*2.4.2 Heavy metals in wastewater from the textile industry*

*Perovskite and Piezoelectric Materials*

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

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.

The group of Zhang et al. synthesized the porous nano-calcium titanate microspheres via a citric acid assisted modified sol-gel method and used for absorption of heavy metals like lead, cadmium, and zinc [103]. Haron et al. reported that the nano-crystalline LaGdO3 perovskite was synthesized by the co-precipitation method could adsorb heavy metal ions (Cd2+ and Pb2+) which should be the attention in an application such as wastewater treatment [104]. Zhang et al. synthesized porous nano-barium-strontium titanate via sol-gel method using sorghum straw as a template and investigate about adsorption mechanism of Pb, Zn, and Cd from contaminated water [105]. LaFeO3 nanoparticles were synthesized by Rao et al. by the sol-gel method in presence of different chelating agents and these nanoparticles utilized for an adsorbent of the removal of heavy metal ions in particular cadmium ion. The LaFeO3 sample prepared with succinic acid (SA) as a chelating agent shows a higher removal efficiency of Cd2+ ions from aqueous systems [106]. Zhang et al. investigated Sr modified LaFeO3 and its structural and catalytic activity. La0.8Sr0.2FeO3 contributed significantly enhanced activity in methane combustion and CO oxidation because the oxygen vacancies accelerated the dissociation of gaseous oxygen on the surface in CO oxidation and facilitated the diffusion of lattice oxygen from the bulk to the surface during CH4 combustion [107]. The perovskite LaAlO3 was manufactured using the co-precipitation method by Haron et al. The structural and efficiency of removal of heavy metal (Cd2+ and Pb2+) were extremely investigated by them. The adsorption performance was studied which fit with the Langmuir isotherm. The results disclosed that LaAlO3 perovskite showed high efficiency as heavy metal ions remover from the contaminated water. This adsorbent could be recycled with an EDTA solution and reprocessed with only slightly less efficient than that of the fresh sample [108]. The group of Chen et al. synthesized ternary photocatalyst ZnTiO3/Zn2Ti3O8/ZnO

demonstrated with mixed cation and surface passivation [96].

**2.4 Removal of heavy metals from wastewater**

*2.4.1 Heavy metals from contaminated water*

**38**

The growing population in our globe, demands to clothe and increase with the taming sense of fashion and lifestyle thus textiles are contrived to meet the growing demands. In several countries such as India and Sri Lanka; the production of textile becomes their source of income that subsidizes their gross domestic product (GDP). However, this has brought both significances to such countries either in a positive way which is an enhancement of the economy or in a negative way indorsed to environmental pollution. The textile industries have been adapted as the worst reprobates of pollution contributors [110]. Especially, in India, according to the Central Pollution Control Board [111], a total of 2324 textile industries are set up. The textile industries employ different types of dyes for the manufacturing of various fabric materials. In reality, about 1 million different dyes are found in the market [112] and roughly 700,000 tons of artificial dyes are produced per year [113]. The disposal of dyes in waters exemplifies a severe environmental issue due to the coinciding presence of various types of pollutants [114–116]. All traditional methods used for the treatment of dyes and/or heavy metals have limitations because of cost, efficiency and operational complications. Among all of them, adsorption was exposed as one of the most effective methods due to its simplicity in operation, adaptability, high-treatment efficiency and low cost, and hence it is extensively applied for wastewaters treatment [117–121].

The perovskite oxide La0.9Sr0.1FeO3, capped with cetyl trimethyl ammonium bromide (CTAB) cationic surfactant, and used as a sorbent for the removal of the anionic Congo red (CR) dye from aqueous solutions was reported by Ali et al. [122]. The group of Chu et al. demonstrated the efficiency of Ag-La0.8Ca0.2Fe0.94O3-δ for the removal of organic and bacterial pollutants by catalytic peroxymonosulfate (PMS) activation. The oxygen vacancies in the B-site of perovskite enhances PMS activation and The SO4• and •OH radicals enhance the biocidal activity [123]. Nanocrystalline LaAlO3:Sm3+:Bi3+ composites are used to adsorb Direct Blue-53 (DB-53) dye was reported by Pratibha et al. [124]. This adsorbent is good and promising in the adsorption capacity and is advantageous in the elimination of toxic and non-biodegradable pollutants from water. The group of Dong et al. hydrothermally synthesized perovskite BaZrO3 in the form of hollow micro- and nano-sphere. This size-tunable BaZrO3 hollow nanospheres exhibited an excellent adsorption performance for reactive dyes in acidic conditions and can be used as excellent circular adsorbents for removing reactive dyes. They show the adsorption capacities are over

#### **Figure 5.**

*Representation of the adsorption process over LaFeO3 nanoparticles surfaces prepared using succinic acid (SA), citric acid (CA), and oxalic acid (OA) [106].*

160 mg g<sup>−</sup><sup>1</sup> for different investigated dyes at a pH value of 2. The adsorbents were easily recovered by using a basic solution with the adsorption performance persistent and the desorption rate is more than 97 wt% [125]. Siddharth et al. synthesized the perovskite structure of Ti-doped BaMnO3 (BaMn0.85Ti0.15O2.93) and its enhanced photocatalytic degradation (~99%) as compared to BaMnO3 toward toxic water impurities like RhB and MB dyes within 270 and 150 min under sunlight [126].
