Graphene quantum dots (GQDs) with uniform sizes of less than 5 nm are synthesized by a novel top-down strategy. Nitric acid as a strong oxidant can be used to cut graphene oxide via sonication and hydrothermal processes. Moreover, purified GQDs are obtained from removing oxygen-containing functional groups in a heat treatment process. Both nanoscale size and edge effect of GQDs improve their abundant active sites and restrain the restack of graphene nanosheets. Meanwhile, their electrochemical performance demonstrates the properties of the GQDs for practical application in energy storage. The GQD electrode material shows an ideal electric double-layer capacitance behavior such as a high specific capacitance of 296.7 F g, a satisfactory energy density of 41.2 W h kg at 1 A g, a low internal resistance, a small relaxation time, and an excellent cycling stability. The results illustrate excellent electrochemical activity, high conductivity, and enhanced ion transport rate on the surface of electrolyte and electrode. The advantages of GQDs confirm their unique characteristics for potential applications in the field of electrode materials for supercapacitors.

The effects of five types of oxygen-containing functional groups (–COOH, –COC–, –OH, –CHO, and –OCH3) on graphene quantum dots (GQDs) are investigated using time-dependent density functional theory (TD-DFT).

The effects of four heteroatoms (B, N, P, and S) with three doping patterns on graphene quantum dots (GQDs) are systematically investigated using time-dependent density functional theory (TD-DFT). The absorption spectra and HOMO-LUMO gaps are quantitatively analyzed to study the correlations between the optical properties and heteroatom doping of doped GQDs. Heteroatom doping can endow GQDs with various new optical and structural properties, depending on the dopants and doping configurations. Compared with the absorption spectra of pristine GQD, both N and S surface doping demonstrate a slight blue shift, whereas B and P doping lead to a blue shift for edge-doped GQDs with heteroatoms in a pentatomic ring. The absorption process is investigated along with excited state analysis, which includes the density of state, natural transition orbital, and charge difference density. The results indicate that large radius atoms assist charge transfer in the excited state and play an important role in recombining the electron density distribution in the doped GQDs.

Surgical mask is recommended by the World Health Organization for personal protection against disease transmission. However, most of the surgical masks on the market are disposable that cannot be self-sterilized for reuse. Thus, when confronting the global public health crisis, a severe shortage of mask resource is inevitable. In this paper, a novel low-cost electrothermal mask with excellent self-sterilization performance and portability is reported to overcome this shortage. First, a flexible, ventilated, and conductive cloth tape is patterned and adhered to the surface of a filter layer made of melt-blown nonwoven fabrics (MNF), which functions as interdigital electrodes. Then, a graphene layer with premier electric and thermal conductivity is coated onto the MNF. Operating under a low voltage of 3 V, the graphene-modified MNF (mod-MNF) can quickly generate large amounts of heat to achieve a high temperature above 80 °C, which can kill the majority of known viruses attached to the filter layer and the mask surface. Finally, the optimized graphene-modified masks based on the mod-MNF filter retain a relatively high particulate matter (PM) removal efficiency and a low-pressure drop. Moreover, the electrothermal masks can maintain almost the same PM removal efficiency over 10 times of electrifying, suggesting its outstanding reusability.

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We propose the physical origin for a directional beam of light emitting from a single subwavelength slit in metallic film that is characterized by a corrugation feature at the exiting side of the film. We theorize that the beaming phenomenon can be explained simply as surface plasmon diffraction along the corrugation as long as the multiple scattering effects are taken into account to restate the dispersion relationship of the surface plasmon. In order to prove our theory, both an experimental setup and numerical simulations were undertaken. Results obtained match well with our theory of an explanation based on a surface plasmon diffraction scheme.

Nitrogen-doped graphene (NG) with wrinkled and bubble-like texture is fabricated by a thermal treatment. Especially, a novel sonication-assisted pretreatment with nitric acid is used to further oxidize graphene oxide and its binding with melamine molecules. There are many bubble-like nanoflakes with a dimension of about 10 nm appeared on the undulated graphene nanosheets. The bubble-like texture provides more active sites for effective ion transport and reversible capacitive behavior. The specific surface area of NG (5.03 at% N) can reach up to 438.7 m g , and the NG electrode demonstrates high specific capacitance (481 F g at 1 A g , four times higher than reduced graphene oxide electrode (127.5 F g )), superior cycle stability (the capacitance retention of 98.9% in 2 m KOH and 99.2% in 1 m H SO after 8000 cycles), and excellent energy density (42.8 Wh kg at power density of 500 W kg in 2 m KOH aqueous electrolyte). The results indicate the potential use of NG as graphene-based electrode material for energy storage devices.

Recently, binary transition metal oxides, phosphates, and sulfides have attracted wide attention due to their potential applications in supercapacitors. The emergence of metal‐organic frameworks (MOFs) provides new opportunities for the synthesis and investigation of porous binary metal compounds with similar microstructures. Herein, binary metal oxide (NiCo‐O) tubular structures are derived from NiCo‐MOF‐74 via a facile annealing process, and then phosphate (NiCo‐P) and sulfide (NiCo‐S) structures are obtained from NiCo‐O by heat treatment and solvothermal process, respectively. Among the three derivatives, NiCo‐S with nanosheet structures has the highest specific capacitance of 930.4 F g−1 at a current density of 1 A g−1 and an excellent rate capability with a retention of ≈80% at 10 A g−1. The long‐term cycling performance of NiCo‐S is superior with 70.5% retention after 10 000 cycles. The hybrid supercapacitor device with NiCo‐S and activated carbon as positive and negative electrodes delivers a high energy density of 22.6 W h kg−1 at a power density of 800 W kg−1. The excellent performance of NiCo‐S can be attributed to its nanosheet structure, which increases the specific surface area and electroactive sites.