Interlayered Interface of a Thin Film Composite Janus Membrane for Sieving Volatile Substances in Membrane Distillation

Abstract

Hypersaline wastewater treatment using membrane distillation (MD) has gained significant attention due to its ability to completely reject nonvolatile substances. However, a critical limitation of current MD membranes is their inability to intercept volatile substances owing to their large membrane pores. Additionally, the strong interaction between volatile substances and MD membranes underwater tends to cause membrane wetting. To overcome these challenges, we developed a dual-layer thin film composite (TFC) Janus membrane through electrospinning and sequential interfacial polymerization of a polyamide (PA) layer and cross-linking a polyvinyl alcohol/polyacrylic acid (PP) layer. The resulting Janus membrane exhibited high flux (>27 L m–2 h–1), salt rejection of ∼100%, phenol rejection of ∼90%, and excellent resistance to wetting and fouling. The interlayered interface between the PA and PP layer allowed the sieve of volatile substances by limiting their dissolution–diffusion, with the increasing hydrogen bond network formation preventing their transport. In contrast, small water molecules with powerful dynamics were permeable through the TFC membrane. Both experimental and molecular dynamics simulation results elucidated the sieving mechanism. Our findings demonstrate that this type of TFC Janus membrane can serve as a novel strategy to design next-generation MD membranes against volatile and non-volatile contaminants, which can have significant implications in the treatment of complex hypersaline wastewater.

Synergistic Effect of Ti3C2Tx MXene Nanosheets and Tannic Acid–Fe3+ Network in Constructing High-Performance Hydrogel Composite Membrane for Photothermal Membrane Distillation

“…Clearly, all the hydrogel composite membranes exhibited a higher LEP than the unmodified PTFE membrane, as shown in Figure f. According to the Young–Laplace equation, the elevation in LEP can be attributed to the relatively dense hydrogel layer and the noninvasive PTFE substrate.…”

Engineering Multinanochannel Polymer-Intercalated Graphene Oxide Membrane for Strict Volatile Sieving in Membrane Distillation

“…Moreover, compared to the substrate, the GO/PP 5/4 membrane also exhibited high rejection efficiency of other typical volatiles (Figure F) and mixture volatiles (Figure S17). Yet, the slight difference in rejection efficiency depended on the physical properties of the volatiles, including volatility, boiling point, and molecular size …”

“…Due to MD’s limitations in rejecting volatiles, traditional hydrophobic macroporous distillation membranes face significant challenges in treating complex hypersaline wastewater. , Lee and Straub recently reported that MD has less than 80% rejection for semi-volatiles with Henry’s constants between 10 –4 and 3 × 10 3 Pa L mol –1 while less than 54% rejection for volatiles with Henry’s constants exceeding 3 × 10 3 Pa L mol –1 . , This is because volatiles can evaporate alongside water and permeate through the hydrophobic macroporous membrane to the permeate side . While pretreatment methods like activated carbon adsorption, catalytic oxidation, or combined separation processes such as RO or nanofiltration (NF) can somewhat treat volatiles, − the diverse composition, low concentration, and large fluctuations of volatiles make direct absorption or mineralization inefficient and costly.…”

“…Selective permeation thin film composite (TFC) membranes, including NF and RO membranes, can separate volatiles via pore sieving due to precise membrane pore control. , Still, when they come into direct contact with hot feed hypersaline wastewater during the MD process, polymer-based TFC membranes tend to swell, enlarging the polymer membrane pores and reducing volatiles rejection efficiency, such as only 52.05% rejection of volatile phenol using a TFC (polyamide) membrane . Two-dimensional (2D) membranes, such as graphene oxide (GO), have garnered interest for small gas molecular separation due to their characteristic 2D channel sizes. , Nevertheless, similar to polymer membranes, GO membranes also encounter severe swelling issues due to weak interlamellar π–π and H bond interactions between GO flakes. , The key to achieving strict molecular separation in the MD process, whether using a dense polymer TFC or a 2D GO membrane, is to create swelled nanochannels that are large enough to allow water to permeate freely across the membrane (with a diameter greater than 0.29 nm, which is the kinetic diameter of water molecules) while being smaller than the size of volatiles and hydrated ions to be excluded. , …”

Nanofiber-Constructed Aerogel Solar Evaporator for Efficient Salt Resistance and Volatile Removal

“…Regarding the issue of trace volatiles in seawater or hypersaline wastewater, photocatalysis can couple with the photothermal process and has the potential as a volatiles removal strategy. − Wang et al found that efficient degradation of tetracycline hydrochloride is achievable with sandwich-type absorbers, facilitated by photocatalytic oxidation on the evaporator’s top layer . However, the local high temperature of the evaporation interface often results in volatiles not being completely degraded before they evaporate to the distilled side, particularly the porous membrane evaporator. , Alternatively, the construction of three-dimensional (3D) multifunction nanofiber aerogel evaporators has emerged as a potential solution for simultaneously alleviating salt crystallization and volatile evaporation into distilled water. , In the 3D nanofibrous aerogel evaporator, salt can be moved from the evaporation interface to the bulk water via the interconnecting pores among the nanofibrous matrix. ,, Simultaneously, they can provide numerous adsorption and light-accessible reactive sites for volatile removal, thus facilitating cleaner water production, as demonstrated in Scheme .…”