Fabrication Of Novel Two-dimensional Nitrogen-rich Carbon Nanosheets With Tunable Nonlinear Optical Properties

Two-dimensional nanomaterials frequently exhibit unique properties superior to their bulk counterparts and have thus attracted ever-increasing interest. For instance, two-dimensional nitrogen-rich graphene and graphitic-carbon nanosheets demonstrate excellent electronic, optical and catalytic properties due to the conjugation between their extended π system and the lone pair electrons of N. In this dissertation, we developed facile methods to fabricate novel two-dimensional nitrogen-rich carbon nanosheets and chemically modified them via metal-doping. It is found that the nonlinear absorption characteristics of these materials can be conveniently tuned via chemical modification and/or acid-induced self-assembly, indicative of promising applications in optical limiting and laser protection. Specifically, the dissertation is organized as the following parts:1. We introduced the research background and reviewed previous literatures.2. We synthesized the nitrogen rich graphitic-carbon nanosheets (g-CN) by one-pot solvothermal method at lower temperature. The morphology and structure information of the as-synthesized nanomaterials were characterized by electron microscopy and spectroscopic methods. It was found considerable active "nitrogen-pots" existed on the g-CN nanosheets, which provided ideal sites to coordinate with metal ions.3. We synthesized the metal dopped nitrogen rich graphitic-carbon nanomaterials (M-g-CN) by adding extra metal ions to the reactants according to the above method. By varying the type and proportion of the metal ions, we obtained different types of metal containing carbon nanomaterials of Co-g-CN, Fe, Co-g-CN and Pb-g-CN. These materials which exhibited interesting acid induced self-assembly behavior, as evidenced by UV-Vis absorption and dynamic laser scattering measurement.4. We studied the nonlinear optical properties of the as-synthesized nanomaterials by Z-scan technique at the532nm incident laser wavelength. The results showed that the g-CN and M-g-CN dispersed in neutral aqueous solution exhibited saturable absorption when the incident energy was low, which however transformed to reverse saturable absorption at higher incident energy, and eventually returned to saturable absorption at highest energy. After the acid was added, the nonlinear optical response of all of the as-synthesized nanomaterials turned into enhanced reverse saturable absorption. The optical limiting performance of certain M-g-CN even surpassed that of C60a well-established benchmark with superior optical limiting properties.