Structural and Functional Composition of Humic Acids Isolated from Soils of Natural and Urbanized Territories of the European Far North and the Arctic

Effects of humic substances on the oxidation of pentachlorophenol by peroxosulfate catalyzed by iron(III)-phthalocyanine-tetrasulfonic acid

The carbon-based adsorbents are promising for adsorptive denitrogenation (ADN) of liquid hydrocarbon streams. The objective of the present study is to develop a fundamental understanding of the role of surface oxygen-containing functional groups on carbon-based adsorbents in adsorption of nitrogen compounds that are known to be present in liquid fuels. The adsorption properties of four representative activated carbons were evaluated in a batch adsorption system for removing quinoline and indole respectively from decane. The adsorption was found to obey the Langmuir adsorption isotherm. The adsorption isotherms were obtained and the adsorption parameters (the maximum capacity and adsorption constant) were estimated. The surface chemical properties of the adsorbents were characterized by temperature-programmed desorption (TPD) technique with a mass spectrometer to identify and quantify the type and concentration of the oxygen-containing functional groups on the basis of the CO2- and CO-evolution profiles. It was found that both the type and the concentration of surface oxygen-containing functional groups play an important role in determining the ADN performance. Higher concentration of the oxygen-containing functional groups on the adsorbents resulted in higher adsorption capacity for the nitrogen compounds. A fundamental insight was gained on the contributions of different oxygen functional groups by analyzing the changes in the monolayer maximum adsorption capacity qm and the adsorption constant K for nitrogen compounds on different carbon adsorbents. The acidic functional groups, such as carboxyl and carboxylic anhydride groups, appear to contribute more for adsorption of quinoline, whereas the basic oxygen-containing groups such as carbonyl and quinone groups may have more contribution to adsorption of indole.

A comparative chemical-structural study of fossil humic acids and those extracted from urban wastes

To study the effect of H2O2 on the content and properties of humic acids (HAs) in lignites, the experimental conditions including oxidation time, H2O2 concentration, and the solid–liquid ratio were investigated. Under the optimum oxidation conditions, the contents of HAs of YL and HB lignite were 45.4 and 40.9%, respectively. The HAs extracted from oxidized and raw lignites were characterized and compared. The results showed that the HAs extracted from oxidized lignites contain more total acidic groups, carboxyl groups, and aliphatic carbon than that in HAs extracted from raw lignites, and their hydrophilic–hydrophobic index value is higher and thermooxidative stability is better than those in HAs extracted from raw lignites. In addition, the composition of polycyclic aromatic hydrocarbons and fluorophore types in HAs extracted from oxidized lignites are similar to the HAs extracted from raw lignites. The results indicated that the oxidation operation can increase the content of HAs in lignites, and simultaneously increase the content of oxygen-containing functional groups and biological activity of HAs, which provided a reference for the subsequent application of HAs.

