<p>The Surface Plasmon Resonance (SPR) effect and the construction of Z-scheme heterojunctions are critical for enhancing photocatalytic rates. Herein, a composite material composed of a Z-scheme heterojunction structure, AgInS₂/g-C₃N₄ (AIS/GCN), was developed and further optimized through the modification of Ag nanoparticles (Ag NPs). The SPR effect of Ag NPs significantly improved the electron transfer characteristics of GCN, leading to enhanced separation efficiency of electron-hole pairs. By leveraging the advantages of the Z-scheme heterojunction, the composite not only effectively enhanced charge carrier separation but also improved light absorption and increased the density of active catalytic sites. To evaluate the photocatalytic degradation efficiency of Rhodamine B (RhB) and the photoreduction efficiency of Cr (VI) using the Ag/AIS/GCN nanocomposite, a systematic characterization analysis was conducted. The results demonstrated that the degradation rate and photoreduction efficiency of the Ag NPs-modified AIS/GCN Z-scheme heterojunction composite were 5.30 times and 7.22 times higher than those of pure GCN, the TOC removal rate of the sample reached 56.19%. The incorporation of Ag NPs and AIS significantly enhanced light energy utilization efficiency, increased the number of surface-active sites, and improved charge carrier transport rates. This study illustrates that the combination of the SPR effect and Z-scheme heterojunction construction markedly enhances the efficiency and stability of the photocatalyst, indicating the broad potential applications of this composite in dye purification and heavy metal removal.</p> Graphical Abstract <p></p>