3D crateriform and honeycomb polymer capsule with nano re-entrant and screen mesh structures for the removal of Multi-component cationic dyes from water

Abstract

In this study, a hybrid sodium alginate-polyvinyl alcohol-silica oxide capsule (SA-PVA-SiO2 capsule, SPSC) was fabricated via the one-step titration-gel method that directly dripped the spherical droplet of the SA, PVA and tetraethyl orthosilicate (TEOS) mixed solutions into the bath with calcium chloride (CaCl2), NaCl and oversaturated boric acid (H3BO3) cross-linking agents. The formation principle of the prepared capsule was investigated. And the adsorptive performance of the SPSC was analyzed by removing the single, binary and multi-component cationic dye solutions [i.e. Methylene Blue (MB), Malachite Green (MG) and Crystal Violet (CV)]. The results indicated that the crateriform and cellular polymer channel with nano screen mesh and re-entrant structures could help to promote the interaction between pollutants and the interface of the SPSC thereby trapping the cationic dyes in its body. In single-component dye solution, the maximal adsorption capacities of the SPSC against MB, MG and CV were respectively found to be 394.077 mg/g, 1034.047 mg/g and 1756.202 mg/g at 25 °C and pH 9. The adsorption mechanism of the cationic dyes by the SPSC was governed by electrostatic attraction and chemisorption. Though the removal capacity of the cationic dyes by the SPSC was reduced in competitive multi-component systems, the saturation adsorption amount of the CV could still maintain above 684,692 mg/g. The affinity between the SPSC and the cationic dyes was in the order of MB > MG > CV. The prepared hydrogel capsule could be used in wide range pH situations. This facile method which was used to produce free-standing spherical support adsorbent with specialized morphology might have good prospects for excessive removing cationic dyes from alkaline wastewater.