The nanocomposites of TiO(2)-graphene (TiO(2)-GR) have been prepared via a facile hydrothermal reaction of graphene oxide and TiO(2) in an ethanol-water solvent. We show that such a TiO(2)-GR nanocomposite exhibits much higher photocatalytic activity and stability than bare TiO(2) toward the gas-phase degradation of benzene, a volatile aromatic pollutant in air. By investigating the effect of different addition ratios of graphene on the photocatalytic activity of TiO(2)-GR systematically, we find that the higher weight ratio in TiO(2)-GR will decrease the photocatalytic activity. Analogous phenomenon is also observed for the liquid-phase degradation of dyes over TiO(2)-GR. In addition, the key features for TiO(2)-GR including enhancement of adsorptivity of pollutants, light absorption intensity, electron-hole pairs lifetime, and extended light absorption range have also been found in the composite of TiO(2) and carbon nanotubes (TiO(2)-CNT). These strongly manifest that TiO(2)-GR is in essence the same as other TiO(2)-carbon (carbon nanotubes, fullerenes, and activated carbon) composite materials on enhancement of photocatalytic activity of TiO(2), although graphene by itself has unique structural and electronic properties. Notably, this key fundamental question remains completely unaddressed in a recent report ( ACS Nano 2010 , 4 , 380 ) regarding liquid-phase degradation of dyes over the TiO(2)-GR photocatalyst. Thus, we propose that TiO(2)-GR cannot provide truly new insights into the fabrication of TiO(2)-carbon composite as high-performance photocatalysts. It is hoped that our work could avert the misleading message to the readership, hence offering a valuable source of reference on fabricating TiO(2)-carbon composites for their application as a photocatalyst in the environment cleanup.

Increasing interest has been devoted to synthesizing graphene (GR)-semiconductor nanocomposites as photocatalysts for potential applications, which is very similar to its forebear carbon nanotube (CNT)-semiconductor photocatalysts. Unfortunately, a thoughtful and inevitable comparison between GR- and CNT-semiconductors as photocatalysts is often neglected in literature. This situation may give incomplete or exaggerated information on the contribution role of GR to enhance the semiconductor photocatalytic activity, as compared to CNT. Thus, our knowledge regarding the specific advantage of GR over CNT on how to design more efficient GR-semiconductor nanocomposites and understanding the origin of their enhanced photocatalytic performance is far from satisfactory. By taking the TiO(2) semiconductor as an example, we conceptually demonstrate how to synthesize a more efficient GR-TiO(2) nanocomposite as a visible light photocatalyst toward selective oxidation of alcohols under mild conditions. Comparison between GR-TiO(2) and CNT-TiO(2) discloses the prominent advantage of GR over CNT on both controlling the morphology of GR-TiO(2) nanocomposite and enhancing the photocatalytic activity of TiO(2). This work clearly highlights the importance and necessity for a comparison investigation between GR- and CNT-semiconductors as photocatalysts, which will promote our in-depth fundamental understanding on the analogy and difference between GR and CNT on controlling the morphology of GR (or CNT)-semiconductor nanocomposites and enhancing the photocatalytic performance. Therefore, we appeal the photocatalysis community to pay attention to this respect rather than separately imposing hype on the miracle of GR in much the same way as its carbon forebears, which could significantly advance our rational fabrication of smart GR-semiconductor nanocomposites for artificial photosynthesis.

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We report the assembly of nanosized ZnS particles on the 2D platform of a graphene oxide (GO) sheet by a facile two-step wet chemistry process, during which the reduced graphene oxide (RGO, also called GR) and the intimate interfacial contact between ZnS nanoparticles and the GR sheet are achieved simultaneously. The ZnS-GR nanocomposites exhibit visible light photoactivity toward aerobic selective oxidation of alcohols and epoxidation of alkenes under ambient conditions. In terms of structure-photoactivity correlation analysis, we for the first time propose a new photocatalytic mechanism where the role of GR in the ZnS-GR nanocomposites acts as an organic dye-like macromolecular "photosensitizer" for ZnS instead of an electron reservoir. This novel photocatalytic mechanism is distinctly different from all previous research on GR-semiconductor photocatalysts, for which GR is claimed to behave as an electron reservoir to capture/shuttle the electrons photogenerated from the semiconductor. This new concept of the reaction mechanism in graphene-semiconductor photocatalysts could provide a new train of thought on designing GR-based composite photocatalysts for targeting applications in solar energy conversion, promoting our in-depth thinking on the microscopic charge carrier transfer pathway connected to the interface between the GR and the semiconductor.

