**2.1 Perovskites as solid oxide fuel cells**

*Perovskite and Piezoelectric Materials*

(30–50 g 100 mL<sup>−</sup><sup>1</sup>

lead on the human body.

for the environmental application point of view.

can be found out in the dental margin of the gums of the patients having poor dental hygiene. Lead harming has been considered as a health hazard, for its bad effects on neurological and cerebral development [10–12]. The main route of absorption in adults is the respiratory region where 30–70% of inhaled lead (typically the inorganic form like oxides and salts) goes into the cardiovascular system. The maximum tolerance of lead in blood ranges from 1.45 to 2.4 mol L<sup>−</sup><sup>1</sup>

lead has few significant biochemical properties that give toxic effects on the human biological system. (i) As lead is electropositive in nature, it shows a very high affinity for the enzymes, which are necessary for the synthesis of hemoglobin. (ii) The divalent lead behaves similarly to calcium preventing mitochondrial oxidative phosphorylation as a result intelligence quotient (IQ ) got reducing. (iii) The transcription of DNA can also disturb by lead by interacting with binding protein and nucleic acids [14, 15]. **Figure 3** illustrated the adverse effect of

Bearing in mind the hazardous effect of Pb in Pb-based compounds, the research communities focused on designing the materials which are basically Pb-free. Hence, this chapter concludes with some Pb-free perovskite-type materials

) with a provision of 6 monthly observations [13]. Basically,

**32**

**Figure 3.**

*Schematic diagram for toxic effect of lead on human body.*

Recently, the inorganic perovskite-type of oxide nanomaterials have been widely applied in the processing of chemically modified electrodes [16, 17]. They have acknowledged considerable attention in the last few decades because of their catalytic activity in diverse processes like purification of waste gas and catalytic combustion.

In the fuel cell, there is a direct conversion of chemical energy into electrical energy similar to a battery. These are attractive because of their great efficiency, low emission, almost zero pollution (basically noise pollution). The solid oxide fuel cells (SOFCs) have come into the picture as effective substitutions to the combustion engines due to their prospective to minimize the environmental impact of the use of conventional fossil fuels. Perovskite oxides exhibited attractive properties like a high electrical and ionic conductivity similar to that of metals and the perfect mix of these two types [18]. This mixed conduction properties of perovskite oxides are advantageous for electrochemical reaction. The working principle of a SOFC is depicted by **Figure 4** [19]. The perovskite Ba0.5Sr0.5Co0.8Fe0.2O3-δ used as an effective cathode for intermediary SOFC reported by Shao and Haile. This cathode unveiled the maximum power density of 402 and 1010 mW cm<sup>−</sup><sup>2</sup> at 500 and 600°C, respectively [20]. The combination of single and double perovskite oxide Ba0.5Sr0.5(Co0.7Fe0.3)0.6875W0. 3125O3−δ (B-SCFW) was investigated by Shin et al. [21] for self-assembled perovskite composites for SOFC. In contrast, Goodenough reported that the double perovskite Sr2MgMnMoO6-δ can act as an anode material for SOFC with dry methane as the fuel and it shows maximum power density of 438 mW cm<sup>−</sup><sup>2</sup> at 800°C. This anode material exhibited long-term stability and having oxygen insufficiency, as well as some good environmental effects like tolerance to sulfur, stability in reducing atmosphere [22]. **Table 1** enlisted with some perovskites used as anode and cathode for SOFCs.

