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

Energy harvested directly from sunlight offers a desirable approach toward fulfilling, with minimal environmental impact, the need for clean energy. Solar energy is a decentralized and inexhaustible natural resource, with the magnitude of the available solar power striking the earth’s surface at any one instant equal to 130 million 500 MW power plants.1 However, several important goals need to be met to fully utilize solar energy for the global energy demand. First, the means for solar energy conversion, storage, and distribution should be environmentally benign, i.e. protecting ecosystems instead of steadily weakening them. The next important goal is to provide a stable, constant energy flux. Due to the daily and seasonal variability in renewable energy sources such as sunlight, energy harvested from the sun needs to be efficiently converted into chemical fuel that can be stored, transported, and used upon demand. The biggest challenge is whether or not these goals can be met in a costeffective way on the terawatt scale.2

http://pubs.acs.org/doi/pdf/10.1021/cr1002326

Solar Water Splitting Cells

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

Semiconductor photocatalysis has received much attention as a potential solution to the worldwide energy shortage and for counteracting environmental degradation. This article reviews state-of-the-art research activities in the field, focusing on the scientific and technological possibilities offered by photocatalytic materials. We begin with a survey of efforts to explore suitable materials and to optimize their energy band configurations for specific applications. We then examine the design and fabrication of advanced photocatalytic materials in the framework of nanotechnology. Many of the most recent advances in photocatalysis have been realized by selective control of the morphology of nanomaterials or by utilizing the collective properties of nano-assembly systems. Finally, we discuss the current theoretical understanding of key aspects of photocatalytic materials. This review also highlights crucial issues that should be addressed in future research activities.

Nano‐photocatalytic Materials: Possibilities and Challenges

A novel photocatalyst, PbBi2Nb2O9 has been discovered that shows high activities for degradation of organic pollutants, generation of photocurrent, and water decomposition into O2 or H2, all under visible right irradiation (λ ≥ 420 nm). This is the first example of an undoped, single-phase oxide photocatalyst that shows such reactivity. Its quantum yields are much higher than those for most of the previously reported materials, especially in water decomposition to generate oxygen (29%). Since it is an oxide, there is much less concern for stability under light irradiation.

/pdf/an-undoped-single-phase-oxide-photocatalyst-working-under-2t26sheryj.pdf

An undoped, single-phase oxide photocatalyst working under visible light.

Fabrication of CaFe2O4/MgFe2O4 bulk heterojunction for enhanced visible light photocatalysis

In the search for efficient photocatalysts working under visible light, we have investigated the effect of cation substitution on a layered perovskite, La2Ti2O7. Among various metal dopants, only Cr and Fe induced intense absorption of visible light (λ > 400 nm), and only these catalysts produced H2 photocatalytically from water in the presence of methanol under visible light irradiation (λ > 420 nm). The polymerized complex method was found to be more efficient for fabrication of the present catalysts producing a more homogeneous structure than the solid-state reaction. The characterization by XRD, UV−vis DRS, XPS, and XANES revealed that doped Cr and Fe were present in the Cr3+ and Fe3+ states substituting for Ti sites in the La2Ti2O7 lattice. The theoretical calculation indicated that the most significant feature in the electronic band structure of the metal-doped La2Ti2O7 was the formation of a partially filled 3d band in the band gap of La2Ti2O7, while the contribution of these dopants on the valence...

Photocatalytic Hydrogen Production from Water over M-Doped La2Ti2O7 (M = Cr, Fe) under Visible Light Irradiation (λ > 420 nm)†

CdS/TiO2 composite photocatalysts were platinized by different methods such as photodeposition (PD), wet impregnation (WI), and chemical reduction (CR), and studied for hydrogen production from water under visible light. All Pt species were in the metallic state, yet PD and WI photocatalysts contained electron-deficient Pt. In particular, Pt−Ti formation was identified in the WI catalyst, which contributed to electron deficiency of Pt. These two photocatalysts of electron-deficient Pt exhibited higher rates of hydrogen evolution due to favorable diffusion of photoelectrons from excited CdS toward the Pt. Between PD and WI photocatalysts, the PD catalyst showed a lower rate because part of the Pt in the catalyst resided on CdS, whereas all Pt species were located on TiO2 nanoparticles for WI and CR catalysts. The results indicate that the location as well as the electronic state of Pt is important for the high performance of platinized CdS/TiO2 photocatalysts in hydrogen production from water.

Hyun Gyu Kim

Papers

An undoped, single-phase oxide photocatalyst working under visible light.

Fabrication of CaFe2O4/MgFe2O4 bulk heterojunction for enhanced visible light photocatalysis

Photocatalytic Hydrogen Production from Water over M-Doped La2Ti2O7 (M = Cr, Fe) under Visible Light Irradiation (λ > 420 nm)†

Location and State of Pt in Platinized CdS/TiO2 Photocatalysts for Hydrogen Production from Water under Visible Light

Photocatalytic water splitting over highly donor-doped (110) layered perovskites