- Thesis topic: Surface n-Alkylsilane hydrophobic grafting of SiO2 plasma-induced coating layer on PVDF membrane surface applied in membrane distillation

- Doi: 

- Abstract: 

        The main purpose of this study is to improve the hydrophobicity of polyvinyl fluoride (PVDF) membrane by combining two modification methods such as plasma and grafting, and then study the performance of the modified membrane in the membrane distillation (MD) system. After the PVDF membrane is modified with an oxygen plasma, it is grafted with a silicon dioxide deposition and two alkyl silane chemicals: tetraethoxysilane, octyl trichlorosilane and decyl trichlorosilane. The modified membrane was studied by aperture, porosity, water contact angle (WCA), scanning electron microscope (SEM), attenuated all-reflection Fourier conversion infrared spectrometer (ATR-FTIR), atomic force microscope (AFM), and X-ray photoelectron spectrometer (XPS). Sexual analysis. This study evaluates the influence of carbon chain length and silica deposition coating on the hydrophobicity of the membrane surface in the chemical structure of the graft. The effect of application of modified membrane is analyzed in the air gap membrane distillation (AGMD) system. The feeding solution is 7%, 10% and 15% wt sodium chloride synthetic wastewater. Through two parameters such as desalination rate and water flux, the applicability of the modified membrane is evaluated during the AGMD operation period. Continuously monitor the changes in conductivity to ensure that the membrane does not rupture. After 24 hr continuous operation, the results show that 10% TEOS, 10% Octyl and 15% Decyl have high salt removal efficiency, and their removal rate is 100.00%. In addition, the water flow of 5% Octyl modified film is 5.15 kg/m2h, which is 31% higher than that of commercial PVDF membrane. 20% Octyl and 25% Decyl modified membrane, the water flux values are 3.93 and 3.90 kg/m2h respectively, and the flux is close to that of ordinary commercial membranes. The reason is that 20% Octyl and 25% Decyl modified membrane are modified by high-concentration silane grafting reaction, resulting in these two membranes being thicker than modified films, thus reducing the flux. The conductivity value of the modified membranes produced by the three modifiers is less than 0.05 mS/cm within 8 hours of operation, which can prove that all the modified membranes did not break during AGMD operation.

Keywords: surface modification, radio frequency plasma, oxygen plasma, grafting, silane coupling agent, silicon dioxide deposition coating, membrane distillation