Preparation Of Magnetic Adsorbents Via Layer-by-layer Assembly And Its Adsorption Properties For Removal Of Heavy Metals

Contamination of heavy metals, arisen from industrial production, has posed a greatthreat to human health. Magnetic adsorbents are excellent candidates in removal ofhazardous metals due to their preferable properties, such as quick separation, highadsorption capacity, easy regeneration, etc. In this thesis, Fe₃O₄microspheres were used asmagnetic cores. After treated with sodium citrate, the Fe₃O₄microspheres were alternatelycoated with polyanions （polyacrylic acid, PAA） and polycations （chitosan, CS） via theelectrostatic layer-by-layer assembly technique to construct polyelectrolyte multilayers asa shell, which was further crosslinked by glutaraldehyde or carbodiimide hydrochloride.The obtained magnetic adsorbent （CS/PAA）_n/Fe₃O₄could be applied in removal of heavymetal ions due to its considerable of active functionalities, such as amino and carboxylgroups. In this work, the preparation conditions for （CS/PAA）_n/Fe₃O₄was firstlyinvestigated, and then the novel magnetic adsrbents was characterized and its adsorptionproperties for Cu²⁺and Pb²⁺was further studied.1. The optimum condition for preparation of （CS/PAA）_n/Fe₃O₄was shown as follows:Fe₃O₄microspheres were firstly pretreated with sodium citrate, then CS and PAA layerswere adsorbed alternately onto the microspheres via electrostatic effect. In the layer bylayer assembly process, the concentration of the polyelectrolyte （CS and PAA） was1mg/mL, containing0.5mol/L of NaCl. Moreover the molecular weight of PAA was100000, and the polyelectrolyte multilayers were chosen （CS/PAA）₄. The as-prepared（CS/PAA）₄/Fe₃O₄was further reaction with NaOH, and then the novel magnetic adsorbent（CS/PAA-Na）₄/Fe₃O₄was obtained, which exhibit enhanced adsorption capacities forheavy metals compared with （CS/PAA）₄/Fe₃O₄.2. The novel magnetic adsorbent （CS/PAA-Na）₄/Fe₃O₄were characterized by IR,XRD, TGA, FESEM, etc. The results indicated that functional groups such as carboxyland amino groups were modified onto the surface of the adsorbent, and the percent of the grafted polymers on the adsorbent was16.7%. The saturated magnetization of theadsorbent was63.7emu/g, suggested the good magnetic separability of the adsorbent.3. The adsorption properties of （CS/PAA-Na）₄/Fe₃O₄for Cu²⁺and Pb²⁺wereinvestigated in detail. The adsorption capacity increased as the pH value increased, andreached the maximum adsorption at about pH5.5, but it is nearly zero at pH2. Theadsorption isotherms were fitted extremely well with the Langmuir isothermal model, andthe maximum capacitiy calculated from this model was30.3and90.9mg/g for Cu²⁺andPb²⁺, respectively. In the kinetic studies, adsorption equilibrium was reached within15and45min for Cu²⁺and Pb²⁺, respectively, and the adsorption process followed thepseudo-second order kinetic model. All the adsorption processes were endothermic. In thebinary metal ion solutions, the adsorbent preferred adsorbing Pb²⁺to Cu²⁺. Additionally,the adsorbent exhibited a promising reusability, of which the adsorption capacities wasonly lost less than9%even after5adsorption-desorption cycles.