**1. Introduction**

Solar energy is one of the primary sources in the field of green and pure energy that points to the power predicament and climate change task. Solar energy consumption is an ecological reconciliation, and then, the chemical change in solar is presence exhaustive, considered throughout global [1, 2]. In general, solar energy is renewed into a wide range of developments, such as degradation of organic pollutants as photocatalysis, splitting of water molecules for producing clean energy, and reduction of CO2 gas [3, 4]. Consuming a similar perception, metal-oxide photocatalysis has also been widely examined for possible exertions in ecological restitution as well as the photodegradation and elimination of organic toxins in the aquatic system [5, 6], decrease of bacterial inactivation [7–9], and heavy metal ions [10–12]. Throughout the earlier few years, excellent applications have been dedicated to evolving well-organized, less expensive, and substantial photocatalysts, particularly those that can become active under visible light such as NaLaTiO6, Ag3PO4/BaTiO3, Pt/SrTiO3, SrTiO3-TiN, noble-metal-SrTiO3 composites, GdCoO3, orthorhombic perovskites LnVO3 and Ln1−xTixVO3 (Ln = Ce, Pr, and Nd), Ca0.6Ho0.4MnO3, Ce-doped BaTiO3, fluorinated Bi2WO6, graphitic

carbon nitride-Bi2WO6, BaZrO3−δ, CaCu3Ti4O12, [13–24], graphene-doped perovskite materials, and nonmetal-doped perovskites [25]. Furthermore, directed to years extended exhaustive investigation exertions on the pursuit of innovative photocatalytic systems, particularly that can produce the overall spectrum of visible-light. Out of a vast assemblage of photocatalysts, perovskite or layered-type perovskite systems and its analogs include a better candidate for capable semiconductor-based photocatalysts due to their framework easiness and versatility, excellent photostability, and systematic photocatalytic nature. In general, the ideal perovskite structure is cubic, and the formula is ABO3. Where A is different metal cations having charge +1 or +2 or +3 nature and B site occupies with tri or tetra and pentavalent nature, which covers the whole family of perovskite oxide materials by sensibly various metal ions at A and B locations [26], aside from a perfect cubic perovskite system, basic alteration perhaps persuaded by several cations exchange. Such framework alteration could undoubtedly vary the photophysical, optical, and photocatalytic activities of primary oxides.

Moreover, a sequence of layered-type perovskite materials contains many 2D blocks of the ABO3 framework, which are parted by fixed blocks. The scope of formulating multicomponent perovskite systems by whichever fractional change of cations in A and B or both positions or injecting perovskite oxides into a layeredtype framework agrees scientists investigate and control the framework of crystals and the correlated electronic and photocatalytic activities of the perovskites. So far, hundreds of various types of perovskite or perovskite-based catalysts have been published, and more outstandingly, some ABO3-related materials became renowned with "referred" accomplishment for catalytic activities. Thus, these systems (perovskite materials) have exposed highly capable of upcoming applications on the source of applying more attempts to them. While several outstanding reviews mean that explained that perovskites performed as photocatalyst for degradation of organic pollutants [27–30], only an insufficient of them content consideration to inorganic perovskite (mostly ABO3-related) photocatalysts [31–33]. A wide range of tagging and complete attention of perovskite materials, for example, layered-type perovskite acting as photocatalysts, is relatively deficient. The purpose of this book chapter is to precise the current progress of perovskite-based photocatalysts for ecological reparation, deliberate current results, and development on perovskite oxides as catalysts, and allow a view on the upcoming investigation of perovskite materials. After a short outline on the wide-ranging structure of perovskite oxides, it was stated that perovskites act as a photocatalyst that are incorporated, arranged and explored based on preparation methods [29, 34], photophysical properties based on bandgap energies, morphology-based framework and the photocatalytic activities depends on either UV or visible light energy of the semiconducting materials. Finally, this chapter is based on the current advancement and expansion of perovskite photocatalytic applications under solar energy consumption. The potential utilization, new tasks, and the research pathway will be accounted for the final part of the chapter [35].

