Biomimetic snowflake-shaped magnetic micro-/nanostructures for highly efficient adsorption of heavy metal ions and organic pollutants from aqueous solution

Abstract

Some conventional micro- or nano-structured adsorbents are subject to the problem that they can hardly show most of their adsorption sites for adsorbing pollutants in solution because of serious aggregation of adsorbents. Here, we present a biomimetic strategy for designing novel adsorbents that promises to address this issue. The ZnO@SiO₂@Fe₃O₄/C micro-/nanostructures prepared have a special snowflake-shaped morphology, which enables them to keep a relatively large space remaining between connected adsorbents, and thereby reduce the overlap and coverage of the adsorption sites. The adsorbents also possess porous and multi-layered structures, which are advantageous to achieve a large surface area for adsorption. The magnetic Fe₃O₄/C coating ensures this adsorbent can be easily collected from solution and recycled for subsequent uses. In adsorption measurements, Pb(II) and As(V) were employed as heavy metal ions, whereas methylene blue was used as an organic probe. The kinetic adsorption process, maximum adsorption capacity, and pH-dependent adsorption effect were investigated systematically. We find that the kinetic process and isotherm can be fitted with a pseudo-second-order model and Langmuir adsorption model, respectively. The adsorption performance of the snowflake-shaped adsorbents has been compared with that of a spherical adsorbent. The mechanism has been demonstrated from the special biomimetic structure; in addition, the recycling performance based on magnetic collection and basic desorption has also been investigated.