Partial Reduction Of Graphene Oxide Research Articles

N,S‐rGO/CuFe2O4 nanocomposite as an efficient photocatalyst for reducing nitroaromatic compounds to their corresponding aminoaromatics using radiation of visible light

This study reports on developing a novel photocatalyst, N,S‐rGO/CuFe2O4, which can efficiently reduce nitroaromatic compounds to corresponding aminoaromatics under visible radiation. The synthesis of this photocatalyst involved simultaneous doping of nitrogen and sulfur elements into the carbon substrate of graphene oxide, its reduction, and coupling of CuFe2O4 nanoparticles in graphene oxide layers via a hydrothermal method. Various techniques such as XRD, XPS, FTIR, Raman, FESEM, TEM, EDAX, map scanning, PL, EIS, BET, and DRS were used to characterize and identify the synthesized product. Hydrazine monohydrate was employed as a hydrogen source for the reaction under investigation. These investigations proved the prosperous doping of nitrogen and sulfur elements into the graphene oxide structure, successful coupling of CuFe2O4 nanoparticles in graphene oxide sheets, and partial reduction of graphene oxide. In addition, we evaluated the recyclability and reusability of the photocatalyst for the reduction of nitroaromatic compounds over seven cycles and found no appreciable changes in reaction conversion.

Green synthesis of Dextrin‐graft‐poly(allyl amine‐co‐methacrylic acid)/reduced graphene oxide composite and its application for dye and pesticide removal from the aqueous medium

AbstractA Dextrin‐graft‐poly(allyl amine‐co‐methacrylic acid)/reduced graphene oxide (DEXTGP/RGO) is synthesized through the grafting of a combination of allyl amine (AAM) and methacrylic acid (MAA) monomers onto the dextrin polysaccharide backbone by using the free radical copolymerization technique in an aqueous medium, with potassium peroxydisulfate serving as the initiator followed by the partial reduction of graphene oxide (GO). Various characterization techniques including FTIR, 1H/13C NMR, XRD, FESEM, EDAX, and BET analysis are utilized to characterize both the synthesized DEXTGP/RGO composite and graft copolymer. Investigations are conducted on multiple operational variables, including adsorption kinetics, isotherms, and thermodynamic parameters, for the adsorption of both MB and PL. Both intra‐particle diffusion kinetic model and pseudo‐second‐order kinetics are observed to follow for the adsorption of MB, while the Langmuir isotherm model provided a good fit for the equilibrium data. In contrast, the adsorption of PL displayed solely pseudo‐second‐order kinetics, while the equilibrium data shows good agreement with both the Langmuir and Dubinin‐Radushkevich isotherm models. Maximum adsorption capacity ( ) of the RGO composite is found to be 932.56 mg/g for MB and 311.63 mg/g for PL. The thermodynamic analysis revealed that the adsorption of dye and pesticide onto the RGO composite is a spontaneous process.

GO-tagged PEI sizing agent imparts self-healing and excellent mechanical properties to carbon fiber reinforced epoxy laminates.

Carbon fiber-reinforced epoxy (CFRE) laminates have attracted significant attention as a structural material specifically in the aerospace industry. In recent times, various strategies have been developed to modify the carbon fiber (CF) surface as the interface between the epoxy matrix and CFs plays a pivotal role in determining the overall performance of CFRE laminates. In the present work, graphene oxide (GO) was used to tag a polyetherimide (PEI, termed BA) containing exchangeable bonds and was employed as a sizing agent to improve the interfacial adhesion between CFs and epoxy. This unique GO-tagged-BA sizing agent termed BAGO significantly enhanced the mechanical properties of CFRE laminates by promoting stronger interactions between CFs and the epoxy matrix. The successful synthesis of BAGO was verified by Fourier-transform infrared spectroscopy. Additionally, the partial reduction of GO owing to this tagging with BA was further confirmed by X-ray diffraction and Raman spectroscopy, and the thermal stability of this unique sizing agent was evaluated using thermogravimetric analysis. The amount of GO in BAGO was optimized as 0.25 wt% of BA termed 0.25-BAGO. The 0.25-BAGO sizing agent resulted in a significant increase in surface roughness, from 15 nm to 140 nm, and surface energy, from 13.2 to 34.7 mN m-1 of CF. The laminates prepared from 0.25-BAGO exhibited a remarkable 40% increase in flexural strength (FS) and a 35% increase in interlaminar shear strength (ILSS) due to interfacial strengthening between epoxy and CFs. In addition, these laminates exhibited a self-healing efficiency of 51% in ILSS due to the presence of dynamic disulfide bonds in BAGO. Interestingly, the laminates with 0.25-BAGO exhibited enhanced Joule heating and enhanced deicing, though the EMI shielding efficiency slightly declined.