### **2. Results and discussion**

#### **2.1 Details of perovskite oxide materials**

#### *2.1.1 Perovskite frameworks*

The standard system of perovskite-based materials could be designated as ABO3, where the A and B are cations with 12-fold coordinated and 6-fold

**5**

**Figure 1.**

*octahedra with green and red balls are oxygen).*

*Significant Role of Perovskite Materials for Degradation of Organic Pollutants*

*√* 

coordinated to concerning oxygen anions. **Figure 1a** describes the typically coordinated basic of the ABO3 system, which consists of a 3D system, BO6 octahedra as located at corner, and at the center, A cation are occupied. Within the ABO3 system, the A cation usually is group I and II or a lanthanide metal, whereas the B is commonly a transition metal ion. The tolerance factor (*t*) = 1 calculated by

of respective ions A and B and oxygen elements for a cubic crystal structure ABO3

For constituting a stable perovskite, it is typically the range of *t* value present in between 0.75 and 1.0. The lower value of t builds a somewhat slanted perovskite framework with rhombohedral or orthorhombic symmetry. In the case of *t*, it is approximately 1; then, perovskite structure is an ideal cubic system at high temperatures. Even though the value of t, obtained by the size of metal ion, is a significant guide for the permanency of perovskite systems, the factor of octahedral (*u*) *u* = *rB*/*rO* and the role of the metal ions composition of A and B atoms and the coordination number of respective metals are considered [37]. Given the account of those manipulating factors and the electro-neutrality, the ABO3 perovskite can hold a broad variety of sets of A and B by equal or dissimilar oxidation states and ionic radii. Moreover, the replacement of A or B as well as both the cations could be partly by the doping of various elements, to range the ABO3

<sup>1</sup>*A*<sup>1</sup>−*<sup>m</sup>* 1 *B*<sup>1</sup> *nB*1−*<sup>n</sup>* 1

of several cations into the either A or B positions could modify the structure of the original system and therefore improve the photocatalytic activities [23]. After various metal ions in perovskite oxide are doped, the optical and electronic band positions, which influence the high impact on the photocatalytic process, are

*Both crystal and layered type perovskite oxides (blue small balls: A-site element; dark blue squares: BO6*

2 (*rB* + *rO*), where *rO*, *rA*, and *rB* are the radii

O3±δ [38]. The replacement

*DOI: http://dx.doi.org/10.5772/intechopen.91680*

using an equation *t* = (*rA* + *rO*)/

perovskite into a wide-ranging family of *Am*

perovskite system [36].

modified [24].

*Significant Role of Perovskite Materials for Degradation of Organic Pollutants DOI: http://dx.doi.org/10.5772/intechopen.91680*

coordinated to concerning oxygen anions. **Figure 1a** describes the typically coordinated basic of the ABO3 system, which consists of a 3D system, BO6 octahedra as located at corner, and at the center, A cation are occupied. Within the ABO3 system, the A cation usually is group I and II or a lanthanide metal, whereas the B is commonly a transition metal ion. The tolerance factor (*t*) = 1 calculated by using an equation *t* = (*rA* + *rO*)/ *√* 2 (*rB* + *rO*), where *rO*, *rA*, and *rB* are the radii of respective ions A and B and oxygen elements for a cubic crystal structure ABO3 perovskite system [36].

