Band structure and crystallinity engineering of polymeric semiconductors provides effective strategies for photocatalytic activity enhancement. Here, a facile one-step ionothermal method was developed to achieve the in situ growth of carbon nitride (CN) isotype heterojunctions (ms-CN-x) using KCl/LiCl eutectic salts as the high-temperature solvent and urea as the starting material, which are demonstrated to be efficient photocatalysts for removal of toxic heavy metal and organic pollutant in a single or coexisting system. The as-obtained ms-CN-x composite material appears as well-ordered nanorod structure with high crystallinity and consists of phases of both heptazine-based CN and triazine-based CN. With structural and morphological merits, the ms-CN-0.5 photocatalyst exhibits remarkable adsorption–photodegradation performance for high-level methylene blue (MB). Moreover, simultaneously enhanced photocatalytic reaction rate of Cr(VI) reduction and MB oxidation over ms-CN-0.5 are achieved and systematical...