<p>This study successfully synthesized heterogeneous SrMoO₄/g-C₃N₅ nanocomposites photocatalyst using a simple hydrothermal method. The optical, structural, and catalytic properties of the proposed catalyst were studied. The photocatalytic activity of the heterogeneous SrMoO₄/g-C₃N₅ nanocomposite catalyst was assessed for the degradation of CR dye under irradiation with visible light (λ &lt; 400&#xa0;nm). The SrMoO₄/g-C₃N₅ photocatalyst has proven to be an excellent catalyst for the degradation of CR dye. The specified consequences indicate that effectively integrating dispersed SrMoO₄ nanoparticles with a g-C₃N₅ matrix can enhance visible-light absorption capacity, increase specific surface area, reduce the mobility of photogenerated charge carriers, and significantly improve the photocatalytic properties of the system. The SrMoO₄/g-C₃N₅ nanocomposite photocatalyst achieved 82% photodegradation of CR dye after 90&#xa0;min, with a sustained degradation rate of 0.0197&#xa0;min^− 1, which is approximately 6 and 1.5 times superior to that of SrMoO₄ and g-C₃N₅ nanomaterials, respectively, under visible light irradiation and thus the SrMoO₄/g-C₃N₅ nanocomposite is demonstrated high photocatalytic activity which follows Z-scheme mechanism. The trapping test confirmed that ^˙O₂⁻ radicals are the predominant reactive species in the catalytic process. A plausible mechanism for catalysis by the SrMoO₄/g-C₃N₅ nanocomposites was demonstrated. A degradation mechanism was suggested based on LC-MS characterization of the reaction intermediates. The SrMoO₄/g-C₃N₅ nanocomposites demonstrated stability, ease of recovery, and recyclability with minimal loss of activity, contributing to sustainable photocatalytic advancements in effectively degrading organic pollutants in environmental wastewater treatment and energy conversion.</p> Graphical Abstract <p></p>