Facile preparation of Al/Mn bimetallic metal-organic frameworks for removing trace benzene indoor

•The pore structure of MIL-53 was tuned by solvent change, creating abundant free 1D channels.•The Mn cluster was feasibly incorporated into the MIL-53 by exchanging BDC2- ligands under mild conditions.•The content of hydroxy group and open metal sites (OMS) were tuned by monocarboxylic modification and ion exchange.•The Al/Mn bimetallic MIL-53 showed superior uptake on trace benzene and remarkable hydrophobicity. The removal of trace benzene under humidity is still challenging in air treatment. Generally, MOFs have shown superior capture capacity than other adsorbents, but their uptake and hydrophobicity still need to be satisfied. Here, we reported a facile ion exchange method to obtain Al/Mn bimetallic MIL-53. The ion exchange of Mn under low temperatures could optimally maintain the structural integrities of obtained samples. Moreover, the in-situ monocarboxylic modulation could decrease the hydroxy content, improving the trace uptake while weakening the hydrophobicity. After ion exchange, the contents of OMS (open metal sites) and hydroxy both increased, upgrading the efficiency of trace benzene capture and improving the hydrophobicity under medium humidity. The optimal sample, Mn-A-25, performed well in trace benzene removal with 161 mg/g capacity under RH = 60 %, beyond two folds of MIL-53. Moreover, its hydrophobicity nearly equals that of MIL-53 (Qwet/Qdry = 0.96). The adsorption mechanism verified that increased adsorption enthalpy caused improved affinity on benzene. However, the adsorption was still driven by physical forces, which allowed for the visible desorption and superior regenerability of this adsorbent.