Synthesis Of GO Research Articles

The evolution of oxygen-functional groups of graphene oxide as a function of oxidation degree

Tuning the ratio of sp2/sp3 is crucial factor for obtaining high aspect ratio of graphene oxide. In this work, we reported a comprehensive study on synthesis of GO with different sp2/sp3 ratios at different oxidation reaction temperatures. The physicochemical properties of the as-prepared GO were characterized by Attenuated total reflectance infrared spectroscopy (ATR-IR), Raman spectroscopy, Solid-state nuclear magnetic resonance (SSNMR), Field emission scanning electron microscope (FESEM), X-ray diffraction (XRD), Transmission electron microscope (TEM), hydrophilicity test and zeta potential. Interestingly, GO-35 showed the smallest contact angle with carbon-to-oxygen (O/C) ratio 0.469. ATR-IR reveals the different intensity of hydroxyl (−OH), carbonyl (−CO), epoxy (C–O–C), as well as carboxyl (−COOH) moieties in the GO samples, and their intermolecular interactions significantly affected the interlayer spacing between consecutive identical planes of carbon atoms which examined using XRD. XPS confirmed that the basal species such as –OH is abundantly available in the GO-35 and unavailable in GO-50. Our results demonstrate that the properties of GO can be tuned using different oxidation reaction temperatures, which significantly influences types of oxygen-functional groups generated at different oxidation levels, thus could pave the way for various applications of graphene-based material.

Synthesis, characterization, photoluminescence, and antibacterial activities of silica-graphene oxide composites

In this research, a novel thin film Si-GO10 and nanopowders Si-GO30 of silica-graphene oxide (GO) composite were prepared via the sol–gel method and deposited on glass substrates using spray pyrolysis. X-ray diffraction (XRD) results showed a relatively strong peak in the graphite layer that corresponds to the (002) plane. Transmission electron microscope (TEM) images showed that SiO2 nanoparticles were randomly distributed on the surface of GO plates, and the particle size in these nanopowders was below 50 nm. Field emission scanning electron microscopy (FESEM) analysis demonstrated that silica nanoparticles on the surface of GO plates exhibited almost spherical and rod-like nanoparticle shape, which in turn confirmed the formation of SiO2–GO nano-hybrids. Photocatalytic investigations revealed that the composite materials exhibit high activity for dye adsorption and decomposition. Si-GO10 thin film did not undergo degradation after 120 min; however, for Si-GO30 nanopowder, the adsorption peak intensity was reduced to 665 nm, indicating a decrease in the dye concentration in the solution. Fourier transform infrared scan (FTIR) analysis demonstrated that carboxylic functional groups are decreased by increasing silica particles. Photoluminescence (PL) spectrum in Si-GO10 thin film showed a sharp emission peak at about 665 nm. This spectrum completely disappeared in Si-GO30 nanopowders. Results of the antibacterial properties emphasized that Si-GO30 nanoparticle would prevent Escherichia coli growth after 20 h. The presented methodology allows for the synthesis of GO supported silicon dioxide nanoparticles for promising applications in photocatalytic and antibacterial fields.

Synthesis of GO and rGO@Fe3O4@Ni as remarkable nanocatalyst systems for solvent‐free and chemoselective coupling reactions of dimedone with aromatic aldehydes

In this work, we synthesized modified GO and rGO@Fe3O4@Ni nanocomposite. The synthesized nanomaterials were characterized using Fourier‐transform infrared spectroscopy (FT‐IR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy‐dispersive X‐ray spectroscopy (EDX), X‐ray powder diffraction (XRD), vibrating sample magnetometer (VSM), Brunauer‐Emmett‐Teller (BET), and inductively coupled plasma optical emission spectroscopy (ICP‐OES). Furthermore, GO and rGO@Fe3O4@Ni were applied as catalysts in multicomponent coupling reactions (MCRs) of dimedone with structurally diverse aromatic aldehydes. All reactions were fulfilled rapidly and efficiently in solvent‐free conditions at 90°C. The results showed that GO and rGO@Fe3O4@Ni expedited the coupling reactions chemoselectively in such a way that GO directed the MCRs to the production of bisdimedones while rGO@Fe3O4@Ni drove the reactions one more step forward and afforded xanthenediones as the cyclization products. In addition, reusability of the examined nanocatalyst systems was carried out for four consecutive cycles without the significant loss of catalytic activity.

