Fabrication of Two Luminescent Imidazolyl Cadmium-Organic Frameworks and Their Sensing Mechanism for 2,6-Dichloro-4-nitroaniline

2,6-Dichloro-4-nitroaniline, alias dicloran (DCN), is
a broad-spectrum
pesticide that can cause irreversible damage to the human body. Therefore,
it is of great significance to develop a technology for the rapid
and convenient detection of DCN. Luminescent metal organic frameworks
have attracted extensive attention in the field of sensing and detection
due to their excellent optical properties. In this study, two kinds
of 2D Cd-MOFs (CdMOF-1 and CdMOF-2) were developed for the detection
of residual DCN in the environment. Both CdMOFs exhibit excellent
solvent and acid–base stability and can respond to DCN quickly
and sensitively in a short time (30 s). CdMOFs not only have good
selectivity and anti-interference toward DCN but also have good reusability.
Under the conditions of DCN concentrations of 1–15 and 0.3–30
μM, the change in fluorescence intensity of CdMOF-1 and CdMOF-2
showed a good linear relationship with DCN concentration (R2 = 0.999/0.991), and the detection limits were
0.36 and 0.12 μM, respectively. Through ultraviolet–visible
absorption spectroscopy (UV–Vis), X-ray photoelectron spectroscopy,
fluorescence lifetime, and density functional theory calculations,
it is revealed that the fluorescence quenching mechanisms of DCN for
two kinds of Cd-MOFs are competitive absorption and photoinduced electron
transfer, and there may be a weak π–π interaction.
Finally, it is demonstrated that by using two types of fluorescent
CdMOFs to make the fluorescent test paper and detect actual soil,
these can be applied to the actual scene and achieve onsite real-time
detection.