Reduced Graphene Oxide Nanoflakes Research Articles

An Enzymatic Biosensor Based on MgO Nanoparticles Grafted on Reduced Graphene Oxide Nanoflakes for the Ultrasensitive Detection of Phenolic Compounds from Wastewater

AbstractIn the present work, an enzymatic biosensor has been fabricated using reduced graphene‐magnesium oxide nanoflakes (rGO‐MgONf). For the fabrication of the bioelectrode, the synthesized rGO‐MgONf were electrophoretically deposited onto indium tin oxide (ITO) coated glass substrate, followed by the covalent immobilization of the Laccase (lac) enzyme. Electrochemical studies show an enhanced diffusion coefficient (10.29×10−12 cm2 s−1), and exchange current per geometric unit area (3.66 μA cm−2) on using the rGO‐MgONf/ITO electrode compared to the GO/ITO and MgO/ITO electrode. Further, the fabricated biosensor (lac/rGO‐MgONf/ITO) displayed excellent performance towards hydroquinone (Hq) detection, with a low limit of detection (0.15 μM), wide linear range (1.0–100.0 μM), and high sensitivity (10.0 μA μM−1 cm−2). The selectivity study suggests that the fabricated biosensor efficiently detects Hq in wastewater. Additionally, the fabricated biosensor shows good stability and reproducibility for detecting Hq in tap and river water with an excellent recovery rate.

MOFs-based core-shell micro-nanostructure covering with curly RGO nanoflakes enabled fire-safe and mechanical-robust EP composites

The extended usage of epoxy (EP) resin has confronted with the notorious issue of high fire hazard. Hence, a metal–organic frameworks (MOFs)-based core–shell micro-nanostructure covering with curly reduced graphene oxide nanoflakes (NRGO-ZIF@CoFe) is constructed and characterized via SEM, TEM, XPS, XRD, etc. Interfacial interaction between filler and matrix is estimated by microstructures analysis of fractured surfaces. Ulteriorly, the influences of NRGO-ZIF@CoFe on flame retardancy and mechanical performance of EP are investigated by cone test and tensile as well as flexural tests. When 2.0 wt% NRGO-ZIF@CoFe is loaded, the peak heat release rate, total heat release, peak smoke production rate, total smoke production are impaired by 42.8%, 23.5%, 41.0%, 39.2%. Meanwhile, the peak CO yield is depressed by 46.6%. Comparison with reported works demonstrates the advantage of NRGO-ZIF@CoFe in hindering heat and smoke productions. The evidences for inhibited releases of toxic volatiles (CO, NO, HCN) are offered via gases phase analysis. Stemming from the strong mechanical interlocking forces, the tensile and flexural strengths are promoted by 40.7% and 37.1%. Also, the elongation at break is elevated by 23.8%. In brief, this work may shed a light on the design of MOFs-based hierarchical architecture, further enabling fire-safe and mechanical-robust polymer composites.

RGO decorated N-doped NiCo2O4 hollow microspheres onto activated carbon cloth for high-performance non-enzymatic electrochemical glucose detection

This paper reports the first effective fabrication of a high-performance non-enzymatic glucose sensor based on activated carbon cloth (ACC) coated with reduced graphene oxide (RGO) decorated N-doped urchin-like nickel cobaltite (NiCo2O4) hollow microspheres. Hierarchically mesoporous N-doped NiCo2O4 hollow microspheres were synthesized using a facile solvothermal method, followed by thermal treatment in a nitrogen (N2) atmosphere. Subsequently, they were hydrothermally decorated with RGO nanoflakes. The resulting composite was dip-coated onto ACC, and its electrochemical and glucose sensing performances were investigated using electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), and chronoamperometric measurements in a three-electrode system. The composite electrode sensor demonstrates admirable sensitivity (6122 μM mM−1 cm−2) with an ultralow detection limit (5 nM, S/N = 3), and it performs well within a substantial linear range (0.5–1.450 mM). Additionally, it exhibits good long-term response stability and outstanding anti-interference performance. These outstanding results can be attributed to the synergistic effects of the highly electrically conductive ACC with multiple channels, the enhanced catalytic activity of highly porous N-doped NiCo2O4 hollow microspheres, and the large electroactive sites provided by its well-developed hierarchical nanostructure and RGO nanoflakes. The findings highlight the enormous potential of the ACC/N-doped NiCo2O4@RGO electrode for non-enzymatic glucose sensing.

