Weed to nano seeds: Ultrasonic assisted one-pot fabrication of superparamagnetic magnetite nano adsorbents from Siam weed flower extract for the removal of lead from water

•Superparamagnetic magnetite NPs were synthesized using Siam weed flower extract.•USMNs displayed rapid, selective adsorption towards Pb(II) ions.•99.6% of Pb(II) removal was attained in 10 min.•Exhausted adsorbents easily separated by magnetic field.•Excellent adsorption capacities retained after several consecutive cycles. A novel phyto-conjugated magnetite nanoadsorbent with appreciable adsorption capacity, minimal ionic interference, and economic reusability for the selective removal of Pb(II) in aqueous solutions have been proposed in this study. PXRD, SEM, surface charge analysis, XPS, TEM and vibrating sample magnetometry were used for the characterization of ultrasmall superparamagnetic magnetite nanoparticles (USMNs). The effect of contact time, adsorbent dosage, initial concentration of the pollutants, temperature, and pH on adsorption efficiency was investigated via adsorption batch experiments. It was observed that the pH of the medium controlled the adsorption process. The equilibrium for the adsorption of Pb(II) ions followed the Langmuir isotherm model. The maximum adsorption capacity recorded was 315.43 mg g−1 for Pb(II) ions. The adsorption process conformed well to pseudo first order kinetics as revealed by the high R2 value. The thermodynamic parameters revealed that the adsorption of Pb(II) ions onto the nanoadsorbents was spontaneous, feasible, and endothermic under the applied conditions. Exhausted USMNs were recovered by pH management and 92% efficiency was retained after 5 consecutive cycles. [Display omitted]