Metal doped graphene oxide derived from Quercus ilex fruits for selective and visual detection of iron(III) in water: Experiment and theory

Iron is one of the most abundant metals and an important micronutrient that needs to be consumed in balanced amounts. Excess consumption or deficiency of this micronutrient can have adverse effects on biological functioning of human organs. Hence, the selective detection of this micronutrient is very important. The present work reports a simple and selective sensing of iron (III) in aqueous solutions using potassium doped graphene oxide (K-doped GO), which is synthesized from Quercus ilex fruits via a greener route of solvo-hydrothermal method. The synthesis of K-doped GO is confirmed with the help of various characterisation techniques viz. X-Ray Diffraction (XRD), Raman Spectroscopy, Transmission Electron Microscopy (TEM), Energy Dispersive X-Ray Analysis (EDX), and Fourier Transform Infrared Spectroscopy (FT-IR).The Density Functional Theory (DFT) based first principle simulations are carried out to understand the interactions between K-doped GO and iron ions. The simulations reveal desorption of K-ions from the GO sheet due to the extremely high binding energy of iron ions on GO surface, which destabilizes the oxide groups as well as the potassium dopant. The desorbed K-ions from GO surface may react with water to form potassium hydroxide and subsequent quenching of fluorescence. Thus, the synthesized K-doped GO demonstrates its utility as a heavy metal ion sensor with detection limit of 0.345*10−7 M iron ions via spectrofluorometer. Moreover, this material is capable of detecting the presence of iron ions in water up to a limit of 7 ppm with naked eye.

Enhanced electrochemical detection of dopamine by graphene oxide/tungsten trioxide nanocomposite

Dopamine plays a vital role in neurotransmission and dopamine level detection in body fluid is very essential for diagnosis of neurological diseases. Finding a novel material, which enhances the electrochemical detection of dopamine is necessary in the present scenario. The Graphene oxide/tungsten trioxide (GO/WO3) nanocomposite were prepared by two-step procedure; modified Hummer's method for GO synthesis, followed by co-precipitation method for the preparation of WO3 with GO. The structural, chemical compositional and surface functional properties of as-synthesized GO/WO3 composite were systematically characterized. The WO3 nanocube shaped particles with an average diameter of 100–200 nm, completely covered the GO surface, during the in-situ growth process. Glassy carbon electrode (GCE) modified with prepared GO/WO3 nanocomposite was used as working electrode and analysed its selective and sensitive detection of dopamine by means of electrochemical measurements. The chronoamperometric results revealed that, GCE has wide linear range of (0.3 μM–1245 μM) of dopamine detection with outstanding selective performances. The limit of detection to 0.306 μM and sensitivity 0.392 μA μM−1cm−1 of electrode was calculated. The as-prepared GCE towards the detection of dopamine was tested in real samples (human urine), the measured results established the great dopamine sensing abilities with high selectivity and good stability in real samples.

Surfactants versus surface functionalization to improve the stability of graphene nanofluids

