木质素磺酸钠改性聚砜膜的制备及其在正渗透膜中的应用

Preparation of Sodium Lignin Sulfonate Modified Polysulfone Membranes and Their Use as Supports for Forward Osmosis Membranes

采用木质素磺酸钠作为亲水添加剂,通过浸没沉淀相转化法制备了木质素磺酸钠共混改性聚砜膜,以改善聚砜膜的亲水性,并用作正渗透膜的支撑层,以降低内浓差极化效应.利用扫描电子显微镜、衰减全反射傅里叶变换红外光谱仪、水接触角仪等研究了不同木质素磺酸钠添加量对聚砜膜的结构和表面性质的影响.结果表明,添加木质素磺酸钠后,聚砜膜的指状孔变得规整且狭长.水接触角实验证实添加木质素磺酸钠能改善聚砜膜的亲水性,当木质素磺酸钠含量为0.4 wt%时,聚砜膜的表面水接触角可降低至65°.正/反渗透测试装置分别用于表征正渗透膜的传质性质和结构参数.结果表明,以0.4 wt%木质素磺酸钠改性聚砜膜为支撑层的正渗透膜的水渗透性能(A=3.12×10^(-5) LMH×Pa^(-1))优于纯聚砜基底正渗透膜(0.76×10^(-5)LMH×Pa^(-1)),而且前者的结构参数(S=2010mm)远小于后者(3450mm),说明木质素磺酸钠改性聚砜膜有效弱化了正渗透膜的内浓差极化效应.

Forward osmosis （FO） becomes an emerging and promising platform of membrane separation technology. Nevertheless, FO processing always suffers from poor water flux performance, resulted from internal concentration polarization （ICP）. Herein, to improve the hydrophilicity of polysulfone （PSf） membranes, sodium lignin sulfonate （LS） was used as a hydrophilic additive to prepare LS/PSf blend membranes by phase inversion. The LS/PSf blend membranes can serve as the hydrophilic support layer of FO membranes in order to weaken the ICP. The effects of LS content on the structure and the properties of LS/PSf blend membranes were investigated by scanning electron microscopy （SEM）, FTIR/ATR spectroscopy, and water contact angle （WCA）. It was shown that the finger-like pores of LS/PSf blend membranes became long and narrow, and the WCA of the membrane was reduced to 65° with LS content of 0.4 wt%. Then, thin film composite （TFC） membranes were fabricated by interracial polymerization on PSf membrane and LS/PSf blend membrane with LS content of 0.4 wt%, which were named TFC and TFC-LS0.4 membranes, respectively. The results from FTIR/ATR spectroscopy and SEM confirmed that polyamide （PA） films were formed with a typical ＂ridge-valley＂ surface morphology on both TFC and TFC-LS0.4 membranes. Moreover, the PA film of TFC-LS0.4 membrane was rougher and thicker than that of TFC membrane. Their FO performances were characterized by FO test, where the draw solution was 0.5, 1.0, 1.5 or 2.0 mol/L NaC1 solution, and the feed solution was DI water. The water flux and reverse salt flux increased with the concentration of draw solution both for TFC and TFC-LS0.4 membranes. With the same draw solution, TFC-LS0.4 membrane showed a larger water flux and reverse salt flux than TFC membrane. Furthermore, reverse osmosis test was conducted to study the transport properties and structural parameters of FO membranes. It is clear that TFC-LS0.4 membrane presented higher water permeability （A = 3.12 × 10^-5 LMH·Pa-1） with smaller structural parameter （S = 2010 gin） than TFC membrane （A = 0.76 × 10^-5 LMH·Pa^-1, S = 3450 μm）. It means that the hydrophilicity of LS/PSf blend membranes facilitated the weakening of ICP effects of FO membranes.