Development of an innovative capsule with three-dimension honeycomb architecture via one-step titration-gel method for the removal of methylene blue.

Abstract

In this study, the capsules were prepared via the one-step titration-gel method by injecting spherical droplets of polyvinyl alcohol (PVA), sodium alginate (SA) and graphene oxide (GO) gelled mixture into the bath with calcium chloride (CaCl2) and oversaturated boric acid (H3BO3) solutions. The prepared capsules were then further modified with glutaraldehyde (GA). The formation mechanism of the prepared capsules was investigated. The morphology of the prepared capsules exhibited distinct micro-porous "3D honeycomb" pattern and hierarchical pore sizes distribution. It was also observed that GA not only acted as a co-cross-linked reagent in the fabricating process to increase the specific surface area of the capsules, but also offered exceptional tolerance property to work under a wide pH range (i.e. 2-12). The PVA-SA-GO capsules performed comparatively much better than PVA-SA capsules and they improved the adsorption capacity by up to 21.94%. Their adsorptive performance well followed the Langmuir isotherm. Moreover, the pH of the MB solution was evidently declined after adsorption, demonstrating the electrostatic attraction or ion-exchange might be the governing removal mechanism of methylene blue (MB) dye by the capsules. Importantly, the prepared capsules could be regenerated by simply washing with water and reused for at least 6 consecutive treatment cycles.