New visible light active semiconductors

CANDAL ROBERTO; MARTÍNEZ DE LA CRUZ

Photocatalytic Semiconductors; Synthesis, Characterization, and Environmental Applications

SPRINGER

Año: 2015; p. 41 - 68

So far, the anatase TiO2 polymorph has been the most studied semiconductor photocatalyst due to its high activity under UV irradiation, high stability against photocorrosion process, and low cost. Nevertheless, from the whole solar energy spectrum that radiates the earth, UV irradiation only represents 4 %. In the same way, other semiconductors such as ZnO, Fe2O3, CdS, ZnS, Nb2O5, Ta2O5, and BiTaO4 have been reported with excellent performance as photocatalysts, among others. In particular, oxides with perovskite structure formed by TaO6 or NbO6 octahedra layers have shown the capability to develop an important catalytic activity have reported photocatalytic activity in tantalates and niobates of the type NaMO3 (M = Ta and Nb) for the stoichiometric decomposition of water. In the same way, photocatalytic activity better than TiO2 has been observed on laminar oxides such as BaLi2Ti6O14, MTaO3 (M = Li, Na, K), and SrM2O7 (M = Nb, Ta) for the degradation of organic pollutants. However, most of these have the same drawbacks that TiO2 has in relation with their limited range of light absorption and an inefficient charge separation which leads to a high recombination process with the concomitant diminishing of their photocatalytic activity. For this reason, different alternatives have been proposed to gather the solar energy and then develop large-scale technological applications. Numerous efforts have been made for the development of new visible-light-induced photocatalysts, and some oxides have shown visible-light-driven catalytic activity, such as In1−x Ni x TaO4, CaIn2O4, InVO4, BiVO4, and Bi2MoO6. In this chapter, some alternatives to the use of TiO2 as photocatalyst will be discussed. In Sect. 2.2, the use of semiconductors doped with a transition metal as photocatalysts will be reviewed, in particular the effect of the introduction of metal in the physicochemical properties of semiconductor and in its improvement as photocatalyst. Other interesting possibility in the development of materials with high photocatalytic activity is the doping with nonmetal elements as is discussed in Sect. 2.3. The sensitization of a semiconductor photocatalyst by the action of chemical species allows taking advantage of the free visible-solar energy. This point is included in Sect. 2.4 for the different types of sensitizers. The association of two or more nanocrystalline semiconductors allows the design of semiconductors heterostructures that are potentially useful in photocatalysis, water splitting, microelectronics, and others. The possibilities of this type of semiconductor coupled photocatalyst are showed in Sect. 2.5. Finally, in Sect. 2.6, the formation of nanostructured semiconductors with photocatalytic activity due to the control of some of their physicochemical properties such as particle size and composition is described.