Introduction of vacancy capture mechanism into defective alumina microspheres for enhanced adsorption of organic dyes

Introducing defects into metal oxides is considered as an effective method to improve their performance. However, to fully understand the role of oxygen vacancies in the adsorption of organic dyes is still a challenging target. Herein, defective alumina (DF-AlOx) microspheres were synthesized and used as adsorbents for removing organic dyes. In contrast to ordinary Al2O3, the DF-AlOx has an amorphous structure. The DF-AlOx possesses abundant coordinatively unsaturated Al-species, oxygen vacancies and oxygen-containing groups. The DF-AlOx exhibited excellent adsorption performance for dyes compared to Al2O3. The maximum adsorption capacities for congo red (CR), methylene blue (MB) and methyl orange (MO) estimated from the Langmuir model are 1156.5, 349.5 and 1270.8 mg/g, respectively. Based on the experimental data and density functional theory (DFT) calculations, a vacancy capture mechanism for enhanced adsorption of dyes was proposed. Compared with Al2O3, oxygen vacancies can be easily generated on the DF-AlOx surface, which mainly act as the capture centers and facilitate the adsorption of dyes. This work may shed light on designing high-efficiency adsorbents and further investigation of adsorption mechanism for organic dyes removal.