Preparation,Photoluminescence Mechanism And Ion-Dtection Studv On Fluorescent Graphene

It is of great important to prepare graphene-based materials with optical bandgap for its development and application in optoelectronics. Deeply understanding the underlying mechanism of fluorescent graphene-based materials and preparing highly luminescent graphene-based materials with high photoluminescence quantum yield (PLQY) also have guiding significance and urgent necessity for their utilization in optoelectronics and biology. In this thesis a new photoluminescence (PL) mechanism was proposed through the systematic research on the PL behaviors of chemically derived fluorescent graphene oxide (GO). Doped graphene quantum dots (GQDs) with relatively high PLQY were successfully prepared via a modified method and their application for selective metal ion detection was also demonstrated and preliminary discussed. The main research contents are described as following:(1) GO was prepared via a modified Hummers method, the PL behaviors of GO washed by different times were discussed and compared in detail, which including the PL excitation (PLE)-dependent, excitation-emission relationship, PL under various pH, transient state PL and so on. Combined with meticulously observing the condition under various pH and the corresponding elemental analysis, and with the contrastive analysis on the energy level of Mn2+and GO, a novel Mn2+ -mediated energy transfer process which may present as a versatile origin in luminescent GO was proposed for the first time, and a multi-energy level was also established to interpret the overall PL behaviors observed in the experiments.(2) Nitrogen-doped (or nitrogen, sulfur co-doped) GQDs were successfully prepared via a novel modified hydrothermal method started with GO and urea (or thiourea). The prepared doped-GQDs with an average size less than 10 nanometers have similar PL behaviors and their blue PL emission (-450nm) is excitation-independent. The PLQY are up to 25% and 31% for nitrogen-doped and nitrogen, sulfur co-doped GQDs, indicating their huge application potential.(3) The optical responses of the above as prepared doped-GQDs to different metal ions with various concentration in aqueous showed significant difference, it turned out that they have pretty good selective detection to Fe3+, with a theoretical detection limit of≈50nM. The mechanism of the selective detection is also preliminarily explored.