Photonic hydrogels for the ultratrace sensing of divalent beryllium in seawater

• Published in: Journal of materials chemistry. C, Materials for optical and electronic devices Materials for optical and electronic devices, 2018, Vol.6 (15), p.4234-4242
• Main Authors: Qin, Junjie, Dong, Bohua, Cao, Lixin, Wang, Wei
• Format: Article
• Language: English
• Subjects: Beryllium; Chelates; Chemical bonds; Color; Functional groups; Gelation; Hydrogels; Photochemical reactions; Photonic crystals; Polyvinyl alcohol; Scaffolds; Seawater
• ISSN: 2050-7526; 2050-7534
• DOI: 10.1039/C8TC00242H

Responsive photonic hydrogels functionalized with crown ether molecules containing the smallest cavities are designed for the detection of the smallest metal ion – beryllium ion (Be 2+ ) – in seawater systems through the exploitation of the volume induced structural color change of non-close packed colloidal photonic crystals (CPCs), which are immobilized in the hydrogels. A new two-step versatile polymerization process has been developed to fabricate these intelligent hydrogel sensing materials. The CPCs in suspension are firstly embedded within a polyvinyl alcohol (PVA) hydrogel scaffold by a cryotropic gelation process, and then the ion-recognition functional groups are covalently bonded to an additional polyacrylamide hydrogel over the PVA via a photochemical reaction. After the removal of the PVA scaffold, the remaining hydrogel exhibits a vivid structural color on account of the diffraction of the photonic crystals in the visible spectral range, while the grafted benzo-9-crown-3 can strongly and selectively chelate with Be 2+ ions in solution. The hydrogel sensor enables the detection of Be 2+ ions quantitatively and achieves a detection of limit of 10 −11 M in seawater. Through this design and fabrication method, a simple and low-cost sensor for the in situ monitoring of toxic ions or compounds in seawater has been demonstrated.