Graphene nanofluids have emerged as potential alternatives to improve the thermal efficiency of different engineering devices. However, their use in different applications that include polar liquids as base fluids is a problem due to the hydrophobic nature of graphene. In this study, we compared methods that use surfactants with those that employ surface oxidation (surfactant-free) to improve the dispersion of graphene in water and its stability over time. Cetyltrimethylammonium bromide and sodium dodecylbenzenesulfonate (SDBS), at their critical micelle concentration in water, were used as surfactants to prepare commercial graphene dispersions, and the electrochemical method was adopted to synthesize GO. Additionally, the effect of the concentration of electrolyte (sodium sulfate, Na2SO4) on oxygen functionalities in GO synthesis was evaluated and associated with nanofluid stability. The nanomaterials were characterized by thermogravimetric analysis, Fourier transform infrared spectroscopy, Raman spectroscopy, and scanning electron microscopy. Nanofluid stability was evaluated using the zeta potential and UV–VIS spectroscopy. The results show that the electrolyte has an important effect on the oxidation degree of the GO obtained: a high electrolyte concentration (0.5 M) produced the highest oxygen functionalities. Finally, the stability of the nanofluid produced with the electrolyte at 0.5 M was similar to that of the graphene nanofluid prepared with SDBS as surfactant.

Facile synthesis of GO as middle carrier modified flower-like BiOBr and C3N4 nanosheets for simultaneous treatment of chromium(VI) and tetracycline

A novel GO modified g-C3N4 nanosheets/flower-like BiOBr hybrid photocatalyst is fabricated by a facile method. The characterization results reveal that wrinkled GO is deposited between g-C3N4 nanosheets and flower-like BiOBr forming a Z-scheme heterojunction. As a mediator, plicate GO plays a positive role in prompting photogenerated electrons transferring through its sizeable 2D/2D contact surface area. The g-C3N4/GO/BiOBr hybrid displays a superior photocatalytic ability to g-C3N4 and BiOBr in photodegrading tetracycline (TC), whose removal efficiency could reach 96% within 2h. Besides, g-C3N4/GO/BiOBr composite can reduce Cr(VI), and simultaneously treat TC and Cr(VI) combination contaminant under the visible light. The g-C3N4/GO/BiOBr ternary composite also exhibits satisfactory stability and reusability after four cycling experiments. Further, a feasible mechanism related to the photocatalytic process of g-C3N4/GO/BiOBr is put forward. This study offers a ternary hybrid photocatalyst with eco-friendliness and hopeful application in water pollution.

Photo-Catalytic and Anti-microbial Activities of rGO/CuO Nanocomposite

In this work, cost-effective reduced graphene oxide/copper oxide (rGO/CuO) nanocomposite was synthesized by the reduction of GO to rGO and deposition of CuO on the surface of rGO using single step simple chemical method. The prepared nanocomposite was characterized using energy-dispersive X-ray spectroscopy (EDX), scanning electron microscopy (SEM), X-ray diffraction (XRD), ultraviolet–visible (UV–Vis) and Fourier-transform infrared (FT-IR) spectroscopy. The appearance of peak at 2θ = 11.03° confirmed the synthesis of GO and peaks at 25.65°, 36.14°, 43.09°, 49.91° and 69.52° indicated the synthesis of the nanocomposite. It was found that the normal particulate size of the prepared nanocomposite was in range of 30 to 50 nm. SEM analysis was done to demonstrate the external morphology of the prepared GO and the nanocomposite. The prepared rGO/CuO nanocomposite was analyzed towards photo-catalytic activity for the degradation of methylene blue (MB) and for the catalytic reduction of 4-nitrophenol (4-NP) to 4- aminophenol (4-AP). It was found that about 81% of MB was degraded in 240 min under UV light and complete conversion of 4-NP to 4-AP was done in only 2 min. The prepared rGO/CuO nanocomposite was also analyzed for anti-microbial activity. It was found that the rGO/CuO nanocomposite exhibits better anti-bacterial and anti-fungal activities than GO. The results indicated the increased biocompatibility of the rGO/CuO nanocomposites than GO.

