CAS OpenIR
超疏水/双疏纳米纤维膜的制备及膜蒸馏性能研究
陆纯
Subtype硕士
Thesis Advisor曹宏斌
2019-07-01
Degree Grantor中国科学院大学
Degree Discipline环境工程
Keyword超疏水,双疏,F-poss,纳米纤维,膜蒸馏
Abstract

膜蒸馏是一种新型膜分离技术,在海水淡化、高盐废水处理等方面有着巨大的应用前景。膜蒸馏过程中普遍存在疏水膜材料的润湿和污染问题,同时可用于膜蒸馏过程的膜材料又非常有限,这些都限制了膜蒸馏技术的工业化发展。本文首先通过静电纺丝技术制备得到亲水性聚乙烯醇 (PVA) 纳米纤维膜,然后通过交联、硅烷偶联、巯基-烯点击化学反应的手段,成功制备出超疏水PVA膜,提供了一种从亲水材料制备疏水膜材料的思路,拓展了膜蒸馏膜材料来源;此外,首次将聚偏氟乙烯-六氟丙烯共聚物 (PVDF-HFP)和表面能极低的含氟聚倍半硅氧烷 (F-POSS) 进行混合静电纺丝制备得到具有双疏性能的复合膜,提高了抗润湿能力和抗污染能力。主要研究结果如下:(1) 将亲水性SiO2纳米颗粒分散在PVA水溶液中,通过静电纺丝法制备得到SiO2掺杂的PVA纳米纤维膜,然后经过多步化学改性得到超疏水的PVA膜 (F-PVA)。研究发现,由于纳米颗粒的引入,SiO2纳米颗粒在纤维表面发生团聚,构筑了具有多级粗糙结构的纳米纤维。化学改性对膜的表面成分和表面润湿性影响大,改性后的F-PVA膜表面的F的含量和CF3官能团含量显著增加,膜表面的疏水性提高,水接触角由改性前的0°增加至改性后的150.1°,滚动角测试结果为12.0°,可近似看成超疏水表面。改性后的膜表面耐化学性强,在持续360 min的DCMD测试中,F-PVA可保持稳定脱盐性能。(2) 以PVDF-HFP和F-POSS为纺丝材料,通过一步静电纺丝法制备出双疏复合纳米纤维膜。研究发现F-POSS的添加量会对膜的形貌结构、表面成分和润湿性产生影响。随着F-POSS添加量的增加,纤维的平均直径和膜的平均孔径增大,疏水性增强,当添加量为PVDF-HFP的50 wt%时,复合膜具有双疏性,乙醇的接触角可达128.1°。此外热处理工艺 (即120 ℃热处理) 也可以提高膜表面的双疏性。因为在热温的驱动下,低表面能的F-POSS发生表面偏析,使得复合膜表面F-POSS含量显著增大,膜表面疏油性提高。其中F-POSS添加量仅为PVDF-HFP的15 wt%时,膜的乙醇接触角由未热处理时的0°增加到120.3°。从双疏性和材料利用效率角度考虑,在本实验条件下,取F-POSS添加量为PVDF-HFP质量的15%为最优化剂量,通过后续120 ℃的热处理工艺得到最优化的双疏膜。(3) 将所制备的PVDF-HFP/F-POSS复合膜用来处理含表面活性剂的含盐废水和含油类有机物的含盐废水。研究发现,基膜 (F-0) 和未热处理的复合膜 (F-15) 均无法抵抗这两类有机物的污染,而热处理后的双疏复合膜 (F-15-H) 可以抵抗表面活性剂的润湿和污染,但是无法避免油类有机物的污染。结合XDLVO理论计算,三种膜与两类有机物间的总的自由能 (ΔGSWL) 均为负值,表现为引力相互作用。其中表面活性剂类污染物与双疏复合膜表面的引力作用相对较小,表面活性剂很难附着,可保持优良的抗润湿性;相比之下,油类污染物与双疏膜表面的界面吸引作用力大,在水下矿物油与膜表面之间存在较强的吸引作用,使得部分矿物油吸附到膜表面,污染问题不可避免。;Membrane distillation (MD) has a great application prospect in seawater desalination and high salty wastewater treatment. Wetting and fouling issues of hydrophobic membranes are common problems in MD process. Besides, materials that can be used in membrane distillation process are very limited, which limits the industrial development of membrane distillation technology. In this paper, hydrophilic PVA nanofiber membrane was firstly prepared by electrospinning technology and then the superhydrophobic PVA membrane was successfully prepared by means of cross-linking, silane coupling and mercapto-ene click reaction. It provides a new way to prepare hydrophobic membrane materials from hydrophilic materials and expands the source of materials for MD. In addition, for the first time, F-POSS were used to prepare omniphobic membrane for MD through one-step electrospinning of PVDF-HFP/F-POSS colloidal solution. The addition of extremely low surface energy materials (F-POSS) can improve the anti-wetting anti-fouling properties of the membrane.The main research results are as follows:(1) The superhydrophobic F-PVA membrane was fabricated by electrospinning of PVA solution blended with hydrophilic SiO2 nanoparticles followed by multi-step of chemical modification. SiO2 nanoparticles agglomerated on the surface of the fibers which can construct multilevel rough structure on the