Green synthesis of reduced graphene oxide by shallots

An environment-friendly and low-cost green reducing agent shallots are used for the facile and effective synthesis of partially reduced Graphene Oxide (prGO). The improved hummers method is used for the synthesis of GO. Synthesis of reduced graphene oxide (rGO) using green reducing agents is recognized as one of the most economical, environmentally friendly, facile and efficient approaches. At the same time, partially reduced graphene oxide have the advantages and convenience of both GO and rGO and can be facilitated for more advanced applications. X-Ray Diffraction, RAMAN spectroscopy, SEM, UV Visible and FTIR spectroscopy are used for the analysis of structural and surface properties of prGO. FTIR analysis established that most of the oxygen-containing functional groups such as hydroxyl, carboxyl carbonyl, and epoxy groups are removed partially during the reduction process. XRD peak is observed at 2θ = 22.5°, and ID/IG ratio in Raman spectra is about 0.92. From all the above studies we got clear information regarding the facile and effective partial reduction of graphene oxide using shallots.

Partial reduction of graphene oxide toward the facile fabrication of desalination membrane

Partial reduction of graphene oxide toward the facile fabrication of desalination membrane

Scalable nanomanufacturing of holey graphene via chemical etching: an investigation into process mechanisms.

Graphene with in-plane nanoholes, named holey graphene, shows great potential in electrochemical applications due to its fast mass transport and improved electrochemical activity. Scalable nanomanufacturing of holey graphene is generally based on chemical etching using hydrogen peroxide to form through-the-thickness nanoholes on the basal plane of graphene. In this study, we probe into the fundamental mechanisms of nanohole formation under peroxide etching via an integrated experimental and computational effort. The research results show that the growth of nanoholes during the etching of graphene oxide is achieved by a three-stage reduction-oxidation-reduction procedure. First, it is demonstrated that vacancy defects are formed via a partial reduction-based pretreatment. Second, hydrogen peroxide reacts preferentially with the edge-sites of defect areas on graphene oxide sheets, leading to the formation of various oxygen-containing functional groups. Third, the carbon atoms around the defects are removed along with the neighboring carbon atoms via reduction. By advancing the understanding of process mechanisms, we further demonstrate an improved nanomanufacturing strategy, in which graphene oxide with a high density of defects is introduced for peroxide etching, leading to enhanced nanohole formation.

Elucidating the role of graphene oxide layers in enhancing N-Nitrosodimethylamine (NDMA) rejection and antibiofouling property of RO membrane simultaneously

Water reclamation using reverse osmosis (RO) has become an indispensable component of the urban water supply system. However, the removal of low molecular weight contaminants of emerging concerns such as N-Nitrosodimethylamine (NDMA) from RO is challenging, thereby raising serious safety concerns about reclaimed water. Herein we modify RO membrane with graphene oxide (GO) using polydopamine (PDA) as crosslinking agent. The modification of commercial RO membrane via co-deposition of PDA-GO subsequently resulted in superior NDMA rejection (83 ± 3.57%) when compared with the membranes modified via GO, PDA, GO on PDA impregnated surface, and pristine RO. The narrow interlayer spacing of the GO (0.36 nm), attributed to its partial reduction occurred due to thin PDA layer formation on its both sides, exhibited enhanced sieving effect in addition to the coverage of free–volume hole-size of the polyamide layers which offered hindrance to NDMA permeation. In addition, CFU-enumeration and confocal laser scanning microscopy revealed that the partial reduction of GO did not significantly affect its associated antibacterial property when compared with the membrane modified via GO after PDA impregnation. However, enhanced antibiofouling performance was observed using optical coherence tomography (OCT) employed in this study for in-situ, real-time, and non-destructive fouling monitoring with better flux performance.

