Dongyun Chen

CTAB-assisted synthesis of single-layer MoS2–graphene composites as anode materials of Li-ion batteries

A facile and scalable process was developed for the synthesis of single-layer MoS2–graphene nanosheet (SL-MoS2–GNS) composites based on the concurrent reduction of (NH4)2MoS4 and graphene oxide sheets by hydrazine in the presence of cetyltrimethylammonium bromide (CTAB), followed by annealing in a N2 atmosphere. The morphology and microstructure of the composites were examined by X-ray diffraction, field emission scanning electron microscopy, high-resolution transmission electron microscopy and Raman spectroscopy. The formation process for the SL-MoS2–GNS composites was also investigated. The SL-MoS2–GNS composites delivered a large reversible capacity and good cycle stability as a Li-ion battery anode. In particular, the composites easily surpassed MoS2 in terms of rate performance and cycle stability at high current densities. Electrochemical impedance spectroscopy revealed that the GNS in the composite not only reduced the contact resistance in the electrode but also significantly facilitated the electron transfer in lithiation and delithiation reactions. The good electrochemical performance of the composites for reversible Li+ storage could be attributed to the synergy between the functions of SL-MoS2 and GNS.

Graphene-Encapsulated Hollow Fe3O4 Nanoparticle Aggregates As a High-Performance Anode Material for Lithium Ion Batteries

Graphene-encapsulated ordered aggregates of Fe(3)O(4) nanoparticles with nearly spherical geometry and hollow interior were synthesized by a simple self-assembly process. The open interior structure adapts well to the volume change in repetitive Li(+) insertion and extraction reactions; and the encapsulating graphene connects the Fe(3)O(4) nanoparticles electrically. The structure and morphology of the graphene-Fe(3)O(4) composite were confirmed by X-ray diffraction, scanning electron microscopy, and high-resolution transmission microscopy. The electrochemical performance of the composite for reversible Li(+) storage was evaluated by cyclic voltammetry and constant current charging and discharging. The results showed a high and nearly unvarying specific capacity for 50 cycles. Furthermore, even after 90 cycles of charge and discharge at different current densities, about 92% of the initial capacity at 100 mA g(-1) was still recoverable, indicating excellent cycle stability. The graphene-Fe(3)O(4) composite is therefore a capable Li(+) host with high capacity that can be cycled at high rates with good cycle life. The unique combination of graphene encapsulation and a hollow porous structure definitely contributed to this versatile electrochemical performance.

Graphene‐Like MoS2/Graphene Composites: Cationic Surfactant‐Assisted Hydrothermal Synthesis and Electrochemical Reversible Storage of Lithium

A cationic surfactant-assisted hydrothermal route is developed for the facile synthesis of graphene-like MoS2 /graphene (GL-MoS2 /G) composites based on the hydrothermal reduction of Na2 MoO4 and graphene oxide sheets with L-cysteine in the presence of cetyltrimethylammonium bromide (CTAB), following by annealling in N2 atmosphere. The GL-MoS2 /G composites are characterized by X-ray diffraction, electron microscopy, high-resolution transmission electron microscopy, and Raman spectroscopy. The effects of CTAB concentration on the microstructures and electrochemical performances of the composites for reversible Li(+) storage are investigated. It is found that the layer number of MoS2 sheets decreases with increasing CTAB concentration. The GL-MoS2 sheets in the composites are few-layer in the case of 0.01∼0.03 mol L(-1) CTAB of hydrothermal solution and single-layer in the case of 0.05 mol L(-1) CTAB. The GL-MoS2 /G composites prepared with 0.01-0.02 mol·L(-1) of CTAB solution exhibit a higher reversible capacity of 940-1020 mAh g(-1) , a greater cycle stability, and a higher rate capability than other samples. The exceptional electrochemical performance of GL-MoS2 /G composites for reversible Li(+) storage could be attributed to an effective integration of GL-MoS2 sheets and graphene that maximizes the synergistic interaction between them.

