Establishment of a molecular structure model for classified products of coal-based fulvic acid

Fulvic acid (FA) is used widely in materials, medicine, and agriculture because of its unique chemical properties. FA has good chemical activity due to its molecular structure which contains many functional moieties such as hydroxyl and carboxyl groups. Moreover, FA is biologically compatible enabling its use in medicine is agriculture. The chemical activity and physical properties of FA polymers differ based on its molecular weight. In order to reveal the specific structural characteristics of FA, column chromatography was used to fractionate FA into three different molecular weight products. Elementary analysis, infrared spectroscopy, and C-13 nuclear magnetic resonance were used to study the composition and content of the classified FA products. The three different molecular weights of FA all contained carboxyl groups and phenolic hydroxyl groups. Our findings show that the carboxyl group was mostly distributed at the end of the aliphatic chain, while a small portion was connected to the benzene ring. The higher molecular weight FA contained more carboxyl groups, and some oxygen elements were present in the form of carbonyl and ether bonds. The chemical formulas of the three molecular weights were C17H19NO10, C33H27NO23, and C48H37NO36, which were calculated by molecular mechanics and dynamics. The molecular structure of FA was optimised by quantum chemical calculation methods. Finally, the average molecular structure model of FA with different molecular weights was established.