| Polymeric semiconductor graphitic carbon nitride (g-C3N4) has received tremendous attentions due to global increasingly environmental, energy and security issues. g-C3N4 has unique electronic structure and excellent chemical inertness, and it is relatively low cost, environment friendly for no toxic substances released in the process of catalytic reactions. g-C3N4 has been widely used as metal-free catalyst or catalyst support for organic functional groups selective conversion, oxygen reduction reactions, photo-catalytic water splitting, and carrier of some precious metal catalysts (Au, Pd, Ag, and Pt, et al.). g-C3N4 has become more and more important in the fields of energy and materials.Herein, computer simulation was used to systematically investigate the basic properties of g-C3N4, so as to excavate the potential applications of g-C3N4 in theory. Besides, compositing and doping ultrasonic peeling, and microwave rapid synthesis methods were proposed to modify the pristine g-C3N4, and the photo-catalytic degradation performance of organic dyes was investigated, as well as the application in fluorescent sensing nitro aromatic explosives (NACs). Main contents of this master graduate dissertation include the following four points:1. First-principle calculation was used to systematically investigate the basic properties of g-C3N4, such as the cell structure, electron cloud distribution, band structure, density of states, thermal and optical properties, etc. The calculated results proved that g-C3N4 was direct band gap semiconductor, with the band gap of 2.7 eV. Besides, good thermal stability and obvious light absorption were observed, and the light absorption corresponds to σ and π transition. The maximum light absorption wavelength was 450 nm, which proved the wide absorption range of g-C3N4, and all these implied that g-C3N4 had potential applications in light-emitting devices, photo-catalysis, etc.2. Inorganic-organic hybrid NiO-g-C3N4 photo-catalysts with different NiO contents were prepared through a simple calcination method, where nickel acetate tetrahydrate and melamine were used as the precursors. And the NiO-g-C3N4 hybrid catalysts exhibited a significantly enhanced photo-catalytic activity in visible-light degrading MB, and the optimum hybrid catalyst (6.3 wt.% NiO) showed a 2.3 times enhanced MB degradation rate. The improved photo-activity could be ascribed to the effective interfacial charge transfer between NiO and g-C3N4, thus suppressing the recombination of the photo-excited electron-hole pairs. What’s more, excellent chemical stability in photo-catalytic degradation reactions was observed.3. Highly fluorescent g-C3N4 nanosheets were facilely fabricated by exfoliating bulk g-C3N4 under ultrasonic irradiation for 1 h. The atomic force microscopy (AFM) image shows that the resultant g-C3N4 nanosheets are ～6-14 nm thick, and the suspension is stable in air for several weeks. Remarkably, the obtained nanosheets exhibited strong fluorescence with an extremely high quantum yield (QY) up to 32%, and high sensitivity, selectivity, as well as a fast response to nitro aromatic explosives were observed. Typically, the quenching efficiency coefficient Ksv for PNP was 30 460 M"1, which proved that the resultant nanosheets possessed an extremely high sensitivity for nitro-phenol PNP detection.4. Microwave method was proposed for the synthesis of g-C3N4, and g-C3N4 was successfully prepared by this method. Over controlling the power, time, and content of heat-transfer agent (ZnCl2), combined with XRD, UV-Vis, and Fourier transform infrared spectroscopy (FT-IR), etc. detections, the optimum microwave synthesis conditions was determined to be microwave for 10 min under high profile, and melamine/ZnCl2 mass ratio was 1.2:1. HRTEM images and XRD spectrum proved that the microscopic structure of the as-prepared g-C3N4 has little difference with the calcined g-C3N4, except the slightly worse crystalline. Typically, the performance of degrading organic dye MB was as well as that of the calcined g-C3N4, and the catalytic mechanism was further confirmed over experiments. All these results demonstrate that microwave method for g-C3N4 preparation is feasible. |
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