A simple coating method to prepare superhydrophobic layers on ceramic alumina for vacuum membrane distillation

In this work, a simple coating method was developed to create a superhydrophobic solid layer on a ceramic alumina substrate for vacuum membrane distillation without sintering. A silica/alumina nanoparticle mixture was formulated to create a gel solution for hydrophobic coating. The oxide nanoparticles were first modified with a fluorinated monolayer, and the solution was stirred overnight for gelation. The gel was coated over an alumina disk and dried to form a superhydrophobic coating with an extremely high water contact angle of 158° and an average pore size of 0.4 μm to prevent water leakage under vacuum conditions. The vacuum desalination performance of the coated membrane was tested by exposing the coated membrane to salt solutions. The influence of operational parameters, such as NaCl concentrations, flow rate, and temperature of feed solutions, were also examined carefully. A high flux of 29.3 L m−2 h−1 with rejection rate of 99.9% can be obtained for 3.5 wt% NaCl solution at 70 °C. With the simple preparation process without sintering and excellent desalination performance, the modification process for ceramic membrane in this work shows great promise in practice and can be further extended for industrial applications.