Graphene is a highly promising material in the development of new photodetector technologies, in particular due its tunable optoelectronic properties, high mobilities and fast relaxation times coupled to its atomic thinness and other unique electrical, thermal and mechanical properties. Optoelectronic applications and graphene-based photodetector technology are still in their infancy, but with a range of device integration and manufacturing approaches emerging this field is progressing quickly. In this review we explore the potential of graphene in the context of existing single photon counting technologies by comparing their performance to simulations of graphene-based single photon counting and low photon intensity photodetection technologies operating in the visible, terahertz and X-ray energy regimes. We highlight the theoretical predictions and current graphene manufacturing processes for these detectors. We show initial experimental implementations and discuss the key challenges and next steps in the development of these technologies. Single photon counting photodetectors require an incident single photon to be absorbed and to give a measurable signal. A number of different photodetector technologies have been developed for optical single photon counting with a wide range of specifications such as energy and time resolution, and operating temperature. For instance photomultipliers, avalanche diodes  and tranThese detectors have many different applications, in areas as diverse as medical and space sciences or security applications. For instance a photon counting photodetector has applications on a satellite for the detection of faint, distant stars, or in fluorescence spectroscopy for use in characterizing biological samples. Single photon counting photodetectors also have quantum information applications, ranging from quantum key distribution (QKD) ,6 to tim2 bonded carbon atoms. It has captured the world’s attention since it was first isolated in 2004 ..W=EphotoA plot of the dependence on the initial photon energy of the distribution of charge carriers produced is shown in However for a photon energy less than Initially we arbitrarily picked the II rate by using a ratio to the phonon rate, −8 s illustrated in If we integrate over the entire active scattering time  then this gives us an estimate of the total number of charge carriers produced. The II rate is then indicative of the active scattering time, with an active scattering time of order 10Our results enabled us to design our prototype detector, based on the schematic from , Figure In summary, our results demonstrate the feasibility of a new type of ultrafast photon counter operating at optical and IR wavelengths. Such a device can be operated at approximately 100 MHz, although higher frequencies may be possible with improved calculations of the impact ionisation rate to give our detector comparable or superior results to other detectors. We obtain a value of the electron-hole pair creation energy, i and Ge . The detA number of different techniques can be used for photodetection at terahertz frequencies, such as the photothermoelectric effect and bolometry . AnotherTomadin  discussed which becomes increasingly sharper with increasing momentum relaxation time, and at regular values of Ω/ωp. For larger momentum relaxation time we also see a lower noise, In ge noise . Figure Across our devices the graphene channels were coupled to a number of different antennae, either a bowtie (or a variant “beetle” antenna) as shown in −1 but has presented difficulties with regards to the speed of detection. As shown in A number of groups are working on the development of graphene-based X-ray detectors using a number of different techniques. The most promising developments are from the Jovanovic group ,47,48,49e design . They haThe detectors developed by the Jovanovic group would be unsuitable for high speed, low intensity single photon counting photodetection, but the graphene channel resistance technique, which has also been shown capable of single molecule sensing , potentiThe graphene channels were etched to different sizes from 5 µm × 10 µm up to ~50 µm × 100 µm. These were connected to nickel-aluminium source and drain pads, as shown in Whilst our eventual aim is to detect low intensity or single photon sources, we chose to undertake initial experiments using illumination from a pulsed optical laser to characterise the behaviour of the detector and, in particular, its likely sensitivity. These pulsed lasers were calibrated using an Excelitas C30742-33 Series silicon photomultiplier (SiPM). The pulsed laser offers many advantages for initial characterisation including simple control of the deposited energy via variation of pulse width or by attenuation with filters, as well as providing a periodic strobe signal with which the detector output pulse, if present, will be synchronised cf. the unknown random arrival time of X-ray events from an X-ray source. The latter capability is critical when trying to measure the sensitivity while looking for the smallest detectable pulse above the noise. In addition the laser pulse can be used to generate a deposited energy at equivalent depths in the substrate to UV and soft X-ray single photons. bias = 10 mV voltage applied between the source and drain contacts, as shown in Pulse, captured on an oscilloscope. The device was initially connected to an Analog Devices ASA4817-1 amplifier in transimpedance mode, with VPulse. In this arrangement we identified the same saturation as in In order to reduce the noise for higher sensitivity we rearranged the GFET measurement circuit. The device was connected to two low noise, high gain, Canberra 2001 charge sensitive preamplifiers on each contact coupled through two 1 pF capacitors, with two 1 kΩ resistors in series with the graphene, as shown in Pulse peak occurs before the charge carriers recombine, with the recombination time driving the fall time of the signal. The calibrated pulsed laser was attenuated using a set of ND filters to simulate a range of X-ray energies. As expected, with increased attenuation we measured a smaller VPulse, as shown in pulse that suggests there are two contributions to the signal. bias = 10 mV and 0 mV respectively). The graphene peak due to the change in resistance is given by the difference between the two peaks. The invariant, larger component of the signal results from charge carriers that accumulate at the dielectric interface and are capacitively coupled to the contact. We attribute this saturation to the generation of a depletion region in the silicon by the application of a negative gate voltage, extracting the majority carriers, holes, from the silicon gate with electrons travelling towards the insulating dielectric and the graphene. Photons are absorbed in this depletion region and generate an electron hole pair which creates a dipole aligned with the field across the silicon ,94, whosPulse saturation, we would operate the device where the current-gate voltage curve has a larger gradient and therefore we would expect a proportional increase in the contribution of the signal attributed to the graphene to the overall signal. In addition, including a top gate would enable variation in the drain-source current and enable the depletion region in the silicon to be created to maximise VPulse.Our results thus far suggest that our current devices have the potential for single photon counting at X-ray energies above 100 keV. Further work is required to improve the signal to noise ratio to improve the sensitivity to lower energies. Our detector shows a significant contribution from capacitively coupled charge carriers in the silicon, and the next step is a redesign to enhance the contribution from the change in the resistance of the graphene which, at the moment, only contributes ~10%. We are currently looking to improve this contribution by increasing the charge carrier dipole field at the graphene using a thinner insulator dielectric, or an intrinsic absorber not requiring a separate insulator, and/or by encapsulating the device to give more reliable and enhanced electrical characteristics. For instance, with an increase in the carrier mobility of the graphene, and the Dirac point located such that we obtained the maximum mobility and operated at gate voltages where we have previously observed VThe devices discussed in the previous sections have specific requirements that create challenges in the fabrication process, such as graphene coverage, stacking and homogeneity. Micromechanical exfoliation provides easy access to graphene flakes and has been widely used experimentally to explore the properties for single-crystalline graphene and related device structures on the nano- to micrometre scale . The maiCVD is rapidly emerging also as industrially preferred technique for other 2D materials, such as h-BN and TMDs ,112,113.2· V−1· s−1 at 1.7 K when encapsulated between h-BN [2 interface from moisture and OH− states respectively. These trap states cause charge carriers to be trapped in these states resulting in two different Dirac points. This detriments the reliablility and instability of devices during measurements.Using a high quality bilayer graphene sample it is practical now to obtain mobilities of 60,000 cmeen h-BN . When prTo overcome such issues en route to scalable future technology it is desirable to encapsulate the device; hBN is the most promising 2D insulator for this purpose and has showed promising results in proof-of-concept devices ,116,117.In this review we have considered the various challenges facing graphene-based single photon counting photodetectors and their prospects at a technological level. The future applications of single photon counting photodetectors requires high detection efficiency with wavelength specificity, good temporal resolution and low dark counts. Graphene’s high mobility, tunable band gap (in bilayer graphene), strong dependence of conductivity on electric field, and other properties make it particularly suitable for this application. Here graphene acts as an (indirect) photoconductor with a high gain of transconductance due to the sharp field effect in graphene. Compared with more conventional detector architectures based on charge sensing, the effective decoupling of the detector (graphene) and the absorber (substrate/electrode for X-ray/THz regime respectively) could offer potential benefits. This will also allow more flexibility in the choice of the absorber material. Graphene, therefore, provides an interesting solution for single photon counting applications due to its unique properties, which will make it more favorable than other 2D materials such as metal chalcogenides. The other advantages which graphene can provide are the ultralow noise and high speed of operation.At visible wavelengths, current detector technologies are able to count single photons such as MKIDs and STJs, but are limited by a temporal resolution of ~1 µs. By contrast graphene photodetectors have shown detection on a femtosecond timescale. In addition, MKIDs are required to be operated at very low temperatures requiring expensive cryogenic techniques. Our simulations of bilayer graphene devices demonstrate wavelength specificity for a photon counter that can be operated over a wide range of temperatures; which can reduce the cost as well as size of an operating system, two factors crucial for implementation in space science. This may also enable more sensitive detectors, owing to the avoidance of wavelength dispersive elements, with potential applications in single photon fluorescence spectroscopy and the ability to sense multiple fluorophores simultaneously.In this review we have also discussed future graphene-based THz detectors that have applications in areas such as security, astronomy and medical sciences. The lack of sensitive commercial devices currently limit opportunities for detection at 1.2 THz, a regime where significant scientific research could be enabled by graphene THz detectors. We have shown simulations and designs of our proposed detector that exploits the Dyakanov-Shur principle and have identified various antennae designs optimized to these frequencies. We have also discussed critical properties of graphene which may provide a future solution required for PCTI.A number of options are available for detection of single X-ray photons, such as STJs and microchannel plate photomultipler tubes. STJs have good energy resolution, but must be operated at cryogenic temperatures, whilst MCP-PMTs have a timing resolution on the order of picoseconds, but provide very poor to no energy resolution. For graphene X-ray detectors, our experimental research with pulsed optical lasers, which simulate X-ray absorption, suggest a potential energy sensitivity of the detector equivalent to ~100 keV X-ray photons. We have also discussed the ample scope for the improvement in the design and operation of the detector to improve future sensitivity.Effective integration of graphene at industrial scale in these different types of photodetectors critically depends on the development of integrated manufacturing pathways, in particular progress in CVD graphene (single- and bi-layer) growth technologies in terms of control over homogeneity of layers, defect density, doping and transfer to device relevant substrates. We have also highlighted the importance of interfacial control and graphene encapsulation to ensure reproducible and reliable device characteristics. Graphene photosensors have the unique capability to cover an energy range from THz to X-rays. Our simulations and experimental results, combined with continuing advances in growth and fabrication techniques suggest that graphene-based new photodetector technologies have a highly promising future.


