**2.3 Photocatalytic properties perovskite oxides**

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 range of 20 nm and a surface area of 34 m2 g<sup>−</sup><sup>1</sup> was attained. C-doped NaTaO3 material 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 existing visible light region then which greater influenced in the photodegradation of organic pollutants. Also, the study of photoluminescence supported improvement of the photocatalytic property due to the effective charge transfer from BiFeO3 to Au. Even though Ba, Ca, Mn, and Gd-doped BiFeO3 nanomaterials have exhibited noticeable photocatalytic property for the degradation of dyes [80–84], several nano-based LaFeO3 with various morphologies such as nanoparticles, nanorods, nanotubes, nanosheets, and nanospheres have also been synthesized for visible light photocatalysts for degradation of organic dyes [85–93]. Sodium bismuth titanate (Bi0.5Na0.5TiO3) has been extensively used for ferroelectric and piezoelectric devices. It was also investigated as a UV-light photocatalyst with a bandgap energy of 3.0 eV [94–97]. Hierarchical micro/nanostructured Bi0.5Na0.5TiO3 was produced by in situ self-assembly of Bi0.5Na0.5TiO3 nanocrystals under precise hydrothermal conditions, through the evolution mechanism was examined in aspect means that during which the growth mechanism was studied [95]. It was anticipated that the hierarchical nanostructure was assembled through a method of nucleation and growth and accumulation of nanoparticles and following in situ dissolution-recrystallization of the microsphere type nanoparticles with extended heating period and enhanced temperature or basic settings. The 3D hierarchical Bi0.5Na0.5TiO3 showed very high photocatalytic activity for the decomposition of methyl orange dye because of the adsorption of dye molecules and bigger surface area. The properties of Bi0.5Na0.5TiO3 were also assessed by photocatalytic degradation of nitric oxide in the gas phase [95]. La0.7Sr0.3MnO3, acting as a photocatalyst, was examined for solar light-based photocatalytic decomposition of methyl orange [96–98]. In addition, La0.5Ca0.5NiO3 [99], La0.5Ca0.5CoO3−δ [100], and Sr1−xBaxSnO3 (x = 0–1) [101] nanoparticles were synthesized for revealing improved photocatalytic degradation of dyes. A-site strontium-based perovskites such as SrTi1−xFexO3−δ, SrTi0.1Fe0.9O3−δ, SrNb0.5Fe0.5O3, and SrCo0.5Fe0.5O3−δ compounds were prepared through solid-state reaction and solgel approaches, and were examined for the degradation of organic pollutants under visible light irradiation [102–105]. Also, some other researchers modified A-site with lanthanum-based perovskites such as LaNi1−xCuxO3 and LaFe0.5Ti0.5O3 were confirmed as effective visible light photocatalysts for the photodegradation of p-chlorophenol [91, 106, 107]. The other ABBI O3 kind photocatalysts with Ca(TiZr)O3 [108], Ba(ZrSn)O3 [109], Na(BiTa)O3 [110], Na(TiCu)O3 [111], Bi(MgFeTi)O3 [112], and Ag(TaNb)O3 [113] have also been studied. Related to AAI BO3-type perovskites, the ABBI O3 kind system means that BI-site substitution by a different cation is another option for tuning the physicochemical or photocatalytic properties of perovskites materials as photocatalyst, due to typically the B-position cations in ABO3 mostly regulate the position of the conduction band, moreover to construct the structure of perovskite system with oxygen atoms. The band positions of photocatalyst can be magnificently modified by sensibly coalescing dual or ternary metal cations at the B-position, or changing the ratio of several cations, which has been fine verified by the various materials as mentioned above. More studies on ABBI O3 kind of photocatalysts are projected to show their new exhilarating photocatalytic efficiency.

The mesoporous nature of LaTiO2N of photocatalyst attended due to thermal ammonolysis process of La2Ti2O7 precursor from polymer complex obtained from the solid-state reaction. The oxynitride analysis revealed that the pore size and shape, lattice defects and local defects, and oxidation states' local analysis related between morphology and photocatalytic activity were reported by Pokrant et al. [114]. Due to the high capability of accommodating an extensive array of cations and valences at both A- and B-sites, ABO3-kind perovskite materials are capable materials for fabricating solid-solution photocatalysts. On the other hand, equally the A and B cations can be changed by corresponding cations subsequent in a perovskite with the formula of (ABO3)x(AI BI O3)1−x. Additional solid solution examples with CaZrO3–CaTaO2N

