rGO Modification Research Articles

Selective electrochemical detection of dopamine based on molecularly imprinted poly(5-amino 8-hydroxy quinoline) immobilized reduced graphene oxide

The dopamine-imprinted conducting polymer film of 5-amino 8-hydroxy quinoline (AHQ) was electrodeposited on reduced graphene oxide (rGO)-modified glassy carbon (GC) electrode and was applied as a molecular recognition element for the selective determination of dopamine. The molecularly imprinted polymer (MIP)-modified electrode showed an excellent affinity towards dopamine due to the presence of imprinted site through hydrogen bonding interaction between dopamine and poly (AHQ) membrane. The molecular recognition ability of MIP-modified electrode was analyzed by cyclic voltammetric and differential pulse voltammetric techniques. The most stable geometry of the template–monomer complex in the pre-polymerization mixture was calculated by computational approaches. The rGO modification augmented both surface area and electron transfer kinetics of the bare electrode. The GC/rGO/MIP electrode possessed 2.83 fold current enhancements when compared to GC/MIP electrode, indicating the improvement in sensitivity due to rGO modification. The limit of detection and sensitivity of GC/rGO/MIP electrode was observed to be 32.7 nM and 13.3 AM−1 cm−2, respectively. The imprinting methodology provided an exceptional selectivity towards the detection of dopamine even in the presence of high concentration of possible physiological interferents. Moreover, the fabricated electrode was successfully employed for the detection of dopamine in human blood plasma samples proving the effectiveness of the sensor for the sensitive detection of dopamine from real samples.

Different solid electrolyte interface and anode performance of CoCO3 microspheres due to graphene modification and LiCoO2||CoCO3@rGO full cell study

Abstracts Hollow and urchin-like CoCO3 dumbbell microspheres (HCCM) and CoCO3@reduced graphene oxide composite microspheres (CC@rGO) were synthesized by one-step solvothermal methods. RGO modification significantly improves the cycling stability of CoCO3 microsphere anodes at low current densities. CC@rGO delivers 1067 and 997 mAh/g after 50 cycles at 0.1 C and 100 cycles at 0.2 C, respectively. Interestingly, HCCM shows rising cycling stability with increased rates while CC@rGO exhibits slight and continuous capacity fading at almost all rates thus declining advantage with rising rates. A competition theory between “protective force” mainly from solid electrolyte interface (SEI) or rGO layer and “destructive force” from volume swing applied on the microspheres was raised to clarify this phenomenon. The changing volume swing degree and SEI formation rate with increased rates, as well as different protective effects of HCCM and CC@rGO's SEI film or rGO layer, determined various competition results of the two forces at each rate thus various structural stability and cycling performance of the two samples. Furthermore, the application prospect of CoCO3 anodes in lithium ion full cells has been explored and the assembled LiCoO2||CC@rGO exhibits an initial coulombic efficiency of 92.9%, a discharge mid-voltage of 2.3 V and stable cycling performance.

Reduced graphene oxide-modified Ni-Co phosphate nanosheet self-assembled microplates as high-performance electrode materials for supercapacitors

It is demonstrated that the incorporation of reduced graphene oxide (rGO) and pseudocapacitance materials often offer an effective strategy toward fast reversible redox reactions while remaining their high pseudocapacitance. In this work, a type of rGO-modified Ni-Co phosphates (Ni(Co)NH4PO4@rGO) microplates were fabricated for supercapacitors electrodes via a one-step hydrothermal method. SEM and TEM tests indicated that the obtained microplates are comprised of well-aligned crystalline Ni(Co)NH4PO4 nanosheets. Moreover, the rGO-modified microplates exhibit a high specific capacitance of 1020 F g−1 at 1 A g−1, which is 16.3% enhanced compared to that of the untreated Ni(Co)NH4PO4) ones (877 F g−1). While the rate capacitor can reach to 92%. Furthermore, it is observed that after 700-cycles, the specific capacitance can increase to their maximum value of 1451 F g−1 at current density of 10 A g−1, and can still remain 1275 F g−1 after 5000 cycles, showing a high cycling stability. The Ni(Co)NH4PO4 showed the same tendency but the low values. These excellent electrochemical performances could be due to rGO modification and self-assembled well-aligned nanosheets. This type of structures cannot only facilitate the transfer electrons, but also offer high electrochemical activity sites and short transport path length for electrolyte ions.

Critical influence of reduced graphene oxide mediated binding of M (M = Mg, Mn) with Co ions, chemical stability and charge storability enhancements of spinal-type hierarchical MCo2O4 nanostructures

This paper reports that addition of reduced graphene oxide (rGO) in MgCo2O4 improves the binding of Mg with Co thereby minimizing magnesium dissolution in aqueous alkaline electrolytes and the resulting MgCo2O4/rGO electrodes offered impressive improvements in charge storage properties. An isostructural high performing material, MnCo2O4, is used as a benchmark material in this work. The Mg analogues stored >30% more charges than the Mn-analogues in the 3M LiOH electrolyte despite the former's lower BET surface area; rGO modification further increased charge storage by >60% than the unmodified analogues. Electrochemical measurements show that a larger surface fraction of the Mg analogue is electrochemically active, irrespective of whether or not rGO is present, which arise from, typically for MgCo2O4/rGO, lower internal resistance, lower Warburg impedance, and lower charge transfer resistance than the other electrodes.

