Use of lignin-based carbons for decolorization of wastewater dyes

Abstract

Hierarchical porous carbons were prepared from several common lignins, including sodium lignosulfonate (SLS), alkali lignin (AL), and calcium lignosulfonate (CLS) via one-step carbonization at 800 °C for 10 h without oxygen or any additional templating/activation agent for the decolorization of dyes from wastewater. The obtained carbons showed high porosity and microporous-mesoporous-macroporous hierarchical porous structures. The specific surface areas of SLS-C, AL-C, and CLS-C were 346 m2/g, 405 m2/g, and 512 m2/g, respectively. The total pore volumes of SLS-C, AL-C, and CLS-C were 0.12 cm3/g, 0.21 cm3/g, and 0.28 cm3/g, respectively. The obtained carbon materials displayed excellent adsorption-decolorization abilities for 5 dyes, including ethyl violet, malachite green, cationic brilliant red, acid blue 92, and direct red 23. The concentrations of these 5 dyes in wastewater were reduced by SLS-C from 20 mg/L to 0.12 mg/L, 0.20 mg/L, 0.32 mg/L, 0.78 mg/L, and 3.77 mg/L, respectively, over a 60 min treatment. AL-C reduced these concentrations from 20 mg/L to 0.02 mg/L, 0.01 mg/L, 0.04 mg/L, 0.71 mg/L, and 1.72 mg/L over the same time period. In addition, the concentrations of these respective dyes were reduced by CLS-C from 20 mg/L to 0.01 mg/L, 0.01 mg/L, 0.02 mg/L, 0.30 mg/L, and 0.20 mg/L.