Liu Hui, Zhao Baowei, Zhang Xin, Li Liujun, Zhao Yue, Li Yingquan, Duan Kaixiang
School of Environmental and Municipal Engineering, Lanzhou Jiaotong University, Lanzhou 730000, China.
Gansu Dust Suppression for Transportation and Storage Engineering Research Center, Lanzhou 730000, China.
Materials (Basel). 2022 May 28;15(11):3865. doi: 10.3390/ma15113865.
Biochar-derived dissolved organic carbon (DOC), as the most important component of biochar, can be released on farmland, improving fertility and playing a role in soil amendment and remediation. The complexity of molecular structures and diversity of DOC compounds have influenced these functions to some extent. A sequential extract protocol consisting of water (25 °C), hot water (80 °C), and NaOH solution (0.05 M) was used to fully extract DOC compounds and gain a thorough understanding of the possible DOC components released from biochar. Rape straw (RS), apple tree branches (ATB), and pine sawdust (PS) were pyrolyzed at 300, 500, and 700 °C, respectively, to make nine distinct biochars. A TOC analyser, ultraviolet-visible spectroscopy (UV-vis), and excitation-emission fluorescence (EEM) spectrophotometer were used in conjunction with parallel factor analysis (PARAFAC) to determine the distribution of DOC content, the diversity of aromaticity, molecular weight characteristics and components of biochar-derived DOC. The results show that the relative distribution of water-extractable fractions ranged from 3.21 to 35.57%, with a low-aromaticity and extremely hydrophilic fulvic-acid-like compounds being found in the highest amounts (C2 and C3). The smallest amount of hot water-extractable components was produced from the release of small-molecule aliphatic compounds adsorbed on biochar and susceptible to migration loss once in a soil solution. More than half of the biochar-derived DOC was released in a NaOH solution, which primarily consisted of humic-acid-like compounds (C1), with higher molecular weights, more aromaticity, and lower bioavailability, according to the distribution of DOC in various extractants. In addition, the pyrolysis temperature and biomass type had a significant impact on the DOC properties released by biochar. As a result, the findings of this study showed that using a sequential extract protocol of water, hot water, and NaOH solution in combination with spectroscopic methods could successfully reveal the diversity of biochar-derived components, which could lead to new insights for the accurate assessment of potential environmental impacts and new directions for biochar applications.
生物炭衍生的溶解有机碳（DOC）作为生物炭的最重要组成部分，可在农田中释放，提高土壤肥力，并在土壤改良和修复中发挥作用。DOC化合物分子结构的复杂性和多样性在一定程度上影响了这些功能。采用由水（25℃）、热水（80℃）和氢氧化钠溶液（0.05M）组成的顺序提取方案，以充分提取DOC化合物，并深入了解生物炭释放的可能的DOC成分。分别将油菜秸秆（RS）、苹果树枝条（ATB）和松木锯末（PS）在300℃、500℃和700℃下热解，制成九种不同的生物炭。使用总有机碳分析仪、紫外可见光谱仪（UV-vis）和激发发射荧光（EEM）分光光度计，并结合平行因子分析（PARAFAC）来确定生物炭衍生DOC的DOC含量分布、芳香性多样性、分子量特征和成分。结果表明，水可提取部分的相对分布范围为3.21%至35.57%，其中低芳香性和极强亲水性的类富里酸化合物含量最高（C2和C3）。热水可提取成分的量最少，是由吸附在生物炭上的小分子脂肪族化合物释放产生的，一旦进入土壤溶液就容易迁移损失。根据DOC在各种提取剂中的分布，超过一半的生物炭衍生DOC在氢氧化钠溶液中释放，其主要由类腐殖酸化合物（C1）组成，分子量较高，芳香性更强，生物有效性更低。此外，热解温度和生物质类型对生物炭释放的DOC性质有显著影响。因此，本研究结果表明，将水、热水和氢氧化钠溶液的顺序提取方案与光谱方法相结合，可以成功揭示生物炭衍生成分的多样性，这可能为准确评估潜在环境影响带来新的见解，并为生物炭应用提供新的方向。
