Sustainable Marine–Terrestrial Biogenic Ag-GO Nanocomposite for Enhanced and Reusable Photocatalytic Degradation of Bromophenol Blue

The development of reusable and efficient photocatalysts through sustainable synthesis strategies is of growing interest aimed at the treatment of dye-contaminated water. In this study, graphene oxide (GO) was synthesized and subsequently functionalized with silver nanoparticles using Sidr (Ziziphus spina-christi) and marine macroalgae (Ulva lactuca) extracts as biogenic agents to obtain an Ag-GO/UL-S nanocomposite. A distinctive feature of this approach is the integration of marine Ulva lactuca and terrestrial Sidr extracts as renewable biogenic resources during the fabrication of the Ag-GO nanocomposite. The structural, morphological, and optical characteristics of synthesized materials were verified using XRD, SEM, FTIR, and UV-Vis spectrophotometry. XRD analysis confirmed the characteristic layered structure of GO and the presence of crystalline Ag phases in Ag-GO/UL-S, while FTIR and SEM provided evidence of surface functionalization and morphological modification. The photocatalytic performance of GO and Ag-GO/UL-S was evaluated toward Bromophenol Blue (BPB) under UV irradiation. After 60 min of irradiation, GO achieved 63.95% BPB degradation, whereas Ag-GO/UL-S exhibited an enhanced degradation efficiency of 73.82%. The corresponding apparent first-order rate constants increased from 0.01534 min−1 for GO to 0.01846 min−1 for Ag-GO/UL-S, indicating an improved photocatalytic degradation rate following Ag incorporation and biogenic functionalization. Furthermore, the Ag-GO/UL-S photocatalyst retained 87.37% of its initial activity after five consecutive cycles, compared with 80.22% for GO. These results demonstrate that the incorporation of Ag together with Sidr and Ulva lactuca biogenic constituents enhances the photocatalytic performance and reusability of GO, highlighting Ag-GO/UL-S as a promising green-synthesized photocatalyst for the treatment of BPB-contaminated water.