Nanoarchitectonics of lignin-sepiolite bionanocomposite foams for application in environmental remediation

Abstract

Innovative bionanocomposite foams based on precipitated Kraft lignin (Lig) and Kraft black liquor (BL) loaded with sepiolite (Sep) were prepared. BL/Sep bionanocomposites were synthesized by emulsion templating and Lig/Sep bionanocomposites were prepared by freeze-drying, resulting in stable and rigid foams. BL/Sep bionanocomposites displayed a closed cell structure, a specific area between 19 and 35 m2/g and macropores of varying sizes. The porosity in this technique is achieved by the mechanical agitation of the emulsion. On the other hand, freeze-dried Lig/Sep bionanocomposites showed open cell morphology with surface areas ranging from 1 to 4 m2/g and uniform macropores due to the ice-templating process. The presence of sepiolite in both types of bionanocomposite foams improved their stiffness, with Young's moduli ranging from 0.21 to 9.6 MPa. The capacity of the foams to adsorb metals, drugs and dyes was evaluated and it was found that the synthesized bionanocomposite foams exhibiting similar adsorption capacities as that reported for lignin. Sepiolite significantly improved the adsorption of Cu(II), Cd(II), acetaminophen (ACT), and methylene blue (MB) in BL/Sep bionanocomposites. Meanwhile, the Lig/Sep bionanocomposites demonstrated superior adsorption capacities for the Cr(VI) anion and aromatic ring compounds, including ACT and MB. In this respect, these lignin-sepiolite foams can be considered as promising materials for the removal of pollutants in aqueous solution.