TiO2 photocatalysis and related surface phenomena

As a fascinating conjugated polymer, graphitic carbon nitride (g-C3N4) has become a new research hotspot and drawn broad interdisciplinary attention as a metal-free and visible-light-responsive photocatalyst in the arena of solar energy conversion and environmental remediation. This is due to its appealing electronic band structure, high physicochemical stability, and “earth-abundant” nature. This critical review summarizes a panorama of the latest progress related to the design and construction of pristine g-C3N4 and g-C3N4-based nanocomposites, including (1) nanoarchitecture design of bare g-C3N4, such as hard and soft templating approaches, supramolecular preorganization assembly, exfoliation, and template-free synthesis routes, (2) functionalization of g-C3N4 at an atomic level (elemental doping) and molecular level (copolymerization), and (3) modification of g-C3N4 with well-matched energy levels of another semiconductor or a metal as a cocatalyst to form heterojunction nanostructures. The constructi...

Graphitic Carbon Nitride (g-C3N4)-Based Photocatalysts for Artificial Photosynthesis and Environmental Remediation: Are We a Step Closer To Achieving Sustainability?

Fujishima and Honda (1972) demonstrated the potential of titanium dioxide (TiO2) semiconductor materials to split water into hydrogen and oxygen in a photo-electrochemical cell. Their work triggered the development of semiconductor photocatalysis for a wide range of environmental and energy applications. One of the most significant scientific and commercial advances to date has been the development of visible light active (VLA) TiO2 photocatalytic materials. In this review, a background on TiO2 structure, properties and electronic properties in photocatalysis is presented. The development of different strategies to modify TiO2 for the utilization of visible light, including non metal and/or metal doping, dye sensitization and coupling semiconductors are discussed. Emphasis is given to the origin of visible light absorption and the reactive oxygen species generated, deduced by physicochemical and photoelectrochemical methods. Various applications of VLA TiO2, in terms of environmental remediation and in particular water treatment, disinfection and air purification, are illustrated. Comprehensive studies on the photocatalytic degradation of contaminants of emerging concern, including endocrine disrupting compounds, pharmaceuticals, pesticides, cyanotoxins and volatile organic compounds, with VLA TiO2 are discussed and compared to conventional UV-activated TiO2 nanomaterials. Recent advances in bacterial disinfection using VLA TiO2 are also reviewed. Issues concerning test protocols for real visible light activity and photocatalytic efficiencies with different light sources have been highlighted.

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A review on the visible light active titanium dioxide photocatalysts for environmental applications

5.1. Nanoalloys of Group 11 (Cu, Ag, Au) 865 5.1.1. Cu−Ag 866 5.1.2. Cu−Au 867 5.1.3. Ag−Au 870 5.1.4. Cu−Ag−Au 872 5.2. Nanoalloys of Group 10 (Ni, Pd, Pt) 872 5.2.1. Ni−Pd 872 * To whom correspondence should be addressed. Phone: +39010 3536214. Fax:+39010 311066. E-mail: ferrando@fisica.unige.it. † Universita di Genova. ‡ Argonne National Laboratory. § University of Birmingham. | As of October 1, 2007, Chemical Sciences and Engineering Division. Volume 108, Number 3

Nanoalloys: From Theory to Applications of Alloy Clusters and Nanoparticles

Metal species with different size (single atoms, nanoclusters, and nanoparticles) show different catalytic behavior for various heterogeneous catalytic reactions. It has been shown in the literature that many factors including the particle size, shape, chemical composition, metal–support interaction, and metal–reactant/solvent interaction can have significant influences on the catalytic properties of metal catalysts. The recent developments of well-controlled synthesis methodologies and advanced characterization tools allow one to correlate the relationships at the molecular level. In this Review, the electronic and geometric structures of single atoms, nanoclusters, and nanoparticles will be discussed. Furthermore, we will summarize the catalytic applications of single atoms, nanoclusters, and nanoparticles for different types of reactions, including CO oxidation, selective oxidation, selective hydrogenation, organic reactions, electrocatalytic, and photocatalytic reactions. We will compare the results o...

Metal Catalysts for Heterogeneous Catalysis: From Single Atoms to Nanoclusters and Nanoparticles.

Nanostructured Oxides in Photo‐Catalysis

The evolution of time-resolved experiments, covering a multipurpose surface and bulk characterization of catalytic solids, during their preparation process and under reaction conditions, is presented. Particular emphasis is given to recent studies that attempt to unveil contemporary unresolved questions concerning the control of physicochemical properties of nanosolids, as well as the evolution of such solid materials under reactive atmospheres. To reach this goal, representative in situ and in operando works, using either modern (mostly synchrotron radiation based) approaches or multi-technique methods (mainly, although not exclusively, X-ray–vibrational coupling), and considering experiments in liquid and gas phase, as well as with amorphous, nanocrystalline and surface-deposited materials, are reviewed.

Surface and Bulk Approach to Time-resolved Characterization of Heterogeneous Catalysts

Different clays have been employed as supports for iron oxide based catalysts prepared by the impregnation method. A basic characterization of the catalysts synthesized has been performed, which includes comparisons between the supports and iron-containing catalysts at bulk and surface levels. The characterization results are correlated with conversion levels achieved during NO x reduction with propene over the iron clay catalysts. Comparison with the catalytic behaviour obtained over an alumina-supported iron oxide catalyst reveals the promising properties of iron clay catalysts for DeNO x reactions.

Supported catalysts for DeNOx reaction based on iron clays

In situ synchrotron X-ray diffraction and diffuse reflectance infrared spectroscopy (DRIFTS) are combined to study the influence of sulfur on the crystallization of pure and Fe-doped titania nano-materials. Using these two tools we have investigated the effect of sulfur on the nucleation and growth processes of the anatase polymorph from amorphous powders and show how the addition of sulfur controls the primary particle size and shape of the materials. As well known, sulfur leads to the stabilization of the oxide particle size against sintering during thermal treatments and here we interpret the physico-chemical basis of such behaviour as an exclusive effect on grain growth kinetics, in turn linked to the dehydration of the surface layers of the materials. In addition this work shows that the presence of sulfur also affects the shape of the anatase particles, favouring the existence of (101)-type surfaces and elongated (along the c crystallographic axis) particles. This combined analysis of how sulfur influences morphological aspects of the anatase phase as it grows provides a basis for understanding of surface and chemical properties of anatase nano-powders that are highly dependent upon particle morphology.

Marcos Fernández-García

Papers

Nanostructured Oxides in Photo‐Catalysis

Surface and Bulk Approach to Time-resolved Characterization of Heterogeneous Catalysts

Supported catalysts for DeNOx reaction based on iron clays

A structural and surface approach to size and shape control of sulfur-modified undoped and Fe-doped TiO2 anatase nano-materials

Oxygen handling properties of Ce-Ca mixed oxides solutions