Adsorption performance and mechanism of mesoporous carbon-doped Al2O3 adsorbent derived from NH2-MIL-53 (Al) for removing Cr(Ⅵ) and methyl orange from aqueous solution

Abstract

A new porous carbon-doped Al2O3 adsorption material was prepared by calcination at 600 °C with the use of aluminum-based metal–organic framework synthesized by hydrothermal method with aluminum as the metal source to solve the problem of instability of MIL-53 in aqueous solution. It was used to remove methyl orange (MO) from single system and aqueous solution with Cr(Ⅵ). The microstructure of the material was characterized by modern analytical techniques, and its adsorption capacity and mechanism were explored. PXRD, SEM, BET and other characterization methods show successfully synthesized NH2-MIL-53(Al) with porous carbon-doped Al2O3 structure. The precursor NH2-MIL-53(Al) and the calcined derivative porous carbon-doped Al2O3 are similar in morphology, and the specific surface area of porous carbon-doped Al2O3 (180.24 m2/g) is larger than that of NH2-MIL-53(Al) (116.73 m2/g). The maximum equilibrium adsorption capacity of Cr(Ⅵ) and MO by porous carbon-doped Al2O3 material could reach 671.56 and 612.09 mg/g, respectively. The fitting results of the adsorption kinetic model show that the adsorption behavior of porous carbon-doped Al2O3 material for Cr(Ⅵ) is more suitable to Langmuir isotherm model, whereas that of MO is more suitable to Freundlich isotherm model. Both are suitable to pseudo-second-order kinetic model. According to XPS analysis, the contents of Cr(III) and Cr(VI) calculated by C600-6 after adsorption are 56.1 % and 44.9 %, indicating that electrostatic interaction and redox action still play a leading role in the adsorption of Cr(VI), while electrostatic interaction and chelation play a leading role in the adsorption of MO. Studies show that the porous carbon-doped Al2O3 material could be used as a Cr(Ⅵ) and MO removal material to achieve efficient removal of Cr(Ⅵ) and MO. The alumina synthesized by MOF is more stable than the traditional industrial alumina, and its acid and alkaline resistance is more excellent. This material not only solves the problem of instability and uneven distribution of MIL-53 crystal and common alumina materials but also provides more adsorption sites.