Self-Assembly of Lanthanide-Based Metallogel Nanoplates into Microcubic Blocks as Self-Calibrating Luminescent Methanol Sensors
Yong Yang, Wensheng Liu, Qiankun Zhong, Juzhou Zhang, Bangben Yao, Xiao Lian, Helin Niu
Abstract
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.