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This work demonstrates a facile one-pot synthesis of graphitic carbon nitride (g-C3N4) quantum dots/graphene hydrogel (CNQ/GH) nanocomposites using a hydrothermal process, which shows excellent electrochemical performances for supercapacitors.

This work demonstrates a facile one-pot method for preparing graphitic carbon nitride (g-C

In this work, a green and simple one-pot route was developed for the synthesis of highly fluorescent amino-functionalized graphene quantum dots (a-GQDs) via hydrothermal process without any further modification or surface passivation. We synthesized the a-GQDs using glucose as the carbon source and ammonium as a functionalizing agent without the use of a strong acid, oxidant, or other toxic chemical reagent. The as-obtained a-GQDs have a uniform size of 3–4 nm, high contents of amino groups, and show a bright green emission with high quantum yield of 32.8%. Furthermore, the a-GQDs show effective fluorescence quenching for Cu2+ ions which can serve as effective fluorescent probe for the detection of Cu2+. The fluorescent probe using the obtained a-GQDs exhibits high sensitivity and selectivity toward Cu2+ with the limit of detection as low as 5.6 nM. The mechanism of the Cu2+ induced fluorescence quenching of a-GQDs can be attributed to the electron transfer by the formation of metal complex between Cu2+ and the amino groups on the surface of a-GQDs. These results suggest great potential for the simple and green synthesis of functionalized GQDs and a practical sensing platform for Cu2+ detection in environmental and biological applications.

In this work, we report on the structural and thermoelectric properties of Sb2Te3 films deposited on GaSb(111) substrates by using molecular beam epitaxy. The effects of the growth temperature on the microstructure and thermoelectric properties of the films were investigated. The results show that Sb2Te3 films grow on GaSb(111) along (00l) axis normal to the substrate and have a hexagonal structure with a layer-by-layer growth mode in growth temperature range from 200 to 250 °C while at 175 and 300 °C, the films show an island growth mode. Te and Sb2Te3 phases coexist at a growth temperature of 175 °C. The films exhibit a metallic behavior for growth temperatures below 250 °C and a semiconductor behavior at 300 °C. By changing growth temperature, we were able to vary the carrier density from 9.96×1018 to 4.55×1019 cm −3. At room temperature, the Seebeck coefficients are 110, 146, and 138 μV/K for growth temperatures of 175, 200 and 250 °C, respectively, and a large value of the power factor 61.67 μW/cm-K2 is achieved for the film grown at 250 °C.

Để phát triển nguồn nhân lực BIM cho ngành xây dựng Việt Nam, việc đầu tiên cần thực hiện là phải tạo ra đội ngũ những người đào tạo về BIM. Do đó, chương trình dạy học các khóa đào tạo giảng viên nguồn cần được thiết kế một cách khoa học, phù hợp với điều kiện Việt Nam. Bài báo trình bày các vấn đề lý luận cơ bản như khái niệm và nội dung chương trình dạy học, cách tiếp cận và các bước thiết kế chương trình dạy học. Bài báo cũng đã chi tiết 8 bước đầu tiên trong việc thiết kế chương trình dạy học này và trình bày nội dung và lịch trình chương trình dạy học đã được xây dựng. Nhận ngày 5/12/2017; sửa xong 21/12/2017; chấp nhận đăng 16/01/2018

A solid solution of Bi0.5K0.5TiO3-BiFeO3 was fabricated by a sol–gel technique. The pure Bi0.5K0.5TO3 samples exhibited weak room-temperature ferromagnetism. The room-temperature ferromagnetism was observed in BiFeO3 solid solution in Bi0.5K0.5TiO3. The optical band gap of Bi0.5K0.5TiO3 was reduced from 3.22 eV to 1.39 eV with the increase in the amount of BiFeO3 solid solution. The room-temperature ferromagnetism and band gap reduction were attributed to the diffusion of BiFeO3 into Bi0.5K0.5TiO3 to form a solid solution. Our work provided a simple method of realizing room-temperature ferromagnetism in lead-free ferroelectric materials.

Boron-doped graphene quantum dots (BGQDs) have been synthesized by a one-step, facile and low temperature method through the hydrothermal treatment of glucose as the precursor in the presence of boric acid. The as-obtained BGQDs possess a high B-doping content up to 4.25% of uniform nm-size. Interestingly, the effect of different types of B–C bond species on the ORR catalytic activity has been investigated to clarify the origin of the electrochemical reduction of O2. Further, the composite of the reduced graphene oxide (rGO) and BGQD (G-BGQDs) was also prepared as a metal-free electrocatalyst for the oxygen reduction reaction (ORR). The G-BGQD composites exhibit a significantly enhanced electrocatalytic activity, including a positive onset potential and a high current density with a one step, four-electron pathway toward the ORR, comparable to the commercial Pt/C catalyst. Among various B–C bond structures in BGQDs, the graphite-like BC3 structure is considered to be an important site for the ORR by improving the electric conductivity and electrocatalytic activity of BGQDs, which is also confirmed by a DFT study. In addition, the G-BGQD composites show an outstanding long-term operational stability and high tolerance to the methanol crossover effect, which are comparable to the commercial Pt/C catalyst. These results demonstrate that the synthesized BGQD, as metal-free catalyst materials, may be inexpensive and efficient electrocatalysts for the replacement of Pt-based catalysts toward the ORR and other electrochemical applications.

