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New Lignin Streams Derived from Heteropoly Acids Enhanced Neutral Deep Eutectic Solvent Fractionation: Toward Structural Elucidation and Antioxidant Performance
journal contribution
posted on 2020-08-06, 22:00 authored by Zongwei Guo, Deqiang Li, Tingting You, Xun Zhang, Feng Xu, Xueming Zhang, Yiqin YangTo improve the fractionation
efficiency of lignins from Miscanthus × giganteus in the neutral DES (choline
chloride/glycerol), three heteropoly acids with environmental origin
and economic viability (phosphotungstic, phosphomolybdic, and silicotungstic
acids) were utilized as catalysts. It was found that the silicotungstic
acid–choline chloride/glycerol system resulted in a high lignin
yield of 78.2% under mild conditions (120 °C, 3 h). This was
attributed to silicotungstic acid acting as tetrahydric acid, which
donated more active protons to selectively cleave ether bonds and
further facilitated lignin removal. The following lignin profiling
indicated that the recovered lignin had a high purity (92.7%), low
molecular weight (Mw 1520–2470
g/mol), low polydispersity (PDI < 1.7), excellent thermal stability,
and good solubility in dimethyl sulfoxide and dimethylacetamide. Additionally,
phosphomolybdic acid (PMA) lignin exhibited a typical structure of
HGS with a relatively higher O/C ratio due to more nativelike C–O-bonded
structures (high β-aryl ether content) after treatment. Interestingly,
nanoscaled lignin was defined in the DES fractionation procedure based
on the SEM and TEM analyses. To further evaluate the potential application
of the isolated lignin streams, the antioxidant activity was performed
by in vitro 2,2-diphenyl-1-picrylhydrazyl (DPPH)
radical scavenging ability. The antioxidant performance (IC50 = 0.042 mg/mL) was better than that of the commercial antioxidant
butylated hydroxytoluene (IC50 = 0.056 mg/mL). The above
results demonstrated that the heteropoly acids–neutral DES
system was significantly efficient for lignin extraction and provided
a new source of lignin with good antioxidant activity.