Performance of sulfur-doped graphtic carbon nitride loaded onto activated carbon in activation of peroxymonosulfate to remove organic pollutants in water

Abstract

With the rise of pharmaceutical pollutants identified as emerging contaminants, it is essential that a cost-effective solution can be implemented to ensure these organic pollutants can be degraded effectively. In this project, various studies have been conducted to investigate how effectively heterogeneous catalyst sulfur-doped graphitic carbon nitride (S-doped g-C3N4) with activated carbon (AC) can activate peroxymonosulfate (PMS) to generate sulfate radicals to degrade sulfacetamide (SAM), a pharmaceutical pollutant, through advanced oxidation processes (AOP). Kinetic studies demonstrated that the catalyst has excellent performance in the presence of high elemental composition of nitrogen and sulfur and pH of 6.0 to 7.0. High catalytic loading of 0.3 g L-1 and high PMS loading of 0.4 g L-1 have high rate constant of 0.36 min -1and 0.17 min-1 respectively due to higher active sites with high catalytic loading and increased availability of sulfate radicals with increasing concentration of PMS. Radical process is proposed which catalyst effectively activates PMS to generate sulfate radicals to degrade SAM. The synergistic adsorption-degradation mechanism is also proposed where SAM is adsorbed onto the surface of catalyst, and sulfate radicals from PMS can effectively degrade SAM due to close proximity by non-radical process. Experiments were also carried out to investigate on the performance of the catalyst in the presence of water matrix species. Nitrate, chloride and phosphate showed insignificant results to degradation of SAM while bicarbonate shows low performance as the anion is an effective sulfate quencher implying weak performance of catalyst in the absence of sulfate radicals. Further studies also showed that catalyst has low durability, and performance dropped significantly after first usage, which can be attributed to pore plugging and intermediate deposits being formed on the surface of the catalyst.