Paraffin–graphene oxide hybrid nano emulsions for thermal management systems

Phase change material nano-emulsions are investigated as potential working fluids for various applications including heat transfer and solar applications. Main hindrances to their application are the difficulty in maintaining emulsion stability and the subcooling effect. In this study, new phase change material nano-emulsions (PCMEs) were designed and characterized as possible heat transfer media to be used at 21 and 55 °C, by investigating two commercial phase change materials melting at these temperatures. In particular, the influence of graphene oxide (GO) and reduced graphene oxide (rGO) on emulsion stability and on thermal and optical properties of PCMEs has been investigated. The stability of emulsions was verified and no phase separation or significant growth of PCM droplets were observed through storage and after freeze–thaw cycles. GO was less successful in case of paraffin melting at 21 °C, while it was effective in reducing subcooling to only 1 °C for nanoemulsion with paraffin melting at 55 °C and strongly influenced heat transfer capability. This resulted in a fluid thermal capacity increase of more than 20% within 10 °C from PCM melting temperature. The partial reduction of GO did not result in significantly changing the thermal properties of nanoemulsions and slightly increased the optical absorption, due to higher optical absorption of rGO with respect to GO.

Graphene oxide/polyvinylpyrrolidone composite coating on 316L SS with superior antibacterial and anti-biofouling properties

Here, we report the fabrication of a graphene oxide (GO)/polyvinylpyrrolidone (PVP) (GP) composite coating on 316L stainless steel (SS) with superior antibacterial and anti-biofouling performance using electrophoretic deposition (EPD). At an optimal EPD condition (10 V, 60 s), PVP and GO concentrations of 0.03 and 0.1 wt%, respectively, a uniform crack free coating with superior antibacterial and anti-biofouling properties is obtained. The morphology and composition of the composite coating were characterized by field emission scanning electron microscope (FESEM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), and Raman spectroscopy. The absence of COOH peak in GO and GP specimen found in the XPS and FTIR confirm the partial reduction of GO by oxidative decarboxylation during the EPD. The shift in the >NCO bond to a higher binding energy, as compared to the pure PVP, indicated the presence of intermolecular hydrogen bonding between the PVP and GO. The antibacterial activity of the coated specimens using marine bacterial isolates of Gram-negative Pseudomonas sp. and Gram-positive Bacillus sp. showed a four order reduction in bacterial density, and a significant decrease in the biofilm thickness on the GP specimens. The enhanced antibacterial activity was due to the disruption of cell membranes by sharp edges of GO surface and oxidative stress imparted due to reactive oxygen species. The enhanced surface hydration by PVP inhibited the adhesion and growth of organic molecules on GP coating. Further, the enhanced photocatalytic activity of GO due to the presence of PVP also increased the generation of H2O2 in GP coatings as compared to GO coating. These results show that GP composite coating is a promising candidate to tailor 316L SS surface with excellent antibacterial and anti-biofouling properties.

Controlling the structure and photocatalytic properties of three—dimensional aerogels obtained by simultaneous reduction and self-assembly of BiOI/GO aqueous colloidal dispersions

Water pollution affects all living habitats, since it is the most basic element that sustains all life forms and, as an exceptional solvent, it readily makes any compound available for living cells, either nutrients or noxious substances. Elimination of molecular contaminants from water quality is one of the most challenging technical problems that conventional treatments like flocculation and filtration fail short to defeat. Particulate photocatalysts, used to degrade contaminants, have the main drawback of their recovery from the water matrices. The inclusion of photocatalytic nanoparticles (NPs) into a large supporting framework, is presented as an innovative approach aiming to ensure a facile separation from water. To this end, three-dimensional (3D) aerogels with photocatalytic properties were prepared by a simple and scalable method based on the reduction—induced self-assembly of graphene oxide (GO) in the presence of BiOI nanoparticles. With the help of ascorbic acid, as a green reducing agent, partial reduction of GO into reduced graphene oxide (RGO) and self-assembly of both kinds of nanostructures into a porous monolith was achieved. BiOI doped RGO aerogels were further stabilized and morphologically controlled using poly (ethylene glycol) as stabilizer. The photocatalytic performance of these aerogels was evaluated by following the discoloration of methylene blue (MB) solution, under visible light irradiation, showing that structure and dispersion degree of NPs to be fundamental variables. Hence, this methodology is proposed to produce hybrid aerogels with controlled morphology and photocatalytic performance that has the potential to be used in water cleaning procedures.

