- Thesis topic: Study on surface modification by n-alkylsilane grafting applied in Membrane Distillation

- Doi: https://doi.org/10.6840/cycu202201048

- Abstract: 

       The main purpose of the report is to improve the hydrophobicity of the polyethersulfone (PES) membrane by combining two membrane modification methods such as plasma and grafting and then investigate the performance of the modified membrane in the MD system. The PES membrane was modified with oxygen plasma and then grafted with four chemicals of alkylsilane: hexyl trichlorosilane, octyl trichlorosilane, decyl trichlorosilane, and dodecyl trichlorosilane. The modified membranes were characterized by pore sizes, porosity, water contact angle (WCA), scanning electron microscopy (SEM), attenuated total reflection-Fourier transform infrared (ATR-FTIR), and atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS). The influence of the carbon chain length in the chemical structures of the grafted agent and the plasma treatment on the hydrophobic properties of the membrane surface was evaluated in this study. Modified membranes were investigated in the air gap membrane distillation (AGMD) system, with the feed solution being 4wt% NaCl synthetic wastewater. The applicability of modified membranes was evaluated by two parameters: salt rejection and permeability flux. The conductivity was also checked during MD operations to make sure the membrane was not broken.
        The research results showed high salt removal efficiency for the following membranes: octyl modified membrane (1-time grafting) (Octyl – 1), octyl modified membrane (2 times grafting) (octyl – 2), and decyl modified membrane (2 times grafting) (Decyl – 2). More specifically, the efficiency values were 99.36%, 99.06%, and 99.79% for Octyl – 1, Octyl – 2, and Decyl – 2, respectively. Besides, the water flux of Octyl – 1 was 9.3 kg/m2.h, which was close to the water flux of PTFE/PP electrospun and PVDF commercial membranes. For Octyl – 2 and Decyl – 2 membranes, the water flux values were 4.27 and 4.61 kg/m2.h, respectively, which were lower than those of commercial membranes. The reason is that Octyl – 2 and Decyl – 2 membranes are modified with 2 consecutive silane grafting reactions, resulting in these two membranes being thicker than Octyl – 1 membrane. The conductivity values of three modified membranes were lower than 0.2 mS/cm during 8 hours of operation, which prove that modified membranes are not broken during MD operation.

Keywords: Surface Modification, Radio Frequency Plasma, Oxygen Plasma, Silane Coupling Agents, Membrane Distillation