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

This critical review shows the basis of photocatalytic water splitting and experimental points, and surveys heterogeneous photocatalyst materials for water splitting into H2 and O2, and H2 or O2 evolution from an aqueous solution containing a sacrificial reagent Many oxides consisting of metal cations with d0 and d10 configurations, metal (oxy)sulfide and metal (oxy)nitride photocatalysts have been reported, especially during the latest decade The fruitful photocatalyst library gives important information on factors affecting photocatalytic performances and design of new materials Photocatalytic water splitting and H2 evolution using abundant compounds as electron donors are expected to contribute to construction of a clean and simple system for solar hydrogen production, and a solution of global energy and environmental issues in the future (361 references)

Heterogeneous photocatalyst materials for water splitting

2.3. Evaluation of Photocatalytic Water Splitting 6507 2.3.1. Photocatalytic Activity 6507 2.3.2. Photocatalytic Stability 6507 3. UV-Active Photocatalysts for Water Splitting 6507 3.1. d0 Metal Oxide Photocatalyts 6507 3.1.1. Ti-, Zr-Based Oxides 6507 3.1.2. Nb-, Ta-Based Oxides 6514 3.1.3. W-, Mo-Based Oxides 6517 3.1.4. Other d0 Metal Oxides 6518 3.2. d10 Metal Oxide Photocatalyts 6518 3.3. f0 Metal Oxide Photocatalysts 6518 3.4. Nonoxide Photocatalysts 6518 4. Approaches to Modifying the Electronic Band Structure for Visible-Light Harvesting 6519

Semiconductor-based Photocatalytic Hydrogen Generation

TiO2 photocatalysis and related surface phenomena

When used as a photocatalyst, titanium dioxide (TiO(2)) absorbs only ultraviolet light, and several approaches, including the use of dopants such as nitrogen, have been taken to narrow the band gap of TiO(2). We demonstrated a conceptually different approach to enhancing solar absorption by introducing disorder in the surface layers of nanophase TiO(2) through hydrogenation. We showed that disorder-engineered TiO(2) nanocrystals exhibit substantial solar-driven photocatalytic activities, including the photo-oxidation of organic molecules in water and the production of hydrogen with the use of a sacrificial reagent.

https://science.sciencemag.org/content/sci/early/2011/01/19/science.1200448.full.pdf

Increasing Solar Absorption for Photocatalysis with Black Hydrogenated Titanium Dioxide Nanocrystals

To use solar irradiation or interior lighting efficiently, we sought a photocatalyst with high reactivity under visible light. Films and powders of TiO 2- x N x have revealed an improvement over titanium dioxide (TiO 2 ) under visible light (wavelength 2 has proven to be indispensable for band-gap narrowing and photocatalytic activity, as assessed by first-principles calculations and x-ray photoemission spectroscopy.

/pdf/visible-light-photocatalysis-in-nitrogen-doped-titanium-np6nklr9gh.pdf

Visible-Light Photocatalysis in Nitrogen-Doped Titanium Oxides

TiO2-based powder, including 0.1 at% of N doped in the rutile lattice, has been synthesized by oxidation of TiN. As a result, a significant shift of the absorption edge to a lower energy in the visible-light region has been observed. The substitutional doping of N into the TiO2 lattice is found to be effective; its 2p states contribute to the band-gap narrowing by mixing with O 2p as shown in ab initio electronic structure calculations.

https://iopscience.iop.org/article/10.1143/JJAP.40.L561/pdf

Band-Gap Narrowing of Titanium Dioxide by Nitrogen Doping

Band-Gap Narrowing of Titanium Dioxide by Nitrogen Doping : Optical Properties of Condensed Matter

We report the photooxidation of toluene over nitrogen doped TiO2 (TiO2−xNx) under visible light irradiation. The photocatalytic oxidation of toluene in air over TiO2−xNx powders was studied using diffuse reflectance Fourier transform infrared spectroscopy (DRIFTS), gas chromatography (GC), ion chromatography (IC), and gas chromatography mass spectrometry (GC-MS), focusing on the photocatalytic decomposition processes of toluene. Results obtained indicate that toluene, weakly adsorbed on the catalyst surface, is initially photooxidized to benzaldehyde which adsorbs onto the TiO2−xNx surface more strongly, leading to the formation of ring-opening products such as carboxylic acids and aldehydes. No gaseous intermediates were detected during the photooxidation. Major intermediates adsorbed at the catalyst surface were oxalic acid, (COOH)2, acetic acid, CH3COOH, formic acid, HCOOH, and pyruvic acid, CH3COCOOH, whereas more complicated carboxylic species, including propionic acid, CH3CH2COOH, isovaleric acid, (CH3)2CHCH2COOH, and succinic acid, (CH2COOH)2, were also found in the early stage of the photooxidation. These intermediate products were gradually photodegraded to CO2 and H2O under visible light irradiation.

Photodegradation of toluene over TiO2−xNx under visible light irradiation

To enhance the photocatalytic performance of titanium dioxide, the structures of both bulk and surface were modified. Doping of sulfur atoms to be substituted for lattice oxygen atoms of titanium dioxide was carried out to extend the light absorption by atmosphere-controlled pulsed laser deposition, which allows direct preparation of impurity-included thin film such as sulfur-doped titanium dioxide. On the other hand, to enhance the surface catalytic reaction, nickel nanoparticles were deposited at the thin film substrate by chemical vapor reductive deposition method, which is a novel preparation technique of metallic nanoparticles on the substrate surface. Obtained sulfur-doped titanium dioxide was found to possess sensitivity to visible light with the wavelength up to 550 nm, indicating the photocatalytic activity in visible region. Sulfur doping induced the dye degradation activity under visible light irradiation. When nickel nanoparticles were deposited, a remarkable enhancement of the hydrogen evolution activity through ethanol decomposition of more than 20 times as much as unmodified titanium dioxide thin film was accomplished. In addition, the stability of sulfur atom doped into titanium dioxide structure was investigated.

Koyu Aoki

Papers

Visible-Light Photocatalysis in Nitrogen-Doped Titanium Oxides

Band-Gap Narrowing of Titanium Dioxide by Nitrogen Doping

Band-Gap Narrowing of Titanium Dioxide by Nitrogen Doping : Optical Properties of Condensed Matter

Photodegradation of toluene over TiO2−xNx under visible light irradiation

Remarkably enhanced photocatalytic activity by nickel nanoparticle deposition on sulfur-doped titanium dioxide thin film