Constructing Hierarchically Porous Nestlike Al₂O₃–MnO₂@Diatomite Composite with High Specific Surface Area for Efficient Phosphate Removal

In this work, Al2O3–MnO2@diatomite composite (AM-Dt) was prepared by a simple hydrothermal method. This composite was formed by using diatomite as a porous substrate to support Al2O3 and MnO2 nanoparticles. It exhibited hierarchically porous structures and a high specific surface area (352 m2/g). The maximum phosphate adsorption capacity of AM-Dt was 63.7 mg of P/g of (Al2O3–MnO2), which is 6 times greater than those of Al2O3 coated diatomite, Al2O3, and Al2O3–MnO2. The composite also showed superior adsorption efficiency, high structural stability, and selectivity for phosphate in the presence of interfering anions (Cl–, NO3–, and CO32–). With the help of X-ray photoelectron spectroscopy and P K-edge X-ray absorption near-edge structure analysis, it can be concluded that electrostatic attraction and formation of surface complexes via phosphate bonding with Al2O3 and MnO2 were the main adsorption mechanisms. The facile preparation method, excellent adsorption performance, and cost effectiveness suggested that this composite possesses a promising potential for phosphate removal from contaminated water.