Two-dimensional (2-D) exfoliated nanomaterials have attracted tremendous attentions because of the unique surface structures and increased reactive sites for various applications. Herein, a one-step pyrolysis method was used to fabricate ultrathin C3N4 photocatalysts, which had significant advantages over conventional post-exfoliation strategies with labor-intensive and time-consuming procedures. We found that oxygen doping by atmospheric air could effectively break the interlayer and intralayer interactions in polymeric C3N4, forming 2-D ultrathin nanocatalysts with high activity for persulfate activation. The integration of photocatalysis and persulfate oxidation resulted in 21- and 15-fold enhancement in the degradation of Bisphenol A pollutants compared to the individual reactions. The significant contributions of atmospheric oxygen doping to the charge separation and surface reactions were fundamentally investigated. This work not only provides a facile strategy to exfoliate polymeric semiconductor into ultrathin nanostructures, but also reveals valuable insight into the exploration of high-performance catalysts for the synergistic removal of environmental contaminants. (C) 2020 Published by Elsevier Inc.