Criteria of active sites in nonradical persulfate activation process from integrated experimental and theoretical investigations: boron–nitrogen-co-doped nanocarbon-mediated peroxydisulfate activation as an example

Abstract

Carbon-catalyzed persulfate activation is a metal-free advanced oxidation process for abating aqueous organic micropollutants. Recently, the electron-transfer mechanism in the activation of peroxydisulfate (PDS) has attracted tremendous interest due to its unknown nonradical reaction pathways. The conventionally used atomic-scale descriptors of adsorption energy (E_ads), O–O bond length (l_O–O) and S–O bond length (l_S–O) cannot accurately reflect the ability of the functionalities of PDS in its activation. In this work, a new descriptor, local electrophilicity index (ω), which represents the oxidative capacity of adsorbed S₂O₈²⁻, was included to identify the intrinsic active sites in carbocatalysts via density functional theory calculations. To verify the reliability of the proposed criteria, the catalytic performances of a series of highly boronated and nitrogenated carbon nanotube/nanosheet composites (BCN-NT/NS) with tailored physicochemical properties were comparatively studied for activating PDS to degrade phenol. By integrating the computational and experimental results, the catalytic activity of BCN-NT/NS was determined to not only be related to the contents of heteroatom dopants (B and N), but also the positions of B and N in the co-doping configurations. This study offers reliable criteria for determining the intrinsic catalytic sites in carbocatalysts for the activation of PDS based on an electron-transfer mechanism, which assists the rational design of nanocarbons as advanced catalysts for metal-free oxidation and water remediation.