanoparticles and the 3D macroporous continuity, which afford a highly accessible area, easy ion accessibility, a short ion diffusion length, and rapid mass and charge transport. The composite described here is practically useful in the development of high-energy-density anode materials for LIBs.

Superhydrophobic SERS Substrates Based on Silver-Coated Reduced Graphene Oxide Gratings Prepared by Two-Beam Laser Interference

Reported here is the fabrication of reduced graphene oxide (RGO) grating structures by two-beam laser interference (TBLI) for the development of highly efficient SERS substrates via simple physical vapor deposition (PVD) coating of silver. TBLI has been utilized to make hierarchical RGO grating structures with microscale gratings and nanoscale folders through a laser treatment induced ablation and photoreduction process. The hierarchical structures contribute to the formation of plasmonic structures after silver coating, giving rise to the formation of plenty of SERS "hot spots", while the RGO substrate would provide chemical enhancement of Raman signal through interaction with analytes molecules. The significantly increased roughness with respect to the hierarchical structures in combination with the removal of hydrophilic oxygen-containing groups endow the resultant substrates with unique superhydrophobicity, which leads to the enrichment of analytes and further lowers the detection limit. The synergistic effects make the silver coated RGO gratings a highly efficient SERS substrate; in the detection of Rhodamine B, our SERS substrates showed high SERS enhancement and good reproducibility, a detection limit of 10(-10) M has been achieved.

In situ growth of Bi2MoO6on reduced graphene oxide nanosheets for improved visible-light photocatalytic activity

A series of hierarchical reduced graphene oxide (RGO)–Bi2MoO6 composites were fabricated via a facile solvothermal route. In the reaction process, Bi2MoO6 nanoflakes were in situ grown on the graphene oxide (GO) nanosheets. Meanwhile, GO was reduced during the solvothermal reaction. Such a synthetic strategy can form effective interfacial contact and strong interaction between Bi2MoO6 nanoflakes and RGO nanosheets, which can facilitate the transfer of photogenerated charge and hence reduce the recombination rate of excited carriers. The enhanced charge transfer properties were proved by surface photovoltage spectroscopy (SPV) and photoluminescence (PL) measurements. The obtained hierarchical RGO–Bi2MoO6 composites showed more significant visible light photoactivity for the degradation of rhodamine B than single Bi2MoO6 and a mechanical mixture of RGO and Bi2MoO6. The enhanced photocatalytic performance could be attributed to the synergistic effect of improved electron–hole pair separation, boosted catalytic active sites and light harvesting.

Improved kinetics of LiNi1/3Mn1/3Co1/3O2 cathode material through reduced graphene oxide networks

An electronically conducting 3D network of reduced graphene oxide (RGO) was introduced into LiNi(1/3)Mn(1/3)Co(1/3)O(2) (LNMC) cathode material in a special nano/micro hierarchical structure. The rate test and cycling measurement showed that the hierarchical networks remarkably improve the high rate performance of LNMC electrode for lithium-ion batteries. The effect of RGO conducting networks on kinetic property was investigated by electrochemical impedance spectroscopy (EIS) and potentiostatic intermittent titration (PITT). The EIS results reveal that the RGO network greatly decreases the resistance of lithium batteries, especially the charge transfer resistance which can be attributed to the significantly improved conducting networks. The enhancement of apparent diffusion coefficient by the RGO conducting networks is shown by PITT. The power performance was found to be limited by the electrical conduction in the two-phase region, which can be greatly facilitated by the hierarchical RGO network together with carbon black. The as-obtained LNMC/RGO cathode exhibits an outstanding electrochemical property supporting the design idea of electronically conducting 3D networks for the high-energy and high-power lithium-ion batteries.