Insight into the dissolving selectivity of ionic liquids for the major components in both parenchyma cells and fiber cells of bamboo (Phyllostachys pubescens Mazel) via X-ray photoelectron spectroscopy

Understanding the dissolving selectivity of ionic liquids for the major components, namely cellulose, hemicellulose, and lignin, in both bamboo parenchyma cells and fiber cells is crucial for achieving efficient pretreatment of bamboo with ionic liquids. In this study, slices of bamboo ( Phyllostachys pubescens Mazel) were treated with 1-butyl-3-methylimidazolium chloride (BmimCl), 1-butyl-3-methylimidazolium bromide (BmimBr), and 1-butyl-3-methylimidazolium iodide (BmimI) at 150 °C for 9 h with substrate-to-ionic liquid ratio of 2:10 and 3:10 (g/g). The X-ray photoelectron spectroscopy (XPS) technique was employed to evaluate the dissolving selectivity of ionic liquids for the main components in both bamboo parenchyma cells and fiber cells, as well as compare differences in the dissolving selectivity. The results indicated that halogen anions with stronger electronegativity and smaller size facilitated the permeation of ionic liquids into the bamboo cell walls, resulting in a higher dissolution rate of bamboo slices and a greater recovery yield of the carbohydrate-rich fraction. In both kinds of bamboo cells, these ionic liquids performed a stronger dissolving selectivity for lignin than for carbohydrates. Moreover, they showed a stronger dissolving selectivity for lignin in bamboo parenchyma cells than that in fiber cells. The orders of selectivity for lignin dissolution from bamboo parenchyma cells and fiber cells varied, for parenchyma cells, it was BmimBr > BmimI > BmimCl, while for fiber cells, it was BmimI > BmimBr > BmimCl. Due to the more porous and looser microstructure of bamboo parenchyma cells than fiber cells, ionic liquids permeated more easily into parenchyma cells. Additionally, the enhancement of bamboo slices addition reduced the pretreatment efficiency of ionic liquids. Overall, this work provides meaningful guidance for selecting efficient ionic liquids to pretreat bamboo parenchyma cells and fiber cells separately. • The kind of halogen anions had great effect on the deconstruction of both bamboo cells. • The ionic liquids had higher dissolving selectivity for lignin than carbohydrates. • The ionic liquids had a weaker dissolving selectivity for lignin in bamboo fiber cells. • The dissolving selectivity for the main components in different bamboo cells varied. • The ionic liquids permeated more easily into bamboo parenchyma cells.