Development of TiO₂/GO Hybrid‑Modified Membrane Configurations to Improve Water Desalination ‎Performance via Membrane Distillation

Abstract

This thesis investigates the development of advanced polymeric membranes to enhance the efficiency, stability, and sustainability of membrane distillation (MD) for desalination and water purification. The research focuses on improving membrane hydrophobicity, antifouling, wetting resistance, and long-term operational performance by incorporating nanomaterials into poly(vinylidene fluoride) (PVDF) and poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) membranes. A comprehensive review of membrane science and MD technologies established the fundamental principles, key challenges, and recent advances in nanomaterial-based modifications. Titanium dioxide (TiO₂) and graphene oxide (GO) commercial material were used as received, while the TiO₂/GO hybrid structure nanomaterial (HSN) was synthesized via a hydrothermal process to enable the uniform deposition of TiO₂ nanoparticles onto GO sheets. The surface-fluorination technique was used not only to deposit the synthesized HSN onto the membrane surface but also to convert its behaviour from hydrophilic to hydrophobic. Extensive characterisation using SEM-EDX, FTIR, contact angle, tensile strength, porosity, and liquid entry pressure (LEP) analyses confirmed the successful incorporation of nanomaterials and the resulting improvements in morphology, surface chemistry, and mechanical integrity. In air-gap membrane distillation (AGMD) tests using a saline feed (3.5 wt% NaCl), all modified membranes exhibited higher flux and complete salt rejection than the pristine PVDF-HFP membrane. Across all fabrication techniques: surface coating, phase inversion, and electrospinning, the HSN-modified membranes consistently showed superior performance compared to those modified with TiO₂ or GO individually. Long-term operation, as well as fouling and wetting assessments using humic acid and Triton X-100, confirmed the excellent resistance of the hybrid membranes to wetting and organic fouling. The synergistic interaction between TiO₂ and GO enhanced surface roughness, hydrophobicity, and structural integrity, enabling stable operation and minimal flux decline over extended periods. The results demonstrate that rationally designed hybrid structure nanomaterial can significantly improve the functional and operational performance of MD membranes. Furthermore, this thesis proposes integrating these membranes with brine crystallization systems to achieve Zero Liquid Discharge (ZLD), advancing membrane distillation toward sustainable, closed-loop desalination. The study also highlights several directions for future work to optimize performance further and promote large-scale implementation. Collectively, these findings contribute to the development of next-generation nanocomposite membranes that address global water scarcity through energy-efficient, environmentally responsible separation technologies.