Novel organic-inorganic pervaporation membrane with a superhydrophobic surface for the separation of ethanol from an aqueous solution

In the pervaporation (PV) of organics from aqueous solutions, the adsorption step is usually the rate-limiting step, which affects membrane separation performance. To enhance the affinity of membrane surface to organics or to weaken the affinity to water in order to increase membrane separation performance, many methods have been developed to modify the characteristics of the membrane surface. In this work, a superhydrophobic surface was introduced to decrease the affinity of the membrane surface to water. A simple and facile casting method was used for the preparation of a pervaporation membrane with superhydrophobic surfaces using SiO₂ and polydimethylsiloxane (PDMS) as membrane materials. The effect of pre-polymerization of PDMS at different temperatures was first investigated. Then, different membrane substrates were studied. The results indicated that a higher roughness of the membrane substrate surface leads to the easy formation of a superhydrophobic surface and that a pervaporation membrane with superhydrophobic surface was obtained, whose water static contact angle is 152 ± 0.6 and water sliding angle is 5. Subsequently, the home-made pervaporation membrane was characterized for its ability to separate a 5 wt% ethanol aqueous solution under different conditions. The results indicated that the separation factor obtained using the membrane with a superhydrophobic surface was nearly five times higher than that obtained using a membrane without a superhydrophobic surface. Furthermore, when the separation was performed at different feed concentrations, the trade-off phenomenon in the PV process was observed to be overcome using the membrane with a superhydrophobic surface. Thus, the results of this work are helpful to gain insight into the control of surface wettability to enhance membrane separation performance in pervaporation process.