Triple transition (Ni, Cu, and Zn) doped hematite nanoparticles (α-Fe2O3 NPs) have made significant advances in biological, environmental, as well as other interdisciplinary fields of study, due to their stability and relative lack of toxicity. The α-Fe2O3 NPs has been made simple, effective, and ecologically benign by utilizing the reducing and capping capability of Azadirachta indica aqueous leaf extract. Synthesized material has been studied by XRD, UV-visible, Raman, FTIR, VSM, SEM, and TEM techniques. Doped α-Fe2O3 NPs possessed a rhombohedral phase and corundum structure that was exceptionally pure and well crystalline. The synthesized α-Fe2O3 NPs had a size of 22.83 nm and were irregular-spheroidal in shape, according to SEM and TEM examination. Synthesized NPs show ferromagnetic characteristics, according to VSM research. The photocatalytic activity of doped α-Fe2O3 NPs was evaluated by methyl orange (MO) (95%), methylene blue (MB) (97%), congo red (CR) (92%), and eosin yellowish (EY) (90%) efficiently dyes degradation, when exposed to visible light for 90–100 minutes. As a result, the NPs are suited for applications where reusability is a crucial essential feature due to the modest drop in the photocatalytic activity after four cycles. This current study examines the effects of α-Fe2O3 NPs on the seed germination of Vigna radiata (mung bean) and phytotoxicity study biomass accumulation Allium cepa (onion) through a series of germination assays. For this reason, it is crucial to manage the materials size, morphology, and magnetic properties in order to produce well-tailored photocatalysts.