Synthesis of Graphene Quantum Dots and Carbon Quantum Dots for their Sensing Applications

Abstract

The thesis entitled Synthesis of Graphene Quantum Dots (GQDs) and Carbon Quantum Dots (CQDs) for their Sensing Applications is divided into five Chapters. Chapter-1. It describes the background of nanomaterials, carbon-based nanomaterials including graphene quantum dots (GQDs) and carbon quantum dots (CQDs) along with literature survey and scope of the work. This Chapter discusses the detailed information about GQDs and CQDs with their optical properties, synthesis methods, fluorescence quenching and restoration mechanisms. Importance of coal-derived GQDs and natural-resource derived CQDs were also described in this chapter. Various sensing applications for the detection of different analytes was also explained. Chapter-2. Coal is an abundant, low-cost, and high carbon content energy source on the planet. Herein, water-soluble graphene quantum dots (GQDs) were prepared from Indian anthracite and bituminous coals labelled as A-GQDs and B-GQDs, respectively by the facile one-step wet chemical route. The size of B-GQDs (7.38 nm ± 0.13) was smaller than A-GQDs (10.25 nm ± 0.19) which was analysed from TEM. The effects of pH, temperature and irradiation time on the fluorescence of the GQDs have been studied which affirmed the stability of GQDs. Moreover, both the synthesized GQDs exhibited tunable photoluminescence (PL) properties and excitation wavelength dependency. The developed GQDs was high selective and sensitivity for Mnn+ (2+, 7+) ions. However, the as-prepared GQDs showed significant change in both the steady state absorption and fluorescence intensity but remain unaltered in the excited state lifetime values in the presence of different Mnn+ quenchers, which validated the static quenching mechanism between GQDsatMnn+ nanoprobes. The prepared nanosensor showed high sensitivity for GSH sensing with a good detection limit of 27 and#61549;M for BGQDatMn7+. Accrediting low-cost productivity and intriguing photoluminescence properties, the current study reveals new potential for sustainable synthesis of GQDs with novel