CO2 geological sequestration in coal seams can be carried out to achieve the dual objectives of CO2 emission reduction and enhanced coalbed methane production, making it a highly promising carbon capture and storage technology. However, the injection of CO2 into coal reservoirs in the form of supercritical fluid (ScCO2) leads to complex physicochemical reactions with the coal seam, altering the properties of the coal reservoir and impacting the effectiveness of CO2 sequestration and methane production enhancement. In this paper, theoretical calculations based on ReaxFF-MD were conducted to study the interaction mechanism between ScCO2 and the macromolecular structures of both low-rank and high-rank coal, to address the limitations of experimental methods. The reaction of ScCO2 with low-rank coal and high-rank coal exhibited significant differences. At the swelling stage, the low-rank coal experienced a decrease in aromatic structure and aliphatic structure, and high-rank coal showed an increase in aromatic structure and a decrease in aliphatic structure, while the swelling phenomenon was more pronounced in high-rank coal. At the dissolution stage, low-rank coal was initially decomposed into two secondary molecular fragments, and then these recombined to form a new molecular structure; the aromatic structure increased and the aliphatic structure decreased. In contrast, high-rank coal showed the occurrence of stretches–breakage–movement–reconnection, a reduction in aromatic structure, and an increase in aliphatic structure. The primary reasons for these variations lie in the distinct molecular structure compositions and the properties of ScCO2, leading to different reaction pathways of the functional group and aromatic structure. The reaction pathways of functional groups and aromatic structures in coal can be summarized as follows: the breakage of the O–H bond in hydroxyl groups, the breakage of the C–OH bond in carboxyl groups, the transformation of aliphatic structures into smaller hydrocarbon compounds or the formation of long-chain alkenes, and various pathways involving the breakage, rearrangement, and recombination of aromatic structures. In low-rank coal, there is a higher abundance of oxygen-containing functional groups and aliphatic structures. The breakage of O–H and C–OH chemical bonds results in the formation of free radical ions, while some aliphatic structures detach to produce hydrocarbons. Additionally, some of these aliphatic structures combine with carbonyl groups and free radical ions to generate new aromatic structures. Conversely, in high-rank coal, a lower content of oxygen-containing functional groups and aliphatic structures, along with stronger intramolecular forces, results in fewer chemical bond breakages and makes it less conducive to the formation of new aromatic structures. These results elucidate the specific deformations of different chemical groups, offering a molecular-level understanding of the interaction between CO2 and coal.

This study investigated the changes in graphitization, surface functional groups, and oxidation behavior of soot particulates along an exhaust pipe of a gasoline direct injection (GDI) engine using Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and thermogravimetric analysis (TGA). The main findings were as follows: The oxidation temperature of soot particulates was between 300 °C and 650 °C. The soot particulates generated for a higher engine load or near the exhaust valve tended to exhibit a lower ratio of a disordered graphite lattice and amorphous carbon. As the engine load increased, the graphitization degree of soot particulates became higher and the content of oxygen-containing functional groups and oxidation activity of soot particulates became lower, meaning that it became more difficult for the soot particulate to be oxidized. Under a light load, as the engine speed increased, the disorder of the edge array of soot particles became higher, the content of oxygen-containing functional groups and oxidation activity became higher, and the soot particles were more easily oxidized. On the other hand, with an increase in engine speed under a heavy load, the microscopic disorder of soot particulates decreased; lower contents of oxygen-containing functional groups and oxidation activity were observed and oxidation became more difficult. Moreover, with increasing transportation distance along the exhaust pipe of the GDI engine, the graphitization degree, content of surface functional groups, and oxidation behavior of soot particulate presented changes similar to the increasing engine speed under a light load, and oxidation became easier.

Chemical characterization of humic substances extracted from organic-waste-amended soils

The effects of humic acid (HA) and its different nominal molecular weight (NMW) fractions on the phenol oxidation by permanganate were studied. Phenol oxidation by permanganate was enhanced by the presence of HA at pH 4-8, while slightly inhibited at pH 9-10. The effects of HA on phenol oxidation by permanganate were dependent on HA concentration and permanganate/phenol molar ratios. The high NMW fractions of HA enhanced phenol oxidation by permanganate at pH 7 more significantly than the low fractions of HA. The apparent second-order rate constants of phenol oxidation by permanganate in the presence of HA correlated well with their specific ultraviolet absorption (SUVA) at 254 nm and specific violet absorption (SVA) at 465 or 665 nm. High positive correlation coefficients (R(2) > 0.72) implied that pi-electrons of HA strongly influenced the reactivity of phenol towards permanganate oxidation which agreed well with the information provided by fluorescence spectroscopy. The FTIR analysis indicated that the HA fractions rich in aliphatic character, polysaccharide-like substances, and the amount of carboxylate groups had less effect on phenol oxidation by permanganate. The negative correlation between the rate constants of phenol oxidation by permanganate and O/C ratios suggested that the oxidation of phenol increased with a decrease in the content of oxygen-containing functional groups.

