Xiaochen Wu

Photo-Fenton Reaction of Graphene Oxide: A New Strategy to Prepare Graphene Quantum Dots for DNA Cleavage

Graphene quantum dots (GQDs) are great promising in various applications owing to the quantum confinement and edge effects in addition to their intrinsic properties of graphene, but the preparation of the GQDs in bulk scale is challenging. We demonstrated in this work that the micrometer sized graphene oxide (GO) sheets could react with Fenton reagent (Fe(2+)/Fe(3+)/H(2)O(2)) efficiently under an UV irradiation, and, as a result, the GQDs with periphery carboxylic groups could be generated with mass scale production. Through a variety of techniques including atomic force microscopy, X-ray photoelectron spectroscopy, gas chromatography, ultraperformance liquid chromatography-mass spectrometry, and total organic carbon measurement, the mechanism of the photo-Fenton reaction of GO was elucidated. The photo-Fenton reaction of GO was initiated at the carbon atoms connected with the oxygen containing groups, and C-C bonds were broken subsequently, therefore, the reaction rate depends strongly on the oxidization extent of the GO. Given the simple and efficient nature of the photo-Fenton reaction of GO, this method should provide a new strategy to prepare GQDs in mass scale. As a proof-of-concept experiment, the novel DNA cleavage system using as-generated GQDs was constructed.

Composite of graphene quantum dots and Fe3O4 nanoparticles: peroxidase activity and application in phenolic compound removal

Graphene quantum dots (GQDs) are graphene sheets with lateral sizes less than 100 nm, and have a higher electron conjugate state and a better dispersion ability in aqueous solution compared to micrometer-sized graphene oxide (GO) sheets. Therefore they can overcome the drawbacks of GO and are an ideal candidate for nano-composites. In this work, composites of GQDs and Fe3O4 nanoparticles (NPs) (GQDs/Fe3O4) were prepared via a one-step co-precipitation approach. The as-prepared GQDs/Fe3O4 composites showed superb peroxidase-like activities, which were much higher than composites of micrometer sized GO and Fe3O4 NPs (GO/Fe3O4), individual GQDs, and individual Fe3O4 NPs. The excellent peroxidase activities of the GQDs/Fe3O4 composites can be attributed to the unique properties of GQDs and the synergistic interactions between the GQDs and Fe3O4 NPs. The GQDs/Fe3O4 composites also exhibited a higher stability and reusability than natural peroxidases. The application of a GQDs/Fe3O4 composite as a catalyst for the removal of phenolic compounds from aqueous solutions was explored with nine phenolic compounds, and showed better or comparable removal efficiencies for some phenolic compounds compared to native horseradish peroxidase (HRP) under the same conditions. The extraordinary catalytic performance and physical properties of the as-prepared GQDs/Fe3O4 composite render it practically useful for industrial wastewater treatment.

The nonlinear relationship between transformation strain and applied stress for nitinol

In the present paper, constant stress tests were conducted, and it was found that the relationship between transformation strain and external stress for NiTi is nonlinear because of the variation of the microstructure of martensite with external stress. Thermodynamical calculation shows that the nonlinear external stress dependence of transformation temperatures was caused by the variation of transformation strain with applied stress.

Composites of boron-doped carbon nanosheets and iron oxide nanoneedles: fabrication and lithium ion storage performance

Novel boron-doped carbon nanosheets were prepared through a facile hydrothermal method using glucose and sodium borohydride as precursors. Taking structural advantage of the as-prepared boron-doped carbon nanosheets, high density Fe3O4 nanoneedle arrays were generated on them, resulting in the composites of boron-doped carbon nanosheets/Fe3O4 nanoneedles. The nanoneedle-like morphology and the unique perpendicular orientation of the Fe3O4 nanoneedles largely suppressed the aggregation of the boron-doped carbon nanosheets in the composites. Therefore, as lithium ion battery anodes, the composites exhibited an excellent lithium ion storage capacity, high rate capability, and decent discharge/charge cycling stability. It was demonstrated that the reversible specific capacity can reach 1132 mA h g−1 at the charge/discharge current density of 0.1 A g−1, and it can be maintained at 980 mA h g−1 after 400 cycles. Even at a high current density of 10 A g−1, the reversible capacity was still retained above 350 mA h g−1, which is much higher than that of other carbon and Fe3O4 composites reported so far. These results render the as-prepared composite as an ideal anode material for high performance lithium ion batteries.

Graphene sheets coated with a thin layer of nitrogen-enriched carbon as a high-performance anode for lithium-ion batteries

Graphene sheets coated with a thin layer of nitrogen-enriched carbon possess excellent rate capability and cycle performance at various current rates as anodes for LIBs, as the nitrogen-enriched carbon not only incorporates the nitrogen atoms, but also reduces the aggregation of graphene sheets, which can facilitate the storage and transportation of the lithium within the anode.