Preparation Of Crosslinked And Grafted Chitosan And Its Adsorption Performance

In this thesis，with chitosan as the raw material，dimethyl diallyl ammonium chloride(DMDAAC) as grafting monomer，formaldehyde as the pre-crosslinking agent，epichlorohydrinas the crosslinking agent，crosslinked quaternary chitosan salt was prepared through inverseemulsion polymerization. With chitosan as the raw material，epichlorohydrin as the crosslinkingagent，triethylenetetramine as the monomer，triethylenetetramine modified chitosan adsorbentwas synthesized. The adsorption performances of Ni(Ⅱ) and Cr(Ⅵ) by the two adsorbents werestudied. The main findings are as follows：Factors that affect reaction were discussed，such as reaction time，reaction temperature andformaldehyde and epichlorohydrin dosages. The reaction condition of crosslinked quaternarychitosan was optimized through the orthogonal experiment. The optimum reaction conditionswere：reaction time2h，reaction temperature50℃，formaldehyde6mL，epichlorohydrin1.5mL.Under30℃，pH=6，the initial concentration of Ni(Ⅱ)1mmol/L，the adsorption amount ofNi(Ⅱ) was1.13mmol/g.The adsorption equilibrium and kinetics of Ni (Ⅱ) and Cr (Ⅵ) by the crosslinkedquaternary chitosan salt were studied. The effects of time，heavy metal ions concentration and pHon adsorption were explored. The results indicated that the adsorption process followed thepseudo-second-order kinetics. The adsorption isotherm was well described by the Langmuirequation. For Ni(Ⅱ) and Cr(Ⅵ)，the best adsorption pH values were7and6respectively，under30℃and the initial concentration of heavy metal ions1mmol/L. The equilibrium adsorptionamounts of crosslinked quaternary chitosan salt to Ni(Ⅱ) and Cr(Ⅵ) were1.18mmol/g and1.99mmol/g respectively.Factors that affect reaction were discussed，such as crosslinking time，crosslinkingtemperature，grafting time，grafting temperature and epichlorohydrin and triethylenetetraminedosages. The optimum reaction conditions were confirmed by orthogonal experiments：crosslinking time2h， crosslinking temperature60℃， epichlorohydrin3.5mL，triethylenetetramine4mL. Under30℃，pH=6，the initial concentration of Cr(Ⅵ)1mmol/L，theadsorption amount of Cr(Ⅵ) was2mmol/g.The adsorption equilibrium and kinetics of Ni (Ⅱ) and Cr (Ⅵ) by the triethylenetetraminemodified chitosan were studied. The results showed that the adsorption process followed thepseudo-second-order kinetics. The adsorption isotherm was well described by the Langmuirequation. For Ni(Ⅱ) and Cr(Ⅵ)，the best adsorption pH value was6under30℃and the initialconcentration of heavy metal ions1mmol/L. The equilibrium adsorption amounts of triethylenetetramine modified chitosan to Ni(Ⅱ) and Cr(Ⅵ) were1.54mmol/g and2mmol/grespectively. Under the optimum conditions， the adsorption amount of Ni(Ⅱ) by thetriethylenetetramine modified chitosan is higher than that by the crosslinked quaternary chitosansalt.The crosslinked quaternary chitosan salt and the triethylenetetramine modified chitosan afteradsorbing Ni (Ⅱ) and Cr (Ⅵ) were regenerated with hydrochloric acid solution and can berecycled well.