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

Raman spectroscopy of graphene and graphite: Disorder, electron phonon coupling, doping and nonadiabatic effects

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

Department of Materials Science, University of Patras, 26504 Rio Patras, Greece, Theoretical and Physical Chemistry Institute, National Hellenic Research Foundation, 48 Vass. Constantinou Avenue, 116 35 Athens, Greece, Institut de Biologie Moleculaire et Cellulaire, UPR9021 CNRS, Immunologie et Chimie Therapeutiques, 67084 Strasbourg, France, and Dipartimento di Scienze Farmaceutiche, Universita di Trieste, Piazzale Europa 1, 34127 Trieste, Italy

Chemistry of Carbon Nanotubes

Nitrogen-doped graphene (N-graphene) was synthesized by chemical vapor deposition of methane in the presence of ammonia. The resultant N-graphene was demonstrated to act as a metal-free electrode with a much better electrocatalytic activity, long-term operation stability, and tolerance to crossover effect than platinum for oxygen reduction via a four-electron pathway in alkaline fuel cells. To the best of our knowledge, this is the first report on the use of graphene and its derivatives as metal-free catalysts for oxygen reduction. The important role of N-doping to oxygen reduction reaction (ORR) can be applied to various carbon materials for the development of other metal-free efficient ORR catalysts for fuel cell applications, even new catalytic materials for applications beyond fuel cells.

/pdf/nitrogen-doped-graphene-as-efficient-metal-free-2c5sl934bm.pdf

Nitrogen-Doped Graphene as Efficient Metal-Free Electrocatalyst for Oxygen Reduction in Fuel Cells

Polyhedral nano- and microstructures with shapes of faceted needles, rods, rings, barrels, and double-tipped pyramids, which we call graphite polyhedral crystals (GPCs), have been discovered. They were found in pores of glassy carbon. They have nanotube cores and graphite faces, and they can exhibit unusual sevenfold, ninefold, or more complex axial symmetry. Although some are giant radially extended nanotubes, Raman spectroscopy and transmission electron microscopy suggest GPCs have a degree of perfection higher than in multiwall nanotubes of similar size. The crystals are up to 1 micrometer in cross section and 5 micrometers in length, and they can probably be grown in much larger sizes. Preliminary results suggest a high electrical conductivity, strength, and chemical stability of GPC.

https://science.sciencemag.org/content/sci/290/5490/317.full.pdf

Graphite polyhedral crystals.

Multiwall open-end and closed carbon nanotubes with the wall thickness from several to more than 100 carbon layers were produced by a principally new method— hydrothermal synthesis—using polyethylene/water mixtures in the presence of nickel at 700–800 °C under 60–100 MPa pressure. An important feature of hydrothermal nanotubes is a small wall thickness, which is about 10% of the large inner diameter of 20–800 nm. Closed nanotubes were leak-tight by virtue of holding encapsulated water at high vacuum and can be used as test tubes for in situ experiments in transmission electron microscope (TEM). Raman microspectroscopy analysis of single nanotubes shows a well-ordered graphitic structure, in agreement with high-resolution TEM. The hydrothermal synthesis has the potential for producing multiwall nanotubes for a variety of applications. The fabrication of nanotubes under hydrothermal conditions may explain their presence in coals and carbonaceous rocks and suggests that they should be present in natural graphite deposits formed under hydrothermal conditions.

Hydrothermal synthesis of multiwall carbon nanotubes

Based upon the analysis of materials cycling and processing on the earth, a thermodynamic concept for energetical and environmental problems has been proposed. It concludes that solution processing using aqueous solutions should be the most important processing even for advanced materials. According to this concept, energetical and environmental features of soft solution processing (SSP) are discussed in general, using also some particular examples, such as BaTiO3. Applications of the SSP are shown with special emphasis on hydrothermal and/or electrochemical synthesis of thin films and integration issues. Soft solution processing allows one to fabricate in aqueous solutions shaped/sized/oriented ceramics in only one step, without excess energies for firing/sintering or melting and without expensive equipment, providing an environmentally friendly route for the preparation of advanced ceramic materials.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/10B7D779AC38EAC0B4DFB144A54795C7/S0884291400043387a.pdf/div-class-title-importance-of-soft-solution-processing-for-advanced-inorganic-materials-div.pdf

Importance of soft solution processing for advanced inorganic materials

Hydrothermal processing of high-quality multiwall nanotubes from amorphous carbon.

A multinary nitride, Eu-doped CaAlSiN3, which had previously been synthesized at 1600–1800 °C as a red-emiting phosphor material, was obtained at 500–800 °C via the reaction of a CaAlSi alloy with a low concentration of Eu (composition Ca0.992Eu0.008AlSi) in ammonia in the present study. In supercritical ammonia (100 MPa), CaAlSiN3 was formed at temperatures ≥ 500 °C both with and without the addition of sodium amide. The addition of sodium amide significantly facilitated the synthesis and prevented the presence of unreacted silicon, which could be due to the formation of sodium ammonometallates as intermediates in the presence of sodium amide. CaAlSiN3 was synthesized even in an atmospheric ammonia flow, but the crystallinity of the product was rather low. Evidence suggested that CaAlSiN3 was insoluble in the pressurized sodium amide−ammonia medium under the present conditions, and the prolonged reaction of the alloy in ammonia at the CaAlSiN3-forming temperatures (500–800 °C) did not result in an effect...

Masahiro Yoshimura

Papers

Graphite polyhedral crystals.

Hydrothermal synthesis of multiwall carbon nanotubes

Importance of soft solution processing for advanced inorganic materials

Hydrothermal processing of high-quality multiwall nanotubes from amorphous carbon.

Synthesis of a Multinary Nitride, Eu-Doped CaAlSiN3, from Alloy at Low Temperatures