Amino‐functionalized lanthanide metal‐organic frameworks encapsulating boron‐doped graphene quantum dots: A paper based fluorescent sensor to visual detection of salicylic acid

Abstract Salicylic acid (SA), a widely distributed environmental pollutant, requires accurate detection for effective water quality monitoring and ecological protection. In this work, we developed a highly sensitive fluorescent sensor by encapsulating boron‐doped graphene quantum dots (B‐GQDs) within amino‐functionalized lanthanum‐based metal‐organic frameworks (NH 2 ‐La‐MOFs). Upon 365 nm excitation, the composite exhibits strong blue emission peaking at 430 nm, which is significantly quenched and red‐shifted to 560 nm as the SA concentration increases to 50 μM. This spectral shift is accompanied by a distinct color change visible to the naked eye, enabling intuitive visual detection. The quenching mechanism is attributed to static interactions and a reduction in the excited‐state bandgap. Spherical aberration‐corrected scanning transmission electron microscopy (Cs‐STEM) confirms the uniform distribution of B‐GQDs within the NH 2 ‐La‐MOFs matrix. Density functional theory (DFT) calculations reveal that hydrogen bonding and π–π stacking greatly enhance SA adsorption, which is consistent with the observed Zeta potential shift from −2.90 mV to −17.6 mV, indicating enhanced surface charge density and improved SA binding affinity. Selectivity tests demonstrate that the quenching efficiency (I 50 /I 40 ≈ 0.15) remains stable even in the presence of 10 μM common interfering species such as Na + , K + , Mg 2+ , glucose, and alanine, indicating excellent anti‐interference performance. By adopting the strategy of metal‐organic frameworks coupled with boron‐doped graphene quantum dots, this work provides a robust, portable, paper‐based, flexible fluorescent sensor for efficient visual detection of salicylic acid in environmental applications.