Veterinary antimicrobials are emerging environmental contaminants of concern. In this study, the sorption of enrofloxacin (ENR) onto humic acids (HAs) extracted from three Brazilian soils was evaluated. HAs were characterized by elemental analysis and solid 13C nuclear magnetic resonance spectroscopy. The sorption of ENR onto HAs was at least 20-fold higher than onto the soils from which they were separated. Ionic and cation bridging are the primary interactions involved. The interactions driven by cation exchange are predominant on HAs, which appear to have abundant carboxylic groups and a relatively high proportion of H-bond donor moieties with carbohydrate-like structures. Interactions explained by cation bridging and/or surface complexation on HAs are facilitated by moieties containing conjugated ligands, significant content of oxygen-containing functional groups, such as phenolic-OH or lignin-like structures. HAs containing electron-donating phenolic moieties and carboxylic acid ligand groups exhibit a sorption mechanism that is primarily driven by strong metal binding, favoring the formation of ternary complexes between functional groups of the organic matter and drugs.

Molecular insights into the Tl(I) binding capacity and response sequences of soil humic acids from different sources.

Materials and methods. 18 native humic acids (HAs) were received from nine representative types of peat of the Tomsk region. Two extraction methods were used: sodium hydroxide and sodium pyrophosphate. Molecular structure parameters were investigated by IR-spectroscopy. The assessement of qualitative and quantitative features of the IR-spectra of 18 different humic acids was made. When HAs with mouse macrophages were cultured their ability to influence the NO-stimulation was determined. Thus, the biological activity of HAs and its dependence on the parameters of the molecular structure were studied. Results. The results of infrared spectroscopy showed that the HAs of upland types of peat contain more carbonyl, carboxyl, and ester groups, and HAs of lowland types of peat contain more aromatic carbon, phenolic and alcoholic hydroxyl, ether and carbohydrate fragments. The results of biological activity showed that HAs from upland types of peat induce the formation of nitrogen oxide, wherein the cell activation decreases with HAs obtained by alkali. All types of HAs from lowland types of peat contain an admixture of endotoxin. Some HAs obtained by sodium pyrophosphate have higher immunotropic activity; the HAs can cause antigen-specific stimulation of cells. The activity of HAs does not depend on endotoxin admixture. The results of molecular spectroscopy showed that the most biologically active HAs have higher aromaticity and higher concentration of oxygen-containing functional groups. This result can be used as a marker factor in the standardization of HAs.

A comprehensive wet chemical procedure was developed by combining acid demineralization, base extraction, and dichromate oxidation for fractionation and quantitative isolation of soil/sediment organic matter (SOM) into four fractions: (1) humic acids + kerogen + BC (HKB); (2) kerogen + BC (KB); (3) humic acid (HA); and (4) BC. The soil/sediment samples tested were collected from the suburban areas of Guangzhou, a rapidly developing city of China. The results show that BC and kerogen constitute 57.8-80.6% of the total organic carbon (TOC) and that the relative content of BC ranges from 18.3% to 41.0% of the TOC, indicating that both BC and kerogen are major organic components in soils and sediments from this industrialized region. Systematic characterization of the isolated SOMs shows that both BC and kerogen have sizes ranging from a few microns to above 100 microm, relatively low O/C and H/C atomic ratios, and low contents of oxygen-containing functional groups. The isolated BC has unique fusinite and semifusinite macerals, highly porous nature, and structures indicative of its possible origins. The study indicates that SOM is highly heterogeneous and that humin, the nonextractable humus fraction, consists mainly of kerogen and BC materials in the tested soil/sediment samples. The presence of these materials in soils and sediments may have significant impacts on pollutant mass transfer and transformation processes such as desorption and bioavailability of less polar organic chemicals in surface aquatic and groundwater environments.

