Direct Conversion of Aluminum Wires into Phase-Controllable Aluminum Oxide Nanoparticles by Anodization for Chromium Adsorption

A facile approach to preparing aluminum (Al) oxide nanoparticles (NPs) with a controllable crystalline phase is proposed. Al wires are directly converted into Al oxide NPs by electrochemical anodization, making the method highly promising for its simplicity, speediness, and ecofriendly nature. The process allows highly pure Al oxide NPs to be produced on a large scale at a low temperature. A strong electric field is applied to the surfaces of thin anode Al wires at a relatively low voltage, causing significant ejection of Al cations (Al3+) from the anode into the electrolyte. The ejected cations react with oxygen species (OH–, O2–) generated from electrolysis and field-assisted deprotonation of water, forming bayerite (α-Al(OH)3) or boehmite (γ-AlO(OH)) depending on the anodization conditions. The mechanism behind the formation of the NPs and the effects of anodization conditions are explored. To assess the adsorption characteristics of the NPs, the chromium adsorption test was performed. Additionally, multiplicability of the process was verified by electric field analysis using COMSOL software.