rGO Modification Research Articles

Hydrothermal Synthesis of (NH4)2V7O16/Reduced Graphene Oxide Composite with Enhanced Storage Performance for Aqueous Lithium‐Ion Batteries

Herein, a facile hydrothermal method is utilized to prepare a (NH4)2V7O16/reduced graphene oxide (rGO) composite. In an aqueous electrolyte, the obtained (NH4)2V7O16/rGO exhibits superior lithium storage characteristics compared to pure (NH4)2V7O16 in both the three‐electrode configuration and full cell. This improvement can be ascribed to the synergistic effects of incorporation of defective oxygen and rGO modification. The present study proposes a feasible strategy for enhancing the electrochemical properties of (NH4)2V7O16 and demonstrates the potential of the (NH4)2V7O16/rGO composite for aqueous rechargeable lithium‐ion batteries.

An electrochemical sensor based on rGO/GaN nanowires for Pb(II) determination

In this work, rGO/GaN nanowires electrochemical sensors were fabricated on sapphire substrates by metal organic chemical vapor deposition (MOCVD) and electrodeposition method, and it was used for the detection of Pb2+ in water. Reduced graphene oxide (rGO) increases the specific surface area and active sites of gallium nitride nanowires (GaN NW), and GaN NW improves the stability of the rGO, thus a highly sensitive electrochemical sensor was established. Square wave anodic stripping voltammetry (SWASV) was used to detect Pb2+. Effects of experimental conditions such as rGO modification amount, pH, Pb2+ deposition potential/time on the detection performance were investigated. With optimized detection conditions, the rGO/GaN NW sensor features high sensitivity (0.7362 μA μg-1 L) in the linear range of 2.5-200 μg L-1, and the detection limit was 2.5 μg L-1. Furthermore, the rGO/GaN NW sensor exhibited a good stability and repeatability.

Janus biomass aerogel for Highly-Efficient steam Generation, Desalination, degradation of organics and water disinfection

Solar-driven water purification has been deemed as a cheap, green and renewable technology to mitigate water shortage and pollution. Herein, a biomass aerogel with hydrophilic-hydrophobic Janus structure has been prepared as solar water evaporator, which is achieved by partially modifying hydrothermal-treated loofah sponge (HLS) with reduced graphene oxide (rGO). It's a rare design philosophy that HLS serves as a substrate with large pores and hydrophilic properties to ensure continuous and effective water transport, and the hydrophobic layer with rGO modification guarantees good salt resistance in seawater desalination with high photothermal conversion efficiency. As a result, the obtained Janus aerogel, p-HLS@rGO-12, exhibits impressive solar-driven evaporation rates of 1.75 kg m-2h−1 and 1.54 kg m-2h−1 for pure water and seawater respectively, with good cycling stability in the evaporation process. Furthermore, p-HLS@rGO-12 also demonstrates outstanding photothermal degradation of rhodamine B (greater than98.8 % in 2 h) and sterilization of E. coli (nearly 100 % in 2 h). This work offers an unusual approach to achieve highly efficient solar-driven steam generation, seawater desalination, organic pollutant degradation, and water disinfection simultaneously. The prepared Janus biomass aerogel holds great potential application in the field of seawater desalination and wastewater purification.

3D Double‐Crosslinked Polyaniline/p‐Phenylenediamine‐Modified Graphene Free‐Standing Electrodes for High‐Performance Supercapacitors

The free‐standing electrodes are important for high‐performance supercapacitors. Polyaniline/graphene (PANI/rGO) composites are extensively researched. However, the structural design of free‐standing PANI/rGO electrodes needs further discussion. Herein, free‐standing PANI/rGO with 3D double‐crosslinked network structures is prepared by rGO modification, freeze drying, in situ polymerization, and gel die‐casting technology. The uniform precipitation of the ammonium persulfate on the surface of modified graphene (P‐rGO) sheets is profit to build a 3D double‐crosslinked network structure with PANI. Besides, the synergistic effect of aniline and p‐phenylenediamine helps to construct crosslinked PANI on the surface and deep in the pores of P‐rGO. The PANI/P‐rGO aerogels with a 3D porous double‐crosslinked structure are pressed into free‐standing electrodes by gel die casting and assembled into symmetrical supercapacitors. The electrodes show good cycling stability, which is much higher than that of P‐rGO or pure PANI.

