Preparation Of Cationic Polymer Modified Magnetic Chitosan And Study On Adsorption Properties Of Heavy Metals And Dyes

Heavy metal wastewater and dyestuff wastewater have always been relatively difficult to treat.Traditional heavy metal and dyestuff wastewater adsorbents have problems such as difficulty in solid-liquid separation,high cost,low adsorption efficiency,low reuse rate,easy to cause secondary pollution and so on.Their practical use is limited.Chitosan-based adsorbents with high efficiency and easy recovery have become a research hotspot due to their wide source,many active groups,unique physical and chemical properties and easy biodegradation.In this paper,two cationic polymer-grafted magnetic chitosan-based adsorbents（Fe₃O₄-CS/PANI and Fe₃O₄-CS/PDAC）were prepared by graft copolymerization with heavy metals Cu（Ⅱ）and Cr（Ⅵ）,dyes Congo red Co R and Sunset Yellow SY as target pollutants.The characterization,adsorption performance and mechanism of the two adsorbents were studied.The main conclusions and contents are as follows:（1）Both Fe₃O₄-CS/PANI and Fe₃O₄-CS/PDAC show uniform microspheres with superparamagnetism,which can meet the requirements of magnetic separation.They have good thermal stability and high organic content.The crystal structure of Fe₃O₄ is always maintained during the synthesis process.Zeta potential was positive and mainly occurred on the a mino group of chitosan.Both Fe₃O₄-CS/PANI and Fe₃O₄-CS/PDAC have mesoporous structures,and their specific surface areas are 52.97 m²/g and 102.9 m²/g,respectively.（2）The adsorption capacities of Fe₃O₄-CS/PANI for Cu（Ⅱ）and SY increased with p H value,and the maximum adsorption capacities were 39.71mg/g and 609.38 mg/g,respectively.Fe₃O₄-CS/PANI dosage can significantly improve the removal rate,the increase of the initial concentration of C_0（Cu）and C_0（SY）can increase the adsorption capacity,increased to a certain extent,the adsorption capacity does not change,adsorption equilibrium time is 5 hours and 7 hours respectively.The adsorption of the two pollutants was in accordance with Langmuir model and PSO second-order kinetics model,indicating the adsorption reaction was monollayer adsorption,and the ration-limiting step was chemical adsorption.The adsorption rate was deter mined by the adsorption site on Fe₃O₄-CS/PANI surface and the concentration of Cu（Ⅱ）and SY.The effect of four coexisting cations on the reduction of Cu（Ⅱ）adsorption is as follows:Ca²⁺>Mg²⁺>K⁺≈Na⁺.The effect of coexisting anions on reducing Sy adsorption is as follows:Cl^-<NO₃^-<SO₄^2-.After five adsorption-desorption cycles for Cu（Ⅱ）and SY,85%and 80%of the initial adsorption capacity can still be reached.The adsorption mechanism of Fe₃O₄-CS/PANI for Cu（Ⅱ）is chelation,cationic-πinteraction and hydrogen bonding.The main mechanisms of Fe₃O₄-CS/PANI adsorption on SY areπ-πinteraction,electrostatic interaction and ion exchange.When the p H value of Fe₃O₄-CS/PANI is greater than 2,the leaching of Fe is inhibited and has good acid resistance stability.（3）The adsorption capacity of Cr（Ⅵ）and Co R by Fe₃O₄-CS/PDAC increased with p H value,and the maximal adsorption capacity was 148.35 mg/g and 1200 mg/g,respectively.The dosage of Fe₃O₄-CS/PDAC can significantly improve the removal rate,and the increase of the initial concentration of C₀（Cr）and C₀（Co R）can increase the adsorption capacity.When the adsorption reaches a certain extent,the adsorption capacity does not change,and the adsorption equilibrium time is 2 hours and 160 minutes,respectively.The adsorption of the two pollutants was consistent with Langmuir model and PSO second-order kinetics model,indicating that the adsorption reaction was monollayer adsorption,and the rate-limiting step was chemical adsorption.The adsorption rate was deter mined by the adsorption site on Fe₃O₄-CS/PDAC surface and the concentration of Cr（Ⅵ）and Cor.The effect of co-existing anions on the reduction of Cr（Ⅵ）and COR adsorption is as follows:Cl^-<NO₃^-<SO₄^2-.After five adsorption-desorption cycles for Cu（Ⅱ）and Sy,the initial adsorption capacity can still reach 79.7%and 77%.The main mechanisms of Fe₃O₄-CS/PDAC adsorption of Cr（Ⅵ）and COR are electrostatic interaction and ion exchange.Fe₃O₄-CS/PDAC has good acid resistance stability.（4）The adsorption capacity of removing SY and Cu（Ⅱ）by Fe₃O₄-CS/PANI and other adsorbents and the adsorption capacity of removing Cr（Ⅵ）and Co R by Fe₃O₄-CS/PDAC and other adsorbents were compared.The results showed that the adsorption capacity of the two adsorbents was at a good level.Fe₃O₄-CS/PANI can effectively remove SY and Cu（Ⅱ）,and Fe₃O₄-CS/PDAC can effectively remove Cr（Ⅵ）and Co R both of which are adsorbents with application potential.（5）The removal rate of Fe₃O₄-CS/PANI in tap water（82.2%）was higher than that in simulated wastewater（70.3%）;The removal rate of Cu（Ⅱ）in tap water（60.5%）was higher than that in simulated wastewater（55.7%）.When the dosage is increased to（2.5g/L）,the removal rate of SY and Cu（Ⅱ）can reach 90%under the simulated wastewater condition.The COR removal rate of Fe₃O₄-CS/PDAC in tap water（75.2%）was higher than that in simulated wastewater（64.3%）.The removal rate of Cr（Ⅵ）in tap water（85.3%）was higher than that of simulated wastewater（75.7%）.