Reusable UV-crosslinked MIL-101(Fe)@CQD/polymer nanocomposite films for fluorescence detection of As(iii) in water

The sensitive determination of trace As(iii) in environmental waters remains challenging, despite the availability of sophisticated instrumental techniques. Herein, a free-standing solid-state fluorescence sensing film was fabricated by immobilizing a MIL-101(Fe)@CQDs composite within a UV-curable polymer matrix. Structural, morphological, optical, and surface analyses using FTIR, XRD, UV-Vis spectroscopy, BET, SEM/STEM, DLS, and XPS supported the formation of the composite and its incorporation into the polymer network. The synthesized CQDs exhibited a photoluminescence quantum yield of 19.2 ± 3.2% (n = 3). Quantitative determination was based on the fluorescence-intensity difference (ΔI = I ₀ - I). The calibration response was linear over 4.44 × 10^-9-6.67 × 10^-8 mol L^-1 (R ² = 0.9919), with an LOD of 1.49 × 10^-9 mol L^-1 and a calculated LOQ of 4.97 × 10^-9 mol L^-1. The method showed high tolerance toward the tested potentially interfering species, including As(v), Sb(iii), Sb(v), carbonate, bicarbonate, phosphate, and common metal ions. Practical applicability was evaluated using environmental water samples and certified reference materials for arsenic, yielding recoveries of 101.3-104.6% with relative standard deviations below 5%. Results for environmental water samples were consistent with direct HG-AAS performed without a separate As(v)-to-As(iii) pre-reduction step; this comparison was used as supporting evidence of analytical consistency rather than as proof of exclusive As(iii) detection. The same sensing film was reused over 150 measurement/regeneration cycles, with a 1.4% difference between the first and final responses. The combined MIL-101(Fe), CQD, and UV-curable polymer platform therefore provides an easy-to-handle and reusable solid-state format for trace As(iii) determination in aqueous samples.