Al-doping driven electronic structure of α-NiS hollow spheres modified by rGO as high-rate electrode for quasi-solid-state capacitor

Developing an optimized electronic structure of α-NiS electrode material is critical for its high-rate electrochemical performance of quasi-solid-state capacitor. Herein, Al3+ have been doped into α-NiS lattice and the reduced graphene oxide (rGO) is employed to modify Al-doping α-NiS, to alleviate the low-mobility charge of α-NiS. The electronic structure and electrochemical properties of α-NiS hollow spheres induced by Al-doping and rGO modification are investigated, both experimental characterization and theoretical results confirm Al-doping affect the electronic structure and electrochemical performance of α-NiS hollow spheres. In the composite of Al-doping α-NiS and rGO (named as AlxNi1-xS/rGO), the doped heteroatom improves the intrinsic electronic structure of α-NiS and the rGO provides a good electric conducting network, leading to an enhanced electrochemical performance of α-NiS as high-rate electrode material. After evaluation, the optimized Al0.2Ni0.8S/rGO composite shows a superior reversible capacity of 1096 C g−1 at 2 A g−1, and retains a capability of 471 C g−1 at a high-rate of 30 A g−1. Moreover, an asymmetric quasi-solid-state hybrid capacitors assembled by Al0.2Ni0.8S/rGO and activated carbon presents a high energy density of 30.6 Wh kg−1. This work provides a foundational strategy for the modification of α-NiS through Al-doping and combining with rGO, which has a positive effect on α-NiS electrode material in quasi-solid-state hybrid capacitors.

Reduced Graphene Oxide Overlayer on Copper Nanocube Electrodes Steers the Selectivity Towards Ethanol in Electrochemical Reduction of Carbon Dioxide

AbstractDeveloping copper‐based electrocatalysts that favor high‐value multi‐carbon oxygenates is desired, given their use as platform chemicals and as a direct fuel for transportation. Combining a CO‐selective catalyst with copper shifts the selectivity of CO2 electroreduction toward C2 products. Herein, we developed a reduced graphene oxide (rGO)‐modified copper nanocube electrocatalyst that could shift the selectivity of CO2 electroreduction towards ethanol (Faradaic efficiency 76. 84 % at −0.9 V vs. reversible hydrogen electrode (RHE)). Spectroelectrochemical Raman analysis reveals a higher population of *C2HxOy intermediates at −0.9 V vs. RHE on the rGO‐modified copper nanocube electrocatalyst surface, which coincides with the highest faradaic efficiency of ethanol upon CO2 electroreduction at the same potential. Our results demonstrate that the rGO modification can enhance ethanol selectivity through a probable tandem electrocatalysis mechanism and provide insights into controlling electrocatalytic activity and product selectivity in the CO2 electroreduction reaction.

Enhanced Gas Sensing Performance of rGO Wrapped Crystal Facet-Controlled Co3O4 Nanocomposite Heterostructures

Crystal facet engineering and graphene modification are both effective means to improve the gas sensing performance of metal oxide semiconductors (MOSs) currently. However, research on the crystal facet effect and synergistic effect of graphene modification of p-type MOS sensors is relatively lacking. Here, p-type Co3O4 nanocrystals with controlled crystal facets ({112} and {100}) were in situ wrapped in the two-dimensional (2D) nanosheet network of graphene. It was found that bare {112} facets showed a significantly higher triethylamine sensing performance than {100} facets, implying a strong crystal facet effect. Interestingly, the triethylamine sensing performance of {112} facets was significantly improved after rGO modification, while the performance improvement of Co3O4 {100} was limited after rGO modification. Further study suggested that {112} facets contained more active Co3+ species and chemically adsorbed oxygen species than {100} facets, which promoted the adsorption of triethylamine and the subsequent sensing reaction. In addition, the strong electronic interaction between Co3O4 {112} crystal facets and rGO promoted efficient charge exchange through the heterogeneous interface. This work provides a new way to improve the gas sensing performance of Co3O4 through the synergistic effect of crystal facet engineering and graphene modification.