Graphene oxide for efficient treatment of real contaminated water by mining tailings: Metal adsorption studies to Paraopeba river and risk assessment

The present study aimed at the GO synthesis by a modified Hummers method; and to evaluate the GO's efficiency for heavy metals adsorption in a real surface water sample, collected after a tailing dam rupture in the state of Minas Gerais Brazil. Furthermore, the acute and chronic risks by using a Hazard Quotient (HQ) method was used in order to assess the environmental impact related to raw surface water, and its reduction after GO treatment. The characterization techniques demonstrated that GO had a few-layers (~8 sheets) with micrometric dimensions containing some submicron sized sheets. Furthermore, the BET revealed that the GO had a considerable specific surface area, which favored the adsorption processes. Total dissolved solids and pH met the criteria established by national standards, even after the tailing dam rupture. Conversely, all heavy metal ions presented concentration values greater than recommended. In terms of removal efficiency, higher values were obtained for copper, manganese and aluminum, which were higher than 90.2%. Due to its high concentration in untreated surface water, iron poses a high risk (39.1 mg/L; HQ > 1) in cases of chronical consumption of the contaminated water. After adsorption process, the hazard index value was lower than one, which suggests that population is unlikely to experience adverse health effects. The results reinforce the GO applicability in surface water treatment, even in real and complex aqueous solutions as considered throughout this study.

The synthesis of GO: SnSbS thin films and the analysis of its electrochemical performance

Abstract GO SnSbS thin films were produced by Chemical Bath Deposition (CBD) method on ITO substrates at different deposition temperatures (20 °C, 40 °C, 60 °C and 80 °C). Structural characteristics of the films were determined by XRD, FTIR, EDX, FESEM and AFM and their optical properties were analyzed. Time-dependent current-voltage (I-V) measurements were performed for each sample at 5 mV/s, 10 mV/s and 20 mV/s in the range of −0.2 Vto 0.8 V and specific capacitance values and energy densities were calculated. At the lowest scanning rates of 5 mV/s, they were found to be 243 F/g, 575 F/g, 224 F/g and 94 F/g for different deposition temperatures (20 °C, 40 °C, 60 °C and 80 °C).

Polyurethane nanocomposite impregnated with chitosan-modified graphene oxide as a potential antibacterial wound dressing.

In this study, a polyurethane nanocomposite film (PU/CS-GO) was synthesized by incorporating chitosan-modified GO nanosheets (CS-GO) into PU matrices. The successful synthesis of unmodified GO and CS-GO nanosheets was confirmed by FTIR, XRD, Raman, SEM, EDS, and TGA analyses. In comparison with polyurethane nanocomposite containing unmodified graphene oxide (PU/GO), the effect of the modification of GO with chitosan on different properties such as morphological, thermal, thermo-mechanical, wettability, antibacterial, and biocompatibility properties was evaluated by various analyses including XRD, FE-SEM, TGA, DMTA, contact angle, antibacterial studies, and MTT assay. FE-SEM images exhibited better dispersion of CS-GO nanosheets within polyurethane matrices compared to GO nanosheets. According to DMTA results, PU/CS-GO showed a higher glass transition temperature (Tg) and storage modulus values than PU/GO sample. Based on antibacterial and MTT assays, in comparison with PU/GO, the PU/CS-GO nanocomposite demonstrated better biocompatibility and also antibacterial activity against both Gram-positive Staphylococcus aureus and Gram-negative Escherichia coli bacteria. Based on results, the PU/CS-GO nanocomposite can be suggested as a promising material for antibacterial wound dressing.

Synthesis and characterization of graphene oxide, reduced graphene oxide and their nanocomposites with polyethylene oxide

This work describes the synthesis of GO, rGO and their nanocomposites with PEO. GO and rGO were prepared by the modified Hummers method and in-situ reduction of GO utilizing green reductant L (+) Ascorbic acid. The nanocomposites were characterized by Fourier-transform infrared spectroscopy (FT-IR), X-ray powder diffraction (XRD), Field emission scanning electron microscopy (FE-SEM), Thermogravimetric Analysis (TGA), and Universal Testing Machine (UTM). FT-IR and XRD confirmed the synthesis of GO and rGO. FE-SEM confirmed the uniformly exfoliated GO and rGO nanosheets in the polymer matrix. Hydrogen bonding was the main interaction mechanism for GO with PEO while no interaction was detected by FT-IR for rGO. Enhanced thermal stability was observed for both GO/PEO and rGO/PEO nanocomposites. The mechanical analysis showed an increase in Young's modulus, tensile strength, and elongation at break for GO/PEO nanocomposites, which is attributed to the homogeneous dispersion and hydrophilic hydrogen bonding interaction of GO with PEO.

