A novel strategy to enhance the desalination stability of FAS (fluoroalkylsilane)-modified ceramic membranes via constructing a porous SiO2@PDMS (polydimethylsiloxane) protective layer on their top

The production of freshwater by desalination has great significance. Membrane distillation (MD) is considered as a promising technique for desalination. As a popular candidate for MD desalination, FAS (fluoroalkylsilane)-modified ceramic membrane suffers from insufficient stability, such as membrane wetting and decline of salt rejection during long-term operation, because of the degradation of hydrophobicity. In the present work, a novel strategy is proposed to enhance the long-term desalination stability of FAS-modified cordierite ceramic mem-branes by constructing a porous SiO2@PDMS (polydimethylsiloxane) protective layer on their tops to obtain a robust hydrophobic property. The results show that such a layer can be successfully fabricated by a two-step spraying method with hydrosoluble NaCl particles as templates. The incorporation of SiO2 nanoparticles into PDMS generates a loose and porous structure in the layer and renders an enhanced hydrophobicity. At a SiO2/PDMS mass ratio of 0.30, the membranes exhibit a notable resistance to both mechanical abrasion and chemical corrosion. The dissolution of NaCl templates leaves behind cavities within the layer, which prevents the SiO2/PDMS species from blocking the membrane pores and thereby helps to reduce the vapor transport resistance. These membranes are highly stable upon long-term desalination (> 300 h) and can preserve a stable water flux of 8.10 kg/m(2)h and a salt rejection close to 100% under the following conditions: a feed temperature of 80 ?degrees C, a NaCl concentration of 3.5 wt% and a feed flow rate of 300 mL/min. The SiO2@PDMS layer is responsible for the outstanding desalination stability since it prevents membrane wetting by reducing the direct contact of the reflux feed solution to the underlying cordierite ceramic membranes.