Red mud supported on reduced graphene oxide as photo-Fenton catalysts for organic contaminant degradation

In this study, the reduced graphene oxide (rGO) modified red mud (RM) composite was successfully prepared and used as the highly effective heterogeneous photo-Fenton catalyst for Rhodamine B (RhB) contaminant degradation. The acid leaching and calcination treatment reduced the impurities in RM, making α-Fe2O3 active for H2O2 decomposing. The rGO modification can not only inhibit the recombination of charge carriers but also accelerate the Fe3+/Fe2+ cycle during heterogenous Fenton process. Attributed to such advantages, 99.8% degradation of RhB within 20 min was achieved by the optimal RM-H/rGO composite. More importantly, the prepared RM-H/rGO showed excellent performance and high stability for various organic contaminants degradation at a wide pH range. This study not only demonstrates that rGO-modified RM can be used as an efficient, low-cost photo-Fenton catalyst for organic pollutants treatment, but also provides an effective approach for RM disposal.

ZnO/BiFeO3 heterojunction interface modulation and rGO modification for detection of triethylamine

A novel 9ZBFO/rGO(1 wt%) composite exhibits excellent gas sensor performance, which is attributed to heterojunction interface modulation and rGO modification.

Influence of rGO and Preparation Method on the Physicochemical and Photocatalytic Properties of TiO2/Reduced Graphene Oxide Photocatalysts

In this study, a series of TiO2/rGO photocatalysts were obtained with a two-step procedure: a solvothermal method and calcination at 300–900 °C in an argon atmosphere. It was noted that the presence of rGO in photocatalysts had an important role in the changes in crystallite size and specific surface area. In TiO2/rGO samples, different surface functional groups, such as C−Cgraph, C−Caliph, C−OH, C=O, and CO(O), were found. It was observed that rGO modification suppressed the anatase-to-rutile phase transformation. The photocatalytic activity of the obtained nanomaterials was investigated through the decomposition of methylene blue under UV and artificial solar light irradiation. It was found that the adsorption degree played an important role in methylene blue decomposition. The experimental results revealed that TiO2/rGO samples exhibited superior removal efficiency after calcination for methylene blue compared toTiO2 without rGO, as well as a commercial photocatalyst KRONOClean 7000. It was noted that photocatalytic activity increased with the increase in the calcination temperature. The highest activity was observed for the sample calcined at 700 °C, which consisted of 76% anatase and 24% rutile. This study clearly demonstrated that TiO2/rGO samples calcined in argon can be used as efficient photocatalysts for the application of methylene blue decomposition.

Near-infrared responsive reduced graphene oxide supported CuS: Enhanced electrocatalytic hydrogen evolution performance

Various reduced graphene oxide supported CuS (RGO-CuS) composites were obtained via a hydrothermal way in this work. The as-obtained RGO-CuS with a low bandgap of ~1.24 eV showed significant light absorption in near-infrared (NIR) region. In acidic media, the optimized 0.1RGO-CuS needed an overpotential of 179 mV (at 10 mA cm−2) to trigger the hydrogen evolution reaction under NIR light. And the lowest Tafel slope of 0.1RGO-CuS (61 mV dec−1), suggesting that the photoelectrocatalytic hydrogen evolution was performed under the Volmer-Heyrovsky mechanism. The 0.1RGO-CuS displayed a good durability after 5000 cycles in acid. According to the results of EIS measurement, both NIR irradiation and RGO modification could effectively lower charge transfer resistance and improve charge transport rate of the photoelectrochemical process. The introduction of RGO could improve the electron and hole separation ability of the photoelectrochemical process, which resulted in an enhanced photoelectrocatalytic HER performance.