Investigation on Interface Temperature and Parametric Optimization During Machining of Reduced Graphene Oxide Nanoflakes Dispersed Polymer-based Carbon Fiber Reinforced (rGO/CF) Nanocomposites

Investigation on Interface Temperature and Parametric Optimization During Machining of Reduced Graphene Oxide Nanoflakes Dispersed Polymer-based Carbon Fiber Reinforced (rGO/CF) Nanocomposites

Exploring Molecular and Electronic Property Predictions of Reduced Graphene Oxide Nanoflakes via Density Functional Theory.

In this research, we perform a theoretical interpretation of molecular and electronic properties of reduced graphene oxide (rGO) nanoflakes through the density functional theory. Here, two pristine graphene nanoflake systems were passivated by hydrogen atoms at their edges, armchair (C58H20) and zigzag (C54H20); besides, we implemented 12 rGO systems with a range of low oxide coverage (1, 3, and 4%). Computational calculations were carried out employing the functional hybrid B3LYP and the basis 6-31G(d, p) and 6-311G(d, p) levels of theory. We brought the proposed molecular structures to a stable minimum. We determined the global reactivity descriptors through chemical potential, hardness, softness, and index of electrophilicity. Besides, the maps of electrostatic potential were generated. We found that the hydroxyl and epoxy functional groups dope the graphene molecule in p-type and n-type forms, respectively. In addition, we could attribute the increases of the oxide coverage and the chemical potential to the softness of the molecule. These results suggest that structures with this type of doping can help in developing advanced electronics of sensors and devices.

Facile Mgo Decorated Reduced Graphene Oxide Nanoflakes for Enzymatic Detection of Hydroquinone in Wastewater

Facile Mgo Decorated Reduced Graphene Oxide Nanoflakes for Enzymatic Detection of Hydroquinone in Wastewater

Enabling Multiplexed Electrochemical Detection of Biomarkers with High Sensitivity in Complex Biological Samples.

The ability to perform multiplexed detection of various biomarkers within complex biological fluids in a robust, rapid, sensitive, and cost-effective manner could transform clinical diagnostics and enable personalized healthcare. Electrochemical (EC) sensor technology has been explored as a way to address this challenge because it does not require optical instrumentation and it is readily compatible with both integrated circuit and microfluidic technologies; yet this approach has had little impact as a viable commercial bioanalytical tool to date. The most critical limitation hindering their clinical application is the fact that EC sensors undergo rapid biofouling when exposed to complex biological samples (e.g., blood, plasma, saliva, urine), leading to the loss of sensitivity and selectivity. Thus, to break through this barrier, we must solve this biofouling problem.In response to this challenge, our group has developed a rapid, robust, and low-cost nanocomposite-based antifouling coating for multiplexed EC sensors that enables unprecedented performance in terms of biomarker signal detection compared to reported literature. The bioinspired antifouling coating that we developed is a nanoporous composite that contains various conductive nanomaterials, including gold nanowires (AuNWs), carbon nanotubes (CNTs), or reduced graphene oxide nanoflakes (rGOx). Each study has progressively evolved this technology to provide increasing performance while simplifying process flow, reducing time, and decreasing cost. For example, after successfully developing a semipermeable nanocomposite coating containing AuNWs cross-linked to bovine serum albumin (BSA) using glutaraldehyde, we replaced the nanomaterials with reduced graphene oxide, reducing the cost by 100-fold while maintaining similar signal transduction and antifouling properties. We, subsequently, developed a localized heat-induced coating method that significantly improved the efficiency of the drop-casting coating process and occurs within the unprecedented time of <1 min (at least 3 orders of magnitude faster than state-of-the-art). Moreover, the resulting coated electrodes can be stored at room temperature for at least 5 months and still maintain full sensitivity and specificity. Importantly, this improved coating showed excellent antifouling activity against various biological fluids, including plasma, serum, whole blood, urine, and saliva.To enable affinity-based sensing of multiple biomarkers simultaneously, we have developed multiplexed EC sensors coated with the improved nanocomposite coating and then employed a sandwich enzyme-linked immunosorbent assay (ELISA) format for signal detection in which the substrate for the enzyme bound to the secondary antibody precipitates locally at the molecular binding site above the electrode surface. Using this improved EC sensor platform, we demonstrated ultrasensitive detection of a wide range of biomarkers from biological fluids, including clinical biomarkers, in both single and multiplex formats (N = 4) with assay times of 37 and 15 min when integrated with a microfluidic system. These biosensors developed demonstrate the vast potential of solving the biofouling problem, and how it can enable potential clinically important diagnostic applications. This Account reviews our antifouling surface chemistry and the multiplexed EC sensor-based biodetection method we developed and places it in context of the various innovative contributions that have been made by other researchers in this field. We are optimistic that future iterations of these systems will change the way diagnostic testing is done, and where it can be carried out, in the future.

