Preparation Of Polymer-functionalized Magnetic Composite Adsorbent And Its Application In Water Treatment

Water is the source of life,how to control water pollution and ensure water quality is one of the most important problems that needs to be solved.As a reliable and efficient water treatment technology,adsorption has attracted the attention of many researchers.In order to solve the severe and complicated water pollution problem,it is meaningful to develop multi-functional adsorbents with excellent adsorption capacity,high separation speed,satisfactory regeneration performance,and good ability to remove multiple pollutants.Magnetic nanoparticles have the potential to become ideal adsorbents due to their low toxicity,small particle size,large surface area and strong magnetic responsiveness.However,they also have the disadvantages such as instability,easy agglomeration and lack of functional groups.Organic polymers are superior functionalized materials,they have abundant functional groups and can bind with pollutants through electrostatic interaction,hydrogen bonding,hydrophobic interaction,etc.,so they are widely used in water treatment.However,organic polymers are usually not easy to be separated from water after treatment,and they may cause secondary pollution.In order to give full play to the advantages of magnetic nanoparticles and organic polymers,it is necessary to develop a simple functionalized method to combine these two materials.For the purpose of increasing adsorption capacity,solid-liquid separation ability,regeneration ability,stability,functionality and biocompatibility,three polymer-functionalized magnetic composite adsorbents were prepared by grafting polymerization or cross-link polymerization.The adsorption behaviors and mechanisms of these self-made adsorbents towards organic dyes and heavy metal ions were detailedly discussed in batch adsorption experiments.The main research contents and conclusions are as follows:（1）In order to obtain an adsorbent with cationic dye adsorption capacity and high solid-liquid separation ability,Fe₃O₄@Si O₂-MPS-g-AA-AMPS（FSMAA）was prepared by grafting acrylic acid（AA）and 2-acrylamido-2-methyl-1-propanesulfonic acid（AMPS）monomers on the surface of vinyl-modified Fe₃O₄@Si O₂.Preparation conditions were optimized by single factor experiments.The optimum grafted monomer concentration was 2.0 mol/L,initiator concentration was 0.9‰and copolymerization time was 7 hours.There were self-polymerization and copolymerization between AA and AMPS monomers in the preparation of FSMAA,so the utilization ratio of monomers was low.In order to solve this problem,functionalized magnetic composite adsorbent was prepared by cross-link method.Sulfonic acid-modified polyacrylamide（P（AM-AMPS））was firstly prepared by radical copolymerization with ultraviolet light as the initiation method.Fe₃O₄@Si O₂/P（AM-AMPS）（FSAA）was then prepared by cross-link reaction with glutaraldehyde（GA）as the crosslinker.In order to further achieve a better heavy metal ion adsorption capacity and biocompatibility,chitosan was served as the basal material.Flexible anionic polyacrylamide was grafted onto rigid chitosan framework and anionic polyacrylamide-chitosan was bound with Fe₃O₄@Si O₂nanoparticles by cross-link method.In this case,anionic polyacrylamide-chitosan magnetic composite nanoparticles Fe₃O₄@Si O₂/CS-P（AM-AMPS）（FSCAA）were prepared.（2）The morphology,structure,physic-chemical and magnetic properties of as-prepared products were fully characterized by different characterization techniques,including TEM,SEM,FTIR,XPS,EDX,TGA,XRD,VSM and so on.As can be seen,three polymer-functionalized magnetic composite adsorbents were successfully prepared by grafting polymerization or cross-link polymerization,and the crystalline form of magnetic core was not destroyed.FSMAA and FSCAA had core-shell structure and nanometer size,FSAA had three-dimensional network structure and good swelling performance.All of the three magnetic adsorbents had good magnetic property,they could be rapidly separated from water with the help of an external magnet.（3）Methylene blue（MB）adsorption experiments showed that the adsorption capacity of FSMAA increased with the increase of solution p H and functional group amount.With the increase of adsorption time and MB initial concentration,adsorption capacity firstly increased sharply,then tended to get equilibrium.Adsorption equilibrium was obtained after 90 min,and the maximum adsorption capacity of FSMAA 2.0 was 421.9 mg/g.Based on XPS analysis,surface adsorption mechanism between FSMAA and MB was electrostatic interaction,hydrogen bonding and hydrophobic interaction.Furthermore,due to the protection of Si O₂ and polymer,FSMAA showed good stability in acid solution and could be regenerated by acid pickling.The adsorption capacity and regeneration ability of FSMAA to MB in model wastewater were almost no different from those in ultrapure water.（4）Adsorption behaviors of FSAA towards CV were carefully investigated.It was found that the adsorption capacity of FSAA towards CV was largely enhanced than that of Fe₃O₄@Si O₂ and maintained at a relatively high level in a wide p H range（p H=4.0-10.0）.The adsorption kinetics and isothermals were in good accordance with the pseudo-second-order model and the Langmuir model,respectively.Due to the three-dimensional network structure,good swelling performance and abundant functional groups,cationic dye molecules could cross over the pores on FSAA and bind with adsorption sites through hydrogen bonding,electrostatic interaction and hydrophobic interaction.After 5 min and 20 min,more than 50%and 80%of the equilibrium adsorption capacity were obtained,respectively.The maximum adsorption capacity of FSAA towards CV was 2106.37 mg/g.Furthermore,FSAA was effectively regenerated with HCl solution,the regeneration rate was higher than 97%after five adsorption-desorption cycles.The removal rate of CV in model wastewater by FSAA was slightly lower than that in ultrapure water due to the competitive adsorption,but the reduction was in an acceptable range.（5）The adsorption behaviors of FSCAA towards cationic dyes and heavy metal ions were systematically investigated in single-pollutant system,binary-pollutant system and model wastewater system.In single system,FSCAA was proved to have superior adsorption capacities of 2330.17 and 1044.06 mg/g respectively for CV and MB at 318.15 K,much higher than other reported adsorbents.And the adsorption performances of FSCAA towards Cu（II）（removal rate>86%）and Ni（II）（removal rate>75%）were satisfactory in a wide p H range（p H>3）.This p H-independent adsorption capability suggested that FSCAA could be used to treat a variety of metal ion wastewaters with different p H values.FTIR and XPS analyses revealed that the electrostatic interaction,hydrogen bonding,cation exchange and chelating effect were involved in the adsorption processes of cationic dyes and heavy metal ions.The regeneration process nearly had no influence on the structure and chemical properties of FSCAA,after five adsorption-regeneration cycles,regeneration rate was still higher than 90%.In binary system,FSCAA can simultaneously remove organic dyes and heavy metal ions.For the adsorption of MB in the presence of Cu（II）,the ratios of adsorption capacities（R_q）were lower than 1 and decreased with increase of Cu（II）concentration.For the adsorption of Cu（II）in the presence of MB,there was no obvious effect on R_q values at both low（i.e.,10 mg/L）and high（i.e.,>100 mg/L）initial Cu（II）concentrations.Besides,the effect of MB on the adsorption of Cu（II）was relatively smaller at lower solution p H.In model wastewater,FSCAA also had good adsorption capability and regeneration ability.All of these superior characteristics demonstrated that FSCAA could be used as a high-efficient adsorbent in the treatment of wastewater containing cationic dyes and heavy metal ions.