PDA夹层调控的荷正电纳滤膜的制备及在水处理中的应用

Preparation of Positively Charged Nanofiltration Membrane Regulated by PDA Interlayer and Its Application in Water Treatment

当前商用纳滤膜在溶液中多显示荷负电,而根据道南效应,荷正电纳滤膜在分离废水中的荷正电物质时更具优势。本工作在掺杂金属有机骨架(MOF)的混合基质基膜上构建聚多巴胺(PDA)中间层,再通过聚乙烯亚胺(PEI)和均苯三甲酰氯(TMC)的交联反应制备了荷正电聚酰胺复合纳滤膜。对多巴胺(DA)沉积浓度和时间及TMC有机相的添加条件进行优化;对比了PDA中间层添加前后两种复合纳滤膜对1 g/L的MgCl2、NaCl、MgSO4、Na2SO4溶液的渗透截留情况;重点考察了改性膜对含Cu2+、Ni2+和Pb2+的重金属溶液及五种阴阳离子染料的处理情况,最后评估了膜的耐污染性能。结果表明,将2 g/L的DA在超滤支撑层上沉积90 min,PEI水相浓度为1.2%、浸没时间为7 min、TMC有机相浓度为0.5%、交联时间为120 s时,所制备的改性膜的综合性能最佳,膜的接触角为51.5°,表面粗糙度下降,等电点在pH为9左右,在溶液中显示荷正电。改性膜对MgCl2的截留率上升到94.26%,在0.8 MPa下,其对Cu2+、Ni2+、Pb2+溶液的水通量均在40 L/(m2·h)以上,且离子截留率分别为96.57%、95.23%、94.73%;同时,其对几种染料的截留率均能达到90%以上。因此,PDA中间层改性的荷正电纳滤膜在废水处理中具有良好的应用前景。

At present,most commercial nanofiltration membranes show negative charge in solution,while according to the Donnan effect,positively charged nanofiltration membranes have more advantages in separating positively charged substances in wastewater.In this work,polydopamine(PDA)interlayer was constructed on MOF doped mixed matrix base membrane,and then positively charged polyamide composite nanofiltration membrane was prepared by crosslinking reaction of polyethyleneimine(PEI)and homobenzoyl chloride(TMC).The concentration and time of dopamine(DA)deposition and the addition conditions of TMC organic phase were optimized;the permeation and interception of 1 g/L MgCl2,NaCl,MgSO4and Na2SO4solutions by two kinds of composite nanofiltration membranes before and after the addition of PDA interlayer were compared;the treatment of heavy metal solutions containing Cu2+,Ni2+and Pb2+and five anionic and ionic dyes by the modified membrane was investigated.Finally,the pollution resistance of the membrane was evaluated.The results showed that when 2 g/L DA was deposited on the ultrafiltration support layer for 90 min,the concentration of PEI aqueous phase was 1.2%,immersion time was 7 min,the concentration of TMC organic phase was 0.5%and crosslinking time was 120 s,the comprehensive performance of the modified membrane was the best.At this time,the hydrophilicity of the modified membrane was improved,the contact angle was 51.5°,the surface roughness of the membrane decreased,and its isoelectric point is about pH=9,showed positive charge in general solution.The retention rate of MgCl2by the modified membrane increased to 94.26%.At 0.8 MPa,the water flux to Cu2+,Ni2+and Pb2+solutions was more than 40 L/(m~2·h),and the ion retention rates were 96.57%,95.23%and 94.73%respectively.At the same time,the rejection rate of several dyes can reach more than 90%.Therefore,the positively charged nanofiltration membrane modified by PDA interlayer has a good application prospect in wastewater.