A smart photonic crystal hydrogel sensor based on 18-crown-6/Ba2+ host–guest interactions for highly selective and visual Ba2+ detection

[Display omitted] •A Ba2+-sensitive photonic crystal hydrogel (PCH) sensor was developed.•This PCH sensor showed high selectivity and visual detection capability to Ba2+.•The Ba2+-detection mechanism was based on 18-crown-6/Ba2+ host–guest interactions.•This PCH sensor showed pH and thermo-dependent Ba2+-detection performances.•This PCH sensor possessed excellent regenerability. Barium ions (Ba2+) contamination is a serious environmental problem worldwide. The currently existing Ba2+-detection techniques are generally expensive, time-consuming, and complicated. Therefore, the development of a simple, inexpensive, rapid, and effective strategy to detect Ba2+ in water is of great importance. Herein, we first report a smart photonic crystal hydrogel (PCH) sensor for simple, highly selective, and naked-eye detection of Ba2+ in water based on 18-crown-6/Ba2+ host–guest interactions. This sensor was composed of a poly(benzo-18-crown-6-acrylamide-co-N-isopropylacrylamide-co-acrylamide) (PBCNA) intelligent hydrogel with embedding Fe3O4@SiO2 colloidal photonic crystals (CPCs). The prepared PBCNA PCH sensor demonstrated pH and temperature-dependent Ba2+-detection performances. Besides, the Ba2+-responded PCH sensor could be easily regenerated via simple washing using hot/cold water at least 20 times without compromising its detection performance. Such a PCH sensor with obvious advantages of portability, ease of operation, cost-effectiveness, high selectivity and excellent regenerability, provides a simple and effective strategy to monitor Ba2+ in contaminated water.