ZnTiO3, Sm2CuO4, and the ZnTiO3/Sm2CuO4 nanocomposite were effectively synthesized through an eco-friendly approach, utilizing pumpkin leaf extract (Cucurbita moschata (Duchesne)) as a natural base and capping agent. FTIR and XRD analyses verified the successful formation of crystalline phases, identifying ZnTiO3 with a rhombohedral structure and Sm2CuO4 with a tetragonal one. The average crystallite dimensions were calculated to be 40.008 nm for ZnTiO3, 44.111 nm for Sm2CuO4, and 31.116 nm for the nanocomposite. UV-DRS results showed that the nanocomposite's band gap energy was 2.77 eV, intermediate between ZnTiO3 (3.78 eV) and Sm2CuO4 (1.93 eV). FESEM-EDX and HRTEM imaging revealed a porous architecture in the nanocomposite with a homogenous distribution of elements and a mean particle size of 49.36 ± 18.71 nm. XPS analysis confirmed the existence of Zn2+, Ti4+, Sm2+/Sm3+, and Cu0/Cu2+, as well as interfacial interactions among the components. In testing its photocatalytic performance for degrading malachite green over 120 min, the ZnTiO3/Sm2CuO4 nanocomposite achieved the highest efficiency of 94.47 ± 1.02 %, outperforming its individual components. PL measurements suggested a significant suppression of electron-hole recombination in the nanocomposite. The degradation followed a pseudo-first-order kinetic model with a rate constant of 21.70 × 10−3 min−1. The nanocomposite also showed strong recyclability, retaining 77.04 % of its degradation capability after four cycles. A zeta potential value of −13.30 mV indicated improved dispersion stability and enhanced attraction toward the positively charged malachite green dye. ROS testing revealed that hydroxyl radicals (•OH) played a major role in the degradation pathway. These outcomes highlight the ZnTiO3/Sm2CuO4 nanocomposite's strong potential as a sustainable photocatalyst for the removal of organic pollutants. © 2025 Elsevier B.V.