**Figure 4.** *Diagram illustrates the working principle of SOFC [19].*


#### **Table 1.**

*Summary report of few Pb-free perovskites used in SOFCs.*

## **2.2 Perovskites as sensor**

#### *2.2.1 Perovskites as glucose sensor*

It is very essential to determine hydrogen peroxide (H2O2) and glucose analytically in any aspect of our daily life. In environmental waste management, chemical and food industries, and medical diagnostics H2O2 widely used as one of the most important oxidizing agents [29]. On the other hand, glucose represents a fundamental component in human blood that delivers energy through the metabolic process. If in human blood, the glucose concentration fluctuates than the normal range of 80–120 mg dL<sup>−</sup><sup>1</sup> (4.4–6.6 mM) is related to the metabolic disorder from insulin insufficiency and hyperglycemia, the so-called diabetes mellitus [30]. To perform the diagnosis and supervision of such health issue it is necessary a tight observation of glucose level of blood. Hence, it is very significant to make the biosensors for the sensitive determination of glucose and H2O2. Basically, there are two types of glucose sensors available: enzymatic and non-enzymatic. Different types of enzymatic glucose sensors were constructed and used in the literature exhibiting the advantages of simplicity and sensitivity. However, enzymatic glucose sensors suffered from the lack of stability and the difficult procedures required for the effective immobilization of the enzyme on the electrode surface. The lack of enzyme stability was attributed to its intrinsic nature because the enzyme activity was highly affected by poisonous chemicals, pH, temperature, humidity, etc. As a result, most attention was given for a sensitive, simple, stable, and selective nonenzymatic glucose sensor. Different novel materials were proposed for the electrocatalytic oxidation of glucose like noble nanometals, nanoalloys, metal oxides, and inorganic perovskite oxides. Inorganic perovskite oxides as nanomaterials exhibited fascinating properties for glucose sensing like ferroelectricity, superconductivity, charge ordering, high thermopower, good biocompatibility, catalytic.

Wang et al. utilized a carbon paste electrode (CPE) modified with LaNi0.5Ti0.5O3 (LNT) as a promising nonenzymatic glucose sensor. This glucose sensor displayed a perfect electrochemical activity and was used to quantify of glucose with great sensitivity of 1630.57 μA mM<sup>−</sup><sup>1</sup> cm<sup>−</sup><sup>2</sup> and a low detection limit of 0.07 μM. This glucose sensor also demonstrated an excellent reproducibility, long-term immovability, as well as outstanding selectivity with no interference from the common interfering

**35**

*Lead-Free Perovskite Nanocomposites: An Aspect for Environmental Application*

exhibiting higher detection properties and improved selectivity [35].

different perovskite oxides for various gas sensing applications.

The consumption of energy has been continuously increasing globally and limitations of sources of fossil fuels leading to perform the research on sustainable, environment-friendly, and renewable energy sources. Due to the abundance of sun rays on

**2.3 Perovskites as solar cell materials**

The clean air is undoubtedly most necessary than water for human health, but unfortunately, human activities accompanying socioeconomic developments are the vital pollution sources. So, it is very important to closely observe the quality of the air, including the indoor air quality (IAQ ) as we spent most of our time (~90%) of our time in the indoor climate, to prevent different unusual symptoms [35–37]. Thus, researchers and scientists across the whole globe have been developing new and advanced material based innovative methods for consistent and careful detection of gases and volatile organic compounds (VOCs) hazardous to human and environmental health [38, 39]. The environmental worries about health hazards due to the existence of poisonous gases, for example, CO, CO2, NO2, O3, etc., and subsequent safety regulations have demanded the enhanced use of sensors in various sceneries from the industrial sites to automobiles, the different workplaces and even homes. Among the several toxic gases, CO and NO2 are the most harmful air pollutants and are dangerous for animals, plants and as well as human beings. The Occupational Safety and Health Administration (OSHA) have also announced the limit lowest tolerance for these type of gases in a particular time period, for example, the limits for CO and NO2 gases are ∼20 ppm and ∼5 ppm over the period of 8 h respectively. Over-acquaintance to these gases could be the reason for diseases and in dangerous cases even loss of human life [40]. There are a number of features that the materials can have to be utilized as gas sensors, explicitly, an excellent similitude with the target gases, easy to synthesize, thermal stability, appropriate electronic structure, and adaptation with present technologies. The perovskite oxides are interesting materials as gas sensors because of their ideal bandgap, excellent thermal stability and the size difference between the Aand B-sites cations, tolerating different dopants addition for monitoring the catalytic properties and their semiconducting properties. Lots of perovskites were synthesized to utilize as gas sensors for detecting different hazardous gases. **Table 2** enlisted with

