Functionalized Microfibers Made From Waste Cotton Fabric And Their Application In Wastewater Treatment

The waste fabric has caused great pressure on the ecological environment.It will take several years or even decades for waste fabric to degrade after landfill,which will cause certain harm to water and soil resources.Burning waste fabric will produce toxic and harmful substances,and the pollution will be more serious.With the rapid development of industry,the output of industrial wastewater has increased rapidly.There are many toxic dye molecules and some dangerous heavy metals in wastewater,which seriously affect the natural environment and even endanger people’s health and personal safety.As a simple and efficient wastewater treatment method,adsorption is particularly important in the wastewater treatment process.Cotton fibers have abundant polar hydroxide groups and fiber cross-section cavity structures,which make it have the potential as adsorption material.However,natural cellulose fibers are limited as adsorbents because of their small absorption capacity and poor chemical selectivity.The presence of a large number of hydroxyl groups on the surface of cellulose provides favorable conditions for chemical modification,thus enhancing the adsorption performance of the fibers.Therefore,this subject takes waste cotton fabric as raw material to prepare cotton microfiber（CE）through alkali treatment and high-speed homogenization,which makes cotton fabric microfibrillar and increases specific surface area.Glutaraldehyde is used as crosslinking agent,and polyethylene imine is added for crosslinking reaction.The chemically modified microfiber（PEI@CE）is obtained through crosslinking modification.The modified cotton fiber surface introduced aminos,which increased its cationic properties.The adsorption performance and mechanism of the modified microfiber on methyl blue solution and silver nanoparticles solution were discussed.The main work was as follows:（1）Preparation and characterization of cotton microfibersCE was obtained from waste cotton fabric after alkali treatment and high-speed homogenization.By changing the speed of high speed homogenizer（6000 rpm,10000 rpm and 15000rpm）,it was found that the fiber diameter showed a decreasing trend,indicating that homogenization was beneficial to fiber refinement.SEM results showed that the fiber began to be spun after homogenization.XRD and FTIR results showed that the fiber kept its original crystal structure after treatment.The results showed that alkali treatment and high speed homogenization did not damage the crystal structure of fiber.（2）Modification and characterization of cotton microfibersPolyethylene imine was crosslinked with CE using glutaraldehyde as crosslinking agent.The result of Zeta potential test showed that PEI@CE was positively charged in both acidic and alkaline conditions,and Zeta potential increased with the increase of p H.SEM showed that PEI@CE presented a fluffy network structure,and the specific surface area increased after modification.TGA results showed that,compared with the unmodified microfibers,the pyrolysis temperature of PEI@CE increased,indicating that the thermal stability of the modified microfibers was improved.The characteristic absorption peak of C=N appeared in the FTIR spectrum of PEI@CE,indicating that the modification process was formed by the discovery of the hydroxyl group in glutaraldehyde and the amino functional group in polyethylene imine.（3）Study on the adsorption performance of modified microfibers on methyl blue solutionThe factors affecting the adsorption of PEI@CE on methyl blue dye were studied.The optimum adsorption conditions were determined as follows: adsorption time 30 min,adsorption temperature 35 ℃,dosage of adsorbent 15 mg,dye concentration 50mg/L,p H 7.Under the optimal adsorption conditions,the removal rate of 50 mg/L methyl blue can reach 98%,and the adsorption capacity of 200 mg/L methyl blue can reach 288 mg/g.After five adsorption and desorption cycles,the removal rate of methyl blue can still reach 85%.（4）Study on the adsorption properties of modified microfibers on silver nanoparticlesBy exploring the factors affecting the adsorption of PEI@CE on silver nanoparticles,the optimal adsorption conditions are determined as follows: adsorption time 30 min,adsorption temperature 20 ℃,dosage of adsorbent 4 mg,concentration of Ag nanoparticles 20 mg/L,p H 5,rotation speed 300 rpm.Under the optimal conditions,the removal rate of 20 mg/L silver nanoparticles can reach 99%,and the maximum adsorption capacity can reach 480 mg/g.TG and SEM results showed that Ag nanoparticles adsorbed on PEI@CE.