In this study，an intelligent sensing material was innovatively constructed for the efficient adsorption and visualization of perfluorooctane sulfonate（PFOS） in water. Owing to the cross-linking and copolymerization

between the quaternary ammonium salt monomer（methacrylatoethyl trimethyl ammonium chloride，MTAC） and polyethylene glycol diacrylate（PEGDA） on a polystyrene（PS） photonic crystal template，a three-dimensional photonic crystal hydrogel（PCH） network with strong cationic characteristics was established. The material，named MTAC-PCH，combined the structural color rendering property of photonic crystal and the stimulus response property of smart hydrogel. When PFOS specifically bound to the cationic sites and the gel skeleton，the detection of the target could be realized by the eye-recognizable color response（red→yellow-green） and the shift of Bragg diffraction wavelength. The successful synthesis of MTAC-PCH and its adsorption ability for PFOS were confirmed by SEM，FTIR，and EDS analysis. The adsorption and optical response mechanism of MTAC-PCH involved triple synergistic effects：（1） electrostatic interaction of quaternary ammonium cations（N⁺） in the gel network with PFOS sulfonate groups（—SO₃

-

）；（2） molecular sieving governed by the pore architecture of the gel matrix，combined with the hydrophobic interactions between the fluorinated carbon chains（C—F） of PFOS and both the PS microsphere and the hydrophobic pockets within the MTAC-PCH framework；（3） the contraction of gel network and the altering of lattice constants of the PCH structure triggered by PFOS binding，which can subsequently cause blue shifting of diffraction peaks and changing of structural color. This multiple synergistic effects enabled MTAC-PCH to maintain the efficient recognition and detection of PFOS in complex environmental matrices. The experimental results showed that the sensor can achieve adsorption equilibrium within 30 minutes，exhibiting a low detection limit of 1.42 μmol/L and excellent selective recognition capabilities for PFOS. Compared with other perfluorocarboxylic acid compounds and the anionic surfactant sodium dodecyl sulfonate（SDS），the response of MTAC-PCH to PFOS was significantly superior to other interferents，demonstrating

good specificity. The material maintained good detection performance after three adsorption-desorption cycles and showed good reliability（spiked recoveries of 92.5%-97.8%） in the detection of PFOS in real water samples. The sensor not only provides the dual functions of pollutant capture and optical signal self-expression，but also possesses the advantages of intuitive visualization，fast response and low cost，which is especially suitable for on-site rapid screening and real-time monitoring of PFOS in polluted water bodies.