To consolidate the position of membrane distillation (MD) as an emerging membrane technology that meets global water challenges, it is crucial to develop membranes with ideal material properties. This study reports a facile approach for a polyvinylidene fluoride (PVDF) membrane surface modification that is achieved through the coating of the surface with poly(dimethylsiloxane) (PDMS) polymeric microspheres to lower the membrane surface energy. The hierarchical surface of the microspheres was built without any assistance of a nano/microcomposite by combining the rapid evaporation of tetrahydrofuran (THF) and the phase separation from condensed water vapor. The fabricated membrane exhibited superhydrophobicity-a high contact angle of 156.9° and a low contact-angle hysteresis of 11.3°-and a high wetting resistance to seawater containing sodium dodecyl sulfate (SDS). Compared with the control PVDF-hexafluoropropylene (HFP) single-layer nanofiber membrane, the proposed fabricated membrane with the polymeric microsphere layer showed a smaller pore size and higher liquid entry pressure (LEP). When it was tested for the direct-contact MD (DCMD) in terms of the desalination of seawater (3.5% of NaCl) containing SDS of a progressively increased concentration, the fabricated membrane showed stable desalination and partial wetting for the 0.1 and 0.2 mM SDS, respectively.
Electrospun
nanofiber membranes (ENMs) have garnered increasing
interest due to their controllable nanofiber structure and high void
volume fraction properties in membrane distillation (MD). However,
MD technology still faces limitations mainly due to low permeate flux
and membrane wetting for feeds containing low surface tension compounds.
Perfluorinated superhydrophobic membranes could be an alternative,
but it has negative environmental impacts. Therefore, other low surface
energy materials such as silica aerogel and polydimethylsiloxane (PDMS)
have great relevancy in ENMs fabrication. Herein, we have reported
the high flux and nonwettability of ENMs fabricated by electrospraying
aerogel/polydimethylsiloxane (PDMS)/polyvinylidene fluoride (PVDF)
over electrospinning polyvinylidene fluoride-co-hexafluoropropylene
(PVDF–HFP) membrane (E-PH). Among various concentrations of
aerogel, the 30% aerogel (E-M3-A30) dual layer membrane achieved highest
superhydrophobicity (∼170° water contact angle), liquid
entry pressure (LEP) of 129.5 ± 3.4 kPa, short water droplet
bouncing performance (11.6 ms), low surface energy (4.18 ± 0.27
mN m–1) and high surface roughness (R
a: 5.04 μm) with re-entrant structure. It also demonstrated
nonwetting MD performance over a continuous 7 days operation of saline
water (3.5% of NaCl), high antiwetting with harsh saline water containing
0.5 mM sodium dodecyl sulfate (SDS, 28.9 mN m–1),
synthetic algal organic matter (AOM).
This review presents the construction of C–X bonds (X = O/N/S) by using intramolecular C–H functionalization for the synthesis of heterocyclic compounds.
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