Super hydrophilic and super oleophobic carbon nanotube/TiO2 composite membranes for efficient separation of algal-derived oil/water emulsions

The separation of oil from microalgae aqueous emulsions is a critical step in producing algal-derived biofuels and nutraceuticals. This study presents the development of super hydrophilic and super oleophobic composite membranes to efficiently separate algal oil from oil/water emulsions. Carbon nanotubes (CNTs) were functionalized with polydopamine (PDA), polyethylene glycol (PEG), and titanium dioxide (TiO2) nanoparticles and coated onto a mixed cellulose ester (MCE) substrate to fabricate the composite membranes. Two distinct incorporation methods were employed for TiO2; direct nanoparticle incorporation and surface coating onto the CNT/PDA network. The membranes were comprehensively characterized using FTIR, SEM, EDS, contact angle measurements, and AFM analysis. The synthesized MCE@CNT/PDA/NP-TiO2 membrane exhibited super hydrophilicity with a water contact angle of 6.3 degrees and underwater super oleophobicity with oil contact angles up to 172 degrees. Membrane performance evaluation using a Nannochloropsis salina microalgae oil/water emulsion revealed excellent flux up to 9238 L m- 2 h- 1 bar- 1 and oil rejection as high as 98.6 % for the TiO2-incorporated membranes. Additionally, these membranes demonstrated superior antifouling properties, maintaining over 90 % of initial flux even after five separation cycles. Incorporating TiO2 nanoparticles significantly enhanced the membrane's hydrophilicity, oleophobicity, antifouling capability, and stability under extreme pH conditions. The developed composite membranes show great potential for efficient and cost-effective separation of algal oil from microalgae cultivation systems.