A low-cost biomimetic heterostructured multilayer membrane with geopolymer microparticles for broad-spectrum water purification.

Membranes have received wide interests in water purification. However, the development of low-cost and eco-friendly membrane with desired structure for broad-spectrum water purification still remains a great challenge. Inspired by the hierarchical structure and functions of wood, a heterostructured multilayer membrane fabricated through a facile and "green" layer-by-layer self-assembly method was reported in this study. Specifically, the hydrophilic geopolymer microparticles were doped into sodium alginate matrix to construct "xylem" layers with numerous microchannels, and chitosan was used to build "phloem" layers with dense structures. The resultant biomimetic multilayer membrane displayed a distinct heterostructure and provided desired rejection to different kinds of pollutants including nanoparticles, soluble dyes and heavy metal ions, as well as emulsified oil droplets. Furthermore, the biomimetic membrane exhibited a superior stability in a long-term operation, and an excellent recyclability for multiple usages for oil droplets removal. The proposed biomimetic membrane prepared in a completely "green" way possesses great potential in practical application for water purification and separation.