Regulating the rate-determining step in photocatalysis is crucial for advancing its application in environmental remediation. However, approaches for tailoring the rate-determining step have been largely overlooked. Herein, Ca-intercalated g-C3N4 is designed as a model photocatalyst to deeply understand the electron transportation behavior and the mechanisms of photocatalytic NO removal. The intercalation of Ca builds an interlayer channel for electron migration between g-C3N4 layers, which extends the sp(2) hybridized planes and enables the electrons to transform from a delocalized state to a localized state around Ca, leading to the formation of localized excess electrons (e(ex)(-)). Under visible light irradiation, these e(ex)(-), are subsequently captured by gas molecules for more efficient reactive oxygen species (ROS) generation and reactant activation. The ROS generated by Ca-intercalated g-C3N4 demonstrate stronger oxidation capability than those generated by pure CN. The ROS directly participate in photocatalytic NO oxidation and tailor the rate-determining step by decreasing the reaction activation energies, resulting in an overall increase in NO removal efficiency and a reduction in NO2 production. The photocatalytic efficiency and selectivity have been significantly improved owing to the functionality of the e(ex)(-). Using closely combined experimental and theoretical methods, this work provides a new approach for understanding the behaviors of e(ex)(-) in environmental photocatalysis and tailoring the rate-determining step to enhance reaction efficiency, achieving efficient and safe air purification.