The structure and surface properties of COOH+/graphene and COOH functionalized graphene were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and contact angle measurement. Compared with graphene, COOH+/graphene and COOH functionalized graphene revealed improvement of cytocompatibility, including in vitro cell viability and morphology. More importantly, COOH+/graphene exhibited better improvement effects than functionalized graphene. For instance, COOH+/graphene with 1 × 1018 ions/cm2 showed the best cell-viability, proliferation and stretching. This study demonstrated that ion implantation can better improve the cytocompatibility of the graphene.Low hydrophilicity of graphene is one of the major obstacles for biomaterials application. To create some hydrophilic groups on graphene is addressed this issue. Herein, COOH In recent years, graphene, as an outstanding two-dimensional 2D) monolayer of carbon atoms, has attracted considerable attention due to its extraordinary properties including large surface area, excellent thermal conductivity, large mechanical fracture strength, high optical transmittance and superb charge-carrier mobility1D monolay3456791011121316via carboxyl should be an ideal approach to extend the potential applications of graphene in biomaterial fieldPrevious studies revealed that the COOH modified carbon nanotubes (COOH-CNTs) exhibited the promising effects on biocompatibility due to the active functional groups8+/graphene with different implant doses were created by adjusting the injecting time. The surface modification via chemical method is also considered to enhance the biocompatibility of graphene+/graphene or COOH functionalized graphene were evaluated by L-929 fibroblast cells in vitro.Ion implantation, which can modify the structure of a target-near-surface though high-energy ions, is one of the most powerful techniques in modifying surfaces18+/graphene  of the graphene increased from 0.92 to 0.97 after surface modified as shown in ID/IG indicate the increased disorder in carbon materialsID/IG.The Raman spectra of graphene, COOH580 cm−1 25. The Gsp2) groups, respectively28+/graphene show five peaks ascribed to C=C, C-C, C=O, C-O, O=C-O26282930via ion implantation and chemical method. These results are consistent with FTIR. On the other hand, the COOH functionalized graphene obviously shows a higher proportion of oxygen containing functional groups than COOH+/graphene. Based on the XPS results, the atomic percentage of oxygen in graphene, COOH functionalized graphene and COOH+/graphene with three inject doses  are 6.97 atm.%, 16.13 atm.%, 10.73 atm.%, 10.77 atm.% and 11 atm.%, respectively. Compared with COOH+/graphene, the COOH functionalized graphene contains more oxygen containing functional groups.The XPS elemental analysis and peak fitting results are shown in +/graphene with three inject doses . And the bar chart . As shown in +/graphene show the maximum at 6d. And the proliferation of cells on COOH+/graphene is obviously enhanced compared with COOH functionalized graphene. Moreover, the cells numbers of COOH+/graphene increase with the dose of ion implantation. Compared with blank (24-well culture plate), the maximum cells of graphene and COOH functionalized graphene don’t significantly increase. But COOH+ ions implantation obviously improves the cytocompatibility of graphene.L929 cells were used to estimate the cytocompatibility of samples by MTT assay +/graphene for 48 h were observed by SEM, as shown in +/graphene exhibits the largest ammout of L929 cells, and its cells are spread well with longer processus pseudopodia  was then removed from the tube center before being cooled from 250 °C to room temperature.Graphene was prepared from natural graphite +/graphene. The COOH+ was obtained from formic acid which was heated and evaporated into ion source+ ions were accelerated at a high voltage onto the graphene samples located at the vacuum chamber. The implantation was done at accelerating power of 30 KeV, the beam current density of 119 μA/cm2, and the pressure of 1.5 × 10−2 Pa. The COOH+/graphene with three doses, 1 × 1017 ions/cm2, 5 × 1017 ions/cm2, and 1 × 1018 ions/cm2, were produced by adjusting the treatment time. The detail process of sample preparation can be found in our previous workA Kaufmann-100 implanter was performed to obtain COOHvia a chemical method. In the first step, the as-prepared graphene was added into liquid mixture (3% conc. nitric acid + 3% conc. sulfuric acid + 79% water), and heated at 120 °C for 12 h. Then, the sample was repeatedly washed with distilled water and centrifuged to remove traces of acid. Finally, the graphene was functionalized with -COOH groups.For comparison, graphene was also functionalized +/graphene and COOH functionalized graphene were observed by field emission scanning electron microscopy  and high resolution transmission electron microscopy . The Fourier transform infrared spectroscopy  was employed to characterize the surface functional groups of samples. Raman spectroscopy  and X-ray photoelectron spectroscopy  were used to identify the functional groups on the surface of materials. The water contact angles (CA) of samples were recorded using the CAM KSV021733 optical contact-angle inclinometer .The morphologies of graphene, COOHin vitro110+/graphene, and COOH functionalized graphene in vitro, L-929 cell line was chosen as the target cells to evaluate the cell viability and proliferation by  (MTT) assay12/95% air incubator at 37 °C where the medium was replaced every 2 days. The cell culture medium  was supplemented with 10% of fetal bovine serum  and 100 units/ml streptomycin/penicillin4 cells/ml) were seeded onto each sample and allowed to culture from day 1 to day 8 at 37 °C in a humidified 5% CO2 incubator29912291+/graphene, and functionalized graphene were observed under the scanning electron microscopy  at 48 h post exposureCytocompatibility is an essential requirement for nanomaterials to be employed in biological systems, which was recommended by the International Standard Organization (ISO) as biocompatibility test model How to cite this article: Zhao, M.-l. et al. Enhancement of interaction of L-929 cells with functionalized graphene via COOH+ ion implantation vs. chemical method. Sci. Rep.6, 37112; doi: 10.1038/srep37112 (2016).Publisher’s note: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.


A relatively high specific capacity of 450 mAh·g−1 can still be retained after 200 cycles at a high rate of 2 C. The synthesis process introduced here is simple and broadly applicable to the modification of sulfur cathode for better electrochemical performance.Here, we report a two-step synthesis of graphene/sulfur/carbon ternary composite with a multilayer structure. In this composite, ultrathin S layers are uniformly deposited on graphene nanosheets and covered by a thin layer of amorphous carbon derived from β-cyclodextrin on the surface. Such a unique microstructure, not only improves the electrical conductivity of sulfur, but also effectively inhibits the dissolution of polysulfides during charging/discharging processes. As a result, this ternary nanocomposite exhibits excellent electrochemical performance. It can deliver a high initial discharge and charge capacity of 1410 mAh·g Li-ion batteries are one of the most popular electrochemical energy storage systems at present, which have been widely used in areas from portable electronics to electric vehicles ,2. Howev−1 and a corresponding theoretical specific energy of 2600 Wh·kg−1 on the assumption of the complete reaction of Li with S to form Li2S [Sulfur can yield a theoretical specific capacity of 1675 mAh·gorm Li2S . Thus, morm Li2S . Meanwhiorm Li2S . In addiorm Li2S .Carbon materials, which have relatively high electrical conductivity and variable structures are extensively used in the modification of sulfur. Sulfur/carbon composites with diverse structures have been synthesized and exhibited remarkably improved electrochemical performance than pure sulfur ,13,14,15One major function of graphene in the modification of sulfur is its high electrical conductivity, which can enormously improve electron transportation in sulfur cathode ,20. MeanIn this paper, a graphene/sulfur/carbon nanocomposite with a multilayer structure (named G/S/C hereafter), in which nanosized sulfur layers deposited on both sides of chemically reduced graphene sheets are then covered with amorphous carbon layers, is designed and successfully prepared. Such a unique structure realizes high conductivity, size miniaturization of sulfur, and surface protection of sulfur simultaneously, and, thus, gives rise to excellent charge/discharge performance. The G/S/C composite shows promising characteristics as a high performance cathode material for Li-S batteries.2S2O3 and HCOOH in the presence of graphene oxide (GO) and nonionic surfactant of Triton TX-100 resulted in the formation of the sulfur-graphene oxide (S-GO) composite  than that of G/S (69.5 wt.%), suggesting a lower content of S in G/S/C because of additional carbon layers from β-cyclodextrin. Taking into account that both pure graphene and pure carbon derived from β-cyclodextrin have the same weight loss of ~7 wt.%  of cells based on three cathode materials are displayed in −1) between 1.0 and 3.0 V. All the discharge curves show two plateaus in the voltage profile, which are consistent with the CV results. The charge/discharge curves for G/S/C and G/S are almost identical. Both samples can deliver a high initial discharge capacity of ~1410 mAh·g−1 and charge capacity of ~1370 mAh·g−1, corresponding to a high initial Coulombic efficiency of ~97%. As a comparison, pure sulfur only has initial discharge/charge capacities of less than 800 mAh·g−1, mainly due to its poor electrical conductivity. Another advantage of carbon modified sulfur over pure sulfur is the enhanced rate capability. As shown in −1 can be reached for both G/S/C and G/S at a high rate of 2 C, while the capacity for sulfur is only 180 mAh·g−1 at the same rate. When the discharge rate was recovered to 0.1 C after cycling at high rates, a reversible capacity of ~1000 mAh·g−1 can still be retained. The above results evidently prove the important role of conductive carbon materials, especially graphene, with a high electrical conductivity in improving the electrochemical performance of sulfur.−1, which is 63.8% of the initial capacity. However, the reversible capacity of G/S fades to 567 mAh·g−1, only 44.4% of its initial capacity, much lower than that of G/S/C. Pure S exhibits the worst capacity retention of 24.7%. The apparently improved cyclic stability of G/S/C over G/S is undoubtedly ascribed to the carbon layer on sulfur, which is able to inhibit the dissolution of polysulfides and immobilize sulfur during charge/discharge cycling. The cyclic stability of G/S/C is further verified by cycling at higher rates. As shown in −1 after 200 cycles at 0.5 C, and the reversible capacity of 600 mAh·g−1 and 450 mAh·g−1 can still be retained after 200 cycles at 1 C and 2 C, respectively.Though G/S/C and G/S exhibit similar initial capacity and rate performance, their notable difference in cycling performance reflects the important role of the carbon layer on the surface of sulfur. As displayed in The electrochemical results shown above clearly indicates that the design of G/S/C nanocomposite with a multilayer structure, in which sulfur is embedded between graphene and thin carbon layers, is an effective approach to improve the electrochemical performance of sulfur. The graphene sheets not only raise the electrical conductivity of sulfur, but also facilitate the formation of ultrathin sulfur layers. The sulfur deposited on graphene has a thickness of less than 10 nm, which is beneficial for enhancing the electrochemical activity and utilization rate of sulfur, resulting in high specific capacity and good rate capability. The carbon coatings on the surface of sulfur, which are derived from β-cyclodextrin, mainly act as a protection layer to prevent the outflow of sulfur during long-time cycling, giving rise to excellent cyclic stability.3 and 6.0 g of natural graphite (300 mesh) were added to 270 mL of concentrated H2SO4 (98 wt.