386
A. Donia et al.
2.2 Degradation of 4-Nitrophenol
4-nitrophenol is a frequently used nitro-aromatic pollutant found in synthetic pesticides, dyes, herbicides, and other chemical products. 4-nitrophenol functions to stimulate and inhibit various nerve endings and can produce undesirable consequences
affecting the human central nervous system. The degradation of 4-nitrophenol could
be effortlessly measured through UV–Vis spectroscopy; hence, it has been used to
gage the catalytic efficiency of nanoparticles (Zhang and Hu 2017; Hosseinpour
et al. 2018). In a recent study, marine bacterium Bacillus sp. GP was used to create
Pd/Au nanoparticles. Thereafter, the catalytic efficiency of the Pd/Au nanoparticles to
reduce 4-nitrophenol was evaluated. The results suggested that biosynthesized Pd/Au
nanoparticles were weak compared to the chemically synthesized kind. Hence, AlO 3 ,
SiO 2 , Fe 3 O 4 and various other metal oxides were utilized in order to improve the
catalytic activity. Resultantly, it was seen that the enhanced activity was dependent
on alloy formation and amount of metal ions because of a number of reasons. Firstly,
ions of metal oxides could be considered as the Lewis acids, promoting the reaction
and secondly, due to alloy formation that disconcerted the action of noble metal sites
(Zhang et al. 2018).
In another study, using Shewanella oneidensis MR-1 on rGO, Au (gold) nanoparticles were biosynthesized in bother culture as well as ambient conditions. The biosynthesized Au-NPs/rGO showed promising impacts on the 4-nitrophenol microbialmediated reduction compared with its chemical parallel. They also displayed higher
levels of catalytic activity and could be reused to degrade other pollutants, e.g.,
nitrobenzene (Cumbal et al. 2003). After ten reduction cycles, catalytic efficiency
was consistent at 72% as of initial value. The rise in performance and reusability was
credited to the synergic effects of Au nanoparticles and rGo. Firstly, because rGO
elevated the concentration level of 4-nitrophenol surrounding the Au nanoparticles
while providing a guide to stop the Au nanoparticles from clustering and secondly,
because of the improvement in electron transport because of conductivity of rGo
(Dong et al. 2015).
In the presence of bio-rGO or in the absence of catalyst, the peak corresponding
to nitrophenolate anion at 400 nm was constant over time. With the addition of bioAuNPs, bioAuNPs/rGO, or chem-AuNPs/rGO, researchers found that there was a
decrease in the absorbance at 400 nm and an increase in the new peak at 300 nm related
to 4-aminophenol, suggesting that there is a catalytic reduction of 4-nitrophenol.
They also found linear correlations between ln(A t /A 0 ) (A t and A 0 are the absorbance
at 400 nm at time t and zero, respectively) and the reaction time in the presence
of various nanomaterials, suggesting that the reactions followed pseudo-first-order
kinetics. The first-order rate constant normalized by Au molar concentration (k) of
bio-AuNPs/rGO was found to be 138.45 s
−1 M
−1 , which was approximately ten times
higher than that of bio-AuNPs (13.47 s
−1 M
−1 ). Moreover, the normalized k values of
other nanohybrids of AuNPs and carbon-nanomaterials that were previously formed
using chemical methods ranged from 1.96 to 33.54 s
−1 M
−1 , which were also much
lower than that of bio-AuNPs/rGO (Dong et al. 2015).
A. Donia et al.
2.2 Degradation of 4-Nitrophenol
4-nitrophenol is a frequently used nitro-aromatic pollutant found in synthetic pesticides, dyes, herbicides, and other chemical products. 4-nitrophenol functions to stimulate and inhibit various nerve endings and can produce undesirable consequences
affecting the human central nervous system. The degradation of 4-nitrophenol could
be effortlessly measured through UV–Vis spectroscopy; hence, it has been used to
gage the catalytic efficiency of nanoparticles (Zhang and Hu 2017; Hosseinpour
et al. 2018). In a recent study, marine bacterium Bacillus sp. GP was used to create
Pd/Au nanoparticles. Thereafter, the catalytic efficiency of the Pd/Au nanoparticles to
reduce 4-nitrophenol was evaluated. The results suggested that biosynthesized Pd/Au
nanoparticles were weak compared to the chemically synthesized kind. Hence, AlO 3 ,
SiO 2 , Fe 3 O 4 and various other metal oxides were utilized in order to improve the
catalytic activity. Resultantly, it was seen that the enhanced activity was dependent
on alloy formation and amount of metal ions because of a number of reasons. Firstly,
ions of metal oxides could be considered as the Lewis acids, promoting the reaction
and secondly, due to alloy formation that disconcerted the action of noble metal sites
(Zhang et al. 2018).
In another study, using Shewanella oneidensis MR-1 on rGO, Au (gold) nanoparticles were biosynthesized in bother culture as well as ambient conditions. The biosynthesized Au-NPs/rGO showed promising impacts on the 4-nitrophenol microbialmediated reduction compared with its chemical parallel. They also displayed higher
levels of catalytic activity and could be reused to degrade other pollutants, e.g.,
nitrobenzene (Cumbal et al. 2003). After ten reduction cycles, catalytic efficiency
was consistent at 72% as of initial value. The rise in performance and reusability was
credited to the synergic effects of Au nanoparticles and rGo. Firstly, because rGO
elevated the concentration level of 4-nitrophenol surrounding the Au nanoparticles
while providing a guide to stop the Au nanoparticles from clustering and secondly,
because of the improvement in electron transport because of conductivity of rGo
(Dong et al. 2015).
In the presence of bio-rGO or in the absence of catalyst, the peak corresponding
to nitrophenolate anion at 400 nm was constant over time. With the addition of bioAuNPs, bioAuNPs/rGO, or chem-AuNPs/rGO, researchers found that there was a
decrease in the absorbance at 400 nm and an increase in the new peak at 300 nm related
to 4-aminophenol, suggesting that there is a catalytic reduction of 4-nitrophenol.
They also found linear correlations between ln(A t /A 0 ) (A t and A 0 are the absorbance
at 400 nm at time t and zero, respectively) and the reaction time in the presence
of various nanomaterials, suggesting that the reactions followed pseudo-first-order
kinetics. The first-order rate constant normalized by Au molar concentration (k) of
bio-AuNPs/rGO was found to be 138.45 s
−1 M
−1 , which was approximately ten times
higher than that of bio-AuNPs (13.47 s
−1 M
−1 ). Moreover, the normalized k values of
other nanohybrids of AuNPs and carbon-nanomaterials that were previously formed
using chemical methods ranged from 1.96 to 33.54 s
−1 M
−1 , which were also much
lower than that of bio-AuNPs/rGO (Dong et al. 2015).