Characterization of Ultrafiltration-Fractionated Humic Acid Derived from Chinese Weathered Coal by Spectroscopic Techniques

Abstract

Weathered coal is a widely used raw material of farm-oriented humic acid in China, while the high heterogeneity impedes its sufficient utilization. In this study, we fractionated the humic acid derived from Chinese weathered coal by ultrafiltration, and three fractions with the molecular range of ≥100 kDa, 10–100 kDa, ≤10 kDa were obtained. Subsequently, the chemical and spectral properties of the fractions were characterized by elemental analysis, potentiometric titration, Fourier transform infrared (FTIR), nuclear magnetic resonance (NMR), and X-ray photoelectron (XPS) and other spectroscopy. The results showed that more than 60% of humic acid by weight was concentrated in the molecular range higher than 100 kDa, while only 3.25% was assigned to that with molecular weight lower than 10 kDa. The humic acid fraction with molecular weight higher than 100 kDa showed more carbon content, lower H/C atomic ratio, while higher E4/E6 ratio, more aromatic structure in FTIR, 13C NMR, and XPS spectra, indicating a higher degree of aromaticity and stronger hydrophobicity. Conversely, there were more carboxyl groups and aliphatic structures, while fewer condensed aromatic rings for the humic acid fraction with molecular weight less than 100 kDa. These differences provide a baseline for the better utilization of weathered coal.

Enhanced Sorption Performance of Natural Zeolites Modified with pH-Fractionated Humic Acids for the Removal of Methylene Blue from Water

“…This finding suggests that sequential pH solubilization progressively leads to HA fractions having higher aromaticity content and, in line with the gel permeation experiments, a higher molecular weight distribution. It is interesting to note that HA exhibiting appreciable aromaticity and sizes are also likely associated with a high degree of hydrophobicity [35]. leads to HA fractions having higher aromaticity content and, in line with the gel permeation experiments, a higher molecular weight distribution.…”

“…leads to HA fractions having higher aromaticity content and, in line with the gel permeation experiments, a higher molecular weight distribution. It is interesting to note that HA exhibiting appreciable aromaticity and sizes are also likely associated with a high degree of hydrophobicity [35]. 2 shows the trend of the total MB concentration in the liquid phase versus time at different initial concentrations of MB and a constant loading of natural zeolite (NYT).…”

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

“…The broad band at 3600–3200 cm –1 corresponds to phenolic groups, but also –OH for hygroscopic water . The signal related to the vibrations of CH and CH 2 in aromatic rings was observed as a shoulder at 3150–3000 cm –1 , and the low intensity peaks observed at 2950 and 2850 cm –1 can be assigned to the stretching of –CH 3 and –CH 2 – in aliphatic chains, respectively. − The intensive signals at about 1650, 1420, and 1220 were associated with the vibrations of the carboxyl structures and correspond to the CO stretches, COO – asymmetric stretching, and the deformation of C–O, respectively. − The signal peaking at 1020 cm –1 represented the C–O stretching of polysaccharides, and the C–H vibrations in aromatic structures were observed in the 860 cm –1 band . The peaks in the region below 700 cm –1 may be attributed to the inorganic constituents of the samples tested …”

Characteristics of Chinese Weathered Coal from Six Geographical Locations and Effects on Urease Activity Inhibition

“…The greater values of A CH2 /A CH3 in samples WH and LF suggest that they had longer alkyl chains bound to aromatic rings than the weathered coal collected from the other coal mines [31]. However, the ratio of A CH2 /A CH3 in sample ZT was 3.12, a third of that in sample WH, implying a relatively compact structure with less space between aromatic clusters and indicating that the aliphatic side chains become more branched [31,44].…”