In situ nitrogenated graphene–few-layer WS2 composites for fast and reversible Li+ storage

Two-dimensional nanosheets can leverage on their open architecture to support facile insertion and removal of Li(+) as lithium-ion battery electrode materials. In this study, two two-dimensional nanosheets with complementary functions, namely nitrogen-doped graphene and few-layer WS2, were integrated via a facile surfactant-assisted synthesis under hydrothermal conditions. The layer structure and morphology of the composites were confirmed by X-ray diffraction, scanning electron microscopy and high-resolution transmission microscopy. The effects of surfactant amount on the WS2 layer number were investigated and the performance of the layered composites as high energy density lithium-ion battery anodes was evaluated. The composite formed with a surfactant : tungsten precursor ratio of 1 : 1 delivered the best cyclability (average of only 0.08% capacity fade per cycle for 100 cycles) and good rate performance (80% capacity retention with a 50-fold increase in current density from 100 mA g(-1) to 5000 mA g(-1)), and may find uses in power-oriented applications.

A Robust and Cost‐Effective Superhydrophobic Graphene Foam for Efficient Oil and Organic Solvent Recovery

Water pollution caused by chemical reagent leaking, industrial wastewater discharging, and crude oil spills has raised global concerns on environmental sustainability, calling for high-performance absorbent materials for effective treatments. However, low-cost materials capable of effectively separating oils and organic solvents from water with a high adsorption capacity and good recyclability are rare on the market. Here, a cost-effective method is reported to fabricate high-performance graphene modified absorbents through the facile thermal reduction of graphene oxide on the skeletons of melamine foam. By integrating the high porosity, superior elasticity, and mechanical stability of raw sponge with the chemical stability and hydrophobicity of graphene sheets, the as-fabricated graphene foam not only possesses a rough and superhydrophobic surface, but also exhibits an excellent adsorption performance and extraordinary recyclability for various oils and organic solvents. It is worth mentioning that the superhydrophobic surface also endows the graphene foam with an excellent efficiency for oil/water separation. More importantly, the cost-effective fabrication method without involving expensive raw materials and sophisticated equipment permits a scale-up of the graphene foam for pollution disposal. All these features make the graphene foam an ideal candidate for removal and collection of oils and organic solvents from water.

Modification of magnetic silica/iron oxide nanocomposites with fluorescent polymethacrylic acid for cancer targeting and drug delivery

Biocompatible and water-soluble magnetic nanoparticles with mesoporous core-shell structure were prepared and successfully modified with a fluorescent polymer chain as a labelling segment and folic acid as the cancer targeting moiety and loaded with a drug for directional release. The porous silica oxide structure and long molecular chains of polymethacrylic acid embedded the drug efficiently in the nanocomposites and did not affect the magnetic properties of the carrier. Sustained release of the loaded drug was observed over 100 h under in vitro conditions. Furthermore, the drug carrier is able to drill into the cell membranes and obtain a sustained release of the anticancer drug into the cytoplasm. The in vitro cellular uptake of the drug demonstrated that the drug-loaded nanocomposites could effectively target the tumor cells. Our model experiments indicated that this multifunctional mesoporous core-shell magnetic nanoparticle can be exploited as an anticancer drug delivery vehicle for targeting and therapy applications.

Micro–Nanocomposites in Environmental Management

Water pollution, a worldwide issue for the human society, has raised global concerns on environmental sustainability, calling for high-performance materials for effective treatments. Since the traditional techniques have inherent limitations in treatment speed and efficiency, nanotechnology is subsequently used as an environmental technology to remove pollutants through a rapid adsorption and degradation process. Therefore, here, various adsorbent and photodegradation composite materials leading to effective water remediation are summarized and predicted. Notably, recent advances in simultaneous adsorption and photodegradation micro-nanocomposites are outlined. Such materials can not only completely adsorb and remove contaminants, but the micro-nanocomposites can also be directly reused without further treatment. Finally, the future development of this unique system is discussed.

