Abstract:

Humic substances (HS) are natural organic materials formed through the decomposition of plant and animal remains and the slow transformation by microbes. Rapid production of HS can be achieved through hydrothermal treatment of biomass; however, the research on the spectroscopic and electrochemical properties of artificial humic substances is still insufficient. In this study, artificial humic acid (AHA) and artificial fulvic acid (AFA) were prepared using corn straw as a raw material through a hydrothermal humification method. Their chemical structures and molecular composition were analyzed through spectroscopy and high-resolution mass spectrometry and compared with humic acid and fulvic acid from black soil and peat soil. Electrochemical analysis was employed to measure the electron accepting capacity (EAC) and electron donating capacity (EDC) of HS. The spectral and mass spectrometry results revealed that the artificial HS is highly consistent with natural HS in chemical structure, presenting the same major chemical groups, including hydroxyl, aliphatic, aromatic, and carboxy ketone groups. Moreover, artificial HS exhibited higher fluorescence indices and lower aromaticity, and were rich in tyrosine-like fluorescent components. Both artificial and natural HS primarily contain lignin/carboxylic-rich alicyclic structures, lipids, and aliphatic/proteinaceous materials. The electrochemical results indicated that AHA had an EAC of 1.85 mmol·g^-1, higher than natural humic acid, and an EDC of 0.5 mmol·g^-1, which is comparable to natural humic acid. AFA had an EAC of 2.07 mmol·g^-1, lower than natural fulvic acid, but an EDC of 0.66 mmol·g^-1, higher than natural fulvic acid. The analysis of correlation revealed that the electron transfer capacity is significantly influenced by the content of lignin/carboxylic-rich alicyclic molecules (CRAM) and lipids. It was found that tyrosine-like fluorescent components and nitrogen-containing organic compounds (CHON) have a positive correlation with electron donating capacity (EDC). Conversely, humic-like fluorescent components, the atomic ratio of oxygen to carbon (O/C), and double bond equivalents (DBE) showed a positive correlation with electron accepting capacity (EAC). This study confirmed that artificial HS possess noteworthy electrochemical characteristics. Furthermore, the research enhances our comprehension of the ability of artificial HS to mimic the functions of natural HS, especially in their role in geochemical electron transfer processes.

Key words: hydrothermal humification, artificial humic substances, spectroscopic characterization, structural characterization, electron transfer capacity

摘要：

腐殖质（HS）是由动植物尸体分解和微生物缓慢转化而成的天然有机物质，其快速制备可通过生物质的水热处理实现，但人工腐殖质的光谱和电化学特性研究仍然不足。运用水热腐殖化法以玉米秸秆为原料制备人工胡敏酸（AHA）和富里酸（AFA）。通过光谱学和高分辨质谱分析了其化学结构和分子组成，并与土壤和泥炭中的胡敏酸和富里酸做了对比。利用电化学分析测定了HS的电子接受能力（EAC）和电子供给能力（EDC）。光谱和质谱结果揭示人工HS与天然HS在化学结构上高度一致，具有相同的主要化学基团，包括羟基、脂肪族、芳香族和羧酮基团。此外，人工和天然HS均较高的含有木质素/富羧酸的脂环结构、脂类和脂肪族/蛋白质，但人工HS具有较高的荧光指数和较低的芳香程度，富含类酪氨酸荧光组分。电化学结果表明，AHA的EAC为1.85 mmol·g^-1，高于天然胡敏酸；其EDC为0.5 mmol·g^-1，与天然胡敏酸相当。AFA的EAC为2.07 mmol·g^-1，低于天然富里酸，但EDC为0.66 mmol·g^-1，高于天然富里酸。相关性分析表明，木质素/富羧基脂环结构（CRAM）和脂质含量对电子转移能力有显著影响。类酪氨酸荧光成分、含氮有机化合物（CHON）与EDC分别呈正相关关系，而类腐殖质荧光组分、原子O/C值及双键当量（DBE）与EAC呈正相关关系。综上，人工腐殖质不仅表现出良好的电化学性能，提升了对人工腐殖质在模拟天然HS功能及其在地球化学电子转移过程中潜在应用的理解。

关键词: 水热腐殖化, 人工腐殖质, 光谱特性, 分子结构, 电子转移能力