Multilayer adsorption of organic dyes on coal tar-based porous carbon with ultra-high specific surface area

Abstract

The coal tar-based carbon with ultra-high specific surface area was synthesized from coal tar using CaO as template coupled with KOH activation by conventional heating. To utilize the existing pores of the porous carbon, the multilayer adsorption of organic dyes, including Congo red and methylene blue, was tested. Results show that the as-made carbon features with hierarchical structure, which is containing both micropores and abundant mesopores. The CTC4-900 made with the mass ratio of activator/carbon source at 4 under activation temperature of 900 °C shows an ultra-high specific surface area of 3101 m2/g with an average of 2.65 nm. The CTC4-900 had the highest adsorption capacity for Congo red with the saturation adsorption capacity of 3885 mg/g in a monolayer adsorption due to its large mesoporous surface area. Then, the CTC4-900-CR can be used for an effective second-layer adsorption for methylene blue with the saturation adsorption capacity of 931 mg/g. For the third-layer adsorption of Congo red, the CTC4-900-CR-MB still shows the excellent adsorption performance with the saturation adsorption capacity of 1001 mg/g due to the electrostatic forces. After several layer adsorptions for different organic dyes, the existing pores of the carbon can be utilized completely, showing that it is an alternative way to regeneration.