Owing to its 100% theoretical salt rejection capability, membrane distillation (MD) has emerged as a promising seawater desalination approach to address freshwater scarcity. Ideal MD requires high vapor permeate flux established by cross-membrane temperature gradient (∆T) and excellent membrane durability. However, it’s difficult to maintain constant ∆T owing to inherent heat loss at feedwater side resulting from continuous water-to-vapor transition and prevent wetting transition-induced membrane fouling and scaling. Here, we develop a Ti3C2Tx MXene-engineered membrane that imparts efficient localized photothermal effect and strong water-repellency, achieving significant boost in freshwater production rate and stability. In addition to photothermal effect that circumvents heat loss, high electrically conductive Ti3C2Tx MXene also allows for self-assembly of uniform hierarchical polymeric nanospheres on its surface via electrostatic spraying, transforming intrinsic hydrophilicity into superhydrophobicity. This interfacial engineering renders energy-efficient and hypersaline-stable photothermal membrane distillation with a high water production rate under one sun irradiation.
Photothermal desalination is a promising approach for seawater purification by harvesting solar energy. Titanium carbide (Ti 3 C 2 T x MXene) membranes have been regarded as potential materials for photothermal desalination by virtue of their excellent light-to-heat conversion. However, achieving a well-balanced synergy between high evaporation rate and good salt resistance remains a significant challenge due to their limited solar absorption and inferior stability. Herein, we report a self-assembled flexible porphyrin-Ti 3 C 2 T x MXene Janus membrane (Janus PMX membrane) for dual-functional enabled photothermal desalination. The self-assembly of porphyrin on MXene not only effectively creates a favorable hydrophobic surface but also simultaneously enables efficient solar utilization. The significant interactions and charge redistribution between MXene and porphyrin lead to a stable hydrophobic/hydrophilic Janus structure with synergistically enhanced photothermal conversion. As a result, the Janus PMX membrane demonstrates highly efficient water pumping, heat localization, vapor generation, and salt resistance during photothermal desalination. This work presents an effective and facile strategy toward advancing a well-performing MXene membrane for efficient seawater desalination.
Removing nitrogen from wastewater by conventional treatment methods requires substantial energy, only to release it back to the atmosphere as gaseous nitrogen. Herein, we investigated the applicability of membrane distillation (MD) in resource recovery from sludge digestate by controlling the volatility and pressure of the vapor transport across the membrane to concentrate ammonia in the permeate stream. A mixture of Nafion ionomer and Multiwall Carbon Nanotubes (MWCNTs) were incorporated into a Poly(vinylidene fluoride-cohexafluoropropene; PVDF-HFP) nanofiber matrix to fabricate a nanoporous honeycomb Nafion membrane featuring high recovery and increased mechanical strength. Theoretical modelling was conducted to predict the expected performance of the fabricated Nafion membrane under different operation conditions and to reveal the mechanism behind the enhanced recovery of Nafion membranes in the MD process. The resultant Nafion (8%)/MWCNT (2.5%)/PVDF-HFP nanofibrous membrane showed up to three times higher ammonia recovery compared to the commercial PVDF membrane from a feed with an ammonia concentration of 300 mg/L. The theoretical analysis quantitatively revealed that the Nafion containing membrane can not only suppress the negative effect of membrane's structural resistance on the ammonia recovery efficiency but also enhance the efficiency. In addition, we also uncovered that the effect of Nafion on ammonia recovery efficiency was maximized when the Nafion 8% membrane was employed. This study demonstrated an innovative and realistically applicable MD treatment process for recovering resource, which integrates low-grade heat and has scaling-up potential for wastewater treatment plants.
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