et al. 2016; Tian et al. 2014). One of the effective ways to minimize these limitations
is to assemble carbon-coated nanostructure where the carbonaceous material
enhances the charge carrier mobility by acting as an electron sink/acceptor. Further,
the codoping of carbon framework with nitrogen and sulfur induces the surface
defects which increase the delocalization of electron (Wu et al. 2007; Pang et al.
2015; Raizada et al. 2018). Thus, one of the prominent nanomaterials ruling nanotechnology is the metal-free carbon-based photocatalytic system employed for the
degradation of pollutant from water. After oxygen, carbon is the second highest
abundant element in the periodic table and also the major constituent of organic
compound. The usage of the most abundant carbon as photocatalytic nanomaterial
makes them more economical and advantageous in which carbon quantum dots
acquire a significant attention.
Earlier, the survey was confined to CdSe/CdS and CdSe/ZnS and ZnSe/CdSe
quantum dots. In these traditional quantum dots, cadmium is the chief constituent
which leads to cytotoxicity due to the leakage of cadmium ions (Xu et al. 2010).
Thus, scientists emphasize to develop cadmium-free quantum dots, for example,
graphene quantum dots, carbon quantum dots, and silicon quantum dots (Al Awak
et al. 2017). Quantum dots have been utilized in a variety of applications including
bio-sensing, bio-imaging, and biomarkers and in medicine (Sharma et al. 2019b;
Jamwal et al. 2015). However, potential cytotoxicity, environmental hazards, and
tedious synthesis procedure were certain limitations that hindered the large-scale
applicability of quantum dots. Conventional quantum dots like PbS, PbSe, HgTe,
CdSe, InAs, and InP (Cademartiri et al. 2006; Moreels et al. 2007; Keuleyan et al.
2011; Guzelian et al. 1996; Micic et al. 1997) have various properties. However,
metal-based quantum dots face major challenges of depositing on the support,
recycling, and extremely hazardous nature which need to be addressed. Limitation
of conventional quantum dots can be obviated by using organic quantum dots as an
alternative; hence, many researchers nowadays are extensively working on it.
Currently, quantum-sized carbon has attracting much attention due to its
tunable band gap with broader absorption range; good conductivity; strong
photoluminescence emission; large-scale synthesis at low cost; less complex synthetic procedure; most abundant and thus inexpensive; high photostability; remarkable optical, electronic, and magnetic property; good biocompatibility; low toxicity;
and high chemical stability that make them chemically inert (Chen et al. 2018b; Ma
et al. 2017; Lim et al. 2015) (Fig. 3.2). All these properties make them widely
utilized in different fields, for example, in optoelectronics, biosensor, drug delivery,
bio-imaging, biomedical engineering, and photocatalysis (Luo et al. 2016; Namdari
et al. 2017). Further, the excellent electronic property of carbon quantum dots makes
them good electron donors and acceptors, resulting in their wide application in
catalysis, semiconductor devices, and sensor (Fig. 3.3).
84
P. Shandilya et al.
is to assemble carbon-coated nanostructure where the carbonaceous material
enhances the charge carrier mobility by acting as an electron sink/acceptor. Further,
the codoping of carbon framework with nitrogen and sulfur induces the surface
defects which increase the delocalization of electron (Wu et al. 2007; Pang et al.
2015; Raizada et al. 2018). Thus, one of the prominent nanomaterials ruling nanotechnology is the metal-free carbon-based photocatalytic system employed for the
degradation of pollutant from water. After oxygen, carbon is the second highest
abundant element in the periodic table and also the major constituent of organic
compound. The usage of the most abundant carbon as photocatalytic nanomaterial
makes them more economical and advantageous in which carbon quantum dots
acquire a significant attention.
Earlier, the survey was confined to CdSe/CdS and CdSe/ZnS and ZnSe/CdSe
quantum dots. In these traditional quantum dots, cadmium is the chief constituent
which leads to cytotoxicity due to the leakage of cadmium ions (Xu et al. 2010).
Thus, scientists emphasize to develop cadmium-free quantum dots, for example,
graphene quantum dots, carbon quantum dots, and silicon quantum dots (Al Awak
et al. 2017). Quantum dots have been utilized in a variety of applications including
bio-sensing, bio-imaging, and biomarkers and in medicine (Sharma et al. 2019b;
Jamwal et al. 2015). However, potential cytotoxicity, environmental hazards, and
tedious synthesis procedure were certain limitations that hindered the large-scale
applicability of quantum dots. Conventional quantum dots like PbS, PbSe, HgTe,
CdSe, InAs, and InP (Cademartiri et al. 2006; Moreels et al. 2007; Keuleyan et al.
2011; Guzelian et al. 1996; Micic et al. 1997) have various properties. However,
metal-based quantum dots face major challenges of depositing on the support,
recycling, and extremely hazardous nature which need to be addressed. Limitation
of conventional quantum dots can be obviated by using organic quantum dots as an
alternative; hence, many researchers nowadays are extensively working on it.
Currently, quantum-sized carbon has attracting much attention due to its
tunable band gap with broader absorption range; good conductivity; strong
photoluminescence emission; large-scale synthesis at low cost; less complex synthetic procedure; most abundant and thus inexpensive; high photostability; remarkable optical, electronic, and magnetic property; good biocompatibility; low toxicity;
and high chemical stability that make them chemically inert (Chen et al. 2018b; Ma
et al. 2017; Lim et al. 2015) (Fig. 3.2). All these properties make them widely
utilized in different fields, for example, in optoelectronics, biosensor, drug delivery,
bio-imaging, biomedical engineering, and photocatalysis (Luo et al. 2016; Namdari
et al. 2017). Further, the excellent electronic property of carbon quantum dots makes
them good electron donors and acceptors, resulting in their wide application in
catalysis, semiconductor devices, and sensor (Fig. 3.3).
84
P. Shandilya et al.