| The pollution of water bodies is a major concern throughout the world, for itsthreats to human health and ecosystems.In the recent years, the treatments of heavy metal ions pollution areincluding physical method, chemical method, physico-chemical method and biological method, in which adsorption has been widely studied on water purification for its convenient operation, high efficiency, low cost and easy regeneration. Adsorbent and the physicochemicalcharacteristics such as particle size and active points of the adsorbent were reported to be important for the adsorption process and the amounts of adsorbed heavy metal ions.Chitosan is a natural linear macromolecular polysaccharide, which is acquired by the taking off the acetyl chitin.Chitosan has been studied as a promising adsorbent extensively over the last decade due to its unique properties in adsorbing heavy metal ions fromindustrial chemical waste streams for itswide availability, nontoxicity, biocompatibility and high chelation capacity andchemical activity. However the single chitosan materialhas limitedits widespread application in the field of metal processing.To overcome these limitations, we proposed carboxylated chitosanmagnetite microspheres (EDCMM) and submicrospheres (EDCMSM)as promising adsorbents, and the comparative studies of the adsorbents for Pb2+ removal were conducted. Briefly, Fe3O4 nanoparticles were coated with silica layer to act as magnetic cores so that the adsorbent could be separated easily even in submicroscale. Then the magnetic cores were wrapped in chitosan layer and cross-linked by glutaraldehyde to increase the stability of the adsorbent in acid solution. Finally, in order to increase the active points of the adsorbent, the magnetic chitosan particles were carboxyl-functionalized with ethylene diamine tetraacetic acid (EDTA).In this study, CMM was synthesized by emulsion crosslinking method and then was carboxyl-functionalized to acquire EDCMM. Some effects, such as the concentration of chitosan. the proportion of chitosan:Fe3O4/SiO2 and the speed of mechanical stirringwere investigated. EDCMM was characterized by scanning electron microscope (SEM), transmission electron microscopy (TEM), fourier transform infrared (FTIR), Brunauer-Emmett-Teller (BET) and vibrating sample magnetometer (VSM).The physicochemical characteristics of EDCMM indicated that thespecific surface area of EDCMM was 0.70 m2/g and sphericity of EDCMM was regular and uniform. The particles size of EDCMM were approximately 100-200 μm after freeze-dried which is smaller than that before freeze-dried. The particles of EDCMM were formed with hollow structure and the volume of hollow structure was 33%.The spectrum ofEDCMM suggested that the carboxylated chitosan magnetic particles were successfully prepared. The points of zero charge of EDCMM laid at pH value of 2.7, which expanded the application of chitosan in acid solution. The saturation magnetization of EDCMM was 14.117 emu/g and the adsorbent could be rapidly separated from water by a magnet.In this study, CMSM was synthesized by micro-emulsion method and was modified by ethylene diamine tetraacetic acid (EDTA) to acquire EDCMSM. EDCMSM was characterized bySEM, TEM, FTIR, BET and VSM. The physicochemical characteristics ofEDCMSM suggested that sphericity was regular and uniformand the particles size of EDCMSM was approximately 100-400 nm. The thickness of chitosan layer of EDCMSM was about of 10-40 nm, while the specific surface area of EDCMSM was6.83m2/g. The FTIR spectrum ofEDCMSM suggested that the carboxylated chitosan magnetic particles were successfully prepared.The saturation magnetization of EDCMSMwas66.563 emu/g and the point of zero charge of EDCMSM laid at pH value of 3.6.EDCMM and EDCMSM were prepaired for the comparative study of Pb2+ removal. Batches of tests were conducted to investigate the Pb2+ adsorption at different pH values, contact time, initial Pb2+ concentrations and temperatures. The results showed that the adsorption equilibrium of EDCMM and EDCMSM could be reached within 40 and 20 min respectively, and the maximum adsorption capacities were 160.7 and 138.9 mg/g respectively, with the same initial Pb2+ concentrations of 400 mg/1. The adsorption kinetics for both adsorbents fitted well with the pseudo-second-order model, while the isotherm data were well described by the Langmuir model. Thermodynamics analysis suggested that the adsorption process was endothermic and spontaneous in nature. Furthermore, the readsorption performance of EDCMM and EDCMSM could remain 94%and 98%(w/w) of the original capacityrespectively, after the fifth adsorption-regeneration cycle. All these results indicated that EDCMMwith high adsorption capacity and EDCMSM with rapid adsorption rate were promisingadsorbentsfor the sorption of Pb2+. |
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