substances such as dopamine, ascorbic acid, and uric acid [31]. The perovskitespinel type composite oxide LaNi0.5Ti0.5O3-NiFe2O4 with different compositions was demonstrated as the glucose sensor by Wang et al. This material also exhibits admirable reproducibility, stability and selectivity in glucose sensitivity with a linear signal-to-glucose concentration range of 0.5–10 mM and a detection limit (S/N = 3) of 0.04 mM [32]. Furthermore, LaxSr1-xCoyFe1-yO3-δ (x = 0.6; y = 0.0 and 0.2) perovskites were studied as electro-catalytic materials for H2O2 and glucose electrochemical sensors by Liotta et al. [33]. The group of Atta et al. has reformed SrPdO3 perovskite with gold nanoparticles to be employed as a non-enzymatic voltammetric glucose sensor. This nanocomposite disclosed an excellent performance to glucose sensing in terms of highly reproducible response, high sensitivity, low detection limit, appreciable selectivity, long-standing stability [34]. He et al. depicted that the perovskite oxide La0.6Sr0.4CoO3-δ can provide superior electro-oxidation activities (to H2O2 and glucose) over La0.6Sr0.4Co0.2Fe0.8O3-δ and LaNi0.6Co0.4O3 that translates to good H2O2 or glucose detection performance. They have modified the sensor by making composite with reduced graphene oxide (RGO) and La0.6Sr0.4CoO3-δ for

*DOI: http://dx.doi.org/10.5772/intechopen.93052*

*2.2.2 Perovskites as a gas sensor*

#### *Lead-Free Perovskite Nanocomposites: An Aspect for Environmental Application DOI: http://dx.doi.org/10.5772/intechopen.93052*

substances such as dopamine, ascorbic acid, and uric acid [31]. The perovskitespinel type composite oxide LaNi0.5Ti0.5O3-NiFe2O4 with different compositions was demonstrated as the glucose sensor by Wang et al. This material also exhibits admirable reproducibility, stability and selectivity in glucose sensitivity with a linear signal-to-glucose concentration range of 0.5–10 mM and a detection limit (S/N = 3) of 0.04 mM [32]. Furthermore, LaxSr1-xCoyFe1-yO3-δ (x = 0.6; y = 0.0 and 0.2) perovskites were studied as electro-catalytic materials for H2O2 and glucose electrochemical sensors by Liotta et al. [33]. The group of Atta et al. has reformed SrPdO3 perovskite with gold nanoparticles to be employed as a non-enzymatic voltammetric glucose sensor. This nanocomposite disclosed an excellent performance to glucose sensing in terms of highly reproducible response, high sensitivity, low detection limit, appreciable selectivity, long-standing stability [34]. He et al. depicted that the perovskite oxide La0.6Sr0.4CoO3-δ can provide superior electro-oxidation activities (to H2O2 and glucose) over La0.6Sr0.4Co0.2Fe0.8O3-δ and LaNi0.6Co0.4O3 that translates to good H2O2 or glucose detection performance. They have modified the sensor by making composite with reduced graphene oxide (RGO) and La0.6Sr0.4CoO3-δ for exhibiting higher detection properties and improved selectivity [35].

#### *2.2.2 Perovskites as a gas sensor*

*Perovskite and Piezoelectric Materials*

**Anode/ cathode In cell**

Ba0.5Sr0.5Co0.8Fe0.2O3-<sup>δ</sup> Cathode Humidified H2

NdFeO3 Anode Sulfur vapor

*Summary report of few Pb-free perovskites used in SOFCs.*

**Perovskite compositions**

**2.2 Perovskites as sensor**

**Table 1.**

range of 80–120 mg dL<sup>−</sup><sup>1</sup>

sitivity of 1630.57 μA mM<sup>−</sup><sup>1</sup>

*2.2.1 Perovskites as glucose sensor*

It is very essential to determine hydrogen peroxide (H2O2) and glucose analytically in any aspect of our daily life. In environmental waste management, chemical and food industries, and medical diagnostics H2O2 widely used as one of the most important oxidizing agents [29]. On the other hand, glucose represents a fundamental component in human blood that delivers energy through the metabolic process. If in human blood, the glucose concentration fluctuates than the normal

**Fuel used Operating** 

(~3% H2O)

or SO2

Ba0.5Sr0.5Co0.2Fe0.8O3-<sup>δ</sup> Cathode Humidified H2 800 266 [23]

La0.6Sr0.4Fe0.8Co0.2O3 Cathode Glycerol 800 Not reported [25] Sm0.5Sr0.5CoO3-<sup>δ</sup> Cathode Not reported 700 936 [26] La0.8Sr0.2Cr0.97V0.03O3 Anode Dry methane 800 Not reported [27] La0.75Sr0.25Cr0.5Mn0.5O3 Anode Methane Not reported Not reported [28]

**temperature (°C)**

**Maximum power density (mWcm<sup>−</sup><sup>2</sup> )**

500 402 [20]

