电辅助磺化聚砜膜分离医药废水传递机理的分子动力学模拟研究

Electro-enhanced SPSf membrane separation of pharmaceutical wastewater transfer mechanism:Molecular dynamics study

医药生产废水的膜法分离技术对实现绿色医药化工意义重大。其中,通过电场辅助强化膜分离效率,阻止荷电医药分子迁移、离子跨膜传递,有较好的应用前景。但目前尚无分子尺度模型揭示相关膜界面和膜传递通道内的分离机制,也制约了相关新型膜材料设计和膜技术研发。利用分子动力学模拟(MD)技术,从分子层面上探究电场辅助下的磺化聚砜膜(SPSf)分离头孢呋辛钠医药废水的机理,并模拟膜内含水量对离子传递行为的影响。模拟过程中能量、温度波动低于10%,证明模型设定与计算方法可靠;所构建模型玻璃化转变温度与实验值接近,证明所选力场合适,所得数据可用于后处理及结果分析。结果表明,外加电场增强膜表面带电基团对同性离子的排斥能力。随着电场在一定程度上的增强(0~0.15 V·Å^(-1)),解离后的荷电膜对带负电粒子排斥能力增强(SPSf解离后,膜表面头孢呋辛离子强度下降15.7%),对Na+吸附更强(Na+强度增加19.4%),证明电增强Donnan效应与电增强吸附/脱附是电辅助荷电纳滤膜分离医药废水的主要作用机理。此外,分析了电场强度与膜内含水量对离子在SPSf膜体系中扩散的影响。在模拟实验范围内,随着含水量与电场强度增大,荷电膜内离子扩散能力增强;在膜内含水量λ=2.0、0.10 V·Å^(-1)时,Na+扩散系数与头孢呋辛离子扩散系数相差1.54×10^(-6)cm^(2)·s^(-1),在这种条件下离子选择性最高。通过分子动力学模拟技术(MD)从微观层面解释电辅助荷电膜分离医药工业废水的调控机理,为理性设计和选择荷电膜材料与膜表面的基团改性提供了有益的理论参考。

Membrane separation technology for pharmaceutical wastewater production is of great signifi-cance for the realization of green chemical industry.In particular,the enhancement of membrane separa-tion efficiency by electric field assisted to promote the migration of charged pharmaceutical molecules has excellent application prospects.However,there are no modeling studies at the molecular scale to reveal the separation mechanisms within the relevant membrane interfaces and membrane transport channels,which also restrict the development of relevant innovative membrane materials.In this paper,we investi-gate the mechanism of separation of cefuroxime sodium pharmaceutical wastewater by sulfonated polysul-fone membrane(SPSf)assisted by electric field at the molecular level using molecular dynamics(MD),and simulate the behavior and dynamic properties of ion transfer by water content in the membrane.The energy and temperature fluctuations during the simulation are less than 10%,which proves that the model setting and calculation method are reliable.The constructed model glass transition temperature is close to the experimental value,which proves that the selected force field is suitable and the obtained data can be used for post-processing and result analysis.The results show that the applied electric field enhances the ability of the charged groups on the membrane surface to repel homogeneous ions.As the external electric field is enhanced to a certain extent,the dissociated charged membrane has a stronger ability to repel negatively charged particles(the intensity of cefuroxime ions on the membrane surface decreased by 15.7%after SPSf dissociation),and enhances the adsorption capacity for Na+(the intensity of Na+on the membrane surface increased by 19.4%after SPSf dissociation).It demonstrates that electrically en-hanced Donnan effect and electrically enhanced adsorption/desorption are the main mechanisms of action of electrically assisted charged nanofiltration membranes for separation of pharmaceutical wastewater.In addition,the effects of electric field strength and water content in the membrane on the diffusion of ions in the SPSf membrane system were analyzed.In the range of simulation experiments in this paper,as the water content and electric field strength increase,the ion diffusion capacity within the charged membrane increases.Atλ=2.0,0.10 V·Å^(-1),the difference between Na+diffusion coefficient and cefuroxime ion diffusion coefficient is 1.54×10^(-6)cm^(2)·s^(-1).The highest ion selectivity was observed under these condi-tions.Based on the MD results,the mechanism of electrically enhanced membrane separation of pharma-ceutical wastewater is illustrated,which provides a useful theoretical reference for the design and selec-tion of charged membrane materials.