To construct an innovative photocatalyst which is competent of utilizing the
whole solar spectrum is still challenging and extremely needed. Though, a visible
light-driven photocatalyst were available for the removal of dyes, yet experiencing a
challenges of high rate charge carrier recombination (Pingmuang et al. 2017; Wang
et al. 2018).The rate of recombination permits only handful of charge carrier to
migrate toward the surface and carry out the process of photocatalysis that retards the
productivity of photocatalyst. Therefore, the better way is either immobilized the
binary metal oxide on the surface as thin films support or we may use magnetic metal
oxide-based nanocomposites that can be recovered easily from the system so as to
maintain the quality of treated water. While using iron-based magnetic
nanocomposites, a lot of iron sludge was generated which produces secondary
pollutant (Sharma et al. 2019a, b).
Spinel cobalt oxide (Co 3 O 4 ) anchored on support carbon spheres has been
synthesized via precipitation deposition and wet impregnation method. The synthesized Co 3 O 4 are evenly distributed on the surface of carbon spheres as justified from
the transmission electron microscopy image results. The obtained photocatalyst
degraded 91% methyl orange dye in 10 min of reaction time with outstanding
reproducibility (Dou et al. 2016). Heterojunction has proven to be an effective
strategy to enhance the photocatalytic degradation efficiency. Han and co-workers
fabricated graphitic carbon nitride coupled with Co 3 O 4 using an easy and economical mixing–heating of precursors melamine and Co(NO 3 ) 2 . The mechanistic insight
for photodegrading methyl orange dye involves O 2 ˙¯ as the key reactive oxidation
species as confirmed from electron spin resonance results. With the increase in
concentration of Co 3 O 4 , shielding of reactive sites with a reduction in absorption
of light through solution was observed. Therefore, after optimization of Co 3 O 4
concentration, it was found that 0.2% of Co 3 O 4 significantly leads to complete
mineralization of methyl orange within 10 min of solar light radiation (Han et al.
2014).
Other than simple metal oxide, photocatalytic activity of coupled semiconductor
was also keep on exploring since 1995 and till date. Xing et al. (2008) prepared a
coupled heterostructure niobium pentoxide Nb 2 O 5 /SrNb 2 O 6 via ball milling and
annealing at 600
C. A comparative study is executed for TiO 2 which showed
60% degradation of methyl orange dye, whereas the obtained heterostructure
Nb 2 O 5 /SrNb 2 O 6 resulted in 92% removal of dye within 30 min of solar irradiation
(Xing et al. 2008). Photocatalytic elimination of toxic water soluble; ponceau S dye
is carried out via Nb 2 O 5 in suspension of carbon which acts as coadsorbent. Here,
researchers have focused on the pH dependence degradation of ponceau S dye which
increases a maximum to 86.2% at pH 8 (Patil et al. 2011). Ibrahim et al. fabricated
nanosized ZrO 2 photocatalyst using various organic acid precursors (maleic, oxalic,
citric, malic, malonic, tartaric, and succinic acids (Ibrahim et al. 2016)). The results
demonstrated tremendous ability to degrade 100% orange G dye in 180 min, with
O 2
˙¯ as main reactive oxidation species (Ibrahim et al. 2016).
CuO is one of the frequently used semiconductors utilized in photocatalysis due
to its easy construction, precise 1.2 eV band gap, and varied appliance (Kumar et al.
2019a, b). A recent research based on the green preparation of curcumin-coupled
4 Photocatalytic Degradation of Azo Dyes in Water
129
whole solar spectrum is still challenging and extremely needed. Though, a visible
light-driven photocatalyst were available for the removal of dyes, yet experiencing a
challenges of high rate charge carrier recombination (Pingmuang et al. 2017; Wang
et al. 2018).The rate of recombination permits only handful of charge carrier to
migrate toward the surface and carry out the process of photocatalysis that retards the
productivity of photocatalyst. Therefore, the better way is either immobilized the
binary metal oxide on the surface as thin films support or we may use magnetic metal
oxide-based nanocomposites that can be recovered easily from the system so as to
maintain the quality of treated water. While using iron-based magnetic
nanocomposites, a lot of iron sludge was generated which produces secondary
pollutant (Sharma et al. 2019a, b).
Spinel cobalt oxide (Co 3 O 4 ) anchored on support carbon spheres has been
synthesized via precipitation deposition and wet impregnation method. The synthesized Co 3 O 4 are evenly distributed on the surface of carbon spheres as justified from
the transmission electron microscopy image results. The obtained photocatalyst
degraded 91% methyl orange dye in 10 min of reaction time with outstanding
reproducibility (Dou et al. 2016). Heterojunction has proven to be an effective
strategy to enhance the photocatalytic degradation efficiency. Han and co-workers
fabricated graphitic carbon nitride coupled with Co 3 O 4 using an easy and economical mixing–heating of precursors melamine and Co(NO 3 ) 2 . The mechanistic insight
for photodegrading methyl orange dye involves O 2 ˙¯ as the key reactive oxidation
species as confirmed from electron spin resonance results. With the increase in
concentration of Co 3 O 4 , shielding of reactive sites with a reduction in absorption
of light through solution was observed. Therefore, after optimization of Co 3 O 4
concentration, it was found that 0.2% of Co 3 O 4 significantly leads to complete
mineralization of methyl orange within 10 min of solar light radiation (Han et al.
2014).
Other than simple metal oxide, photocatalytic activity of coupled semiconductor
was also keep on exploring since 1995 and till date. Xing et al. (2008) prepared a
coupled heterostructure niobium pentoxide Nb 2 O 5 /SrNb 2 O 6 via ball milling and
annealing at 600
C. A comparative study is executed for TiO 2 which showed
60% degradation of methyl orange dye, whereas the obtained heterostructure
Nb 2 O 5 /SrNb 2 O 6 resulted in 92% removal of dye within 30 min of solar irradiation
(Xing et al. 2008). Photocatalytic elimination of toxic water soluble; ponceau S dye
is carried out via Nb 2 O 5 in suspension of carbon which acts as coadsorbent. Here,
researchers have focused on the pH dependence degradation of ponceau S dye which
increases a maximum to 86.2% at pH 8 (Patil et al. 2011). Ibrahim et al. fabricated
nanosized ZrO 2 photocatalyst using various organic acid precursors (maleic, oxalic,
citric, malic, malonic, tartaric, and succinic acids (Ibrahim et al. 2016)). The results
demonstrated tremendous ability to degrade 100% orange G dye in 180 min, with
O 2
˙¯ as main reactive oxidation species (Ibrahim et al. 2016).
CuO is one of the frequently used semiconductors utilized in photocatalysis due
to its easy construction, precise 1.2 eV band gap, and varied appliance (Kumar et al.
2019a, b). A recent research based on the green preparation of curcumin-coupled
4 Photocatalytic Degradation of Azo Dyes in Water
129