620 0.154 [24]

600 1010

650 0.265

**Reference**

insulin insufficiency and hyperglycemia, the so-called diabetes mellitus [30]. To perform the diagnosis and supervision of such health issue it is necessary a tight observation of glucose level of blood. Hence, it is very significant to make the biosensors for the sensitive determination of glucose and H2O2. Basically, there are two types of glucose sensors available: enzymatic and non-enzymatic. Different types of enzymatic glucose sensors were constructed and used in the literature exhibiting the advantages of simplicity and sensitivity. However, enzymatic glucose sensors suffered from the lack of stability and the difficult procedures required for the effective immobilization of the enzyme on the electrode surface. The lack of enzyme stability was attributed to its intrinsic nature because the enzyme activity was highly affected by poisonous chemicals, pH, temperature, humidity, etc. As a result, most attention was given for a sensitive, simple, stable, and selective nonenzymatic glucose sensor. Different novel materials were proposed for the electrocatalytic oxidation of glucose like noble nanometals, nanoalloys, metal oxides, and inorganic perovskite oxides. Inorganic perovskite oxides as nanomaterials exhibited fascinating properties for glucose sensing like ferroelectricity, superconductivity,

charge ordering, high thermopower, good biocompatibility, catalytic.

cm<sup>−</sup><sup>2</sup>

Wang et al. utilized a carbon paste electrode (CPE) modified with LaNi0.5Ti0.5O3 (LNT) as a promising nonenzymatic glucose sensor. This glucose sensor displayed a perfect electrochemical activity and was used to quantify of glucose with great sen-

sensor also demonstrated an excellent reproducibility, long-term immovability, as well as outstanding selectivity with no interference from the common interfering

and a low detection limit of 0.07 μM. This glucose

(4.4–6.6 mM) is related to the metabolic disorder from

**34**

The clean air is undoubtedly most necessary than water for human health, but unfortunately, human activities accompanying socioeconomic developments are the vital pollution sources. So, it is very important to closely observe the quality of the air, including the indoor air quality (IAQ ) as we spent most of our time (~90%) of our time in the indoor climate, to prevent different unusual symptoms [35–37]. Thus, researchers and scientists across the whole globe have been developing new and advanced material based innovative methods for consistent and careful detection of gases and volatile organic compounds (VOCs) hazardous to human and environmental health [38, 39]. The environmental worries about health hazards due to the existence of poisonous gases, for example, CO, CO2, NO2, O3, etc., and subsequent safety regulations have demanded the enhanced use of sensors in various sceneries from the industrial sites to automobiles, the different workplaces and even homes. Among the several toxic gases, CO and NO2 are the most harmful air pollutants and are dangerous for animals, plants and as well as human beings. The Occupational Safety and Health Administration (OSHA) have also announced the limit lowest tolerance for these type of gases in a particular time period, for example, the limits for CO and NO2 gases are ∼20 ppm and ∼5 ppm over the period of 8 h respectively. Over-acquaintance to these gases could be the reason for diseases and in dangerous cases even loss of human life [40]. There are a number of features that the materials can have to be utilized as gas sensors, explicitly, an excellent similitude with the target gases, easy to synthesize, thermal stability, appropriate electronic structure, and adaptation with present technologies. The perovskite oxides are interesting materials as gas sensors because of their ideal bandgap, excellent thermal stability and the size difference between the Aand B-sites cations, tolerating different dopants addition for monitoring the catalytic properties and their semiconducting properties. Lots of perovskites were synthesized to utilize as gas sensors for detecting different hazardous gases. **Table 2** enlisted with different perovskite oxides for various gas sensing applications.

#### **2.3 Perovskites as solar cell materials**

The consumption of energy has been continuously increasing globally and limitations of sources of fossil fuels leading to perform the research on sustainable, environment-friendly, and renewable energy sources. Due to the abundance of sun rays on