Application of sodium dodecyl sulfate intercalated Co[sbnd]Al LDH composite materials (RGO/PDA/SDS-LDH) in membrane separation

Layered double hydroxides (LDHs) is a typical type of anionic clay minerals. In this study, an SDS-LDH with sodium dodecyl sulfate (SDS) intercalation was prepared by the ion exchange method, and the modified SDS-LDH was successfully combined with graphene oxide (GO). In the presence of dopamine, partial reduction of GO to reduced graphene oxide (RGO). RGO/PDA/SDS-LDH (RPS) composite material was prepared successfully and used in the field of membrane separation. The RPS-2 composite membrane combines the advantages of GO and SDS-LDH, which can increase GO flux while maintaining a high rejection rate. The flux was increased from 10.21 L·m−2h−1bar−1 of GO to 79.24 L·m−2h−1bar−1 of RPS-2, and the rejection rate of various dyes was above 97%. The rejection rate of methylene blue (MB) 97.34% was maintained after 10 cycles, and its flux loss rate is only 45.32%. The composite membrane had good stability under different pH conditions, which provides a basis for the practical application of the membrane.

Catalytic Reduction of Graphene Oxide Membranes and Water Selective Channel Formation in Water-Alcohol Separations.

Graphene oxide (GO) is a promising membrane system for chemical separation applications due to its 2-D nanofluidics properties and an ability to control interplanar spacing for selectivity. The permeance of water, methanol (MeOH) and isopropyl alcohol (IPA) through 5 µm thick membranes was found to be 0.38 ± 0.15, 0.33 ± 0.16 and 0.42 ± 0.31 LMH/bar (liter/m2·h·bar), respectively. Interestingly, the permeance of a water–alcohol mixture was found to be dramatically lower (~0.01 LMH/bar) than any of its components. Upon removing the solvent mixture, the transmembrane flux of the pure solvent was recovered to near the original permeance. The interlayer space of a dried GO membrane was found to be 8.52 Å, which increased to 12.19 Å. 13.26 Å and 16.20 Å upon addition of water, MeOH and IPA. A decrease in d-space, about 2 Å, was consistently observed when adding alcohol to water wetted GO membrane and an optical color change and reduction in permeance. A newly proposed mechanism of a partial reduction of GO through a catalytic reaction with the water–alcohol mixture is consistent with experimental observations.

Preparation, characterization, and nonlinear optical properties of graphene oxide thin film doped with low chirality metallic SWCNTs

We present non-linear optical properties of graphene oxide (GO) doped with low chirality metallic single walled carbon nanotubes (m-SWCNTs) thin films. The weight percentage of the m-SWCNTs was 5, 10, and 20 wt%. High-resolution transmission electron microscope (HRTEM), high resolution scanning electron microscope (HRSEM), Raman, and UV–vis spectroscopy were used to characterize the prepared samples. We have investigated their nonlinear optical properties using open and closed Z-scan technique at Nd:YAG laser at 1064 nm laser pulses (7 ns, 10 Hz). The nonlinear absorption coefficient β, nonlinear refractive index n2, and third order nonlinear susceptibility χ3 were calculated. The results show that all samples exhibit reverse saturable absorption (RSA) because of increasing metallicity and/or partial reduction of GO during laser illumination. The nonlinearity response of the GO/m-SWCNT films increase as the m-SWCNTs percentage increases. The high non-linear optical parameters of the GO/m-SWCNTs films make them as superior candidates for near-infrared (NIR) laser protection applications.

Plant extract assisted synthesis of reduced graphene oxide sheet and the photocatalytic performances on cationic and anionic dyes to decontaminate wastewater

Green synthesis of reduced graphene oxide (RGO) has gained momentum over chemical methods due to its environmental compatibility. The present study deals with the green synthesis of the RGO sheet using the bark extract of Alstonia scholaris by the simple heating method in less time duration. Different characterizations such as x-ray diffraction (XRD), ultraviolet-visible (UV-Vis) spectroscopy, Fourier-transform infrared (FTIR) spectroscopy confirm the formation of RGO and the transmission electron microscopy (TEM) study shows that the synthesized material is a few-layered RGO sheet. The result of the photoluminescence (PL) study explores the partial reduction of graphene oxide (GO). The photocatalytic activities of the synthesized product were investigated via photo-degradation of methylene blue (MB) and methyl orange (MO). The results show that the synthesized RGO is more fruitful in cationic dye (MB) degradation than that of anionic dye (MO) depending on the electrostatic interaction between RGO and the dyes. The rate of photocatalytic performance of the nanocomposite on MB dye is 40 times greater than that of MO dye.

