Lakhasly

‏sotherms Studies. For isotherms studies, 0.01g of either ZnFe2 O4 , NiFe2 O4 , or CoFe2 O4 ferrite samples was mixed with 10 mL of aqueous solution at pH = 2 for different concentrations of Pb(II) (10, 40, 80, and 100 mg/L). Then, the mixtures were shaken for 180 min in a rotary shaker at room temperature. This pH value was chosen in order to avoid metal precipitation and also because of the high yield shown at this value. The supernatants were centrifuged at 4500 rpm for 5 min and decanted. The concentration of lead metals in the supernatant was analyzed by AAS.
‏Langmuir and Freundlich isotherm models are com- monly used by various researchers to describe the equilib- rium of heavy metal ions between solid and solution phases [35]. This allows determining whether the sorption is of a monolayer or multilayer nature, which can be specifically useful to predict the type of adsorption mechanism involved. The Langmuir isotherm model considers that the binding sites are homogeneously distributed on the adsorbent surface and the adsorption takes place at specific homogeneous sites within the adsorbent. The Langmuir equation is expressed as
‏𝑞𝑒 = 𝑞𝑚𝐾𝐿𝐶𝑒 , (7) 1+𝐾𝐿𝐶𝑒
‏where 𝑞𝑒 is the amount adsorbed at equilibrium (mg/g), 𝐶𝑒 is the equilibrium concentration (mg/L), 𝐾𝐿 is the Langmuir constant related to the affinity of binding site (L/mg), and 𝑞𝑚 is the maximum amount of solute adsorbed (mg/g). The constants in the Langmuir isotherm can be obtained from the slope and intercept by plotting (1/𝑞𝑒) versus (1/𝐶𝑒) and making use of the above equation rewritten as
‏1111 𝑞=𝑞+𝑞𝐾⋅𝐶. (8)
‏𝑒𝑚𝑚𝐿𝑒
‏On the other hand, the Freundlich isotherm is commonly used to describe the adsorption on the heterogeneous surface. The mathematical expression for the Freundlich isotherm is given as
‏Constants 𝐾𝐹 and 𝑛 are obtained from the slope and intercept of the plot of ln(𝑞𝑒 ) versus ln(𝐶𝑒 ).
‏2.4. Characterization Techniques. The structure and phase identification of CoFe2 O4 , NiFe2 O4 , and ZnFe2 O4 ferrite samples were done by X-ray diffraction. For this purpose, an APD 2000 PRO X-ray diffractometer was used. XRD patterns of the materials were obtained using CuK𝛼 radiation (𝜆 = 1.5418A ̊) at 35kV and 25mA and a variation of 2𝜃 = 10∘ to 70∘, with a scanning speed of 0.025deg/s and a step time of 10 s. The Fourier transformed infrared (FTIR) technique was conducted using a Nicolet Nexus 670 FTIR infrared spectrometer within a range from 4000 to 400 cm−1 with a resolution of 4 cm−1 in a KBr wafer. Micro-Raman spectra were recorded with an Almega XR dispersive Raman spectrometer. An Olympus microscope, 50 and 0.85NA (numerical aperture), was used for focusing the laser on solid samples. Raman spectra were accumulated over 25s with a resolution of 4 cm−1 . The excitation source was 532 nm radiation from a Nd:YVO4 laser (frequency-doubled) and the laser power on the sample was 5 mW. Magnetic properties were examined using a Quantum Design PPMS DynaCool-9 System with a vibrating sample magnetometer (VSM) option. Isothermal magnetization (𝑀) versus applied magnetic field (𝐻) measurements, were performed at 300 and 10 K using fields up to ±80 kOe. Saturation magnetization 𝑀𝑠 values were calculated through the interception of 𝑀 versus 1/𝐻 curve with the vertical axis.)