SnS2 Nanosheets with RGO Modification as High-Performance Anode Materials for Na-Ion and K-Ion Batteries.

To date, the fabrication of advanced anode materials that can accommodate both Na+ and K+ storage is still very challenging. Herein, we developed a facile solvothermal and subsequent annealing process to synthesize SnS2/RGO composite, in which SnS2 nanosheets are bonded on RGO, and investigated their potential as anodes for Na+ and K+ storage. When used as an anode in SIBs, the as-prepared SnS2/RGO displays preeminent performance (581 mAh g−1 at 0.5 A g−1 after 80 cycles), which is a significant improvement compared with pure SnS2. More encouragingly, SnS2/RGO also exhibits good cycling stability (130 mAh g−1 at 0.3 A g−1 after 300 cycles) and excellent rate capability (520.8 mAh g−1 at 0.05 A g−1 and 281.4 mAh g−1 at 0.5 A g−1) when used as anode for PIBs. The well-engineered structure not only guarantees the fast electrode reaction kinetics, but also ensures superior pseudocapacitance contribution during repeated cycles, which has been proved by kinetic analysis.

Reduced graphene oxide/VSB-5 composite micro/nanorod electrode for high energy density supercapattery

Nickel Phosphate (Ni20[(OH)12(H2O)6][(HPO4)8(PO4)4]•12H2O) – VSB-5 nano/micro rods composite with reduced graphene oxide (rGO) was successfully synthesized using a Polyvinyl Pyrrolidone (PVP) aided hydrothermal technique and applied as a battery-type cathode for supercapatteries. The uniform meso/microporous structure provides more electro-active sites for surface redox reaction and nano-paths for electrolyte ion diffusion which can significantly improve the device performance. From the electrochemical analysis, it was found that VSB-5/rGO exhibited a specific capacity of 117.3 mAh g−1 (1056.1 F g−1) which was noticeably higher than the pristine VSB-5 (60.7 mAh g−1) at 5 mA cm−2. These excellent electrochemical performances may be due to rGO modification and well-defined nano/micro rods. Furthermore, supercapatteries were fabricated by pairing a commercially available activated carbon (AC) electrode with VSB-5/rGO as a positrode. The fabricated cell was tested and showed a high specific capacity of 86.8 mAh g−1 (208.4 F g−1) with 88% capacity retention after 5000 cycles. Finally, the assembled supercapattery delivered a maximum specific energy of 80.5 Wh kg−1 at a power output of 2216.5 W kg−1. In comparison with a pristine VSB-5 based device, the AC/VSB-5/rGO device shows remarkable electrochemical performance, demonstrating that VSB-5/rGO is a promising, new electrode material for high performance supercapatteries.

Influence of the calcination of TiO2-reduced graphite hybrid for the photocatalytic reduction of carbon dioxide

In this work, a conversion of carbon dioxide (CO2) into methane, carbon monoxide, as well as hydrogen was investigated. The TiO2/rGO photocatalysts were prepared by two steps: solvothermal method and calcination at 500, 800, and 1000 °C in an argon atmosphere. The obtained samples were characterized by X-ray diffraction (XRD), UV–vis diffuse reflection spectroscopy (UV–vis/DRS), N2 adsorption-desorption and analysis of carbon content. The activity of photocatalysts was evaluated in the photocatalytic reduction of CO2. The TiO2/rGO-10 without calcination showed the highest activity toward CO2 conversion. It was found that all samples after rGO modification exhibited good activity toward H2 generation with high selectivity. The enhanced photocatalytic performance was attributed mainly to the presence of graphene due to its excellent electron transport/collection ability.

