Mechanistic investigation of nitrogen-doped carbon nanotubes for enhancing periodate reactions

In recent years, carbon catalysts have emerged as an efficient choice for green treatment of organic wastewater. Despite extensive research on carbonaceous materials in advanced oxidation processes, challenges such as low activation efficiency and limited reusability hinder their large-scale application. Therefore, a deeper understanding of the catalytic mechanisms of non-metallic carbon materials in advanced oxidation processes is crucial for optimizing their performance. In this study, nitrogen-doped carbon nanotubes are investigated as effective activators of periodate for the degradation of sulfisoxazole which is a sulfonamide antibiotic and a potential carcinogenic frequently detected in wastewater. Experimental results of this study demonstrated that under optimized conditions nitrogen-doped carbon nanotubes/periodate system attained 100% sulfisoxazole elimination efficiency within 20 min, with the apparent degradation rate increasing by up to 3.5 times as the nitrogen doping level increased. Comprehensive mechanistic studies involving quenching experiments, chemical probe analysis and electron paramagnetic resonance revealed two fundamental degradation pathways: 1) a radical pathway in which the graphitic nitrogen sites on nitrogen-doped carbon nanotubes significantly activated periodate to produce hydroxyl radicals and 2) a non-radical pathway, facilitated by structural defects of nitrogen-doped carbon nanotubes that mediate direct electron transfer between sulfisoxazole and periodate and continue to oxidize sulfisoxazole. This study highlights the potential of N-doped carbon nanotubes to enhance periodate-based oxidation and furnishes critical insights for the rational design of carbon-based catalysts in environmental remediation applications.