Carbonaceous nanomaterials for the enhancement of TiO2 photocatalysis

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 ...

Graphene Transforms Wide Band Gap ZnS to a Visible Light Photocatalyst. The New Role of Graphene as a Macromolecular Photosensitizer

Initially envisaged as rather unreactive, aromatic-like molecules, the fullerenes instead undergo a wide variety of reactions characteristic of alkenes. The many derivatives of C60, and the few of C70, that have now been reported offer new directions for organic chemistry.

The Chemistry of Fullerenes

Redox-active fullerenes can be covalently bound to a variety of donors; their photophysical properties have been investigated. Their photochemical processes, including electron transfer and energy transfer, are varied, depending on the donor, linkage between the donor and C 60 , and solvent. Regardless of the solvent and linkage, the charge-separated state is produced efficiently in zinc porphyrin-C 60 systems, showing that C 60 is a good electron acceptor. The most intriguing characteristic of C 60 in electron transfer is that C 60 accelerates photoinduced charge separation and retards charge recombination in the dark. The long-lived charge-transfer state of the C 60 -porphyrin dyad was successfully converted to photocurrent using a self-assembled monolayer technique. These findings will provide a new strategy for the design and synthesis of artificial photosynthethic systems and photoactive materials using C 60 as a building block.

Donor‐Linked Fullerenes: Photoinduced electron transfer and its potential application

Photosensitized degradation of a textile azo dye, Acid Orange 7, has been carried out on TiO2 particles using visible light Mechanistic details of the dye degradation have been elucidated using diffuse reflectance absorption and FTIR techniques Degradation does not occur on Al2O3 surface or in the absence of oxygen The dependence of the dye degradation rate on the surface coverage shows the participation of excited dye and TiO2 semiconductor in the surface photochemical process Diffuse reflectance laser flash photolysis confirms the charge injection from the excited dye molecule into the conduction band of the semiconductor as the primary mechanism for producing oxidized dye radical The surface-adsorbed oxygen plays an important role in scavenging photogenerated electrons, thus preventing the recombination between the oxidized dye radical and the photoinjected electrons Diffuse reflectance FTIR was used to make a tentative identification of reaction intermediates and end products of dye degradation

Environmental Photochemistry on Semiconductor Surfaces: Photosensitized Degradation of a Textile Azo Dye, Acid Orange 7, on TiO2 Particles Using Visible Light

The singlet and triplet excited states of C{sub 60} and C{sub 70} have been characterized in poly(methyl methacrylate) (PMMA) films by using picosecond and nanosecond laser flash photolysis techniques. The absorption properties and lifetimes of these excited states are very similar to those observed in solutions. When complexed with dimethylaniline (DMA) in the PMMA films, these fullerenes exhibit decreased lifetimes in their excited states. Photoinduced electron transfer between C+{sub 60} (or C{sub 70}) and DMA in the PMMA film was carried out with 532-nm laser pulse excitation. The polymeric environment facilitated the stabilization of electron-transfer products. 38 refs., 10 figs.

Photochemistry of fullerenes. Excited-state behavior of C60 and C70 and their reduction in poly(methyl methacrylate) films

Visible laser-induced degradation of C70 is observed on titanium dioxide particles; diffuse reflectance laser flash-photolysis experiments, which highlight the photochemical oxidation of C70 on TiO2 particles, are described.

Matt Gevaert

Papers

Photochemistry of fullerenes. Excited-state behavior of C60 and C70 and their reduction in poly(methyl methacrylate) films

Visible laser-induced oxidation of C70 on titanium dioxide particles

Photochemistry on Semiconductor Surfaces. Visible Light Induced Oxidation of C60 on TiO2 Nanoparticles.

Visible Laser-Induced Oxidation of C70 on Titanium Dioxide Particles.