%) at room temperature, and stirred for 10 minutes before slowly adding 36 g of KMnO4 into the mixture. The mixture was then heated to 40 °C and stirred for 6 h. Subsequently, under vigorous stirring, 480 mL of water was rapidly added and the slurry was continuously stirred at ~80 °C for another 30 min before 1200 mL of water and 36 mL of H2O2 solution (30 wt.%) were added sequentially to dissolve insoluble manganese species. The resulting graphite oxide suspension was washed repeatedly in water to be neutral. The graphite oxide became delaminated during washing, and graphene oxide powders were obtained by a freeze drying method.Graphite oxide was prepared using a modified Hummers’ method. The typical synthesis process is as follows: 6.0 g of KNO2S2O3·5H2O was added to the GO dispersion in the presence of 0.5 mL of Triton TX-100. The mixture was sonicated for another 1 h and then directly titrated into 2 mol/L HCOOH solution at a rate of 30–40 drops/min until the pH reached 1.5 and stirred for another 0.5 h, and the intermediate nanocomposite of S-GO was obtained. Afterwards, 50 mg of β-cyclodextrin was added into the above suspension containing S-GO composites, and stirred for 1 h to dissolve β-cyclodextrin before the suspension was transferred into a Teflon-lined stainless steel autoclave with a volume of 50 mL. The autoclave was then placed in an oven and heated at 180 °C for 12 h. After cooling to room temperature, the black cake-like precipitate was isolated by filtrating and washing with deionized water and absolute ethanol several times. Finally, the as-prepared product was dried in vacuum at 60 °C for 10 h. Graphene/sulfur (G/S) nanocomposite was also prepared using the same experimental process except for the addition of β-cyclodextrin.One hundred and fifty milligrams of as-prepared graphite oxide were suspended in 60 mL of ultrapure water and then sonicated for 1 h to form a stable graphene oxide (GO) dispersion. Then, 3 g of Na2 atmosphere with a heating rate of 10 °C/min.The morphology and structure of the materials were analyzed by a Hitachi S-4800 field emission scanning-electron microscope (SEM) and an FEI Tecnai G2 F20 transmission-electron microscopy (TEM) at an accelerating voltage of 200 kV. Atomic Force Microscopy (AFM) characterization was conducted by a Veeco Dimension 3100 V scanning probe microscope at ambient conditions using the tapping mode. Thermogravimetric analysis (TGA) was recorded in N−1 lithium bis-trifluoromethanesulfonylimide + 0.1 mol·L−1 LiNO3 in 1,2-dimethoxyethane/1,3-dioxolane  solution was used as the electrolyte. The cathode was prepared by mixing the active materials, carbon black, and polyvinylidene difluoride at a weight ratio of 80:10:10 in NMP solvent to form a slurry. The resultant slurry was uniformly spread via doctor blade on pure aluminum foil and dried at 60 °C for 48 h. The loading amount of active materials on aluminum foil is 2–3 mg·cm−2. Galvanostatic discharge and charge experiments of the coin cells were conducted using a cell testing system  between cut-off potentials of 1.0 and 3.0 V. All of the electrochemical performance measurements were obtained at a constant temperature of 25 °C.CR2032-type coin cells were fabricated by sandwiching a porous polypropylene separator  between the cathode and a lithium metal foil  in an Ar-filled glove box. 1 mol·LWe synthesized a novel graphene/sulfur/carbon ternary nanocomposite with a multilayer structure as a cathode material for Li-S batteries. Ultrathin sulfur layers were embedded between graphene nanosheets and amorphous carbon layers obtained by hydrothermal treatment of β-cyclodextrin. Graphene nanosheets mainly enhance the electrical conductivity of sulfur, while amorphous carbon coatings on the surface play a critical role in suppressing the dissolution of polysulfides. The electrochemical properties of G/S/C nanocomposite were systematically investigated, and compared with those of G/S binary nanocomposite without carbon coating and also pure sulfur cathode. G/S/C exhibited the best electrochemical performance among three cathode materials, including high initial specific capacity, good rate capability, and cycling stability, which can be ascribed to its unique multilayer structure. This work offers a new strategy to the rational design and synthesis of sulfur cathode for high performance Li-S batteries.


A graphene-based plasmonic metasurface which can independently control different polarized electromagnetic waves with reasonably small losses in terahertz regime is proposed and demonstrated in this paper. This metasurface is composed of graphene based elements. Owing to anisotropic plasmonic resonance of the graphene-based elements, the reflected phases and magnitudes of orthogonally polarized waves can be independently controlled by varying dimensions of the element. Four types of graphene-based plasmonic metasurfaces with different reflected phases distributions are synthesized and simulated, exhibiting diverse functions such as polarized beam splitting, beam deflection, and linear-to-circular polarization conversion. The simulation results demonstrate excellent performances as theoretical expectation. The proposed graphene-based plasmonic metasurface can be applied to realize extremely light-weight, ultra-compact, and high-performances electromagnetic structures for diverse terahertz applications. On the other hand, based on the general Snell’s law4, the metasurface has been created as an interface to produce discontinuous phase shifts, yielding anomalous refractions and reflections. It can pattern series of planar sub-wavelength structures to realize desired amplitude, phase, or polarization properties, offering extra, but important degrees of freedom to manipulate the electromagnetic waves. Many novel and exciting applications of metasurfaces have been proposed, such as wave-front shaping5, polarization-controlled plasmonic coupler6, reflect-array7, transmit-array8, photonic spin Hall effect9, holography11, and analog computing12. Meanwhile, focusing on polarization controlling, prominent works such as polarization beam splitters13, cross-polarization converters14, and linear to circular converters15, have been presented. All above-mentioned researches exhibit that the metasurfaces can provide powerful controlling capability, low-cost manufacturing and extremely suitable for device integration. However, most metasurfaces are based on metallic sub-wavelength structures which become quite lossy in terahertz band16, limiting their applications. Therefore, it is still a huge problem to independently manipulate different polarized electromagnetic waves with reasonably small losses in the terahertz band.Controlling polarized waves at will has become a desired research topic from microwave to optical applications. It can be widely utilized in systems such as polarization multiplexing18, has emerged as a promising, alternative candidate for terahertz applications27. Thanks to the two- dimensional (2-D) nature of graphene, graphene surface plasmons present extremely small wavelengths and tight field confinement, while maintaining quite small loss in the terahertz regime. Moreover, through chemical doping or electrical gating34, the mechanical, electronic, optical, and thermal properties of graphene are highly tunable, which is impossible or inefficient if metals are applied. Naturally, graphene is extended into metasurface, and several meaningful works on graphene-based metasurfaces are conceptually reported and demonstrated. Ref. Fortunately, graphene, a monolayer of carbon atoms arranged in a honeycomb latticeIn this paper, we propose graphene-based plasmonic metasurfaces, which can manipulate the transverse electric (TE) and transverse magnetic (TM) reflected waves independently with reasonably small losses in the terahertz regime. The unit cells of this graphene-based plasmonic metasurface are series of rectangular graphene based patches, which has anisotropic responses for each of orthogonal polarizations (TE and TM waves). The normally incident waves are totally reflected by the metal-grounded plane on the bottom of metasurface, but the reflection phases of both TE and TM waves are controlled independently by changing the dimensions of anisotropic unit cells of metasurface. Based on the proposed metasurfaces, four kinds of functional devices are designed for polarization beam splitting, beam deflection, and linear-to-circular polarization conversion with a deflection angle.40. But for practical applications, wave-graphene interactions have to be further improved. Therefore, we design a Fabry-Perot resonant unit element, which is composed of a rectangular graphene patch and a square grounded quartz glasses (SiO2) substrate. When we periodically extent these elements along both of the μm, and 2) spacer and bottom metallic ground plane are μm and 2) substrate is 41. Figure Graphene can strongly interact with electromagnetic waves in terahertz regime through plasmonic resonanceμm and varied μm to 15 μm. It is demonstrated acceptable TM wave reflection magnitudes above −3.3 dB and reflection phases varied from 50° to −240°. Meanwhile, the TE wave reflection magnitudes and phases are kept in constant. If we change μm to 15 μm, and keep 42. Here, we cannot achieve a full phase range of 360°, the reason is that the intrinsic losses of graphene patch limits the phase shift range, and the structure performs as a damped oscillator. But we obtain a maximum phase range of 290° which is enough for practical applications. Furthermore, we can achieve reflectivity larger than −3.3 dB, enabling the design of novel functional graphene-based metasurfaces to steer reflected electromagnetic waves with acceptable efficiency. It is worth noting here that the plasmonic response of metals becomes less pronounced as operating in terahertz bands because of the weaker interaction between waves and electrons.Therefore, the metallic reflected metasurfaces operating in terahertz band often have reflectivity less than 30%45, which obviously have lower efficiency than our proposed graphene metasurface.Figure 4, we can introduce an in-plane phase gradient 3737As above mentioned, we can utilize specific surface reflection phase distributions to manipulate electromagnetic waves arbitrarily. According to generalized laws of reflection and refraction15Due to we can independently control TM and TE waves by changing only one dimensional parameters, we can easily extent the generalized laws of reflection into two dimensional cases, where the surface reflection phase distribution can be calculated asAccording to the proposed graphene-based element, We design four functional metasurfaces, named type 1, type 2, type 3, and type 4, respectively. Here, type 1 and type 2 act as two kinds of polarization beam splitters (PBSs), type 3 operates as a beam deflector, and type 4 is a linear-to-circular polarization converter, respectively. It is worth mention here that the Figures Then, the type2 metasurface aims to deflect the TM and TE reflected waves to the direction of  between the graphene and the polysilicon. Detailed technology to fabricate these kinds of graphene metasurface can be found in ref. , supportIt is worth emphasizing that the general design procedure formulated herein facilitates further production of such devices for various applications. Considering the existence metasurfaces, the proposed graphene plasmonic metasurface can be applied to realize extremely light-weight, ultra-compact, and high-performances electromagnetic structures for diverse terahertz applications, extending the range of applications even further.4748. Such an approach has been widely used in many numerical work. However, it imposes significant meshing load and simulation time. Here, we apply transition boundary condition in COMSOL Multiphysics software, which assigns the conductivity to a single interface of a film with finite thickness. As a result, we are able to greatly relieve the meshing difficulty, save memory, and shorten the simulation time.In the terahertz region, the complex surface conductivity 2) substrate. The quartz glasses(SiO2) substrate has a relative permittivity of 2) substrate, respectively. In the simulation, Floquet ports were placed at The reflected magnitudes and phases of the proposed element were full-wave simulated using the Floquet’s periodic condition in COMSOL Multiphysics software, taking into account the inter-element coupling. The unit-cell depicted in Fig. The full-wave simulations of the proposed graphene plasmonic metasurface were performed in COMSOL Multiphysics 5.1 software. According to the specific surface phases distribution, we implement four types of metasurfaces by properly choosing the local element dimensions. To reduce the computation complexity, we apply perfectly matched layer (PML) boundary condition to the rest of the simulation space, ensuring proper numerical evaluation of the fields surrounding the metasurface.Supplementary Information


