An MOF-Based Composite with the Applications in Anticounterfeiting and Fluorescence Detection for 4-Nitrophenol in Water and Extracts of Rice, Soil, and Plant

Toxic 4-nitrophenol (4-NP) poses risks to human health and the ecological environment, whose detection is of significance. A 3D metal–organic framework of [Zn(tr)(OAc)] (Zn-tr) (Htr = 1H-1,2,4-triazole; OAc– = acetate) and its Rh6G@Zn-tr (Rh6G = rhodamine 6G) composite were presented. Zn-tr is topologized as a (3,4,6)-connected 3,4,6T56 topological {3.72}2{32.4.73}{32.4.76.86} network. Ratiometric fluorescence Rh6G@Zn-tr sensor exhibits a high sensitivity to 4-NP with a linear relationship of I365/I554 = −0.01745C4-NP + 1.03741 (I365/I554 is the ratio of the emission intensities at 365 and 554 nm; C4-NP = 4-NP concentration) within C4-NP = 0–40 μM and limit of detection = 0.48 μM. Rh6G@Zn-tr sensing 4-NP will not be interfered by common ions and some analogues, showing high anti-interference. Rh6G@Zn-tr can accurately sense 4-NP in lake water and some environmental extracts, showing high reliability. ASCII binary code defined by blank and Rh6G@Zn-tr hydrogel in a 4 × 8 array can encrypt or decrypt information. With the two-tier secret keys of 4-NP and 254 nm UV light, a QR code becomes readable by a smartphone and returns the encrypted information. This work provides a visual fluorescence 4-NP detection method and an anticounterfeiting platform by designing an allochroic MOF-based composite.