Moghadamfar Tanaz, Rocha de Oliveira Rodrigo, Cortina José Luis, Del Valle Luis J, de Juan Anna, Reig Mònica
Chemical Engineering Department, Escola d'Enginyeria de Barcelona Est (EEBE), Universitat Politècnica de Catalunya (UPC)-Barcelona TECH, Campus Diagonal-Besòs, 08930 Barcelona, Spain.
Barcelona Research Center for Multiscale Science and Engineering, Campus Diagonal-Besòs, 08930 Barcelona, Spain.
ACS Appl Polym Mater. 2025 Jun 26;7(13):8471-8485. doi: 10.1021/acsapm.5c00815. eCollection 2025 Jul 11.
Nanofiltration (NF) membranes are essential in wastewater treatment, battery industries, and brine management for selectively removing multivalent ions. However, fouling reduces their lifespan and necessitates harsh cleaning. The layer-by-layer (LBL) technique addresses this by modifying surface properties, enhancing rejection of divalent cations, such as magnesium and calcium, and minimizing fouling. This study evaluated a semiaromatic-based polyamide NF membrane (Fortilife-XN) modified using a LBL technique. Surface properties such as contact angle (CA), roughness, morphology, uniformity, and thickness were analyzed before and after modification. FTIR characterization revealed the membrane's structure, comprising a polyethylene terephthalate (PET) support, a polysulfone (PS) substrate, and a polyamide (PA) active surface. Poly-(sodium 4-styrenesulfonate) (PSS) was used as the polyanion, while poly-(diallyldimethylammonium chloride) (PDADMAC) and poly-(allylamine hydrochloride) (PAH) served as strong and weak polycations, respectively. Modifications in varying bilayers (1.5-6.5 BLs) with a positive terminal half-layer introduced peaks at 1034 and 923 cm, corresponding to sulfonate and C-N bonds. CA and roughness analysis showed that (PDADMAC/PSS)-4.5 (CA 20°, roughness 77 nm) and (PAH/PSS)-1.5 (CA 61°, roughness 79 nm) achieved superior wettability and roughness, confirmed by initial NF testing with a permeability of around 10 L/(m h bar). Ellipsometry, using Cauchy and Sellmeier models, measured multilayer thickness, estimating bilayers at ∼2 nm. Raman imaging visualized cross-sectional modifications, distinguishing raw and modified layers. Surface imaging revealed more uniform PAH deposition, while PDADMAC showed higher swelling with increased layers due to stronger affinity. These combined analytical techniques provided insights into the impact of LBL modification on membrane morphology and properties, aiding performance optimization. All membranes were preliminarily tested with a mixed salt solution (NaCl, CaSO, and MgSO). The average selectivity of Na/Ca for the bare membrane was 2.6 ± 0.4, increasing by 108% for (PDADMAC/PSS)-5.5 and 134% for PAH 6.5. For Na/Mg, the selectivity was 4.5 ± 0.3, rising by 49% for (PDADMAC/PSS)-5.5 and 131% for PAH 6.5.
纳滤（NF）膜在废水处理、电池行业和盐水管理中对于选择性去除多价离子至关重要。然而，膜污染会缩短其使用寿命，需要进行严苛的清洗。层层（LBL）技术通过改变表面性质、提高对镁和钙等二价阳离子的截留率以及减少污染来解决这一问题。本研究评估了采用LBL技术改性的一种基于半芳香族的聚酰胺纳滤膜（Fortilife-XN）。对改性前后的表面性质如接触角（CA）、粗糙度、形态、均匀性和厚度进行了分析。傅里叶变换红外光谱（FTIR）表征揭示了该膜的结构，包括聚对苯二甲酸乙二酯（PET）支撑层、聚砜（PS）基底和聚酰胺（PA）活性表面。聚（4-苯乙烯磺酸钠）（PSS）用作聚阴离子，而聚（二烯丙基二甲基氯化铵）（PDADMAC）和聚（烯丙胺盐酸盐）（PAH）分别用作强聚阳离子和弱聚阳离子。用带正电的半层进行不同双层数（1.5 - 6.5个双层）的改性在1034和923 cm处引入了峰，分别对应于磺酸根和C - N键。接触角和粗糙度分析表明，（PDADMAC/PSS）-4.5（接触角20°，粗糙度77 nm）和（PAH/PSS）-1.5（接触角61°，粗糙度79 nm）实现了优异的润湿性和粗糙度，初始纳滤测试的渗透率约为10 L/(m² h bar)证实了这一点。使用柯西和塞尔迈耶模型的椭偏仪测量了多层膜的厚度，估计双层膜厚度约为2 nm。拉曼成像可视化了横截面改性情况，区分了原始层和改性层。表面成像显示PAH沉积更均匀，而PDADMAC由于亲和力更强，随着层数增加显示出更高的溶胀。这些综合分析技术深入了解了LBL改性对膜形态和性能的影响，有助于性能优化。所有膜都用混合盐溶液（NaCl、CaSO₄和MgSO₄）进行了初步测试。裸膜的Na/Ca平均选择性为2.6 ± 0.4，（PDADMAC/PSS）-5.5提高了108%，PAH 6.5提高了134%。对于Na/Mg，选择性为4.5 ± 0.3，（PDADMAC/PSS）-5.5提高了49%，PAH 6.5提高了131%。
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