For constituting a stable perovskite, it is typically the range of *t* value present in between 0.75 and 1.0. The lower value of t builds a somewhat slanted perovskite framework with rhombohedral or orthorhombic symmetry. In the case of *t*, it is approximately 1; then, perovskite structure is an ideal cubic system at high temperatures. Even though the value of t, obtained by the size of metal ion, is a significant guide for the permanency of perovskite systems, the factor of octahedral (*u*) *u* = *rB*/*rO* and the role of the metal ions composition of A and B atoms and the coordination number of respective metals are considered [37]. Given the account of those manipulating factors and the electro-neutrality, the ABO3 perovskite can hold a broad variety of sets of A and B by equal or dissimilar oxidation states and ionic radii. Moreover, the replacement of A or B as well as both the cations could be partly by the doping of various elements, to range the ABO3 perovskite into a wide-ranging family of *Am* <sup>1</sup>*A*<sup>1</sup>−*<sup>m</sup>* 1 *B*<sup>1</sup> *nB*1−*<sup>n</sup>* 1 O3±δ [38]. The replacement of several cations into the either A or B positions could modify the structure of the original system and therefore improve the photocatalytic activities [23]. After various metal ions in perovskite oxide are doped, the optical and electronic band positions, which influence the high impact on the photocatalytic process, are modified [24].

#### **Figure 1.**

*Both crystal and layered type perovskite oxides (blue small balls: A-site element; dark blue squares: BO6 octahedra with green and red balls are oxygen).*

*Perovskite and Piezoelectric Materials*

photocatalytic activities of primary oxides.

carbon nitride-Bi2WO6, BaZrO3−δ, CaCu3Ti4O12, [13–24], graphene-doped

perovskite materials, and nonmetal-doped perovskites [25]. Furthermore, directed to years extended exhaustive investigation exertions on the pursuit of innovative photocatalytic systems, particularly that can produce the overall spectrum of visible-light. Out of a vast assemblage of photocatalysts, perovskite or layered-type perovskite systems and its analogs include a better candidate for capable semiconductor-based photocatalysts due to their framework easiness and versatility, excellent photostability, and systematic photocatalytic nature. In general, the ideal perovskite structure is cubic, and the formula is ABO3. Where A is different metal cations having charge +1 or +2 or +3 nature and B site occupies with tri or tetra and pentavalent nature, which covers the whole family of perovskite oxide materials by sensibly various metal ions at A and B locations [26], aside from a perfect cubic perovskite system, basic alteration perhaps persuaded by several cations exchange. Such framework alteration could undoubtedly vary the photophysical, optical, and

Moreover, a sequence of layered-type perovskite materials contains many 2D blocks of the ABO3 framework, which are parted by fixed blocks. The scope of formulating multicomponent perovskite systems by whichever fractional change of cations in A and B or both positions or injecting perovskite oxides into a layeredtype framework agrees scientists investigate and control the framework of crystals and the correlated electronic and photocatalytic activities of the perovskites. So far, hundreds of various types of perovskite or perovskite-based catalysts have been published, and more outstandingly, some ABO3-related materials became renowned

with "referred" accomplishment for catalytic activities. Thus, these systems (perovskite materials) have exposed highly capable of upcoming applications on the source of applying more attempts to them. While several outstanding reviews mean that explained that perovskites performed as photocatalyst for degradation of organic pollutants [27–30], only an insufficient of them content consideration to inorganic perovskite (mostly ABO3-related) photocatalysts [31–33]. A wide range of tagging and complete attention of perovskite materials, for example, layered-type perovskite acting as photocatalysts, is relatively deficient. The purpose of this book chapter is to precise the current progress of perovskite-based photocatalysts for ecological reparation, deliberate current results, and development on perovskite oxides as catalysts, and allow a view on the upcoming investigation of perovskite materials. After a short outline on the wide-ranging structure of perovskite oxides, it was stated that perovskites act as a photocatalyst that are incorporated, arranged and explored based on preparation methods [29, 34], photophysical properties based on bandgap energies, morphology-based framework and the photocatalytic activities depends on either UV or visible light energy of the semiconducting materials. Finally, this chapter is based on the current advancement and expansion of perovskite photocatalytic applications under solar energy consumption. The potential utilization, new tasks, and the research pathway will be accounted for the

The standard system of perovskite-based materials could be designated as ABO3, where the A and B are cations with 12-fold coordinated and 6-fold

**4**

final part of the chapter [35].

