g-C3N4, preparation, characterization

The aim of this work was to prepare graphitic carbonitride g-C3N4 for adsorption purposes. The prepared material was characterized by available analytical techniques. The first step was thermal analysis of melamine decomposition. This precursor was used as the starting material for the preparation of graphitic carbonitride g-C3N4. The thermal analysis shows that the first significant weight loss occurs around 370 oC. The next step is about 550 oC, then the material is thermally stable up to about 700 oC. Total weight loss to 700 oC is approximately 70%. Graphitic carbonitride g-C3N4 was prepared by decomposing melamine in a closed crucible at 550 oC, decomposing for 2 hours. After cooling, the product was washed with ethanol and distilled water. The thermal analysis of the product showed the presence of moisture, however the product was stable up to 700 oC. Elemental analysis showed the following composition in weight percent: C 36%, N 63%, H 1%. The FTIR method also demonstrated the presence of N-H bonds. In order to eliminate the presence of hydrogen, a higher decomposition temperature of melamine was chosen as well as a longer pyrolysis time. The analysis of FTIR spectrum shows that the g-C3N4 is a graphitic mixture probably of C3N3 and C6N7 units. The specific surface area, pore volume and surface area were determined by adsorption/desorption of liquid nitrogen. The total surface area is 20 m2/ g, it is primarily a mesoporous material, the average pore width is 3.4 nm. Zeta potential has negative values throughout the pH range, with the exception of a very acidic area below pH 2.5. The negatively charged surface of the material gives good preconditions for adsorbing positively charged particles from a liquid medium, for example heavy metal cations.