Facile synthesis of MoS2/graphene composites: effects of different cationic surfactants on microstructures and electrochemical properties of reversible lithium storage

MoS2/graphene composites were synthesized through the concurrent reducing of (NH4)2MoS4 and graphene oxide sheets with assistance of different cationic surfactants (DTAB, OTAB and TBAB) followed by heat treatment in a nitrogen atmosphere. The effects of the three cationic surfactants on the microstructures and electrochemical performances of the composites for reversible lithium storage were investigated. The MoS2 in the composites prepared with assistance of DTAB or OTAB displays single-/few-layer structure, while the layered MoS2 sheets with about 6–7 layers are observed in the composite prepared with assistance of TBAB. The former two composites exhibit greatly enhanced electrochemical performance for reversible Li+ storage. In particular, MoS2/graphene composite prepared with assistance of OTAB delivered a high reversible capacity of 1056 mA h g−1 with excellent cycle stability and good rate capability. The significant improvement in the electrochemical performances is attributed to the roubest composite structure and the synergistic interactions between graphene and single-/few-layer MoS2. This work also presented a facile process to prepare MoS2/graphene composites, in which the layer number of MoS2 sheets could be adjusted to a certain extent by using different cationic surfactants.

Facile preparation of coating fluorescent hollow mesoporous silica nanoparticles with pH-sensitive amphiphilic diblock copolymer for controlled drug release and cell imaging

A smart fluorescent drug carrier based on hollow mesoporous silica (HMS) nanoparticles was prepared step by step. First, HMS nanoparticles were doped with lanthanide rare-earth nanocrystals (YVO4:Eu3+). Then the surface of HMS@YVO4:Eu3+ was modified by octadecyltrimethoxysilane (C18). Afterwards, it was coated by designed pH-sensitive amphiphilic diblock copolymer (poly(MPEG-b-DBAM), PMD) through hydrophobic van der Waals interactions. The results of characterization such as transmission electron microscopy (TEM) and Fourier transform infrared spectroscopy (FT-IR) reveal that the material shows excellent monodisperse spherical morphology and narrow size distribution (180 nm) with hollow-core@mesoporous-silica-shell@thin-polymer-film structure. The multifunctional system HMS@YVO4:Eu3+@C18@PMD was utilized to deliver the model drug ibuprofen (IBU), and the drug loading content of the system is as high as 834 mg/g (drug/carrier). Due to the coated pH-sensitive polymer film, the loaded drug is selectively released in mildly acidic environment. The time of release of about 80% drug was however prolonged from 50 to 150 h (at pH = 5.0) by the effect of modified C18, which has thus achieved longer-term release. Besides, the prepared material is easily imported into human mouth epidermal carcinoma (KB) cells and showed good and stable red fluorescence, which is suitable for cell imaging.

Visible-light degradable polymer coated hollow mesoporous silica nanoparticles for controlled drug release and cell imaging

A core-shell nanocomposite based on photo-degradable polymer coated hollow mesoporous silica nanoparticles (HMS) was successfully prepared for targeted drug delivery and visible-light triggered release, as well as fluorescence cell imaging. The HMS nanoparticles were first modified by the long-chain hydrocarbon octadecyltrimethoxysilane (C18) and fluorescent agent Rhodamine B isothiocyanate (RITC), and then encapsulated by a photodegradable amphiphilic copolymer via a self-assembly process. The obtained nanocarrier showed a high drug loading content due to the hollow core and mesopores of the HMS and could target folic acid receptor over-expressed tumor cells efficiently for conjugating folic acid (FA) in the amphiphilic polymer. The drug release could be triggered by the irradiation of green light (500-540 nm) due to the photodegradation of amphiphilic copolymer coated on the HMS. Furthermore, the targeted drug delivery and controlled release processes could be tracked by fluorescence imaging for the doping of RITC on the HMS. The In vitro results suggested that a smart visible light responsive drug delivery system was successfully prepared for the potential applications of cancer diagnosis and therapy.