**2. Results and discussion**

*2.1.1 Perovskite frameworks*

**2.1 Details of perovskite oxide materials**

#### *2.1.2 Layered perovskite-related systems*

Moreover, to the overall ABO3 system, further characteristic polymorphs of the perovskite system are Brownmillerite (BM) (A2B2O5) framework [39]. BM is a type of oxygen-deficient perovskite, in which the unit cell is a system of wellorganized BO4 and BO6 units. The coordination number of cations occupied by A-site was decreased to eight because of the oxygen deficiency. Perovskite (ABO3) oxides have three dissimilar ionic groups, construction for varied and possibly useful imperfection chemistry. Moreover, the partial replacement of A and B ions is permitted even though conserving the perovskite system and shortages of cations at the A-site or of oxygen anions are common [40]. The Ion-exchange method is used for the replacement of existing metal ions with similar sized or dissimilar oxidation states; then, imperfections can be announced into the system. The imperfection concentrations of perovskites could be led by doping of different cations [24]. Oxygen ion interstitials or vacancies could be formed by the replacement of B-position cations with higher or lower valence, respectively, fabricating new compounds of AB(1−m)Bm I O3−δ [41]. A typical oxygen-deficient perovskite system is Brownmillerite (A2B2O5), in which one part of six oxygen atoms is eliminated. Moreover, the replacement of exciting a site cation to new cation with higher oxidation state metal ions then the formed new materials with new framework with different stoichiometry is A1−mAm I BO3 [41]. In the case of the replacement of A-site ions with smaller oxidation state cations, consequences in oxygen-deficient materials with new framework such as A1−mAm I BO3−x are developed. Thermodynamically, the replacement of B-position vacancies in perovskite systems is not preferable due to the compact size and the high charge of B cations [42]. A-position vacancies are more detected due to the BO3 range in perovskite system forms a stable network [43]; the 12 coordinated sites can be partly absent due to bigger-size A cations. Lately, presenting suitable imperfections on top of the surface of perovskite oxides has been thoroughly examined as a means of varying the bands' position and optical properties of the starting materials. For this reason, perovskite materials afford a tremendous objective for imperfection originating to vary the photocatalytic activity of perovskite material-based photocatalysts [44].

The typical formula for the furthermost recognized layered perovskite materials is designated as An+1BnO3n+1 or A2 I An−1BnO3n+1 (Ruddlesden-Popper (RP) phase), AI [An−1BnO3n+1] (Dion-Jacobson (DJ) phase) for {100} series, (AnBnO3n+2) for {110} series and (An+1BnO3n+3) for {111}, and (Bi2O2)(An−1BnO3n+1) (Aurivillius phase) series. In these systems, n represents the number of BO6 octahedra that duration a layer, which describes the width of the layer. Typical samples of these layered systems are revealed in **Figure 1c**–**g**. For RP phases, their frameworks consist of AI O as the spacing layer for the intergrowth ABO3 system. These materials hold fascinating properties such as ferroelectricity, superconductivity, magnetoresistance, and photocatalytic activity. Sr2SnO4 and Li2CaTa2O7 systems are materials of simple RP kind photocatalysts. A common formula for DJ phase is A<sup>I</sup> [An−1BnO3n+1] (n > 1), where AI splits the perovskite-type slabs and is characteristically a monovalent alkali cation. The typical DJ kind photocatalysts are RbLnTa2O7 (n = 2) and KCa2Nb3O10 (n = 3). Associates of the AnBnO3n+2 and An+1BnO3n+3 structural sequences with dissimilar layered alignments have also been recognized in some photocatalysts like Sr2Ta2O7 and Sr5Ta4O15 (n = 4). For Aurivillius phases, their frameworks are constructed by one after another fluctuating layers of [Bi2O2] 2+ and virtual perovskite blocks. Bi2WO6 and BiMoO6 (n = 1), found as the primary ferroelectric nature for Aurivillius materials, lately have been extensively investigated as visible light photocatalysts.

