Controllable pore size of super-hydrophobic magnetic core-shell nanospheres with dendritic architecture and their pore-dependent performances in oil/water separation

The fundamental properties of porous materials strongly rely on their pore sizes. Pore-size-dependent performances play significant roles in their applications like catalysis, adsorption, delivery, and so forth. In this work, a feasible pore-expanding approach has been successfully explored to control the pore size of magnetic core-shell nanospheres with dendritic architecture (Fe3O4@DMSNs). The size can be adjusted from ca. 10 nm to 25 nm and further to 60 nm in an unprecedented wide range. Further, a concise modification route has been adopted to endow Fe3O4@DMSNs particles with super-hydrophobic abilities by the usage of a long-chain silane (Fe3O4@DMSNs-OTES). The as-prepared nanospheres with magnetic response function can not only form magnetic liquid marbles (MLMs) easily, but also separate n-hexane in oil-water mixtures or oil-in-water emulsions rapidly and efficiently. However, the above three particles display certain differences in their basic properties (like pore volume) and application performances (like oil removal efficiency). Most importantly, Fe3O4@DMSNs-OTES with 60 nm pores exhibit the best super-hydrophobicity in contact angles of H2O and MLMs, Fe3O4@DMSNs-OTES with 25 nm pores possess the maximum adsorption capacity, while the ones with 10 nm pores show the quickest adsorption rate (removal efficiency). The relationship between the performances and the pore size has been thoroughly revealed and well deciphered by wettability theory (e.g., Cassie-Baxter equation) and surface tension theory. In a word, all Fe3O4@DMSNs-OTES hold promising potentials as candidates for the practical wastewater purification on the basis of their characteristics.