Post-Functionalized Mof-on-Mof Strategy to Construct a Siqds@Zif-8@Eu3+@Hpu-14 with Ratiometric Fluorescence Sensing for Salicylaldehyde, Al3+, and Pb2+

Abstract

Herein, we developed a hybrid material, denoted as SiQDs@ZIF-8@Eu3+@HPU-14, serving as a multifunctional platform for different analytes. In this probe, we selected SiQDs encapsulated in ZIF-8 as the responsive fluorescent fragment for salicylaldehyde (SA) yielding a turn-on signal, which was attributed to the reaction between -NH2 and the aldehyde group of SA via a C=N binding Schiff base linkage. Simultaneously, Eu3+ functionalized HPU-14 was employed as the turn-off switch for SA, which was resulted by the competitive absorption and the reduced ligand-metal energy transfer effect. The two different signals enable SiQDs@ZIF-8@Eu3+@HPU-14 to show specific recognition for SA with a low detection limit of 138 nM. Notably, this probe, after sensing SA, also exhibited target-specific recognition of Al3+ and Pb2+ through different responsive modes. Specifically, the emissions of SiQDs were enhanced by Al3+, whereas the Eu3+ emissions at 618 nm remained unchanged. In the presence of Pb2+, both SiQDs and Eu3+ emissions were perturbed. The detection limits for Al3+ and Pb2+ are 321 and 165 nM, respectively. Furthermore, mixed substrate film and two logical gate systems were designed, offering prospects for intelligent and portable sensing. This work introduces innovative ideas for synthesizing sophisticated hybrid materials with integrated functionalities.

Keywords: MOF-on-MOF, SA, Al3+, Pb2+, film