A sustainable route to inorganic porous hollow fibers with superior properties

This paper presents a method for the fabrication of inorganic porous hollow fibers, using ecologically benign feed materials instead of organic solvents and harmful additives. Our method is based on ionic cross-linking of an aqueous mixture of sodium alginate, inorganic particles, and a carbonate. The mixture is spun into an acidic coagulation bath, where the low pH triggers the dissociation of the carbonate into multivalent cations and carbon dioxide. The multivalent cations cross-link the alginate, thereby consolidating the 3D structure and arresting the inorganic particles. In a subsequent thermal treatment the polymer is removed and the particles are sintered together. Adequate gelation requires a sufficiently low pH of the acid bath and a sufficing buffering capacity of the acid. In addition, to facilitate thermal treatment, it appears to be crucial that the acid has a conjugated base with limited propensity for complexing cations. The environmentally-safe and sustainable lactic acid and acetic acid are shown to be convenient acids. The fibers prepared via our method have outstanding properties, such as high mechanical strength, homogeneous morphology, and sharp distribution of small pores. In addition, they are prepared using sustainable chemicals such as lactic acid and calcium