Dual-mode humidity detection using a lanthanide-based metal–organic framework: towards multifunctional humidity sensors

Abstract

Combined photoluminescence and impedance spectroscopy studies show that a europium-based metal-organic framework behaves as a highly effective and reliable humidity sensor, enabling dual-mode humidity detection.

Designed Synthesis of Multiluminescent Materials Using Lanthanide Metal‐Organic Frameworks and Carbon Dots as Building‐Blocks

“…[33] Therefore, by combining water soluble CDs with the EuM-MOF reported earlier, [45] it is possible to obtain a material with different luminescence properties as a result of replacing the coordinated water of the EuM-MOF with the carboxylate groups from the surface of the CDs (see Figure 1). The carboxylic groups are known to coordinate strongly to the lanthanide ions.…”

“…Eu-MOFs/N,S-CDs, CQDs/ ZIF-8 composites). [44][45][46] These materials are obtained using a molecular building-block approach which employs the self-assembly of mononuclear lanthanide complexes, [Ln(mpca) 2 ] + (Ln 3+ = Eu, Tb, Gd, mpca = 5-methyl-2-pyrazinecarboxylate) and octacyanometallate ions, [M(CN) 8 ] 4-(M 4+ = Mo, W) [44][45][46] in aqueous solution. Moreover, they are environmentally friendly and have excellent biocompatibility, therefore they are widely employed to make smart multifunctional materials.…”

“…[30,[33][34][35][36] Notably, the CDs containing heteroatoms such as N, O, S are also known to have multiple emissions. [45] Taking advantage of this structural flexibility, we aimed to further extend the general applicability of our building-block approach and to design novel functional MOF-based composites using a one-pot synthetic method. [30,[39][40][41] Their synthesis involves multiple-step procedures, including the post-infiltration of the guest precursors into the preformed MOF host, [30] premodification of the CDs, [42] or post-functionalization of the composite.…”

Lanthanide Photoluminescence in Heterometallic Polycyanidometallate-Based Coordination Networks

“…It enables the observation of visible and NIR photoluminescence of accompanying emissive chromophores [32]. In effect, a considerable number of photoluminescent d–f coordination networks based on octacyanidometallates were reported (Figure 7 and Figure 8, Table 4) [101,102,103,104,105,106,107,108,109,110]. In the aqueous solution, trivalent lanthanide(3+) and [M V (CN) 8 ] 3− ions produce the cyanido-bridged [Ln III (H 2 O) 5 ][M V (CN) 8 ] (Ln = Sm, Eu, Gd, Tb; M = Mo, W) layered frameworks of a square grid topology [101,102,103].…”

“…Moreover, the Eu 3+ emission was found to be strongly sensitive to the amount of water molecules occupying the interstitial space within the crystal structure. Therefore, the emission intensity of the EuMo network increases significantly with decreasing humidity of the air around the solid sample, which makes this material an efficient humidity sensor working in the whole relative humidity range from 0 to 100% [106]. …”