Using the Nationwide Inpatient Sample and US weather data, we estimated the probability of community-acquired pneumonia (CAP) being diagnosed as Legionnaires’ disease (LD). LD risk increases when weather is warm and humid. With warm weather, we found a dose-response relationship between relative humidity and the odds for LD. When the mean temperature was 60°–80°F with high humidity (>80.0%), the odds for CAP being diagnosed with LD were 3.1 times higher than with lower levels of humidity (<50.0%). Thus, in some regions , LD is rarely the cause of hospitalizations. In other regions and seasons , LD is much more common. Thus, suspicion for LD should increase when weather is warm and humid. However, when weather is cold, dry, or extremely hot, empirically treating all CAP patients for LD might contribute to excessive antimicrobial drug use at a population level. Legionella spp. are aerobic, gram-negative bacilli, common in the environment, that were identified as pathogenic after an outbreak of illness among attendees of a 1976 American Legion convention   and Google Maps’ Geocoding API . We located 2,079 unique hospitals  Nationwide Inpatient Sample (NIS) for 1998–2011. The University of Iowa Institutional Review Board deems such studies as non–human subjects research. The NIS, a stratified 20% sample of discharges from nonfederal US hospitals, contains data from 47 states; after excluding the 21 NIS states that do not report the American Hospital Association identifier (AHA ID), patient race, or admission month, we used data from 26 states: Arizona, Arkansas, California, Colorado, Connecticut, Illinois, Iowa, Kentucky, Maryland, Massachusetts, Mississippi, Missouri, Montana, Nevada, New Hampshire, New Jersey, New York, North Carolina, Oregon, Pennsylvania, Rhode Island, Utah, Vermont, Virginia, Washington, and Wisconsin. Next, we mapped the hospitals in these 26 states to the AHA-reported addresses using the AHA ID; we then converted the addresses to geographic coordinates by using the US Census Bureau Geocoder  from the International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9-CM). The primary diagnosis in the NIS is the condition chiefly responsible for the hospital admission  and 482 and subcodes  excluding 482.84 (pneumonia due to Legionnaires’ disease). We refer to the combination of the codes 481 and 482 as bacterial pneumonia. Because these codes were assigned to patients as their primary diagnosis code for admission, we assumed that this collection of codes identified cases of community-acquired bacterial pneumonia. Finally, using CDC surveillance results (>1 weather station within 100 km (62 miles).We excluded records for persons <18 years of age and records that omitted any of our variables of interest: age, sex, payer, race, admission month and year, and hospital location. We also required the hospital to have We obtained weather observations from the Integrated Surface Database (ISD) provided and maintained by the National Climatic Data Center of the National Oceanic and Atmospheric Administration. Because the NIS database provides only the month of admission, we aggregated the average temperature, relative humidity, and total rainfall by month for each weather station. We recorded each hospital’s monthly weather data as the mean of these values observed at nearby (within 100 km [62 miles]) weather stations. Using only the states with hospital location reported, we considered different definitions of “nearby.” Average temperatures computed using only the nearest station and stations within 10 or 25 miles were highly correlated with the average temperature using a 62-mile radius (r>0.99).3 to some temperature-specific maximum, which introduces problems because often the lowest observed absolute humidity at high temperatures is impossible at lower temperatures. Second, the values of absolute humidity were extremely correlated with temperature (r = 0.85), whereas the correlation was much lower with relative humidity (r = −0.23). The correlation of temperature with relative humidity is negative because relative humidity is often much higher at cold temperatures. To make the results easier to interpret and because the expected responses are not linear, we converted humidity and temperature into bins: relative humidity <50.0%, 50.0%–55.0%, 55.1%–60.0%, 60.1%–65.0%, 65.1%–70.0%, 70.1%–75.0%, 75.1%–80.0%, and >80.0%; and mean temperature <60°F, 60.1–80°F, >80°F. Additionally, monthly rainfall was binned into dry , normal , and wet . Patient age was binned by decade, and we included hospital latitude and squared hospital latitude. The squared hospital latitude was included to enable the effect of latitude to be nonlinear.Using logistic regression, we modeled whether a hospitalization for bacterial pneumonia had a diagnosis of LD on the basis of patient age, patient sex, payer, patient race, admission month, admission year, hospital latitude, total monthly rainfall, mean relative humidity, mean temperature, and an interaction between temperature and relative humidity. The interaction is required because relative humidity depends on temperature. We used mean temperature because it captures the nighttime and daytime temperature effects more accurately than does mean high temperature. However, the average high temperature and the average temperature for a month are highly correlated (r = 0.988). We used relative humidity rather than absolute humidity for 2 reasons. First, relative humidity ranges from 0% to 100% for any temperature, whereas absolute humidity ranges from 0 g/mTo visualize the model and how LD risk varies with space and season, we computed the fitted values from this model using location and weather information and set the demographic variables to their individual modal values for cases of bacterial pneumonia observed in the NIS data. Because the weather data are nationally complete, unlike the NIS data, we can take a given demographic profile  and estimate the probability of an LD diagnosis for any location, given the weather data for each location and month.>18 years and provision of a complete set of predictor variables), we had data on 3,005 LD cases and 189,412 hospitalizations for pneumonia. The most common reasons for exclusion were lack of the AHA ID, admission month and year, and race, because some states elected not to report these variables.The NIS data provided a total of 5,172 LD cases from 447,132 hospitalizations for bacterial pneumonia . After aWe compared several demographic and severity measures between the portion of the data dropped because of missing values and the proportion retained . Among tIn general, hospitalized persons with LD were younger than those with other bacterial pneumonia and more likely to be male . We foun2 test statistic = 350.42; p<0.0001)  . AlthougThe combination of the temperature and humidity main effects and interactions can make understanding the combined effect difficult. For this reason, we separately reported the estimated composite odds ratios for each combination . AdditioWe determined the monthly percentage of bacterial pneumonia discharges for which an LD diagnosis had been given within HCUP by US Census region . PercentWe also determined the probability of a case of bacterial pneumonia being diagnosed as LD in 2011 using the local weather data. We restricted this prediction to the states used to estimate the model . We set >80.0%) months. For example, the odds of LD being diagnosed in a pneumonia patient during a month when the rainfall is <18 mm and the temperature is 60°–80°F was 3.1 (1.70/0.55) times higher when the relative humidity was >80.0% than when it was <50.0%. When rainfall amounts were greater, the risk also increased; however, regardless of rainfall, warm and humid weather was a major risk factor. Also, we found a dose-response relationship between relative humidity and the odds of an LD diagnosis during periods of warm weather. In contrast, hot, cool, or dry weather patterns produce no meaningful increase in LD.Our results suggest that the incidence of LD varies considerably by season and local weather patterns. Specifically, LD is more likely to occur in warm (60°–80°F) and very humid , and resistance has increased for both . Although we found no meaningful differences between the parts of the sample we retained and parts we dropped, it is possible that participation/reporting varies nonrandomly. In addition, we do not have information about medications, test results, or microbiology data, so we cannot confirm an LD diagnosis or determine whether and what microbiological testing was performed. Thus, future work should incorporate alternative case-finding approaches, including more granular information about cases, specifically the CDC legionellosis database. Alternative data sources may also enable the generation of more granular geographic estimates and age-based estimates of disease risk. We also are unable to confirm without more clinical data the extent to which having a primary diagnosis of pneumonia correlates with CAP for the control patients in our analysis. Second, some of the geographic differences in the predicted probabilities may be due to differences in propensity to test for, and therefore diagnose, LD. Third, the NIS reports only the month of admission. Thus, we aggregated weather information by month. Future work needs to consider more granular  data. Fourth, we consider the weather around a hospital, not the weather experienced by the patients admitted to the hospital. Fifth, meteorologic variables are interdependent: relative humidity depends on temperature because the maximum amount of water suspended in the air rises with the temperature, and our model may inadequately specify these relationships. Finally, our analysis did not contain possibly important geographic differences .The experience of warm and humid weather patterns common during summer resulting in substantial increases in LD might have driven the current view about the frequency of LD in the United States. Our results demonstrate the need to investigate the effects of incorporating recent weather patterns, particularly wet, warm, and humid weather, as an additional consideration in the clinical decision-making process for CAP. Our results suggest that the risk for LD is highly related to temperature and humidity regionally. We found locations where LD relatively rarely causes hospitalization for CAP, such as the Southwest and Rocky Mountains, but also the Mid-Atlantic region during the winter. Information about weather exposures for patients also should help inform the design and interpretation of CAP-treatment trials. Future work examining more granular environmental data may ultimately enable clinicians to safely limit initial empiric antimicrobial drug selection for CAP to monotherapy with a β-lactam in specific seasons and regions.


