Research On Modification Of Bacterial Cellulose And Their Adsorption Properties On Metal Ions

With the development of industry and the discharge of waste water containing heavy metals increasing,the removal of toxic and polluting heavy metal ions from wastewater has received much attention in recent years.While searching for a method of treating this kind of waste water,we reach a consensus:an effective treatment should be efficient,convenient and will not have the secondary pollution.Bacterial cellulose(BC),synthesized by Gluconacetobacter xylinum,is a kind of ultra-fine and highly pure fiber.In comparison with other plant cellulose in nature, BC displays unique properties,including higher purity,higher crystallinity,higher water absorption capacity,higher tensile strength and good biocompatibility. Benefiting from its unique properties,BC has been applied in many fields such as food,medical materials,paper and so on.In this paper,we prepared diethylenetriamine bacterial cellulose(EABC) and amidoximated bacterial cellulose (Am-BC) by modifying BC.The adsorption properties for metal ions of these materials were investigated.The research work mainly concentrated on the following parts:1.Preparation and adsorprion properties of EABCThe EABC was synthesized and characterized by EA,FT-IR.The adsorption properties of EABC for Cu²⁺,Pb²⁺ were investigated.The results show that the adsorption rate could be well fitted by pseudo-second-order rate model,and adsorption isotherm could be described by the Langmuir model.The maximum adsorption capacity of Cu²⁺ and Pb²⁺ were found to be 63.09 mg/g,87.41 mg/g, respectively,in the solution of pH = 4.5.The prepared EABC could be regenerated successfully without significantly affecting its adsorption efficiency after five regeneration cycles.2.Preparation and adsorprion properties of Am-BCAm-BC was prepared through successive reactions with acrylonitrile in an alkaline medium followed by aqueous hydroxylamine.EA,FT-IR,SEM,CP/MAS ¹³C NMR,XRD were used to characterize it.Removal of Cu²⁺ and Pb²⁺ from aqueous solutions by adsorption onto Am-BC was investigated.The adsorption equilibrium was established after 180 min.The experimental data fit well to the pseudo-second-order kinetic model.The equilibrium adsorption data fit to the Langmuir isotherm.The maximum adsorption capacity of Cu²⁺ and Pb²⁺ reached 191.94 mg/g and 191.57 mg/g,respectively,at about pH = 5. The adsorption process was spontaneous and exothermic.The mechanism for the adsorption onto Am-BC could be mainly attributed to chelation between metal ions and nitrogen atom in the amidoxime groups or oxygen atom in the hydroxyl groups, precipitation and electrostatic interaction.The prepared Am-BC could be regenerated successfully without significantly affecting its adsorption efficiency after five regeneration cycles.The Am-BC has a good performance of selective adsorption, which can selectively adsorb Cu²⁺ when the Cu²⁺,Hg²⁺ and Pb²⁺ exist at the same time.