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.

Acoustic and optical phonons in EVOH TiO2 nanocomposite films: Effect of aggregation

A series of CuO-Cu2O/TiO2 nanocomposite samples were prepared by the sol-gel method Before applying the sol-gel method, the Cu(OH)2 nanostructure on Cu powders were formed by in-situ solution treatment The samples were characterized through some techniques and the photocatalytic performance of CuO-Cu2O/TiO2 nanocomposites for gas-phase 2-propanol photo-oxidation under UV and sunlight type illumination was evaluated The effect of calcination process on the synthesis and photocatalytic activity of the samples was studied The calcination process plays an important role in improving the properties of nanocomposite powders The results showed that the nanocomposite formed successfully in desirable structure and morphology The nanocomposite is composed by the mixture of TiO2 particle with an average particle size of about 300 nm and the copper oxide nanorods with a diameter of 50-100 nm In this nanocomposite, the copper oxides nanostructures and TiO2 particles are the main components to form the heterojunction structure and provide enhanced photocatalytic performance compared to the TiO2 sample The reaction rate of the most active nanocomposite sample prepared at the optimum conditions is almost 6 times larger than the TiO2 references

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Effect of calcination process on the gas phase photodegradation by CuO-Cu2O/TiO2 nanocomposite photocatalyst

Studies of Ceria-Containing Catalysts Using Magnetic Resonance and X-Ray Spectroscopies.

The photocatalytic activity in the 2-propanol degradation, under UV and sunlight (SL)-type irradiations, of a series of Zr-TiO2materials, prepared using the sol–gel method, with a Zr content ranging from 0.25 to 1 wt%, was evaluated in this work. The physicochemical properties of the solids were characterized using X-ray diffraction, BET and porosity measurements, IR, UV–vis, Photoluminescence and X-ray photoelectron spectroscopy. The XRD data showed that the TiO2 was stabilized as anatase phase in all the samples and that the incorporation of Zr4+ into TiO2 lattice has led to a decrease of the crystallite size. The BET analysis confirmed that the addition of zirconium onto TiO2 support affected the surface area which increases with the increase of Zr4+ content. The UV-DRS spectra showed that, the incorporation of zirconium into TiO2 lattice leads to a slight decrease of the band gap energy of TiO2. The results of the photocatalytic test showed an enhancement on the photocatalytic activity of TiO2, in the 2 propanol degradation, by the doping with a low amount of zirconium. All the samples were found more active under UV illumination than under SL. In all cases, the highest efficiency in the 2-propanol photodegradation was observed for the 0.5% Zr-TiO2 sample and was essentially related to its lowest optical band gap energy. 

Photodegradation of 2-propanol in gas phase over Zirconium doped TiO2: Effect of Zr content

In the context of band gap engineering of the ZnO photoactive material for solar harvesting applications via W doping, a number of a priori discrepant experimental observations in the literature concerning ZnO c axis expansion/contraction, band gap red- or blue-shifting, the Zn-substitutional or interstitial nature of W atoms, or the W6+ charge compensation view with ZnO native defects are addressed by thorough density functional theory calculations on a series of bulk supercell models encompassing a large range of W contents. The present results reconcile the observations, which are dissimilar at first sight, by showing that interstitial W (Wi) is only energetically preferred over substitutional (WZn) at large W doping concentrations; the WZn c lattice expansion can be compensated by a W-triggered Zn-vacancy (VZn) c lattice contraction. The presence of WZn energetically fosters nearby VZn defects, and vice versa, up to a double VZn situation. The quantity of mono- or divacancies explains the lattice cont...

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Marcos Fernández-García

Papers

Acoustic and optical phonons in EVOH TiO2 nanocomposite films: Effect of aggregation

Effect of calcination process on the gas phase photodegradation by CuO-Cu2O/TiO2 nanocomposite photocatalyst

Studies of Ceria-Containing Catalysts Using Magnetic Resonance and X-Ray Spectroscopies.

Photodegradation of 2-propanol in gas phase over Zirconium doped TiO2: Effect of Zr content

Understanding W Doping in Wurtzite ZnO