The device performances, in terms of relative conductance variations, upon exposure to NO2 at standard ambient temperature and pressure, are analysed. In addition, we examine the effect of the substrate morphology and, more specifically, of the ink/substrate interaction on the device performances, by comparing the response of different chemiresistors fabricated by dispensing the same suspension also onto Al2O3 and Si/SiO2 substrates and carrying out a supportive atomic force microscopy analysis. The results prove the possibility to produce sensor devices by means of a wholly environmentally friendly, low-cost process that meets the requests coming from the increasing field of paper-based electronics and paving the way towards a flexible, green-by-design mass production.The extremely high sensitivity to the external environment and the high specific surface area, as well as the absence of bulk phenomena that could interfere with the response signal, make graphene highly attractive for the applications in the field of sensing. Among the various methods for producing graphene over large areas, liquid phase exfoliation (LPE) appears to be very promising, especially if combined with inkjet printing (IJP), which offers several advantages, including the selective and controlled deposition of small ink volumes and the versatility of the exploitable inks and substrates. Herein we present a feasibility study of chemiresistive gas sensors inkjet-printed onto paper substrates, in which a LPE graphene suspension dispersed in a water/isopropanol (H In the recent years, the potential of graphene for sensing applications has been largely explored because of its outstanding properties : extreme2O/IPA) mixture as sensing ink onto paper substrates. Analogous paper-based graphene sensors, relying on different fabrication processes, such as CVD  grown transferred graphene [2 exposure at standard ambient temperature and pressure. Moreover, as comparison, inkjet-printed sensors have been manufactured on standard insulating substrates, namely alumina (Al2O3), and silicon dioxide (Si/SiO2). They have been characterized through gas sensing and atomic force microscopy (AFM) analyses, in order to investigate the effect of the substrate morphology and, more specifically, of the ink–substrate interaction on the device performances.The aim of the current research is a feasibility study of chemiresistive gas sensors by inkjet printing a LPE graphene suspension dispersed in a water/isopropanol  of the printhead of the inkjet system. As a result, the performed analyses point out that the physical parameters of the dispersion are suitable for the IJP technique.Based on these considerations, the LPE graphene dispersion has been investigated by dynamic light scattering (DLS) to determine the size distribution profile of the suspended graphene flakes. An almost monomodal distribution characterized by a low polydispersity has been detected, so indicating the homogeneity of the sample. The average size distribution profile is displayed in 2O3 and Si/SiO2. The devices have been manufactured according to the geometry described in the Experimental part, taking care to attain a final base resistance in the range of 1–100 kΩ. In detail, two devices have been fabricated on paper, differing for the number of printed layers, namely 17  and 25 . The device printed on alumina (device D-AO) resulted in 31 overlapped layers, so driving the base resistance to 30 kΩ, similar to those of the paper-based devices. The fourth typology of device has been fabricated on silicon dioxide. It should be pointed out that the wetting of the aqueous graphene ink-Si/SiO2 system was very poor inducing a not continuous and not controlled deposition. This is expected since the measured surface energy of the substrate (30.95 mN/m) is comparable with the surface tension of the solution (26.30 mN/m). Hence, an UV–ozone treatment of the substrate was necessary to increase its surface energy, allowing for a more uniform deposition of the material. Nonetheless, the macroscopic aspect of the film printed on the treated substrate looks different from the others, with the material distributed over a larger area  has been fabricated printing 38 layers, with base resistance R0 = 15 kΩ. Pictures of the four devices is displayed in After having verified the jettability, the graphene ink has been dispensed onto paper and on two the standard insulating substrates Alger area . In addiI–V curve of the device D-P17 is reported in The voltamperometric characteristics of all the fabricated devices show a linear feature, confirming the formation of an ohmic contact between graphene and gold electrodes. As an example, the 2, the analyte towards which LPE graphene is more specific [2 for paper-based devices are reported. After an exposure of ten minutes, the devices reach a different percentage increase of the conductance G, defined as:The sensing properties of the chemiresistors have been tested by exposing the devices to NOspecific . In FiguG0 being the base conductance, measured immediately before the NO2 exposure. It is worth noting that the device fabricated with a lower number of printed layers (D-P17) shows a remarkably higher response (ΔG10 = 18%) respect to the device based on a thicker film  and even after several months of storage in air the same values were measured , and even lower (about 6%) in the third step. In 2 injections at different concentrations (in the range of 0.24–2 ppm). The measured ΔG10 values are reported as a function of the concentration in the inset. Both the dynamic behavior and the plot “response vs concentration” demonstrate how the device is still clearly sensitive to 0.24 ppm NO2, even starting very far from its “zero state”. Anyway, as elsewhere reported, the highlighted issues related to the slow recovery could be circumvented by recurring to suitable analyses of the sensing signal [Typical for graphene-based chemiresistors operating at room temperature, the sensing curves show slow recovery behavior. This implies several hours for reaching the initial conductance values or the recourse to UV or heating treatments . This isg signal .2O3 and SiO2, and the sensing performances of devices obtained with these conventional substrates were compared with those of paper-based devices. All chemiresistors have been exposed according to the same protocol . This behavior is rather unexpected and it deserves to be further investigated in a future work since, according to our experience, devices prepared with the same type of graphene dispersion onto Al2O3 and Si/SiO2 by drop-casting are stable and show better sensing performances over much longer times [Despite the fact that all the devices are constituted of the same sensing material, they exhibit quite different values of relative response to the analyte . The layoperties , while Der times .G(t), during the gas exposure. On D-P17, G(t) can be well fitted by the following law:In order to better understand the different sensing behavior, and possibly to obtain information about the underlying microscopic mechanisms, we have studied the time evolution of the conductance, G, with a characteristic time constant τ, from the initial value G0 to the asymptotic value G∞. The above written law, however, fails to satisfyingly fit G(t) on the other devices. This is particularly true for D-SO on which to the initial exponential increase follows further increase that is nearly linear. This suggests that the most appropriate function for G(t) should include an additional linear term to the previous exponential form:representing an exponential increase of G(t) over the whole time range of the increase of G for all the devices. As an example, in the inset of G of D-SO during the exposure to NO2, together with the best fit curves obtained with the two illustrated choices of G(t). It is easy to note how in this case the pure exponential fit fails and how a linear term must be added. A parameter is almost zero. On the contrary, the exponential term exhibits the highest τ value, which corresponds to the slowest increase of the conductance signal followed in sequence by D-P25, D-AO and D-SO, as observed from the curves in This function yields a more suitable fit for The overall electrical features and the detected differences in the sensing behaviors of the devices on different substrates have been further investigated, in order to understand whether there is any correlation with the surface features of the printed material. To this end, a morphological investigation with AFM has been performed.2 substrate: A marked material accumulation on the edge of the drop due to a significant coffee ring effect is visible. This ring constitutes an effective bulk path, which results in a lower base resistance. The edge accumulation is also responsible of the difficulties in controlling the base conductance value as a function of the number of inkjet-printed layers.Concerning the recorded base resistances, a poorer electrical connection between separated planar structures than between grains could be at the origin of the higher number (nearly double) of printed layers necessary to make the conductance of D-AO similar to the one of D-P17. The anomalous behavior of D-SO can be ascribed to the observed peculiar spreading of LPE graphene on the SiO2 carbon atoms (low interaction energy) and defects such as vacancies, dangling bonds, coordination defects and functionalizations (high interaction energy). In the specific case of our LPE graphene, defects are mostly ascribed to edge defects that are not chemically modified by the interaction with the substrates  of D-AO and D-SO compared to the devices on paper, indicating that the planar surface of the flakes promotes larger adsorption. In this perspective, the higher value of ΔG10 for D-P17 compared with D-P25 seems to contradict the higher statistical abundance of planar structures on the latter. Such apparent discrepancy could be explained by considering the additional effect related to the sensing film thickness as previously mentioned, i.e., the higher surface-to-volume ratio of D-P17 with respect to D-P25. From these premises, we can deduce the coexistence of two different adsorption mechanisms which provide a physical meaning to the functional terms employed to model G(t): the adsorption of the analyte on the surface and the consequent diffusion of NO2 molecules inside the bulk, i.e., the portion of the sensing film not directly exposed to the gas.A first analysis of the experimental results suggests that the clear difference in surface appearance could be the reason for the larger response (quantified by ΔA) when the amount of planar structures increases.As the time scale of the diffusion process is much longer than the measuring time, the behavior of this mechanism can be approximated by a linear function, leading to the linear term in 2. In this process D-SO also exhibited the fastest behavior. Once again, this agrees well with the overall picture and with the higher surface-to-volume ratio of graphene on this device.In addition, the adsorption probability of a single incident molecule increases when the direction of incidence approaches the normal of the local surface  . This is2 and Al2O3. All devices have been tested towards 1 ppm NO2 and showed to work at standard ambient temperature and pressure. Atomic force microscopy allowed to probe the effect of the morphology of the printed materials onto different substrates on the gas sensing behavior. Inkjet-printed paper-based devices exhibited poorer performances with respect to those