**1. Introduction**

Photocatalysis is the acceleration of a photoreaction in the presence of a catalyst. The ability to generate electron–hole pairs and free radicals is very important parameters to understand the photocatalytic activity (PCA) in photogenerated catalysis [1]. On other words we can describe the photocatalysis process as two parts, "photo" and "catalysis". Let us define the catalysis as the process in which a material participates in modifying the rate of a chemical transformation of the reactants without altering or consuming in the end. This material is so called catalyst,

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

**Figure 1.** Nano TiO2 photocatalyst and chlorophyll of plants is a typical natural photocatalyst [2].

which the activation energy is reduced that may lead to acceleration of the reaction. In general, light is used to activate a substance, which modifies the rate of a chemical reaction without being involved itself, and the photocatalyst is the substance, which can modify the rate of chemical reaction using light irradiation [1]. Chlorophyll of plants is good example for the natural photocatalyst. The difference between chlorophyll photocatalyst and nano TiO<sup>2</sup> photocatalyst (see **Figure 1**) [2] is, usually chlorophyll captures sunlight to turn water and carbon dioxide into oxygen and glucose, while photocatalyst creates strong oxidation agent and electronic holes to breakdown the organic matter to carbon dioxide and water in the presence of photocatalyst, light and water [2]. So many materials are developed daily to be applied as photocatalysis and nanocompsites that have perovskites-like structure are promising materials for these applications.

Solar energy is clean and till now its utilization is limited. A strong need to develop a sustainable and cost-effective manner for harvesting solar energy to satisfy the growing energy demand of the world with a minimal environmental impact [4]. Photo-catalysis plays an important role for the conversion of solar energy into chemical fuel, electricity, the decompo-

**Figure 2.** Schematic diagram showing the photocatalysis mechanism by producing both holes and electrons as a result

Perovskite Strontium Doped Rare Earth Manganites Nanocomposites and Their Photocatalytic Performances

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The degradation behaviors were studied by Sher Bahadar Khan et al. [5] and the degradation pattern of AO by Langmuir–Hinshelwood (L–H) model was defined and given from the relationship between the rate of degradation and the initial concentration of AO in photo-catalytic

The rate of photo-degradation was calculated according to the following equation; Eq. (1)

r = −dC/dt = *K*r*K*C = *K*appC (1)

where r in this equation is defined as the degradation rate of organic pollutant, *K*r is describing the reaction rate constant, *K* is constant equal to the equilibrium constant, C is the concentration of the reactant. From Eq. 1, we can neglect KC when C becomes very small so this equation could describe the first order kinetic. Applying the following initial conditions,

−ln C/C0 = *k*t (2)

t1/<sup>2</sup> = 0.693/*k* (3)

The photo degradation of AO in the presence of CeO<sup>2</sup> **1** nano-particles is shown in **Figure 3**. Different materials are used as photocatalysis and research is going on to apply a new material for this applications. The rare earth manganite is one of the promising materials for

) in Eq. (1), that may lead to a new equation; Eq. (2).

sition of organic pollutants etc.

reaction [6].

of illumination [3].

(t = 0, C = C0

Half-life, t1/2 (in min) is
