Phytogenic magnetic nanoparticles (PMNPs) were fabricated using plant leaves' extract of Fraxinus chinensis Roxb. and then, the surfaces of the PMNPs were functionalized by 3-mercaptopropionic acid (3-MPA) to investigate the adsorptive removal of the toxic dye malachite green (MG) from aqueous solutions. The preparation and coating of 3-MPA on the surface of the PMNPs was confirmed and characterized using different techniques, which are UV-visible spectroscopy, Fourier transform infrared spectroscopy (FTIR), X-ray diffractometry (XRD), scanning electron microscopy with integrated energy dispersive X-ray analysis (SEM-EDX), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), vibrating sample magnetometry (VSM), Brunauer–Emmett–Teller (BET) analysis and thermogravimetric analysis (TGA). The hysteresis loops of 3-MPA@PMNPs depicted an excellent superparamagnetic nature with saturation magnetization values of 50.95 emu g⁻¹. The prepared material showed the highest adsorptive rate (98.57% MG removal within 120 min) and an estimated comparable adsorptive capacity of 81.2 mg g⁻¹ at 25 °C. The experimental data were well fitted to the Langmuir isotherm, indicating the monolayer adsorption of MG onto 3-MPA@PMNPs. Furthermore, the kinetic data agreed well with the pseudo-second-order model, indicating the removal of MG by chemisorption and/or ion-exchange mechanism. Thermodynamic study confirmed that the adsorption of MG was exothermic and spontaneous. The high adsorptive removal of the dye not only persisted over a wide pH range (6–12), but the material also demonstrated high selectivity in the presence of co-existing ions (i.e. Pd²⁺ and Cd²⁺) along with the fastest separation times (35 s) from aqueous solutions. The recovered adsorbent (3-MPA@PMNPs) was reused five times and maintained a removal efficiency of more than 85%. Therefore, the prepared novel 3-MPA@PMNPs can be employed as an alternative low-cost sorbent material for the removal cationic dyes from textile wastewater. In addition, this green nanotechnology/strategy can easily be implemented in low-economy countries for wastewater treatment.

Presently, there is an emerging research trend in the fabrication of Phytogenic Magnetic Nanoparticles (PMNPs) and their applications in the water/wastewater treatment (WWT), due to their dynamic morphology, desired size, super paramagnetic behavior and high saturation magnetization value. Green fabrication of PMNPs is clean, non-toxic, eco-friendly, fast and cost-effective as compared to other physico-chemical technologies, which make it a promising technology. However, certain aspects such as the optimization of the fabrication protocol in order to produce desired quality of PMNPs, regeneration and reusability, are the main hindrances in the transfer of this technology from the laboratory scale to the commercial applications. Therefore, the present study highlights the performance of PMNPs for the removal of aqueous pollutants from wastewater. In addition, the research developments of PMNPs regarding fabrication mechanism, regeneration and reusability for WWT are discussed. The study also provides a model of PMNPs based on zero effluent discharge and consequently, the WWT process is proposed. Finally, future perspectives and challenges are discussed to make PMNPs based green nanotechnology technically more feasible and economically sustainable.