Direct deposition of Ti/MgF2 photoabsorber on PTFE membrane with enhanced robustness via plasma pretreatment for photothermal membrane distillation

Abstract

Deposition of metal-dielectric hybrid composite on the polymer based membrane is important for the electrochemical, photochemical and photothermal reactions on the membrane surface. The hydrophilic reactants such as catalysts and photothermal materials are not easy to be deposited directly on the hydrophobic membrane surface, so in most cases, binder material has been adapted to stably combine them. In this study, commercial PTFE membrane and Ti/MgF2 photothermal layers were combined without any binder. Ar plasma pretreatment was applied to a membrane surface before depositing optimized Ti/MgF2 stacks to fabricate a mechanically robust photothermal membrane. The successful fabrication of Ar plasma pretreated Ti/MgF2 photothermal membrane was demonstrated by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), atomic force microscope (AFM) characterization. Through Ar plasma pretreatment, an increase in Ti/MgF2 photothermal membrane heating temperature of 40.5 % was achieved under 1 sun condition compared with unpretreated membrane. This membrane showed improved performance and reduced energy loss in solar desalination. Utilizing these membranes in a membrane distillation system, water flux increased by up to 26.9 %, performance ratio (PR) increased by 18.9 % and thermal efficiency improved by 21.9 %. After 24-h stress test, the Ar plasma pretreated Ti/MgF2 photothermal membranes demonstrated durability and maintained thermal efficiency.