on standard substrates in terms of conductance variation. This can be ascribed to the peculiar arrangement of the deposited material. Notwithstanding, a reliability in the control of the base parameters  has been clearly observed on paper substrate. In this frame, inkjet printing with its ability to control the thickness of the deposited ink appears a more powerful tool to device fabrication in comparison to other techniques commonly used, e.g., drop-casting deposition.A feasibility study on the fabrication of graphene-based chemiresistors, employing sustainable technologies and materials, namely by inkjet printing a hydro-alcoholic ink on paper, has been carried out. DLS, UV–vis and surface tension characterizations showed the suitability of the LPE graphene dispersion as ink for implementing inkjet printing on paper. The influence of the substrate morphology on the sensing performance has been examined further considering two standard insulating substrates as comparison, Si/SiO2O3-based device, which shows a surface characterized by planar structures, exhibited remarkably higher response. For this reason, future perspectives are oriented towards the development of proper surface treatments to promote the planar assembling of graphene flakes onto the paper substrate. In every respect, the results indicate the possibility to produce sensor devices by means of a wholly environmentally friendly, low-cost process that meets the requests coming from the increasing field of paper-based electronics and paving the way towards a flexible, green-by-design mass production.Overall, the main drawback in paper-based devices is the surface morphology of the sensing film, induced by the granular surface of the substrate. The Al2O (1:7) and sonicating in an ultrasonic bath (output power ca. 30 W) for about 48 h. In order to avoid undesired overheating of the water bath during the prolonged sonication, the temperature of the bath has been fixed at 50 °C. The water level has been kept constant by installing a syphon system.Graphite flakes (product 332461) and isopropyl alcohol  have been purchased from Sigma-Aldrich and Carlo Erba, respectively. Ultrapure water has been obtained with a Type 1 (Ultrapure) Milli-Q system. Colloidal suspensions have been prepared by mixing graphite flakes at 1 mg/mL in a solvent mixture IPA/HAfterwards, the suspension has been centrifuged for 45 min at 1000 rpm in order to remove unexfoliated graphite crystallites. The final ink has been obtained by taking 20 mL of this as-prepared graphene suspension, drying it in vacuum at 40 °C overnight, then adding 10 mL of fresh solvent mixture and briefly sonicating for 10 min.660> = 1920 ± 13 L·g−1·m−1  transmittance spectra of a diluted set of this dispersion have been performed by means of a Shimadzu UV-1800 UV–vis spectrophotometer. In all cases, UV–vis absorbance spectra have been measured that appeared flat and featureless [0 nm tranThe same system in static sessile drop configuration has been employed to perform substrate surface energy (SE) measurements. This analysis has been carried out by using water as polar solvent and dichloromethane as nonpolar solvent and the measurement results, coming from a sampling of five measurements, have been evaluated by the Owen, Wendt, Rabel and Kaelble (OWRK) method . Both diT = 25 °C by means of a Zetasizer Nano . DLS measurements have been collected over two weeks.Dynamic light scattering (DLS) analysis has been performed at Atomic force microscopy (AFM) images of the fabricated devices (substrates and deposited graphene) have been taken by means of an XE100 Park instrument operating in non-contact mode  at room temperature and under ambient conditions.2 , with gold electrodes have been employed as transducers. For all the substrates, interdigitated Cr/Au (30 nm/120 nm) electrodes have been realized by e-beam evaporation (chamber pressure at about 10−7 mbar) through a shadow mask.Different substrates, paper , alumina  and Si/SiOThe inkjet equipment has been a piezoelectric drop-on-demand Dimatix materials printer 2831 (DMP2831) of FUJIFILM USA suitable for the print of functional inks onto flexible and rigid substrates through multi-nozzles printheads.2.The graphene-based ink has been printed by keeping the electrode/substrate system at 30 °C and by employing 4 nozzles with a drop space of 25 μm. The chosen pattern of the printed sensing material is a rectangular surface of 9 × 1.75 mmThe chemiresistors have been prepared by inkjet printing the graphene dispersion onto the pre-patterned substrates and electrically characterized just after the fabrication. The devices have been manufactured with a different number of printed sensing layers depending on the substrates. The number of overlapped printed layers and the base conductance have been taken into account as parameters to address the device-to-device variation. All devices, after printing, have undergone a thermal treatment on a hot plate at 100 °C for 15 min for removing the residual solvent.2 have been performed in the gas sensor characterization system  equipped with a stainless steel chamber placed in a thermostatic box, keeping constant the temperature (T = 22 °C), the relative humidity (RH = 50%) and under controlled nitrogen environment at atmospheric pressure, by keeping the flow constant at 500 sccm.Tests for sensing measurements upon NOAll devices, biased at 1 V, have been analyzed through a measurement protocol consisting of an exposure towards the analyte for 10 min, preceded and followed by 20 min long phases in inert atmosphere .File 1Additional experimental data.


The tribological behaviors of graphene and graphene oxide (GO) as water-based lubricant additives were evaluated by use of a reciprocating ball-on-plate tribometer for magnesium alloy-steel contacts. Three sets of test conditions were examined to investigate the effect of concentration, the capacity of carrying load and the endurance of the lubrication film, respectively. The results showed that the tribological behaviors of water can be improved by adding the appropriate graphene or GO. Compared with pure deionized water, 0.5 wt.% graphene nanofluids can offer reduction of friction coefficient by 21.9% and reduction of wear rate by 13.5%. Meanwhile, 0.5 wt.% GO nanofluids were found to reduce the friction coefficient and wear rate up to 77.5% and 90%, respectively. Besides this, the positive effect of the GO nanofluids was also more pronounced in terms of the load-carrying capacity and the lubrication film endurance. The wear mechanisms have been tentatively proposed according to the observation of the worn surfaces by field emission scanning electron microscope-energy dispersive spectrometer (FESEM-EDS) and Raman spectrum as well as the wettability of the nanofluids on the magnesium alloy surface by goniometer. Magnesium and its alloys are attractive materials for a wide range of applications in such demanding fields as transportation, electronics or aerospace ,2. This To address these issues, lubricants can be employed. So far, there are no suitable forming fluids for the forming process of Mg alloy; even in some conditions, the forming fluid used for Al alloy is casually used and the result is not satisfied. The commonly used Al alloy forming lubricants relies heavily on sulfur-, chlorine- and phosphorous-containing organic compounds as additives. The discharge of these lubricants has caused a series of issues such as high cost, environmental pollution and others . FurtherLately, a wide variety of nanomaterials as lubricant additives is a rapidly progressing field of research owing to their unique chemical and structural attributes ,16,17. CThe aim of this study was to evaluate the tribological performances of graphene and GO as water-based lubricant additives for the magnesium alloy/steel contacts using a ball-on-plate tribotester. The lubrication mechanism was investigated by analyzing the worn surface using FESEM-EDS and Raman spectroscopy. It is anticipated that graphene or GO water-based nanofluids may find broad potential applications in the forming process of magnesium alloy.The graphene and GO used in this work were commercially obtained from Hengqiu Graphene technology Co., Ltd., Suzhou, China. The morphology and structure of the samples were observed with JEM 1200EX transmission electron microscope  and VG model Escalab 250 X-ray photoelectron spectroscopy . As shown in TEM images a,b, grap−1 at room temperature. In tensile test, at least three samples were tested for each condition and the average value was then obtained. The mechanical behaviors of the extruded AZ31 magnesium alloy are presented in The commercial AZ31 (Mg–3.07Al–0.78Zn–0.38Mn in wt.%) magnesium alloy ingots with 82 mm in diameter were homogenized at 380 °C for 2 h, and then were extruded to plates with dimensions of 56 mm in width and 3 mm in thickness at 380 °C. Several tensile tests were performed by a CMT6305-300 KN universal testing machine  with an initial speed of 1.5 mm·min0.01, surface roughness Ra 0.05 μm) was sliding with a speed controlled by a DC servomotor. Three sets of test conditions  in the ambient environment. Experimental set up of the tribotester is presented in shown in  were exaw was estimated by Equation (1):V = wear volume (mm3), NF = applied normal load (N), S = slidingdistance (m).The plate samples were cleaned in an alcohol ultrasonic bath for 5 min to eliminate the contaminants prior to the surface analysis. The rubbing surfaces on the magnesium alloys were analyzed by Zeiss AURIGA field emission scanning electron microscope  integrated with energy dispersive spectrometer . The Raman spectroscopy  of the wear tracks on the plates was used to analyze the characteristics of the graphene or GO residue. The wettability of the sliding counterparts was evaluated by determining the static contact angle of pure water and nanofluids droplets on the magnesium alloy surface (Ra ~ 0.08 μm) using JC-2000C1 goniometer . A 5 μL volume droplet was placed on the magnesium alloy surface using a syringe, and the reported values in this study were reproducible for five identical samples. The wear volume of the lower magnesium alloy plate was measured by Olympus OLS4000 laser scanning confocal microscope . Three replicates of friction and wear measurements were performed to minimize data scattering. In addition, then, the wear rate It is well known that the concentration of nanoparticles in the base lube plays a predominant role to control the friction coefficient and wear rate . In thisFor a prospective lubricant to be considered effective, it is also necessary to safeguard the underlying surface from wear and damage. The steel ball experienced little wear because its hardness is much greater than that of the magnesium alloy plates. Therefore, the worn scars on the AZ31 magnesium alloy plate were mainly analyzed in the present study. The variation of wear rate in The friction-reducing and anti-wear ability of 0.5 wt.% graphenenanofluids and 0.5 wt.