requires costly and special equipment. Thus, there is an urgency of developing an
adequate and cost-effective synthetic strategy for carbon quantum dot preparation.
3.4 Photocatalytic Activity of Carbon Quantum Dot-Based
Nanocomposites
As per the previously reported literature, fabrication of carbon quantum dots, metal
oxide, and metal sulfide-based carbon quantum dots has gained substantial attention.
A remarkable efficiency is assigned because of broader range of solar spectrum. The
aim of enhancing the photo-efficiency can be achieved by constructing a
heterojunction system between the carbon quantum dots and the semiconductor. Li
et al. (2010b) reported facile one-step electrochemical technique for uniform and
mono-dispersed carbon quantum dots synthesized in alkaline medium with sizes
ranging from 1.2 to 3.8 nm. Further, the design of carbon quantum dots is based on
TiO 2 and SiO 2 nanocomposites by sol–gel strategy and utilized for the
photodegradation of methyl blue. The complete photodegradation was observed in
25 min and 15 min for TiO 2 /carbon quantum dots and SiO 2 /carbon quantum dots,
respectively. The excitation of TiO 2 and SiO 2 photocatalyst is due to the
up-conversion process. Similarly, tetraethyl orthosilicate was added for the preparation of SiO 2 /carbon quantum dots in a similar fashion. The photocatalytic activity
was evaluated against methyl blue. The photodegradation analysis was carried out in
3100 mL conical flask containing 50 mgL
À1 dye solution with 10 mg
nanocomposites, and 300 W halogen lamp was used as light source.
Deng et al. (2015) synthesize 2D BiOCl/carbon quantum dot composites by
template-free coprecipitation method. The composites exhibit enhanced efficiency,
and almost 100% removal of 2-nitrophenol was observed. The higher efficiency of
the composites was attributed to excellent light absorption capacity in the visible
region and effective electron–hole pair separation which slowers the rate of recombination. Carbon dots/ZnO composites were also used for the photodegradation of
various azo dyes under visible light using 250 W Xe lamp (Ding et al. 2016). The
photodegradation follows the trend methyl blue > rhodamine B > methyl orange,
respectively.
Feng et al. (2015) synthesized porous nanorods of carbon dots/ZnO by
solvothermal deposition method. The photocatalytic activity was assessed against
phenol under visible light. The pollutant was 94% degraded in 60 min. Further, Li
et al. (2013) synthesized carbon dot/ZnO heterostructure via sol–gel method
followed by spin coating method and evaluated the photo-efficiency against rhodamine B dye. Thirty percent of rhodamine B was photodegraded in 120 min using
18 W ultraviolet lamp. The heterostructure exhibit three times higher photoefficiency as compared to base ZnO.
Besides ZnO, TiO 2 is also a promising photocatalyst to be utilized in
photodegradation of various pollutants due to its high oxidizing ability and high
102
P. Shandilya et al.
adequate and cost-effective synthetic strategy for carbon quantum dot preparation.
3.4 Photocatalytic Activity of Carbon Quantum Dot-Based
Nanocomposites
As per the previously reported literature, fabrication of carbon quantum dots, metal
oxide, and metal sulfide-based carbon quantum dots has gained substantial attention.
A remarkable efficiency is assigned because of broader range of solar spectrum. The
aim of enhancing the photo-efficiency can be achieved by constructing a
heterojunction system between the carbon quantum dots and the semiconductor. Li
et al. (2010b) reported facile one-step electrochemical technique for uniform and
mono-dispersed carbon quantum dots synthesized in alkaline medium with sizes
ranging from 1.2 to 3.8 nm. Further, the design of carbon quantum dots is based on
TiO 2 and SiO 2 nanocomposites by sol–gel strategy and utilized for the
photodegradation of methyl blue. The complete photodegradation was observed in
25 min and 15 min for TiO 2 /carbon quantum dots and SiO 2 /carbon quantum dots,
respectively. The excitation of TiO 2 and SiO 2 photocatalyst is due to the
up-conversion process. Similarly, tetraethyl orthosilicate was added for the preparation of SiO 2 /carbon quantum dots in a similar fashion. The photocatalytic activity
was evaluated against methyl blue. The photodegradation analysis was carried out in
3100 mL conical flask containing 50 mgL
À1 dye solution with 10 mg
nanocomposites, and 300 W halogen lamp was used as light source.
Deng et al. (2015) synthesize 2D BiOCl/carbon quantum dot composites by
template-free coprecipitation method. The composites exhibit enhanced efficiency,
and almost 100% removal of 2-nitrophenol was observed. The higher efficiency of
the composites was attributed to excellent light absorption capacity in the visible
region and effective electron–hole pair separation which slowers the rate of recombination. Carbon dots/ZnO composites were also used for the photodegradation of
various azo dyes under visible light using 250 W Xe lamp (Ding et al. 2016). The
photodegradation follows the trend methyl blue > rhodamine B > methyl orange,
respectively.
Feng et al. (2015) synthesized porous nanorods of carbon dots/ZnO by
solvothermal deposition method. The photocatalytic activity was assessed against
phenol under visible light. The pollutant was 94% degraded in 60 min. Further, Li
et al. (2013) synthesized carbon dot/ZnO heterostructure via sol–gel method
followed by spin coating method and evaluated the photo-efficiency against rhodamine B dye. Thirty percent of rhodamine B was photodegraded in 120 min using
18 W ultraviolet lamp. The heterostructure exhibit three times higher photoefficiency as compared to base ZnO.
Besides ZnO, TiO 2 is also a promising photocatalyst to be utilized in
photodegradation of various pollutants due to its high oxidizing ability and high
102
P. Shandilya et al.