As-synthesized rGO Research Articles

Polystyrene-reduced graphene oxide composite as sorbent for oil removal from an Oil-Water mixture

This study enhanced the adsorptive capacity of polystyrene (PS) by infusing reduced graphene oxide (rGO) nanoparticles obtained from the synthesis of graphene oxide to produce PS-rGO composites via electrospinning method. Physicochemical characterization of as-synthesized rGO and PS-rGO were carried out through scanning electron microscopy, N2 physisorption among others. Oil sorption performance of synthesized rGO in crude oil, vegetable oil, fresh engine oil and used engine oil are 130.96 g/g, 121.77 g/g, 105.01 g/g and 100.56 g/g. Oil sorption capacities of electrospun pure PS in crude oil, vegetable oil, fresh engine oil and used engine oil were 46.32 g/g, 38.54 g/g, 35.14 g/g and 32.57 g/g and those of PS-rGO infused with 4 wt% of rGO were found to be 105.52 g/g, 98.86 g/g, 86.25 g/g and 83.47 g/g for crude oil, vegetable oil, fresh engine oil and used engine oil samples respectively. Pseudo second order (PSO) kinetic model fits the sorption data of the four oil samples on the four composite sorbents produced. Intra-particle diffusion (IPD) model evidently showed that sorption of the four oil samples on the four composite sorbents, occurred in three (3) phases. Composites demonstrate high oil adsorption capacity, and are reusable upto three sorption–desorption cycles.

Polyethylene glycol embedded reduced graphene oxide supramolecular assemblies for enhanced room-temperature gas sensors

Herein, we present the gas-dependent electrical properties of a reduced graphene oxide nanocomposite. The reduced graphene oxide (rGO) was synthesized by reducing GO with sodium borohydride (NaBH4). As-synthesized rGO was dispersed in DI water containing 1, 2, 3, 4, and 5 wt% polyethylene glycol (PEG) to prepare PEG-rGO supramolecular assemblies. The successful preparation of supramolecular assemblies was verified by their characterization using XRD, FESEM, EDS, TEM, FTIR, and Raman spectroscopy. At room temperature, the gas-dependent electrical properties of these supramolecular assemblies were investigated. The results showed that sensors composed of PEG-rGO supramolecular assemblies performed better against benzene and methanol at 3% and 4% PEG, respectively. However, high selectivity and a wide range of activation energies (∼1.64–1.91 eV) were observed for H2 gas for 4% PEG-modified supramolecular assemblies. The PEG-rGO supramolecular assemblies may be an excellent candidate for constructing ultrahigh-performance gas sensors for a variety of applications due to their high sensitivity and selectivity.

Tailoring the redox ability of carbon nitride quantum dots/reduced graphene oxide-black phosphorus (CNQDs@rGOBP) ternary heterojunctions for photodegradation of organic pollutants

The direct utilization of solar energy in chemical transformations has paved the way for widespread use of photocatalysis for degradation. However, the state-of-the-art photocatalytic systems for various applications have not yet reached the desired level due to poor visible-light absorption and the high-cost requirements of the developed photocatalysts. Recently, the combination of different semiconductors via band engineering has been regarded as a highly efficient strategy to construct metal-free photocatalysts. In this study, a novel ternary heterojunction photocatalyst was fabricated by decorating reduced graphene oxide/black phosphorus binary heterojunctions (rGOBP) with carbon nitride quantum dots (CNQDs) via the ultrasound-assisted liquid exfoliation method. Different ratios of rGOBP binary and CNQDs@rGOBP ternary heterojunctions were prepared to investigate how the content is correlated synergistically to the coupling of the materials at their interfaces, thus possessing a superior photophysical properties. Combining the polar functional groups of as-synthesized rGO and CNQDs with the non-bonding electrons of BP on the surface led to the formation of a chemically stable photocatalyst with high catalytic performance. Harmonizing the salient features of each material boosted the degradation efficiency of organic pollutants 2.5 times in aqueous media compared to their pristine components. The photocatalytic performance of CNQDs@rGOBP heterojunctions was screened by studying different pollutants and catalyst concentrations. Moreover, the photogenerated charge migration pathway was proved by considering the results of the scavenger experiments and changes in the work functions of materials. A nonclassical type-I heterojunction, occurring at the farthest charges of band edges, was proposed as the underlying mechanism behind the superior photocatalytic activity of CNQDs@rGOBP ternary heterojunctions.

Biological Impacts of Reduced Graphene Oxide Affected by Protein Corona Formation.

