| With the advancement of industrialization process in China,the pollution of heavy metal ions has become increasingly serious.At present,the heavy metal wastewater treatment methods commonly used at home and abroad include chemical precipitation method,ion exchange method,redox method,adsorption method and membrane separation method.Among them,the adsorption method,as a universally feasible technology,has attracted much attention due to its high efficiency,low cost and environmental friendliness.Montmorillonite(MMT)is a green and natural adsorbent material,which is often used as an adsorbent for heavy metal wastewater due to its lamellar structure and the ion exchange performance of low-cost cations between layers.However,due to its strong suspensibility,it has problems such as being difficult to separate and recover in the wastewater treatment process and easily causing re-contamination.Porous fiber materials have a large specific surface area and a certain solid loading capacity,and are often used as a supporting substrate for certain adsorbent materials.Centrifugal spinning technology as a green process for the efficient preparation of porous fiber membranes has certain industrial application prospects.In this study,cellulose acetate(CA)with good biocompatibility and degradability was selected as the MMT supporting substrate,and the porous composite fiber membrane was constructed by centrifugal spinning equipment,which made the CA fiber membrane more excellent while making up for the drawbacks of MMT.Adsorption performance.The main research contents and results are as follows:(1)Centrifugal spinning control of porous CA fiber membraneThrough the investigation of the solvent type and ratio of the spinning solution,it was found that the CA with porous structure was successfully prepared when the mass ratio of the selected solvent dichloromethane(DCM)to dimethyl sulfoxide(DMSO)was 8:2.Fiber membrane;based on the ratio of other spinning parameters in the centrifugal spinning system,the effect of other spinning parameters on the morphology of porous CA was investigated.The results showed that when the mass ratio of solvent DCM to DMSO was 8:2,the spinning range of CA spinning solution is 11～14wt%.The diameter of porous CA fiber increases with the increase of the diameter of the spinning wire,and decreases with the increase of the rotating speed.When the concentration of CA is 12wt%,the rotation speed is 8000rpm.The orifice diameter of the orifice is 0.4mm,the fixed collection distance is 12cm,and a porous CA fiber membrane having a good morphology is obtained.(2)Modification of MMT and preparation of porous composite fiber membraneA porous composite fiber membrane was prepared by introducing MMT based on the centrifugal spinning parameters of the porous CA fiber membrane.In order to increase the loading of MMT in the composite fiber membrane,three modified MMTs were prepared by two modification methods and blended with CA into a porous composite fiber membrane.The morphology changes of MMT before and after modification and the effects on the porous composite fiber membrane were investigated.The results showed that the characteristic groups of the corresponding modified materials were introduced into the modified MMT,the maximum variation of layer spacing increased from 0.963nm up to 1.077nm.Compared with the maximum amount of natural MMT of 3wt%,the maximum addition amount of the modified MMT is increased to 5wt%,the composition ratio in the composite fiber membrane is about 16.45%.(3)Study on adsorption properties of porous composite fiber membrane for Cu2+The prepared porous composite fiber membrane was applied to the adsorption experiment of Cu2+to explore its adsorption performance.The results show that the maximum adsorption capacity of Cu2+ can reach 60.272mg/g after the adsorption of 5wt%CTS-MMT composite fiber membrane at pH=5.The adsorption isotherm curve of Cu2+ on porous composite fiber membrane is in accordance with the Langmuir model,which belongs to monolayer adsorption.The adsorption kinetics of Cu2+on porous composite fiber membrane is in accordance with the pseudo-second-order model,and multiple kinetic mechanisms are used in the adsorption process.After five desorption cycles,the porous composite fiber membrane can still remain Cu2+ adsorption efficiency of 83%,indicating that had good recycling properties. |
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