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In this work, we numerically study the tunable light absorption of monolayer graphene at the near-infrared region by the guided mode resonance in a compound grating-coupled waveguide structure. A biased graphene capacitor is placed below the coupled waveguides. The electromagnetically induced transparency phenomenon is demonstrated by the resonant coupling of guided modes. The light absorption of monolayer graphene at the transparency window can be dynamically tuned by shifting the Fermi energy of graphene in capacitor. The absorption modulation depth of monolayer graphene at the transparency window can vary quickly from zero to nearly 100 % around the interband transition of graphene in capacitor. These results have potential applications in the active photodetectors and photoconductive devices. • The monolayer graphene is not directly biased, but the tunable optical absorption of monolayer graphene is realized by shifting the Fermi energy of the biased graphene capacitor. • The active absorption modulation of monolayer graphene assisted by electromagnetic induced transparency phenomenon is achieved at the near-infrared region. • The absorption modulation depth of monolayer graphene could vary quickly from zero to nearly 100 % around the interband transition of graphene. [ABSTRACT FROM AUTHOR]

The homogeneous distribution of nano-sulfur onto 3D structures for the development of high-performance Li-S batteries (LSBs) is a top concern to solve the low utilization of sulfur, sluggish redox kinetics, and lithium polysulfide (LiPS) shuttle effect. Herein, a novel "egg tray" hierarchical architecture of confining and uniformly distributing nano-sulfur into a 3D holey graphene (HG) framework with polyaniline crosslinking (3DHG/NS/CPANI) via photo-assisted method was designed for high-mass-loading LSB cathode. Notably, HG contains both conductive skeletons as electron transfer paths and abundant void spaces in favor of homogenous sulfur anchoring. This configuration improves the contact between nano-sulfur and graphene for effective charge transportation and provides buffering space for volume variations during electrochemical processes. Moreover, a facile photo-assisted method was developed to cross link HG with polyaniline to act as an efficient polysulfide adsorbent, allowing nano-sulfur (NS) to be firmly embedded into the holes of graphene through physical and chemical effects, thus prohibiting the dissolution and shuttle effect of polysulfide. Considering these advantages, the prepared 3DHG/NS/CPANI electrode exhibited excellent performance with high sulfur utilization and specific capacity, resulting in specific discharge capacities at 0.5 and 1C of 1082 and 921 mA h −1, respectively, and small capacity decay of 0.04% per cycle over 500 cycles at 1C. The strategy in this work, which synergistically combines morphology control, nano-sulfur positioning, and structural engineering to enhance the electrochemical performance for Li−S batteries, will offer a valuable reference to energy storage and conversion advances. A novel "egg tray" hierarchical architecture of confining and uniformly distributing nano-sulfur into a 3D holey graphene (HG) framework with polyaniline crosslinking (3DHG/NS/CPANI) via photo-assisted method was designed. HG contains both conductive skeletons as electron transfer paths and abundant void spaces in favor of homogenous sulfur anchoring. This configuration improves the contact between nano-sulfur and graphene for effective charge transportation and provides buffering space for volume variations during electrochemical processes. Moreover, interchain cross-linking of polyaniline and covalent bonding of polyaniline to graphene oxide were realized by a photo-assisted cross-linking strategy to improve the chemical immobilization for polysulfides. Considering these advantages, the prepared 3DHG/NS/CPANI electrode exhibited excellent performance with high sulfur utilization and specific capacity. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • Nitrogen-doping enhances the H+ and D+ permeability of graphene. • D+ permeates across pyridinic-N defects faster than H+, showing an inverse KIE (0.75). • A normal KIE (1.56) is observed in pyrrolic-N defects. • KIE is influenced by the chemisorption and effective size imparted by defects. Graphene is becoming an increasingly popular platform for developing high-efficiency hydrogen isotope separation technologies operated at room temperature. However, its performance can be strongly affected by contributions from atomic defects. Understanding the influence of defects on the hydrogen isotope selectivity of graphene is thus imperative but remains elusive. In this work, we investigated the electrically driven proton/deuteron permeation through nitrogen-doped graphene membranes with varying N concentrations and configurations. The results show that N-doping significantly enhances the proton and deuteron permeability of graphene (by one order of magnitude). More importantly, deuterons are found to permeate faster through pyridinic N-containing defects than protons, demonstrating a pronounced inverse kinetic isotope effect (KIE) with k H / k D of 0.75. Conversely, pyrrolic N-containing defects exhibit a normal KIE (k H / k D = 1.56). The exclusive contribution of the pyridinic N to the inverse KIE is confirmed by the reversed KIE factor of the pyridinic N-dominated sample subjected to modification. Theoretical calculations indicate that the explicit dependence of KIE on N configuration originates from the different leading mechanisms of proton/deuteron permeation through these N-containing defects, which is governed by the size and the chemisorption imparted by defects. These findings provide fundamental insights into the correlation between defect characteristics and proton/deuteron transport in graphene, and contribute to developing economical hydrogen isotope separation technologies through the defect engineering of graphene. [ABSTRACT FROM AUTHOR]

A supercapacitor is a device which can store electrical energy on conductive materials with a highly porous structure. Carbon-based electrochemical capacitors exhibit fast charge/discharge rate and high power density but limited by low energy density compared with lithium ion batteries. We used the self-assembly method to construct a three-dimensional graphene-based nanoporous carbon derived from graphene/carbonized metal-organic frameworks composite, which exhibits a high specific surface area (1849 m2 g−1) and a remarkable capacitance of 472 F g−1 at 1 mV s−1 and 420 F g−1 at 1 A g−1 in aqueous electrolyte. The specific capacitance of 397 F g−1 at 1 A g−1 measured in the organic electrolyte with voltage window up to 3 V leads to a high energy density of 124.1 Wh kg−1 achieved in a symmetrical capacitor device. The progress of this material is close to the theoretical capacitance of carbon-based material (550 F g−1) and readily scalable to practical applications. Image 1 [ABSTRACT FROM AUTHOR]

