Chapter 3 - An overview of optical, physical, biological, and catalytic properties of carbon dots

Abstract

In recent years, carbon dots (CDs) have gained considerable attention in diverse field of sciences due to their fascinating physico-chemical and optical properties such as photoluminescence, high quantum yield, high water solubility, excitation-dependent emission behavior, and low toxicity. Basically, CDs are the zero-dimensional quasi-spherical nanoparticles composed of sp2/sp3 hybridization with less than 10nm size. Therefore CDs can be consider as a highly defected material comprising of aromatic and aliphatic regions such as graphene, graphene oxide, and diamond in different proportions depending upon the surface groups. Moreover, the bonding between graphene sheets is weak and therefore insertions of sp3 hybridized carbon atoms provide the stabilization to the CDs in three-dimensional network. Moreover, these surface defects may interrupt the π-electronic conjugation between the graphene sheets, which influence optical properties of CDs. The CDs exhibited the bright and colorful fluorescence emissions at different excitation wavelengths from UV to near IR range due to the passivation of surface defects with the chemical functionalization with the various functional groups. The effect of surface passivation of CDs with various functional groups and their impact on optical properties of CDs is discussed in this chapter. The importance of metal doping to improve the properties of CDs is also highlighted. Moreover, physical, biological, and catalytic properties of CDs are also briefly discussed.