Showing papers by "Dengyu Pan published in 2017"

Metallic 1T MoS2 nanosheet arrays vertically grown on activated carbon fiber cloth for enhanced Li-ion storage performance

Abstract: We have developed a controllable solvothermal method to grow intrinsically conductive MoS2 nanosheet arrays in a metastable 1T phase on carbon fiber cloth (CFC) as binder-free, high-activity Li-ion battery (LIB) anodes By introducing surface hydroxyl groups on the CFC and tuning the DMF content in the mixed solvent, MoS2 nanosheet arrays were perpendicularly grown to the surface of the carbon fibers with a high coverage Electrochemical measurements reveal that the 1T phase nanosheet arrays have excellent Li-ion storage performances, including high specific capacity, high rate capability and good cycling stability, outperforming 2H phase arrays Because of the metallic 1T phase and the highly oriented array architecture, after subtracting the total capacity of CFC, the 1T arrays also deliver a high reversible specific capacity of 1789 mA h g−1 at 01 A g−1 and a retained capacity of 853 mA h g−1 after 140 cycles at 1 A g−1

Scalable synthesis of organic-soluble carbon quantum dots: superior optical properties in solvents, solids, and LEDs.

Abstract: Carbon quantum dots (CQDs) have attracted much attention owing to their unique optical properties and a wide range of applications. The fabrication and control of CQDs with organic solubility and long-wavelength emission are still urgent issues to be addressed for their practical use in LEDs. Here, organic-soluble CQDs were produced at a high yield of ∼90% by a facile solvent engineering treatment of 1,3,6-trinitropyrene, which were simultaneously used as the nitrogen and carbon sources. The optical properties of the organic-soluble CQDs (o-CQDs) were investigated in nonpolar and polar solvents, films, and LED devices. The CQDs have a narrow size distribution around 2.66 nm, and can be dispersed in different organic solvents. Significantly, the as-prepared CQDs present an excitation-independent emission at 607 nm with fluorescence quantum yields (QYs) up to 65.93% in toluene solution. A pronounced solvent effect was observed and their strong absorption bands can be tuned in the whole visible region (400–750 nm) by changing the solvent. The CQDs in various solvents can emit bright, excitation-independent, long-wavelength fluorescence (orange to red). Furthermore, benefiting from the unique oil-solution properties, the as-prepared CQDs can be processed in thin film and device forms to meet the requirements of various applications, such as phosphor-based white-light LEDs. The color coordinate for these CQD modified LEDs is realized at (0.32, 0.31), which is close to pure white light (0.33, 0.33).

Industrial production of ultra-stable sulfonated graphene quantum dots for Golgi apparatus imaging.

Abstract: The wide use of functionalized graphene quantum dots (GQDs) in stable dispersions is currently hampered by the lack of industrially scalable, low-cost, and eco-friendly methods. Herein we report the first realization of the industrial-scale (20 L) production of high-quality fluorescent GQDs via a molecular fusion route from a low-cost, active derivative of pyrene. By a wholly "green", conventional sulfonation reaction at low hydrothermal temperature, the molecular precursor is wholly converted into highly water-soluble, sulfonated GQDs without byproducts such as insoluble carbon. The GQDs show superior optical properties including strong excitonic absorption bands extended to ∼530 nm, bright photoluminescence (PL) at 510 nm with a quantum yield of up to 42%, and a wide PLE spectrum. The edge-site sulfonic functionalization enables the GQDs to stably re-disperse in water and maintains high fluorescence activities even after annealing up to 250 °C, whereas amino GQDs and graphene oxide sheets markedly aggregate after drying at low temperature. The GQDs are applied as biological fluorescent probes for visualizing and targeting Golgi apparatus in Hela and MCF7 live cells. The low-cost mass production, excellent biocompatibility, and superior optical properties make the GQDs an attractive alternative probe for efficient Golgi targeted imaging in biomedical applications.

Graphene hydrogel-based counter electrode for high efficiency quantum dot-sensitized solar cells

Abstract: Although copper sulfide and/or carbon materials have been utilized in counter electrodes (CEs) due to their good catalytic activity and conductivity, the efficiency of the assembled quantum dot-sensitized solar cells (QDSCs) is still unsatisfactory because of the relatively low photovoltage (Voc), which is commonly less than 0.7 V. In this study, graphene hydrogels (GHs) compressed onto titanium mesh served as the CE and the assembled CdSeTe QDSCs exhibited a photovoltaic conversion efficiency (PCE) of 9.85% and a Voc as high as 0.756 V, which increased by 19.0% and 14.9%, respectively, and are higher than those of the conventional CuS on FTO. By incorporating CuS nanoparticles into GH during gelation, the as-prepared GH–CuS CEs show further improved performance and the maximum PCE and Voc obtained were 10.71% and 0.786 V, respectively. The fill factor of the cells was also continuously increased. The excellent performance of the devices could be attributed to the synergistic effects of the water-rich GH (having a 3D porous structure accompanied by good conductivity) and highly catalytic CuS, reflected from the small series resistance, high catalytic activity, small electron transfer resistance, and stability, which have been confirmed by EIS, Tafel polarization, and CV curves.

Facile conversion of coal tar to orange fluorescent carbon quantum dots and their composite encapsulated by liposomes for bioimaging

Abstract: Carbon quantum dots (CQDs) are considered ideal fluorescent probes owing to their excellent optical properties and low cytotoxicity. We report a low-cost solvothermal method to synthesize orange fluorescent CQDs from coal tar. The as-fabricated CQDs exhibit bright and stable photoluminescence with long wavelength emission at 605 nm. To improve the biocompatibility of the oil-soluble CQDs, we chose liposomes as a carrier. After being encapsulated by liposomes, the CQDs become water-soluble and show a redshift of fluorescence to 640 nm. The in vitro and in vivo imaging application of the liposome-CQDs is demonstrated. Our work has provided a way for the conversion of low-value coal tar into high-value fluorescent carbon materials.