Colorimetric detection and removal of radioactive Co ions using sodium alginate-based composite beads

•Organic/inorganic hybridized alginate beads were newly synthesized via sol-gel chemistry.•Interaction between the azopyridine and metal ion is the main cause of Co ion detection.•The beads showed improved stability and least leakage of azopyridine during use.•Removal of Co ion was assessed by the ion-exchange of carboxylate groups in alginate.•The beads with dual functions of detection and removal of Co ion were successfully accomplished. We demonstrate a simple method for the visual determination and removal of Co ions using a bead-shaped, capturing probe based on hybridized sodium alginate. For Co ions, the designed protocol consisted of three main constituents: an azopyridine-based Co ion-probe for visual detection; sodium alginate as an adsorbent for the Co ion and a bead construct for removal and structure; silica as a linker for the probe and the alginate, leading to a robust structure. When the composite beads were exposed to Co ions, the yellow color of the beads turned to intensive violet and the color intensity was associated with the Co ion concentration. The color variation was quantified using red-green-blue (RGB) color values that were obtained with a scanner and evaluated with Photoshop. The technique achieved both visual recognition with obvious color change of the beads and efficient removal of the radioactive 60Co ion. The sensing and removal of any radioactive isotope could be achieved with an appropriate sensing probe, to provide a simple and universal platform for remediation.