Self-Assembly of Lanthanide-Based Metallogel Nanoplates into Microcubic Blocks as Self-Calibrating Luminescent Methanol Sensors

Because of the serious physiological toxicity of methanol, detection of methanol in ethanol medium is tremendously significant. Herein, excellent luminescent lanthanide-based supramolecular metallogels were prepared with the conventional low-molecular-weight-gelator 1,3,5-benzenetricarboxylic acid (BTC) and the lanthanide trivalent cations (Tb3+ and Eu3+), which exhibit distinctive characteristic photoluminescent emission of lanthanides. These metallogels were synthesized depending on the one-step method of a high-concentration reaction synergized with heat-assisted ultrasound. The mechanical characteristics of the supramolecular metallogels were investigated through a rheological study. The scanning electron microscopy study revealed the supramolecular interconnection structure of microcubic blocks formed through irregular self-assembly of nanoplates. The bi-metallogel (Eu/Tb-G) with an obvious brilliant yellow emission signal was favorably fabricated via utilizing the lanthanide co-doping strategy and manifests the characteristic emission bands of lanthanide trivalent ions (Eu3+ and Tb3+) simultaneously. The energy-transfer behavior between Tb3+ and Eu3+ was systematically studied. What is striking is that methanol facilitates the increase of Tb3+ fluorescence intensity without affecting the characteristic emission of Eu3+, and this phenomenon induces a unique emission proportion between Tb3+ and Eu3+ ions. Inspired by this, a self-calibrated fluorescence sensor of methanol is acquired, which adopts the dynamic emission of Tb3+ that can vary continuously and regularly as the target identification detection signal and utilizes the static emission of Eu3+ as the internal reference system. The change of fluorescence lifetime and quantum yield confirmed that this obvious visual optical color signal varying phenomenon can be ascribed to the internal energy-transfer process conversion caused by the unique host–quest interaction between methanol and Eu/Tb-G. In addition, the prepared Eu/Tb-G paper-based sensor has good stimulation response and recyclability to methanol vapor. The above discussion can establish Eu/Tb-G as a ratiometric and colorimetric fluorescent sensor for the detection of methanol and its vapor.