Engineering Surface Wettability to Alleviate Membrane Scaling in Photothermal Membrane Distillation

Abstract

To address the growing demand for fresh water with a smaller carbon footprint, photothermal membrane distillation (PMD) has been proposed by combining membrane distillation with solar irradiation. Due to its low level of energy consumption and portability, PMD is becoming increasingly attractive for water production in off-grid areas. However, it still suffers from several challenges, including membrane scaling. To address this issue, we developed photothermal membranes with different wettabilities. #PCNT-2 with a hydrophobic surface was obtained by electrospinning a polyvinylidene fluoride (PVDF) nanofibrous substrate and a hydrophobic PVDF/carbon nanotube (CNT) surface layer. The surface was then modified by depositing a polydopamine (PDA) layer to make it hydrophilic (#PCNT-D). It was found that #PCNT-D exhibited the highest surface temperature under both dry and wet conditions and the highest evaporation rate due to its broad light absorption and high photothermal efficiency. PMD tests show that #PCNT-D with a hydrophilic surface possessed the best antiscaling performance under illumination. This can be attributed to it having the highest surface temperature and lowest mass transfer resistance, the highest salt solubility on a membrane surface, and the best heat transfer efficiency between the heated membrane surface and absorbed water in the PDA layer.

Polyamide Thin-Film Composite Janus Membranes Avoiding Direct Contact between Feed Liquid and Hydrophobic Pores for Excellent Wetting Resistance in Membrane Distillation

“…The flux dropped to 0 when the volume concentration factor reached 1.30. The faster scaling could be explained by the surface carboxyl functional groups of the TFC Janus membrane (Figure a); for that, calcium was enriched at the surface through calcium bridging, which facilitated CaSO 4 scaling through surface nucleation and growth. , However, until the end of the experiment, the distillate conductivity remained unchanged, indicating that no wetting occurred. According to the SEM observation at the end of the experiment, the surface of both membranes was covered with acicular gypsum crystals (Figure S12a,b).…”

2024 roadmap on membrane desalination technology at the water-energy nexus

“…Recently, thermoplasmonic effects have been successfully exploited for photothermal cancer therapy [80,[83][84][85][86][87][88], photothermal actuators [89], nanofurnaces for heterogeneous catalysis [90], solar-driven hydrogen generation [91][92][93], and solar-driven water evaporation [94][95][96][97][98][99][100][101]. Interestingly, the embodiment of thermoplasmonics in membranes has gained great attention demonstrating the potential to mitigate the water-energy nexus in MD by reducing the anthropic energy input required to heat-up the feed and increasing the productivity of the desalination operation by overcoming the TP [102][103][104][105][106][107][108][109].…”

Membranes in Solar‐Driven Evaporation: Design Principles and Applications

“…[76] Some researchers reported that Janus membranes with a hydrophilic surface toward the feed side exhibited superior anti-scaling properties compared with hydrophobic ones because of the promoted salt solubility on the membrane surface. [156,86] Therefore, the effects of surface wettability on membrane scaling and fouling during photothermal MD need further investigation. Beyond surface wettability, an ideal MD membrane is supposed to facilitate mass transfer while hindering heat transfer.…”