Applications of reduced graphene oxide (rGO) in many different areas have been gradually increasing owing to its unique physicochemical characteristics, demanding more understanding of their biological impacts. Herein, we assessed the toxicological effects of rGO in mammary epithelial cells. Because the as-synthesized rGO was dissolved in sodium cholate to maintain a stable aqueous dispersion, we hypothesize that changing the cholate concentration in the dispersion may alter the surface property of rGO and subsequently affect its cellular toxicity. Thus, four types of rGO were prepared and compared: rGO dispersed in 4 and 2 mg/mL sodium cholate, labeled as rGO and concentrated-rGO (c-rGO), respectively, and rGO and c-rGO coated with a protein corona through 1 h incubation in culture media, correspondingly named pro-rGO and pro-c-rGO. Notably, c-rGO and pro-c-rGO exhibited higher toxicity than rGO and pro-rGO and also caused higher reactive oxygen species production, more lipid membrane peroxidation, and more significant disruption of mitochondrial-based ATP synthesis. In all toxicological assessments, pro-c-rGO induced more severe adverse impacts than c-rGO. Further examination of the material surface, protein adsorption, and cellular uptake showed that the surface of c-rGO was coated with a lower content of surfactant and adsorbed more proteins, which may result in the higher cellular uptake observed with pro-c-rGO than pro-rGO. Several proteins involved in cellular redox mediation were also more enriched in pro-c-rGO. These results support the strong correlation between dispersant coating and corona formation and their subsequent cellular impacts. Future studies in this direction could reveal a deeper understanding of the correlation and the specific cellular pathways involved and help gain knowledge on how the toxicity of rGO could be modulated through surface modification, guiding the sustainable applications of rGO.

Fabrication of zinc oxide-decorated phytoreduced graphene oxide nanohybrid via Clerodendrum infortunatum

The present paper reports eco-friendly preparation of a mesoporous phytoreduced graphene oxide (rGO)–zinc oxide (ZnO) nanohybrid (NH) using the leaf extract of Clerodendrum infortunatum as a green reducing agent at room temperature. The as-synthesized rGO–zinc oxide NH was characterized by diverse analytical techniques such as X-ray diffraction (XRD), Fourier transform infrared spectroscopy, energy-dispersive X-ray spectroscopy (EDS), ultraviolet-diffuse reflectance spectroscopy (UV-DRS), X-ray photoelectron, Raman spectroscopy, Brunauer–Emmett–Teller (BET) analysis, thermogravimetry and photoluminescence (PL) spectroscopy to study its structure, morphology, surface area, porosity, thermal behavior and optical properties. XRD patterns revealed the decoration of hexagonal wurtzite zinc oxide on the surface of rGO, and its composition was confirmed by EDS. UV-DRS showed slight blueshift of the rGO–zinc oxide NH absorption spectrum, suggesting the successful anchoring of zinc oxide on the rGO surface. The scanning electron microscopy images revealed sheetlike morphology with 20–25 nm thick zinc oxide platelets decorating the rGO surface. Raman shifts showed higher I D/I G ratios for rGO and rGO–zinc oxide than for GO, indicating a decrease in the average size of the sp2-hybrid carbon (C) domain. The BET isotherm confirmed the mesoporous nature of the rGO–zinc oxide NH having average pore size (18 nm) and surface area (67.3 m2/g). The rGO–zinc oxide NH showed diminished PL intensity compared with zinc (Zn), suggesting that the recombination of electron–hole (e−–h+) pairs was effectively reduced. rGO–zinc oxide nanocrystals showed enhanced radical-scavenging activity against 1,1-diphenyl-2-picrylhydrazyl free radicals compared with GO and zinc oxide.

