Optimizing the Microscopic Structure of MIL-68(Al) by Co-Doping for Pollutant Removal and Mechanism

Four different MIL-68(Al) catalysts were synthesized and characterized by XPS, SEM, TEM, XRD, DLS, Nitrogen adsorption removal, and other methods. An aluminum-based MOF (Metal Organic Framework) (MIL-68(Al))/graphite oxide (GO) composite with TiO2 showed the largest BET specific area with best adsorption performance. Representation demonstrated that MIL-68(Al) and TiO2 nanoparticles are uniformly dispersed on the surface of the GO lamellar, and a tight heterojunction structure is formed between them. The MIL-68(Al)/GO/TiO2 exhibits good pore characteristics, structural morphology, and catalytic performance. Adsorption experiments of methyl orange can reach 99.7% with the effect of MIL-68(Al)/GO/TiO2 in water for 20 min. Moreover, the pH range can be applied to 1–13 and a high concentration of 200 mg/L methyl orange solution also worked well. In addition, this kind of catalyst can also be used for rhodamine B, methylene blue, congo red, and tetracycline in 20 min with good adsorption. Meanwhile, simple filtration can quickly recover MIL-68(Al)/GO/TiO2 and effectively reuse it. Free radical capture experiments showed a large number of •OH radicals during the adsorption of MO (Methyl Orange) solution by MIL-68(Al)/GO/TiO2. Meanwhile, the electrostatic interaction, π-π packing and hydrogen bonding make MIL-68(Al)/GO/TiO2 have a higher adsorption capacity for MO. Therefore, co-doping optimized the structure of MIL-68(Al), enhancing its stability in strong acids and bases while improving adsorption performance across a broader pH range than previously reported. This work addresses the instability of MIL-68(Al) under extreme conditions, demonstrating its significant potential for wastewater treatment applications.