**7**

*Significant Role of Perovskite Materials for Degradation of Organic Pollutants*

A broad array of perovskite photocatalysts have been advanced for organic pollutant degradation in the presence of ultraviolet or visible-light-driven through

NaTaO3 has been a standard perovskite material for a well-organized UV-light photocatalyst for degradation of organic pollutants and production of H2 and O2 through water splitting [46–57]. It can be prepared by various methods such as solid-state [46–48, 53, 56], hydrothermal [49, 52, 54, 55], molten salt [57] and sol-gel [50, 51] and with wide bandgap of 4.0 eV. In order to enhance the surface area of NaTaO3 bulk material, many investigators tried to use further synthetic ways to make nanosized particles as an additional study on the NaTaO3 photocatalyst for degradation of organic pollutants. Kondo et al. prepared a colloidal range of NaTaO3 nanoparticles consuming three-dimensional mesoporous carbon as a pattern, which was pretend by the colloidal arrangement of silica nanospheres. After calcining the mesoporous carbon matrix, a colloidal arrangement of NaTaO3 nanoparticles with a

g<sup>−</sup><sup>1</sup>

rial was tested for degradation of NOx under UV light [36]. Several titanates such as BaTiO3 [58–60], Rh or Fe-doped BaTiO3 [61, 62], CaTiO3 [63, 64] and Cu [65], Rh [66], Ag and La-doped CaTiO3 [67], and PbTiO3 [68, 69] were also described as UV or visible light photocatalysts. Magnetic BiFeO3, recognized as the one of the multi-ferric perovskite materials in magnetoelectric properties, was also examined as a visible light photocatalyst for photodegradation of organic pollutants because of small bandgap energy (2.2 eV) [70–79]. In a previous account, BiFeO3 with a bandgap of around 2.18 eV produced by a citric acid-supported sol-gel technique has revealed its visible-light-driven photocatalytic study by the disintegration of methyl orange dye [70]. The subsequent investigations on BiFeO3 are primarily concentrated on the synthesis of new framework BiFeO3 with various morphologies. For instance, Lin and Nan et al. prepared BiFeO3 unvarying microspheres and

microcubes by a using hydrothermal technique as revealed in **Figure 2** [73]. The bandgap energies of BiFeO3 compounds were found to be about 1.82 eV for BiFeO3 microspheres and 2.12–2.27 eV for microcubes. This indicated that the absorption edge was moved toward the longer wavelength that is influenced by the crystal-field strength, particle size, and morphology. The microcube material showed the maximum photocatalytic degradation performance of congo red dye under visible-light irradiation due to the quite low bandgap energy. Further, a simplistic aerosol-spraying method was established for the synthesis of mesoporous BiFeO3 hollow spheres with improved activity for the photodegradation of RhB dye and 4-chlorophenol, because of improved light absorbance ensuing from various light reflections in a hollow chamber and a very high surface area [71]. Moreover, a unusually improved water oxidation property on Au nanoparticle-filled BiFeO3 nanowires under visible-light-driven was described [77]. The Au-BiFeO3 hybrid system was encouraged by the electrostatic contact of negatively charged Au nanoparticles and positively charged BiFeO3 nanowires at pH 6.0 giving to their various isoelectric points. An improved absorbance between 500 and 600 nm was found for Au/BiFeO3 systems because of the characteristic Au surface plasmon band

BO3,

BBIIO3-type perovskites

was attained. C-doped NaTaO3 mate-

the last two decades [45]. These typical examples and brief investigational consequences on perovskites are concise giving to their systems, then perovskite materials categorized into six groups. Precisely, ABO3-type perovskites, AA<sup>I</sup>

O3 and AB(ON)3-type perovskites, and AA<sup>I</sup>

*DOI: http://dx.doi.org/10.5772/intechopen.91680*

**2.2 Perovskite systems for photocatalysis**

**2.3 Photocatalytic properties perovskite oxides**

range of 20 nm and a surface area of 34 m2

AI

ABO3, ABB<sup>I</sup>

are listed in **Table 1**.
