The highly symmetrical structure of heptazine in C3N4 often results in charge localization effects, which hinder the migration of carriers and the formation of active sites. In this study, well-designed C3N4 materials were prepared with carboxylic acid edge sites (ECCN) through a simple polycondensation method. DFT calculations and experimental results demonstrate that the presence of edge COOH units significantly disrupts carrier delocalization on the C3N4 framework, leading to an enhancement of material polarization and inherent electric field. This enhancement facilitates charge transfer and exciton dissociation. Moreover, it exerts a substantial impact on the surface characteristics of ECCN, promoting electron exchange and molecular polarization for As(III). Consequently, it improves capabilities for oxidizing trivalent arsenic by 4 times compared to pure C3N4. Our research represents significant progress in photocatalytic degradation of harmful compounds and provides enhanced understanding regarding control over carrier dynamics and surface reactivity.