Fe₃O₄-Based Nanocomposites: Preparation And Its Application In Adsorption Removing Of Heavy Metal Ion From Aqueous Solution

Due to high chemical toxicity, bio-accumulative effect, without self-purification ability, easy migration and transformation, the heavy metal pollution has brought a serious threat to the ecological environment and human survival. Heavy metals pollution and treatment have attracted intensive attention all over the world. In this work, Fe₃O₄-based nanomaterials were prepared and used for adsorption removing heavy metal ions from aqueous solution.Carbon biomass materials, graphene and metal oxide were used to hybridize with Fe₃O₄ to improve its adsorption performance, which was charactized by using Cr（VI）and Cu（II） as the target pollutants.Fe₃O₄, Fe₃O₄/Pinecone, Fe₃O₄/Graphene, Fe₃O₄/TiO2, Fe₃O₄/TiO2/Graphene adsorbents were prepared by hydrothermal method. The effect of reaction conditions,such as the reactants composition, reaction temperature and reaction time, on the adsorption performance of the adsorbents were discussed. The nanocomposites were characterized by X-ray diffraction（XRD）, scanning electron microscopy（SEM） and N2 adsorption-desorption isotherm. The adsorption activities of the adsorbents were evaluated by using heavy metal ions, such as Cr（VI） and Cu（II） as target contamant.The kinetics, such as pseudo-first-order kinetic, pseudo-second-order kinetic, and isotherm models（Langmuir model, Freundlich model and Temkin model） were used to investigate the adsorption mechanism for heavy metal removal. There were threesteps in the adsorption process, such as the instantaneous adsorption step, the intraparticle diffusion and the final equilibrium stage. It was inferred that the adsorption removal mechanism of the Fe₃O₄-based composite adsorbents for heavy metal ions was mainly physical process, The investigation details were listed as follows.（1） The single-phase cubic nano-Fe₃O₄ adsorbent was prepared through hydrothermal method by using FeCl3?6H2O as the iron source. The adsorption activities were investigated by using Cr（VI） as a target pollutant. The typical spherical nano-Fe₃O₄ adsorbent obtained at reaction conditions of 200 ℃ and 8h,was used for the removal of 50mg?L-1 Cr（VI） from aqueous solution. It reached adsorption equilibrium in no more than 3h, and the removal efficiency for Cr（VI）was 78%. The maximum adsorption capacity was 39.5 mg?g-1. The kinetics and isotherm study showed that the pseudo-second-order kinetic and Langmuir isotherm models could well fit the adsorption data. In no more than 5h, about 96% Cr（VI）were desorbed from the surface of Fe₃O₄, which indicated the adsorption-desorption process for Cr（VI） was reversible.（2） Fe₃O₄ nanoparticles hybridized with carbonaceous materials, such as Pinecone and Graphene, were successfully synthesized by a facile hydrothermal method, which could be applied for Cr（VI） removal in aqueous solution. Due to the combination of pinecone and graphene, both the surface properties and morphologies of Fe₃O₄ were modified. The specific surface area increased from23.85 to 27.86 and 121.17 m2·g-1 for Fe₃O₄/P and Fe₃O₄/G respectively. It enhanced the adsorption capacity for Cr（VI） of Fe₃O₄/P（62.5mg·g-1） and Fe₃O₄/G（78.8mg·g-1）. The kinetics and isotherm study showed that the pseudo-second-order kinetic and Langmuir isotherm models could well fit the adsorption data. There were three steps in the adsorption process, such as the instantaneous adsorption step, the intraparticle diffusion and the final equilibrium stage. The reaction rate decreased along with temperature increasing, which indicated the adsorption for Cr（VI） was an exothermic process. The Ea were 25.77 and 34.92 kJ·mol-1 for Fe₃O₄/P and Fe₃O₄/G respectively, which illustrated the adsorption of Cr（VI） onto the surface of nanocomposite was a physical process. In no more than 5h, about 92.6% and 94%Cr（VI） were desorbed from the surface of Fe₃O₄/P and Fe₃O₄/G, respectively, which indicated the adsorption-desorption process for Cr（VI） was reversible, The results demonstrated that Fe₃O₄/P and Fe₃O₄/G exhibited excellent adsorption performancein the removal of Cr（VI）.（3） A novel magnetic Fe₃O₄/TiO2 nanocomposite was synthesized by a facile hydrothermal method, which was used as environmental remediation to remove Cu（II） contaminant in aqueous solution. The specific surface area of Fe₃O₄/TiO2 was32.31m2?g-1, which lead to the excellent adsorption capacity for Cu（II）（58.29mg?g-1）. The Ea was 37.62 kJ?mol-1 for Fe₃O₄/TiO2, which illustrated the adsorption of Cu（II） onto the surface of ternary nanocomposite was a physical process. In no more than 5h, about 91.44% Cu（II） were desorbed from the surface of Fe₃O₄/TiO2,which indicated the adsorption-desorption process for Cu（II） was reversible.（4） A novel magnetic Fe₃O₄/TiO2/Graphene（FTG） ternary nanocomposite was synthesized by a facile hydrothermal method, which was used as environmental remediation to remove Cu（II） contaminant in aqueous solution. The specific surface area of FTG was 422.84 m2?g-1, which lead to the excellent adsorption capacity（67.4 mg?g-1） for Cu（II）. The adsorption kinetics and isotherm study showed that the pseudo-second-order kinetic and Langmuir isotherm model could well fit the adsorption data. There were three steps in the adsorption process, such as the instantaneous adsorption step, the intraparticle diffusion and the final equilibrium stage. The reaction rate decreased along with temperature increased, which indicated the adsorption for Cu（II） was an exothermic process. The Ea was 17.32 kJ?mol-1 for FTG, which illustrated the adsorption of Cu（II） onto the surface of ternary nanocomposite was a physical process. In no more than 5h, about 90.9% Cu（II）were desorbed from the surface of FTG, which indicated the adsorption-desorption process for Cu（II） was reversible.