Low-dosage thiourea-assisted p-toluenesulfonic acid pretreatment of bamboo for lignin condensation suppression and residue valorization

Low-dose thiourea enhanced p -TsOH delignification of bamboo by 24.6%. • Thiourea increased total β- O -4 retention from 35.6% to 79.3%. • Thiourea improved the glucose yield from 71.4% to 87.5%. • Enzymatic hydrolysis residue was upgraded into S-doped HC and S/N-doped CQDs. Acid pretreatment improves cellulose accessibility and promotes lignin removal, but reactive benzylic intermediates often induce lignin condensation and redeposition, limiting enzymatic hydrolysis and lignin valorization. In this work, low-dosage thiourea was introduced into a p -toluenesulfonic acid ( p -TsOH) system to nucleophilically stabilize dissolved and residual lignin intermediates while introducing S/N functionalities. The addition of thiourea increased the lignin removal from 62.1% for PTB to 77.4% for PTSN1%B and the glucose yield from 71.4% to 87.5%, while increasing total β-O-4 retention of recovered lignin from 35.6% to 79.3%. After enzymatic hydrolysis, the lignin-rich residue was converted by one-pot hydrothermal treatment into hydrochar and carbon quantum dots. The introduction of S functionalities into hydrochar increased the maximum methylene blue adsorption capacity from 87.6 mg/g for HC-C to 115.1 mg/g for HC-SN while the incorporation of S/N functionalities into carbon quantum dots enhanced blue-green fluorescence intensity from 100000 to 400000 a. u. This work provides an integrated route for suppressing lignin condensation, improving carbohydrate conversion, and upgrading enzymatic hydrolysis residue into functional carbon materials in a bamboo biorefinery. Download: Download high-res image (411KB) Download: Download full-size image