Jian Ru Gong

Highly Efficient Visible-Light-Driven Photocatalytic Hydrogen Production of CdS-Cluster-Decorated Graphene Nanosheets

The production of clean and renewable hydrogen through water splitting using photocatalysts has received much attention due to the increasing global energy crises. In this study, a high efficiency of the photocatalytic H(2) production was achieved using graphene nanosheets decorated with CdS clusters as visible-light-driven photocatalysts. The materials were prepared by a solvothermal method in which graphene oxide (GO) served as the support and cadmium acetate (Cd(Ac)(2)) as the CdS precursor. These nanosized composites reach a high H(2)-production rate of 1.12 mmol h(-1) (about 4.87 times higher than that of pure CdS nanoparticles) at graphene content of 1.0 wt % and Pt 0.5 wt % under visible-light irradiation and an apparent quantum efficiency (QE) of 22.5% at wavelength of 420 nm. This high photocatalytic H(2)-production activity is attributed predominantly to the presence of graphene, which serves as an electron collector and transporter to efficiently lengthen the lifetime of the photogenerated charge carriers from CdS nanoparticles. This work highlights the potential application of graphene-based materials in the field of energy conversion.

Noble Metal-Free Reduced Graphene Oxide-ZnxCd1–xS Nanocomposite with Enhanced Solar Photocatalytic H2-Production Performance

Design and preparation of efficient artificial photosynthetic systems for harvesting solar energy by production of hydrogen from water splitting is of great importance from both theoretical and practical viewpoints. ZnS-based solid solutions have been fully proved to be an efficient visible-light driven photocatalysts, however, the H(2)-production rate observed for these solid solutions is far from exciting and sometimes an expensive Pt cocatalyst is still needed in order to achieve higher quantum efficiency. Here, for the first time we report the high solar photocatalytic H(2)-production activity over the noble metal-free reduced graphene oxide (RGO)-Zn(x)Cd(1-x)S nanocomposite prepared by a facile coprecipitation-hydrothermal reduction strategy. The optimized RGO-Zn(0.8)Cd(0.2)S photocatalyst has a high H(2)-production rate of 1824 μmol h(-1) g(-1) at the RGO content of 0.25 wt % and the apparent quantum efficiency of 23.4% at 420 nm (the energy conversion efficiency is ca. 0.36% at simulated one-sun (AM 1.5G) illumination). The results exhibit significantly improved photocatalytic hydrogen production by 450% compared with that of the pristine Zn(0.8)Cd(0.2)S, and are better than that of the optimized Pt-Zn(0.8)Cd(0.2)S under the same reaction conditions, showing that the RGO-Zn(0.8)Cd(0.2)S nanocomposite represents one of the most highly active metal sulfide photocatalyts in the absence of noble metal cocatalysts. This work creates a green and simple way for using RGO as a support to enhance the photocatalytic H(2)-production activity of Zn(x)Cd(1-x)S, and also demonstrates that RGO is a promising substitute for noble metals in photocatalytic H(2)-production.

Controllable N-Doping of Graphene

Opening and tuning an energy gap in graphene are central to many electronic applications of graphene. Here we report N-doped graphene obtained by NH3 annealing after N(+)-ion irradiation of graphene samples. First, the evolution of the graphene microstructure was investigated following N(+)-ion irradiation at different fluences using Raman spectroscopy, showing that defects were introduced in plane after irradiation and then restored after annealing in N2 or in NH3. Auger electron spectroscopy (AES) of the graphene annealed in NH3 after irradiation showed N signal, however, no N signal was observed after annealing in N2. Last, the field-effect transistor (FET) was fabricated using N-doped graphene and monitored by the source-drain conductance and back-gate voltage (Gsd-Vg) curves in the measurement. The transport property changed compared to that of the FET made by intrinsic graphene, that is, the Dirac point position moved from positive Vg to negative Vg, indicating the transition of graphene from p-type to n-type after annealing in NH3. Our approach, which provides a physical mechanism for the introduction of defect and subsequent hetero dopant atoms into the graphene material in a controllable fashion, will be promising for producing graphene-based devices for multiple applications.

Visible Light Photocatalytic H2-Production Activity of CuS/ZnS Porous Nanosheets Based on Photoinduced Interfacial Charge Transfer

Visible light photocatalytic H(2) production through water splitting is of great importance for its potential application in converting solar energy into chemical energy. In this study, a novel visible-light-driven photocatalyst was designed based on photoinduced interfacial charge transfer (IFCT) through surface modification of ZnS porous nanosheets by CuS. CuS/ZnS porous nanosheet photocatalysts were prepared by a simple hydrothermal and cation exchange reaction between preformed ZnS(en)(0.5) nanosheets and Cu(NO(3))(2). Even without a Pt cocatalyst, the as-prepared CuS/ZnS porous nanosheets reach a high H(2)-production rate of 4147 μmol h(-1) g(-1) at CuS loading content of 2 mol % and an apparent quantum efficiency of 20% at 420 nm. This high visible light photocatalytic H(2)-production activity is due to the IFCT from the valence band of ZnS to CuS, which causes the reduction of partial CuS to Cu(2)S and thus enhances H(2)-production activity. This work not only shows a possibility for substituting low-cost CuS for noble metals in the photocatalytic H(2) production but also for the first time exhibits a facile method for enhancing H(2)-production activity by photoinduced IFCT.

Strong two-photon-induced fluorescence from photostable, biocompatible nitrogen-doped graphene quantum dots for cellular and deep-tissue imaging.

