Synthesis of 2D and 3D hierarchical β-FeOOH nanoparticles consisted of ultrathin nanowires for efficient hexavalent chromium removal

Abstract The self-assembly of 1-dimensional nanorods into free-standing multi-dimensional (2D and 3D) nanostructures is a considerable challenge. Here, 2D β-FeOOH nanobundles (NBs) and 3D spiky particles (SPs) were prepared without a substrate using a one-pot hydrothermal method. The oriented aggregation of nanoparticles (NPs) induced at the initial stage an unusual growth pathway beyond a reversed crystal growth route, forming spindle-like or spiky structure, which was confirmed by structural analyses. Then, with a surface-to-core extension of crystallization and nanorod self-assembly, 2D NBs with ultrathin and well-aligned nanorods and 3D SPs were finally generated. The reduction of the surface free energy served as a primary driving force for the oriented self-assembly. The initial concentrations of sodium sulfate and polyethyleneimine, which are used as reducing reagent and electrostatic stabilizer, are crucial adsorption parameters. The adsorption capacity of the NBs and SPs for Cr(VI) was 68.3 mg g−1 and 83.4 mg g−1, respectively. The adsorption mechanism study showed that electrostatic interaction and reduction concomitantly affected the adsorption. The molecular dynamic simulation indicated that the adsorption performance depends on the crystallographic surface of the materials. The suggested synthesis route provides an atypical strategy to prepare 2D and 3D nanostructures with promising sorbent characteristics.