Green and Efficient Al-Doped LaFexAl1–xO3 Perovskite Oxide for Enhanced Phosphate Adsorption with Creation of Oxygen Vacancies

La-based metal oxide materials are environmentally friendly and show promise for phosphate adsorption. A series of Al-doped perovskite oxides, such as LaFexAl1-xO3, were prepared using a facile citric acid-assisted sol-gel method. The characterization results demonstrated that with optimized Al doping, there was a significant increase in the specific surface area and increased defect content of perovskite oxide LaFexAl1-xO3. Adsorption experiments showed that the performance of phosphate removal by LaFexAl1-xO3 was largely enhanced due to the improved adsorption capacity, which is maximum eight times higher compared with control perovskites prepared under neutral conditions. The mass transfer rate for adsorption was considerably boosted with phosphate removal within the initial 15 min. Spectroscopy analysis and density functional theory calculation results showed that the process of phosphate removal by the Al-doped perovskite oxides LaFexAl1-xO3 involved electrostatic interactions, an inner-sphere complex, and surface oxygen vacancies, among which the creation of oxygen vacancies caused by the Al doping was the predominant mechanism for reducing the bonding barrier during adsorption and generating adsorption sites. The results enable the development of a green and efficient perovskite adsorbent with a La-based perovskite material for phosphorus removal.