Capacitive Performance of Reduced Graphene Oxide Modified Sodium Ion-Intercalated Manganese Oxide Composite Electrode

Abstract The reduced graphene oxide modified sodium ion-intercalated manganese oxide (RGO-NaxMnO2) is designed as a supercapacitor electrode material. The layered intercalation compound NaxMnO2 is prepared through a solid-state reaction process. RGO-NaxMnO2 is then formed by the chemical reduction of graphene oxide coated NaxMnO2 through a hydrothermal process. RGO-NaxMnO2 is supported on the substrate of nickel form (NF) and titanium nitride (TiN) to form RGO-NaxMnO2/NF and RGO-NaxMnO2/TiN composite electrodes. NaxMnO2 has a particle aggregate structure with the individual particle size of 1–2 µm. RGO-NaxMnO2 composite shows the densely packed arrangement of particles with the particle aggregate size of 8 µm. RGO modification can well improve the electrical conductivity of RGO-NaxMnO2. The current response is highly enhanced from 0.127 A g−1 for NaxMnO2/NF to 0.372 A g−1 for RGO-NaxMnO2/NF at 2 mV s−1. Furthermore, the TiN substrate with superior electrical conductivity and electrochemical anti-corrosion contributes to improving the electrochemical capacitance and cycle stability of RGO-NaxMnO2. RGO-NaxMnO2/TiN reveals higher specific capacitance (244.2 F g−1 at 2.0 A g−1) and higher cycling capacitance retention (99.7%) after 500 cycles at 2.0 A g−1 than RGO-NaxMnO2/NF (177.1 F g−1, 43.6%). So, RGO-NaxMnO2/TiN exhibits much higher capacitive performance than RGO-NaxMnO2/NF, which presents a potential application for electrochemical energy storage.

Photovoltaic Properties of an rGO/Pt Counter Electrode With AZO Photoanode for Dye-Sensitized Solar Cells Under Low Light Intensity

This study used reduced graphene oxide (rGO) applied to a platinum (Pt) counter electrode to improve light conversion efficiency. The study also used an Al-doped Zinc Oxide (AZO) nanosheet/TiO2 photoanode for the dye-sensitized solar cell (DSSC). Photovoltaic characteristics, electrochemical impedance spectroscopy (EIS), field-emission scanning electron microscopy (FE-SEM) and Raman spectroscopy were used to analyze DSSC. The different light intensities and photovoltaic characteristics were analyzed to determine optimal light intensity conditions. The unmodified Pt counter electrode was compared with the rGO/Pt counter electrode, photovoltaic conversion efficiency ( ${\eta }$ ) increased from 3.60% to 4.04% due to the rGO modification as it possesses a higher specific surface area. Its low cost also makes it suitable for mass production. In addition, an AZO nanosheet/TiO2 photoanode was fabricated to form a double-layer structure in which photovoltaic conversion efficiency was 4.47 %. Finally, a DSSC with an AZO/TiO2 photoanode and rGO/Pt counter electrode was fabricated and had an photovoltaic conversion efficiency of 5.05 %. This study also analyzed the photovoltaic parameters of DSSC under different light intensities, which shows the optimal photovoltaic conversion efficiency of 5.54% under 30mW/cm2.

Substantial doping engineering in Na3V2-xFex(PO4)3 (0≤x≤0.15) as high-rate cathode for sodium-ion battery

Due to its high theoretical capacity and stable structure, Na3V2(PO4)3 has gained much attention as a potential cathode for sodium-ion batteries (SIBs) in large-scale energy storage applications. However, poor electronic conductivity usually results in the low rate capacity and poor cyclability, limiting its application. Herein, we successfully introduce Fe3+ to substitute V3+ through doping engineering. Compared with Na3V2(PO4)3/C, an excellent initial high-rate capacity of 91.2 mAhg−1 (77.5% of the theoretical capacity) at 20 C (2.35 A g−1) has been achieved in Na3V1.9Fe0.1(PO4)3/C + rGO due to the improved electronic conductivity introduced by Fe doping and rGO modification, and a stable cyclability with 88.7% capacity retention after 100 charge/discharge cycles, implying the perfect structural stability of the composite. It is expected that the results obtained will grasp new insights into designing the optimal cathode and realizing the commercial synthesis for the large-scale rechargeable sodium energy storage devices.

