Lignin has a unique chemical structure that can effectively adsorb dye cations in sewage. In this paper, a non-polluting ethanol-assisted hot water pretreatment method was used to extract lignin from the cotton stalk. The structure and properties of lignin were investigated, and the adsorption isotherm model, internal diffusion model, and adsorption kinetic equation for the adsorption of methylene blue were verified. The extraction yield of lignin was 15.65%. The molecular mass of lignin was only about 900 Da. Both Infrared Spectroscopy and 2D-Nuclear Magnetic Resonance showed that it contained the type of grass lignin units (guaiacyl, syringyl, and p-hydroxyphenyl) phenolic hydroxyl units. The morphology of the lignin was that there were many burr particles on the blocky surface. The lignin had a good effect in removing methylene blue, with 17.11 mg/g, and its pH range was wide from 3 to 8. The Dubinin–Radushkevich model is the best isothermal model that matches the experimental data, R² = 0.988, the pseudo-second-order kinetic equation is the best-matching model, R² = 0.9369. In the intraparticle diffusion model test, intra-particle diffusion occurs in the second stage of the matching line.

Graphical Abstract

中文翻译：

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无污染乙醇辅助热水预处理棉秆木质素的结构与性质及其在亚甲基蓝去除中的高值化利用

木质素具有独特的化学结构，能有效吸附污水中的染料阳离子。本文采用无污染的乙醇辅助热水预处理方法从棉花秸秆中提取木质素。研究了木质素的结构和性质，验证了吸附亚甲蓝的吸附等温线模型、内扩散模型和吸附动力学方程。木质素的提取率为15.65%。木质素的分子量只有900 Da左右。红外光谱和二维核磁共振均表明它含有草木素单元类型（愈创木基、紫丁香基和对羟基苯基）酚羟基单元。木质素的形态为块状表面有许多毛刺颗粒。木质素对亚甲蓝的去除效果较好，为17。²  = 0.988，伪二级动力学方程是最佳匹配模型，R ²  = 0.9369。在粒子内扩散模型测试中，粒子内扩散发生在匹配线的第二阶段。

图形概要