Titanium Dioxide Nanomaterials: Synthesis, Properties, Modifications, and Applications

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

Surface Science Studies of the Photoactivation of TiO2New Photochemical Processes

A surface science perspective on TiO2 photocatalysis

Nitrogen-doped titanium dioxide as visible-light-sensitive photocatalyst: designs, developments, and prospects.

Titanium dioxide powders prepared by a wet method, i.e., the hydrolysis of titanium tetra-isopropoxide or titanium tetrachloride with an aqueous ammonia solution, followed by calcination at temperatures above 330 °C, exhibit photocatalytic activity in the visible-light region owing to N doping. The maximum absorption of visible light by the N-doped TiO 2 was about 50% at around 440 nm. Thermal analysis revealed that N doping occurs upon the oxidation of ammonia included in titanium hydroxide with lattice oxygen in TiO 2 . XPS analysis showed that the N doped in TiO 2 is less than 1.3 at.% and is not bound directly to Ti. The oxidation state of doped N was found close to that of NO. Quantum yield for the CO photooxidation on the N-doped TiO 2 in the visible region was less than that in UV region. These results show that the N doping by the wet method is similar to impurity doping such as metal ion doping.

Shinji Abe

Papers

Visible-light sensitization of TiO2 photocatalysts by wet-method N doping