Enhanced Photoelectrochemical Cathodic Protection Performance of the Secondary Reduced Graphene Oxide Modified Graphitic Carbon Nitride

Graphitic carbon nitride (g-C3N4) is a promising material in the area of photoelectrochemical (PEC) cathodic protection. However, the fast secondary recombination of photogenerated charge carriers and the amphoteric property of g-C3N4 restrict its further application. In this work, the secondary reduced graphene oxide modified g-C3N4 (R-rGO-C3N4) was prepared by a thermal polycondensation method and subsequently secondary reduction process. The presence of reduced graphene oxide (rGO) and the increased reduction degree of rGO were proved by the X-ray photoelectron spectroscopy and UV/Vis diffuse reflectance spectroscopy. The rGO modification enhanced the electrical conductivity of g-C3N4, promoting the transfer and separation of the photogenerated charge carriers. It adjusted the band structure of g-C3N4 toward more negative direction, making it show stronger “n-type” semiconductor property. The properties were further improved after the secondary reduction of the rGO. These help to increase the PEC properties of g-C3N4, which makes a step toward the practical application of g-C3N4.

Synthesis of high-performance LiMnPO4/C /rGO composite via a mechanical-activation-assisted polyol process

A mechanical-activation-assisted polyol method for efficient preparation of high-performance rod-like LiMnPO4 composite is developed. The nanosized [Mn3(PO4)2·8H2O + Li3PO4]/graphene oxide (GO) precursors are prepared via a mechano-chemical liquid-phase activation–assisted technique from LiH2PO4 and manganese powder. LiMnPO4/reduced graphene oxide (rGO) samples are obtained by polyol process in boiling triethylene glycol (TEG) and then followed with pyrolytic carbon coating to prepare the LiMnPO4/C/rGo nanocomposite. The characterized results prove that well-crystallized LiMnPO4 nanorods can be successfully synthesized by polyol processing. The LiMnPO4 nanorods have a large percentage of highly oriented (020) facets, which provide a high pore density for Li-ion insertion/extraction. Both rGO modification and further carbon coating significantly improve the conductivity and reduce the charge-transfer resistance. The optimized LiMnPO4/C/rGO composite delivers good electrochemical performance.

Hierarchical Fe3O4 microsphere/reduced graphene oxide composites as a capable anode for lithium-ion batteries with remarkable cycling performance

A facile one-pot solvothermal method has been used to synthesize hierarchical Fe3O4 microsphere and reduced graphene oxide (rGO) composite. The Fe3O4 microspheres are assembled with nanoparticles as primary building blocks and covered by the rGO sheets. When used as an anode material for lithium-ion batteries, the composite displays a high specific capacity, good cycle stability, remarkable rate capability. The synergetic effect of the unique nano/micro hierarchical structure and high conductivity rGO modification promise a good soakage of electrolyte, high structure stability and enhanced electronic transition, leading to an excellent electrochemical performance. This work would open a new doorway for designing the electrode materials of lithium-ion batteries with superior performance.

Synergetic effects of Al3+ doping and graphene modification on the electrochemical performance of V2O5 cathode materials.

A series of V2O5-based cathode materials that include V2O5 and Al0.14 V2O5 nanoparticles, V2O5/reduced graphene oxide (RGO), and Al0.16 V2O5/RGO nanocomposites are prepared by a simple soft chemical method. XRD and Raman scattering show that the Al ions reside in the interlayer space of the materials. These doping ions strengthen the V−O bonds of the [VO5] unit and enhance the linkage of the [VO5] layers, which thus increases the structural stability of V2O5. SEM and TEM images show that the V2O5 nanoparticles construct a hybrid structure with RGO that enables fast electron transport in the electrode matrix. The electrochemical properties of the materials are studied by charge-discharge cycling, cyclic voltammetry, and electrochemical impedance spectroscopy. Of all the materials tested, the one that contained both Al ions and RGO (Al0.16 V2O5/RGO) exhibited the highest discharge capacity, the best rate capability, and excellent capacity retention. The superior electrochemical performance is attributed to the synergetic effects of Al(3+) doping and RGO modification, which not only increase the structural stability of the V2O5 lattice but also improve the electrochemical kinetics of the material.

Fast and Sensitive Detection of Pb2+ in Foods Using Disposable Screen-Printed Electrode Modified by Reduced Graphene Oxide

In this study, reduced graphene oxide (rGO) was electrochemically deposited on the surface of screen-printed carbon electrodes (SPCE) to prepare a disposable sensor for fast detection of Pb2+ in foods. The SEM images showed that the rGO was homogeneously deposited onto the electrode surface with a wrinkled nanostructure, which provided 2D bridges for electron transport and a larger active area for Pb2+ adsorption. Results showed that rGO modification enhanced the activity of the electrode surface, and significantly improved the electrochemical properties of SPCE. The rGO modified SPCE (rGO-SPCE) was applied to detect Pb2+ in standard aqueous solution, showing a sharp stripping peak and a relatively constant peak potential in square wave anodic stripping voltammetry (SWASV). The linear range for Pb2+ detection was 5∼200 ppb (R2 = 0.9923) with a low detection limit of 1 ppb (S/N = 3). The interference of Cd2+ and Cu2+ at low concentrations was effectively avoided. Finally, the rGO-SPCE was used for determination of lead in real tap water, juice, preserved eggs and tea samples. Compared with results from graphite furnace atomic absorption spectroscopy (GFAAS), the results based on rGO-SPCE were both accurate and reliable, suggesting that the disposable sensor has great potential in application for fast, sensitive and low-cost detection of Pb2+ in foods.