Metal-Organic Framework-Based Sensors for Environmental Contaminant Sensing

Abstract

Increasing demand for timely and accurate environmental pollution monitoring and control requires new sensing techniques with outstanding performance, i.e., high sensitivity, high selectivity, and reliability. Metal-organic frameworks (MOFs), also known as porous coordination polymers, are a fascinating class of highly ordered crystalline coordination polymers formed by the coordination of metal ions/clusters and organic bridging linkers/ligands. Owing to their unique structures and properties, i.e., high surface area, tailorable pore size, high density of active sites, and high catalytic activity, various MOF-based sensing platforms have been reported for environmental contaminant detection including anions, heavy metal ions, organic compounds, and gases. In this review, recent progress in MOF-based environmental sensors is introduced with a focus on optical, electrochemical, and field-effect transistor sensors. The sensors have shown unique and promising performance in water and gas contaminant sensing. Moreover, by incorporation with other functional materials, MOF-based composites can greatly improve the sensor performance. The current limitations and future directions of MOF-based sensors are also discussed.

Keywords: Electrochemical sensor; Environmental contaminant; Field-effect transistor sensor; Metal–organic frameworks; Micro- and nanostructure; Optical sensor.

Fig. 1

a Working principle of NH₂-MIL-53-based sensor for ClO⁻ sensing. b Fluorescence emission spectra of NH₂-MIL-53(Al)-based sensor toward various concentrations of ClO⁻: 0, 0.05, 0.1, 0.5, 0.8, 1, 2, 3, 5, 7, 10, 15, and 20 μM from top to bottom. Inset shows corresponding photographs of NH₂-MIL-53(Al) nanoplates in the absence (left) and presence of 10 μM (middle) and 20 μM (right) ClO⁻ under 365 nm UV light. Reprinted with permission from [57]. Copyright (2016) American Chemical Society

Fig. 2

Sensing mechanism of Hg²⁺-responsive disassembly of Ru-MOFs and release of guest material of Ru(bpy)₃²⁺. Reprinted with permission from [60]. Copyright (2015) American Chemical Society

Fig. 3

a Post-synthetic modification of UiO-bpy with Eu³⁺. b Emission profiles and c bar diagram depicting relative intensity ratios (I_L/I_Eu), after addition of VOCs. d Two-dimensional map displaying relative emission intensities and quantum yields of various VOC encapsulated phases. Reprinted with permission from [63]. Copyright (2016) Royal Society of Chemistry

Fig. 4

a Schematic of sensing strategy. b Amperometric i–t curves of different nanomaterials: (1) Fe-MOFs, (2) Fe-MOFs/AuNPs, (3) Fe-MOFs/PtNPs, (4) Fe-MOFs/PdNPs, and (5) Fe-MOFs/PdPt NPs. c CV characterization of electrodes at various stages of modification: (1) bare GCE, (2) rGO-TEPA-Au/GCE, (3) streptavidin/rGO-TEPA-Au/GCE, (4) substrate strand/streptavidin/rGO-TEPA-Au/GCE, (5) BSA/substrate strand/streptavidin/rGO-TEPA-Au/GCE, (6) catalytic strand/BSA/substrate strand/streptavidin/rGO-TEPA-Au/GCE, and (7) Pb²⁺/catalytic strand/BSA/substrate strand/streptavidin/rGO-TEPA-Au/GCE. Reprinted with permission from [76]. Copyright (2018) Elsevier

Fig. 5

Schematic and detection strategy of electrochemical sensor based on MOF Cu₃(BTC)₂ and CS/rGO for DBIs detection. Reprinted with permission from [80]. Copyright (2016) American Chemical Society

Fig. 6

a Schematic of MOF-based SERS platform and b SERS spectra of rhodamine 6G on Au NP/MIL-101 substrate (blue lines), Au colloids substrate (red line), and MIL-101 (black line). Reprinted with permission from [89]. Copyright (2014) American Chemical Society. (Color figure online)

Fig. 7

a Schematic illustration of FET sensor with source and drain electrodes, channel material, gate oxide, and gate electrode. b Sensor current change after gas adsorption and desorption. Reprinted with permission from [97]. Copyright (2017) Royal Society of Chemistry

Fig. 8

a Schematic of acetone sensing mechanism with Pd–ZnO/ZnCo₂O₄ hollow spheres. b Temperature-dependent acetone sensing characteristics to 5 ppm in temperature range of 150–300 °C. c Dynamic acetone sensing responses in concentration range of 0.4–5 ppm at 250 °C of ZnCo₂O₄ powders, ZnCo₂O₄ hollow spheres, ZnO/ZnCo₂O₄ hollow spheres, and Pd–ZnO/ZnCo₂O₄ hollow spheres. d Selective acetone detection characteristics of Pd–ZnO/ZnCo₂O₄ hollow spheres. e Dynamic resistance transition properties of samples toward 5 ppm acetone at 250 °C. Reprinted with permission from [103]. Copyright (2017) Macmillan Publishers Limited

Fig. 9

a Schematic illustration of anisotropic synthesis of Au@ZnO@ZIF-8. b Dynamic response of Au@ZnO@ZIF-8 to HCHO with concentrations from 0.25 to 100 ppm. c Plots of sensor responses to HCHO concentration of three samples: (I) pristine Au@ZnO, (II) synthetic Au@ZnO@ZIF-8, and (III) completed Au@ZnO@ZIF-8. Inset shows TEM images of samples. Reprinted with permission from [104]. Copyright (2017) Springer

Fig. 10

a Preparation of ZnO@ZIF-8 core–shell nanorod films. b Temperature-dependent response curves of ZnO nanorod and ZnO@ZIF-8 sensors to 50 ppm H₂. c, d Dynamic response curves of two sensors to different H₂ concentrations at 250 °C. e Concentration-dependent H₂ response curves of two sensors at 250 °C. Reprinted with permission from [110]. Copyright (2017) John Wiley & Sons, Inc.