There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

TiO2 photocatalysis and related surface phenomena

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.

Semiconductor-mediated photocatalysis has received tremendous attention as it holds great promise to address the worldwide energy and environmental issues. To overcome the serious drawbacks of fast charge recombination and the limited visible-light absorption of semiconductor photocatalysts, many strategies have been developed in the past few decades and the most widely used one is to develop photocatalytic heterojunctions. This review attempts to summarize the recent progress in the rational design and fabrication of heterojunction photocatalysts, such as the semiconductor–semiconductor heterojunction, the semiconductor–metal heterojunction, the semiconductor–carbon heterojunction and the multicomponent heterojunction. The photocatalytic properties of the four junction systems are also discussed in relation to the environmental and energy applications, such as degradation of pollutants, hydrogen generation and photocatalytic disinfection. This tutorial review ends with a summary and some perspectives on the challenges and new directions in this exciting and still emerging area of research.

Semiconductor heterojunction photocatalysts: design, construction, and photocatalytic performances

Generations Yi Ma,† Xiuli Wang,† Yushuai Jia,† Xiaobo Chen,‡ Hongxian Han,*,† and Can Li*,† †State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics, Chinese Academy of Sciences and Dalian National Laboratory for Clean Energy, 457 Zhongshan Road, Dalian 116023, China ‡Department of Chemistry, College of Arts and Sciences, University of Missouri-Kansas City, 5100 Rockhill Road, Kansas City, Missouri 64110, United States

Titanium dioxide-based nanomaterials for photocatalytic fuel generations.

Photoelectrochemical reduction of carbon dioxide (CO2) on p-type silicon (p-Si) electrodes modified with small metal (Cu, Ag, or Au) particles has been studied. The electrodes in CO2-saturated aqueous electrolyte under illumination produce methane, ethylene, carbon monoxide, etc., similar to the metal (Cu, Ag, or Au) electrodes, but at ca. 0.5 V more positive potentials than the corresponding metal electrodes, contrary to continuous-metal-coated p-Si electrodes. The results clearly show that the metal-particle-coated p-Si electrodes not only have high catalytic activity for electrode reactions but also generate high photovoltages and thus work as an ideal type semiconductor electrode. It is discussed that the CO2 photoreduction proceeds with an upward shift of the surface band energies of p-Si in order to get energy level matching between the semiconductor and solution reactants, though hydrogen photoevolution occurs without such an upward shift. It is also discussed that the control of surface structure ...

An Approach to Ideal Semiconductor Electrodes for Efficient Photoelectrochemical Reduction of Carbon Dioxide by Modification with Small Metal Particles

Formation of porous silicon by metal particle enhanced chemical etching in HF solution and its application for efficient solar cells

Nucleation behavior in electroless displacement deposition of metals on silicon from hydrofluoric acid solutions

Metal-assisted chemical etching of silicon is an electroless method that can produce porous silicon by immersing metal-modified silicon in a hydrofluoric acid solution without electrical bias. We have been studying the metal-assisted hydrofluoric acid etching of silicon using dissolved oxygen as an oxidizing agent. Three major factors control the etching reaction and the porous silicon structure: photoillumination during etching, oxidizing agents, and metal particles. In this study, the influence of noble metal particles, silver, gold, platinum, and rhodium, on this etching is investigated under dark conditions: the absence of photogenerated charges in the silicon. The silicon dissolution is localized under the particles, and nanopores are formed whose diameters resemble the size of the metal nanoparticles. The etching rate of the silicon and the catalytic activity of the metals for the cathodic reduction of oxygen in the hydrofluoric acid solution increase in the order of silver, gold, platinum, and rhodium.

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Catalytic activity of noble metals for metal-assisted chemical etching of silicon

A widely used approach to obtain smooth oxide-free and (partially) H-terminated silicon (Si) surfaces is to immerse Si wafers into CP4A (a mixture of H2O, HNO3, CH3COOH and HF in a volume ratio of 22:5:3:3) and/or HF solutions of varying concentrations. It is usually assumed that such treatments result in a dramatic reduction of the surface density of states and that, therefore, no surface band bending can occur. In our experiments we investigated the electronic surface structure of a number of CP4A/HF treated n- and p-Si wafers with varying doping densities by x-ray photoelectron spectroscopy (XPS). XPS allows a straightforward detection of surface stoichiometry as well as one of band bending and surface photovoltages (SPV) on semiconductor materials because the positions of the core level peaks directly depend on the position of the Fermi level within the band gap at the surface. Our experiments show that on all surfaces investigated Fermi level pinning still exists after the samples were immersed in th...

Shinji Yae

Papers

An Approach to Ideal Semiconductor Electrodes for Efficient Photoelectrochemical Reduction of Carbon Dioxide by Modification with Small Metal Particles

Formation of porous silicon by metal particle enhanced chemical etching in HF solution and its application for efficient solar cells

Nucleation behavior in electroless displacement deposition of metals on silicon from hydrofluoric acid solutions

Catalytic activity of noble metals for metal-assisted chemical etching of silicon

Fermi level pinning on HF etched silicon surfaces investigated by photoelectron spectroscopy