Facile one-pot synthesis of polyethyleneimine functionalized α-FeOOH nanoraft consisted of single-layer parallel-aligned ultrathin nanowires for efficient removal of Cr (VI): Synergy of reduction and adsorption

Two-dimensional (2D) iron oxide-hydroxide (FeOOH) nanomaterials as low-cost and environmental-friendly composites are promising materials for application in heavy metal elimination. However, developing 2D FeOOH adsorbents with high adsorption capacity and excellent durability toward Cr (VI) removal is still a challenge due to the intrinsically non-layered structure. Here, a novel polyethyleneimine (PEI) functionalized 2D single-layer nano-raft-like α-FeOOH (α-FeOOH NF) consisted of parallel-aligned ultrathin nanowires was obtained via a facile one-pot hydrothermal approach. It was found that the 2D α-FeOOH NF nanostructure was formed by an in-plane iterative self-assembly mechanism, where α-FeOOH nanoparticles acted as intermediates and iterative seeds with anisotropic growth. The as-prepared 2D α-FeOOH NF possessed porous structure and high surface area, which provided a strong ability to capture the Cr (VI) ions in water. Benefiting from the unique structure and PEI modification, it exhibited fast adsorption kinetic rate, high reusability, and high adsorption capacity toward Cr(VI) removal. The removal mechanism involved adsorption and reduction process. Besides, the molecular dynamic simulations disclosed a facet-dependent Cr(VI) adsorption behavior of α-FeOOH. The maximum adsorption capacity was 67.1 mg/g and the removal efficiency still maintained 83.9 % in the fifth cycle. This work demonstrated that 2D α-FeOOH NF could be a promising adsorbent for Cr(VI) removal.