In order to remit the membrane wetting in membrane distillation (MD), polytetrafluoroethylene (PTFE) flat membrane with low surface free energy and high water contact angle (WCA) was prepared by a simple heat setting process. Membrane morphology evolution, such as breakage of fibrils and fusion of PTFE resin, and its influence on membrane characters including pore size, porosity and roughness were discussed. The effect of the heat setting process on the membrane wetting was evaluated by the membrane wetting time (MWT) in a static absorption experiment (SAE) and sweep gas membrane distillation (SGMD). The results show that the crystallinity decreases with increasing the heat setting temperature and time, which leads to low surface free energy and therefore low adsorbing capacity of penetrating agent and the long wetting time in the static absorption experiment and SGMD. In addition, pore size increases firstly and then decreases due to the breakage of fibrils and fusion of PTFE resin, respectively, which further affects the permeate flux . Therefore, we propose that the anti-fouling property and separation performance of PTFE flat membrane in SGMD can be well handled and hope that such a PTFE flat membrane would be potentially useful in seawater desalination .
Lin Li,Jun-Wei Wang,Hao Zhong,Lu-Yuan Hao,Hamidreza Abadikhah,Xin Xu,Chu-Sheng Chen,Simeon Agathopoulos
The α-Si 3 N 4 membrane was prepared by tape casting of silicon slurry, followed by calcination at 1300 °C in flowing NH 3 gas. It comprised of α-Si 3 N 4 nanowire of diameter 70 nm which were converted from silicon powder via the vapor–liquid–solid (VLS) growth mechanism. The surface of the obtained membrane was transformed from hydrophilic to superhydrophobic , with a high water contact angle of ~ 160°, by coating with a vesicular SiNCO nano-layer. The experimental results showed that nanowire structure also favored superhydrophobicity. Water desalination performance of the membrane was tested with a sweeping gas membrane distillation (SGMD) device. High water flux of 8.09 l m −2 h −1 was achieved for 20 wt% NaCl aqueous solution in the feed at 90 °C, which was maintained for more than 500 h.
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