Preparation And Properties Of Amino-functionalized Graphene Quantum Dots

Graphene quantum dots(GQDs) have extensive applications in environment protection, energy conversion, biotechnology and other fields due to their unique structure and numerous novel properties. In this dissertation, we focus on the synthesis and optical properties of graphene quantum dots. And we also study their applications to supercapacitor and photocatalytic. The main contents are as follows:1. Amino-functionalized GQDs via alkali-mediated hydrothermal using pyrene molecule as the precursor have been synthesized. Interestingly, the as-prepared GQDs can emit blue fluorescence, and its fluorescence quantum yield is 12.74%. The watersoluble GQDs have uniform size(average diameter of 2.2 nm, average thickness of 2.1 nm). In addition, the as-prepared GQDs offer outstanding optical properties such as strong excitonic absorption bands within the visible region. More importantly, Aminofunctionalized GQDs did not have the excitation wavelength dependency, that was, the fluorescence spectra of GQDs hardly moves when excitation wavelength changed.2. In-situ method was used to prepare Amino-functionalized GQDs/TiO2 nanotube arrays(GQDs/TNA) three-dimensional electrode. The cyclic voltammetric studies have shown that pseudocapacitance reaction had occurred between amino functional groups of GQDs and ions of electrolyte. When the concentration of polyethyleneimine was 0.8 g·L-1, we obtained the best capacitance performance of composite electrode. The areal capacitance of GQDs/TNA electrode was achieved as 379 m F·cm-2 at a scanning speed of 10 m V·s-1 in acid electrolyte, and showed a long cycle life with only 9.6% reduction of capacitance after 5000 cycles.3. GQDs-sensitized Ti O2(GQDs/Ti O2) were synthesized by hydrothermal method. In comparison with Ti O2, we found that the light absorption of GQDs/Ti O2 shifted from 400 nm to 500 nm and the photocurrent intensity increased about eightfold. The photodegradation efficiency is up to 95% in 120 min with GQDs/Ti O2 complex acting as photocatalyst. However, the efficiency was only 60% with Cd Se/Ti O2 catalysts, 17% with GQDs and 18% with Ti O2. Moreover, the photocatalytic reaction rate ofGQDs/Ti O2 were 18.4, 15.2 and 3.3 times larger than that of GQDs, Ti O2, Cd Se/Ti O2, respectively. The results proved that the GQDs’ s stability is perfect and do not occur photooxidation. In addition, we used cyclic voltammetry method to explore and analyze the cause of improving of photocatalysis.