**9**

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

[115], SrTiO3–LaTiO2N [116], La0.8Ba0.2Fe0.9Mn0.1O3−x [117], Na1−xLaxFe1−xTaxO3 [118], Na0.5La0.5TiO3–LaCrO3 [119], Cu-(Sr1−yNay)-(Ti1−xMox)O3 [120], Na1−xLaxTa1−<sup>x</sup> CrxO3 [121], BiFeO3–(Na0.5Bi0.5)TiO3 [122], and Sr1−xBixTi1−xCrxO3 [123] have been

alkaline earth, or rare earth metals, respectively, while B states to transition met-

cuboctahedral and 9-fold coordination to the anions, respectively, whereas B cations are sited inside the perovskite system with anionic squares, octahedra, and pyramids. The tantalum-based RP phase materials have been examined as photocatalysts for degradation of organic pollutants under UV light irradiation conditions; such materials are K2Sr1.5Ta3O10 [124], Li2CaTa2O7 [125], H1.81Sr0.81Bi0.19Ta2O7 [126], and N-alkyl chain inserted H2CaTa2O7 [127]. A series of various metals and N-doped perovskite materials were synthesized, such as Sn, Cr, Zn, V, Fe, Ni, W, and N-doped K2La2Ti3O10, for photocatalysis studies under UV and visible light irradiation [128–133]. Still, only Sn-doping efficiently decreased the bandgap energy of K2La2Ti3O10 from 3.6 eV to 2.7 eV. The bandgap energy of N-doped K2La2Ti3O10 was measured to be around 3.4 eV. Additional RP phase kind titanates like Sr2SnO4 [134], Sr3Ti2O7 [135], Cr-doped Sr2TiO4 [136], Sr4Ti3O10 [137], Na2Ca2Nb4O13 [138], and Rh- and Ln-doped Ca3Ti2O7 [139] have also been examined. Bi2WO6 (2.8 eV) shows very high oxygen evolution efficacy than Bi2MoO6 (3.0 eV) from aqueous AgNO3 solution under visible-light-driven. Because of the appropriate bandgap energy, comparatively elevated photocatalytic performance, and good constancy, Bi2MO6 materials have been thoroughly examined as the Aurivillius phase kind that acts as photocatalysts under visible light. In this connection, hundreds of publications associated to the Bi2MoO6 and Bi2WO6 act as photocatalysts so far reported. Most of the investigations in the reports are concentrated on the synthesis of various nanostructured Bi2MoO6 and Bi2WO6 as well as nanofibers, nanosheets, ordered arrays, hollow spheres, hierarchical architectures, inverse opals, and nanoplates, etc., by various synthesis techniques like solvothermal, hydrothermal, electrospinning, molten salt, thermal evaporation deposition, and microwave. All these methods of hydrothermal process have been frequently working for the controlled sizes, shapes, and morphologies of the particles. The photocatalytic properties of these perovskite materials are mostly examined by the photodegradation of organic pollutants. Moreover, the investigations on the simple Bi2MoO6 and Bi2WO6, doped with various metals and nonmetals such as Zn, Er, Mo, Zr, Gd, W, F, and N, into Bi2MoO6 and Bi2WO6 was studied for increasing the photocatalytic performance under visible light. Therefore, these Bi2MO6-based photocatalysts is not specified here, due to further full deliberations that can be shown in many reviews [140–142]. ABi2Nb2O9 where A is Ca, Sr, Ba and Pb is other type of the AL-like layered perovskite material [143–150]. The bandgap energy of PbBi2Nb2O9 is 2.88 eV and originally described as an undoped with single-phase layered-type perovskite material used as photocatalyst employed under visible light irradiation [144]. Bi5FeTi3O15 is also Aurivillius (AL) type multi-layered nanostructured perovskite material with a low bandgap energy (2.1 eV) and also shows photocatalytic activity under visible light [151, 152]. Mostly, these materials were synthesized using the hydrothermal method that has been frequently working for the controlled shapes such as flower-like hierarchical morphology, nanoplate-based, and the complete advance process from nanonet-based to nanoplate-based micro-flowers was shown. The photocatalytic activity of Bi5FeTi3O15 was studied by the degradation of rhodamine

I

cations are placed in the perovskite layer and boundary with 12-fold

BnO3n+1, A and AI

are alkali,

used as photocatalysts for splitting of water molecules under visible light.

**2.4 Photocatalytic activity of layered perovskite materials**

In the general formula of the RP phase, An−1A2

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

als. A and AI

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

[115], SrTiO3–LaTiO2N [116], La0.8Ba0.2Fe0.9Mn0.1O3−x [117], Na1−xLaxFe1−xTaxO3 [118], Na0.5La0.5TiO3–LaCrO3 [119], Cu-(Sr1−yNay)-(Ti1−xMox)O3 [120], Na1−xLaxTa1−<sup>x</sup> CrxO3 [121], BiFeO3–(Na0.5Bi0.5)TiO3 [122], and Sr1−xBixTi1−xCrxO3 [123] have been used as photocatalysts for splitting of water molecules under visible light.
