Preparation And Heavy Metal Ions Adsorption Of Oxidized Cellulose/chitosan Composite Aerogel

In recent years,with the development of industrialization and urbanization,metal plating,mining and other industrial activities may cause pollution to the environment and the indiscriminate discharge of heavy metal ions from industrial wastewater directly or indirectly caused irreversible ecosystem damage,which ultimately affect the ecological cycle.Therefore,it is urgent to design a synthesis high efficiency,economic and sustainable materials of treatment of heavy metal pollution in water system.Since cellulose had unique molecular conformation,good biocompatibility and abundant derivatives,cellulose was widely used in people’s production and life.However,with ordered macromolecules,dense hydrogen bond structure and strong interaction between macromolecules,it was insoluble in many organic solvents and water.Therefore,by modifying cellulose into water-soluble substances and introducing different functional groups,cellulose derivatives were further obtained,thereby imparting new functions to cellulose.Chitosan was the second natural resource.There were a large number of active amino groups and hydroxyl groups in it,which had a strong affinity and electrostatic attraction for heavy metal anions,organic dyes,drug molecules and other substances with negative points.It can be used as a easy,non-toxic,sustainable biosorbent.In this paper,microcrystalline cellulose(MCC)was selected as the raw material,and during selective oxidation of cellulose with sodium periodate solution.And then through the Schiff base reaction of oxidized cellulose and chitosan(CS).After swelling,oxidation,Schiff base and freeze drying,ultralight and highly porous cellulose aerogels were prepared.In order to systematically studied the adsorption properties,lead nitrate and cadmium nitrate were used as heavy metal sources.At the same time,study the adsorption performance of the four samples MCC,DAC10,CS3,1DAC/CS3 from the two aspects of adsorption time and solution pH.The specific research contents are as follows:(1)Preparation of oxidized cellulose and control its microstructure and propertiesTaking microcrystalline cellulose as raw material and oxidized by sodium periodate aqueous solution.Choosing different concentration of sodium periodate,time and solution pH as single factor variables,the synthesis process of oxidized cellulose was optimized.Through aldehyde group content analysis,scanning electron microscopy and porosity,the microscopic morphology and structure properties of oxidized cellulose were adjusted.The oxidized cellulose aerogel had a three-dimensional interlinked network structure with interconnected pores.At the same time,characterization methods such as infrared spectroscopy(FTIR),EDS and XRD were used to prove that cellulose retained the crystalline structure and stable atomic content of cellulose after oxidation.Considering the properties of oxidized cellulose comprehensively,when the oxidation concentration was 0.1 mol/L,the oxidation time was 6 h and the oxidation pH was 4.85,the prepared aerogel of oxidized cellulose was light and highly porous,with the highest porosity up to 94.93 % which showed better performance.(2)Preparation of oxidized cellulose/chitosan composite aerogel and control their microstructure and propertiesWith the best microscopic morphology and structure properties obtained by oxidation of sodium periodate solution as raw material,and during Schiff base reaction with CS.After that using freeze drying to form oxidized cellulose/chitosan aerogel.The micro-morphology and structure properties of chitosan aerogel and oxidized cellulose/chitosan aerogel were controlled by scanning electron microscopy(FE-SEM)and porosity.The chitosan aerogel had smooth surface,three-dimensional porous and macroporous structure.And the oxidized cellulose/chitosan composite aerogel retained the three-dimensional network cross-linked structure of the oxidized cellulose aerogel as well as the micropores increased.At the same time,characterization methods such as infrared spectroscopy(FTIR),EDS,XRD and thermogravimetric(TG)proved that the crystalline structure of cellulose degraded to a certain extent.In addition,its thermal stability decreased and retained stable atomic content after Schiff base reaction.Considering the properties of the microstructure properties of oxidized cellulose/chitosan composite aerogel,the composite aerogel prepared with a solubility concentration of 2 wt% of chitosan and a mass ratio of 50/50 of oxidized cellulose/chitosan had good three-dimensional porous structure,with porosity of up to 95.92%,which showed better performance.(3)Study on heavy metal ions adsorption of oxidized cellulose/chitosan composite aerogelUsing prepared from above the preparation of the cellulose aerogel(MCC),oxidized cellulose aerogel(DAC10),chitosan aerogel(CS3)and oxidized cellulose/chitosan composite aerogel(1DAC/CS3)as adsorption material,this paper study the influence of the contact time and pH value of heavy metal solution ions with the sample on the adsorption performance of the four materials.Further,Freundlich isothermal adsorption model and quasi first order and quasi second order kinetic models were established to fit the adsorption process.Research showed that four kinds of materials for Pb(Ⅱ)and Cd(Ⅱ)adsorption performance of ordering: 1DAC/CS3>DAC10 > MCC > CS3.The four adsorption materials fitted by the Freundlich adsorption isotherm model had good linear correlation,indicating that the four materials had strong adsorption properties for Pb(Ⅱ)and Cd(Ⅱ).The parameters after fitting of the four materials and the equilibrium adsorption amount obtained by the quasi-second stage were closer to the experimental equilibrium value,further verifying that chemical adsorption affected the entire adsorption process which also included physical effects.In summary,1DAC/CS3 was the best of the four kinds of materials which achieved efficient adsorption of heavy metal ions,saveing time and economic cost.It was expected as heavy metal ions adsorption material for the efficient oxidation useing in water treatment.Further,it provided a strategic support for the preparation of highly effective oxidized cellulose/chitosan aerogel adsorbent.