Dense Janus membranes (JMs) are potential candidates in hypersaline wastewater treatments for membrane distillation (MD). However, dense surface layers generally add obvious membrane mass transfer resistance, limiting its practical application. In this study, a novel dense JM was facilely developed by controlled interfacial polymerization utilizing a phosphonium functional monomer (THPC) on hydrophilic polyvinylidene fluoride (PVDF) substrate. MD desalination performance results showed that the optimized THPC/PVDF JM surprisingly achieved a flux even 21.3% higher than that of its substrate and exhibited robust stability to surfactants, oil, and gypsum. Importantly, potential mechanism of remarkable flux enhancement of dense JMs was revealed. Raman and DSC analyses showed that THPC/PVDF JM with elevated intermediate water content had minimal enthalpy for water evaporation, thus facilitating water vaporization. Dynamic water contact angle measurements, advanced microstructural characterization by positron annihilation spectroscopy and water permeability experiments etc. showed that THPC/PVDF JM with high hydrophilicity and appropriately enlarged effective pore sizes provided strong water-absorption capacity and water permeability, contributing to rapid water replenishment. Both synergistically contributed to an incredible increase in membrane flux. Meanwhile, the dense surface layer, featured by its strong hydrophilicity and abundant hydroxyl groups, effectively prevented complex contaminants from intruding hydrophobic substrate and discouraged oil/gypsum adhesion, ensuring stable MD operation. This study shall provide useful insights and strategies to design high-flux dense JMs with minimal membrane failure propensity, highlighting its great potential for efficient hypersaline wastewater treatments.
Liu Xiaoman,Tian Chang,Zhao Yanxia,Xu Weiying,Dong Dehua,Shih Kaimin,Yan Tao,Song Wen
Application of ceramic membrane (CM) with outstanding characteristics, such as high flux and chemical-resistance, is inevitably restricted by membrane fouling. Coagulation was an economical and effective technology for membrane fouling control. This study investigated the filtration performance of ceramic membrane enhanced by the emerging titanium-based coagulant (polytitanium chloride, PTC). Particular attention was paid to the simulation of ceramic membrane fouling using four widely used mathematical models. Results show that filtration of the PTC-coagulated effluent using flat-sheet ceramic membrane achieved the removal of organic matter up to 78.0%. Permeate flux of ceramic membrane filtration reached 600 L/(m 2 · h), which was 10-fold higher than that observed with conventional polyaluminum chloride (PAC) case. For PTC, fouling of the ceramic membrane was attributed to the formation of cake layer, whereas for PAC, standard filtration/intermediate filtration (blocking of membrane pores) was also a key fouling mechanism. To sum up, cross-flow filtration with flat-sheet ceramic membranes could be significantly enhanced by titanium-based coagulation to produce both high-quality filtrate and high-permeation flux.
Huiting Shan,Jun Liu,Xipeng Li,Yi Li,F. Handan Tezel,Baoan Li,Shichang Wang
Membrane distillation, which can utilize low grade energy, has attracted significant attention recently. However, membrane fouling is a big issue impeding its development and industrialization. Hence, it is essential to prepare amphiphobic membrane for comprehensive anti-fouling performance. Herein, a facile and biomimetic method is explored to design amphiphobic surface with special structure and controllable wettability . Commercial polyvinylidene fluoride (PVDF) was primarily functionalized with polydopamine (PDA) coatings and then nanoscale roughness was introduced on the membrane surface, followed by the fluorination of 1H,1H,2H,2H-perfluorodecanethiol. It is revealed that the amphiphobic property can be accurately controlled by controlling the dosage of Ag + . When the concentration of Ag + is 300 mM, the water and oil contact angle of the optimal membrane can achieve 167.6 ± 0.27° and 136.9 ± 0.4°, respectively, while the water sliding angle is only 3 ± 0.1°, which demonstrates prominent superhydrophobicity and oleophobicity. Furthermore, the amphiphobic membrane exhibits excellent chemical and thermal stability under harsh conditions as well as outstanding comprehensive anti-fouling capacity with higher flux and excellent salt rejection in the long-term direct contact membrane distillation (DCMD) experiments, which shows promising potentials for application in the field of membrane distillation.
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