Synchronous synthesis of Cu2O/Cu/rGO@carbon nanomaterials photocatalysts via the sodium alginate hydrogel template method for visible light photocatalytic degradation

A series of Cu2O/Cu/rGO@carbon nanomaterial (Cu2O/Cu/rGO@CN) heterogeneous photocatalysts were successfully synthesized synchronously via a novel sodium alginate hydrogel method. Cu2O nanoparticles (~50nm) were synthesized by calcination under the protection of a nitrogen atmosphere. Cu nanoparticles (~6nm) inevitably appeared on the surface of Cu2O, thereby forming a Cu2O/Cu heterostructure which is known as a Schottky junction. Graphene oxide (GO) nanosheets were synchronously reduced in situ by sodium alginate during the synthesis process and eventually acted as a 3-D structure with the assistance of the hydrogel skeleton. Because of the 3-D rGO modification, both the adsorption capacity and the photocatalytic activity of Cu2O/Cu/rGO@CN were significantly improved. The rate of p-nitrochlorobenzene (p-NCB) degradation catalyzed by Cu2O/Cu/rGO@CN was ~1.97×10−2min−1, which was much higher than that of the degradation catalyzed by Cu2O/Cu@CN (~0.239×10−2min−1). This result could be attributed to the two-stage Cu2O/Cu/rGO heterostructure, which facilitated efficient electron-hole separation. This method has the advantages of nontoxic raw materials, facile synthesis and reduced auxiliary usage, providing a new technique for designing heterogeneous photocatalysts.

Hydrothermal synthesis of reduced graphene oxide-modified NiCo2O4 nanowire arrays with enhanced reactivity for supercapacitors

Supercapacitors have attracted great attentions for their excellent performance in the energy devices. In this work, the reduced graphene oxide (rGO) modified NiCo2O4 (rGO/NiCo2O4) are fabricated by a simple hydrothermal route. After the rGO modification, the sea urchin-like structure of NiCo2O4 was broken and the NiCo2O4 nanowires would intertwine with each other. Benefit from the large surface areas and the active sites of this unconsolidated structure, the as-prepared rGO/NiCo2O4 exhibited the excellent specific capacitance of 1003 F g−1 at the current density of 1 A g−1 and enhanced rate capability (89% from 1 to 10 A g−1). And the cycle stability could reach 57% retention after the 10000 cycles. The rGO/NiCo2O4 composite might hold great promise for future application of the high-performance supercapacitor.

Enhanced degradation performance of organic dyes removal by bismuth vanadate-reduced graphene oxide composites under visible light radiation

As a photocatalyst, bismuth vanadate coupled with reduced oxide graphene (BiVO4-rGO) has been reported for dye degradation. However, this catalyst faced the disadvantages of low catalytic efficiency and long catalytic time. In this paper, BiVO4-rGO composites were synthesized by a modified hydrothermal method, and characterization results showed the monoclinic BiVO4 surface successfully coupled with a layer of rGO. The dye removal performance of BiVO4-rGO composites were evaluated by the degradation of malachite green and rhodamine B under visible light irradiation and photocatalytic results showed that the BiVO4 with rGO modification could effectively enhance the dyes removal performance. In a specific photocatalytic experiment, BiVO4-rGO-300 could remove 99.5% MG in two hours and 99.84% RhB in four hours, which was superior to previous studies. Furthermore, application of catalyst in practical wastewater was also taken into account. MG and RhB were degraded by BiVO4-rGO in several kinds of actual wastewater and experimental results showed that this catalyst could efficiently remove dye in actual environment. This improvement could be ascribed to the increase of special surface area, efficient charge transfer and reduction of electron-hole pair recombination with the incorporation of rGO. The influences of pH, supporting electrolyte and mechanism of the dye degradation were also investigated in details.