Ammonia modified graphene oxide – Gold nanoparticles composite as a substrate for surface enhanced Raman spectroscopy

Simple treatment of graphene oxide (GO) with ammonia solution at room temperature changes its chemical composition as revealed by infrared, Raman and X-ray photoelectron spectroscopy results. Both - pristine GO and GO modified with ammonia solution (NH3-GO) were combined with spherical gold nanoparticles (AuNPs) or gold nanourchins (AuNURs) and studied as possible substrates for surface enhanced Raman spectroscopy (SERS) using Rhodamine 6G (R6G) as probe. AuNPs or (AuNURs) were adsorbed on thin layers of either as-prepared GO or NH3-GO. The AuNPs/NH3-GO support enables easy identification of the characteristic bands of R6G at the 10−7 M concentration, while for AuNPs/GO the R6G concentration must be at least ten times higher in order to obtain the same quality spectra. For AuNURs the difference between NH3-GO and GO is even more significant. The observed enhancement factors are higher for AuNURs too. The improved SERS intensity results mainly from more efficient adsorption of AuNPs on NH3-GO comparing to pristine GO, as suggested by SEM and EDS results. Another possible factor affecting the SERS activity may be partial reduction of GO by NH3 and introduction of nitrogen functionalities which in turn affects the chemical and dipole contribution to SERS enhancement.

Laser Reduction of Graphene Oxide/Zinc Oxide Nanoparticle Nanocomposites as a One‐Step Process for Supercapacitor Fabrication

Herein, the laser reduction of graphene oxide (GO) and zinc oxide nanoparticle (ZnONP) nanocomposite films is proposed as a one‐step process for supercapacitor fabrication. The films, deposited by casting onto a flexible poly(ethylene terephthalate) (PET) substrate coated with indium‐doped tin oxide (ITO), are subjected to laser irradiation (5 mW, 405 nm) to reduce the GO phase and produce laser‐reduced GO (LRGO). Scanning electron microscopy/energy dispersion spectroscopy (SEM–EDS), micro‐Raman spectroscopy, and current versus voltage (I × V) analyses show a partial reduction of GO to LRGO, forming several conductor‐insulating (LRGO/GO) microporous interfaces, and thereby favoring the formation of a supercapacitor structure. Moreover, the topmost LRGO film layer is extensively reduced, making it sufficiently conducting to work as the counter electrode as well. However, the reduction process is less effective when ZnONPs are introduced into the GO matrix because ZnONPs get clustered and scatter the incident laser before reaching the GO phase. The capacitive behavior, assessed by cyclic voltammetry and galvanostatic charge–discharge measurements, reveals the following specific capacitances: 2.68 F g−1 (GO/LRGO) and 1.44 F g−1 (GO/LRGO/ZnONP). The method proposed herein is advantageous because it produces the microcapacitor structures and LRGO counter electrode in a single laser reduction step.

Hybridization of graphene oxide and mesoporous bioactive glass: Micro-space network structure enhance polymer scaffold

Graphene oxide (GO) and mesoporous bioactive glass (MBG) are commonly used to improve the mechanical and biological properties of polymer scaffolds, respectively. Nevertheless, their single introduction to polymers may encounter problems with uneven dispersion due to nano-aggregation effects. In this work, a GO and MBG hybrid with micro-space network structure were prepared by a chemical reduction-coagulation method to solve these problems. GO and MBG were first uniformly mixed in an alkaline aqueous dispersion. Subsequently, GO was partially reduced by introducing dopamine and co-coagulated with MBG, and then assembled into a GO@PDA@MBG hybrid structure under electrostatic effect. Specifically, the ring opening and deoxygenation reaction between the oxygen-containing functional group of GO and the amine group of dopamine achieves functionalization and partial reduction of GO. In addition, the hydrogen bond between the amine group of dopamine and the silanol hydroxyl group of MBG promotes the coagulation of MBG on GO@PDA. The hybrid structure was then mixed into polymer matrix to prepare a composite scaffold by a laser additive manufacturing process. The results showed that GO @ PDA @ MBG hybrid structure increased the tensile strength and modulus of polymer scaffold from 5.8 MPa and 312.2 MPa to 14.1 MPa and 539.7 MPa, respectively. The enhanced mechanical properties can be attributed to the “pinning” and “crack strengthening” effect of GO@PDA@MBG hybrid structure in polymer matrix. Besides, the scaffold also significantly promotes adhesion and proliferation of osteoblasts, demonstrating good biological properties.

