Preparation And Adsorption Properties Of Poly (Ethyllenimine) Modified Chitosan Microspheres

Chitosan,a natural amino-polysaccharide,is an environmental friendly adsorbent due to its abundant amino and hydroxyl groups.To avoid the degradation in acid environment,the crosslinked chitosan microspheres(CCS)was usually prepared for the adsorption.However,the crosslinking reaction normally occurs at adsorption sites,resulting in the reduction of adsorption capacity.To enhance the adsorption capacity,the surface of CCS was grafted with poly(ethylenimine)(PEI)in this work.Consequently,a series of PEI modified CCS(PEI-CCS)with different ion exchange capacities(IEC)was obtained,and the adsorption performance of PEI-CCS was studied.Firstly,PEI-CCS was prepared and characterized by Fourier transform infrared spectrum,scanning electron microscopy,and X-ray diffraction.The results showed that the surface of PEI-CCS was smooth,and the mean diameter of PEI-CCS was 85 ?m.The crosslinking reaction mainly occurred on the amino groups of chitosan,whereas the grafting reaction occurred on the aldehyde group of the crosslinking agent and did not affect the morphology of microspheres.After modification,the IEC of PEI-CCS increased with the increase of the initial PEI concentration.The highest IECof PEI-CCS reached 1275 ?mol/g,which is much higher than that of CCS(418 ?mol/g).The increase of microsphere IEC facilitated its adsorption properties.Then,the adsorption performance of PEI-CCS toward methyl orange and xylenol orange was studied.The adsorption capacities of two dyes onto PEI-CCS were much higher than that onto CCS in acid solution.The adsorption performance of PEI-CCS for two dyes increased significantly with the increase of the microsphere IEC,and the maximum adsorption capacities of 400.00 mg/g and 813.01 mg/g were achieved at 303 K for methyl orange and xylenol orange,respectively,by PEI-CCS-1275 with the highest IEC.The adsorption process of two dyes well fitted the pseudo-second-order kinetic and Langmuir isotherm models.Thermodynamic analysis showed that the adsorption of two dyes onto PEI-CCS was spontaneous and exothermic reaction,and the adsorption processes were favorable at low temperature.Furthermore,PEI-CCS exhibited good adsorption capacity within seven cycles of adsorption–desorption.Finally,the adsorption properties of PEI-CCS were studied for sodium dodecylbenzenesulfonate(SDBS).At acid pH,the amine groups of PEI-CCS carried positive charges by protonation,and could adsorb anions in aqueous solution.Thus,PEI-CCS exhibited excellent adsorption performance toward SDBS.The adsorption process was spontaneous and exothermic,and was well described by the pseudo-second-order kinetic and Langmuir isotherm models.The maximum adsorption capacity of PEI-CCS increased with the increase of IEC.The maximum adsorption capacity of PEI-CCS-1275 with the highest IEC reached 1487.61 mg/g and was 2.92-fold higher than that of CCS(510.20 mg/g).The adsorption capacity of PEI-CCS-1275 decreased by 17.8% after seven cycles of adsorption-desorption,indicating that PEI-CCS had good reusability for the adsorption of SDBS.