Nowadays, graphene quantum dots (GQDs) have gained a huge interest in the field of visible-range photocatalysts because of their tunable band gap and stable photochemical properties. In this work, amine-functionalized GQDs (AGQDs) were successfully prepared by one-step microwave-assisted conversion of glucose, H2O2, and NH3 solution. The obtained quantum dots possess the high quality of graphene structure with the average size of 3.78 nm as well as exhibit a strong green fluorescence with a high quantum yield. Interestingly, the amine-functionalized dots perform outstanding visible-light absorption. To further investigate photocatalytic properties, a composite of AGQDs and TiO2 was then prepared by a simple mixing route. The hybrid material showed high catalytic activity of dye degradation under visible light irradiation, which indicates the key role of AGQDs in enhancing light absorption and induced electron–hole separation. The current study may open a new way for construction of effective visible light photocatalytic systems with a cost-effective, simple approach.

Here, we demonstrate a high performance ultraviolet (UV) light sensor based on graphene quantum dots (GQDs)/reduced graphene oxide (RGO) hybrid film with a simple and inexpensive solution process. To fabricate the GQDs/RGO hybrid film, GQDs synthesized by the carbonization of citric acid are simply sprayed on RGO film prepared by spin-coating on a SiO 2 /Si substrate. The RGO film is employed as the transport channel of the photogenerated electrons from GQDs due to its superior electron mobility and conductivity. By the integration of GQDs and RGO, the UV sensor device shows a high photo responsibility of 8.7 × 10 2 A/W and an excellent specific detectivity of 7.7 × 10 13 Jones at a low operating voltage. These results are attributed to the strong absorption of GQDs and the photogenerated charge transfer to RGO. Our novel approach based on the integration of GQDs and RGO can be extended for the design of the other promising optoelectronic applications.

This study presents a simple and facile method for preparing three-dimensional (3D) porous reduced graphene oxide (rGO) and NiO nanoparticles composites (3D-RGNi) as high performance supercapacitor electrodes. The 3D porous graphene framework is first produced by the self-assembly of poly(methyl methacrylate) (PMMA) particles and graphene oxide (GO), followed the adsorption of Ni precursor on GO. High-temperature treatment is simultaneously carried out to fabricate the 3D porous structured rGO decorated with NiO nanoparticles. The as-synthesized 3D-RGNi electrode exhibits a high specific capacitance of 1328 F g −1 at a current density of 1 A g −1 and an excellent cycling stability with 87% retention of the capacitance after 2000 cycles of galvanostatic charge–discharge. These high capacitance performances are attributed to the synergistic effects from the incorporation of the rGO network and NiO nanoparticles, and the highly porous structure of 3D-RGNi. Hence, it is expected that 3D-RGNi might serve as a promising materials for electrochemical energy storage applications.

Cystenine–functionalized graphene quantum dots (cys–GQDs) were synthesized by a simple and facile method, which involves chemical bond formation between L-cysteine and the graphene quantum dots (GQDs) prepared by the carbonization of citric acid. The obtained cys–GQDs show a strong green fluorescence and a uniform lateral size distribution with high crystallinity. The cys–GQDs are further demonstrated as highly sensitive and selective fluorescence probes for Hg2+. In the Hg2+ detection process, the cys–GQDs shows significant fluorescence quenching through a charge transfer process within the cys–GQDs and Hg2+ complex.

Three-dimensional hollow balls of graphene and polyaniline (3D-HBGP) hybrid were fabricated through the self-assembly of graphene oxide (GO) and poly(methyl methacrylate) (PMMA) particles, followed by the polymerization of polyaniline (PANI) and removal of the core PMMA particles. Using the resulted unique porous microstructures, the supercapacitor based on the 3D-HBGP electrodes exhibited an enhanced electrochemical performance, including the specific capacitance and cycling stability. The 3D-HBGP electrodes showed an enhanced specific capacitance of 331 F g−1 at a current density of 1 A g−1 and excellent cycling stability with a 14% loss of the capacitance after 500 charging–discharging cycles. Furthermore, due to the mechanical stability of 3D-HBGP, we have demonstrated flexible supercapacitors using the 3D-HBGP electrodes, which exhibited a specific capacitance of 182 F g−1 at the bending state with good cycling stability.

Here we demonstrate a simple and effective method to fabricate graphene ribbon with a sub-micrometer width down to 260 nm by using an electrospun polymer nanofiber as a physical etch mask. Our method involves electrospinning polystyrene nanofiber onto chemical vapor deposition-grown graphene film, followed the oxygen plasma etching to remove the exposed graphene without disturbing the underlying graphene. This work shows that the width of the resulting graphene ribbons can be engineered by controlling the nanofiber size and etch conditions. Based on this graphene ribbon, we fabricated a graphene-field effect transistor with a bottom-gated geometry, which shows an ambipolar characteristic with a hole and electron mobility of 1636 and 134 cm2/(V s), respectively. Our approach here may allow the fabrication of sub-micrometer graphene ribbon for graphene-based electronics.