Size effects of carboxylated magnetite nanoparticles on the membrane dehumidification performance

Abstract This study aims to understand the effects of different nanoparticle sizes on the dehumidification performance of thin-film nanocomposite membranes (TFN). Carboxylated magnetite (C-Fe3O4) nanoparticles of different sizes (5~30 nm) were embedded in a polyamide layer (PA) over the polysulfone (PSf) substrate. The structural and morphological characteristics of the nanoparticles and coated membranes were explored using various analytical techniques such as FT-IR, SEM, DLS, the zeta-potential, EDS, AFM, and the water contact angle. Mixed-gas permeation tests showed that there were performance peak points at specific nanoparticle concentrations. These performance peaks shifted toward a high concentration of nanoparticles with a decrease in the magnetite size. The M5(0.3) membrane with 0.3 w/w% of 5 nm magnetite particles showed the highest water vapor permeance of 1886 GPU and the highest water vapor/nitrogen gas selectivity of 688 at 30 oC and 70% relative humidity (RH). These results are in good agreement with data pertaining to the hydrophilicity of the TFN membrane. The amounts of C-Fe3O4 nanoparticles deposited on the surfaces of the M5(0.3), M15(0.3) and M25(0.3) membranes were found to be 6.95, 6.27 and 5.44 µg/cm2, respectively. The impact of the pressure, RH% and temperature on the water vapor permeation were also studied and discussed.