384
A. Donia et al.
2 Degradation of Pollutants
The microbial biosynthesis of various nanoparticles such as metal oxides, metallic,
and non-metallic nanoparticles by multiple bacterial strains, molds, microalgae, and
yeast has been studied previously (Hulkoti and Taranath 2014). Large production of
pesticides, pharmaceuticals, chemicals, and dyes used in various industries has led
to pollution of water and soil (Doshi et al. 2018; Hu et al. 2018). The waste produced
by these big industries is rich in metalloids and heavy metals that have been proven
hazardous for the environment (Schröfelet al. 2014; Choi et al. 2018). By exploiting
the waste as a means to manufacture nanoparticles through a biological mechanism,
degradation of these pollutants can be made possible (Seifan et al. 2018; Huang et al.
2018; Zhang et al. 2018).
2.1 Degradation of Industrial Dyes
Dyes, very frequently and in very large quantities, are used in numerous industries
such as textile, pharmaceutical, and food processing. Although many techniques have
been designed and employed to eliminate residual dye present in industrial waste,
none has been able to yield efficient results. This poses a severe threat to a large
number of organisms. Dyes have proven to be dangerous owed to their toxicity and
ability of eutrophication.
Biosynthesized nanoparticles in comparison with polycrystalline materials have
not only a bigger specific surface area but also a larger number of active sites (Fang
et al. 2019). The photocatalytic effectiveness of biosynthesized SnO 2 nanoparticles in degradation of three commonly used dyes was evaluated. With the help of
absorption spectra for the breakdown of dyes, taken at multiple time intervals, SnO 2
nanoparticles were observed to have high catalytic efficiency. The degradation efficiency of the Erichrome Black T was seen to be approximately 97.8%, while that of
methyl orange and methylene blue was seen to be 94.0% and 93.3%, respectively.
Another valuable feature of SnO 2 nanoparticles is that they can be removed from the
reaction mixture effortlessly through centrifugation (Srivastava and Kowshik 2017).
Dyes such as rhodamine B are difficult to be degraded by reason of their resistance
against UV light irradiation and bio-mediated degradation. In a study performed to
evaluate the photo-degradation of RhB, photocatalytic efficiency of biosynthesized
ZnS nanoparticles was evaluated, where tert-butanol was used as hydroxyl radicals,
whereas ammonium oxalate was used as scavengers of holes. These photo-generated
holes were seen to have played a central role in decolorizing. It was also observed
that ZnS nanoparticles carry high degrading ability for RhB (Fang et al. 2019).
In another study investigating the photocatalytic capability of Se nanoparticles
for degradation of RhB, Se nanorods and nanospheres which were reduced using
Lysinibacillus sp. ZYM-1 were used. While the nanorods did not show substantial
catalytic effect on Rhb degradation, the nanospheres-H2O2 system exhibited greater
A. Donia et al.
2 Degradation of Pollutants
The microbial biosynthesis of various nanoparticles such as metal oxides, metallic,
and non-metallic nanoparticles by multiple bacterial strains, molds, microalgae, and
yeast has been studied previously (Hulkoti and Taranath 2014). Large production of
pesticides, pharmaceuticals, chemicals, and dyes used in various industries has led
to pollution of water and soil (Doshi et al. 2018; Hu et al. 2018). The waste produced
by these big industries is rich in metalloids and heavy metals that have been proven
hazardous for the environment (Schröfelet al. 2014; Choi et al. 2018). By exploiting
the waste as a means to manufacture nanoparticles through a biological mechanism,
degradation of these pollutants can be made possible (Seifan et al. 2018; Huang et al.
2018; Zhang et al. 2018).
2.1 Degradation of Industrial Dyes
Dyes, very frequently and in very large quantities, are used in numerous industries
such as textile, pharmaceutical, and food processing. Although many techniques have
been designed and employed to eliminate residual dye present in industrial waste,
none has been able to yield efficient results. This poses a severe threat to a large
number of organisms. Dyes have proven to be dangerous owed to their toxicity and
ability of eutrophication.
Biosynthesized nanoparticles in comparison with polycrystalline materials have
not only a bigger specific surface area but also a larger number of active sites (Fang
et al. 2019). The photocatalytic effectiveness of biosynthesized SnO 2 nanoparticles in degradation of three commonly used dyes was evaluated. With the help of
absorption spectra for the breakdown of dyes, taken at multiple time intervals, SnO 2
nanoparticles were observed to have high catalytic efficiency. The degradation efficiency of the Erichrome Black T was seen to be approximately 97.8%, while that of
methyl orange and methylene blue was seen to be 94.0% and 93.3%, respectively.
Another valuable feature of SnO 2 nanoparticles is that they can be removed from the
reaction mixture effortlessly through centrifugation (Srivastava and Kowshik 2017).
Dyes such as rhodamine B are difficult to be degraded by reason of their resistance
against UV light irradiation and bio-mediated degradation. In a study performed to
evaluate the photo-degradation of RhB, photocatalytic efficiency of biosynthesized
ZnS nanoparticles was evaluated, where tert-butanol was used as hydroxyl radicals,
whereas ammonium oxalate was used as scavengers of holes. These photo-generated
holes were seen to have played a central role in decolorizing. It was also observed
that ZnS nanoparticles carry high degrading ability for RhB (Fang et al. 2019).
In another study investigating the photocatalytic capability of Se nanoparticles
for degradation of RhB, Se nanorods and nanospheres which were reduced using
Lysinibacillus sp. ZYM-1 were used. While the nanorods did not show substantial
catalytic effect on Rhb degradation, the nanospheres-H2O2 system exhibited greater