Synthesis And Characterization Of Graphitic Carbon Nitride

The compound carbon nitride, which was born in the eighties of twenty century, was predicted that it owned the hardness comparable to diamond, as well as the good toughness and good friction, electronics, chemical properties. These characteristics make it a wide range of applications in the electronic excitation device, variable band semiconductors, hard transparent films, and so on. For nearly two decades, carbon nitride both in theoretical calculations and in experiments on synthesis has become a hot research and obtains the corresponding results. In theory, at least five structures of this compound have been predicted, namely: graphite phase,α-phase,β-phase, quasi-cubic phase and cubic phase. As the hardness is concerned, only the cubic phase in these five structures can be comparable to diamond, but it is also the most difficult in the experiment on preparation. Experimental workers are competing to prepare for the most hard material in the world, but it was reported that no one can really prepare such a cubic phase structure, the synthesis of almost all are most likely the structure of the graphite phase, and their synthesis methods not only are vary, but also have a very harsh synthetic conditions.These theses give two relatively easy implementation of the synthesis method: high-energy ball milling method and solvothermal method. Both of these methods are simple, no harsh synthetic conditions, and the synthesized graphite-like carbon nitride was better in crystallinity. Control of the synthesis conditions can change the morphology of synthetic samples. The authors assert that these two synthetic methods will be widely used in synthesizing carbon nitride and even other substances.At the high-energy ball milling experiments, we used cyanuric chloride (C₃N₃Cl₃) and lithium nitride (Li₃N) as the precursor, and trickled-down a few drops (about 5 ml) acetone to make precursors to become mushy at ball milling process. Samples generated from milling were annealed at low temperature. After dealing with solvents, it was the graphite-like carbon nitride. Powder X-ray diffraction data indicate that the no treatment samples contain the by-products LiCl and an intermediate product with tetragonal structure, according to the type and the elements of precursor; we can infer that the inevitable product of the middle contains carbon and nitrogen at least. The treatment samples have to be our synthetic graphite-like C3N4. And the sample washed with diluted hydrochloric acid can not only see a clear diffraction peak (002) of graphite-like C₃N₄, but also can see the crystal face (101) and (102) diffraction peaks. Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy give the synthetic samples of different inter-atomic bonding state, found in full compliance with the graphite-like C₃N₄ bonding characteristics with carbon atoms in the form of sp2 hybrid combination with the nitrogen atom, and nitrogen atoms have two types of bond status with carbon atoms. Transmission electron microscope photographs give the morphology of the sample; found that samples washed with distilled water mainly exist in the leaf-like structure and the form of nanoparticles, and leaf-like structure constituted by nano-particles; samples washed with diluted hydrochloric acid are mainly the diameter of 200-300 nm quasi-spherical particles.In the solvothermal synthesis experiments, we used cyanuric chloride (C₃N₃Cl₃) and sodium azide (NaN₃) as precursors, using distilled water, CCl₄ and benzene as a solvent respectively, to carry out a number of experiments. Does the water solvent for the synthesis of white powder, powder X-ray diffraction data give the synthetic samples in good condition for the crystallization of g-C₃N₄, elemental analysis give a high internal N content of samples, FTIR and XPS data confirmed the internal samples sp2C structure and two different combination of N, but also give the C-C structure of sample surface and amino or imino of the internal structure. CCl4 as solvent, crystallization status of the synthesized samples is very well, small particle size of graphite-like C₃N₄. Characterization of different means give a combination of the internal atomic state, as well as the morphology of samples in the synthesis process. Elemental analysis gives the slightly higher N, C ratio result (1.63) than theory. The mixed liquid H2O and CCl4 as solvent, synthetic samples are significantly fewer samples and the crystallization degree is better than when a single solvent. FTIR and XPS also give a similar conclusion. But N element is relatively less in the XPS. The results generated by benzene thermal reaction are a noticeably different with the above conclusions. Although the synthesized samples are also the graphite-like C₃N₄, the Samples in N, C content and the ratio of two atoms are a clear distinction. N, C elemental ratio in the aynshesized samples (0.94) is serious lower than theoretical value (1.33). Other characterizations give a reason for such a result, caused by benzene carbonation. Transmission electron microscopy gives the cavernous nanofibers structure for the main morphology of the sample.High-temperature treatment of graphit-like C₃N₄ gives the Change of g-C₃N₄ at a high temperature. With increasing temperature, powder X-ray diffraction data in other diffraction peak of the graphite phase C₃N₄ did not occur. In contrary, the characteristics diffraction peak (002) hasn't become relatively obvious, which indicate the degree of crystallinity even worse, and then cause calculated particle diameter became smaller. By weighing the quality change of the samples, one can see the sample has a quality loss at about 200℃and a most obvious mass loss at 600℃. These two mass losses are internal water molecules losses and the decomposition of C₃N₄ samples respectively. TGA curves confirm our conclusion, and it is not set in stone and the quality of the sample should be gradually lost between 200-600℃. XRD analysis of the remaining material on the wall of quartz tube finds that the gradually lost quality of internal samples should be NH4Cl and a small amount of g-C₃N₄. This shows that there are two main movements for the samples after treatment at high temperatures: 1, volatilization with NH3 and HCl decomposition from NH4Cl to the low temperature zone on the wall; 2, high temperature treatment makes them eventually decomposed into carbon and nitrogen.To summarize, we synthesize graphite-like C₃N₄ making use of high-energy ball milling technology and solvothermal methods. A variety of characterizations further confirmed our conclusions, and found the different methods of treatment, as well as using the different solvent can give the different morphologies of graphite-like C₃N₄ powders. The rapid development in science and technology today, to master one of the most effective ways to solve the problems encountered in experiments are of critical. The above two methods should be most effective, so in future they should be widely adopted in the field of synthesizing C₃N₄ phase, even other materials'industry.