Synthesis, Characterization And Applications Research Of Carbon Nitride

In 1989, Liu and Cohen proposed a hypothetic covalent carbon-nitrogen compoundβ-C₃N₄, on the basis ofβ-Si₃N₄ structure. According to this formula and on the basis of theβ-Si₃N₄ structure, the authors have claimed that it might have bulk modulus and hardness comparable to that of diamond. Then C₃N₄ has attracted considerable interest and attention from physicists, chemists and materials scientists, due to its unique mechanical, optical and tribological properties. Intensive experimental and theoretical investigations of C₃N₄ and other derived polymorphs have been performed.In this thesis, the literature related to research history, crystal structure and research state of carbon nitride are reviewed. Based on the reported work, a novel way to research on carbon nitride is proposed and systematic investigations have been carried out The major results are as follows:We firstly develop a new route called constant-pressure solvothermal synthesis, which is used in the synthesis of carbon nitride. In this reaction system, the reaction parameters, i.e., reaction temperature and pressure factors have been primarily discussed. Herein, graphite-like C₃N₄ (g-C₃N₄) nanocrystals have been synthesized by the reaction between C₃N₃Cl₃ and N₂H₄·2HCl. The process was carried out at 40 MPa (220,250,280℃) and 80℃(50,80,120 MPa), respectively. The results indicate that the temperature and the pressure play an important role in affecting the crystalline perfection and morphology of C₃N₄ products.The application of template-assisted method in the synthesis of carbon nitride nanocrystals and nanotubes has been explored. Herein, mesoporous molecular sieves (SBA-15) are used as the template. Nanocrystals of C₃N₄ have been prepared via the reaction of C₃N₃Cl₃ with NaN₃ at 300℃in DMF solution through constant-pressure solvothermal method. The introduction of SBA-15 improved yield and crystallinity of the desired products, indicating the functions of surface adsorption and coordination-catalysis of hydroxyls. In addition, carbon nitride nanotubes (CNNTs) have been synthesized with porous anodic aluminum oxide (AAO) membrane as template by the thermal polymerization of sol-gel precursors (600℃). Measurement on stability and electrochemical performance of carbon nitride nanotubes are carried out in 0.5 mol·dm^-3 H₂SO₄ and 0.5 mol·dm^-3 H₂SO₄ + 1 mol·dm^-3 CH₃OH in the conventional three electrodes system. The experimental results show that the nanotubes are stable and electrocatalytic for methanol oxidation to an extent.Graphite-like carbon nitride (g-C₃N₄) was prepared in large quantities at 300℃under nitrogen via the reaction of C₃N₃Cl₃ with NaN₃ by a solid-state reaction route, of which the structure and the composition were characterized. The electrochemical properties of g-C₃N₄ were studied using both cyclic voltammetry and charge-discharge recycling. It was found that the g-C₃N₄ sample showed certain reversible intercalation capacity of Li⁺, but the capacity was small and the recycling time was short. Furthermore, the intercalated carbon nitrides with Li⁺, Mg²⁺, Al³⁺, SO₄^2- and NO₃^2- as guest ions were prepared by electrolysis of carbon nitride powder in the saturated solution of lithium nitrate, magnesium sulfate, aluminum sulfate, potassium nitrate and potassium sulfate. In the experiments, the electron density within the layers was adjusted by changing the intercalation time, and the corresponding intercalation compounds were obtained. The structure, composition, morphology and thermal stability of intercalation compounds were characterized by X-ray powder diffraction (XRD), Fourier transform infrared spectra (FTIR), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and thermogravimetry (TG). The possible structure model of intercalation compounds is proposed. The cation-Ï€interactions and electrostatic interactions are used to explain the changes of microstructure and chemical bonds before and after intercalation.At last, g-C₃N₄/TiO₂ composite was prepared by hydrolysis of tetrabutyl titanase and the precursors of g-C₃N₄ at room temperature and annealing in nitrogen atmosphere. The structure and the composition of g-C₃N₄/TiO₂ were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and so on. The photocatalytic activity of g-C₃N₄/TiO₂ composite for the UV and visible-light degradation of Rhodamine B was studied. In summary, the experiment results presented here provide useful information on the synthesis, property, and application of carbon nitride.