Synthesis and characterization of GO doped bio-resource based composites for NLO and multifaceted applications

The objective of the present work is to synthesize three different types of cardanol based benzoxazines such as cardanol-{1,4-bis(4-aminophenoxy)ethane}benzoxazine (CBAE2Bz), cardanol-{1,4-bis(4-aminophenoxy)butane} benzoxazine (CBAE4Bz) and cardanol-{1,4-bis(4-aminophenoxy)octane}benzoxazine (CBAE8Bz) by varying aliphatic ether link chain length through solventless method. The benzoxazines obtained with varying chain length were converted in to three different types of composites using paraphenylenediamine (PPDA) functionalized gaphene oxide (f-GO) as nano-reinforcement with varying weight percentage and were characterized by different analytical techniques. The molecular structure of the monomers was confirmed from Fourier transform infrared (FTIR) spectroscopy, 1HNMR, 13C NMR and MALDI mass. Data obtained from thermal studies infer that the prepared composites possess good thermal stability and enhanced values of Tg with respect to weight percent of functionalized graphene oxide content. However, the values of thermal stability, Tg, dielectric constant and dielectric loss were marginally decreased with respect to increase in length of the spacer aliphatic chain. The SEM and TEM studies confirm the homogeneous dispersion and single layer thickness of graphene sheet, respectively. The feasibility of usage of f-GO/PCAE2Bz composite in both gram positive bacteria (Bacillus subtilis, Staphylococcus aureus) and gram negative bacteria (Pseudomonas aeruginosa, Escherichia coli) environments were checked and the results obtained were discussed. Further, third-order NLO properties of open and closed aperture Z–scan results conclude that GO doped bio-resource based composites exhibit saturable absorption and self-defocusing type optical non-linearity. The third-order NLO susceptibility (χ3) of GO doped bio-resource based composites are increased with respect to quantity of reinforcement of GO to bio-based polymer. The maximum value of 1.03X 10−4 esu was observed and this nonlinearity is thermal in nature. Thus, the prepared composites may find wide range of applications in diverse surrounding conditions.

Synthesis of Graphene Oxide/Polypyrrole (GO/PPy) from Used Batteries as Electrodes in Supercapacitor Cells

Fabrication with graphite-modified GO/PPy composites have been studied from used batteries using the Hummers method. This research was performance in four steps: graphite powder preparation, GO synthesis, GO/PPy composite synthesis, and supercapacitor cell manufacturing. The results of the study were characterized using X-Ray Diffraction (XRD) to see the character of the diffraction patterns formed by carbon batteries used before and after calcination and Fourier Transform Infra-Red (FTIR) to identify compound functional groups and conduct initial tests in the form of voltage, capacitance and life cycle by measuring charge and discharge times. The graphite preparation stage is carried out by the calcination method at 900°C to produce graphite with an angle of 2θ which is 26° with reflection from (d002). FTIR data showed that GO/PPy composites showed a successful combination of characteristics similar to pure polypyrrole and GO which included a broad absorption band located at 3500-2300 cm-1 which was estimated to be stretching the amine from polypyrrole and O-H group in the GO layer and the emergence of peaks new in the absorption band with a wave number 909 cm-1 is the CN vibration of the polymerized pyrrole. Meanwhile, based on the LCR meter measurement results in the best supercapacitor cells in the sampel GO/PPy ratio (3:10) with voltage value of 74.1 mV; a capacitance value of 15.14 µF and the best charge and discharge times.

