Preparation Of Chitosan-based Magnetic Composites And Their Adsorption Properties Of Dyes And Heavy Metals

Environmental pollution has become a major problem,especially more and more industrial wastewater is discharged into aquatic ecosystems.There are various of dyes and heavy metal ions in industrial wastewater,which has seriously affected human health and polluted ecological environment.Therefore,the study on wastewater treatment method and technology has become the focus of attention.By virtue of its outstanding advantages,such as simpler operation,high treatment efficiency and no secondary pollution,adsorption method has been playing an important role in wastewater treatment.Although activated carbon is the most widely used adsorbent,however,relatively expensive cost of commercial activated carbon hampered its further application in wastewater treatment.Therefore,to seek cheaper and highly effective adsorbents is an attractive goal.Compared with traditional adsorbents,magnetic adsorbents can be rapidly separated by an external magnetic field rather than filtration and centrifugation,which can effectively reduce labor cost and improve work efficiency.So,in this present thesis,we selected chitosan,which were the most abundant in nature,cheaper and biodegradable natural polymers,as base materials to prepare several environment-friendly,cheaper and efficient new-style adsorbents by graft modification and composition with other materials and studied their application performance in wastewater treatment.The thesis consists of following four part:Chapter 1.The source and endanger of dyes and heavy metal ions pollution were reviewed and the treatment methods of wastewater were summarized.At the same time,applications of the natural polymer material chitosan in the preparation of adsorbents were decribed in detail.Chapter 2.At first,magnetic chitosan adsorbent（MCS）was prepared by using glutaraldehyde to crosslink chitosan（CS）and pre-prepared Fe₃O₄@SiO₂ nanoparticles obtained.Then a novel quaternary ammonium salt modified magnetic chitosan adsorbent（QMCS）was synthesized by a surface modification of MCS with glycidyl trimethyl ammonium chloride（GTA）.The structures,morphologies and properties of the prepared adsorbents were characterized by scanning electron microscopy（SEM）,fourier transform infrared spectroscopy（FTIR）,X-ray powder diffraction（XRD）and thermogravimetric analysis（TG）,their adsorption properties for removal of methyl orange（MO）were investigated,and some factors influencing the adsorption capacity including pH,initial dye concentration,contact time and adsorbent dosage were optimized.The results revealed that QMCS could be used at wide pH range and possessed a high adsorption capacity and a rapid adsorption rate for methyl orange（MO）,as well as rapid magnetic separation.The pseudo-second order kinetic model could describe the adsorption process,and their equilibrium data were fitted well with the Langmuir isothermal model.The maximum adsorption capacity of QMCS for MO was 338.4 mg·g^-1,which is much higher than that of MCS(225.6 mg·g^-1).These results dsmonstrated that QMCS prepared is an efficient and separated-easily adsorbent.Chapter 3.Magnetic graphene oxide（MGO）was at first prepared by simple chemical coprecipitation of Fe₃O₄ nanoparticles on graphene oxide sheets obtained through Hummers method.And then a magnetic graphene oxide-chitosan composite adsorbent（MGO-CS）was successfully synthesized by using glutaraldehyde as crosslinking agent.The composites were characterized by SEM,FTIR,XRD and TGA and their adsorption behavior for removal of Pb²⁺from aqueous solution was also investigated.The results revealed that the maxmum adsorption capacity of Pb²⁺on MGO-CS was 81.8 mg.g^-1and the removal rate was 98.0%,much higher than those on MGO,and the composite adsorbent could be rapidly separated from the solution under applied magnetic field,indicating that the adsorbent had a good application prospect in Pb²⁺wastewater treatment.The adsorption of these two sorbents to Pb²⁺obeyed Langmuir isotherm adsorption model and the pseudo-second-order kinetic equation,showing the adsorption process was a chemically controlled monolayer adsorption process.Chapter 4.Magnetic attapulgite-chitosan（MATP-CS）composite was obtained by a simple composition of CS with magnetic attapulgite（MATP）,which was synthesized by means of chemical coprecipitation of Fe₃O₄ nanoparticles on ATP.The composites were characterized by SEM,FTIR,XRD and TGA and their adsorption behaviors for removal of acid magenta（AC）from aqueous solution were studied.The results displayed that MATP-CS had a high adsorption capacity for acid magenta.The adsorption isotherms and kinetic were in good agreement with Langmuir equation and pseudo-second-order equation respectively.The maximum adsorption capacity of MATP-CS was 433.9 mg·g^-1and the highest removal rate was 97.3%for AC,which is much higher than that of MATP.High adsorption capacity and rapid separation promised a potential application for AC to remove anionic dye in wastewater.