Multi-component deep eutectic solvents pretreatment using different pKa dependent acids as hydrogen bond donors to enhance enzymatic saccharification of bamboo

A deep eutectic solvent (DES) composed of triethylbenzylammonium chloride and oxalic acid (TEBAC/OA) was employed to pretreat D. giganteus (DG). To enhance the pretreatment efficiency, acids with varying pKa values—including p-toluenesulfonic acid (PTSA), salicylic acid (SA), formic acid (FA), glycolic acid (GA), acetic acid (AA), and propionic acid (PA)—were incorporated into the binary TEBAC-based DES. It was found that the pKa of the third acid component exhibited a negative correlation with the removal of lignin and xylan, as well as with the subsequent enzymatic saccharification yield. Notably, the SA-assisted DES pretreatment resulted in 98.74% xylan removal and 92.24% delignification. Moreover, the enzymatic hydrolysis efficiency improved from 53.21% for the binary DES-pretreated DG to 70.69% for the TEBAC/OA-SA-pretreated DG. Computational modeling revealed a reduction in both the number of hydrogen bonds and the interaction forces among cellulose-hemicellulose-lignin within the TEBAC/OA-SA system, which facilitated effective fractionation of bamboo. The TEBAC/OA-SA pretreated DG exhibited marked morphological and structural alterations, characterized by the lowest crystallinity-to-cellulose ratio and hydrophobicity, along with the highest cellulose accessibility. Furthermore, DES lignin (DL) and surface lignin (SL) displayed lower molecular weights and reduced hydrophobicity compared to residual lignin (RL), and their inhibitory effect on enzymatic saccharification was considerably weaker. By adjusting the pKa of the DES system, this study successfully achieved efficient fractionation of bamboo and enhanced enzymatic saccharification, thereby offering valuable insights for the design of tailored DES-based pretreatment strategies.