Abstract
BackgroundRecently developed iron cocatalyst enhancement of dilute acid pretreatment of biomass is a promising approach for enhancing sugar release from recalcitrant lignocellulosic biomass. However, very little is known about the underlying mechanisms of this enhancement. In the current study, our aim was to identify several essential factors that contribute to ferrous ion-enhanced efficiency during dilute acid pretreatment of biomass and to initiate the investigation of the mechanisms that result in this enhancement.ResultsDuring dilute acid and ferrous ion cocatalyst pretreatments, we observed concomitant increases in solubilized sugars in the hydrolysate and reducing sugars in the (insoluble) biomass residues. We also observed enhancements in sugar release during subsequent enzymatic saccharification of iron cocatalyst-pretreated biomass. Fourier transform Raman spectroscopy showed that major peaks representing the C-O-C and C-H bonds in cellulose are significantly attenuated by iron cocatalyst pretreatment. Imaging using Prussian blue staining indicated that Fe2+ ions associate with both cellulose/xylan and lignin in untreated as well as dilute acid/Fe2+ ion-pretreated corn stover samples. Analyses by scanning electron microscopy and transmission electron microscopy revealed structural details of biomass after dilute acid/Fe2+ ion pretreatment, in which delamination and fibrillation of the cell wall were observed.ConclusionsBy using this multimodal approach, we have revealed that (1) acid-ferrous ion-assisted pretreatment increases solubilization and enzymatic digestion of both cellulose and xylan to monomers and (2) this pretreatment likely targets multiple chemistries in plant cell wall polymer networks, including those represented by the C-O-C and C-H bonds in cellulose.
Highlights
Developed iron cocatalyst enhancement of dilute acid pretreatment of biomass is a promising approach for enhancing sugar release from recalcitrant lignocellulosic biomass
Researchers in recent studies have reported that the ferric form of iron (FeCl3) is efficient in functioning as a catalyst for releasing hemicellulose from corn stover (CS) by hot water pretreatment [4] and that the enzymatic digestibility and cellulose recovery can be enhanced after hot ethanosolv/FeCl3 pretreatment of barley straw [5]
The first step toward understanding the role of the Fe2+ ion cocatalyst in enhancing biomass degradation was to investigate the effects of dilute acid/Fe2+ ion pretreatments on the model celluloses, that is, filter paper (FP)
Summary
Developed iron cocatalyst enhancement of dilute acid pretreatment of biomass is a promising approach for enhancing sugar release from recalcitrant lignocellulosic biomass. Our aim was to identify several essential factors that contribute to ferrous ion-enhanced efficiency during dilute acid pretreatment of biomass and to initiate the investigation of the mechanisms that result in this enhancement. The results showed that all bands of sugar skeletal vibration modes and all C-O-H and C-O vibration modes of glucose were shifted in metal ion/D-glucose complexes [2]. Researchers in recent studies have reported that the ferric form of iron (FeCl3) is efficient in functioning as a catalyst for releasing hemicellulose from corn stover (CS) by hot water pretreatment [4] and that the enzymatic digestibility and cellulose recovery can be enhanced after hot ethanosolv/FeCl3 pretreatment of barley straw [5]. It was reported that Fe2+ and Fe3+ ions are effective in enhancing the Lewis acid cocatalyzed dilute sulfuric acid pretreatment of lignocellulosic biomass [6]
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