Synthesis and Characterization of a New Collagen-Alginate Aerogel for Tissue Engineering

Scaffolds have been used as extracellular matrix analogs to promote cell migration, cell attachment, and cell proliferation. The use of aerogels and carbon-based nanomaterials has recently been proposed for tissue engineering due to their properties. The aim of this study is to develop a highly porous collagen-alginate(-graphene oxide) aerogel-based scaffold. The GO synthesis was performed by Hummers method; a collagen-alginate and collagen-alginate-GO hydrogel were synthetized; then, they were treated by a supercritical drying process. The aerogels obtained were evaluated by SEM and FTIR. Osteoblasts were seeded over the scaffolds and evaluated by SEM. According to the characterization, the aerogels showed a highly porous interconnected network covered by a nonporous external wall. According to the FTIR, the chemical functional groups of collagen and GO were maintained after the supercritical process. The SEM images after cell culture showed that a collagen-alginate scaffold promotes cell attachment and proliferation. The alginate-collagen aerogel-based scaffold could be a platform for tissue engineering since it shows adequate properties. Further studies are needed to determine the cell interactions with GO.

Sol-gel synthesized spin coated GO: ZnO composite thin films: optical, structural and electrical studies

In the present work, we report on the structural, optical and electrical properties of solution-processed transparent conducting Graphene Oxide and Zinc oxide (GO: ZnO) composite thin films. Eco-friendly top-down modified Hummer’s method was adopted for the synthesis of GO. The ZnO and GO:ZnO thin films were grown on the glass substrates employing a simple and cost-effective spin coating technique. To get a stable solution for spin coating, an efficient solvent, 2-methoxyethanol is used to disperse GO. The structural properties of the GO: ZnO thin films were analyzed using XRD pattern wherein the average crystallite size decreases with the increase in GO% in ZnO. UV–vis spectroscopy studies showed that the optical band gap and the transmittance (>80%) of thin films are decreased with the increment of GO% in ZnO. FESEM and XRD data revealed a decrease in the particle size. GO: ZnO composite thin films exhibit an ohmic nature when silver is used as a contact with increase in current in composite thin films compared to ZnO thin film. The increase in current is due to the removal of oxygen moieties in GO and partial restoration of the graphene structure occurred during the pre and post-annealing of thin films. Thus, the reduced graphene oxide (rGO) acts as a conductive frame for ZnO. The optical and electrical parameters procured for GO: ZnO composite thin films propel the possibility of using composite thin films for transparent conducting electrode applications.

Facile synthesis of GO and g-C3N4 nanosheets encapsulated magnetite ternary nanocomposite for superior photocatalytic degradation of phenol

In this study, the synthesis of Fe3O4@GO@g-C3N4 ternary nanocomposite for enhanced photocatalytic degradation of phenol has been investigated. The surface modification of Fe3O4 was performed through layer-by-layer electrostatic deposition meanwhile the heterojunction structure of ternary nanocomposite was obtained through sonicated assisted hydrothermal method. The photocatalysts were characterized for their crystallinity, surface morphology, chemical functionalities, and band gap energy. The Fe3O4@GO@g-C3N4 ternary nanocomposite achieved phenol degradation of ∼97%, which was significantly higher than that of Fe3O4@GO (∼75%) and Fe3O4 (∼62%). The enhanced photoactivity was due to the efficient charge carrier separation and desired band structure. The photocatalytic performance was further enhanced with the addition of hydrogen peroxide, in which phenol degradation up to 100% was achieved in 2 h irradiation time. The findings revealed that operating parameters have significant influences on the photocatalytic activities. It was found that lower phenol concentration promoted higher activity. In this study, 0.3 g of Fe3O4@GO@g-C3N4 was found to be the optimized photocatalyst for phenol degradation. At the optimized condition, the reaction rate constant was reported as 6.96 × 10−3 min−1. The ternary photocatalyst showed excellent recyclability in three consecutive cycles, which confirmed the stability of this ternary nanocomposite for degradation applications.

