Low‐cost hydrophobic geopolymer membrane for water desalination through direct contact membrane distillation

Abstract This research introduces environmentally friendly, sintering‐free, and cost‐effective hydrophobic geopolymer membranes developed through two distinct raw material routes, metakaolin (MK) and fly ash (FA), for water desalination via direct contact membrane distillation (DCMD). The MK, FA, and alkaline activator were used to prepare a geopolymer slurry. Hydrogen peroxide and egg albumin served as foaming agents and surfactants, respectively. Methyltrichlorosilane (MTCS), methyltriethoxysilane (MTES), and polymethylhydrosiloxane (PMHS) were compared as coating agents for the geopolymer membrane substrates. Results showed that MK‐MTCS exhibited the highest surface contact angle of 136.5 ± 1.8°. Additionally, the average pore size and vapour flux for MK‐MTCS were measured at 0.1339 μm and 11 ± 0.4 kg/m 2 ·h, respectively, and the membrane's salt rejection was calculated at 97.4 ± 0.7%. The study concluded that MTCS is an appropriate hydrophobic coating agent for geopolymer membranes used in DCMD‐based water desalination.