Modification Of Chitosan Microsphere By Amination Reaction And Study On Its Adsorption Properties To Cupric Ions

Chitosan is a natural polymer with linear poly(amino glucose)structures,and possesses the non-toxic,odorless,alkali-resistant,corrosion-resistant,and environment benign features etc,hence it has been widely applied in various fields.Chitosan has a strong affinity and great selectivity to transition metal ions due to its structural characteristics and surface chemical properties.Therefore,chitosan has a promising perspect in wastewater treatment.The chitosan microspheres can be functionalized by using physical or chemical modification methods to increase the surface density of active adsorptive sites,and thus leading to the adsorption capability of heavy metal ions.In this study,the amine-containing compounds,including diethylamide,triethylamine and polyethylene mine(PEI)were used to modify chitosan microspheres to increase the amount of active adsorptive sites for the enhancement of Cu(II)adsorption.The crosslinked chitosan microspheres were first prepared by precipitation-crosslinking method,followed by immobilizing the alkyl-bromide containing ATRP initiators on the microsphere surfaces by condensation reaction.Subsequently,the poly(glycidyl methacylate)(PGMA)polymer brushes were grafted from the initiator-immobilzied surface via surface-initiated atom transfer radical polymerization(ATRP).Finally,the respective amine-containing compounds,including diethylamine,triethylamine and polyethylenemine,were grafted onto the microsphere surfaces by the ring-opening reaction of epoxide groups of the PGMA brushes.The functionalized microspheres were characterized by Fourier transform infrared spectrometer(FTIR)and scanning electron microscope(SEM).The adsorption capacity of modified chitosan microspheres to aqueous Cu(II)ions,as well as,the influence of pH on adsorption capacity,was investigated.Experimental results demonstrated that the adsorption capacity and adsorption rate of the modified chitosan were improved with the increase in temperature.The adsorption capability of the modified chitosan was substantially enhanced above p H 5.The main conclusion in this study were drawn as follows:The crosslinked chitosan microsphres were synthesized by the precipitation-crosslinking methods and the optimal preparation conditions were involved: 2.0g chitosan was dissolved in 50 ml of 2%(v/v)glacial acetic acid.1 mol/L sodium hydroxide solution,using a No.7 syringe to pipet chitosan acetic acid solution into sodium hydroxide solution,and then titrating the formed white chitosan microspheres with deionized water to pH=7.Finally,chistosan microspheres were tansfered to a 200 ml flask to prepare for the cross-linking reaction.In Chapter 3,the surface of the CCS-Br microspheres was tested by contact angle,it shows that the contact angle increased to 70±2° because of its hydrophobicity.A polymer brush was present on the grafted CCS-g-PMAA with a large amount of hydrophilic carboxyl groups on the surface,resulting in a contact angle of 31±2°.The contact angle of CCS-g-PGMA-c-PEI chitosan microspheres,CCS-g-PGMA-ETA chitosan microspheres and CCS-g-PGMA-DTA chitosan microspheres will increase,respectively.51±2°,54±2° and 56±2°.By infrared spectroscopy,the peak at 908cm-1 disappeared because the epoxy bond of GMA was turned on,diethylamine(ETA),diethylenetriamine(DTA),polyethyleneimine(PEI)and methacrylic acid Glycidyl esters(GMA)react to cause the disappearance of epoxy bonds.It shows that diethylamine(ETA),diethylenetriamine(DTA)and polyethylenimine(PEI)are grated successfully.In Chapter 4,Cu(II)Adsorption experiments,CCS-g-PGMA-c-ETA,CCS-g-PGMA-c-DTA,and CCS-g-PGMA-c-PEI microspheres adsorb Cu(II).The number of ions has a significant increase when the pH is greater than 5.Adsorption data and secondary kinetics of CCS-g-ETA,CCS-g-PGMA-DTA,CCS-g-PGMA-PEI microspheres,and CCS microspheres can be matched.For the adsorption of Cu(II)of CCS-g-PGMA-PEI chitosan microspheres,the Freundlich adsorption model is more consistent with the actual adsorption of CCS-g-PGMA-PEI chitosan microspheres,while the adsorption of Cu(II)of CCS-g-PGMA-c-ETA chitosan microspheres,the Langmuir adsorption model is more consistent with the actual adsorption of CCS-g-PGMA-ETA chitosan microspheres.The maximum adsorption capacity of CCS-g-PETA microspheres at 25°C,35°C and 45°C can reach 1.79mmol/g,1.98mmol/g and 2.27mmol/g,respectively.The maximum adsorption capacity of CCS-g-PGMA-c-PEI microspheres at 25°C,35°C and 45°C can reach 2.74 mmol/g,2.88 mmol/g,and 2.95 mmol/g,respectively.