Abstract: To improve the visible light utilization of graphitic carbon nitride(g-C₃N₄), K⁺ doped g-C₃N₄ (CN-K_x) are fabricated via one-step thermal condensation through the simultaneous heating of urea and potassium hydroxide. XRD, SEM, TEM and EDX mapping analysis demonstrate that K⁺ is successfully doped onto g-C₃N₄; the FTIR and XPS analysis results confirm the formation of cyano groups on the surface of the g-C₃N₄; PL spectra, EIS and the transient photocurrent response indicate the synergistic effect of the cyano groups and K⁺, which favors the separation and transfer of photogenerated electron-holes for boosting photocatalytic activity. The experiments prove that the rhodamine B (RhB) removal rate of optimized CN-K_0.009 sample is 100% within 80 min; its degradation rate (k) is 0.054 min^-1, 4.2 times that of pristine CN (k=0.013 min^-1), and its RhB removal rate is 100% within 80 min; further band analysis suggests that the bandgap of CN-K_0.009 reduces from 2.67 eV (for CN) to 2.59 eV owing to K⁺ assisted polymerization enhanced visible light harvesting and carriers′ transportation. Kinetic investigations reveal that superoxide radicals and holes (h⁺) dominate the oxidation process of RhB. Moreover, the CN-K_0.009 can be expanded to efficient degradation of many organic pollutants, such as basic fuchsin (91.7%), Congo red (85.7%) and tetracycline (74%).