Bright two-photon fluorescent probes are highly desirable to be able to optically probe biological activities deep inside living organisms with larger imaging depth, minor autofluorescence background, and less photodamage. In this study, we report the biocompatible nitrogen-doped graphene quantum dots (N-GQDs) as efficient two-photon fluorescent probes for cellular and deep-tissue imaging. The N-GQD was prepared by a facile solvothermal method using dimethylformamide as a solvent and nitrogen source. The two-photon absorption cross-section of N-GQD reaches 48,000 Göppert-Mayer units, which far surpasses that of the organic dyes and is comparable to that of the high performance semiconductor QDs, achieving the highest value ever reported for carbon-based nanomaterials. More importantly, a study of penetration depth in tissue phantom demonstrates that the N-GQD can achieve a large imaging depth of 1800 μm, significantly extending the fundamental two-photon imaging depth limit. In addition, the N-GQD is nontoxic to living cells and exhibits super photostability under repeated laser irradiation. The high two-photon absorption cross-section, large imaging depth, good biocompatibility, and extraordinary photostability render the N-GQD an attractive alternative probe for efficient two-photon imaging in biological and biomedical applications.

Graphene-Based Materials for Hydrogen Generation from Light-Driven Water Splitting†

Hydrogen production from solar water splitting has been considered as an ultimate solution to the energy and environmental issues. Over the past few years, graphene has made great contribution to improving the light-driven hydrogen generation performance. This article provides a comprehensive overview of the recent research progress on graphene-based materials for hydrogen evolution from light-driven water splitting. It begins with a brief introduction of the current status and basic principles of hydrogen generation from solar water splitting, and tailoring properties of graphene for application in this area. Then, the roles of graphene in hydrogen generation reaction, including an electron acceptor and transporter, a cocatalyst, a photocatalyst, and a photosensitizer, are elaborated respectively. After that, the comparison between graphene and other carbon materials in solar water splitting is made. Last, this review is concluded with remarks on some challenges and perspectives in this emerging field.

Switchable Ternary Nanoporous Supramolecular Network on Photo-Regulation

Controlled regulation of the switchable behavior of the supramolecular network is central to the potential application in the molecular scale nanodevices. In this work, it is reported that the reversible accommodation of the guest molecules in the nanoporous supramolecular network can be regulated by the UV/visible light. The nanoporous complex template of TCDB/4NN-Macrocycle(trans,trans,trans,trans) with photosensitive units is well-defined. After the UV irradiation, the template can be switched on to encapsulate coronene molecules due to the formation of a new photoisomer(trans,cis,trans,cis) and switched off to expel coronene from the inner cavities under the visible light. The photoregulated switchable multicomponent supramolecular guest-host network provides a novel strategy for fabricating the functional nanodevices at the molecular scale.

Label-free attomolar detection of proteins using integrated nanoelectronic and electrokinetic devices.

High-sensitivity screening of biomarkers is critical to areas ranging from early disease detection and diagnosis to bioterrorism surveillance. Here the development of integrated nanoelectronic and electrokinetic devices for label-free attomolar detection of proteins is reported. Electrically addressable silicon nanowire field-effect transistors and electrodes for electrokinetic transport are integrated onto a common sensor chip platform, and the nanowire devices are subsequently functionalized with receptors for selective biomarker detection. Nanowire devices modified with monoclonal antibody for prostate specific antigen exhibit close to a 10(4) increase in sensitivity due to streaming dielectrophoresis and corresponding electrostatic contribution to the binding affinity after application of an AC electric field. The devices are also modified with receptors for cholera toxin subunit B and achieve a similar enhancement. These results show general applicability of this method, and could open up opportunities in early stage disease detection and the analysis of proteins from single cells.

A photoelectrochemical investigation on the synergetic effect between CdS and reduced graphene oxide for solar-energy conversion.

CdS modified with reduced graphene oxide (RGO) has been widely demonstrated to be effective in the field of solar-energy conversion. However, the inherent mechanism of this superior property is still not thoroughly understood. Thus the photoelectrochemical method was employed to systemically investigate the synergetic effect between CdS and RGO. The result shows that the photoelectrochemical properties of RGO/CdS samples are sensitive to the relative ratio of RGO to CdS, and the photoelectrode with 1.0 wt% ratio of RGO possesses the best photoelectrochemical performance. Further investigation demonstrates that the synergetic effect between CdS and RGO directly influences the charge-transport property and band-structure of the composite, which is also supported by the X-ray photoelectron spectroscopy data and first-principle simulation, respectively.

TiO2 Single Crystal with Four‐Truncated‐Bipyramid Morphology as an Efficient Photocatalyst for Hydrogen Production

Diverse titanium dioxide (TiO2 ) nanostructures have attracted much attention recently due to their potential application in photocatalytic and photovoltaic fields. Here, the synthesis of a TiO2 single crystal with a novel four-truncated-bipyramid morphology is reported for the first time, produced by a simple hydrothermal method. Both peroxo titanic acid precursor and hydrofluoric acid capping agent are essential for the formation of this unique morphology. Moreover, the as-prepared TiO2 photocatalyst exhibits excellent hydrogen production activity from an ethanol-water solution, which is attributed to exposure of both high-energy {001} oxidative and low-energy {101} reductive facets in an optimal ratio. The current findings will contribute greatly to development of more novel photocatalysts with controllable microscopic structures for hydrogen production.