Chunzhong Li

Graphene quantum dots: emergent nanolights for bioimaging, sensors, catalysis and photovoltaic devices

Similar to the popular older cousins, luminescent carbon dots (C-dots), graphene quantum dots or graphene quantum discs (GQDs) have generated enormous excitement because of their superiority in chemical inertness, biocompatibility and low toxicity. Besides, GQDs, consisting of a single atomic layer of nano-sized graphite, have the excellent performances of graphene, such as high surface area, large diameter and better surface grafting using π-π conjugation and surface groups. Because of the structure of graphene, GQDs have some other special physical properties. Therefore, studies on GQDs in aspects of chemistry, physical, materials, biology and interdisciplinary science have been in full flow in the past decade. In this Feature Article, recent developments in preparation of GQDs are discussed, focusing on the main two approaches (top-down and bottom-down). Emphasis is given to their future and potential development in bioimaging, electrochemical biosensors and catalysis, and specifically in photovoltaic devices that can solve increasingly serious energy problems.

3D carbon based nanostructures for advanced supercapacitors

Supercapacitors have attracted intense attention due to their great potential to meet the demand of both high energy density and power density in many advanced technologies. Various carbon-based nanocomposites are currently pursued as supercapacitor electrodes because of the synergistic effect between carbon (high power density) and pseudo-capacitive nanomaterials (high energy density). This feature article aims to review most recent progress on 3D (3D) carbon based nanostructures for advanced supercapacitor applications in view of their structural intertwinement which not only create the desired hierarchical porous channels, but also possess higher electrical conductivity and better structural mechanical stability. The carbon nanostructures comprise of CNTs-based networks, graphene-based architectures, hierarchical porous carbon-based nanostructures and other even more complex carbon-based 3D configurations. Their advantages and disadvantages are compared and summarized based on the results published in the literature. In addition, we also discuss and view the ongoing trends in materials development for advanced supercapacitors.

Hierarchical porous NiCo2O4 nanowires for high-rate supercapacitors

We demonstrate a simple and scalable strategy for synthesizing hierarchical porous NiCo(2)O(4) nanowires which exhibit a high specific capacitance of 743 F g(-1) at 1 A g(-1) with excellent rate performance (78.6% capacity retention at 40 A g(-1)) and cycling stability (only 6.2% loss after 3000 cycles).

Preparation of graphene–TiO2 composites with enhanced photocatalytic activity

The photocatalytic activity of TiO2 is limited by the aggregation of nanoparticles and the fast electron–hole pair recombination. Graphene sheets, with high specific surface area and unique electronic properties, can be used as a good support for TiO2 to enhance the photocatalytic activity. Herein, we prepared graphene–TiO2 (G–TiO2) composites through a one-pot solvothermal reaction by using graphite oxide (GO) and tetrabutyl titanate as starting materials. TiO2 particles with anatase phase and a narrow size distribution were dispersed on the surface of graphene sheets uniformly. The fluorescence quenching confirmed that graphene acted as an electron-acceptor material to effectively hinder the electron–hole pair recombination of TiO2. The product prepared with 30 mg of GO and 8 h of reaction time exhibited excellent photocatalysis to methylene blue (MB) degradation under irradiation of simulated sunlight. Such intriguing photocatalyst may find significant applications in various fields.

Facile Ultrasonic Synthesis of CoO Quantum Dot/Graphene Nanosheet Composites with High Lithium Storage Capacity

In this paper, we report a facile ultrasonic method to synthesize well-dispersed CoO quantum dots (3-8 nm) on graphene nanosheets at room temperature by employing Co(4)(CO)(12) as cobalt precursor. The prepared CoO/graphene composites displayed high performance as an anode material for lithium-ion battery, such as high reversible lithium storage capacity (1592 mAh g(-1) after 50 cycles), high Coulombic efficiency (over 95%), excellent cycling stability, and high rate capability (1008 mAh g(-1) with a total retention of 77.6% after 50 cycles at a current density of 1000 mA g(-1), dramatically increased from the initial 50 mA g(-1)). The extraordinary performance arises from the structure advantages of the composites: the nanosized CoO quantum dots with high dispersity on conductive graphene substrates supply not only large quantity of accessible active sites for lithium-ion insertion but also good conductivity and short diffusion length for lithium ions, which are beneficial for high capacity and rate capability. Meanwhile, the isolated CoO quantum dots anchored tightly on the graphene nanosheets can effectively circumvent the volume expansion/contraction associated with lithium insertion/extraction during discharge/charge processes, which is good for high capacity as well as cycling stability. Moreover, regarding the anomalous behavior of capacity increase with cycles (activation effect) observed, we proposed a tentative hypothesis stressing the competition between the conductivity increase and the amorphorization of the composite electrodes during cycling in determining the trends of the capacity, in the hope to gain a fuller understanding of the inner working of the novel nanostructured electrode-based lithium-ion batteries.

