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

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.

Rising atmospheric levels of carbon dioxide and the depletion of fossil fuel reserves raise serious concerns about the ensuing effects on the global climate and future energy supply. Utilizing the abundant solar energy to convert CO2 into fuels such as methane or methanol could address both problems simultaneously as well as provide a convenient means of energy storage. In this Review, current approaches for the heterogeneous photocatalytic reduction of CO2 on TiO2 and other metal oxide, oxynitride, sulfide, and phosphide semiconductors are presented. Research in this field is focused primarily on the development of novel nanostructured photocatalytic materials and on the investigation of the mechanism of the process, from light absorption through charge separation and transport to CO2 reduction pathways. The measures used to quantify the efficiency of the process are also discussed in detail.

Photocatalytic reduction of CO2 on TiO2 and other semiconductors.

A review on highly ordered, vertically oriented TiO2 nanotube arrays: Fabrication, material properties, and solar energy applications

A surface science perspective on TiO2 photocatalysis

Fe(III)-doped TiO2 nanoparticles have been prepared in three different ways using inorganic or organic precursors, respectively. Transmission electron microscopic (TEM) structure characterization of the obtained particles reveals that TiO2 particles with and without the Fe(III) dopant possess the crystal structure of anatase. Cryo-TEM of vitrified samples confirms earlier assumptions that TiO2 nanoparticles tend to form three-dimensional networks in solution. A novel energy transfer mechanism is suggested employing these three-dimensional networks as antenna systems which lead to improved photocatalytic activities of the colloidal preparations. The performance of the nanostructured TiO2 with and without Fe-dopant for the photocatalytic oxidation of methanol producing HCHO is strongly dependent on the preparations and the Fe-content. Fe(III)-doped TiO2 nanoparticles prepared from organic precursors by the novel method (≤2.5 atom% Fe) exhibit a greatly enhanced photocatalytic activity (quantum yield of HCHO up to ca. 15%).

A comparative study of nanometer sized Fe(III)-doped TiO2photocatalysts: synthesis, characterization and activity

A novel preparation of iron-doped TiO2 nanoparticles with enhanced photocatalytic activity

UV illumination of aqueous TiO2 suspensions yields hydroxyl radicals which can be trapped by methanol yielding formaldehyde (HCHO). The photonic efficiency of HCHO formation (345±35 nm cw illumination) in aqueous, oxygenated TiO2 suspensions (2.4 nm diameter TiO2 particles, Degussa P25 and Sachtleben Hombikat UV 100) containing methanol at pH ca. 1–12 has been determined as well as the respective quantum yield in case of 2.4 nm TiO2. Differences in the activity of the three photocatalysts have been found and are discussed. The photonic efficiency in the presence of P25 and Hombikat UV 100 depends on the catalyst loading (g l−1) and the pH. Below 2.5 g l−1 the photonic efficiency is higher for P25 than for Hombikat UV 100 and vice versa at above 2.5 g l−1. Optimum pH values for P25 and Hombikat UV 100 resulting in maximum photonic efficiencies (ca. 0.13 for P25 and 0.07 for Hombikat UV 100) are 7.7 and 10.4, respectively. Other than with P25 and Hombikat UV 100, which scatter light strongly, the quantum yield of HCHO formation in the colloidal 2.4 nm TiO2 suspension varies but little with the pH and virtually does not change with the photocatalyst loading (0.1–1.0 g/l). Employing these colloidal particles as photocatalysts the quantum yield varies as the inverse square root of light intensity. It increases from 0.02 to 0.08 when the absorbed photon flux decreases from 8.1×10−7 to 4.9×10−8 Einstein l−1 s−1. A simple model is presented to explain this observation.

Photonic efficiency and quantum yield of formaldehyde formation from methanol in the presence of various TiO2 photocatalysts

Colloidal TiO2 (2.4 nm average particle diameter) has been prepared and modified by photodeposition of Pt (PtTi-S1) and by mixing with Pt nanoparticles (PtTi-S2). Transmission electron microscopy reveals particle aggregation in colloidal TiO2 and large networks of agglomerated particles in the platinized samples. The photocatalytic activity of the samples (0.1 g L-1) has been investigated by measuring the quantum yield, φHCHO, of HCHO formed from aqueous methanol at pH 3.5 under different conditions. In CW photolysis of the oxygenated suspensions (300−400 nm UV light, 8 × 10-7 einstein L-1 s-1 photon absorption rate) the platinized photocatalysts (1 wt % Pt) enhance φHCHO by a factor of 1.5−1.7 with respect to neat colloidal TiO2 where φHCHO is 0.02. In addition to the action of Pt as an electron sink, the strong promotion of photocatalytic methanol oxidation by PtTi-S2 at the small Pt/TiO2 particle ratio of ca. 1:1060 is proposed to arise from transfer of excitation energy or of photogenerated charge car...

Quantum Yield of Formaldehyde Formation in the Presence of Colloidal TiO2-Based Photocatalysts: Effect of Intermittent Illumination, Platinization, and Deoxygenation

Jürgen K. Dohrmann

Papers

A comparative study of nanometer sized Fe(III)-doped TiO2photocatalysts: synthesis, characterization and activity

A novel preparation of iron-doped TiO2 nanoparticles with enhanced photocatalytic activity

Photonic efficiency and quantum yield of formaldehyde formation from methanol in the presence of various TiO2 photocatalysts

Quantum Yield of Formaldehyde Formation in the Presence of Colloidal TiO2-Based Photocatalysts: Effect of Intermittent Illumination, Platinization, and Deoxygenation

Antenna mechanism and deaggregation concept: novel mechanistic principles for photocatalysis