Graphene Oxide and Reduced Graphene Oxide Nanoflakes Coated with Glycol Chitosan, Propylene Glycol Alginate, and Polydopamine: Characterization and Cytotoxicity in Human Chondrocytes.

Recently, graphene and its derivatives have been extensively investigated for their interesting properties in many biomedical fields, including tissue engineering and regenerative medicine. Nonetheless, graphene oxide (GO) and reduced GO (rGO) are still under investigation for improving their dispersibility in aqueous solutions and their safety in different cell types. This work explores the interaction of GO and rGO with different polymeric dispersants, such as glycol chitosan (GC), propylene glycol alginate (PGA), and polydopamine (PDA), and their effects on human chondrocytes. GO was synthesized using Hummer’s method, followed by a sonication-assisted liquid-phase exfoliation (LPE) process, drying, and thermal reduction to obtain rGO. The flakes of GO and rGO exhibited an average lateral size of 8.8 ± 4.6 and 18.3 ± 8.5 µm, respectively. Their dispersibility and colloidal stability were investigated in the presence of the polymeric surfactants, resulting in an improvement in the suspension stability in terms of average size and polydispersity index over 1 h, in particular for PDA. Furthermore, cytotoxic effects induced by coated and uncoated GO and rGO on human chondrocytes at different concentrations (12.5, 25, 50 and 100 µg/mL) were assessed through LDH assay. Results showed a concentration-dependent response, and the presence of PGA contributed to statistically decreasing the difference in the LDH activity with respect to the control. These results open the way to a potentially safer use of these nanomaterials in the fields of cartilage tissue engineering and regenerative medicine.

Activated Carbon Blended with Reduced Graphene Oxide Nanoflakes for Capacitive Deionization.

Capacitive deionization is a second-generation water desalination technology in which porous electrodes (activated carbon materials) are used to temporarily store ions. In this technology, porous carbon used as electrodes have inherent limitations, such as low electrical conductivity, low capacitance, etc., and, as such, optimization of electrode materials by rational design to obtain hybrid electrodes is key towards improvement in desalination performance. In this work, different compositions of mixture of reduced graphene oxide (RGO) and activated carbon (from 5 to 20 wt% RGO) have been prepared and tested as electrodes for brackish water desalination. The physico-chemical and electrochemical properties of the activated carbon (AC), reduced graphene oxide (RGO), and as-prepared electrodes (AC/RGO-x) were characterized by low-temperature nitrogen adsorption measurement, scanning electron microscope (SEM), X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), Fourier transform infra-red (FT-IR), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). Among all the composite electrodes, AC/RGO-5 (RGO at 5 wt%) possessed the highest specific capacitance (74 F g−1) and the highest maximum salt adsorption capacity (mSAC) of 8.10 mg g−1 at an operating voltage ∆E = 1.4 V. This shows that this simple approach could offer a potential way of fabricating electrodes of accentuated carbon network of an improved electronic conductivity that’s much coveted in CDI technology.

Dielectric Polarization and Electrorheological Response of Poly(ethylaniline)-Coated Reduced Graphene Oxide Nanoflakes with Different Reduction Degrees.

We prepared poly(ethylaniline)-coated graphene oxide nanoflakes and then treated them with different concentrations of hydrazine solution to form dielectric composite nanoflakes having different reduction degrees of reduced graphene oxide core and insulating polyethylaniline shell (PEANI/rGO). The morphology of PEANI/rGO was observed by scanning electron microscopy, while the chemical structure was confirmed by Fourier transform infrared spectroscopy and X-ray photoelectron spectrometer. The influence of reduction degrees on the conductivity, dielectric polarization and electrorheological effect of PEANI/rGO in suspensions was investigated by dielectric spectroscopy and rheological test under electric fields. It shows that the PEANI/rGO has two interfacial polarization processes respectively due to rGO core and PEANI shell. As the number of hydrazine increases, the conductivity and polarization rate of rGO core increase. As a result, the difference between the polarization rate of rGO core and that of the PEANI shell gradually becomes large. This increased difference does not significantly decrease the yield stress but causes the flow instability of PEANI/GO suspensions under the simultaneous action of electric and shear fields.

