Preparation Of Modified Chitosan Composite Aerogel Microbeads And Study On The Adsorption Property Of Cr(Ⅵ)

With the continuous development of human industrialization process,for mining use of various resources,such as metal and oil,resulting in organic and metal pollution.metal trace elements pollution is the main pollutant of the top three and is also one of the main materials of water pollution,therefore,to seek economic,efficient and environmental treatment of heavy metal ions pollution is of great significance.Chitosan is a natural alkaline cationic polysaccharide,which has a lot of amino and hydroxyl on the molecular chain,has good adsorption capacity of heavy metal ions.The sources of raw materials are extensive,low-cost and green biodegradable.But chitosan shows the distinct disadvantages such as poor chemical stability in acidic media,lack of active adsorptive sites and smaller specific surface.This paper will useβ-cyclodextrin and melamine which have a large number of active adsorption sites grafted onto chitosan molecular chain to increase its adsorption capacity,then composite inorganic particles like artificial zeolite or carbon nanotubes by coagulation bath and the method of vacuum freeze-drying preparation to make the system turn into aerogel with the large specific surface area.Study on the various aerogel adsorption behavior of hexavalent chromium ion,and the adsorption mechanism was explored.The main research results are as follows:(1)Using chitosan(CS)as raw material,grafting melamine(Me)by glutaraldehyde(GA),and then composite carbon nanotube(CNT)by the sodium hydroxide coagulation bath and freeze-drying preparation to get the chitosan/melamine/carbon nanotubes(CS-Me-CNT)aerogel,It was characterized by the XRD and FT-IR,~1H-NMR,BET,SEM,TG and other methods.The results showed that the melamine modified chitosan reaction was successful;The specific surface area of the CS-Me-CNT aerogel was 25.54 times higher than that of the raw material.The specific surface area of the chitosan powder was only 0.82 m~2/g,while that of the CS-Me-CNT aerogel was increased to 20.92 m~2/g.The swelling degree of CS-Me-CNT is reduced from 1485%to 997%.Aerogel has the best adsorption capacity of Cr(Ⅵ)at p H 3.0,the adsorption behavior accords with the Langmuir isothermal adsorption model and the secondary dynamic adsorption model,and the adsorption process is a spontaneous endothermic reaction.CS powder maximum adsorption capacity of Cr(Ⅵ)is 90.95 mg/g,the maximum adsorption capacity of CS-GA aerogels was 207.74 mg/g,CS-Me aerogel and CS-Me-CNT aerogel was 268.62 mg/g and 225.33 mg/g respectively,which were higher than that of CS-GA aerogel.Moreover,CS-Me-CNT aerogel had the best recycling performance.After repeated five times,the adsorption capacity retention rate was 67.10%,which was significantly higher than that of CS-GA aerogel and CS-Me aerogel which was 51.24%and42.87%respectively.(2)Using chitosan(CS)as raw material,graftingβ-cyclodextrin(β-CD)by glutaraldehyde(GA),and then composite artificial zeolite by the sodium hydroxide coagulation bath and freeze-drying preparation to get the chitosan/β-cyclodextrin/zeolite(CS-β-CD-PT)aerogel,It was characterized by the XRD and FT-IR,~1H-NMR,BET,SEM,TG and other methods.The results showed that theβ-cyclodextrin modified chitosan reaction was successful;The specific surface area of the CS-β-CD-PT aerogel was 28.59 times higher than that of the raw material.The specific surface area of the chitosan powder was only 0.82m~2/g,while that of the CS-β-CD-PT aerogel was increased to 23.44 m~2/g.The compression modulus of CS-β-CD aerogel was 224.28 KPa,CS-β-CD-PT aerogel compression modulus increases to 1054.22 KPa,and swelling degree is reduced from 1556%to 891%.Aerogel has the best adsorption capacity of Cr(Ⅵ)at p H 3.0,the adsorption behavior accords with the Langmuir isothermal adsorption model and the secondary dynamic adsorption model,and the adsorption process is a spontaneous endothermic reaction.CS powder maximum adsorption capacity of Cr(Ⅵ)is 90.95 mg/g,the maximum adsorption capacity of CS-GA aerogels was 217.91 mg/g,CS-β-CD aerogel and CS-β-CD-PT aerogel was 285.84 mg/g and 236.73mg/g respectively,which were higher than that of CS-GA aerogel.Moreover,CS-β-CD-PT aerogel had the best recycling performance.After repeated five times,the adsorption capacity retention rate was 67.12%,which was significantly higher than that of CS-GA aerogel and CS-β-CD aerogel which was 55.41%and 51.38%respectively.The results showed that the modified chitosan composite aerogel microbeads had a large adsorption capacity and good recycling performance for Cr(Ⅵ),and had a certain application prospect for the treatment of wastewater polluted by heavy metal ions.