High-alumina fly ash as sustainable aluminum sources for the in situ preparation of Al-based eco-MOFs

Abstract

High-alumina fly ash (HAFA) is one of the categories of industrial solid wastes and the extraction of aluminum from HAFA could offer an alternative to the commercially available aluminum salts to prepare advanced materials such as Al-based metal–organic frameworks (MOFs). In the present work, eco-MIL-53(Al) has been successfully fabricated through a one-pot method by reacting the HAFA or sintered product (obtained by alkaline fusion activation treatment of HAFA) with terephthalic acid, respectively. Furthermore, their adsorption properties for the dye molecules in wastewater were investigated. In addition, the sintering conditions and decomposition rates of HAFA were explored. Experimental results manifested that the mixture of HAFA and Na2CO3 was sintered at 890 °C for 90 min, the ash-alkali ratio was 1:0.6, and the optimal decomposition rate could reach 97.75%. The obtained eco-MIL-53(Al) could maintain a stable skeleton up to 500 °C. The scanning electron microscopy results demonstrated that the MIL-53(Al) grew into columnar crystals from the surface of the raw material, and the addition of HCl in the synthesis process was beneficial to the formation of larger grains. Particularly, the SINTER-MIL had excellent adsorption performance for methylene blue (MB). The maximum adsorption amount of MB was calculated to be 28.80 mg g–1 at room temperature, and its adsorption removal rate could reach 79.53% at equilibrium adsorption. The MB adsorption onto the obtained samples conformed to the pseudo-second-order model and the Freundlich model, respectively. Therefore, the employment of sustainable aluminum sources such as HAFA to prepare MOFs has certain significance for economical aspects and environmental protection.