Detection of pesticide residues in water using two dual-emitting lanthanide metal-organic frameworks

To optimize the limitations of the exisiting fluorescent sensors: conventional single-emitting fluorescent sensors have limited sensitivity because the single emission can be easily affected by environmental factors, and the limited sensitivity and selectivity of dual/multiple-emitting fluorescent sensors because the internal energy transfer between lanthanide ions is susceptible to environmental factors like temperature. Two dual-emitting lanthanide metal-organic frameworks (Ln-MOFs) were utilized to achieve qualitative and quantitative detection of different pesticides simultaneously in water. Tb-MOF and Eu-MOF2 were synthesized, and their structures and properties were characterized. The prepared Ln-MOFs were used for qualitative and quantitative analysis of six pesticides (napropamide, picloram, imazethapyr, tebuconazole, flutriafol and benalaxyl). Combined with the UV-visible absorption spectra of each pesticide, the results showed that the energy transfer efficiency between Ln³⁺ and organic ligand in Ln-MOFs was regulated through interaction and competitive excitation energy absorption, and different pesticides had different effects on the energy transfer efficiency of organic ligand to Tb³⁺ and organic ligand to Eu³⁺. The values of lg(I₅₄₅/I₆₁₆) and lg(I₅₄₅/I₃₄₀) had a good linear relationship with the concentration, and R² was above 0.97. This study provides a feasible strategy for developing a convenient, effective and universal ratiometric fluorescent sensor.