HO 2
•
, H 2 O 2 , OH
• and HO 2
•À
) play significant role. These species make
photodegradation processes more effective by increasing dye removal through the
production of various intermediates like aromatic amines, phenolic compounds, and
different organic acids. On the basis of azo dye structure, hydroxylated derivatives,
aromatic amines, naphthoquinone, phenolic compounds, and several organic acids
are chief intermediates formed during degradation reaction.
The usage of nanosized magnetic Fe 3 O 4 photocatalyst via sonochemical method
was also employed for degradation of azo dyes, methyl red, and congo red, respectively (Solomon et al. 2012). The synthesized photocatalyst is a novel photocatalyst
due to its facile separation by the virtue of its magnetic property and good recyclability. Besides these good properties, it is cost-effective, non-toxic, and
noncarcinogenic in nature. A detailed study on the degradation of azo dyes at
different pH and concentrations of photocatalyst, dye, and hydrogen peroxide was
revealed. The results indicate that photodegradation increases as the photocatalyst
quantity increased and reached a peak value followed by substantial decreases due to
enhancement in suspension opacity, diminished radiation invasion, high scattering
of light, and availability of low surface area of nanoparticles due to aggregation. Due
to agglomeration of photocatalyst, the photo-activated volume of suspension
shortens (Konstantinou and Albanis 2004). Langmuir–Hinshelwood kinetic analysis
was used to analyze the kinetics of reaction which follows pseudo-first-order
reaction for the photodegradation of pollutant. The successive order of degradation
is: Photo-Fe 3 O 4 > Photo-H 2 O 2 > Fe 3 O 4 > H 2 O 2 .
Al-Anbari et al. (2016) synthesized Fe 3 O 4 and used for the eradication/decolorization of red azo dye from simulated wastewater. To eliminate azo dye, various
parameters like concentration, pH, photocatalyst dose, and H 2 O 2 concentration have
been employed, and all these features were assessed to find the optimal operation
situations. Furthermore, pH, oxidation reduction potential, and electrical conductivity of solution were scrutinized to evaluate dye degradation. From the investigational
findings, it was noticed that the optimal pH value for Fe 3 O 4 was 6.5, and catalyst
dose was 300 mg/L, respectively. Moreover, the most influential concentration of
H 2 O 2 was 200 mg/L for Fe 3 O 4 . The co-workers have employed response surface
methodology, a mathematical model which explains photodegradation process.
From the results, it was concluded that Fe 3 O 4 displayed approx. 85.51% degradation
efficacy of reactive red dye under solar light illumination.
Manivel et al. (2015) fabricated one-dimensional molybdenum trioxide (MoO 3 )
nanoparticles for the degradation of azo dye via catalytic ozonation. The thermal,
microwave, and sonochemical method were used to fabricate MoO 3 nanoparticles.
The sonochemical synthetic route was considered as the most reliable method among
all due to well dispersion of fine MoO 3 nanoparticles, and total dye removal was
observed within 20 min.
Chen (2009) analyzed the degradation of reactive orange 16 one of the earliest
nonbiodegradable azo dyes known since 1863. Almost 100% of dye is mineralized
in 80 min by employing TiO 2 under ultraviolet light and obeys the condition of firstorder reactions. The analysis of mineralized product was carried out using gas
chromatography–mass spectroscopy. The fragmentation may be due to the breaking
4 Photocatalytic Degradation of Azo Dyes in Water
127
•
, H 2 O 2 , OH
• and HO 2
•À
) play significant role. These species make
photodegradation processes more effective by increasing dye removal through the
production of various intermediates like aromatic amines, phenolic compounds, and
different organic acids. On the basis of azo dye structure, hydroxylated derivatives,
aromatic amines, naphthoquinone, phenolic compounds, and several organic acids
are chief intermediates formed during degradation reaction.
The usage of nanosized magnetic Fe 3 O 4 photocatalyst via sonochemical method
was also employed for degradation of azo dyes, methyl red, and congo red, respectively (Solomon et al. 2012). The synthesized photocatalyst is a novel photocatalyst
due to its facile separation by the virtue of its magnetic property and good recyclability. Besides these good properties, it is cost-effective, non-toxic, and
noncarcinogenic in nature. A detailed study on the degradation of azo dyes at
different pH and concentrations of photocatalyst, dye, and hydrogen peroxide was
revealed. The results indicate that photodegradation increases as the photocatalyst
quantity increased and reached a peak value followed by substantial decreases due to
enhancement in suspension opacity, diminished radiation invasion, high scattering
of light, and availability of low surface area of nanoparticles due to aggregation. Due
to agglomeration of photocatalyst, the photo-activated volume of suspension
shortens (Konstantinou and Albanis 2004). Langmuir–Hinshelwood kinetic analysis
was used to analyze the kinetics of reaction which follows pseudo-first-order
reaction for the photodegradation of pollutant. The successive order of degradation
is: Photo-Fe 3 O 4 > Photo-H 2 O 2 > Fe 3 O 4 > H 2 O 2 .
Al-Anbari et al. (2016) synthesized Fe 3 O 4 and used for the eradication/decolorization of red azo dye from simulated wastewater. To eliminate azo dye, various
parameters like concentration, pH, photocatalyst dose, and H 2 O 2 concentration have
been employed, and all these features were assessed to find the optimal operation
situations. Furthermore, pH, oxidation reduction potential, and electrical conductivity of solution were scrutinized to evaluate dye degradation. From the investigational
findings, it was noticed that the optimal pH value for Fe 3 O 4 was 6.5, and catalyst
dose was 300 mg/L, respectively. Moreover, the most influential concentration of
H 2 O 2 was 200 mg/L for Fe 3 O 4 . The co-workers have employed response surface
methodology, a mathematical model which explains photodegradation process.
From the results, it was concluded that Fe 3 O 4 displayed approx. 85.51% degradation
efficacy of reactive red dye under solar light illumination.
Manivel et al. (2015) fabricated one-dimensional molybdenum trioxide (MoO 3 )
nanoparticles for the degradation of azo dye via catalytic ozonation. The thermal,
microwave, and sonochemical method were used to fabricate MoO 3 nanoparticles.
The sonochemical synthetic route was considered as the most reliable method among
all due to well dispersion of fine MoO 3 nanoparticles, and total dye removal was
observed within 20 min.
Chen (2009) analyzed the degradation of reactive orange 16 one of the earliest
nonbiodegradable azo dyes known since 1863. Almost 100% of dye is mineralized
in 80 min by employing TiO 2 under ultraviolet light and obeys the condition of firstorder reactions. The analysis of mineralized product was carried out using gas
chromatography–mass spectroscopy. The fragmentation may be due to the breaking
4 Photocatalytic Degradation of Azo Dyes in Water
127