**Table 2.** *Tabulated with different perovskite oxides for various gas sensing applications.*

**37**

*Lead-Free Perovskite Nanocomposites: An Aspect for Environmental Application*

our globe, the transformation of sunlight into electricity is one of the most favorable studies for increasing energy demands without having any adverse effect on the global climate. Solar cell technology offers an eco-friendly and renewable energy path to convert photon energy into electricity openly [65]. Nowadays a large effort has been put in the research to develop high efficiency, low-cost photovoltaic devices but regrettably did not succeed yet. During the last decade, research into perovskite solar cells (PSCs) has increased and it also been nominated as a runner-up for the top 10 breakthroughs research of 2013 by the editors of Science [66]. The organic-inorganic perovskite having the general formula ABX3 where A is cesium (Cs), methylammonium (MA), or formamidinium (FA); B is Pb or Sn; and X is Cl, Br, or I, have recently appeared as an exciting class of semiconductors which can act as solar cell materials [67]. These organic-inorganic halide perovskite solar cells have shown substantial improvement of power conversion efficiency (PCE) from the preliminary efficiency of 3.8% [68] to about 22.1% [69]. The maximum theoretical power conversion efficiency accomplished by perovskite (CH3NH3PbI3) is about 31.4% [70]. The organic-halide perovskites owing extraordinary performance because of some unique properties like (i) high absorbing coefficient, (ii) high charge carrier mobility, (iii) long diffusion length, (iv) direct bandgap which can be engineered easily and (v) moreover easy to fabricate [71]. The normally used Pb-based perovskites have numerous advantages such as (i) large diffusion length, (ii) absorption range, (iii) low exciton binding energy, and (iv) high carrier mobility. Conversely, the Pb-based perovskite solar cell has a serious toxic issue on both humans and the environment [72]. Generally, PV panels are positioned on the roof of houses or in the open field, their exposure to rainfall is inescapable. In the manifestation of rain and moisture the degradation of PbI2 may cause mild to acute health issues, like effects on cardiovascular, neurological, reproductive system [73] mainly it is carcinogenic [72, 74] Additionally, lead pollution has severe effects on water and soil resources and emission of greenhouse gasses [75, 76]. Hence, in PSCs, it is essential to replace Pb for economical green energy conversion devices which may

To develop Pb-free PSCs, Sn2+ metal cation was the first another candidate to replace Pb2+ as of its comparable electronic configuration and effective ionic radius (Sn2+: 115 pm) to lead (Pb2+: 119 pm) [78]. The hybrid organic-inorganic

small monovalent organic molecule, MIV is a divalent group-IVA cation and XVII is a halogen anion, have recently attracted remarkable attention in the photovoltaic community MASnI3 and MASn-(I3−xBrx) have been shown to the efficiencies of 6.4% [79] and 5.73% [80] respectively. CH3NH3SnI3, HC(NH2)2SnI3, NH2NH3SnI3, and NH2(CH2)3SnI3 is the promising candidate to be a light sensitizer with suitable inorganic hole-transport material to achieve cost-effective and efficient lead-free perovskite solar cell [81, 82]. Gagandeep et al. uses the graphene as the layer for charge transport and is demonstrate the structure like n-Graphene/CH3NH3SnI3/p-Graphene which shows the efficiency of 10.67–13.28% [83]. Giorgi et al. substituted Pb by TlBi (MATl0.5Bi0.5I3) and InBi (MAIn0.5Bi0.5I3) and depicted that these systems are quietly equivalent to MAPbI3 and can be good replacements for PSCs [84]. Germanium is also assumed as a possible candidate for Pb substitution in halide perovskites. The theoretical structure and electronic properties of AGeI3 (A = MA, FA, Cs) were investigated by Krishnamoorthy et al. [85]. There are several elements like: Bi [86–88], Sb [89–91], Ti [92], Cu [93, 94] that use to substitute Pb to decrease the lead pollution. The group of Song et al. has reported the photovoltaic application of Sn-based halide perovskite materials having the general formula ASnI3 (A = Cs, methylammonium and formamidinium tin iodide as the representative light absorbers). Among all the perovskites, CsSnI3 devices accomplished a maximum power conversion efficiency of 4.81% [95]. Nishimura et al. synthesized

3, where A represents a

halide perovskites having the chemical formula of AMIVXVII

*DOI: http://dx.doi.org/10.5772/intechopen.93052*

use mankind in future endeavors [77].