Graphene Oxide and Its Derivatives: Their Synthesis and Use in Organic Synthesis

Since Geim and co-workers reported their groundbreaking experiments on graphene, research on graphene oxide (GO) and its derivatives has greatly influenced the field of modern physics, chemistry, device fabrication, material science, and nanotechnology. The unique structure and fascinating properties of these carbon materials can be ascribed to their eminent chemical, electronic, electrochemical, optical, and mechanical properties of GO and its derivatives, particularly compared to other carbon allotropes. The present Review aims to provide an overview on the recent developments in the preparation of GO and its derivatives and their applications in organic reactions. We will first outline the synthesis of GO and its derivatives. Then, we will discuss the major sections about their application as stoichiometric and catalytic oxidants in organic reactions, a particular emphasis on the carbon-carbon, carbon-oxygen, and carbon-nitrogen single bond-forming reactions, as well as carbon-oxygen and carbon-nitrogen double bond-forming reactions. Simultaneously, this Review also describes briefly transition metal supported on GO or its derivatives as a catalyst for organic reaction. Lastly, we will present an outlook of potential areas where GO and its derivatives may be expected to find utility or opportunity for further growth and study.

Sustainable fabrication of graphene oxide/manganese oxide composites for removing phenolic compounds by adsorption-oxidation process

To develop effective strategies for removing phenolic compounds, in-situ graphene oxide/manganese oxide (GO/MnOX, X = 2, 3/4) composites were fabricated via a sustainable method by synchronously utilizing manganese ions and acidic liquid waste during synthesis of GO. Comparatively, traditionally ex-situ GO/MnO2 composites were synthesized to verify the difference between in-situ and ex-situ synthesis. Based on the schematic and mass flow analysis, in-situ synthesis exhibited better atom economy and less waste emission than ex-situ synthesis. Then, the results of batch experiments exhibited that GO/MnOX composites possessed higher removal efficiency and wider pH range for p-cresol (p-CR) and p-tert-butylphenol (p-TBP) than GO/MnO2 composites. The maximum removal capacities of GO/MnOX composites were 107.68 mg/g for p-CR and 135.41 mg/g for p-TBP. And GO/MnOX composites could retain high removal efficiency for p-TBP (>90%) after five recycles. For in-situ GO/MnOX composites, GO sheets not only promoted the adsorption of phenolic compounds and by-products, but also enhanced the oxidation capacity of MnOX via an electron transfer interaction. Especially, the detection of ring cleavage products indicated further oxidation for p-TBP. Possessing an eco-friendly fabrication strategy and augmented adsorption-oxidation capability, in-situ GO/MnOX composites are expected to be applied in the removal of phenolic compounds.

An ultrafast quantum thermometer from graphene quantum dots.

We report an ultra-sensitive temperature sensor derived from graphene quantum dots (GQDs) embedded in a self-standing reduced graphene oxide (RGO) film. The GQDs are obtained as a natural derivative during synthesis of GO to RGO. A fundamental study on low temperature transport mechanisms reveals the applicability of temperature zone specific ‘variable range hopping (VRH)’ conduction models, i.e. Mott-VRH, Efros–Shklovskii-VRH and activation energy supported VRH. On the basis of transport behavior and confirmed by characterization analyses, the RGO film is modeled as GQD arrays where graphitic (sp2) domains behave as QDs and oxygenated (sp3) domains between interdots act as tunneling barriers. Temperature dependent resistance and current–voltage (I–V) characteristics indicate high sensitivity where sensor resistance changes by almost six orders of magnitude as the temperature is varied between 300 and 12 K. In convection mode, the developed temperature sensor shows a temperature coefficient of resistance (TCR) of ∼−1999% K−1 in the 300–77 K temperature range, which is much higher than the TCR values reported so far. Additionally, the sensor exhibits an extremely fast response (∼0.3 s) and recovery (0.8 s) time; and such high TCR leads to ultra high resolution of ∼ μK. The sensor shows excellent repeatability with negligible drift over several cycles. These studies are crucial for modern day thermal management and sensitive cryogenic applications.