High-Capacity Reusable Chitosan Absorbent with a Hydrogel-Coated/Aerogel-Core Structure and Superhydrophilicity under Oil for Water Removal from Oil.

Abstract

In this work, inspired by the self-cleaning surfaces of fish scales, we prepared a porous chitosan aerogel (CSA) through a simple freeze-drying process. With the three-dimensional interconnected microstructure, the aerogel was highly porous (porosity > 98.16%) and ultralight with a density ranging from 10.19 to 36.05 mg/cm3. The core/shell structure of the CS-hydrogel-coated/CS-aerogel core (CSHA) was fabricated through a simple spray process. The aerogel with low-adhesion CS-hydrogel-coating exhibited superoleophobicity (θoil ∼ 162°) under water and superhydrophilicity (θwater ∼ 0°) in oil. The hydrogel coating as a switch of the absorbent resists the oil phase and induces permeation of the water phase into the aerogel easily and quickly. The dry aerogel core with a porous structure has become a huge storage space. Taking advantage of this structure, an absorption capacity of 147 times could be obtained for water. The unique water absorption process along with switching between the aerogel and hydrogel gives the CSHA incredible potential for oil purification applications on site. Using the CSHA for oil purification, the purity of the obtained oil can be as high as 99.8%. Importantly, two facile approaches, including redissolving and drying, were applied to recycle the aerogels. The natural hydrophilic aerogels are made from dissolution and regeneration of chitosan powder, which is green, low-cost, simple and easy to scale-up. Using the as-obtained high-capacity recyclable CSA for oil/water separation, the mixture can be separated with high efficiency, making it a favorable candidate for applications in large-scale separation of oil-water mixtures in the future.