碳纳米管的改性及应用于反渗透膜仿生制备的脱盐行为的研究

Development of new membrane materials to solve the low water flux and high energy consumption of current conventional reverse osmosis membrane is of great significance to make the desanlination technology more practical. New type of reverse osmosis membranes composed of carbon nanotubes has given promise to novel technologies in desalination. Theoretical simulations prove that only the carbon nanotubes of diameter less than 1nm can effectively prevent salts pass through. With the increament of CNT diameter, the salt rejection rate continue to drop more seriously. By now, people can only fabricate carbon nanotube membranes with CNTs of minimun diameters from 1 to 2 nm, and have to fuctionalize them to get desalination characteristics. Research papers show that the present modifications have not yet solved the contradictions of the water flux and salt rejection rate. Inspired by high permeability and high selectivity of aquaporin and ion channel in biofilm, the appalicants plan to use molecular dynamics simulation to functionalize the tips and the innner core of carbon nanotubes as well as double-wall or multi-wall carbon nanotubes, and to determine the effects of modification groups through some microscopic indicators like computation of Potential of Mean Force (PMF) of ions through the nanotubes, the dehydration energy of ions in the confined environment and some macro indicators such as water fluxes and salt rejection rate more directly. Through our work, we hope to introdude modified CNT membranes with high salt rejection rate and high water fluxs and solve the difficulties that small diameter CNT membranes are hard to fabricate while big diameter CNT membranes can not block ions, and to lay the foundation for actual fabrication of this new class of reverse osmosis membranes.

开发新型膜材料以解决目前常规反渗透膜水通量较低、能耗大的问题，对海水淡化技术发展具有重要意义。基于碳纳米管的反渗透膜新材料研究是值得探索的方向之一。计算表明能有效截盐的碳纳米管直径应小于1nm，且管径越大，截盐率越低。但目前实验易生成的碳纳米管膜结构中碳管的直径最小在1～2nm，必须通过改性才可做成膜材料。文献表明目前的改性仍未摆脱水通量与截盐率的矛盾。受生物膜水通道及离子通道高效渗透性以及高超选择性的启发，申请人拟利用分子模拟及实验相结合的研究手段，针对大尺寸碳纳米管（大于1nm），在其内部、端口以及对双壁或多壁碳纳米管接入改性基团，并通过离子平均力势（PMF）、脱水能量等微观性质以及水通量、截盐率等宏观指标来确定改性基团的效果，设计并制备出具有高水通量、高截盐率的碳纳米管反渗透膜，以期解决目前反渗透膜存在的水通量与截盐率的矛盾及能耗高的问题。为海水淡化过程提供新型膜材料。

本项目按照基金任务要求，首先在计算机上做实验，通过分子动力学模拟的方法模仿生物水通道蛋白结构，分别对直径为1.356nm、1.763nm、2.034nm的（10，10）、（13，13）、（15，15）的直径大于1nm的扶手椅型碳纳米管（单壁/多壁）进行了一系列仿生改性。分别从端口，内壁，以及端口及内壁三个方面建立了连续的碳纳米管反渗透膜模型。通过分子动力学模拟的方法研究了在200MPa压力条件下，盐浓度在250mol/l条件下水分子以及Na+和Cl-在改性碳纳米管中的扩散过程并计算了其通量和水、Na+和Cl-进入碳纳米管时的平均力势，探索了水以及两种离子在碳纳米管内的轴向密度分布，观察了Na+和Cl-个别离子在管内的运动轨迹。为后期碳纳米管反渗透膜的制备提供理论基础。主要包括从五个方面内容进行了研究：1，用不同数量的NH3+、COO-、CONH2、OH短链亲水基团对直径1.356nm（10，10）单壁碳纳米管的端口和内壁改性；2，对直径1.763nm、（13，13）单壁碳纳米管的端口和内壁改性、；3，对直径2.034nm（15，15）单壁碳纳米管进行内壁和端口改性；4，对直径大于2nm（15，15）添加含长脂肪链的亲水基团进行端口和内壁改性；5，对多壁（双壁和三壁）碳纳米管进行端口和内壁改性。. 在模拟工作的基础上，本项目展开了一系列碳纳米管仿生改性工作。分别以直径为3.2nm，4.8nm的多壁碳纳米管（MWNTs）为研究对象，通过混酸、氯化亚砜、碳酸铵、吡啶、甲醇、液溴等化学试剂对其进行改性，产物经过FTIR，XPS，TGA，UV-vis，TEM等进行表征，结果显示在端口以及内壁成功接上了羧基，酰氯，酰胺以及氨基。且改性后的多壁碳纳米管的水分散性和稳定性都达到较好的状态。