Yao Wang

A novel method to decorate Au clusters onto graphene via a mild co-reduction process for ultrahigh catalytic activity

To achieve high catalytic activity and stability with low noble-metal loadings on special supports has triggered much research interest in the past few years. Herein, a mild co-reduction strategy was exploited to fabricate glutathione decorated Au clusters (with a size of ∼1.4 nm) on reduced graphene oxide (Au@HSG-rGO) with low Au loadings and high catalytic activity in an aqueous medium. The resultant Au@HSG-rGO complex exhibited 20.8 times higher catalytic activity than Au nanoparticle supported graphene for catalysis of the reduction of 4-nitrophenol (4-NP). The Au@HSG-rGO was packed in a filtering platform to afford a fixed-bed system, with which the catalytic conversion reached 96.03% for 0.2 mM 4-NP solution at a flow rate of 1 mL min−1. In addition, the poly(2-(dimethylamino) ethyl acrylate) modified Au@HSG-rGO (Au@HSG-rGO-PDMAEA) via π–π stacking interactions exhibited good recyclability and tunable catalytic activity and only showed slight loss of activity after recycling five times. The PDMAEA served as forest-like shelters to efficiently protect the Au@HSG clusters from aggregation and also endowed the system with enhanced stability and temperature-controlled catalytic activity. Meanwhile, the Au@HSG-rGO showed excellent electrocatalytic activity for the oxygen reduction reaction in alkaline electrolytes. This simple, economical and mild strategy could be generalized to the preparation of other metal cluster complexes for broad catalytic and analytical applications.

Simultaneous Synthesis of WO3−x Quantum Dots and Bundle‐Like Nanowires Using a One‐Pot Template‐Free Solvothermal Strategy and Their Versatile Applications

Tungsten oxide (WO3-x ), a new alternative to conventional semiconductor material, has attracted numerous attentions owning to its widespread potential applications. Various methods have been reported for the synthesis of WO3-x nanostructures such as nanowires or nanodots. However, templates or surfactants are often required for the synthesis, which significantly complicate the process and hinder the broad applications. Herein, one-pot template/surfactant-free solvothermal method is proposed to synthesize the WO3-x nanostructures including fluorescent quantum dots (QDs) and bundle-like nanowires simultaneously. The as-prepared WO3-x QDs can be well dispersed in aqueous medium, exhibit excellent photoluminescent properties, and show an average size of 3.25 ± 0.25 nm as evidenced by transmission electron microscopy. Meanwhile, the diameter of the WO3-x nanowires is found to be about 27.5 nm as manifested by the scanning electron microscope images. The generation mechanism for these two WO3-x nanostructures are systematically studied and proposed. The WO3-x QDs have been successfully applied in efficient fluorescent staining and specific ferric ion detection. Moreover, the WO3-x nanowires can be utilized as effective dielectric materials for electromagnetic wave absorption.

Controllable synthesis of mesoporous carbon nanoparticles based on PAN-b-PMMA diblock copolymer micelles generated via RAFT polymerization as electrode materials for supercapacitors

Mesoporous carbon nanoparticles (MCNs) were prepared through a series of annealing procedures using well-controlled diblock copolymer micelles as precursors. The micelles were prepared from poly(acrylonitrile)-block-poly(methylmethacrylate) (PAN-b-PMMA), and synthesized via reversible addition–fragmentation chain transfer (RAFT) polymerization. The RAFT-controlled synthesis of block copolymer, PAN-b-PMMA was conducted either in solution or emulsion conditions. It was found that micelles with well-defined morphology could be directly formed from the emulsion polymerization. The as-synthesized micelles containing hydrophilic PAN corona as the carbon source and hydrophobic PMMA core as the sacrificing template underwent a microphase-separation process to form a nanostructure at 250 °C, followed by carbonization at 800 °C to afford MCNs. Whats more, the MCNs based supercapacitor exhibited a good capacitance value of 220 F g−1 and an excellent cycling performance of 91% capacitance retention after 10000 cycles. The as-prepared MCNs are envisioned to provide broad practical applications in the fields of energy storage and nanotechnology.

Recent developments in graphene-based/nanometal composite filter membranes

Significant achievements have been made in the development of next-generation filtration and separation membranes using graphene materials; graphene-based membranes are promising in many areas, such as membrane separation, water desalination, proton conductors, and energy storage and conversion. In recent years, based on the excellent barrier and permeability of graphene sheets, researchers have conducted considerable research on graphene-based composite filter membranes and have made great progress. In this review paper, we summarize the key research contributions in graphene-based/nanometal composite membranes, analyze the existing problems, and elaborate on the potential application in water treatment and development trend of this kind of membrane. Graphene-based/nanometal composite membranes not only have good antibacterial activity and adsorbability, but also have potential application in seawater desalination and sewage treatment. Therefore, we can foresee that graphene-based/nanometal composite membranes will play an important role in water treatment. This review will serve as a valuable platform to fully understand filtration and adsorption mechanism through graphene-based membranes as well as the latest progress in graphene-based/nanometal composite filter membranes.

