Xuan Zhang,Liang Shen,Chen-Yu Guan,Chu-Xuan Liu,Wan-Zhong Lang,Yan Wang
This work provides a facile and effective way of incorporating SiO 2 @MWNTs in polyvinylidene fluoride (PVDF) substrate to alleviate the internal concentration polarization (ICP) impact of the resultant thin film composite forward osmosis (TFC-FO) membranes for the first time. The in-situ decoration of multi-walled carbon nanotubes (MWNTs) using tetraethyl orthosilicate (TEOS) as precursor was conducted, resulting in improved hydrophilicity and the excellent dispersion of synthesized SiO 2 @MWNTs in PVDF membrane substrates accordingly. Effects of the SiO 2 @MWNTs concentration on the morphologies and properties of the modified substrates, and further impact on the polyamide (PA) layer structure are investigated via various characterizations. Besides, the intrinsic separation properties and forward osmosis performance of resultant TFC-FO membranes are also systemically studied. In comparison with the control TFC membrane, SiO 2 @MWNT-modified TFC membranes exhibit higher water fluxes with the enhanced membrane selectivity, as indicated by the decreased J S /J V values (from 1.10 to 0.19 g/L). This work therefore presents an alternative approach to prepare TFC-FO membranes with enhanced water flux as well as increased selectivity.
The membrane contactor has been considered an effective device to capture CO 2 , but its performance is limited by membrane wetting phenomena. In this work, the ZIF-8/ZIF-L (zeolitic imidazolate framework) based composite membrane with excellent hydrophobic stability and CO 2 permeability was successfully fabricated by coating the dense layer on the porous PVDF (polyvinylidene fluoride) substrate. The dense layer was developed by evenly incorporating ZIF-8 nanocrystals and ZIF-L nanosheets into the polydimethylsiloxane (PDMS) polymer. The as-prepared membrane possessed competitive hydrophobicity with a water contact angle (WCA) of 131.8°. And after a ten-day immersion test in CO 2 absorbent, the WCA only declined by 9.8%, exhibiting excellent hydrophobic stability. Besides, the CO 2 permeability of the composite membrane was 61.8×10 −8 ·mol·m −2 ·s −1 ·Pa −1 with an ideal CO 2 /N 2 separation factor of ∺20, which was effectively improved in comparison with the control membrane. In the CO 2 absorption experiment, the prepared membrane achieved the competitive CO 2 flux of 3.02×10 −3 ·mol·m −2 ·s −1 when the liquid velocity was 0.25 m·s −1 and displayed robust long-term operating stability. Finally, the AC impedance technique was applied to continuously monitor the wetting state of composite membranes, which further investigated their anti-wetting ability.
Zhuo Li,Shoutian Qiu,Xiang Ying,Fangli Zhang,Xianli Xu,Zhaoliang Cui,Yong Wang
Membrane distillation (MD) is receiving growing interest because of its >99.9% salt rejection even with low-grade waste heat as the energy supply. However, MD membranes are prone to be wetted and usually require complicated modification strategies to gain sufficient hydrophobicity . In this work, we report a new type of MD membranes with hydrophobic films carrying pores in the ultrafiltration range as the separation layers. Such membranes are prepared by coating an A-B-A triblock copolymer polystyrene- block -polydimethylsiloxane- block -polystyrene (PS- b -PDMS- b -PS, further abbreviated as SDS) on the macroporous PVDF substrate, followed by soaking in alkanes to cavitate the SDS coating layers following the mechanism of selective swelling. The PDMS microdomains in the SDS layers are converted to interconnected nanopores , and the PDMS blocks are enriched along the pore walls and membrane surface, endowing the membranes with intrinsic hydrophobicity. Thus-prepared SDS membranes exhibit stable rejection to NaCl (>99.99%) and high permeate flux up to 32.8 kg m −2 h −1 , better than most MD membranes with large pores in the microfiltration range. Moreover, the SDS membranes display excellent wetting resistance, good heat resistance, and long-term stability. This work provides a new strategy to prepare MD membranes enabled by selective swelling of hydrophobic block copolymers, and demonstrates the great potential of hydrophobic ultrafiltration membranes in the long-term use in membrane distillation.
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