One-pot hydrothermal synthesis of graphene quantum dots surface-passivated by polyethylene glycol and their photoelectric conversion under near-infrared light

A novel and simple approach for preparing graphene quantum dots surface-passivated by polyethylene glycol (GQDs-PEG) has been developed by a one-pot hydrothermal reaction, using small graphene oxide (GO) sheets and polyethylene glycol (PEG) as starting materials. The prepared GQDs-PEG show excellent luminescence properties, the PL quantum yield of the GQDs-PEG with 360 nm emission was about 28.0%, which was two times higher than the pure GQDs. Interestingly, the GQDs-PEG possess the upconversion photoluminescence (UCPL) properties. Blue PL was clearly shown both under the ultraviolet and 808 nm laser in the fluorescent microscopy images. So the GQDs-PEG may provide a new type of fluorescence and upconversion material for applications in bioscience and energy technology. Especially, the GQDs-PEG showed higher photocurrent generation capability. And their photoelectrode generated an obvious and stable photocurrent under a 808 nm near-infrared (NIR) laser. Due to the low cost and simple method, GQDs-PEG thus provide a cost-effective dopant material for solar energy conversion.

Rational Design of MnO/Carbon Nanopeapods with Internal Void Space for High-Rate and Long-Life Li-Ion Batteries

Searching the long-life MnO-based materials for lithium ion batteries (LIBs) is still a great challenge because of the issue related to the volumetric expansion of MnO nanoparticles (NPs) or nanowires (NWs) during lithiation. Herein, we demonstrate an unexpected result that a peapod-like MnO/C heterostructure with internal void space can be facilely prepared by annealing the MnO precursor (MnO-P) NW/polydopamine core/shell nanostructure in an inert gas, which is very different from the preparation of typical MnO/C core/shell NWs through annealing MnO NW/C precursor nanostructure. Such peapod-like MnO/C heterostructure with internal void space is highly particular for high-performance LIBs, which can address all the issues related to MnO dissolution, conversion, aggregation and volumetric expansion during the Li(+) insertion/extraction. They are highly stable anode material for LIBs with a very high reversible capacity (as high as 1119 mAh g(-1) at even 500 mA g(-1)) and fast charge and discharge capability (463 mAh g(-1) at 5000 mA g(-1)), which is much better than MnO NWs (38 mAh g(-1) at 5000 mA g(-1)) and MnO/C core/shell NWs (289 mAh g(-1) at 5000 mA g(-1)). Such nanopeapods also show excellent rate capability (charged to 91.6% in 10.6 min using the constant current mode). Most importantly, we found that MnO/C nanopeapods show no capacity fading even after 1000 cycles at a high current density of 2000 mA g(-1), and no morphology change. The present MnO/C nanopeapods are the most efficient MnO-based anode materials ever reported for LIBs.

2D Monolayer MoS2–Carbon Interoverlapped Superstructure: Engineering Ideal Atomic Interface for Lithium Ion Storage

A novel strategy for the controlled synthesis of 2D MoS2/C hybrid nanosheets consisting of the alternative layer-by-layer interoverlapped single-layer MoS2 and mesoporous carbon (m-C) is demonstrated. Such special hybrid nanosheets with a maximized MoS2 /m-C interface contact show very good performance for lithium-ion batteries in terms of high reversible capacity, excellent rate capability, and outstanding cycling stability.

High-performance supercapacitor material based on Ni(OH)2 nanowire-MnO2 nanoflakes core–shell nanostructures

Ni(OH)(2)/MnO(2) core-shell nanowires with a nanoflake surface have been designed and synthesized, and can be applied not only in neutral electrolytes (355 F g(-1), 70.4 wt% MnO(2)) but are also appropriate for alkaline electrolytes (487.4 F g(-1), 35.5 wt% MnO(2)), with high cycling stability due to the synergistic effect between the core and shell.

Ultra-thin anatase TiO2 nanosheets dominated with {001} facets: thickness-controlled synthesis, growth mechanism and water-splitting properties

Ultra-thin anatase TiO2 nanosheets with dominant {001} facets (∼82%) and controllable thickness (1.6–2.7 nm) were synthesized by using a modified one-pot hydrothermal route. As a morphology controlling agent, the concentration of hydrofluoric acid has a significant impact on the thickness of the as-synthesized TiO2 nanosheets. In addition, according to the XRD patterns and TEM images of the products on different reaction stages, the growth process of TiO2 nanosheets was clarified for the first time. We further measured the efficiency for H2 evolution of the ultra-thin anatase TiO2 nanosheets loaded with 1 wt% Pt from photochemical reduction of water in the presence of methanol as a scavenger. The TiO2 nanosheets exhibited a H2 evolution rate as high as 7381 μmol h−1 g−1 under UV-vis light irradiation, attributing to their exposed reactive {001} facets and high crystallinity.