Multi-walled carbon nanotubes (MWNTs) were used to adsorb low concentration erythromycin from natural water. The kinetic curves and adsorption isotherms were measured and the thermodynamic parameters were calculated. The effects of pH value, ionic strength and humic acid on the adsorption process were investigated. The results showed that the adsorption of carbon nanotubes to erythromycin was rapid in the first 40 min, and reached equilibrium within 200 min. The dynamics curve conforms to the quasi-second-order dynamics model. The Freundlich model can better fit the adsorption test data. Thermodynamic parameters show that the adsorption of Erythromycin by MWNTs is a spontaneous endothermic process. The adsorption activation energy Ea shows that the adsorption between MWNTs and erythromycin is a chemisorption process, and the content of oxygen-containing functional groups on the surface of CNTs determines the equilibrium adsorption amount. Ionic strength has obvious effect on adsorption. Increasing the pH value of the solution from 5 to 9 was beneficial to increasing the adsorption capacity of erythromycin. The adsorption capacity of carbon nanotubes to erythromycin was significantly increased with appropriate humic acid.

The Maillard reaction represents a pivotal biochemical pathway for the abiotic formation of humic-like substances (HLSs); however, the regulatory role of gibbsite (α-Al(OH)3) in mediating this process remains insufficiently explored. This study systematically evaluated the effects of glycine concentration (0-0.24 mol/L) on the abiotic humification of catechol (0.06 mol/L) and glucose (0.06 mol/L) in the presence of gibbsite, using a sterile liquid shake-flask incubation system. The molecular complexity of the supernatant, total organic carbon (TOC) retention efficiency, and structural evolution of HLSs isolated from the dark-brown residue were analyzed through UV-Vis spectroscopy, TOC quantification, Fourier-transform infrared (FTIR) spectroscopy, and elemental analysis. Results demonstrated that: (1) The Gly0.24 treatment (0.24 mol/L glycine) achieved the minimal TOC loss, with a reduction of only 26.0% compared to 49.8% in the control group (without glycine). This carbon-preserving effect was attributed to the formation of Al-C complexes. (2) At a glycine concentration of 0.12 mol/L, the resulting HLSs exhibited the highest degree of aromatic condensation-evidenced by the lowest E4/E6 ratio (2.11)-and the richest content of oxygen-containing functional groups (O/C atomic ratio = 1.38). Concurrently, FTIR analysis indicated suppressed vibration of Al-O bonds in this treatment, suggesting that moderate glycine concentrations could modulate gibbsite-organic interactions to favor humification. (3) The Gly0 (no glycine) and Gly0.06 (0.06 mol/L glycine) treatments yielded the maximum humic-like acid (HLA) content, with respective increases of 1295.9% and 1034.6% relative to the control. This observation implies that low glycine levels (or its absence) primarily promoted the polymerization of catechol and glucose into HLA, rather than diverting carbon toward other reaction products. (4) Higher glycine concentrations (0.12-0.24 mol/L) significantly enhanced the accumulation of nitrogen-containing compounds in HLA, leading to a marked decrease in the C/N ratio (down to 8.7 in Gly0.24). This trend confirmed that excess glycine served as a nitrogen donor, facilitating the incorporation of nitrogen moieties into HLA structures during humification. These findings highlighted that 0.12 mol/L glycine represented the optimal concentration for optimizing abiotic humification in the gibbsite system, as it balances two critical processes: aromatic polycondensation (a hallmark of humification degree) and the enrichment of oxygen-containing functional groups (key for HLS reactivity). This study provided novel mechanistic insights into gibbsite-catalyzed Maillard pathways, thereby advancing the development of strategies for efficient carbon sequestration in terrestrial ecosystems and the valorization of lignin-rich agricultural/industrial wastes into high-value humic-based products.

The influence mechanism of water-liquid CO2 treatment on the hydrophobicity of vitrinite and inertinite