Abstract <p>A plate-like CoTiO_3/TiO₂ nanocomposite was synthesized via H₂O₂ pretreatment of layered hydrogen titanate (HTO) followed by Co²⁺ ion exchange and topotactic transformation. The H₂O₂ pre-intercalation expanded the interlayer spacing and introduced active peroxy groups, facilitating subsequent ion exchange. The resulting composite retained the plate-like morphology and exhibited enhanced visible-light photocatalytic degradation of rhodamine B (RhB). Under optimal conditions, the degradation efficiency reached 96.4%. A strong synergistic effect between the catalyst and peroxymonosulfate (PMS) was observed, significantly accelerating RhB removal. The catalyst also showed good reusability (&gt; 90% after 5 cycles). Structural, morphological, and optical characterizations (XRD, SEM, TEM, XPS, Raman, FTIR) were performed. This work provides a novel strategy for designing 2D heterojunction photocatalysts with efficient PMS activation.</p> Highlights <p>• A novel “H₂O₂ pre-intercalation–topotactic transformation” strategy is pioneered for the controllable synthesis of 2D CoTiO₃/TiO₂ heterojunctions.</p> <p>• A remarkable synergy between photocatalysis and PMS activation is achieved, leading to &gt;96% degradation efficiency of RhB with excellent cycling stability (&gt;90% after 5 runs).</p> <p>• The interfacial charge-transfer pathway and the dual-channel radical generation mechanism are unraveled, establishing a clear structure–activity relationship.</p> Graphical Abstract <p>Synthesis route (left) and Z‑scheme charge transfer mechanism with PMS activation (right) of the plate‑like CoTiO₃/TiO₂ composite.</p> <p></p>