Fabrication And Oil-water Separation Performance Of Superhydrophobic Polyurethane (PU) Sponges

Oil-water separation is of great importance in industry, agriculture and daily life. Recently, special wettable materials for oil-water separation have attracted increasing attention because they exhibit high oil-water separation efficiency. However, the existing materials still have limitations for practical applications in absorption capacity, oil collection, material reusability, and so on. In this dissertation, special wettable materials with3D porous skeletons and elasticity were developed to solve the above problems for oil-water separation. The resulting materials exhibited the characteristics of high absorption capacity, oil collection and high reusability. The findings of this study have an important practical application for developing new kinds of oil-water separation materials.Based on polyurethane (PU) sponge with200~400μm pore size, the superhydrophobic and superoleophilic PU/Cu composite was fabricated by electroless copper deposition and modified with dodecanoic acid. The composite selectively absorbed oils up to13~18times of the composites’ weight. The absorbed oils were readily collected by a simple mechanical squeezing and then the composite could be reused for oil-water separation. Nevertheless, the superhydrophobicity of the composite was lost after the9th oil-water separation cycle.To solve the problems of complex fabrication processes and poor reusability of the superhydrophobic PU/Cu composite, we fabricated reusable superhydrophobic and superoleophilic PU/polysiloxane composite, which involved the hydrolysis of methyltrichlorosilane in a hexane solution. The sponge was coated with porous polysiloxane through a one-step solution immersion method. Besides high selectivity and oil collection, the composite could absorb oils up to15~25times of its own weight, exhibiting high absorption capacitites. More importantly, owing to the cross-linked polysiloxane on the sponge, the composite was able to reuse at least300cycles in oil-water separation.To achieve controllable oil-water separation, magnetic superhydrophobic and superoleophilic PU/Fe3O4composite was fabricated through a one-step method, which involved immobilization of Fe3O4particles and n-dodecanethiol on sponge in an aqueous solution of dopamine. The research results showed that dopamine and n-dodecanethiol addition played an important role for the superhydrophobicity of composite surfaces. Trace amount of dopamine was oxidized to dopaminequinone in air atmosphere, which could react with thiol via Michael addition. Then the resulting catecholic derivatives anchored onto Fe3O4particles and substrates to form―anchoring sites‖through bidentate modes of H-bonding. On one hand, part of o-quinone might directly react with-NH2group of the―anchoring sites‖via intermolecular Schiff base reaction. Another possibility was that o-quinone form intermolecular interactions with the―anchoring sites‖through H-bonding, π-π stacking, etc. Trace o-quinone linked the―anchoring sites‖through covalent bonding and noncovalent interactions, resulting in the immobilization of the Fe3O4particles to form micro-nano hierarchical structures on the substrates. It was reasonable that the anchoring of thiolate-grafted catecholic moieties gave rise to superhydrophobicity of the composite. The composite could be manipulated to absorb oils and separate from water surface under external magnetic field, providing a magnetic-actuated method for oil-water separation. The composite not only maintained high absorption capacity and oil collection, but also showed high volume utilization greater than90%. Owing to the immobilization of Fe3O4particles and n-dodecanethiol through covalent bonding and noncovalent interactions, the composite still exhibited superhydrophobicity after separating octane and lubricating oil from water surface for125and50cycles, respectively.