Novel approach to surface functionalization of mullite-kaolinite hollow fiber membrane using organosilane-functionalized Co3O4 spider web-like layer deposition for desalination using direct contact membrane distillation

Abstract

This work investigated a novel omniphobic mullite ceramic hollow fiber membrane (MCHFM) with low fouling and wetting propensity for use in direct contact of membrane desalination (MD) processes. The MCHFM was surface-coated with a spider web-like (SWL) cobalt oxide (Co3O4) rough layer via hydrothermal method at different reaction time (10, 13, 16, and 19 h) before a fluorination step using 1H,1H,2H,2H-perfluorodecyltriethoxysilane (97%) (FAS-17). After surface modification, the synthesized super hydrophilic membrane became highly repellent to water and other low surface tension liquids such as olive oil and engine oil with 32 and 31 mN/m of force, respectively. The surface-modified omniphobic membrane showed super-omniphobic properties towards engine oil at 154°, deionized water at 165°, and near superomniphobicity at 142.1° towards olive oil. The hydrothermal reaction time of the omniphobic membranes was studied using the DCMD test at 60 °C, while utilizing 30 g/L of NaCl and 8 mg/L of humic acid as feed. It was found that the hydrothermal reaction time at 16 h/FAS (Hy-16h/FAS) achieved a long-term stability as the rejection rate and water flux values were relatively constant (99.99%) and 22.8 kg/m2.h for about 4.3 h of the MD process. SEM analysis showed no fouling on the surface modified membrane. This was attributed to the Co3O4 spider web-like particles, which achieved superior anti-fouling properties. This implied the suitability of the fabricated omniphobic MCHFM with a SWL structure for DCMD and seawater desalination, in spite of organic contaminants.