Synthesis Of Functionalized Magnetic Nano-materials And Their Applications To Pollutants Removal From Water

Generally, Magnetic nanopaticles are composed of magnetic elements and themetallic oxides, such as iron, cobalt, nickel, etc. They are always coated with organicor inorganic shell to make them stable against oxidation, corrosion and aggregation.Because of the unique superparamagnetic property, high specific surface area,chemical stability and ease in synthesis, magnetic nanopaticles have attractedextensive attentions.The ability of functionalization by anchoring specific functional groups on thesurface makes possible the synthesis of different types of magnetic nanopaticles forthe removal of the contaminants from water. These nano-materials not only have alarge removal capacity, fast kinetics and high reactivity for contaminants removal dueto the high surface area and the functional groups, but also one more importantproperty, superparamagnetic. After the adsorption process, the multifunctionalnano-materials together with the adsorbed pollutants can be easily pulled by anexternal magnetic field from the solution.This work presents the performance of different types of magnetic adsorbtents inthe treatment of polluted waters with dyes and toxic microcystin-LR (MC-LR). Themain contents and conclusions are as follows:1. We prepared the organo-functionalized nanopaticles with the mesoporoussilica shell and magnetic core Fe3O4for removing anionic dye (Solvent green7) fromwastewaters. The nanopaticles were evaluated to be magnetizable, with a diameter ofabout290nm and an average pore diameter of2.57nm. Zeta potential data in the pHrange between2.0and10suggested that the magnetic nanopaticles were with positivecharge due to the modified cetyltrimethylammonium bromide on the magnetic core.Additionally, the nanopaticles exhibited a high adsorption capacity and separationconvenience, and therefore with the help of an applied magnetic field they can be usedas powerful adsorbent for anionic dye pollutants removal. The pseudo-second-order kinetic model provided the best correlation of the experimental data. Furthermore, theexperimental results showed that electrostatic interaction was the possiblemechanisms for the adsorption of Solvent green7. After extracted with anhydrousethanol, the adsorbent can be regenerated and reuse in dye removal. It can be usedrepeatedly for six times at least with a good adsorption capacity of294mg/g forSolvent green7.2. We prepared the hydroxyl-zirconium pillared bentonite material (Fe3O4@Zr-B)with Fe3O4nanopaticles on the surface by a simple solvothermal reaction. Itconfirmed that, in comparison to the conventional co-precipitation methods, themagnetic bentonite materials prepared by our strategy had a smoother surface, greatermagnetism and higher surface area. Fe3O4nanopaticles had a nearly uniform size ofabout200nm, and they created the homogeneous structures distributed on the surfaceof Fe3O4@Zr-B. Fe3O4@Zr-B then was developed for removing anionic dyepollutants, e.g., Congo red from wastewaters. The results showed that the as-preparedadsorbent exhibited high adsorption capacity, rapid adsorption rate and separationconvenience for anionic dye pollutants removal. The pseudo-second-order kineticmodel provided the best correlation of the experimental data. It indicated that theadsorption rate was determined by the number of the empty sites on the surface ofFe3O4@Zr-B. The Langmuir equation and Freundlich equation were used fordescribing the adsorption of Congo red by Fe3O4@Zr-B. Adsorption capacity ofCongo red onto Fe3O4@Zr-B was calculated to be63.29mg/g by Langmuir equation.3. We prepared a magnetic hydroxyl-aluminum pillared bentonite material(Fe3O4@Al-B) to remove MC-LR from water. Fe3O4@Al-B had a surface area of110m2/g and a saturation magnetization of36.18emu/g. Adsorption of MC-LR on themagnetic adsorbent increased with pH decrease, with a maximum adsorption at pH=2.1. The equilibrium adsorption data were also analyzed by using the Langmuir andFreundlich models to evaluate the adsorption capacity of magnetic adsorbent and aresult of161.29mg/g was achieved. At the same time, the Fe3O4@Al-B had a strongsurface affinity toward MC-LR both in Mili-Q water and river water samples.Therefore, Fe3O4@Al-B is an effective technology and has a great potential in removing MC-LR from drinking water resources.4. We examined the adsorption of MC-LR onto CoFe2O4microspheres fromwater. Factors influencing the adsorption behavior included MC-LR concentration, pHwere studied. The resultes showed that the adsorption capacity increased withdecreasing pH, with a maximum adsorption around pH=2.1. Adsorption of MC-LRon CoFe2O4microspheres was primarily attributed to coordination and electrostaticinteractions, although hydrophobic interactions may also play a role. Removal ofMC-LR from Songhua river samples showed that the adsorption was not significantlyaffected by the presence of salt and impurity in the solution due to the coordinationinteractions between the MC-LR molecules and CoFe2O4microspheres. Furthermore,the as-prepared adsorbent can be regenerated by simple washing with methonal andwater solution to recover both the adsorbents and MC-LR.In summary, several types of magnetic nano-materials were prepared through thenew synthesis methods and the products were successfully applied to removepollutants from water. This approach provided a simple and economical method forpreparation of multifunctional adsorbents possessing well magnetic responsibility anddispersibility in solvents. The adsorbents were also evaluated to bear excellentadsorptivity for dyes and biological contaminant (MC-LR). Although the techniquesstill have not been widely applied in water treatment systems, the functionnalmagnetic adsorbents were recommended for potential applications to remove dyes orbiological contaminants from polluted water. More importantly, the research andconclusion of relevant mechanism in this paper will provide some guidance for thefurther development of environmental friendly materials.