This study presents a sustainable route for fabricating a novel ZnO/EuFeO3 nanocomposite via an eco-friendly sol–gel process employing aqueous extract of Salvinia molesta (Kariba weed) as a natural hydrolysis and capping agent. Phytochemicals such as alkaloids, saponins, and steroids facilitated the formation of ZnO and EuFeO3 nanoparticles and their assembly into a heterostructured composite. Structural and optical analyses (FTIR, UV–Vis DRS, XRD, FESEM-EDS, HRTEM, XPS, and PL) confirmed successful composite formation and heterojunction establishment. The nanocomposite displayed a reduced band gap (2.08 eV) compared with ZnO (3.12 eV) and suppressed electron–hole recombination, indicating efficient charge separation. Under visible light, the material achieved 90.30 % degradation of malachite green with a pseudo-first-order rate constant of 6.00 × 10−3 min−1, significantly outperforming pristine ZnO (64.03 %) and EuFeO3 (74.68 %). This optimal performance was confirmed across various conditions and demonstrated stability despite the presence of common co-existing anions, with all critical degradation experiments to ensure accuracy. Band structure analysis and XPS results revealed a Z-scheme charge transfer pathway within a Type-II heterojunction, enabling effective separation of photoinduced charges. Scavenger studies further confirmed the dominant role of ●OH− radicals and holes in dye oxidation. This work demonstrates the dual novelty of utilizing an invasive aquatic weed as a sustainable precursor and introducing the ZnO/EuFeO3 composite as a new Z-scheme photocatalyst, highlighting its strong potential for wastewater remediation. © 2025 Elsevier Ltd