Dynamic-Stacking of Reduced Graphene Oxide for Active Hydrogen Evolution

Despite remarkable electronic and mechanical properties of graphene, improving catalytic activity of graphene, an atomically-flat, inert and stable carbon network, remains a challenging issue in both fundamental and application studies. In particular, the adsorption of most molecules and ions, including hydrogen (H2 or H+), on graphene is not favorable, underlining the challenge for efficient electrochemical catalytic reaction on graphene electrode. Various defects, edges, and functionalization have been suggested to resolve the issue aiming to have catalytic graphene, but cost-effective, clean and active catalysis with graphene has not been realized yet. Here, we introduce dynamic-stacking of reduced graphene oxide (rGO) via an electrochemical way; conventional hydrogen evolution reaction (HER) was used as a dynamic process, generating hydrogen bubbles during electrochemical deposition of rGO on metallic WTe2, which creates a unique porous rGO structure on the atomically-distorted WTe2 surface with optimized edges and surface acidic groups. The hydrogen bubble template method enables an ideal, stable carbon structure for active HER with a Tafel slope of 39 mV·dec-1 and a double layer capacitance of 12.41 mF·cm-2. As our new dynamic synthesis method improves the catalytic activity of one of the most inert materials, graphene, new strategies for designing novel catalysts could be conceived for promising energy applications. Figure 1. 1a) schematically description of the electrochemical synthesis of the rGO film on WTe2 by hydrogen bubble template method. Fig. 1b) shows the graphite and WTe2 shows poor HER activity (blue and black curve). Meanwhile, a striking HER activity is observed with our hybrid rGO-WTe2 (red curve) with a much smaller onset overpotential (vs reversible hydrogen electrode, RHE) and Tafel slope 39 mV·dec-1 (Fig. 1c). The unique HER performance of our rGO-WTe2 catalyst was investigated in terms of electrochemical surface area via double-layer capacitance (Cdl) measurements in Fig. 1d). The Cdl value was calculated by the slope of current density (at a voltage of 0.135 V vs. RHE) versus scan rate, and the value was 12.41 mF·cm-2, which is 5,000 times higher than that of state-of-the-art 3D graphene networks.[3] Fig. 1e) shows the optical microscopy image of rGO. The as-synthesized rGO on WTe2 substrate exhibits a highly porous structure in the SEM images in Fig. 1 (f-g). The characteristic dimension of the porous structure ranges from 100 nm - 2 μm in diameters with many edges exposed between rGO porous walls; the rGO flakes are stacked in a random way to have many edges as HER active sites. As HR-TEM images shown in Fig. 1 (h-i), the rGO flakes are mixed with crystal and amorphous graphene with an interlayer spacing of 0.43 nm. Keywords: hydrogen evolution reaction, hydrogen bubble template, reduced graphene oxide, tungsten ditelluride (WTe2)

A new sustainable green protocol for production of reduced graphene oxide and its gas sensing properties

Abstract In this report, we report a green, rapid and scalable synthetic route for the production of reduced graphene oxide (rGO) using an environment-friendly reducing agent ( l -glutathione/L-Glu) to test its feasibility for CO & NO2 gas sensing. The structure, morphology, and thermal stability of as-synthesized rGO are investigated via Raman spectroscopy, Fourier infrared spectroscopy, X-ray diffraction, Field emission scanning electron microscope, and thermal gravimetric analysis. The L-Glu-rGO shows higher sp2 carbon hybridization (42at.%) than graphene oxide (GO) (29 at.%). The results indicate that L-Glu-rGO exhibits good relative response at 150 °C to both gases (10 ppm of NO2 and CO). Further, L-Glu-rGO shows a smaller response time (∼10.61 s for NO2 and ∼5.05 s for CO) than GO (∼16.64 s, ∼11.92 s to NO2 and CO respectively) at 150 °C, indicating the potential application of L-Glu-rGO for gas sensing.

Bio-Reduced Graphene Oxide as a Nanoscale Antimicrobial Coating for Medical Devices

Antimicrobial coating on biomedical devices to prevent bacterial colonization is of great interest in healthcare industry nowadays. In this context, graphene nanomaterial has created an excellent opportunity in the biomedical research. The whole cell biomass of Rhizopus oryzae has been explored as a reducing agent for eco-friendly synthesis of reduced graphene oxide (rGO) and minimizing the extensive use of toxic chemicals. The as-synthesized rGO was then characterized by UV–vis spectroscopy, thermo gravimetric analysis, and high-resolution transmission electron microscopy (HRTEM) studies. The hydrodynamic size and surface charge were analyzed by dynamic light scattering and ζ potential studies, and the values were found to be 4350 ± 25 nm and −21.2 ± 5.22 mV, respectively. The HRTEM analysis depicted the ultrathin sheet-like morphology of rGO. The graphene oxide (GO) and as-prepared rGO were then coated onto the surface of aluminum plate for testing antibacterial properties. The attenuated total reflect...

Fabrication of Nontoxic Reduced Graphene Oxide Protein Nanoframework as Sustained Antimicrobial Coating for Biomedical Application.

