Porosity enhancement of activated carbon by hydrolyzed lignin from black liquor

Abstract

In this work, the porosity enhancement of activated carbon by hydrolyzed lignin extracted from black liquor was studied. Lignin was treated before activation and carbonization using H2SO4 hydrolysis. The effects of H3PO4 concentration (0–66 wt%) as an impregnation agent and impregnation time (0–12 h) on the activated carbon were investigated. The cadmium adsorption capacity and isotherm were also determined. Results showed that the specific surface area (SSA) of activated carbon increased with increases in H3PO4 concentration and impregnation time. The maximum specific surface area of 1,653 m2 per gram of hydrolyzed lignin was obtained using 66wt% H3PO4, impregnation time of 8 h, and carbonization at 500 °C. The adsorption isotherms of all samples were type-I, based on the International Union of Pure and Applied Chemistry. The pore size distribution of activated carbon prepared from lignin and hydrolyzed lignin without H3PO4 activation fell within the range of micropore. With 66wt% H3PO4 activation, activated carbon prepared from the lignin and the hydrolyzed lignin showed a mesoporous structure. The activated carbon prepared from hydrolyzed lignin in this study enhanced the Brunauer–Emmett–Teller-specific surface area up to 38.44% compared to that of non-hydrolyzed lignin. The maximum adsorption capacity of 9.50 and 9.69 mg of cadmium per gram of activated carbon prepared from lignin and hydrolyzed lignin, respectively, was achieved with 66wt% H3PO4 activation and 1 h of impregnations time. The adsorption isotherms of the cadmium fitted linearly with the Langmuir model. This study thus showed a promising production of highly porous activated carbon from the pulp and paper industry waste through a simple and low-cost method. Graphical abstract: [Figure not available: see fulltext.]