Jenny Schneider,*,† Masaya Matsuoka,‡ Masato Takeuchi,‡ Jinlong Zhang, Yu Horiuchi,‡ Masakazu Anpo,‡ and Detlef W. Bahnemann*,† †Institut fur Technische Chemie, Leibniz Universitaẗ Hannover, Callinstrasse 3, D-30167 Hannover, Germany ‡Faculty of Engineering, Osaka Prefecture University, 1 Gakuen-cho, Sakai Osaka 599-8531, Japan Key Lab for Advanced Materials and Institute of Fine Chemicals, East China University of Science and Technology, Shanghai 200237, China

Understanding TiO2 photocatalysis: mechanisms and materials.

Titanium dioxide (TiO2) has been the most intensively investigated binary transition metal oxide in the past four decades as indicated by Figure S1. Furthermore, the annual number of papers published on TiO2 has seen a continuous increase, particularly since the beginning of this century (Figure S2). This is understandable when one considers the wide range of applications of TiO2 from the conventional areas (i.e., pigment, cosmetic, toothpaste, and paint) to the later developed functional areas such as photoelectrochemical cell,(1-3) dye-sensitized solar cells (DSSCs),(4-11) photocatalysis,(12-24) catalysis,(25-31) photovoltaic cell,(32-34) lithium ion batteries,(35-41) sensors,(42-46) electron field emission,(47-51) microwave absorbing material, biomimetic growth, and biomedical treatments.(52-57) Nearly all these functional applications of TiO2 fall in the scope of energy, environment, and health, which are definitely the three most important and challenging themes facing the Human race that need to be addressed in this century. Besides the apparent merits including nontoxicity, elemental abundance, good chemical stability, and easy synthesis, TiO2 has attracted strong research interest worldwide due to its physicochemical properties for realizing various functions.(15, 58, 59) Especially, very encouraging progresses in photocatalysis and DSSCs with the involvement of TiO2 have greatly stimulated the rapid development of TiO2 crystals with controllable phase, size, shape, defect, and heteroatom.(58, 60-68)

Titanium dioxide crystals with tailored facets

Hydrothermal conversion of biomass waste to activated carbon with high porosity: a review.

In recent years, heterogeneous photocatalysis has received much research interest because of its powerful potential applications in tackling many important energy and environmental challenges at a global level in an economically sustainable manner. Due to their unique optical, electrical, and physicochemical properties, various 2D graphene nanosheets-supported semiconductor composite photocatalysts have been widely constructed and applied in different photocatalytic fields. In this review, fundamental mechanisms of heterogeneous photocatalysis, including thermodynamic and kinetics requirements, are first systematically summarized. Then, the photocatalysis-related properties of graphene and its derivatives, and design rules and synthesis methods of graphene-based composites are highlighted. Importantly, different design strategies, including doping and sensitization of semiconductors by graphene, improving electrical conductivity of graphene, increasing eloectrocatalytic active sites on graphene, strengthening interface coupling between semiconductors and graphene, fabricating micro/nano architectures, constructing multi-junction nanocomposites, enhancing photostability of semiconductors, and utilizing the synergistic effect of various modification strategies, are thoroughly summarized. The important applications including photocatalytic pollutant degradation, H2 production, and CO2 reduction are also addressed. Through reviewing the significant advances on this topic, it may provide new opportunities for designing highly efficient 2D graphene-based photocatalysts for various applications in photocatalysis and other fields, such as solar cells, thermal catalysis, separation, and purification.

/pdf/graphene-in-photocatalysis-a-review-1oawvvl4tw.pdf

Graphene in Photocatalysis: A Review

Basic concepts and recent advances in nitrophenol reduction by gold- and other transition metal nanoparticles

Tailored synthesis of well-defined anatase TiO2 nanocrystals with a high percentage of reactive facets has attracted widespread attention due to the scientific and technological importance. Here, high-quality nanosized anatase ultrathin TiO2 nanosheets, mainly dominated by {001} facets, were grown on graphene nanosheets by a simple one-pot solvothermal synthetic route. The obtained samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), ultraviolet–visible (UV–vis) diffuse reflectance spectroscopy, and X-ray photoelectron spectroscopy (XPS). The photocatalytic activity of as-prepared TiO2/graphene composites for degradation of methylene blue (MB) under visible-light irradiation at λ ≥ 400 nm was investigated. The results show that TiO2/graphene nanocomposites have a higher photocatalytic activity than pure TiO2 and P25. This enhanced photocatalytic activity suggests that the photoinduced electrons in TiO2 pref...