Bacterial colonization on medical devices is a major concern in the healthcare industry. In the present study, we report synthesis of environmental sustainable reduced graphene oxide (rGO) on the large scale through biosynthetic route and its potential application for antibacterial coating on medical devices. HRTEM image depicts formation of graphene nanosheet, while DLS and ζ potential studies reveal that in aqueous medium the average hydrodynamic size and surface charge of rGO are 4410 ± 116 nm and -25.2 ± 3.2 mV, respectively. The Raman, FTIR, and XPS data suggest in situ conjugation of protein with rGO. The as-synthesized rGO protein nanoframework exhibits dose-dependent antibacterial activity and potential of killing of 94% of Escherichia coli when treated with 80 μg/mL of rGO for 4 h. The hemolytic and cytotoxicity studies demonstrate that rGO protein nanoframework is highly biocompatible at the same concentration showing significant antimicrobial properties. The rGO coated on the glass surface obtained through covalent bonding exhibits potent antibacterial activity. Antibacterial mechanism further demonstrates that rGO-protein nanoframework in dispersed state (rGO solution) exerts bactericidal effect through physical disruption accompanied by ROS-mediated biochemical responses. The rGO subsequently entering into the cytoplasm through the damaged membrane causes metabolic imbalance in the cells. In sharp contrast, physical damage of the cell membrane is the dominant antibacterial mechanism of rGO in the immobilized state (rGO coated glass). The obtained results help indepth understanding of the antibacterial mechanism of the biosynthesized rGO and a novel way to develop nontoxic antibacterial coating on medical devices to prevent bacterial infection.

High-Level Supercapacitive Performance of Chemically Reduced Graphene Oxide

Summary Reduction of graphene oxide (GO) is an important process because it holds promise for the production of reduced graphene oxide (rGO) with physicochemical properties similar to those of pristine graphene. In conventional chemical reduction, strong reducing agents, such as sodium borohydride and hydrazine, cannot be recycled. Also, fast reaction kinetics bring an imbalance in the desirable properties of rGO. Here, we present one-pot chemical reduction of GO in aqueous medium by an unconventional mild reducing agent (FeCl 2 /HCl) where rGO is isolated as the precipitate and the reducing agent is recycled upon simple treatment of the filtrate with HCl. The fabricated all-solid-state supercapacitors of as-synthesized rGO exhibited significantly higher specific capacitance than those obtained with rGO derived from conventional reducing agents. The cycling stability of the all-solid-state supercapacitor (>80% retention of capacitance beyond 100,000 continued cycles) and its flexibility (>500 bending cycles) were remarkable. Use of commercially available organic electrolyte further boosted the supercapacitor performance.

High-sensitive nitrogen dioxide and ethanol gas sensor using a reduced graphene oxide-loaded double split ring resonator

A reduced graphene oxide (rGO) incorporated double split ring resonator (DSRR) portable microwave gas sensor is proposed in this work. The sensor is fabricated using two major steps: the DSRR is fabricated on the FR-4 substrate, which is excited by a high impedance microstrip line. The rGO is synthesized via a chemical route and coated inside the smaller ring of the DSRR. The SEM micrographs reveal crumpled sheets of rGO that provide a large surface area, and the XRD patterns of the as-synthesized rGO reveal the two-dimensional structure of the rGO nanosheets. The sensor performance is measured at room temperature using 100–400 ppm of ethanol and NO2 target gases. At 400 ppm, the sensor reveals a shift of 420 and 390 MHz in the S21 frequency for NO2 and ethanol gases, respectively. The frequency shifts of 130 and 120 MHz in the S21 resonance frequency are obtained for NO2 and ethanol gases, respectively, at a very low concentration of 100 ppm. The high sensitivity of the proposed rGO gas sensor is achieved due to the combined effect of the large surface area of the rGO responsible for accommodating more gas molecules, and its increased conductivity due to the transfer of the electron from the rGO. Moreover, an exceedingly short response time is observed for NO2 in comparison to ethanol, which allows the proposed sensor to be used for the selective detection of NO2 in a harsh environment. The overall approach used in this study is quite simple, and has great potential to enhance the gas detection behaviour of rGO.

Application of Few-Layered Reduced Graphene Oxide Nanofluid as a Working Fluid for Direct Absorption Solar Collectors.