Self-assembled reduced graphene oxide nanoflakes assisted by post-sonication boosted electrical performance in gold interdigitated microelectrodes

Reduced graphene oxide (rGO) is widely utilised to develop various types of biosensors; however, producing self-assembled rGO nanoflake networks through single-droplet drop-casting remains inconsistent. In the present work, we systematically used three different methods to prepare rGO suspensions in order to produce large scale self-assembled rGO nanoflake networks through single-droplet drop-casting. The rGO suspensions were prepared using only deionised water with no added any chemicals/organic solvents, which we considered to be a low-cost method. Subsequently, the most effective preparation method was used to deposit rGO nanoflakes onto commercial gold interdigitated microelectrodes (Au-IDE) to examine their electrical performance. Assessment of the yields, developed methods, surface morphologies, spectroscopy and structural analyses of the as-prepared rGO nanoflakes were conducted. The results revealed that method-3 (involving sonication, centrifugation and post-sonication) produced large self-assembled rGO nanoflake networks with strong adhesion to glass substrates. Furthermore, the as-prepared rGO/Au-IDE modified sensors showed excellent electron mobility where the electrical conductivity was enhanced approximately ~ 1000 fold compared to the bare devices. The present work provided new insights for depositing large self-assembled interconnected rGO nanoflake networks through single-droplet drop-casting which will be beneficial for biosensor development and other downstream applications.

Controlled volume production of simultaneously B/N co-doped reduced graphene oxide nanoflakes using femtosecond laser ablation

B and N co-doped reduced graphene oxide (B/N-rGO) nanoflakes were produced from a mixed aqueous solution of graphene oxide nanoflakes and boron nitride quantum dots, using high intensity femtosecond laser ablation. We observed a controlled production of B/N-rGO nanoflakes with an average flake size of 2.3 μm to 2.7 μm, with up to 5.9 at% boron and 4.1 at% nitrogen co-doping. The B/N-rGO nanoflakes were obtained in as low as 30 min, at ambient room temperature, and without the use of harsh chemicals.

Porous magnetic iron- manganese oxide nanocubes derived from metal organic framework deposited on reduced graphene oxide nanoflake as a bi-functional electrocatalyst for hydrogen evolution and oxygen reduction reaction

In this work, the porous spinel-type of magnetic iron-manganese oxide nanocubes with a hollow structure deposited on the reduced graphene oxide nanoflakes (PMFMO@RGONF nanocomposite) is synthesized and examined as a non-noble electrocatalyst for hydrogen evolution reaction (HER) and oxygen reduction reaction (ORR). The Tafel slope of PMFMO@RGONF nanocomposite is about 107 mV dec−1 in the 0.50 mol L−1 H2SO4 solution and suggests the Volmer–Heyrovsky mechanism for HER. The results show that this electrocatalyst has an excellent stability (at least 10000 cycles) in the sulfuric acid solution. Hence, The LSV curve shows that the Pt(20%)/C has a better onset-potential than present electrocatalyst for HER but PMFMO@RGONF nanocomposite produces current density (j) of 300 mA cm−2 at overpotential (ɳ) of −721 mV (ɳ300 = −721 mV(vs. Ag/AgCl)) which is smaller than Pt(20%)/C (ɳ300 = −802 mV). The PMFMO@RGONF nanocomposite as an electrocatalyst follows four electrons mechanism for ORR in 0.10 mol L−1 KOH. As an important result, after addition of methanol into the electrolyte, this electrocatalyst is stable for a long time (at least 10000s) while the catalytic activity of Pt (20%)/C is quickly lost in the presence of methanol.

Immobilization of reduced graphene oxide nano-flakes on inert ceramic surfaces using self-assembled monolayer technique

Bioinert ceramic, such as zirconia, provides the mechanical strength required in implants, but its limited bioactivity renders it incapable of osseointegration. Thus, its biomedical application is limited. Graphene and its derivatives possess excellent bioactivity and can enhance osseointegration, hemocompatibility and antibacterial properties. Here, we introduce an innovative technique for functionalizing bioinert ceramic by immobilizing reduced graphene oxide (rGO) onto the surface by tailored self-assembled monolayer (SAM). Three routes have been applied for immobilization: i) spontaneous reaction between OH groups of zirconia and organic functional groups of rGO, ii) spontaneous reaction between NH2 functionalized ZrO2 attained by silanization and COOH groups of rGO and iii) reaction between NH2 functionalized zirconia and activated COOH groups of rGO attained by using the catalysts EDC and NHS. The most efficient immobilization was obtained between activated COOH groups of rGO and NH2 functionalized zirconia. Thereby, for the first time rGO was successfully coupled to ZrO2 using SAM technique. Through this technique, the properties of rGO and zirconia could be merged to create a versatile biomaterial.

Supernucleation and Orientation of Poly(butylene terephthalate) Crystals in Nanocomposites Containing Highly Reduced Graphene Oxide.

