Structural characteristics of humic acids derived from Chinese weathered coal under different oxidizing conditions

Abstract

Humic acids derived from Chinese weathered coal were oxidized with hydrogen peroxide (H 2 O 2 ) under various conditions, and their chemical composition and structure were examined. The raw material humic acids (HA) and oxidized humic acids (OHAs) were characterized by elemental analysis and ultraviolet visible (UV-Vis), Fourier transform infrared (FTIR), and solid-state 13 C nuclear magnetic resonance (NMR) spectroscopy. Our results show that aromatic functional groups accounted for more than 70% of the HA and OHAs and there were significant differences in their structures and compositions. Compared to the HA, the average H and N contents of the OHAs decreased by 5.15% and 2.52%, respectively, and the average O content of those of the OHAs increased by 5.30%. The hydrophobicity index (HI) of HA is higher than those of the OHAs. Importantly, in the hypothesis test between the properties and preparation conditions of humic acid using SPSS, the partial η 2 of the temperature, hydrogen peroxide concentration, liquid-solid ratio, and time were 0.809, 0.771, 0.748 and 0.729, respectively; thus, among the preparation conditions, temperature is the most important factor affecting the humic acids properties.

Active chemical fractions with high fungistatic activity of humic‐like substances obtained via different extraction solvents

“…While the basic aromatic properties of HULIS were also found in previous studies of Wei et al . and Zhou et al ., in which the examined AROs of weathered coal were both more than 50%. Both values are similar to the values determined in this work, which indicates that all HULIS extracted from weathered coal with NaOH and KOH solvents are aromatic.…”

Combining humic acid with phosphate fertilizer affects humic acid structure and its stimulating efficacy on the growth and nutrient uptake of maize seedlings

“…The peaks at 3418 and 3415 cm −1 were attributed to –OH stretching in alcohols and phenols. The stretching vibration of carboxyl group C=O was found at 1707 and 1709 cm −1 and the C–O–H in-plane bending vibration of carboxylic acid at 1421 and 1417 cm −1 17 , 19 . According to the integration in Table S1 (see Supplementary Table S1 online), the vibration intensity of the above functional groups in HA was weaker than that in PHA, which indicated that the relative carboxyl content of PHA was higher than that of HA.…”

“…Zhang et al 18 reported that high temperatures (> 400 °C) will also cause a serious loss of humic acid by weight, especially for aliphatic compounds. Zhou et al 19 also reported that the temperature of the reaction system is the most important factor affecting the properties of humic acids. However, the effect of the high temperature generated during the production process of HAP on the structure of humic acid has not been reported.…”

Characterization of humic acids from original coal and its oxidization production

“…Meanwhile, large number of H and O atoms are introduced into coal, which can increase the richness of functional group 25 , 26 . Recently, some studies have shown that the properties of HAs change and have promoting effect on corn growth after the oxidation by H 2 O 2 27 . In practical, coal oxidation or HAs processed by H 2 O 2 both show excellent performance.…”