Study On Adsorptive Removal Of Organic Dyes And Metal Ions From Aqueous Solution Using Magnetic Carbon-based Composites

Three magnetic carbon-based composites were synthesized, characterized and thenwere applied to uptake several organic dyes and metallic ions from aqueous solution,including that magnetic carbon microsphere was used to adsorb MB, magnetic grapheneoxide composite was used to uptke MG, magnetic bamboo based carbon was used toremove Pb²⁺, Cd²⁺and Cu²⁺and the later two materials were used to decontaminate Cr（Ⅵ）for comparison. Influencing factors, adsorption properties and adsorptionmechanism of these magnetic complex materials were investigated, respectively. Themain dissertation results are as follow:（1）The magnetic composite （Fe₃O₄@C）, coated with carbon microspheres over themagnetic Fe₃O₄nanoparticle, was prepared, characterized and then applied for removalof organic dyes from aqueous solution. Methylene blue （MB） as the typical dye wasselected to evaluate the properties of the adsorption, regeneration and reuse of theFe₃O₄@C. It is demonstrated that the prepared Fe₃O₄@C displayed good adsorptiveproperty while magnetic Fe₃O₄just assisted the separation rather than attributed toadsorption efficiency. Three regenerated approaches of acid extraction, microwaveirradiation and heating were tried to regenerate the exhausted adsorbent, which had notbeen completely collected by a magnet until it was saturated. Among them, microwaveirradiation displays good regeneration efficiency by sustaining16adsorption/regeneration cycles and keeping a high regeneration efficiency of more than90%. The results show that the adsorption of MB onto both the initial and regeneratedFe₃O₄@C obeys Langmuir isotherm model and follows the pseudo-second-orderadsorption kinetics. The adsorption capacity of regenerated and initial Fe₃O₄@C inLangmuir isotherm is476.5mg/g and694.4mg/g at323K, respectively. Afterregeneration, the adsorption capacity of Fe₃O₄@C decreases while the adsorption rate isincreasing. Due to its high adsorption capacity and excellent reusability, the preparedFe₃O₄@C will be a promising and feasible adsorbent alternative. （2）Graphene oxide/Fe₃O₄（GO/Fe₃O₄） was synthesized by coprecipitation of FeSO4and FeCl3mixed with graphene oxide （GO） as raw materials. The adsorption oftriphenylmethane dyes with the typical target of malachite green onto GO/Fe₃O₄wasinvestigated. The effect of GO content in the material on MG adsorption was evaluated,and the dynamic adsorption behaviors caused by factors of pH and temperatures wereanalyzed. It was demonstrated that the adsorption obeys pseudo second order reactionrate kinetics. Comparing Langmuir with Freundlich isotherm, the later results in thebetter fit indicating that GO/Fe₃O₄is one heterogeneous embedded composite withmore than one sort of reactive site. In addition, desorption on the condition of waterbath at80℃is feasible.（3）Magnetic Bamboo-based Carbon （MBC） synthesized from old bamboo bymicrowave irradiation technique was used for studying the adsorptive removal of threemetal ions (Pb²⁺, Cd²⁺and Cu²⁺). The adsorptive conditions, including adsorptive time,pH, ionic strength, and the initial concentration of metal ions, were analyzed. Theadsorption properties and adsorption mechanism of three metal ions onto MBC werethen investigated. The results demonstrated that the adsorption of metals ions onto MBCobeys Langmuir isotherm model and pseudo second order kinetics; Adsorptionmechanism is surmised as the ion exchange between metallic cations and H+on MBC,and the tendency of adsorption efficiency is Pb²⁺>Cd²⁺>Cu²⁺, which can be related tothe radius of metal ions.（4）Comparative studies of GO/Fe₃O₄and MBC, which were both used forchromium（Ⅵ） adsorptive removal, were carried out and compared. According to themorphologies of GO/Fe₃O₄and MBC in SEM, the MBC possesses similar structure ofthin sheets as GO/Fe₃O₄, which providing a large amount of adsorptive sites for theadsorption of chromium（Ⅵ）. As for adsorbent of GO/Fe₃O₄, the optimal adsorptioncondition is that equilibrium adsorption time is50mins, at pH1and30℃. As for MBC,the optimal adsorption condition is that besides equilibrium adsorption time is85mins,the other optimized conditions are the same as the adsorbent of GO/Fe₃O₄. Theadsorption property of hexavalent chromium onto both two magnetic materials obeysLangmuir isotherm and pseudo-second-order kinetics. The adsorption mechanism canbe explained by hydrogen-bond interaction between HCrO4-and groups of-COOH and -OH on the surface of GO/Fe₃O₄and MBC under acid condition.