Clean Water and Sanitation (SDG 6), Climate Action (SDG 13)
Reusable water-purity luminescent sensor using metal-organic nanosheets
Dylan A. Sherman*, Judit F. Pérez, Joaquin Silvestre-Albero, Jin-Chong Tan University of Oxford, United Kingdom
Unsafe water is responsible for 829 000 deaths pa globally, with at least 25% of the global population using drinking water that is contaminated.1 Pharmaceuticals, pesticides and organic waste from industry are emerging sources of contamination while traditional microbial contamination remains. Large-scale water quality monitoring is feasible in industry, while electronic hand-held devices exist to test local water source purity.2 These rely on non-renewable rare earth metals, however and operate at significant costs with low re-usability. There is a need for reliable and reusable local-source water purity indicators. Luminescent Metal-Organic frameworks (LMOFs) are promising materials for water purity indicators and toxic material sensors.3 Due to their tuneable porous structure with high surface area and programmability, LMOFs can be adapted for use within a range of optoelectronic devices for sensing water or a myriad of organic molecules.4 Yet the 3D nature of LMOFs creates challenges for optical transparency, sensing sensitivity and device integration. Metal-Organic Nanosheets (MONs) have the potential to overcome these limitations by retaining the benefits of MOFs but in an atomically thin morphology of large planar dimensions.
Figure 1: Cor@Z7-NS mixed-matrix membrane in pure water (left) vs contaminated water (right).
Here, we report the in-situ encapsulation of coronene in zeolitic-imidazolate framework 7 (Zn2(bim)4, bim= benzimidazole) nanosheets (Cor@Z7-NS) to enable water-sensing capabilities. The nanosheets exhibit a thin morphology (6 nm) with wide lateral dimensions (5-6 um), synthesised using a scalable and low energy salt-templating bottom-up (NaCl) synthesis.5 NanoFTIR, SEM, TEM, electron diffraction and fluorescence microscopy reveal the intercalation of coronene between nanosheet layers and luminescence derived from coronene for each nanosheet particle. The encapsulation within the host framework was found to result in turn-on aggregation-enhanced excimer emission (AEEE) by coronene only when in the presence of water, rather than all polar protic molecules for free molecular coronene. This results in a vivid shift in luminescence chromaticity from dark blue to green in the presence of ppm of pure water. In contrast, the ppm presence of organic impurities within pure water led to turn-off AEEE behaviour enabling calibration curves to be calculated for determine the quantity of impurity presence. Finally, mixed-matrix membranes of polymer mixed with Cor@Z7-NS were formed to synthesise reusable luminescent water-quality indicators that avoid leaching of Cor@Z7-NS into tested solutions while improving the quantum yield and luminescent intensity of Cor@ Z7-NS. References 1. World Health Organisation (Ed by A. Grojec), Progress on Drinking Water, Sanitation and Hygeine, 2017: Update and SDG Baselines, 2017. 2. P. Kruse, J. Phys. D: Appl. Phys. 51 203002. 3. A. Chaudhari et al. Adv. Opt. Mater., 2020, 8(8), 1901912; M. Gutiérrez, et al. Appl. Mater. Today, 2020, 21, 100817. 4. T. Xiong, et al. ACS Appl. Nano Mater., 2021, 4, 10, 10321-10333; M. Gutiérrez, et al. Adv. Opt. Mater., 2020, 8(16), 2000670. 5. D. Sherman, M. Gutierrez, S. Mollick, J.C. Tan, Adv. Funct. Mater. 2022 (in press).
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© The Author(s), 2023
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