Photodegradation of organic pollutants by synthesis of g-C3N4 derived from different precursors

In recent years, there has been a great increase in environmental pollution problems worldwide. The increase in water pollution negatively affects ecosystems and human health. In particular, dye waste originating from the textile industry raises great concerns about water pollution. Effectively eliminating pollution in water is important in terms of protecting the environment against the harms that pollutants cause to humans and living organisms. Physical, chemical and biological methods are used in the treatment of textile wastewater. Physical methods mainly include sorption processes. When these methods are used, a secondary waste occurs by accumulating pollutants on the solid. Chemical methods are generally based on oxidation, and organic compounds are oxidized to water and carbon dioxide or some other products such as alcohols, aldehydes, ketones and carboxylic acids that are easily biodegradable. Photocatalytic treatment technologies using heterogeneous photocatalysts are a technique that absorbs light (UV or visible) to create electron-hole pairs and degrade the dye. It has a great advantage in the treatment of dye-polluted wastewater due to its environmental friendliness, complete degradation of dye molecules, high efficiency and not creating secondary waste. The aim of this study is to investigate the synthesis of g-C3N4, which is used as a photocatalyst in the visible region degradation of dye pollutants in water, from different precursors (Urea and Melamine). Thermal condensation method was used for the synthesis of g- C3N4 from Melamine and Urea. The optimum synthesis condition for the synthesis of urea and melamine, which were selected as starting materials for g- C3N4 synthesis, was determined according to the degradation of 20 ppm methylene blue at different temperatures (500, 525, 550, 575 and 600 °C), heating rates (1, 2, 5 and 10 °C/min) and times (2, 4, 6 and 8 hours) by thermal condensation. All synthesized catalysts were characterized by crystal structure, surface properties, and elemental analysis. The (100) and (002) structures were confirmed for typical g- C3N4 in the crystal structure by XRD analysis. According to the elemental analysis results, the C/N ratio is in the range of 0.55-0.60 on average, unlike the value of 0.64 reported in the literature. In the syntheses carried out with urea, an increase in surface area, pore volume, and pore size was observed with increasing temperature and time. As a result of the experiments carried out with 50 mL of 20 ppm methylene blue in the experimental setup consisting of a 500 W LED light system, the highest methylene blue degradation was obtained from the sample subjected to thermal condensation at 575 °C for urea at a heating rate of 1 °C/min in 4 hours, and for melamine at 600 °C at a heating rate of 5 °C/min in 2 hours.