<p>Modification of graphitic carbon nitride (g-C₃N₄), which is characterized by a small specific surface area, rapid recombination of photogenerated charge carriers, and low visible-light utilization efficiency, has remained a focal point of research. This study employs vermiculite as a hard template to synthesize g-C₃N₄. Subsequently, Mn²⁺ was doped into g-C₃N₄ by the hydrothermal method. The vermiculite as a hard template can regulate the size and morphology of precursor materials. Doping with Mn²⁺ introduces defect states that reduce the bandgap of the photocatalytic material, effectively suppressing the recombination of photogenerated carriers. The specific surface area, pore area-pore volume distribution, and total pore volume of composites were determined via physical adsorption. The morphological features and internal structure of the composites were characterized using scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD). Its photocatalytic performance was investigated through ultraviolet diffuse reflectance spectroscopy (UV–Vis–DRS) and photoluminescence emission spectra (PL). The electrochemical properties were analyzed via open-circuit potential measurements, electrochemical impedance spectroscopy (EIS), and photocurrent testing (I-t). Additionally, the carrier transport and recombination lifetimes were examined using microwave photoconductivity transient spectroscopy (MD-PICTS). Simulated wastewater with methyl orange solution was used to evaluate the photocatalytic activity of manganese-doped modified photocatalysts under visible-light conditions. Under the conditions of an oxidant (30% H₂O₂) dosage of 40&#xa0;mL/L and a photocatalyst (g-C₃N₄@MnSO₄) concentration of 2&#xa0;g/L, a degradation efficiency of 99.3% was achieved after 4&#xa0;h. This research offers valuable insights into the design of highly efficient visible-light-responsive photocatalysts for environmental remediation.</p> Graphical abstract <p></p>