The Study Of Electrospun Chitosan-based Composite Membranes For Copper Ions Adsorption

With the continuous development of industrialization and urbanization,environmental pollution has become serious.In particular,industrial and urban wastewater with heavy metal ions threaten the ecological environment and human health.Heavy metal ions are easily soluble in water and migrate to the surrounding soil and groundwater.They can not be decomposed in nature,which endangers human health.Among the heavy metal ions,copper ion（Cu（II））is a widespread environmental toxicant and pollutant which is produced by the industries such as plating baths,electrical,wood pulp production and fertilizer industry,etc.Excessive copper ions in the human body can lead to physical weakness,anorexia,cirrhosis and neurological diseases,etc.Hence,it is necessary for removing Cu（II）from contaminated water resources.Up to now,various methods have been explored to treat heavy metal contaminated wastewater including chemical precipitation,membrane adsorption,ion exchange and evaporations,etc.Adsorption is the most common method because of its easy operation,low cost,high efficiency,and low secondary pollution impact.There are many kinds of adsorbents such as biomaterials,carbon materials,metal oxide nanoparticles,synthetic polymers,et al.Chitosan（CS）,a natural polymer material,has high adsorption capacity for heavy metals because of its large number of amino and hydroxyl functional groups on the molecular chain,which can coordinate with heavy metal ions to form complexes.Therefore,CS has been widely used as an adsorption material for removing metal ions.Electrospinning is an effective and versatile technology for preparing nanofiber mats,which can obtain polymer composite nanofibers with outstanding characteristics such as large surface area,high porosity and gas permeability.In this paper,the electrospinning technology was used to study the basic natural polymer material CS as the research object.CS-based blended fiber membrane and stacking structure membrane were prepared by adding TiO₂ nanoparticles and changing CS morphology,respectively.The adsorption properties of Cu（II）on different composite membranes were investigated.The main research were described as following three aspects:（1）The titanium dioxide/CS/poly（lactide-co-caprolactone）（TiO₂/CS/P（LLA-CL））composite membranes were electrospun as the adsorbent for the adsorption of Cu（II）.The effects of TiO₂ content,pH value,adsorption time and initial solution concentration on the adsorption performance of the composite membrane were investigated.According to the adsorption experimental data,maximum adsorption amount was 190.5 mg/g using 2%TiO₂ in TiO₂/CS/P（LLA-CL）membrane.BET analysis showed that the addition of TiO₂ nanoparticles could increased the specific surface area and adsorption sites of the composite nanofibers.FTIR and XPS analysis approved that chelation and ion exchange occurred during adsorption process.The adsorption kinetics data followed the quasi-second-order model and the adsorption isotherms date followed the Langmuir isotherm model.The adsorption-desorption experiments indicated that the composite adsorbent has good stability.（2）While ensuring the stability of the CS-based adsorbent,in order to further increase the adsorption ability,the controlled electrospinning of the multi-morphological CS membranes were studied to increase the specific surface area and adsorption site.The different morphologies of CS were obtained by controllable electrospinng.The results showed that pure CS fibers were successfully prepared by using formic acid/hexafluoroisopropanol（FA/HFIP）mixed solvent with volume ratio of 1:9 at 3%CS concentration.When CS concentration was2%with 90%acetic acid as solvent,CS concave hemispheric particles with uniform size were prepared with an average diameter of 1.22 um.These are the basis for desingning of CS stacking adsorption membrane.（3）In this study,we prepared CS stacking structure membrane by alternating electrospinning/electrospray technology.Before adsorption,the CS membrane was immersed in 1 M sodium carbonate to improve its stability.The effects of stacking structure,pH value,adsorption time and initial solution concentration on adsorption abilities of composite membrane were investigated.Adsorption experiments showed that compared to other structures CS membranes,the sandwich structure CS membranes could reach adsorption equilibrium in only 60 minutes,and the maximum adsorption capacity was 276.2 mg/g.The sandwich structure CS adsorbent exhibited nearly 100%removal rate for Cu（II）at an initial concentration of 100 mg/L.The adsorption experiments showed that the adsorption behavior of CS stacking adsorbent followed pseudo-second-order model and Langmuir isotherm model.The adsorption mechanism was analyzed by XPS and FTIR,which indicated that the hydroxyl and amino functional groups of CS were involved in the chelation with Cu（II）.And the synergy of CS microstructure,the adsorption efficiency was greatly improved using stacking structure CS adsorbent.