Preparation of a graphene/silver hybrid membrane as a new nanofiltration membrane

In this study, we describe the preparation, characterization, water flux and rejection performance of a composite membrane formed from reduced graphene oxide (RGO) and silver nanoparticles (AgNP) via a rapid thermal reduction method. The nanocomposite is characterized by transmission electron microscopy (TEM), UV-visible spectroscopy (UV-vis), X-ray diffraction (XRD), scanning electron microscopy (SEM), field emission scanning electron microscopy (FESEM), and Fourier transform infrared spectroscopy (FTIR). The average diameter of the Ag nanoparticles is around 20–40 nm. The RGO membranes and RGO–AgNP composite membranes were prepared by vacuum filtration of RGO–AgNPs dispersions through mixed cellulose filter membranes. We evaluated the water separation performance of the membranes, including water flux and rejection rate. The water flux is not only related to the concentration of silver particles and to the volume of solution used. High water flux and high rates of rejection of rhodamine B (85–99.9%) are achieved.

Direct generation of Ag nanoclusters on reduced graphene oxide nanosheets for efficient catalysis, antibacteria and photothermal anticancer applications

There is considerable interest in understanding the catalytical, antibacterial, and photo-thermal properties of Ag nanoparticles. Herein, a simple, scalable and effective method is explored to generate Ag nanoclusters (∼3.57u202fnm) directly on reduced graphene oxide (rGO) (denoted as AgNC/GSH-rGO) using glutathione (GSH) as a green and mild co-reduction agent. Due to the good electrical conductivity of rGO, the extremely small particle size of Ag nanoclusters and the synergistic effect between Ag nanoclusters and rGO, high catalytic activity for reduction of 4-nitrophenol is achieved for AgNC/GSH-rGO at a very low Ag nanoclusters loading of 8.67u202fwt% on rGO. The conversion could reach 96.69% in 16u202fmin and the apparent rate constant based on rGO is derived to be 0.55u202fmin-1 when the concentration of AgNC/GSH-rGO is 0.04u202fmgu202fmL-1. Moreover, the AgNC/GSH-rGO nanohybrids are also proven to be an efficient antibacterial and photothermal ablation agent for avoiding wound infection and cancer therapy applications.

Synthesis of graphene oxide/polyacrylamide composite membranes for organic dyes/water separation in water purification

To obtain nanofiltration membranes with high-performance in desalination and water purification, membranes of graphene oxide (GO), reduced graphene oxide (rGO) and GO/polyacrylamide (PAM) are prepared by a vacuum filtration method. This method is conducted in aqueous solution without any organic solvents. The graphene-based membranes (GBMs) are characterized by UV–visible spectroscopy, Fourier-transform infrared spectroscopy, transmission electron microscopy, atomic force microscopy, scanning electron microscopy, thermogravimetric analysis and X-ray photoelectron spectroscopy. The hydrophilicity of GBMs is also evaluated by contact angle measurement. The interlayer spacing of GO membrane (0.85xa0nm), GO/PAM membrane (0.68xa0nm) and rGO membrane (0.36xa0nm) are measured by X-ray diffraction. The performance of the GBMs is evaluated on a dead-end filtration device. The water flux and retention of rhodamine B of the membranes are 399.04xa0Lxa0m−2xa0h−1xa0bar−1 and 85.03% (GO), 188.89xa0Lxa0m−2xa0h−1xa0bar−1 and 95.43% (GO/PAM), 85.85xa0Lxa0m−2xa0h−1xa0bar−1 and 97.06% (rGO), respectively. The GO/PAM membrane has the best comprehensive separation performance because of its proper interlayer spacing. GO/PAM membranes provide potential advantages in the design of high-performance membranes for molecular separation and water purification.

Reduced graphene oxide–gold nanoparticle membrane for water purification

ABSTRACT The reduced graphene oxide–gold nanoparticle (rGO–Au NP) membranes are prepared by vacuum filtration method. The sizes of the Au NPs on the surface of the rGO are about 8–10 nm, and the lattice spacing of Au NPs is 0.0241 nm, which is relative to the cubic lattice of the gold crystal. The layer-by-layer stacking structure of rGO–Au NP membrane can be observed clearly by field emission scanning electron microscopy. The water flux of the rGO–Au NP membrane is as high as 204.1 L m−2 h−1 bar−1, and its retention for Rhodamine B (RhB) is as high as 99.79%.

Smart PTFE Membrane with Hydrophilicity and pH Sensitivity through MAA-grafting

ABSTRACT In this article, the microporous membrane of stretched polytetrafluoroethylene (S-PTFE) film was modified through grafting hydrophilic methacrylic acid (MAA). SEM image showed that the grafted poly(methacrylic acid) (PMAA) covered uniquely on regular nanofiber-frame in S-PTFE. The surface contact angle of the membrane minishes rapidly with the increase of grafting ratio and falls down to the minimum point at 57° when the grafting ratio is about 4.7%. The water flux of the PTFE-g-PMAA membrane is very sensitive to pH values. At lower pH, the larger water flux was obtained. This contribution indicate the possibility of adjustable water flux by pH. GRAPHICAL ABSTRACT

Design of enzyme micelles with controllable concavo-convex micromorphologies for highly enhanced stability and catalytical activity

Concavo-convex micelles with controllable sizes and nanostructures are prepared via self-assembling polymer-enzyme (e.g., shellac enzyme) conjugates with heterogeneous polymer chains, which exhibit higher enzyme stability (300%) and bioactivity (760%) comparing with the well-defined ones. The applied amphiphilic and negatively charged copolymer, poly (methyl methacrylate)-block-poly (sodium p-styrene sulfonate), is synthesized via reversible addition-fragmentation chain transfer polymerization to modify shellac enzyme and immobilize the enzyme bioactivity inducer by covalent conjugation and electrostatic attraction, respectively. The degradation test of catechol confirms the application potential of as-prepared micelles as an efficient and economical decontaminant.