Carbon monolith from rf gels and lignocellulosic materials from agricultural wastes

Abstract

In this work, the dissolution and regeneration of lignocellulosic residues from agricultural wastes have been studied. First, the optimal condition of a solvent (NaOH/H2O2) for dissolving lignocellulosic residues (rice straw, kapok, luffa and betel palm) has been investigated. Furthermore, all lignocellulosic solutions are regenerated with 2 M H2SO4. The regeneration of the lignocellulosic solution from betel palm fiber yields the most lignocellulosic material (LCM). The fractions of the obtained lignocellulosic material are 34.51% of lignin and 65.39% of hemicelluloses. Besides, the lignocellulosic material from betel palm fiber is used to prepare carbon gels by mixing with resorcinol-formaldehyde (RF) and the carbon monoliths are obtained by carbonization with N2.This work focuses on the effect of lignin, hemicelluloses and lignocellulosic material as well as the initial pH of mixed gel solutions on porous properties and pore structure of carbon monolith. The comparison of the porous properties and pore structure of carbon monolith prepared from RF-lignocellulosic material gels (C-LCM) and RF-lignin-hemicellulose gels (C-LH) is investigated. Moreover, carbon monoliths prepared from RF-lignin gels (C-L) and RF-hemicellulose gels (C-H) have also been studied. The nitrogen adsorption-desorption results show that addition of lignin can lead to increasing SBET and total pore volume of carbon monoliths (from 333 m2/g to 482 m2/g and from 0.23 m3/g to 0.98 m3/g, respectively). In addition, the porous structure of carbon monolith prepared from RF can be varied from microporous to mesoporous structure when lignin is added to RF (for C-L 4:1). Furthermore, it was found that the initial pH has an effect on cross-linking between lignin and RF as well as the diameter of the nodules on the structure of carbon monolith. This meso-/microporous carbon monolith preparation is more convenient than other methods such as using a hard template of inorganic material and etc. Hence, this work will provide a promising way to use natural resources as a raw material to prepare the hierarchical carbon monoliths.