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

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.

Since the discovery of mechanically exfoliated graphene in 2004, research on ultrathin two-dimensional (2D) nanomaterials has grown exponentially in the fields of condensed matter physics, material science, chemistry, and nanotechnology. Highlighting their compelling physical, chemical, electronic, and optical properties, as well as their various potential applications, in this Review, we summarize the state-of-art progress on the ultrathin 2D nanomaterials with a particular emphasis on their recent advances. First, we introduce the unique advances on ultrathin 2D nanomaterials, followed by the description of their composition and crystal structures. The assortments of their synthetic methods are then summarized, including insights on their advantages and limitations, alongside some recommendations on suitable characterization techniques. We also discuss in detail the utilization of these ultrathin 2D nanomaterials for wide ranges of potential applications among the electronics/optoelectronics, electrocat...

Recent Advances in Ultrathin Two-Dimensional Nanomaterials

Over the past several years, cerium oxide and CeO2-containing materials have come under intense scrutiny as catalysts and as structural and electronic promoters of heterogeneous catalytic reactions. Recent developments regarding the characterization of ceria and CeO2-containing catalysts are critically reviewed with a special focus towards catalyst interaction with small molecules such as hydrogen, carbon monoxide, oxygen, and nitric oxide. Relevant catalytic and technological applications such as the use of ceria in automotive exhaust emission control and in the formulation of SO x reduction catalysts is described. A survey of the use of CeO2-containing materials as oxidation and reduction catalysts is also presented.

Catalytic Properties of Ceria and CeO2-Containing Materials

The adsorption of CO and CO2 on cerium oxide has been studied by Fourier-transform infrared spectroscopy (F.t.i.r.). For CO adsorption at room temperature, in addition to linearly adsorbed CO (2177 and 2156 cm–1), two kinds of carbonate (unidentate: 854, 1062, 1348 and 1454 cm–1 and bidentate: 854, 1028, 1286 and 1562 cm–1) and inorganic carboxylate (1310 and 15⊙0 cm–1) species were identified spectroscopically. As for CO2 adsorption, apart from weak bands at 1728, 1396, 1219, and 1132 cm–1 attributed to bridged carbonate species, bands due to unidentate carbonate, bidentate carbonate and inorganic carboxylate species, similar to those aising from CO adsorption, were observed. Except for the linearly adsorbed-CO, all species arising from CO and CO2 are stable at room temperature in vacuo. The desorption of these species at elevated temperatures shows that the order of thermal stability is bridged carbonate <bidentate carbonate < inorganic carboxylate < unidentate carbonate species, and the residual of unidentate carbonate species can remain on the surface up to 773 K under evacuation. Forming carbonte and inorganic carboxylate species proved that the CeO2 surface could be partially reduced by CO even at room temperature. No bands in the region 2300–800 cm–1 were detected below 373 K for CO adsorption on hydroxylated CeO2. This indicates that CO adsorption depends on the degree off dehydroxylation of the surface. The mechanism of CO adsorption is also discussed.

Carbon monoxide and carbon dioxide adsorption on cerium oxide studied by Fourier-transform infrared spectroscopy. Part 1.—Formation of carbonate species on dehydroxylated CeO2, at room temperature

Nickel-loaded K4Nb6O17 photocatalyst in the decomposition of H2O into H2 and O2: Structure and reaction mechanism

{sup 16}O{sub 2} ({sup 18}O{sub 2}) adsorption on well-outgassed and partially reduced cerium oxide has been investigated by Fourier transform infrared spectroscopy (FT-IR) in the temperature range 200-373 K. Superoxide species (O{sub 2}{sup {minus}}{sub ads}) with a pair of characteristic bands at 1126 (1063) and 2237 (2112) cm{sup {minus}1} were detected from oxygen adsorption on both surfaces of well-outgassed and partially reduced cerium oxide. One additional band at 883 (835) cm{sup {minus}1} attributed to peroxide species (O{sub 2}{sup 2{minus}}{sub ads}) was observed together with the bands at 1129 and 2238 cm{sup {minus}1} after oxygen adsorption on partially reduced cerium oxide. The formation of these dioxygen species is strongly dependent on the pretreatment of cerium oxide. It is concluded that the superoxide species is mainly generated on a coordinatively unsaturated cerium ion while the peroxide species were formed on a pair of surface cerium ions with lower oxidation state created by reduction.

Dioxygen adsorption on well-outgassed and partially reduced cerium oxide studied by FT-IR

The adsorption of CO on partially reduced CeO2[CeO2(573-H) and CeO2(673-H), CeO2 reduced in H2 at 573 and 673 K for 1 h, respectively] has been studied by Fourier-transform infrared spectroscopy (F.t.i.r.). The observation of formate species (771, 1329, 1369, 1558, 1587, 2852 and 2945 cm–1) formed by the reaction of CO with the surface of CeO2(673-H) at room temperature is reported. Two weak bands at 2796 and 2706 cm–1, tentatively attributed to formyl species, were also detected at room temperature when the bands of the formate species no longer appeared to grow. No band was observed when CO was dosed on CeO2(573-H) or CeO2(673-H2O)(CeO2 hydrated at 673 K for 1 h) at room temperature and 373 K. Two sharp bands at 3685 and 3643 cm–1, due to isolated hydroxyl groups, and a broad band centred at 3421 cm–1 were generated on CeO2(673-H) through H2 reduction. Among these only the OH groups giving the 3685 cm–1 band manifest activity to CO at room temperature. A mechanism involving a formyl intermediate was proposed to explain the formation of formate species on partially reduced CeO2. The partial reduction of CeO2 causes pronounced inhibition of the formation of carbonate-like species from CO at room temperature. This is consistent with the conclusions reported in Part 1 of this work.

Adsorption of carbon monoxide and carbon dioxide on cerium oxide studied by Fourier-transform infrared spectroscopy. Part 2.—Formation of formate species on partially reduced CeO2 at room temperature

Ken-ichi Maruya

Papers

Carbon monoxide and carbon dioxide adsorption on cerium oxide studied by Fourier-transform infrared spectroscopy. Part 1.—Formation of carbonate species on dehydroxylated CeO2, at room temperature

Nickel-loaded K4Nb6O17 photocatalyst in the decomposition of H2O into H2 and O2: Structure and reaction mechanism

Dioxygen adsorption on well-outgassed and partially reduced cerium oxide studied by FT-IR

Adsorption of carbon monoxide and carbon dioxide on cerium oxide studied by Fourier-transform infrared spectroscopy. Part 2.—Formation of formate species on partially reduced CeO2 at room temperature

Spectroscopic Identification of Adsorbed Species Derived from adsorption and decomposition of formic acid, Methanol, and Formaldehyde on Cerium Oxide