In situ saccharification of metal-containing ionic liquid pretreated (ligno)cellulose via alginate encapsulated cellulase@functionalized ZIF-8

The present work aimed to develop mixed-metal salts (MMs) assisted ionic liquid (IL) pretreatment for efficient in situ saccharification of (ligno)cellulose. To accommodate MMs-IL involved in situ saccharification, a novel immobilized cellulase based on amine-functionalized ZIF-8 and calcium alginate beads (Ce@ZIF-8-A/CA) was established. XRD, FT-IR and SEM were employed to characterize the immobilization carrier and immobilized cellulase. Compared to free cellulase, Ce@ZIF-8-A/CA showed enhanced tolerance to IL, MMs and temperature. Ce@ZIF-8-A/CA preserved more than 80% of original activity at a wide temperature range (40–70 °C) in 30% 1-butyl-3-methylpyridinium chloride ([BMPy]Cl), and retained 73.0% of initial activity in 1% MMs (FeCl3/LiCl) assisted 30% [BMPy]Cl. After pretreatment with MMs assisted [BMPy]Cl, 40%-60% (ligno)cellulose was decomposed into soluble lower-molecular-weight fragments without regeneration of cellulose after adding buffer. After in situ saccharification of pretreated slurries with Ce@ZIF-8-A/CA, total reducing sugars yields of 84.7% and 71.3% from cellulose and bagasse were obtained during 12 h, saving at least 12 h compared to traditional enzymatic in situ saccharification of (ligno)cellulose in IL.