Overcoming temperature polarization in membrane distillation by thermoplasmonic effects activated by Ag nanofillers in polymeric membranes

Abstract

In recent years, Membrane Distillation (MD) has emerged either as a promising alternative or as a complement to Reverse Osmosis (RO) in seawater desalination. However, the performance of MD is significantly offset by temperature polarization, a phenomenon intrinsically related to water evaporation that causes the decrease of the solution temperature at the membrane surface and, ultimately, the loss of driving force. In this work, we show that temperature polarization can be withdrawn by exploiting thermal collective effects activated by the excitation of plasmonic modes in UV-irradiated Mixed Matrix Membranes composed of silver nanoparticles (Ag NPs) incorporated in polyvinylidene fluoride (PVDF) microporous films. For experimental tests carried out under vacuum (VMD) and with an absorbed radiant heating power of 2.3 · 104 W/m2, best results were obtained using PVDF membranes loaded with 25%Ag NPs. In this case, measured transmembrane fluxes to pure water and 0.5 M NaCl solution were 32.2 and 25.7 L/m2 h, respectively, i.e. about 11- and 9- fold higher than the corresponding values for unloaded membranes. Remarkably, energy analysis revealed that the heat generation of Ag NPs under plasmonic resonance was able to withdrawn temperature polarization, resulting in estimated temperature polarization factor (TPF) values of 106.5% for 0.5 M NaCl solution.