Fabrication of hemicellulose-derived supercapacitor and Pd@lignin nanosphere catalyst by targeted lignocellulose fractionation

Abstract

Upgrading lignocellulose resources into value-added products is charming but encounters challenges due to their structural heterogeneity and product complexity. A tandem fractionation technique combining hydrothermal pretreatment (HTP) and deep eutectic solvent (DES) extraction was tailored to separate lignocellulosic three components selectively. HTP achieved almost 100 % hemicellulose dissolution into the aqueous stream, while subsequent DES extraction enabled efficient lignin removal (29–68 %) with high cellulose retention (>80 %). The water-soluble hemicellulose fraction was converted into activated nanocarbons (ANCs) via in-situ hydrothermal carbonization and KOH activation, yielding hierarchical porous materials with specific surface areas up to 2782 m² g⁻¹ . When applied in supercapacitors, rice straw-derived ANC exhibited a high specific capacitance of 284 F g⁻¹ at 0.5 A g⁻¹ and exceptional cycling stability (99 % retention after 10,000 cycles). Simultaneously, DES-extracted lignin riched in phenolic hydroxyl groups and condensed structure after tandem fractionation, was self-assembled into lignin nanospheres (LNSs) serving as supports for Pd nanoparticles (Pd@LNSs). The resulting catalyst demonstrated outstanding catalytic activity for toxic Cr (VI) reduction to Cr (III) under solar irradiation, achieving complete conversion within 8 min and maintaining > 90 % efficiency over eight cycles. This work establishes a closed-loop pathway for lignocellulose valorization, transforming underutilized hemicellulose and lignin into high-performance energy storage materials and robust catalysts, thereby enhancing the economic viability of biorefineries.