Relationship of cellulose and lignin contents in biomass to the structure and RB-19 adsorption behavior of activated carbon

Abstract

In order to investigate the relationship between different material compositions and the structure of activated carbon (AC), a series of AC were prepared with different mass ratios of cellulose and lignin as the raw materials and initiating ZnCl₂ activation through microwave heating, and the ratios were set to pure cellulose (AC-1), 3.5 : 1 (AC-2), 3.5 : 3.5 (AC-3), and 3.5 : 5 (AC-4). All the samples were characterized by N₂ adsorption–desorption, scanning electron microscopy, elemental analysis, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. In addition, the adsorption behavior of AC to reactive blue 19 (RB-19) was carried out by batch experiments, which further explained the effect of cellulose and lignin contents on the performance of AC. When the ratio of cellulose and lignin for the preparation of AC was 3.5 : 3.5, AC-3 presented the lowest polarity ((O + N)/C = 0.22) and highest aromaticity (H/C = 0.17), as well as exhibiting a well-developed mesoporous structure: the adsorption capacity reached up to 488.46 mg g⁻¹ at 293 K. This was probably because cellulose played a key role in maintaining the mesopore structure and lignin promoted the formation of a layered and microporous structure during the preparation of AC. Moreover, the experimental adsorption data of AC fitted well with the pseudo-second-order kinetic and Langmuir isotherm models, and the adsorption process was spontaneous and endothermic. Thus, AC can be feasibly obtained from cellulose and lignin, and the contents significantly affected the performance of AC. These findings can serve as the basis for the preparation high-performance biomass-based AC.