Novel Ag₂CO₃/AgX heterojunctions are achieved from the surface modification of Ag₂CO₃ with AgX (X = Cl, Br and I) nanoparticles by a facile and efficient ion-exchange method, which distinctly enhances the degradation activity for typical RhB, MB, and MO dyes compared with Ag₂CO₃. The formation of the heterostructure is evidenced by XRD, SEM, EDS, XPS and UV-vis DRS analyses, which indicates the bonding interaction between Ag₂CO₃ and AgX reduces the potential transfer barrier of charge carriers on their interface and extends visible light harvesting at 480–640 nm. Photocurrent responses and PL spectra demonstrate the Ag₂CO₃/AgX heterojunctions can effectively separate electron–hole pairs and suppress their recombination. The dye sensitization effect indicates that the effective electronic injection from RhB to the heterojunction is in favor of improving the photocatalytic ability. The possible transferred and separated behavior of electron–hole pairs and photocatalytic mechanisms are illustrated in detail.