The utilization of biomass as a raw material and production of hydrothermal humic acid (HHA) through hydrothermal method using hydrochar as an intermediate product is a sustainable approach for the preparation of humic acid. In this study, hydrochar was prepared through acid hydrothermal treatment of corn straw and then oxygen was introduced to alkaline hydrothermal treatment of hydrochar to improve the yield of humic acid. It was discovered that an oxygen pressure of 5 bar could significantly enhance the yield of HHA from 41.9 wt% to 49.2 wt% at a hydrothermal temperature of 180 °C, while oxygen pressures of 10 bar and 20 bar led to a decrease in HHA yield (41.5 wt% to 28.2 wt%). Oxygen addition could also reduce the energy input and the economic cost required for hydrothermal reactions. Further study revealed that the increase in HHA yield was the oxidation of aliphatic carbon in the solid residue derived from hydrochar by oxygen, which became part of the HHA and resulted in weaker fluorescence intensity of the HHA. However, excessive oxygen could increase the oxygen-containing functional groups of the HHA while also causing further cleavage of macromolecular components with high carbon numbers, generating smaller molecules that partially dissolve in the liquid phase. The HHA synthesized at an oxygen pressure of 5 bar showed good performance in promoting Chinese cabbage seedlings growth and was superior to the HHA synthesized in the absence of oxygen in terms of cadmium adsorption. This study proved an improved hydrothermal humification method and provided technical support for industrial applications.

以生物质为原料，以水热炭为中间产物，通过水热法生产腐植酸（HHA），是一种可持续的腐植酸制备方法。本研究通过对玉米秸秆进行酸性水热处理制备水炭，然后将氧气引入到水炭的碱性水热处理中以提高腐植酸的得率。研究发现，在180℃的水热温度下，5 bar的氧气压力可以显着提高HHA的产率，从41.9 wt%提高到49.2 wt%，而10 bar和20 bar的氧气压力会导致HHA产率下降（41.5 重量％至 28.2 重量％）。添加氧气还可以减少水热反应所需的能量输入和经济成本。进一步研究发现，HHA产率的增加是由于氢炭固体残渣中的脂肪族碳被氧气氧化，成为HHA的一部分，导致HHA的荧光强度减弱。然而，过量的氧气会增加HHA的含氧官能团，同时也会导致高碳数大分子组分进一步裂解，产生部分溶解在液相中的较小分子。在5 bar氧气压力下合成的HHA表现出良好的促进大白菜幼苗生长的性能，并且在镉吸附方面优于在缺氧条件下合成的HHA。该研究证明了一种改进的水热腐殖化方法，为工业化应用提供了技术支撑。