Highly cross-linked and organic–inorganic hybrid poly(cyclotriphosphazene-co-curcumin) microspheres (PCPC-MS) were facilely prepared by a one-step precipitation copolymerization method, and served as a fluorescent chemical sensor for the detection of picric acid (PA) in solution phase. The photochemically inert cyclotriphosphazene moieties intentionally introduced into the structure of the sensor could play a role not only in connecting curcumin fluorophores to construct a highly cross-linked fluorescent architecture with excellent thermal stability and photobleaching stability, but also in effectively enriching PA from bulk solution to the surface of the sensor by the acid–base interaction between the acidic phenolic hydroxyl groups of PA molecules and the electron-rich nitrogen atoms of the cyclotriphosphazene units, which might facilitate the formation of a ground-state non-fluorescent complex of the microspheres and PA as well as the excited-state energy transfer from the microspheres to PA. Therefore, PCPC-MS exhibited a fluorescence quenching response towards PA with high sensitivity, efficiency, and selectivity over a number of other analytes such as 2,4,6-trinitrotoluene, 2,4-dinitrotoluene, 1,3-dinitrobenzene, 4-nitrotoluene, nitrobenzene, 4-benzoquinone, chlorobenzene, and nitromethane in methanol. In addition, PCPC-MS could also effectively detect PA in the presence of the other analytes, indicating their remarkable ability for resisting interferences and specific recognition of PA. This study provides new insights into the design and preparation of a polymer-based fluorescence chemical sensor for PA with low toxicity, a simple preparation process, and high selectivity.

Nitrogen-enriched and organic–inorganic hybrid polymer submicro-spheres based on highly cross-linked poly(cyclotriphosphazene-co-4,4′-sulfonyldiphenol) (PZS) were prepared using one-step precipitation copolymerization route. The chemical structure and morphology of the submicro-spheres were characterized. The adsorption behaviors of the submicro-spheres towards different organic dyes in an aqueous solution were investigated systematically. The results showed that PZS submicro-spheres could effectively adsorb methylene blue (MB), Bismarck brown Y (BY), neutral red (NR), rhodamine B (RhB), and calcein (Cal) with high adsorption capacities, but they could hardly adsorb orange G (OG), Ponceau S (PS), and methyl orange (MO), indicating that PZS submicro-spheres could adsorb guest dyes selectively. The adsorption process was found to follow the pseudo-second-order kinetic model rather than the pseudo-first-order one. Isotherm studies revealed that the Langmuir model was more suitable for describing the adsorption behavior of the PZS submicro-spheres than the Freundlich model. A probable mechanism based on the unique host–guest interactions between the submicro-spheres and the dyes was proposed and experimentally verified to explain the selective adsorption. The nitrogen-enriched PZS submicro-spheres possess electron-donating and proton-attracting abilities and could act as bases, and thus the dyes that are classified as Lewis acids (electron acceptor) and/or Brønsted acids (proton donor) could be selectively adsorbed onto the submicro-spheres by acid–base interactions. Because of the selective adsorption behavior towards different organic dyes, PZS submicro-spheres also exhibited a strong ability for separating dye mixtures in an aqueous solution.