#### *Lead-Free Perovskite Nanocomposites: An Aspect for Environmental Application DOI: http://dx.doi.org/10.5772/intechopen.93052*

our globe, the transformation of sunlight into electricity is one of the most favorable studies for increasing energy demands without having any adverse effect on the global climate. Solar cell technology offers an eco-friendly and renewable energy path to convert photon energy into electricity openly [65]. Nowadays a large effort has been put in the research to develop high efficiency, low-cost photovoltaic devices but regrettably did not succeed yet. During the last decade, research into perovskite solar cells (PSCs) has increased and it also been nominated as a runner-up for the top 10 breakthroughs research of 2013 by the editors of Science [66]. The organic-inorganic perovskite having the general formula ABX3 where A is cesium (Cs), methylammonium (MA), or formamidinium (FA); B is Pb or Sn; and X is Cl, Br, or I, have recently appeared as an exciting class of semiconductors which can act as solar cell materials [67]. These organic-inorganic halide perovskite solar cells have shown substantial improvement of power conversion efficiency (PCE) from the preliminary efficiency of 3.8% [68] to about 22.1% [69]. The maximum theoretical power conversion efficiency accomplished by perovskite (CH3NH3PbI3) is about 31.4% [70]. The organic-halide perovskites owing extraordinary performance because of some unique properties like (i) high absorbing coefficient, (ii) high charge carrier mobility, (iii) long diffusion length, (iv) direct bandgap which can be engineered easily and (v) moreover easy to fabricate [71]. The normally used Pb-based perovskites have numerous advantages such as (i) large diffusion length, (ii) absorption range, (iii) low exciton binding energy, and (iv) high carrier mobility. Conversely, the Pb-based perovskite solar cell has a serious toxic issue on both humans and the environment [72]. Generally, PV panels are positioned on the roof of houses or in the open field, their exposure to rainfall is inescapable. In the manifestation of rain and moisture the degradation of PbI2 may cause mild to acute health issues, like effects on cardiovascular, neurological, reproductive system [73] mainly it is carcinogenic [72, 74] Additionally, lead pollution has severe effects on water and soil resources and emission of greenhouse gasses [75, 76]. Hence, in PSCs, it is essential to replace Pb for economical green energy conversion devices which may use mankind in future endeavors [77].

To develop Pb-free PSCs, Sn2+ metal cation was the first another candidate to replace Pb2+ as of its comparable electronic configuration and effective ionic radius (Sn2+: 115 pm) to lead (Pb2+: 119 pm) [78]. The hybrid organic-inorganic halide perovskites having the chemical formula of AMIVXVII 3, where A represents a small monovalent organic molecule, MIV is a divalent group-IVA cation and XVII is a halogen anion, have recently attracted remarkable attention in the photovoltaic community MASnI3 and MASn-(I3−xBrx) have been shown to the efficiencies of 6.4% [79] and 5.73% [80] respectively. CH3NH3SnI3, HC(NH2)2SnI3, NH2NH3SnI3, and NH2(CH2)3SnI3 is the promising candidate to be a light sensitizer with suitable inorganic hole-transport material to achieve cost-effective and efficient lead-free perovskite solar cell [81, 82]. Gagandeep et al. uses the graphene as the layer for charge transport and is demonstrate the structure like n-Graphene/CH3NH3SnI3/p-Graphene which shows the efficiency of 10.67–13.28% [83]. Giorgi et al. substituted Pb by TlBi (MATl0.5Bi0.5I3) and InBi (MAIn0.5Bi0.5I3) and depicted that these systems are quietly equivalent to MAPbI3 and can be good replacements for PSCs [84]. Germanium is also assumed as a possible candidate for Pb substitution in halide perovskites. The theoretical structure and electronic properties of AGeI3 (A = MA, FA, Cs) were investigated by Krishnamoorthy et al. [85]. There are several elements like: Bi [86–88], Sb [89–91], Ti [92], Cu [93, 94] that use to substitute Pb to decrease the lead pollution. The group of Song et al. has reported the photovoltaic application of Sn-based halide perovskite materials having the general formula ASnI3 (A = Cs, methylammonium and formamidinium tin iodide as the representative light absorbers). Among all the perovskites, CsSnI3 devices accomplished a maximum power conversion efficiency of 4.81% [95]. Nishimura et al. synthesized

*Perovskite and Piezoelectric Materials*

Ca modified LaFeO3

LaFeO3 and rGO-LaFeO3

BaTiO3/LaFeO3 nanocomposite

**Perovskites Sensing for Response ratio % Reference**

sensor achieved a high sensing response of

detected at ~275°C by the LaCaFeO3 samples, and it shows 15% higher efficiency than LaFeO3 [41]

