MOF-on-MOF Membrane with Cascading Functionality for Capturing Dichromate Ions and <i>p</i>-Arsanilic Acid Turn-On Sensing
Ke Zhu, Ruiqing Fan, Jingkun Wu, Bowen Wang, Haoyang Lu, Xubin Zheng, Tiancheng Sun, Shuang Gai, Xuesong Zhou, Yulin Yang
Abstract
It is very significant that functional porous metal–organic frameworks are used to manufacture hierarchical components to achieve cascading functions that cannot be achieved by a single-layer metal–organic framework (MOF). Here, we report two cases of novel MOFs constructed by the same ligand, Cu(I)-tpt and Cu(II)-tpt (Htpt = 5-[4(1H-1,2,4-triazol-1-yl)]phenyl-2H-tetrazole), and prepared a Cu(II)-tpt-on-Cu(I)-tpt membrane by a layer-by-layer approach ignoring the lattice mismatch problem. The first Cu(I)-tpt layer is grown on an oriented Cu2O nanostructured array by a “one-pot” approach. The aligned second Cu(II)-tpt layer can be deposited using liquid-phase epitaxy. Notably, the prepared Cu(II)-tpt-on-Cu(I)-tpt membrane combines adsorption and fluorescence sensing, which exhibited significant adsorption for Cr2O72– (203.25 mg g–1) as typical highly poisonous ions with a fluorescence quenching response. Hence, based on the oxidation–reduction between Cr2O72– and p-arsanilic acid (p-ASA), the Cu(II)-tpt-on-Cu(I)-tpt membrane’s ability to adsorb Cr2O72– could be used to design “on-off-on” mode fluorescence probes to detect p-ASA with high sensitivity (limit of detection (LOD) = 0.0556 μg L–1). p-ASA can be degraded into highly toxic inorganic arsenic compounds in the natural environment and has received widespread attention. Therefore, the integration of adsorption and fluorescence properties makes the Cu(II)-tpt-on-Cu(I)-tpt membrane a feasible multifunctional material for pollution control and detection.