Direct absorption solar collectors (DASC) convert solar energy into heat energy and transfer this heat energy to a carrier fluid. Numerical and experimental studies have shown that replacing the absorber medium with nanofluids in DASC increases the efficiency of solar collector significantly. Present work investigates the dispersion stability, optical and thermal properties of reduced few-layered graphene oxide (rGO) dispersed nanofluids for DASC. The synthesis of rGO was carried out by hydrogen exfoliation of graphene oxide at 200 °C. As-synthesized rGO was suitably functionalized to impart the hydrophilic nature. Different characterization techniques were employed to analyze the surface morphology of the sample. Nanofluids were prepared by dispersing calculated amount of functionalized rGO in DI water and ethylene glycol. Optical properties study reveals that the nanofluids exhibit good absorption ability over base fluids. The extinction coefficient of nanofluids showed significant improvement even at low concentration. Furthermore, the temperature dependent thermal conductivity study with different volume fractions, carried out for DI water and ethylene glycol-based nanofluids, shows considerable enhancement.

Preparation of Reduced Graphene Oxide and Copper Sulfide Nanoplates Composites as Efficient Photothermal Agents for Ablation of Cancer Cells

A novel strategy toward one-pot hydrothermal synthesis of copper sulfide nanoplates-decorated reduced graphene oxide (RGO–CuS) composites was developed. CuS nanoplates were successfully loaded onto the surface of RGO in the hydrothermal procedure, which was confirmed by transmission electron microscopy, UV-Vis–NIR and Raman spectroscopy. The as-synthesized RGO–CuS composites showed pronounced enhanced optical absorbance in near infrared (NR) region and higher photothermal conversion efficiency than noncomposite GO and CuS nanoplates. The RGO–CuS materials were used in photothermal ablation of cancer cells with a 980[Formula: see text]nm laser irradiation and showed improved performance than CuS nanoplates.

Microwave-assisted synthesis of graphene–Ni composites with enhanced microwave absorption properties in Ku-band

Recently, graphene has been applied as a new microwave absorber because of its high dielectric loss and low density. Nevertheless, the high dielectric constant of pristine graphene has caused unbalanced electromagnetic parameters and results in a bad impedance matching characteristic. In this study, we report a facile microwave-assisted heating approach to produce reduced graphene oxide–nickel (RGO–Ni) composites. The phase and morphology of as-synthesized RGO–Ni composites are characterized by XRD, Raman, FESEM and TEM . The results show that Ni nanoparticles with a diameter around 20 nm are grown densely and uniformly on the RGO sheets. In addition, enhanced microwave absorption properties in Ku-band of RGO–Ni composites is mainly due to the synergistic effect of dielectric loss and magnetic loss and the dramatically electron polarizations caused by the formation of large conductive network. The minimum reflection loss of RGO–Ni-2 composite with the thickness of 2 mm can reaches −42 dB at 17.6 GHz. The RGO–Ni composite is an attractive candidate for the new type of high performance microwave absorbing material. • Ni nanoparticles are grown densely and uniformly on the RGO sheets via microwave-assisted heating approach. • Ni resistance effect is proposed to explain the mechanism to decrease the permittivity with the rising combination of Ni and RGO. • The microwave absorption properties in Ku-band of RGO–Ni composites are effectively enhanced. • The mechanism to improve the microwave absorption properties is discussed.

In situ growth of hollow CuNi alloy nanoparticles on reduced graphene oxide nanosheets and their magnetic and catalytic properties

Hollow CuNi nanocrystals supported on reduced graphene oxide (RGO–CuNi) are synthesized by in situ co-reduction of Cu2+, Ni2+ and graphene oxide (GO) in a one-pot reaction. The as-synthesized RGO–CuNi nanocomposites were characterized by X-ray diffraction, transmission electron microscopy, energy-dispersive X-ray spectrometry, inductively coupled plasma optical emission spectrometry, Raman spectroscopy, and magnetic measurement. It is revealed that hollow CuNi nanocrystals with an average size of about 35.1nm are uniformly deposited on the surface of RGO nanosheets. The formation mechanism of the hollow CuNi nanostructures is also proposed based on the galvanic displacement reaction. The as-synthesized RGO–CuNi nanocomposite exhibits excellent electrocatalytic performance toward the oxidation of glucose in alkaline media, and also shows superior catalytic activity and recycling stability toward the reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP). Moreover, the RGO–CuNi catalysts can be easily recollected from the reaction system by an external magnetic field due to their considerable saturation magnetization. It is anticipated that loading hollow nanostructures on RGO sheets would open up a new avenue for developing multifunctional catalysts with low cost and high catalytic performance.

Unique quasi-vertical alignment of RGO sheets under an applied non-uniform DC electric field for enhanced field emission

Quasi-vertical alignment of as-synthesized RGO sheets under a non-uniform electric field deposited over a carbon cloth substrate and its field emission characteristics.