Unzipping carbon nanotubes to nanoribbons for revealing the mechanism of nonradical oxidation by carbocatalysis

Graphitic multi-walled carbon nanotubes (MWCNTs) are controllably unzipped into edge-rich graphene nanoribbons to reveal the roles of edges and defects in persulfate activation for bisphenol A (BPA) oxidation. Enriched carbon edges remarkably enhance the catalytic performance and can serve as hosting sites for heteroatom (N, S) doping to promote carbocatalysis. A sample (NS-2) presented a complete BPA removal in 20 min at a rate constant of 0.182 min(-1). The rate constants were relating to the defect speciation in a negative correlation to an indicator (I-D/I-D') from Raman spectra. Excessive edges induce defects and structure transformation of sp(2) to sp(3), resulting in deterioration of the organic oxidation. Furthermore, unzipped MWCNTs were clarified to follow a nonradical electron transfer pathway by radical screening tests, in situ Raman and electrochemical characterizations. The unveiled mechanism emphasizes the importance of an essential graphitic degree and conductivity in the edge-enriched carbocatalysts for better catalytic performance.