% GO nanofluids for magnesium alloy/steel contacts were further investigatedin detail. Except for nanofluids, the pure water was chosen for comparison. The effect of load on the tribological properties of pure water and nanofluids are discussed and the results are shown in The stability of the lubrication film with time is a very important property in mechanical systems needed for their functionality during their service life. In order to evaluate the lubrication film endurance during sliding, the severity of the contact conditions was increased by increasing the applied normal load and sliding time and reducing the sliding velocities. The wetting of the water-based nanofluids on the metal surface is very critical to lubricant performances. Generally, the excellent wettability intends to promote the formation of a tribofilm, which can separate the asperity contact . Figure −1, 2D-band at 2712 cm−1 and a G-band at 1580 cm−1, which are the typical Raman signals of graphene. This means that some graphene would be inlaid into the worn surface of the specimen to improve the tribological behaviors. However, the Raman spectrum for the deposited graphene on the worn surface is some different characteristics in comparison with the pristine powder. The intensity ratio of D to G band increased as compared to that of the pristine graphene powder, illustrating significant modification had occurred to graphene during sliding by converting it into the disordered graphitic structure. The GO on the worn surface was confirmed by the Raman spectra analysis of the two most intense features of the D band (1345 cm−1) and G band (1587 cm−1) as shown in D/IG, in contrast that of the pristine GO powder. This should not be a surprise considering that those flakes were lying in between the two sliding surfaces standing a pressure of several hundred MPa. Such phenomenon has been well documented in the previous reports [Raman spectroscopy was carried out to further confirm that the excellent tribological performance is attributed to the presence of graphene or GO on the worn surface.  reports ,36.λ in Equation (2), where hmin refers to the theoretical minimum film thickness separating the contact interfaces. The hmin can be calculated by the Hamrock-Dowson model displayed in Equation (3), and Rq is the combined surface roughness determined according to Equation (4) [The tribological properties of potentially useful graphene and GO as water-based lubricant additives for magnesium alloy/steel contacts have been investigated in the present study. It is observed that both of the friction reduction and anti-wear ability of graphene or GO nanofluids were improved compared with those of pure water. Prior to any speculation of the friction-reducing and anti-wear mechanism, it is necessary to investigate the lubrication regime of the test situation. The lubrication regime in the tribological contacts can be divided into three categories, including boundary lubrication, mixed lubrication and hydrodynamic lubrication. The corresponding lubrication regime should be evaluated based on the value of tion (4) .(2)λ=hmWy is the applied normal load, ue is the linear velocity, η is the bulk viscosity of the nanofluids, E’ is the effective elastic modulus, and ’R is the radius of the ball. On the basis of the material characteristics and test condition, the thickness of the lubricant film at the point of contact is 25, 20, 18, 16 nm for 1, 3, 5, 8 N, respectively. The corresponding λ values were confirmed to be 0.26, 0.21, 0.19, 0.17, respectively. The lubrication regime is usually defined by the following regulations: boundarylubrication (0.1 < λ < 1), mixed lubrication (1 ≤ λ ≤ 3), elastohydrodynamic lubrication (λ > 3) [Of which  (λ > 3) . It is sThe high friction generally occurs in the boundary lubrication regime where a beneficial fluid lubricant film is unable to form and separate the rubbing surfaces. Therefore, the addition of nanoparticles in the base media is essential to provide a surface protective layer. In this study, when 0.5 wt.% graphene is dispersed into water, the friction coefficient and wear rate are respectively reduced by 21.9% and 13.5% as compared to that of the benchmark water. We know that, during sliding process, graphene with water tends to penetrate into the interface of contact pairs and gradually accumulate on the magnesium alloy surface, resulting in the formation of a transfer films between the rubbing surfaces. This outlook was supported by the FESEM–EDS spectra and Raman imaging shown in 2O3 (27% friction and 22% wear reduction with the addition of 1 wt.%) [2 nanoparticles (50% friction and 27% wear reduction with the addition of 0.8 wt.%) [In contrast, GO displayed higher friction-reducing and anti-wear capability than graphene did. The 0.5 wt.% addition of GO in the water offered reduction of friction coefficient by 77.5% and reduction of wear rate by 90% compared with the pure water, which is also larger than the reported values for other nanomaterial water-based additives, e.g., Al 1 wt.%) , TiO2 na.8 wt.%) , and nan.8 wt.%) . It can .8 wt.%)  demonstr.8 wt.%) . Thus, i.8 wt.%) ,46 and w(1)Graphene and GO as water-based lubricant additives improved the friction-reducing and anti-wear abilities. The best tribological response of the magnesium alloy/steel pairs evaluated was obtained when graphene or GO at a concentration of 0.5 wt.% was added to water.(2)Graphene and GO exhibited different friction-reducing and anti-wear efficiencies, and the tribological performances of GO are superior to that of graphene. Meanwhile, the positive effect of the GOnanofluids was also more pronounced in terms of the load-carrying capacity and the lubrication film endurance.(3)The prominent lubricant performance of GO nanofluids can be attributed to the strong affinity between GO sheets and magnesium alloy surface, superior dispersion in the water and excellent wetting of the GO nanofluids on the magnesium alloy surface.In this paper, the tribological behaviors of graphene or GO as water-based lubricant additives for magnesium alloy/steel contacts were evaluated by a reciprocating sliding ball-on-plate contact configuration. According to the analysis of the experimental results, the following conclusions can be drawn.


A novel hybrid flame retardant combining graphene oxide (GO) with long-chain phosphaphenanthrene was fabricated via surface grafting reaction. Taking advantageous of the double barrier effects, including the physical shield contributed by graphene nanoplates during the initial stage and the chemical char contributed by phosphaphenanthrene during the later stage, greatly decreased the release rate of decomposed volatiles from the resin, as well as minimized the release of oxygen and combustion heat. Hence, such hybrid flame retardant can overcome the shortcomings of early acid catalyzed degradation effects caused by conventional flame retardants containing phosphorus. Satisfactory flame retardance was achieved (UL94 V-0 rating) with only 4% addition of the hybrid flame retardant to the epoxy resin laminate. Due to the long-chain and bulky phosphaphenanthrene groups, the interlayer attractive forces of the modified GO were effectively weakened, thus favoring the exfoliation and dispersion of graphene sheets. As a result, the incorporation of the flame retardant slightly enhanced the mechanical properties of the polymer composites, rather than deteriorating them, as occurs with traditional additive flame retardants. As a potential application for graphene, it is believed that the reported hybrid flame retardant has promising future prospect. The working mechanism of most PFRs can be described as catalysis charring during polymer combustion2. At high temperature, PFRs decompose into phosphoric acids, which effectively catalyze the transformation of the polymer matrix into graphitized char, and the resultant dense charring layer can cover the material surface to isolate the fire, oxygen and heat4. However, the existing PFRs still have some problems. On one hand, almost all additive flame retardants, including PFRs, lead to obvious deterioration of the processability and mechanical properties of polymers due to poor compatibility between materials6. On the other hand, the acids released from PFRs have two catalytic actions: they not only catalyze the charring process7 (during the high-temperature stage), but also promote polymer decomposition8 . The latter can accelerate the release of combustible volatiles from the decomposed polymer and actually intensify the flame in the initial stage, which results in a decrease in the flame retarding efficiency of PFRs to an extent.Polymers are widely applied in modern society due to their excellent properties and abundant product forms. However, high flammability is a general shortcoming of these materials. To endow polymers with flame retardance, various flame retardants are introduced into the polymer matrix. As an important halogen-free flame retardant, phosphorus flame retardants (PFRs) have attracted extensive attention for their high efficiency11. For the latter, organic Si is converted to inorganic SiO2 networks at high temperature, which incorporate the graphitized char contributed by PFRs, thus greatly improving the strength, stability and barrier properties of the char layer14. In addition, it has been reported that the incorporation of metal salts with PFRs can also show synergistic effects15. The formation of metal phosphate, caused by Lewis acid–base interactions between the metal (acid) and phosphate (base), provides a very effective barrier in the condensed phase16. It is clear that the above synergistic systems improve the flame retardance by forming charring layers with higher quality. However, for synergistic technologies, it is difficult to overcome the rapid release of combustible volatiles caused by the catalytic decomposition of PFRs during the initial combustion stage.To further improve the efficiency of PFRs, synergistic systems with other flame retardants , are generally employed. P-N and P-Si are representative synergistic systems that are usually applied. For the former, inert gases from N elements can expand the char to form an intumescent and cellular structure, which can more effectively block the fire18. As a physical carbon source, graphene can reduce the heat release and inhibit the transfer of combustible gases during combustion, however, the real flame retardance of polymers, reflected by the vertical flame test rating and limiting oxygen index (LOI), is not notably increased by using graphene alone as a flame retardant. Another challenge is to achieve a good dispersion of graphene throughout the polymer matrix by weakening the attractive van der Waals forces between the graphene sheets. Graphene oxide (GO) obtained using the Hummers’ method contains various oxygen-containing functional groups on the basal planes and edges, which provide an effective approach to realizing the surface decoration of GO19. As is well known, decorated GO can be better dispersed in polymers. In addition, as a nano plate-shaped filler that can be well-dispersed in a resin matrix, decorated GO can also enhance the mechanical properties of polymers from a structural point of view22. Hu23 synthesized the functionalized graphene oxide (FRGO) via in situ condensation polymerization and applied it to an epoxy resin. A notable reduction in the fire hazard of the nanocomposite was achieved by the addition of FRGO. The effect of graphene nanosheets (GNS) combined with traditional flame retardants was systematically studied by Wang24, and different synergistic mechanisms were proposed for different flame retardant systems. In addition, a series of novel graphene-based flame retardants26 were also prepared by grafting various substances onto the surface of GO. However, few papers have reported the application of graphene in improving the flame retarding efficiency of PFRs, by taking advantage of the barrier properties of graphene sheets.Graphene, a two-dimensional carbon material with excellent barrier properties, has been introduced into polymeric materials to enhance their flame retardance, as discussed in previous referencesIn this research, a type of GO decorated by a PFR, 10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide-g- propyltrimethoxysilane (DPP) was prepared via surface grafting. As a novel flame retardant, this material shows the advantages of both GO and PFR, and meanwhile can overcome their respective shortcomings. Making use of the physical carbonaceous shield formed by the GO sheets, this material can prevent the rapid release of combustible gases during the initial combustion stage due to the acid-catalysis degradation effect of PFR, therefore effectively controlling the extension of the early flame. The initial barrier effects contributed by the graphene sheets allow the slower chemical charring behaviour of PFR to occur. The later-produced chemical chars encapsulates the graphene sheets to construct a composite carbonaceous layer with better strength, compactness and stability compared with a single physical or chemical method. As a result, the flame retardant system can maintain good shield effects during the entire process, and for this reason, the system exhibits higher efficiency. Moreover, the long-chain and bulky PFR grafted onto GO weaken the van der Waals forces and expand the space between neighboring GO sheets due to “steric propping-open effects”, which promotes the dispersion and exfoliation of the GO nanosheets. In addition, the extended chains on the graphene sheets easily entangle with the polymer chains and thus enhance the interfacial combination between graphene and the polymer matrix.