Self-assembled lignin nanospheres (LNS) have attracted much attention due to the new opportunities provided for the preparation of value-added products derived from lignin. However, the internal connections of the LNS generally depend on weak intermolecular forces, leading to low solubility resistance and thermostability. In this study, we present a simple method for the fabrication of covalent–noncovalent forces stabilizing lignin nanospheres (HT-LNS) through utilizing the natural characteristic that lignin molecules undergo irreversible condensation under high-temperature stimulation. Experiments demonstrated that the action of temperature resulted in the fracture of β-O-4 ether and C_α–C_β bonds, as well as hydroxyl and −OCH₃ lignin molecule groups, leading to the formation of free radicals in the LNS. In addition, a large number of adjacent intramolecular and intermolecular radicals almost simultaneously generated chemical cross-linking via α-5, β-5, β–β′ bonds, and so forth. The amount of lignin molecules participating in the cross-linking reaction increased with temperature, which gradually reduced the HT-LNS diameter from 597 to 477 nm and enhanced the maximum decomposition peak from 367.7 to 395.1 °C. The solubility of nanospheres in ethanol and tetrahydrofuran (THF) decreased from 93.92 to 10.39% and from 98.09 to 22.45% with increasing treatment temperature, respectively. The HT-LNS can be employed in the preparation of superhydrophobic coatings, replacing non-environmentally friendly silica nanoparticles. The water contact and slide angles were determined as 151.9 ± 1.4 and 9.4 ± 0.5°, respectively. Moreover, the application of HT-LNS for the preparation of lignin-based carbon nanospheres maintained a perfect spherical structure with tiny graphitic area and the content of carbon atoms reached up to 94.99%. This study provides a simple and effective technology platform for the development of green materials.

中文翻译：

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稳定木质素纳米球的共价-非共价力的制备，形成机理及其在超疏水碳材料中的应用

自组装木质素纳米球（LNS）由于提供了制备木质素衍生的增值产品的新机会而备受关注。然而，LNS的内部连接通常取决于弱的分子间力，从而导致低的抗溶性和热稳定性。在这项研究中，我们提出了一种简单的方法，通过利用木质素分子在高温刺激下会发生不可逆的缩合的自然特性来稳定木质素纳米球（HT-LNS）的共价-非共价力。实验表明温度的作用导致β-O-4醚和C的断裂_α -C _β债券，以及羟基和-OCH ₃木质素分子基团，导致LNS中自由基的形成。此外，大量相邻的分子内和分子间自由基几乎同时通过α-5，β-5，β-β'键等产生化学交联。参与交联反应的木质素分子的数量随着温度的升高而增加，从而使HT-LNS的直径从597 nm逐渐减小到477 nm，最大分解峰从367.7°C上升到395.1°C。随着处理温度的升高，纳米球在乙醇和四氢呋喃（THF）中的溶解度分别从93.92％降低至10.39％和从98.09％降低至22.45％。HT-LNS可用于制备超疏水性涂料，替代非环境友好型二氧化硅纳米粒子。水接触角和滑动角分别确定为151.9±1.4和9.4±0.5°。此外，HT-LNS在制备木质素基碳纳米球中的应用保持了理想的球形结构，石墨面积很小，碳原子含量高达94.99％。这项研究为开发绿色材料提供了一个简单有效的技术平台。