Solid–liquid convertible hydrogel mediated by dual-functional cellulose nanofiber/Eu–dipicolinic acid/carbon dot complexes for high-precision sequential luminescence detection of cupric ion and oxytetracycline

A portable, sensitive, rapid, specific, and environment-friendly polyvinyl alcohol–borax (PB) hydrogel fluorescence probe was synthesized for the sequential sensing of Cu 2+ and oxytetracycline (OTC) in wastewater. The aminated 2,2,6,6-tetramethylpiperidinooxy-oxidized cellulose nanofibers/europium complexes/carbon dot (ATOCN/Eu(DPA) 3 /CD) complex was added to the PB matrix. With the assistance of ATOCNs, the in-situ polymerized ATOCN/Eu(DPA) 3 /CD complexes were well-dispersed in the hydrogel and enhanced the mechanical properties of the hydrogel. The prepared hydrogel could be converted from solid to liquid by adjusting the water content to reduce the deviations caused by the solid probe detection. The probe not only induced evident fluorescence quenching and instantaneous response to Cu 2+ at 430 nm and OTC at 617 nm but also exhibited a high selectivity to Cu 2+ and OTC. The detection limits for Cu 2+ and OTC were 0.031 and 0.019 mg L −1 , respectively. Fluorescence recover was achieved by adding S 2− for CuS precipitate formation and for the thermal decomposition of OTC. After repeatedly recovering the fluorescence for 10 times, the fluorescence intensity at 430 nm was restored to 79% of the original intensity and that at 617 nm was stored to 95%. The results show that hydrogels have remarkable potential applicability in detecting Cu 2+ and OTC in wastewater.