To 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 (M_w 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.

中文翻译：

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杂多酸衍生的新木质素流增强中性深共晶溶剂的分馏：结构阐明和抗氧化性能

为了提高中性DES中来自芒草（Miscanthus×giganteus）的木质素的分馏效率（氯化胆碱/甘油），使用了具有环境起源和经济可行性的三种杂多酸（磷钨酸，磷钼酸和硅钨酸）作为催化剂。研究发现，在温和的条件下（120°C，3 h），硅钨酸-氯化胆碱/甘油系统可产生78.2％的高木质素。这归因于硅钨酸充当四氢酸，它贡献了更多的活性质子来选择性地裂解醚键并进一步促进了木质素的去除。以下木质素谱分析表明回收的木质素具有高纯度（92.7％），低分子量（M _w1520–2470 g / mol），低多分散度（PDI <1.7），出色的热稳定性以及在二甲亚砜和二甲基乙酰胺中的良好溶解性。此外，磷钼酸（PMA）木质素具有HGS的典型结构，具有较高的O / C比，这是由于处理后具有更多类似天然的C-O键结构（高β-芳基醚含量）。有趣的是，基于SEM和TEM分析，在DES分级程序中定义了纳米级木质素。为了进一步评估分离的木质素流的潜在应用，通过体外2,2-二苯基-1-吡啶并肼基（DPPH）自由基清除能力进行了抗氧化活性的研究。抗氧化性能（IC ₅₀ = 0.042 mg / mL）优于市售抗氧化剂丁基化羟基甲苯（IC₅₀ = 0.056 mg / mL）。以上结果表明，杂多酸-中性DES系统对木质素的提取非常有效，并提供了具有良好抗氧化活性的木质素新来源。