A series of cadmium sulfideÀgraphene (CdSÀGR) nanocomposites with different weight addition ratios of graphene (GR) have been synthesized via a facile one-step hydrothermal approach, during which the formation of CdS nanoparticles and the reduction of graphene oxide (GO) occur simultaneously. X-ray diffraction (XRD), UVÀvis diffuse reflectance spectra (DRS), field-emission scanning electron microscopy (FE-SEM), transmission scanning electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX), nitrogen adsorptionÀdesorption, photoluminescence spectra (PL), and electron spin resonance spectra (ESR) are employed to determine the properties of the samples. It is found that the CdS nanoparticles evenly overspread on the graphene scaffold, and the properties of the samples, including morphology, pore structure, optical, and electronic nature, are able to be tuned by the addition of GR as compared with blank-CdS prepared in the absence of GR. The photocatalytic activities of the as-prepared CdSÀGR nanocomposites are evaluated by selective oxidation of a range of alcohols under mild conditions. To our best knowledge, it is the first time to use CdSÀGR nanocomposites as visible light photocatalyst for selective organic transformation. Our results demonstrate that the as-prepared CdSÀGR nanocomposites can serve as a promising visible-light-driven photocatalyst for selective oxidation of alcohols to corresponding aldehydes. The high photoactivity of CdSÀGR can be ascribed to the integrative effect of enhanced light absorption intensity, high electron conductivity of GR, and its significant influence on the morphology and structure of the samples. It is hoped that our current work could widen the application of CdSÀGR nanocomposites and open promising prospects for the utilization of GR-based semiconductor nanocomposites as visible light photocatalyst for selective organic transformations.

Incessant interest has been shown in the synthesis of graphene (GR)-semiconductor nanocomposites as photocatalysts aiming to utilize the excellent electron conductivity of GR to lengthen the lifetime of photoexcited charge carriers in the semiconductor and, hence, improve the photoactivity. However, research works focused on investigating how to make sufficient use of the unique electron conductivity of GR to design a more efficient GR-semiconductor photocatalyst have been quite lacking. Here, we show a proof-of-concept study on improving the photocatalytic performance of GR-TiO(2) nanocomposites via a combined strategy of decreasing defects of GR and improving the interfacial contact between GR and the semiconductor TiO(2). The GR-TiO(2) nanocomposite fabricated by this approach is able to make more sufficient use of the electron conductivity of GR, by which the lifetime and transfer of photoexcited charge carriers of GR-TiO(2) upon visible light irradiation will be improved more efficiently. This in turn leads to the enhancement of visible-light-driven photoactivity of GR-TiO(2) toward selective transformation of alcohols to corresponding aldehydes using molecular oxygen as a benign oxidant under ambient conditions. It is anticipated that our current work would inform ongoing efforts to exploit the rational design of smart, more efficient GR-semiconductor photocatalysts for conversion of solar to chemical energy by heterogeneous photocatalysis.

The fabrication and electrochemical characterization of truncated cone-shaped nanopore electrodes are reported. A nanopore electrode is a Pt disk electrode embedded at the bottom of a conical pore, the circular orifice of the pore having nanometer dimensions. The electrochemical properties of nanopore electrodes with orifice radii of 39 and 74 nm are presented. Both the steady-state and transient voltammetric behavior of the nanopore electrode are reported and compared to predictions obtained using finite-element simulations. The truncated cone-shaped pore electrode possesses a unique transport property-the steady-state flux of molecules into a deep pore is limited by the restriction near the pore orifice, and thus, the steady-state current is independent of the pore depth. This characteristic is potentially useful in studying transport through nanometer-scale orifices.

Glycerol, being either a primary by-product of biodiesel manufacture or a platform molecule from sugars, is of significant interest as a renewable biomass because it is a highly functionalized and versatile organic building block for the synthesis of value-added fine chemicals. In particular, selective oxidation of glycerol to various industrially valuable products by heterogeneous photocatalysis using solar light as free energy and molecular oxygen as benign oxidant under ambient conditions is extremely attractive. However, a highly selective, heterogeneous visible-light photocatalyst utilized for aerobic oxidation of glycerol has been unavailable. To date, the discovery or design of a visible-light-driven, highly selective photocatalyst for selective oxidation of glycerol to a specific product is particularly challenging in heterogeneous photocatalytic selective transformation. Herein, we for the first time, report the identification of flower-like Bi 2 WO 6 as a highly selective visible-light photocatalyst toward aerobic selective oxidation of glycerol to dihydroxyacetone using oxygen as oxidant in water at room temperature and atmospheric pressure. A rationale for the observed high selectivity over photocatalyst flower-like Bi 2 WO 6 is provided.