−1(O-H stretching vibration), 1726 cm−1 (C = O stretching vibration), 1625 cm−1 (C = C stretching vibration), 1410 cm−1 (O-H bending vibration), 1223 cm−1 (C-O stretching vibration of epoxide) and 1048 cm−1 . In the spectrum of DPP-GO, the peaks at 2850 cm−1 and 2919 cm−1 were assigned to the symmetric and antisymmetric vibrations of methylene, while the peak at 1210 cm−1 was assigned to the Si-O stretching vibration, and the typical absorption peaks between 1400 and 1600 cm−1 were assigned to the benzene ring. The appearance of the above characteristic absorption peaks indicated that DPP was successfully grafted onto the GO surface.First, the morphologies of GO and the synthesized DPP-GO system were compared by TEM as shown in Fig. The quantitative analysis of the chemical elemental compositions of DPP-GO was performed by XPS Fig. . It can The XRD patterns of GO and DPP-GO are shown in Fig. −1 and the disorder band (D band) at approximately 1355 cm−1 were detected in the spectrum of both GO and DPP-GO27. The intensity ratio of the D and G band is a key parameter to evaluate the structure of graphene. The ID/IG ratio was 0.902 and 1.060 for GO and DPP-GO, respectively. The slight increase in the D/G intensity ratio of the latter indicates an increase in amorphous carbon compared to the sp2-hybridized graphene due to the introduction of DPP.Raman spectroscopy was conducted to further investigate the corrugated structure of GO and DPP-GO as shown in Fig. Both the XRD and Raman analysis confirmed an increase in the interlayer distance and disorder degree for DPP-GO compared to GO. The difference resulted from the long-chain and bulky groups of the former generating remarkable steric hindrance effects, which “props open” the graphene sheets. The mechanism is illustrated in Fig. The dispersion and interface problems are key factors for preparation of the polymer/graphene composites. Functionalization of the graphene surface can generally enhance its dispersion. Here, the dispersion behaviors of reduced graphene oxide (rGO) and DPP-GO in different solvents including water, o-xylene, THF, acetone and DMF, were evaluated. From the photos as shown in Fig. Thermal properties of GO, DPP and DPP-GO were studied using TGA, and their degradation curves are plotted in Fig. The flame retardance of the different flame retardant EP composites was estimated by UL94 vertical burning test and LOI test Table . The nonMCC was adopted to further evaluate the heat release behavior of the flame retardant EP systems (without glass fiber). The plotted heat release rate (HRR) curves are shown in Fig. The efficient flame retardance of DPP-GO relative to DPP can be explained as follows. As is well known, the mechanism of PFRs including DPP mainly relies on chemical production of a protective char layer that covers the material surface to isolate the fire. However, the production of the chemical char results from a catalysis reaction in the presence of phosphorus-containing acids at high temperature, accordingly, a certain amount of time is needed for the release of acids, as well as the formation of the barrier chars when flame occurs. This means that PFRs play ineffective roles during the initial combustion of materials. In comparison, DPP-GO itself is a carbon-based flame retardant, and its two-dimensional graphene sheets can provide barrier shields in the beginning of flame. Such an advantage overcomes the lagging effect of chemical charring to a degree. The following analysis further confirms the above mechanisms.The TG curves reflecting the influence of the additives on the thermal degradation of EP (without glass fibers) are shown in Fig. The different morphologies of the residues after carbonization are displayed in Fig. Additionally, it was found in Fig. Finally, the mechanical properties of the flame retardant materials were evaluated Fig. . It can In summary, a graphene-based flame retardant was designed and successfully prepared by grafting long-chain phosphaphenanthrene, DPP, onto the GO surface. This system displayed promising results as a flame retardant EP laminate. The hybrid flame retardant had the following advantages, leading to potential commercial prospect.Double barrier effects: the GO sheets effectively blocked and delayed the rapid release of volatile gases during the initial combustion stage, and afterwards, composite chars  were formed to greatly improve the barrier properties in the condensed phase.High exfoliation and dispersion: the long-chain and bulky group grafted onto the GO sheets, weakened the van der Waals forces and expanded the space between neighboring graphene sheets due to steric hindrance, which is advantageous for obtaining a functional resin with well-dispersed flame retardant.4), sulfuric acid , hydrogen peroxide (H2O2), sodium nitrate (NaNO3), N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), thionyl chloride (SOCl2), tetrahydrofuran (THF), ethanol and acetone were purchased from Aladdin Chemical Co., Ltd. 9,10-dihydro-9-oxa-10-phos-phaphenanthrene-10-oxide (DOPO) and Silane coupling agent (SCA), g-glycidyloxypropyltrimethoxysilane, was purchased from Chengdu Thinkbond Chemical Co. Ltd., China. Epoxy resin  was provided by Huntsman Advanced Materials Co., Ltd., and a phenolic novolac resin hardener  was supplied by Momentive Chemical Co., Ltd. Glass fabrics, 7628#, were obtained from Jushi Group Co., Ltd. DPP was synthesized in our laboratory.Graphite powder was kindly supplied by Nanjing XFNano Materials Tech Co., Ltd. Potassium permanganate (KMnO29. A mixture of graphite (2.5 g) and NaNO3 (2.5 g) was diluted in 120 ml of concentrated H2SO4, and the mixed solution was cooled to 0 °C in an ice bath. KMnO4 (15 g) was added slowly in small doses to maintain the reaction temperature below 20 °C. Then, the solution was heated to 50 °C and stirred for 12 h. Then H2O2 was added slowly with stirring for 30 min, and finally, the mixture was centrifuged. The remained solid material was then washed with water and centrifuged again until the pH was neutral. Then, the obtained GO from the acid reaction (200 mg) was refluxed in 40 ml of SOCl2 in the presence of 1.0 ml of DMF at 70 °C for 24 h, using a CaCl2 guard tube. The excess SOCl2 was removed by distillation after the end of the reaction. The modified GO (0.5 g) dispersed in THF (100 ml) was added into a 250 ml three-necked flask equipped with a mechanical stirrer, nitrogen inlet and reflux condenser. A calculated amount of DOPO powder and SCA were mixed in an oven and heated for 6 h at 160 °C, then the obtained mixture was dissolved in ethyl alcohol–water (weight ratio = 1: 2) mixed solvent with stirring for 30 min at room temperature. The DPP was prepared after the excess solvent was removed by distillation. DPP (2.0 g) was added to the suspension with stirring, and the reaction was performed at 70 °C for 24 h. The obtained DPP-GO was filtered, washed with THF and ethanol, and then dried under vacuum at 60 °C for 24 h. Figure First, GO was prepared from graphite using the modified Hummers methodh. KMnO4  g was adThe flame retardant (DPP or DPP-GO) was first suspended in acetone and sonicated for 10 min in an ultrasonic bath. Subsequently, the EP prepolymer glue (including 7.50 g resin and 1.7 g phenolic novolac resin) was added. Then the above flame retardant EP glue was stirred for 30 min and evenly coated on a piece of glass fabric, which was then heated in an oven at 155 °C for 5 min to remove the solvent. Subsequently, a certain number of glass fabric pieces (the number was adjusted by the thickness of the test samples: 8 pieces for 1.6 ± 0.1 mm and 10 pieces for 2.0 ± 0.1 mm) were laminated and cured in a vulcanizing machine through a heating program at 190 °C for 2 h. Finally, the obtained laminates were cut into the standard bars. The corresponding preparation procedure is illustrated in Fig. 3 according to the American National UL-94 test (ANSI/UL 94-2013). The LOI was measured using an automatic oxygen index analyzer (Shandong Textile Science Research Institute) according to ASTM D2863. The sample dimensions were 120 × 6.5 × 3.0 mm3. Microscale combustion calorimetry analysis was carried out by using a FAA-PCFC microscale combustion calorimeter (Fire Testing Technology Limited UK), and about 2 mg powder (without glass fiber involved) scraped from the EP composites surface was heated from the ambient temperature to 800 °C at a heating rate of 1 °C/s under air atmosphere. The surface morphology and elemental composition of the samples carbonized at 600 °C for 10 min were observed by using a scanning electronic microscope (SEM)  with a conductive gold layer coating at an accelerating voltage of 10 kV. The mechanical properties, including tensile strength and flexural strength, of the composites were measured at ambient temperature using a RGM-4010 university testing machine of  according to ASTM D638-10 and ASTM D790-10, respectively.The Fourier transform infrared (FT-IR) spectra were recorded on a Nicolet 20SXB infrared spectrometer (Thermo Fisher USA). X-ray photoelectron spectroscopy (XPS) was conducted using a Shimadzu/Kratos AXIS Ultra DLD multifunctional X-ray photoelectron spectrometer . The morphology and structure of GO and DPP-GO were studied by transmission electron microscopy (TEM) using a Tecnai G2 F20 electron microscope at an accelerating voltage of 200 kV. TG analysis was performed using a TA Q-500 TGA thermal analyzer at a heating rate of 10 °C /min, over the temperature range of 30 to 650 °C, with a nitrogen flow of 100 ml/min. Approximately 8~10 mg of the sample was used in each test. XRD patterns were recorded using a DX-1000 diffractometer , with a CuKα generator system operated at 40 kV and 25 mA, over a 2θ range of 5° to 40° at a scanning rate of 1°/s. Raman spectra were recorded on a Labram HR spectrometer (HORIBA Jobin Yvon) using 532 nm laser excitation with a power of 1 mW. The vertical burning tests were conducted on a HK-HVR vertical burning tester  with the dimensions of 127 × 12.7 × 1.6 mm