Ultralight sponge made from sodium alginate with processability and stability for efficient removal of microplastics

Due to natural agents and human activities, large quantities of microplastics enter the marine environment. As an emerging pollutant, MPs have attracted worldwide attention and become a great challenge in recent years. Sodium alginate is a kind of natural polysaccharide with non-toxic, stability, and low cost. In this study, sodium alginate sponge was prepared by secondary freeze-drying technology. Alginate sponge contains a large number of hydrophilic groups; thus, alginate sponge has super water-absorbed (the water absorption rate range from 1193-5232%). Meanwhile, the alginate sponge has high porosity of 81.93% and excellent mechanical properties. The removal efficiency of 100 mg·L^-1 microplastics by alginate sponge reached up to 92.3%. The 1 mg·L^-1 and 10 mg·L^-1 microplastics can be completely absorbed in 27 h and 60 h, respectively. The adsorption mechanism of microplastics adsorbed onto alginate sponge included intra-particle diffusion, hydrogen bonds interactions, and π-π interactions. In addition, the adsorption of MPs loaded Cu²⁺/Na⁺ by sponge in complex aqueous environments is still significant. This study expands the development prospect of sodium alginate sponge materials in the field of water treatment and provides a new green approach for the removal of microplastics.