Nanobiocatalysts for efficient conversion of microwave aided ionic liquid pretreated rice straw biomass to biofuel

Growing energy demand, devastating effects of excess fossil fuel usage and its declining reserves, and grave environmental/climate change issues are the major motivational points for developing renewable, sustainable, safer, and green energy alternatives. The current research examined the rice straw biomass (RSB) as the potential feedstock for producing biofuel-ethanol. RSB was subjected to a sequential pretreatment with ionic liquid tris (2-hydroxyethyl) methylammonium methyl sulphate ([TMA][MeSO₄]) and microwave irradiation, and the pretreated RSB was hydrolyzed with either free cellulase/xylanase enzyme preparation, or the one immobilized on magnetic nanoparticles (MNPs), i.e., nanobiocatalysts, to achieve a sugar content, respectively, of 159.77 mg/g biomass and 157.03 mg/g biomass. Sugar hydrolysate obtained from free or nanobiocatalysts mediated hydrolysis was fermented to bioethanol content of 78.48 mg/g and 78.05 mg/g biomass, respectively. An ionic liquid stable cellulase/xylanase enzyme preparation was in-house developed by submerged fermentation from Aspergillus niger B4. Nanobiocatalysts exhibited significant reusability potential for several successive hydrolysis cycles. The structural alterations in the pretreated biomass were elucidated by XRD, FTIR, and SEM analyses. MNPs and nanobiocatalysts were examined by VSM, SEM, DLS, TG–DTA, and FTIR analysis for structural/functional/operational characteristics. The current study is the first ever report of combined pretreatment of RSB using IL ([TMA][MeSO₄]) and microwave irradiation followed by saccharification with IL-stable, in-house developed cellulase/xylanase enzymes from Aspergillus niger B4. The study unravels new avenues for economic and eco-benign bioconversion of rice straw biomass into biofuel-ethanol.

Graphical Abstract