In this work, l-tyrosine modified magnetite nanoparticles (TMNPs) are prepared by a facile ultrasound assisted solution route and used for adsorption of both methylene blue (MB) and methyl orange (MO), the typical cationic and anionic dye, respectively. The as-prepared magnetic adsorbents TMNPs are characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), Brunauer–Emmett–Teller (BET), Fourier transform infrared (FT-IR), and vibrating sample magnetometer (VSM). The influential factors (solution pH and contact time) to the adsorption of the dyes by the magnetite nanoparticles are investigated. The adsorption kinetics illustrates the suitability of employing the pseudo-second-order kinetic model. Three isothermal adsorption models (Langmuir, Freundlich, and Temkin) are tested to investigate the adsorption properties. The results show that the adsorption behavior fits quite well with the Langmuir model. Thermodynamic parameters (ΔG°, ΔH°, and ΔS°) are estimated and implied that the adsorption process is spontaneous and exothermic in nature. Moreover, TMNPs can be successfully regenerated and reused for at least five cycles without compromising the adsorption capacity, which is greatly reduced the using cost.

In this work, carboxyl functionalized magnetite nanoparticles (CMNPs) are developed for the adsorption of Pb(II), Cd(II), and Cu(II). The characterization of CMNPs was performed by Fourier transform infrared spectroscopy, powder X-ray diffraction, and transmission electron microscopy. Studies show that the adsorption kinetics are found to follow the pseudo-second-order kinetic model. The experimental equilibrium adsorption data are fitted well to the Freundlich model. The maximum adsorption capacity at 25 °C could reach up to (74.63, 45.66, and 44.84) mg g–1 for Pb(II), Cd(II), and Cu(II), respectively. Thermodynamic analyses show that the adsorption is exothermic and spontaneous, and thermodynamic parameters, ΔG, ΔH, and ΔS, are calculated. In addition, CMNPs can be used as the recyclable adsorbent for the adsorption of Pb(II), Cd(II), and Cu(II) from aqueous solutions.