Large Ultrathin Anatase TiO2 Nanosheets with Exposed {001} Facets on Graphene for Enhanced Visible Light Photocatalytic Activity

N-doped TiO2 nanoparticles modified with carbon (denoted N–TiO2/C) were successfully prepared by a facile one-pot hydrothermal treatment in the presence of L-lysine, which acts as a ligand to control the nanocrystal growth and as a source of nitrogen and carbon. As-prepared nanocomposites were characterized by thermogravimetric analysis (TGA), X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), Raman spectroscopy, ultraviolet–visible (UV–vis) diffuse reflectance spectroscopy, X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), electron paramagnetic resonance (EPR) spectra, and N2 adsorption–desorption analysis. The photocatalytic activities of the as-prepared photocatalysts were measured by the degradation of methyl orange (MO) under visible light irradiation at λ ≥ 400 nm. The results show that N–TiO2/C nanocomposites increase absorption in the visible light region and exhibit a higher photocatalytic activity than pure TiO2, commercial P25 and previously reported N-doped TiO2 photocatalysts. We have demonstrated that the nitrogen was doped into the lattice and the carbon species were modified on the surface of the photocatalysts. N-doping narrows the band gap and C-modification enhances the visible light harvesting and accelerates the separation of the photo-generated electrons and holes. As a consequence, the photocatalytic activity is significantly improved. The molar ratio of L-lysine/TiCl4 and the pH of the hydrothermal reaction solution are important factors affecting the photocatalytic activity of the N–TiO2/C; the optimum molar ratio of L-lysine/TiCl4 is 8 and the optimum pH is ca. 4, at which the catalyst exhibits the highest reactivity. Our findings demonstrate that the as-obtained N–TiO2/C photocatalyst is a better and more promising candidate than well studied N-doped TiO2 alternatives as visible light photocatalysts for potential applications in environmental purification.

One-step hydrothermal synthesis of N-doped TiO2/C nanocomposites with high visible light photocatalytic activity.

Direct fabrication of core–shell or yolk–shell functional nanomaterials via a facile template-free method remains a challenge. In this work, we present a novel approach that involves straightforward chemical transformation and thermal treatment of the infinite coordination polymer particles to obtain composition-tunable CeO2 yolk–shell structures. Uniform CeO2 yolk–shell hollow spheres with a high surface area are promising support materials for tiny gold nanoparticles (ca. 4 nm), forming Au–CeO2 nanocomposites which exhibit a remarkable catalytic activity and high stability for the reduction of p-nitrophenol. A possible mechanism for the formation of CeO2 yolk–shell microspheres is also proposed.

Novel CeO2 yolk–shell structures loaded with tiny Au nanoparticles for superior catalytic reduction of p-nitrophenol

Teflon films, made from polytetrafluoroethylene (PTFE), are widely known hydrophobic materials. In this paper, we utilize Teflon films as concentrators to construct active surface-enhanced Raman scattering (SERS) substrates to achieve a higher sensitivity for SERS detection. The fabrication method is simple via directly depositing a drop of silver colloidal solution on a piece of commercial Teflon film and drying it under ambient conditions. SERS measurements are carried out on Rhodamine6G (R6G) molecules, showing strong enhanced SERS signals even at a concentration of 10−15 M and allowing single-molecule detection. Silver nanoparticles (Ag-NPs) supported on the Teflon films exhibit a higher SERS enhancement and better reproducibility compared with that on glass slides. Such a high enhancement effect is primarily attributed to the hydrophobic condensation effect of Teflon films towards both silver colloids and R6G molecules, thus causing the aggregation of Ag-NPs for more “hot-spots” and delivering R6G molecules to the hot-spot areas thereby overcoming the limit of diffusion.

Hydrophobic Teflon films as concentrators for single-molecule SERS detection

Here we report a silver nanoparticle based surface enhanced resonance Raman scattering (SERRS) probe for the ultrasensitive and selective detection of formaldehyde. The detection limit reaches as low as 10−11 M.

Li-Qiang Lu

Papers

Large Ultrathin Anatase TiO2 Nanosheets with Exposed {001} Facets on Graphene for Enhanced Visible Light Photocatalytic Activity

One-step hydrothermal synthesis of N-doped TiO2/C nanocomposites with high visible light photocatalytic activity.

Novel CeO2 yolk–shell structures loaded with tiny Au nanoparticles for superior catalytic reduction of p-nitrophenol

Hydrophobic Teflon films as concentrators for single-molecule SERS detection

A silver nanoparticle based surface enhanced resonance Raman scattering (SERRS) probe for the ultrasensitive and selective detection of formaldehyde