Reduced graphene oxide/SnO2 nanocomposites for the photocatalytic degradation of rhodamine B: Preparation, characterization, photosensitization, vectorial charge transfer mechanism and identification of reaction intermediates

2 dimensional-reduced graphene oxide (RGO) was anchored on the surface of tin oxide (SnO2) to extend the absorption to visible region. Rutile structure is confirmed for SnO2 and RGO-SnO2. Partial reduction of graphene oxide to RGO is confirmed by infrared and Raman spectroscopic techniques. RGO-SnO2 shows 30% reduced recombination of charge carriers. The enhanced photocatalytic activity of RGO-SnO2 can be attributed to vectorial electron transfer process in the continuous network of RGO with large specific surface area, synergistic interaction between RGO and SnO2, unique double layer characteristics and photosensitization process. Major photocatalytic degradation reaction intermediates were identified by GC-MS technique.

Performance improvement of organic resistive memories by exploiting synergistic layered nanohybrid dispersed polymer composites

Functionalized layered nanohybrid materials have been thoroughly explored in numerous practical applications including photocatalysis, supercapacitors, and sensors, and have inherent potential to excel in the field of organic resistive random access memory devices as well. Herein, we report an efficient, facile, and cost-effective in situ synthesis route to prepare a layered nanohybrid by grafting cadmium sulfide (CdS) nanorods with exfoliated graphene oxide (GOs) sheets via the one-step hydrothermal functionalization technique. Such a nanohybrid material displays advantageous characteristics possessed by them due to the formation of organic–inorganic heterojunctions at their interface. Sandwiched devices, with a configuration of ITO/reduced graphene oxide–CdS/poly-methyl methacrylate (PMMA)/Al, are fabricated by dispersing different wt. % of the layered nanohybrid in a poly-methyl methacrylate (PMMA) matrix. Detailed current density vs voltage (J–V) studies exhibit excellent bipolar resistive switching characteristics reaching a very low set voltage of ∼−0.48V, high current ION/IOFF ratios of ∼106, and ultralow set/reset power densities of ∼10−8/10−6W/cm2 for devices containing 0.4 wt. % nanohybrid nanofillers. Partial reduction of GOs and the formation of heterojunctions during the synthesis process undoubtedly boost the resistive memory performances resulting from the synergistic effect in layered nanohybrid materials. The fabricated devices have been subjected to various analyses in order to test their stability, repeatability, and reliability, all of which have been found to display encouraging results.

Electrochemical sensing of glucose by chitosan modified graphene oxide

Graphene oxide (GO) coated electrodes provide an excellent platform for enzymatic glucose sensing, induced by the presence of glucose oxidase and an electrochemical transduction. Here, we show that the sensitivity of GO layers for glucose detection redoubles upon blending GO with chitosan (GO+Ch) and increases up to eight times if covalent binding of chitosan to GO (GO−Ch) is exploited. In addition, the conductivity of the composite material GO−Ch is suitable for electrochemical applications without the need of GO reduction, which is generally required for GO based coatings. Covalent modification of GO is achieved by a standard carboxylic activation/amidation approach by exploiting the abundant amino pendants of chitosan. Successful functionalization is proved by comparison with an ad-hoc synthesized control sample realized by using non-activated GO as precursor. The composite GO−Ch was deposited on standard screen-printed electrodes by a drop-casting approach. Comparison with a chitosan-GO blend and with pristine GO demonstrated the superior reliability and efficiency of the electrochemical response for glucose as a consequence of the high number of enzyme binding sites and of the partial reduction of GO during the carboxylic activation synthetic step.