The ring-opening polymerization of cyclic butylene terephthalate into poly(butylene terephthalate) (pCBT) in the presence of reduced graphene oxide (RGO) is an effective method for the preparation of polymer nanocomposites. The inclusion of RGO nanoflakes dramatically affects the crystallization of pCBT, shifting crystallization peak temperature to higher temperatures and, overall, increasing the crystallization rate. This was due to a supernucleating effect caused by RGO, which is maximized by highly reduced graphene oxide. Furthermore, combined analyses by differential scanning calorimetry (DSC) experiments and wide-angle X-ray diffraction (WAXS) showed the formation of a thick α-crystalline form pCBT lamellae with a melting point of ∼250 °C, close to the equilibrium melting temperature of pCBT. WAXS also demonstrated the pair orientation of pCBT crystals with RGO nanoflakes, indicating a strong interfacial interaction between the aromatic rings of pCBT and RGO planes, especially with highly reduced graphene oxide.

Polymeric nanofibers decorated with reduced graphene oxide nanoflakes

Polymeric nanofibers decorated with reduced graphene oxide nanoflakes

Exploring the main function of reduced graphene oxide nano-flakes in a nickel cobalt sulfide counter electrode for dye-sensitized solar cell

Abstract Addition of carbonaceous materials into transition metal sulfide counter electrode (CE) of a dye-sensitized solar cell (DSSC) is a common method to improve the performance of the CE and consequent photovoltaic performance. This improvement is almost without exception attributed to the improvement of overall conductivity after the carbonaceous material addition; however, the root function of these carbonaceous materials in promoting the solar cell efficiency is seldom discussed. In this study, highly crystallized nickel cobalt sulfide (NCS) micro-particles were mixed with a small portion of home-made reduced graphene oxide (rGO) nano-flakes. This NCS/rGO hybrid is subjected to extensive characterizations including X-ray diffraction, Raman spectroscopy, field emission scanning microscopy and electrochemical impedance spectroscopy. It is found that the rGO acts bi-functionally including a co-catalyst in accelerating the tri-iodide reduction for the main NCS catalysts, conductivity promotor to decrease the series resistance of the CE. Proved by electrochemical impedance spectroscopy, it is confirmed that the decrease in series resistance is less insignificant than that in charge transfer resistance, indicating rGO functions more profoundly as a co-catalyst than as a conductivity promotor. Moreover, an argument to highlight the requirement of a CE in a dim-light optimized DSSC is also proposed.

Ni-Co-Se nanoparticles modified reduced graphene oxide nanoflakes, an advance electrocatalyst for highly efficient hydrogen evolution reaction

The present manuscript reports a simple one-step wet chemical approach to synthesis reduced graphene oxide nanoflakes (RGONF) from graphite by a thermal reduction at low temperature. The optical, Fourier Transform Infrared, X-ray diffraction, Raman, X-ray photoelectron spectroscopy, electrochemical impedance spectroscopy and transmission electron microscopy are used to demonstrate the synthesis RGONF. This method is simple and avoids the usage of harmful chemical reductants. Then, Ni-Co-Se nanoparticles were solvothermal deposited on RGONF in aqueous media (RGONF/Ni-Co-Se) with an average size of 80nm. Then, a glassy carbon electrode (GCE) was modified with RGONF/Ni-Co-Se and is used as an electrocatalyst for hydrogen evolution reaction (HER) in 0.50molL−1 sulfuric acid. The results showed an excellent catalytic activity of RGONF/Ni-Co-Se with an overpotential of 5mV (vs. RHE) to achieve high current densities of 600mA.cm−2 (at −780.0mV). As well, the applied overpotential and slope for HER is better than expensive Pt/C (20%) catalyst, which used in fuel cells. Also, the Tafel slope was about 30±3mVdecade−1 and suggested the Tafel mechanism for HER.

Enhancement of laser action in ZnO nanorods assisted by surface plasmon resonance of reduced graphene oxide nanoflakes

We report the discovery of an enhancement of the random laser action in a nanocomposite comprising reduced graphene oxide nanoflakes and ZnO nanorods. We show that both emission intensity and lasing threshold exhibit an obvious improvement. Based on our theoretical calculations, the mechanism underlying the enhanced stimulated emission can be attributed to coupling between the optical transition and the surface plasmon resonance of the reduced graphene oxide nanoflakes, induced by the ZnO nanorod surface roughness. The approach we describe here will be very useful for the future development of high-efficiency optoelectronic devices and offers an alternative route for application of reduced graphene oxide.