fibrous surface. The chemical modification of the membrane had great influence on the composition and surface wettability of the membrane. The surface contents of fluorine and CF3 functional group on the F-PVA membrane increased significantly after chemical modification. The water contact angel of F-PVA membranes increased to 150.1° while the rolling angle reaches to 12°, which can be regard as superhydrophobic surface. The F-PVA membrane has strong chemical resistance and can maintain stable desalination performance in 360 min DCMD test.(2) The omniphobic membrane was fabricated through one-step electrospinning of PVDF-HFP/F-POSS colloidal suspension solution. The addition of F-POSS could affect the morphology, surface composition and wettability of the membrane. With the increasing loading of F-POSS, the average diameter and average pore diameter of the nanofibers both `increased. The composite membrane exhibited great omniphobicity with ethanol contact angle of 128.1° with the addition of F-POSS reached to 50 wt% of PVDF-HFP. Besides, the omniphobicity of the membrane can be tailored through post-thermal treatment (120 ℃) alternatively. After additional post-thermal treatment (120 ℃), the surface contents of F-POSS increased significantly due to the substantial surface migration of F-POSS molecules. In such case, the ethanol contact angel can reach to 120° for the membrane with F-POSS dosage only 15 wt% of PVDF-HFP. Considering the influence of F-POSS on the properties of the composite membrane, the optimal dosage of F-POSS was 15 wt% of PVDF-HFP.(3) The prepared PVDF-HFP/F-POSS composite membranes were tested in MD process using NaCl solution containing surfactant and oil respectively. Result showed the two foulants caused severe wetting or fouling for the pristine membrane (F-0) and the composite membrane without post-thermal treatment (F-15), respectively. In contrast, the omniphobic membrane after post-thermal treatment (F-15-H) showed good anti-wetting property toward surfactant foulant while had fouling problems in the presence of oil organics. The calculation result of XDLVO showed that the interaction force between the three membranes and the two foulants is attraction. For surfactant pollutants, the attractive force of omniphobic membrane is smaller compared to that of the other two membranes. The surfactant is difficult to adsorb on the omniphobic membrane. For oil foulants, the attractive force of omniphobic membrane is as large as that of the other two membrane. Oil foulants would easily absorb on the surface of omniphobic membrane and the fouling problem is inevitable in such case. 

Language中文
Document Type学位论文
Identifierhttp://ir.ipe.ac.cn/handle/122111/40620
Collection中国科学院过程工程研究所
Recommended Citation
GB/T 7714
陆纯. 超疏水/双疏纳米纤维膜的制备及膜蒸馏性能研究[D]. 中国科学院大学,2019.
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