Preparation and Molecular Structural Characterization of Fulvic Acid Extracted from Different Types of Peat

Abstract

Humic acid is a type of polymeric, organic weak acid mixture with a core aromatic structure and main-component oxygen-containing functional group. Fulvic acid is a type of humic substance that can be dissolved in acid, alkali, or water. This study discusses the influence of different peptides on the molecular structure of fulvic acid, which was extracted from herbaceous, woody, and mossy peats using alkaline dissolution and acid precipitation methods. Analyses using infrared, UV-Vis, 13C-NMR, and X-ray photoelectron spectroscopies, as well as X-ray diffraction (XRD), were conducted to compare the effects of different peat types on the content and molecular structure of fulvic acid. The woody peat fulvic acid content was the highest among all peat fulvic acids (0.38%). However, the yield of fulvic acid from herbaceous peat was the highest (2.53%). Herbaceous peat fulvic acid contains significant quantities of carbonyl, amino, methylene, carboxyl, and phenolic hydroxyl groups and ether bonds. Woody peat fulvic acid contains carbonyl and methoxy groups, benzenes, aromatic carbons, aromatic ethers, and phenols. The degree of aromatization of woody peat fulvic acid was the highest. Mossy peat fulvic acid contains high levels of hydroxy, methyl, methylene, and phenol groups and aromatic ethers. The structural differences in fulvic acids in the different types of peat were primarily manifested in the content of functional groups, with little influence from the types of functional groups. XRD analysis of the different peats revealed that their structures all comprised benzene rings. However, mossy peat contained more C=O and –COOH groups, whereas herbaceous peat contained more C–O groups.

Application of Alkaline Deep Eutectic Solvents as a Green Alternative to the Traditional Extractants for the Isolation of Humic Substances

“…The results of the E 365 / E 250 ratio for the evaluated samples indicate that the molecular size and degree of condensation of HSs depended mainly on the type of raw material from which the HSs were isolated, which is consistent with the conclusions about the degree of humification and points to the correlation between the degree of organic matter conversion and the molecular structure of the HSs, which were isolated from a given raw material. − Based on the comparison of the E 365 / E 250 values for the isolated humic extracts (HSP, HSL, HSP NaOH , and HSL NaOH ) with the samples purchased from Sigma-Aldrich (HA SIGMA and NaH SIGMA ), it can be observed that the HSs obtained in this study were characterized by lower condensation, which is caused by the presence of fulvic substances in the humic extracts, which are a fraction with a lower degree of condensation and molecular weight, compared to humic acids and humates. , The values of the last absorbance ratio determined in this study ( E 270 / E 400 ) for the samples analyzed indicated a higher carboxyl content in the samples extracted using ADESs. When comparing the results by raw material type, a higher value of E 270 / E 400 was observed for HSs extracted from peat.…”