Study On Removal Of Cr(?) And Methyl Orange From Aqueous Solutions By Functionalized Magnetic Chitosan Micospheres

With the development of industrial activities and acceleration of the urban modernization process,a large amount of toxic wastes?e.g.heavy metals and dyes?are discharged into environment,which put humm health and environment at risk.Therefore,it is vital to study the removal of heavy metals and dyes pollutants.Chistan?CTS?,one of most important natural polymers,has obtained great interests in removal of heavy metals and dyes,due to its low-cost,large amounts of source,environmental-friendly and no secondary pollution.Unfortunately,unmodified CTS hardly have excellent performance on removing pollutants in most cases.Besides,the magnetic composite draws considerable interests as it can be separated easily.However,most traditional methods for preparing magnetic CTS composite are little bit of complex.In this study,we prepared magnetic CTS composite in a simple and efficient way while adopting different methods to modify Chistan with amino groups,studied its performance on removing Cr???and Methyl Orange,optimized the best removal conditions and discussed the removal machenism.The main contents are showing as follows:1.We prepared magnetic chitosan by hydrothermal method firstly,then grafted polyethyleneimine?PEI?on it by Glutaric dialdehyde cross-linking to get the final products PEI modified magnetic chitosan?PEI-MCTS?.The result composite was characterized by XRD,TGA,FT-IR,Raman,Saturation magnetization.We evaluated its performance on removing Cr???by studying the effect of the initial pH value of medium,the amount of PEI,the dosage of adsorbents,the ionic strength,the initial concentration of Cr???and contact time on adsorption efficiency systematiclly.The results are as followed:?1?The removal of Cr???by PEI-MCTS is largely depended on the initial pH value of medium with PEI-MCTS adsorbing Cr???efficiently under acid condition and the optimum pH appearing at 3.The high adsorption can be attributed to the strong electrostatic interaction between protonated surface of PEI-MCTS and anionic Cr???.?2?The adsorption isotherm results showed that the adsorption process can be fitted by Langmuir model?r²>0.99?and the maximum adsorption capacity reached 193.57 mg·g^-1.?3?The adsorption kinetics results showed that the adsorption process could be described by pseudo-second order kinetic models?r²>0.99?and can reach equilibrium within 4 h.?4?PEI-MCTS can be separated easily from solution by external magnetic field and has good affinity with anion.At the same time,the PEI-MCTS nanocomposite has good stability and regeneration,and can be used as a highly effective adsorbent to remove anions from aqueous solution,which demonstrate PEI-MCTS has great potential in environment application.2.We adopted one-pot hydrothermal method for directly synthesis of amino-functionalized magnetic chitosan?AF-MCTS?.The synthesis method has some clear advantages including low-cost,simplicity,high quality,ease of scale-up and good reproducibility.The result composite's structure and properties were characterized by using XRD,XPS,TEM,FT-IR,TGA,Raman and other analytical methods.The adsorption effects of Cr???in aqueous solution was investigated.The effects of the amount of chitosan,initial pH,ionic strength,Cr???initial concentration,adsorption time and temperature on the adsorption of Cr???were systematically studied.The results are as followed:?1?In the range of pH 2-9,the optimum adsorption capacity was at pH3;NaCl had a significant impact on the adsorption capacity as its concentration greater than 0.1M AF-MCTS could almost lose ability to adsorb Cr???.?2?The adsorption isotherms at different temperatures showed that the adsorption process was in accord with the Langmuir model?r²>0.999?with a maximum adsorption capacity of208.33 mg·g^-1 and adsorption process was a spontaneous endothermic process.?3?adsorption kinetics showed that the adsorption equilibrium can be reached within 5 min when Cr???initial concentration is 100 mg·L^-1,and the adsorption process can be described by pseudo-second order kinetic models?r²>0.99?.?4?Adsorption–desorption cycling experiments showed that AF-MCTS-4 after adsorbing Cr???could be easily regenerated by 0.5 M NaOH and its adsorption capacity,compared with that of first cycle,had little loss until in the eleventh cycles and still remaining 85%after fifteenth cycles.?5?We also proposed a mechanism for the removal of Cr???by AF-MCTS:under the acidic condition,the protonated surface of AF-MCTS adsorbs Cr???by electrostatic adsorption,accompanied by a small amount of Cr???reduction.3.In view of the excellent removal ability of AF-MCTS on Cr???,we applied it for the removal of anionic dye methyl orange.It is found that AF-MCTS has a strong ability to remove methyl orange.The results were as follows:?1?the effect of pH in the range of 4-9 on the adsorption was studied.The results showed that the lower pH,the better adsorption capacity will be.?2?The adsorption kinetics was studied.The results showed that the adsorption process can be described by pseudo-second order kinetic models?r²>0.99?and the adsorption adsorption reached equilibrium within 40 min;The adsorption isotherm results showed that the adsorption process can be fitted by Langmuir adsorption model,the maximum adsorption capacity is 521.34 mg·g^-1.?3?The salt concentration had a significant effect on the adsorption with the adsorption capacity decreasing to 89%as concentration of NaCl was over 1 M.