[43]

[46]

[47]

[52]

[54]

[55]

[57]

[58]

[61]

[63]

[64]

LaCoO3 CO Under 5000 ppm CO at 500°C, the thick film

Ag-LaFeO3 Methanol The maximum response to the other test gases is 8

Ag-LaFeO3 Formaldehyde Best response to 0.5 ppm formaldehyde (24.5) at 40°C

α-Fe2O3/LaFeO3 Acetone Response 48.3% at 100 ppm concentration at 350°C

ZnSnO3 n-Propanol gas The detection limit of ZnSnO3 nanospheres to

Ba-BiFeO3 Ethanol Temperature dependent sensing performance

La doped BiFeO3 Acetone The morphotropic phase boundary (MPB) phase

Sr doped BaTiO3 NH3 and NO2 0.2 mol% doping of Sr showed enhanced

BaSnO3 LPG Addition of noble metal Pt, the operating

*Tabulated with different perovskite oxides for various gas sensing applications.*

LaBO3 (B = Fe, Co) Acetone At a low operating temperature of 120°C showed

14 and 49 s

∼279.86

La0.9Ce0.1CoO3 CO 240% with respect to 100 ppm CO in air [42]

NdFe1–xCoxO3 CO 1215% at 170°C for 0.03% CO gas [44] LaFeO3 Ethanol Not reported [45]

SrFeO3 Ethanol Not reported [48] LaFeO3 NO2 Not reported [49] GaFeO3 Ethanol Ethanol sensing down to 1 ppm at 350°C [50] SrTi1 − xFexO3 <sup>−</sup> <sup>δ</sup> Hydrocarbons Not reported [51]

YCo1-xPdxO3 CO, NO2 Different for the different composition [53]

NO2 and CO Response 183.4% for 3 ppm concentration of NO2 at a 250°C

sensitivity at 400°C

Pr doped BiFeO3 Formaldehyde 50ppm, 190°C, Rgas/Rair = 17.6 [59] BaTiO3 thick films H2S BaTiO3 sensor operated at 350°C [60]

BaSnO3 SO2 10 ppm of SO2 [62]

detection of 50 ppb acetone

gases at room temperature

for the detection of LPG

500 ppb n-propanol gas could reach 1.7

Ethanol Response 102.7% to 100 ppm ethanol at 128°C [56]

toward 100 ppm ethanol gas; maximum

Bi0.9La0.1FeO3 shows ultra-low concentration

performance for sensing of both NO2 and NH3

temperature decreases and the sensitivity improved but also imparted partial selectivity

that the LaFeO3 NFs based sensor displayed high stable and selective response toward 40 ppm acetone with fast response and recovery time of

SO2 Maximum resistive response of 3 ppm SO2 was

**36**

**Table 2.**

GeI2 doped FA0.98EDA0.01SnI3 and GeI2 doped EA0.98EDA0.01SnI3 PSCs and shows the power conversion efficiency of 13.24% for lead-free perovskite solar cell has been demonstrated with mixed cation and surface passivation [96].

### **2.4 Removal of heavy metals from wastewater**

To survive on this planet the clean air, water, and foods are essential to all forms of life. The surface and the groundwaters are only the sources of clean water which help to all living systems as well as human activities such as consuming, irrigation of crops, industrial application, etc. [97]. Water pollution is one of the most worldwide common issues as the population outbursts and industrial evolutions are there. Day by day, the heavy metals (maybe in the form of ions) are released into water bodies by various industries [98] and are exceedingly water-soluble, non-decomposable, oncogenic agents and cause adverse health complications on the animals as well as human beings. Wastewaters coming out from various industries contain many heavy metal ions, for example, Cu2+, As5+, Ni2+, Sb5+, Zn2+, Cd2+, and Pb2+ [99]. In addition to heavy metal ions, the different organic and inorganic dyes are alternative pollutant releases from different industries for example papers, textiles, and plastics where the dyes are used for coloring their product and also generate significant volumes of wastewater. Many of these dyes containing heavy metal ions have a tendency to store in the living entities causing a different type of diseases and disorders [100–102]. Hence, it is essential to purify the metal-contaminated water before its discharge to the environment. Among all compare to current methods to remove heavy metal from the contaminated water [100, 101] adsorption method is the most likely one because it low cost-effective, high efficiency, and simple to run.