Sulfur-doped graphene quantum dots (S-GQDs) decorated with high-quantum-yield titanium dioxide (TiO 2 ) nanocomposite are synthesized by a simple hydrothermal method. Photoluminescence characterization shows that S-GQDs exhibit stronger absorption peaks at ultraviolet (UV) region than GQDs. Photocatalytic activity of the obtained S-GQD/TiO 2 nanocomposite reaches 70% in 8 min; this activity is significantly enhanced compared with those of GQDs/TiO 2 and pure TiO 2 . Improved UV light absorption and effective transfer of photogenerated electrons can be attributed to integration of S-GQDs with TiO 2 in a cladding manner. The present work provides a new approach for development of attractive GQD-based nanocomposites with controllable structures and photocatalytic performance. [ABSTRACT FROM AUTHOR]

[Display omitted] • Auxetic PU/PDA/GR composite foam with high EMI SE was prepared via simple method. • The relationship between EMI SE and reentrant structure was studied at first time. • The high EMI SE of auxetic foam results from the reentrant structure and high SE A. • The auxetic foam is promising as temperature-regulated EMI shielding material. In this work, two kinds of auxetic composite foams of polyurethane (PU) with polydopamine (PDA) and graphene (GR) (PU/PDA/GR) were prepared by dip-coating and ultrasonic immersing, then followed by triaxial compression-heating process. The electromagnetic interference (EMI) shielding effectiveness (SE) value of the PU/PDA/GR auxetic composite foam with a Poisson's ratio of −2.36 from PU foam with open cellular structure reaches 59.75 dB, which is 8.9 times of the positive Poisson's ratio composite foam with the same GR content. Furthermore, the relationship of the EMI shielding performance of auxetic foam with different forms of reentrant structure was studied for the first time, in which the absolute value of negative Poisson's ratio was used to quantitatively describe the difference of the reentrant structure in the obtained auxetic foam. The larger the absolute value of negative Poisson's ratio is, the better the EMI shielding performance of the composite foam is. The high absorption EMI SE and the existence of reentrant structure are the key factors for the high EMI shielding performance of the auxetic composite foam. In addition, it is found that the EMI SE of the auxetic foam can be adjusted via simple heating treatment, showing that the auxetic composite foam may be used as a temperature-regulated EMI shielding material in the future. [ABSTRACT FROM AUTHOR]

• We synthesized a new diatomic-doped graphene quantum dots, namely, nitrogen and phosphorus co-doped GQDs, and it exhibits high efficiency and stability in pollutant photodegradation. • Under visible and ultraviolet irradiation, NP-GQDs/g-C 3 N 4 can rapidly decompose 97.5% and 96% Methyl Orange (MO) in 8 min and 120 min, respectively. • NP-GQDs/g-C 3 N 4 exhibits high stability after repeated usage in MO degradation. • All the results demonstrate NP-GQDs/g-C 3 N 4 is highly prospective in pollutant photodegradation. In metal-free g-C 3 N 4 based materials, the rapid recombination of photoexcited carriers limits its photocatalytic activity. In this work, for the first time, we synthesized a new kind of diatomic-doped graphene quantum dots (GQDs), namely, nitrogen and phosphorus co-doped GQDs (NP-GQDs), and then loaded on g-C 3 N 4 surface to obtain NP-GQDs/g-C 3 N 4 composite photocatalyst. Under visible and ultraviolet irradiation, the MO photodegradation rate of NP-GQDs/g-C 3 N 4 is as high as 97.5% and 96%, respectively, which was 1.71 and 1.85 times higher than that of pure g-C 3 N 4. The remarkable enhancement of photodegradation activity is mainly attributed to the introduction of NP-GQDs could promote the formation, transportation and separation of photoexcited carriers. Furthermore, the photocatalyst exhibits outstanding recycle stability without a significant decrease in activity after three reused runs. This study provides a new understanding of the roles played by diatomic-doped graphene quantum dots in photocatalytic systems and provides a new prospect in developing highly efficient g-C 3 N 4 -based photocatalysts. [ABSTRACT FROM AUTHOR]

In this work, we report a strategy for enhancing the pseudocapacitive performance of MoS 2 materials by the introduction of nitrogen-doped graphene quantum dots (N-GQDs) and helical carbon tubes (HCNT). By a simple hydrothermal process, the hybrid composite (MoS 2 , N-GQDs and HCNT) were coated on the carbon cloth (CC) without any binders, which can be directly used as advanced electrode material for high-performance solid-state flexible supercapacitors. In this hybrid structure, N-GQDs are inserted between the layers of MoS 2 nanosheets, which induce and expose more active sites for pseudocapacitance contributions in MoS 2 electrode materials. Meanwhile, HCNT acts as electrically conducting bridge for enhancing the electrical conductivity of MoS 2 nanosheets and speeding up transport of electronic. As results, the hybrid composite (MoS 2 , N-GQDs and HCNT) show higher capacitive performance than pure MoS 2. The specific capacitance of hybrid composite is high up to 3360 mF cm−2. Further, the assembled solid-state flexible supercapacitor shows high specific capacitance of 1893 mF cm−2, outstanding cycle life (capacitance retention of 86% after 2500 cycles), good mechanical stability and great flexibility. Our work provides a reference for the preparation of MoS 2 composites with high supercapacitive performance. Image, graphical abstract [ABSTRACT FROM AUTHOR]